Symposium Organizers
Matthew Pelton, University of Maryland-Baltimore County
Jennifer Dionne, Stanford University
Alexander Govorov, Ohio University
Maksym Kovalenko, ETH Zurich
Symposium Support
Angstrom Engineering
NNCrystal US Corporation (NN-Labs)
Princeton Instruments
NM06.01: Time-Resolved and Nonlinear Characterization
Session Chairs
Alexander Govorov
Matthew Pelton
Monday PM, November 27, 2017
Hynes, Level 3, Room 311
9:15 AM - NM06.01.01
Relaxation Dynamics of Photoexcited Electron-Hole Pairs in Methylammonium Lead Iodide Nanoplatelets
Verena Hintermayr 1 2 , Bernhard Bohn 1 2 , Lakshminarayana Polavarapu 1 2 , Alexander Urban 1 2 , Jochen Feldmann 1 2
1 Chair for Photonics and Optoelectronics, Ludwig-Maximilians-Universität, Munich Germany, 2 , Nanosystems Initiative Munich (NIM), Munich Germany
Show AbstractWithin the last four years two-dimensional organic/inorganic halide perovskite nanoplatelets have drawn the attention of many research groups. Here, we present results from optical spectroscopy experiments on methylammonium lead iodide nanoplatelets. In these studies we were able to control the nanoplatelet thickness down to a single perovskite monolayer yielding absorption spectra typical for two-dimensional semiconductors [1]. As a function of the number of monolayers we observed pronounced shifts of the absorption spectrum due to quantum confinement effects and dramatic changes in the exciton binding energy reaching values up to 300 meV for single monolayers, i.e. more than 10 times that of bulk films. In order to investigate the relaxation dynamics of photoexcited electron-hole pairs and excitons we performed transient absorption and four-wave mixing experiments. In particular, the carrier cooling behavior as well as the exciton formation dynamics are found to depend on the thickness of the platelets.
[1] V.A. Hintermayr et al. Adv. Mater. 2016, 28, 9478
9:30 AM - NM06.01.02
Probing Energy Migration in Ligand Exchanged Nanocrystal Solids with Time-Resolved Electronic Spectroscopies
Michael Azzaro 1 , Amro Dodin 2 , Diana Zhang 3 , Adam Willard 2 , Sean Roberts 1
1 Chemistry, University of Texas at Austin, Austin, Texas, United States, 2 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Chemical Engineering, University of Texas at Austin, Austin, Texas, United States
Show AbstractWhile semiconductor nanocrystals (NCs) have shown great promise as active components in optoelectronic devices due to their size-tunable absorption and solution processability, low carrier mobility and poor conductivity have ultimately limited their integration into commercial electronics. The native ligands (NLs) that passivate NC surfaces create large physical separations between NCs in a close-packed film, and present large energetic barriers at the NC-ligand interface, hindering transport. Methods to exchange these insulating NLs have primarily focused on the use of shorter ligands to decrease inter-particle spacing to improve energy transport. However another method is to exchange NLs for ones that can electronically couple to NC states, decreasing the energetic barrier at the organic-inorganic interface. Using a class of ligands known as “exciton-delocalizing ligands”, which have been shown to couple strongly to NC states, we employ a facile, room-temperature exchange procedure to alter the electronic structure of the NC film and improve transport. The effect of this ligand exchange on energy transport is probed through a combination of femtosecond electronic spectroscopies and Kinetic-Monte Carlo simulations. Using femtosecond transient absorption, we find that post-synthetic ligand exchange of NC films leads to a rapid (~1 ps) downhill energy migration of charge carriers (~80 meV) that persists for tens of picoseconds, while no such carrier migration is present in oleic acid capped films. Kinetic Monte-Carlo simulations are used to extract both rates and length scales for exciton diffusion in the system and are compared to native ligand capped nanocrystal films. Finally, principles of ligand design for the formation of strongly coupled nanocrystal arrays will be discussed.
9:45 AM - NM06.01.03
Non-Equilibrium Electron Distribution in Metal Particles at High Intensity and Temperatures—Application for Photo-Catalysis
Yonatan Sivan 1 , Yonatan Dubi 1
1 , Ben-Gurion University, Beer-Sheva Israel
Show AbstractRecently, intriguing experimental results of the scattering of intense visible CW light from single Au and Ag nanoparticles were reported. Specifically, it was shown that at moderately high incident intensities (typically 0.1-1 MW/cm2), the scattering was lower than the linear prediction, showing "saturation-like" behaviour, whereas for even higher incident intensities, the scattering grew rapidly, even exceeding the linear prediction; the results were fully reversible, and no damage to particles was observed. Notably, this is one of the highest nonlinear responses ever reported, as more than a 100% strong effect is obtained within a deep subwavelength volume, and probably the first quantitative experimental study of the slow nonlinearity of metals. Most remarkably, no convincing explanation to the physical origin of this effect was reported.
Recently, we showed that the initial decrease of the scattering can be explained by the thermal nonlinear optical response of the metal to CW light. This was done using newly measured permittivity data of Au under increasing temperatures, revealing the strong slow nonlinearity of Au. However, to date, the consequent increase of scattering remains a mystery.
In this contribution, we study the relation between the increase of scattering to the deviation of the electron distribution from its equilibrium (Fermi) distribution (hot carriers), made possible by the elevated temperature, intense illumination and strong field enhancement within the metal sphere.
We further study quantitatively the effect of the hot carriers on possible chemical reactions occurring near the metal particle surface. We show that the photo-catalytic enhancement grows exponentially with the population of the relevant high energy electron state, and demonstrate the feasibility of order of magnitude enhancements of the reaction rate when high intensities are used. In parallel, we study the induced temperature increase and show how to limit it to modest values.
Lastly, we report initial calculations of thermo-optical metamaterials, whereby the thermal nonlinearity of the metal spheres, embedded in a dielectric host can give rise to rather high intrinsic and effective nonlinear coefficients. Importantly, unlike the standard nonlinear metamaterials based on an ultrafast nonlinearity, we are able to maintain a low overall absorptivity for the composite for increasing metal fill factor. This is enabled by the long range nature of the thermal response.
We believe that this work is only the first out of a series of future studies of the slow nonlinearity of metals, and its exploitation in applications of high temperature nonlinear plasmonics, especially for photo-chemistry applications.
10:30 AM - NM06.01.04
Breakdown of “Universal” Volume Scaling of Auger Recombination Rates as a Function of Quantum Confinement in Semiconductor Nanocrystals
Istvan Robel 1 , Nikolay Makarov 1 , Shaojun Guo 1 , Wenyong Liu 1 , Kirill Velizhanin 1 , Victor Klimov 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractSemiconductor quantum dots have size-tunable, stable emission that can approach unity photoluminescent quantum yields, making them near-ideal phosphors. Their application as active materials in lasers and light-emitting diodes, however, is impacted by efficient nonradiative Auger recombination, often limiting performance.1,2 Previous studies have established some general empirical trends of Auger recombination in quantum dots such as the barrierless nature of the process (being insensitive to the size of the band gap),3 and the linear volume scaling of Auger rates over a wide range of materials compositions, including both direct- and indirect-gap semiconductors.4 These observations are in contrast to bulk behavior and emphasize the importance of quantum size effects in these systems. Most previous studies on Auger recombination in nanocrystals were carried out in the strong confinement regime, where the particle size is smaller than the exciton Bohr diameter. Our recent measurements on CsPbX3 (where X is Cl, Br, I, or their combination) nanocrystals indicated a departure from the “universal” volume scaling of Auger recombination,5 confirmed independently by others.6 To establish the effect of quantum confinement on Auger recombination, here we study CsPbX3 nanocrystals of constant nanocrystal volume and only vary the exciton Bohr radius by systematically exchanging the halide component, thereby probing the strong, intermediate, and weak confinement regimes. Our results show that volume scaling of Auger rates breaks down with a sharp onset in the intermediate confinement regime at a given ratio of exciton Bohr radius to particle size, and a new trend emerges.7 The potential mechanism for this behavior and its practical implications on device applications will be discussed.
References:
1. Y.-S. Park, W. K. Bae, T. Baker, J. Lim, V. I. Klimov, Nano Lett. 15, 7319-7328, 2015
2. W. K. Bae, Y.-S. Park, J. Lim, D. Lee, L. A. Padilha, H. McDaniel, I. Robel, C. Lee, J. M. Pietryga, V. I. Klimov, Nat. Commun. 4, 2661, 2013
3. J. M. Pietryga, K. K. Zhuravlev, M. Whitehead, V. I. Klimov, R. D. Schaller, Phys. Rev. Lett. 101, 217401, 2008
4. I. Robel, R. Gresback, U. Kortshagen, R. D. Schaller, V. I. Klimov, Phys. Rev. Lett. 102, 177404, 2009
5. N. S. Makarov, S. Guo, O. Isaienko, W. Liu, I. Robel, V. I. Klimov, Nano Lett. 16, 2349-2362, 2016
6. J. A. Castaneda, G. Nagamine, E. Yassitepe, L. G. Bonato, O. Voznyy, S. Hoogland, A. F. Nogueira, E. H. Sargent, C. H. Brito Cruz, L. A. Padilha, ACS Nano 10, 8603-8609, 2016
7. N. S. Makarov, S. Guo, W. Liu, K. A. Velizhanin, I. Robel, V. I. Klimov, in preparation, 2017
10:45 AM - *NM06.01.05
In Situ Accurate Analysis of Colloidal Nanoparticles via Four Wave Mixing
Reuven Gordon 1
1 , University of Victoria, Victoria, British Columbia, Canada
Show AbstractHere we will report a highly accurate method of analysis of colloidal nanoparticles by means of four wave mixing. Other optical methods exist to analyze nanoparticles in solution, such as extinction and dynamic light scattering. Extinction is widely used in plasmonic nanoparticle analysis; however, it is not very sensitive to particle size, even though it is quite sensitive to particle shape. For accurate sizing, usually transmission electron microscopy is used as alternative measure.
In four-wave mixing, two laser beams are interfered with a slight frequency difference (in the 10 GHz – 10 THz range). This drives oscillations in the nanoparticles via electrostriction. When the oscillation frequency matches a natural vibration resonance of the nanoparticles, extremely strong four-wave mixing is observed by scattering of a third beam off of a dynamic grating induced by the electrostriction force.
The vibration resonances allow for accurate sizing and size distribution information. For example, 2 nm gold nanoparticles give a resonance at 1.5 THz. The resonance frequencies allow for precise determination of nanoparticle size and shape, as has been verified by electron microscopy measurements. We have also demonstrated that this method can be used for in-situ growth characterization of nanoparticles.
The observed four wave mixing signal is extremely strong and it shows a turn-on threshold. We have ruled out a stimulated threshold here, and so we believe that this strong response is really the result of a sudden reduction in damping from the water environment, akin to cavitation. We are molecular dynamics simulations to test this hypothesis.
11:15 AM - NM06.01.06
Surface Plasmon Polariton Interference in Gold Nanoplates
Gary Beane 1 , Tuphan Devkota 1 , Paul Johns 1 , Kuai Yu 2 , Gregory Hartland 1
1 , University of Notre Dame, Notre Dame, Indiana, United States, 2 College of Optoelectronic Engineering, Shenzhen University, Shenzhen, Guangdong, China
Show AbstractTransient absorption and Fourier imaging techniques were used to study the optical properties of gold nanoplates. For sufficiently thin gold nanoplates the transient absorption microscopy images show an oscillatory variation in the signal across the plate. This pattern is attributed to interference between surface plasmon polaritons (SPP) modes at the glass-gold interface (the ‘bound mode’) and the gold-air interface (the ‘leaky mode’). The wavelength of the interference pattern is very sensitive to the dielectric constant of the material above the gold nanoplate. For example, changing from air to water changes the wavelength from ca. 1 to 5 µm. Back focal plane imaging was also used to measure the wave-vector of the leaky mode. In combination with the Dk information from the transient absorption images, this allows the wave-vector for the bound mode to be determined. This is the first experimental measurement for the bound SPP mode wave-vector. The measured wave-vectors are in good agreement with the results from finite element simulations, confirming the assignment. The combination of transient absorption microscopy and back focal plane imaging provides unique information about SPPs in metal nanostructures.
11:30 AM - NM06.01.07
Mechanical Vibrations of Metal Nanoparticles for Sensing Applications and Fundamental Fluid Dynamics
Matthew Pelton 1
1 , University of Maryland, Baltimore County, Baltimore, Maryland, United States
Show AbstractPlasmonic metal nanoparticles have been widely investigated as a means of enabling sensitive chemical sensing, primarily using surface-enhanced Raman scattering or refractive-index-induced shifts in plasmon resonance frequencies. Mechanical vibrations of the nanoparticles offer another potential sensing mechanism: adsorption of molecules on the nanoparticle surfaces will reduce the vibration frequency, and the small mass of the nanoparticles means the fractional frequency change will be large. However, in order for a precise frequency measurement to be possible damping of the vibrations within the nanoparticles and by the surrounding media cannot be too strong. This is a particular concern in the liquid environments that are relevant for biomolecular sensing.
Ultrafast laser spectroscopy enables sensitive measurement of the vibrations: an incident pump laser heats the nanoparticles, leading to their expansion and the excitation of mechanical vibrations. The vibrations produce oscillations in the plasmon resonance frequency of the nanoparticles, which are monitored by measuring the change in transmission through the sample of a second, probe laser pulse. By making such measurements on a highly monodisperse sample of bipyramidal gold nanoparticles, we were able to determine both the frequency and the decay rate of the vibrations. Measurements on nanoparticles in different solvents made it possible to determine the portion of damping and the vibrational frequency shift that are due to coupling to the surrounding liquid environment. In high-viscosity fluids, conventional viscous damping could not explain the observations, and it was necessary to take into account the viscoelastic response of the liquids. This occurs because the vibrational periods are comparable to the intrinsic molecular response times of the liquids. These measurements demonstrate the ability of vibrating metal nanoparticles to serve as a sensitive, high-frequency probe of their mechanical environment, and to reveal new phenomena on the nanoscale.
11:45 AM - NM06.01.08
Transient Melting and Recrystallization of Semiconductor Nanocrystals
Matthew Kirschner 1 2 , Daniel Hannah 1 2 , Benjamin Diroll 2 , Xiaoyi Zhang 2 , George Schatz 1 , Lin Chen 1 2 , Richard Schaller 1 2
1 , Northwestern University, Evanston, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractQuantum-confined semiconductor nanocrystals (NCs) possess tunable band-gaps and facile synthesizes making them extremely appealing for numerous applications. While some applications involve low-intensity photoexcitation, others require the generation of multiple electron-hole pairs (usually referred to as ‘excitons’ regardless of binding energy owing to spatial confinement within the NC). Thermal energy is transferred to the NC lattice upon both intraband cooling of each photogenerated exciton and multiexcitonic Auger-recombination that, given the reduced volume to dissipate heat and the depressed melting point, could affect the integrity of the NC in these high intensity excitation regimes. To investigate this dilemma, transient x-ray diffraction experiments were performed on CdSe NCs as a function of particle size, excitation power, and polytype. Changes in the diffraction pattern relayed the NCs transiently melting under surprisingly modest fluences. NCs reverting to initial crystal structures after high intensity excitation suggests that melting is primarily occurring at the surface, which is consistent with analysis done using molecular dynamics. Further, electron structure calculations on melted NCs demonstrated a significantly decreased NC bandgap. Taken as a whole, this work suggests the need to evaluate the physical stability of nanomaterials and the related electronic implications in high brightness display devices and lasers.
NM06.02: Optical and Photonic Properties and Applications
Session Chairs
Alexander Govorov
Masaru Kuno
Monday PM, November 27, 2017
Hynes, Level 3, Room 311
1:30 PM - NM06.02.01
Function Follows Form—Correlation between the Growth and Local Emission of Perovskite Nanostructures
M. Ibrahim Dar 1 , Neha Arora 1 , Shaik Mohammed Zakeeruddin 1 , Michael Graetzel 1
1 , Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractInvestigating local structural, compositional, and emission properties of organic-inorganic lead halide perovskite structures can provide direct evidence regarding the performance of light harnessing and light emitting devices. To resolve emission characteristics at the nano-regime, we exploited cathodoluminescence to carry out temperature dependent emission studies on individual well-faceted perovskite single crystals, and on different perovskite thin films. Interestingly, the local structural features of these perovskite nanostructures investigated using advanced X-ray scattering techniques exhibited a strong correlation with the local emission characteristics. Furthermore, the studies based on scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDS) establish that the compositional heterogeneity can considerably influence the optoelectronic properties of the perovskite nanostructures and the overall performance of the devices based on them. In my presentation, I will discuss the fundamental understanding gained through advanced X-ray scattering, STEM-EDS and cathodoluminescence studies of organic-inorganic lead halide perovskite nanostructures.
References:
Dar, M. I. et al. ACS Photonics 2016, 3, 947-952.
Dar, M. I. et al. Adv. Funct. Mater. 2017, 1701433, doi:10.1002/adfm.201701433
Li, X.; Dar, M. I. et al. Nat. Chem. 2015, 7, 703-711.
Dar, M. I. et al. Adv. Mater. 2015, 27, 7221-7228.
Dar, M. I. et al. Nano Lett. 2014, 14, 6991-6996.
1:45 PM - *NM06.02.01
Existence of a Size-Dependent Stokes Shift in CsPbBr3 Perovskite Nanocrystals
Masaru Kuno 1
1 , University of Notre Dame, Notre Dame, Indiana, United States
Show AbstractColloidal hybrid and all-inorganic perovskite (APbX3; A = CH3NH3+, CH(NH2)2+, and Cs+; X = Cl-, Br-, and I-) nanocrystals (NCs) are excellent candidates for a number of next-generation photovoltaic and light emitting applications due to exceptional optoelectronic properties such as high photoluminescence quantum yields (40-90%), narrow emission linewidths (70-140 meV), and size-/composition-tunable band gaps across the visible. However, a better understanding of their underlying photophysics, specifically the nature of the emitting state, is needed to realize their eventual implementation into devices. In this regard, a Stokes shift exists between the emission and the band edge absorbing state which is universal among hybrid and all-inorganic NCs as well as their thin film counterparts. The presence of a Stokes shift is interesting because it suggests that the absorbing and emitting states are not necessarily the same. We report for the first time a size-dependent Stokes shift for CsPbBr3 NCs and reveal that it does not arise from extrinsic factors such as residual ensemble size distributions. We then go on to investigate an intrinsic origin for this Stokes shift.
2:15 PM - NM06.02.02
Probing Linewidths and Biexciton Quantum Yields of Single Perovskite Nanocrystals in Solution
Hendrik Utzat 1 , Katherine Shulenberger 1 , Odin Achorn 1 , Michel Nasilowski 1 , Moungi Bawendi 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractCesium lead halide perovskite nanocrystals (PNCs, e.g. CsPbX3 X=Cl,Br,I) have become one of the most promising nano-material for a plethora of optoelectronic applications such as LEDs, light down-conversion, and low-threshold lasing.[1] They exhibit high emission quantum yields even in the absense of surface passivating shells, can be obtained via remarkably facile syntheses, and demonstrate band-gap tunability via both halide composition and size confinement.
Despite their tremendous success, our understanding of the fundamental excited state dynamics in single PNCs is still very limited. Their poor photo-stability has hampered single nanocrystal spectroscopic interrogation, and only a handful of studies - all on the least unstable PNCs in the weak confinement regime - have reported biexciton quantum yields and single PNC emission spectra. [2,3,4] As a result, the linewidth broadening mechanism, and Auger recombination dynamics - in particular for confined PNCs - remain illusive.
Here we report the first comprehensive spectroscopic survey of single PNCs, including highly confined and blue emitting PNCs previously inaccessible to single NC spectroscopy. Using solution-phase photon-correlation-Fourier spectroscopy (s-PCFS)[5], we gauge the effect of inhomogeneous broadening, and identify the single PNC emission linewidths. With anti-bunching measurements in soltuion (solution-g(2)) we investigate the biexciton quantum yield in the absence of particle photo-degradation, and under low-flux excitation conditions.[6] For the first time, we identify clear trends in the single NC linewidth and underlying Auger rates with size and halide composition. By correlating our single NC spectroscopic data with the ensemble Stokes shift and photoluminescence lifetime, we develop a comprehensive understanding of the exciton and biexciton dynamics in PNCs. Our results highlight some of the similarities and differences of PNCs compared to established II-IV NCs, and provide clear directions for their synthetic improvement.
1) L. Protesescu et al. Nano Lett. 2015,15,6.
2) G. Raino et al., ACS Nano, 2016, 10,2485-2490.
3) Y. Park et al., J. Am. Chem. Soc., 2015, 10, 10386-10393.
4) F. Hu et al., ACS Nano., 2015, 9,12, 12410-12416.
5) J. Cui et al., Nat.Chem., 2013, 5,7, 602-607.
6) A. Beyler et al., Nano Lett., 2014, 14, 6792-6798.
2:30 PM - NM06.02.03
Bright Triplet Excitons in Lead Halide Perovskites Nanocrystals
Alexander Efros 1 , Michael Becker 2 , Roman Vaxenburg 3 , Georgian Nedelcu 4 , Peter Sercel 5 , Andrew Shabaev 3 , Michael Mehl 6 , John Michopoulos 1 , Sam Lambrakos 1 , Noam Bernstein 1 , John Lyons 1 , Thilo Stoeferle 2 , Rainer Mahrt 2 , Maksym Kovalenko 4 , David Norris 4 , Gabriele Raino 4
1 , Naval Research Laboratory, Washington, District of Columbia, United States, 2 , IBM Research, Zurich Switzerland, 3 , George Mason University, Fairfax, Virginia, United States, 4 , ETH Zurich, Zurich Switzerland, 5 , California Institute of Technology, Pasadena, California, United States, 6 , U.S. Naval Academy, Annapolis, Maryland, United States
Show AbstractThe growing attention to perovskite nanocrystals is connected with their unusual and potentially useful electronic and optical properties. The radiative decay times of these structures at low temperature are in the sub-nanosecond time range and the samples show a quite high photoluminescence quantum yield. To understand the unusually short radiative decay times of excitons in these structures we have carried out size- and composition-dependent fluorescence measurements at the single nanocrystal level and have modelled the spectra and emission dynamics. The theoretical model is based on calculations of the bulk energy band structure of CsPbX3 (X = I, Cl, and Br) perovskites using a first principles approach. To analyze the electronic and optical properties of perovskite nanocrystals we have used the results of these calculations to derive a four band effective mass Hamiltonian. Using this Hamiltonian we calculate the lowest quantum confined levels of the electrons and holes and the spectra of the optically allowed exciton transitions. Calculations show that fast exciton photoluminescence is connected with three orthogonal linearly polarized dipoles reflecting the orthorhombic symmetry of perovskite nanocrystals. The cubic shape of the perovskite nanocrystals results in an inhomogeneous electric field of the emitted and absorbed photons and requires a novel approach for description of the radiative decay time and the polarization properties of the excitons. Taking the shape effect into account, we show that the dramatic shortening of the radiative decay time is connected with the giant oscillator transition strength of excitons weakly confined in large size nanocrystals. The results of our theoretical calculations are in good agreement with the experimental data measured in single CsPbI3, CsPbBr3 and CsPbCl3 nanocrystals.
3:15 PM - *NM06.02.04
One-Dimensional Carrier Confinement in “Giant” CdS/CdSe Excitonic Nanoshells
Mikhail Zamkov 1
1 , Bowling Green State University, Bowling Green, Ohio, United States
Show AbstractWe demonstrate an inverse energy-gradient nanocrystal architecture that supports the formation of two-dimensional excitons in the shell domain. The developed geometry places a wide-gap semiconductor (CdS) at the core of the composite nanoparticle in order to funnel the photoinduced energy into the low-gap CdSe surface layer. As a result, the quantum confinement is achieved in nanoparticles ranging 20-30 nm in size. The formation of excitons in the CdSe shell layer was manifested through a size-tunable emission and the characteristic step-like absorption profile. Transient absorption measurements further elucidate the dynamics of the photoinduced energy relaxation in CdS/CdSe nanoshells providing evidence that excitations of the bulk-like core domain result in a rapid, ~ 2-ps recovery of the CdS bleach attributed to electron cooling. The charge transport characteristics of nanoshell assemblies were evaluated through a side-by-side comparison with CdSe quantum dot solids. According to photocurrent measurements, nanoshell solids showed a 7-fold enhancement in the photoconductivity relative to similarly processed films of spherical CdSe nanocrystals, which was attributed to the reduced interfacial area of “large-grain” nanoshell assemblies. We expect that the developed nanoshell architecture could potentially be extended to a broader range of semiconductors (e.g. CdS/PbS, ZnS/CdS) facilitating the development of quantum dot solids offering improved charge transport characteristics.
3:45 PM - NM06.02.05
Strongly Confined HgTe 2D Nanoplatelets as Narrow Near Infrared Emitter
Eva Izquierdo 1 , Adrien Robin 1 , Livache Clément 2 , Sean Keuleyan 3 , Nicolas Lequeux 1 , Emmanuel Lhuillier 2 , Sandrine Ithurria 1
1 , LPEM, ESPCI, Paris France, 2 INSP, UPMC, Paris France, 3 , Voxtel, Eugene, Oregon, United States
Show AbstractCurrently, some colloïdal nanocrystals such as PbS or CIS (copper indium sulfur) are promising candidates for IR imaging because of ease of size control. However, these materials have extremely broad luminescence features (>100 nm). Two-dimensional semiconductors nanoplatelets (NPLs) recently developed provide a great control of the optical features for cadmium chalcogenide nanocrystals in UV-visible. Consequently, 2D mercury chalcogenides nanoplatelets are considered as colloidal nanocrystals absorbing in near infrared. However these materials can not directly be obtained from a single step synthesis, thus cation exchange appears as an alternative solution to make these materials. CdTe NPLs are used as initial nanocrystals and the cation exchange is performed with bulky mercury amine complex. HgTe NPLs present exceptionally narrow near IR optical feature (57 meV for an emission around 890 nm) and an emission quantum yield in the order of 10%. We demonstrated by EDX analysis that the exchange is completed and by XRD that zinc blende structure is preserved after cation exchange. Owing to the strong quantum confinement in HgTe NPLs, the band edge energy can be tune thanks to the surface chemistry because of the partial delocalization of the wavefunction into the ligand shell. Thin films of HgTe NPLs are integrated into electrolytic transistors and exhibit n- or p-type depending on their capping ligands with either ethanedithiol or sulfide ligands.
4:00 PM - NM06.02.06
Radiative and Nonradiative Recombination of Carriers in Colloidal CdSe Nanoplatelets
Roman Vaxenburg 1 , Steven Erwin 2 , Alexander Efros 2
1 , George Mason University, Fairfax, Virginia, United States, 2 , U.S. Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractColloidal semiconductor nanoplatelets show outstanding optical properties such as tunable emission wavelength, short radiative lifetime, and high quantum yield. To describe these properties, we investigate theoretically the electronic structure and recombination dynamics of charge carriers in CdSe nanoplatelets. We use a combination of first-principles calculations and the 8-band effective mass model to describe the ligand-passivated nanoplatelet surfaces within the general boundary condition formalism. This allows us to calculate the thickness-dependence of the 2D band structure of electrons and holes, their radiative and nonradiative recombination rates, and exciton binding energy. In particular we find that the short radiative decay time is explained by a small radius of the 2D excitons. We further calculate the rate of nonradiative Auger recombination which shows a non-monotonic dependence on the nanoplatelet thickness. We discuss the effects of dielectric confinement in these 2D materials on their electronic and optical properties and carrier recombination processes. The results of our calculations are compared with available experimental data.
4:15 PM - *NM06.02.07
Colloidal Nanorod Heterostructures—From Synthesis to Next-Generation Displays
Moonsub Shim 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractUnderstanding and developing materials that can efficiently separate, recombine, and/or direct charge carriers with nanoscale precision are critical for next-generation electronics, optoelectronics and energy technologies. As heterostructures have enabled today’s semiconductor devices, the introduction of active heterojunctions and interfaces that are atomically well-defined in nanoscale materials can be beneficial for these fundamentally important processes. The ability to engineer band structure/alignment within nanoscale materials that have size and shape dependent properties should lead to new and exciting opportunities in general. If such materials can be made in a way that allows easy and cost-effective processing while maintaining high performance, fast advances to practical applications can be realized. With anisotropic shapes that can be exploited for assembly, charge carrier manipulation and optical anisotropy, incorporating heterojunctions and other functional interfaces into solution processable colloidal semiconductor nanorods represents such a direction. I will first discuss general challenges to the synthesis of complex-yet-well-defined colloidal nanorod heterostructures. Approaches such as spatially selective solution epitaxy, catalytic growth, cation exchange and combinations thereof can be exploited to address these challenges to achieve unique heterostructures with useful properties.1,2 I will then highlight a specific example of double-heterojunction nanorods especially with respect to improvement in performance and new functionality they bring to solution processed LEDs and LED arrays that could open up new directions in displays and related areas.3,4
1 ChemPhysChem 17, 741 – 751 (2016).
2 J. Am. Chem. Soc. 138, 10444 (2016).
3 Nanoscale, 9, 6103 – 6110 (2017).
4 Science 355, 616 – 619 (2017).
4:45 PM - NM06.02.08
Solution-Cast Quantum Dot Photocathodes for the X-Ray Light Sources of the Future
Jeffrey Pietryga 1 , Jaehoon Lim 1 , Nikolay Makarov 1 , Istvan Robel 1 , Qianglu Lin 1 , John Lewellen 1 , Nathan Moody 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractLight-emitting applications for solution-synthesized nanocrystal quantum dots (QDs) make use of over three decades of developments in QD structure designed to prevent photoexcited carriers from being lost to surface defects or to ionization. This is somewhat ironic, given that QDs first gained attention as a material class for use in photocatalysis, which intentionally uses charges photoionized from QDs to drive redox reactions. In the midst of a recent increase in exploration of QD photocatalysis, we are exploring the use of QDs in another application that also exploits photoionization: QD photocathodes for use in the next generation of X-ray light sources. After a brief discussion of the potential benefits of QD films as photocathodes, we present our measurements of the efficiency of electron photoemission of conductive, solution-cast QD films of a variety of compositions in a typical electron gun configuration. By quantifying photocurrent as a function of excitation photon energy, excitation intensity and pulse duration, we demonstrate efficiencies superior to standard copper cathodes in films that are even more robust against degradation under ambient conditions. In our experiments, photoemission from QD films is a multi-photon process. By measuring efficiency under excitation at several different photon energies, we also establish the role of hot-carrier states in electron emission in the multi-photon excitation regime. Finally, we discuss and evaluate the promise of multiple pathways for further efficiency enhancements.
NM06.03: Poster Session I: Optical, Electronic and Magnetic Properties
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - NM06.03.01
Effect of Surface Molecules on Heat Transport at the Interface of Plasmonic Nanoparticle
Ali Rafiei Miandashti 1 , Susil Baral 1 , Hugh Richardson 1
1 Chemistry and Biochemistry, Ohio University, Athens, Ohio, United States
Show AbstractNanoscale thermal transport from a single noble metal nanoparticle (NP) is important in heat-transfer fluids, laser-induced transformation of NPs, optothermal imaging, and targeted photothermal therapies. In most of the reports, the bulk temperature of the medium is measured to study the heat generation/dissipation at the solid liquid interface. Since temperature is localized at nanoscale and the behavior of the system at nanoscale is different from that of bulk, most of these estimations lack precision and accuracy. Here we developed a system to study the heat generation and dissipation from noble metal nanoparticles at the nanoscale. The primary objective of this paper is to investigate the heat generation and dissipation from noble metal nanoparticles to the environment using luminescence thermometry. In our system NaYF4:Yb3+: Er3+ nanocrystals, decorated with gold nanoparticles are used for luminescence thermometry. 532 nm laser was used to illuminate gold nanoparticles and 980 nm laser was used to excite NaYF4:Yb3+: Er3+ nanocrystals. Through illumination of gold nanoparticles, heat was generated from gold nanoparticles and through observation of luminescence emission of Er3+ ions as a function of time, the cooling rate of gold nanoparticles is monitored via luminescence thermometry. The heat dissipation was studied in physiological/non-physiological mediums and the effect of the polar/non-polar mediums was investigated. Finally, the effect of different molecules at the surface of gold nanoparticles was studied through time-resolved temperature measurements.
8:00 PM - NM06.03.02
Effective Charge Separations in Ag2S-CdS-ZnS 1D Heterostructures
Hoying Chen 1 , Yu-Lin Chen 1 , Hsiu-Fang Fan 2 , Yihsin Liu 1
1 Chemistry, National Taiwan Normal University, Taipei City, TW, Taiwan, 2 Life and Genome Science, National Yang-Ming University, Taipei City, TW, Taiwan
Show AbstractSulfide-based 1D heterostructures are effective sensitizers in photovoltaic devices for adjustable band structures. Match-like heterojunctions composed of Ag2S, CdS and ZnS segments were successively confined within the same confinement regimes. Despite of individual Bohr radii (2.2nm, 5.8nm, 2.5nm), tri-metal sulfide 1D heterostructures demonstrated unusual optical and electrical properties of type-II band structures, resulting PNP bipolar junctions in regimes below 10nm. The heterostructures in 1D morphology (>500 nm) and compositions were characterized in TEM/STEM with spatial EDS mapping. The band structures were revealed by multiple fluorescence profiles in UV, visible and NIR regimes, resulting in different lifetimes for recombination pathways. The quantum yields of the tri-heterostructures were estimated above 10%, comparable to published records in 1D nanowires. Epifluorescence from single wires further confirmed the ensemble emission profiles as well as blinking phenomenon, suggesting effective charge separations in the 1D heterostructures.
8:00 PM - NM06.03.03
Carrier Dynamics in Ternary CdSxSe1-x Nanowires
Ismail Ibrahim 1 , Cristal Deharo 1 , Biswadev Roy 1 , Marvin Wu 1
1 , North Carolina Central University, Durham, North Carolina, United States
Show AbstractMetal chalcogenide nanowires have direct bandgaps in the visible region leading to potential applications in advanced photovoltaics and photodetectors, and are excellent model systems for the studies of carrier dynamics in ternary semiconductors due to their ease of growth. CdSxSe1-x nanowires can be produced in low vacuum across the full compositional range, offering band gaps and band positions that can be tailored for particular device requirements. These ternary nanowires, however, often exhibit process-dependent composition and structure variations that strongly affect relaxation pathways for photogenerated charge carriers. Motivated by recent reports of strong, long-lived photoconductivity in CdSxSe1-x, we use photoluminescence microscopy, transient absorption microscopy and a novel time resolved photoconductivity technique to elucidate the mechanisms underlying this phenomenon in CdSxSe1-x nanowires produced through the vapor – liquid – solid mechanism. Photoluminescence (PL) spectra in samples produced with rapid post-growth cooling feature two or more distinct peaks. The narrow width of these peaks, combined with results from selective excitation experiments, show composition variations occur over length scales below the sub-micron optical spot size. Time resolved PL and transient absorption data reveal charge transfer to the narrower bandgap region. The time resolved photoconductivity data, obtained by measuring the transmission of a continuous wave 110 GHz – 150 GHz probe through a CdSxSe1-x sample excited by a 532 nm, 350 ps laser pulse, show significantly longer lifetimes (up to 1 ms) than the transient absorption and PL data. We suggest that this long-lived photoconductivity results from use of significantly lower excitation fluences combined with alloy-broadening effects.
8:00 PM - NM06.03.04
Exciton Transport in Silicon Nanocrystal Films
Zachary Robinson 1 , K Reich 1 2 , Yunxiang Qin 1 , Uwe Kortshagen 1 , B. Shklovskii 1
1 , University of Minnesota, Minneapolis, Minnesota, United States, 2 , Ioffe Institute, St Petersburg Russian Federation
Show AbstractA recent theory by Reich and Shklovskii (ACS Nano, 2016, 10 (11)) proposes a novel exciton “tandem tunneling” mechanism is the dominant interparticle transfer process in films of direct contact Si nanocrystals (NCs). Here, we study exciton diffusion in plasma-produced Si NC films via time and spectrally resolved photoluminescence (PL). The plasma synthesis process has the advantage of depositing clean surface, touching NCs onto substrate from the plasma, with the option to add ligands in solution later. Si is earth abundant and nontoxic, and due to its indirect bandgap exciton lifetimes are long, ten to hundreds of microseconds. Therefore, diffusion lengths could be large if efficient interparticle transport is facilitated. Numerous studies have observed the “stretched exponential” behavior (I(t) ∝ exp((-t/τ)β) in porous and NC silicon films, but diffusion length (LD) and hopping rates have not been determined.
We begin by studying alkene functionalized Si NC films. The ligands allow the particles to be dispersed in solution, where we dope the Si NC films with Au NCs before spin coating onto substrate. The Au NCs serve as bulk quenchers which extinguish excitons non-radiatively. As the Au concentration is increased we decrease the available volume in the film for radiative recombination, and observe systematic changes in the radiative lifetime τ and exponent β, indicative of exciton diffusion. In the PL response, at short times we observe a redshift in peak emission due to exciton diffusion to lower energy sites. At long times (> 500 μs) the peak emission stabilizes, indicating the exciton has reached the transport energy. We model the short time data with diffusion to lower energy sites in a Gaussian DOS, akin to in organic molecules. We combine this with a random walk in lattices with traps model proposed by Balagurov and Vaks (1973). In this model, at large times the surviving excitons are overwhelmingly located in regions with very low trap density, leading to a stretched exponent survival probability with β=3/5. We then use the PL emission vs time to extract hopping time, intrinsic lifetime, and intrinsic trap concentration.
Second, we create films of touching NCs via direct film synthesis beneath the plasma, and achieve photoluminescence after several days of oxidation. Using TRPL we study the transport of excitons in these films of touching NCs via the peak emission red shift as a function of time on the ns and μs scale. We use this data in conjunction with the aforementioned theory to study the effect of interparticle contact area on exciton transport. This is the first time that exciton diffusion in touching NCs has been studied, and yields novel insight into the mechanisms involved in transport through touching NCs, and on the fundamental limits of exciton diffusion in disorder NC systems.
8:00 PM - NM06.03.05
Electronic Properties of PbS Colloidal Quantum Dot Solids Studied with Photoemission Yield Spectroscopy in the Air (PYSA)
Yoshiyuki Nakajima 1 , Haibin Wang 2 , Zeguo Tang 2 , Takaya Kubo 2 , Hiroshi Segawa 2
1 , Riken Keiki Co Ltd, Tokyo Japan, 2 RCAST, The University of Tokyo, Tokyo Japan
Show AbstractTo construct efficient solar cells, the ionization potential (IP) and work function (WF) of constituent materials are one of the most important properties to achieve a good energy level matching. We developed a photoemission yield spectrometer (Photoemission Yield Spectroscopy in Air; PYSA, Riken Keiki Co. Ltd.) to measure WF and/or IP in the air. The PYSA includes a specially designed detector, the “open counter” [1-3], enabling us to detect low energy photoelectrons emitted form materials under atmospheric conditions. Unlike conventional photoelectron spectroscopies of XPS and UPS, the PYSA can carry out a non-vacuum measurement with a high energy-resolution and low photo-excitation energies. A non-vacuum measurement is very suitable for organic semiconductors in powdered or liquid states. Moreover, low energy excitation can ionize electrons at energy levels about the highest occupied molecular orbital (HOMO) with a relatively high efficiency, and make the irradiation damages of samples negligible.
In this paper, the electronic properties of PbS colloidal quantum dots (QCD) and transparent conductive oxides (F-doped SnO2, Sn-doped In2O3 and so on) used for PbS QD/ZnO NW solar cell devices were studied with the PYSA. A PYSA measurement was carried out as follows. UV light emitted from a deuterium lamp were dispersed by a monochromator and focused on a sample. The photoelectrons emitted from the sample were counted by the open counter. Here, the energies of monochromatized UV photons can be scanned from 4.0 eV to 7.0 eV with an increment of 0.05 eV. When UV photons with energies higher than 6.20 eV are required, most of the air in the monochromator must be replaced with N2 gas to minimize the absorption loss of UV light by air. PbS QD layers were spin-coated on glass substrates from an octane solution containing PbS CQDs bearing oleic acid ligands. The oleic acid ligands of the CQDs were then exchanged for halogen ions I- or Cl-. The IPs of the layers were derived from an observed photoemission threshold energy. The IPs of PbS QD-I ligands and PbS QD-Cl ligands were 5.86eV and 5.46eV, respectively.
As evidenced by our measurements, the electronic properties of colloidal QD solids can be tuned through modification of the QD surface with ligand exchange. The PYSA is useful to measure such electronic properties.
[1] M. Uda and H. Kirihata, Japanese Patent S55-179922 (1980), 1447157 (1988)
[2] H. Kirihata, and M. Uda, Rev. Sci. Instr. 52, 68 (1981).
[3] M. Uda, Jpn. J. Appl. Phys. 24, 284 (1985)
8:00 PM - NM06.03.06
Evaluation of ‘Giant’ Nanocrystal Quantum Dots (gQDs) as Donors in FRET Sensing Applications
Margaret Chern 1 , Thuy Nguyen 1 , Andrew Mahler 1 , Allison Dennis 1
1 , Boston University, Boston, Massachusetts, United States
Show AbstractHeterostructured quantum dots consisting of an ultra-thick shell, or ‘giant’ nanocrystal quantum dots (gQDs), exhibit optical properties surpassing those of traditional single material or thin shelled quantum dots (QDs). For example, the reduced or non-blinking nature of gQDs is a valuable asset for single particle tracking studies. We synthesized both CdSe/xCdS and CdSe/xCdS/2ZnS core/shell and core/shell/shell heterostructures with varying thicknesses of the CdS shell (x) in order to assess the benefits and limitations of the more complex materials for typical bioimaging applications. We quantified the impact of shell thickness on the nanoparticle molar extinction coefficient, quantum yield, and brightness in hexane as well as in aqueous media following ligand exchange with a dithiol-based zwitterionic small molecule ligand. The large molar extinction coefficients of the thick-shelled QDs contributed to their high brightness, even though quantum yields dropped at the thickest shells (13 or 16 atomic monolayers of CdS). When the thick CdS shells were coupled with the passivating ZnS cap, post-ligand exchange quantum yields approached 40%-- 5-10x higher than either commercial QDs or gQDs without the ZnS cap with the same coating. The core/shell/shell QDs were systematically assessed for their capacity as Förster resonance energy transfer (FRET) donors as well. Logically, the thick shells contributed to an increase in the donor-acceptor distance when QDs were conjugated to dye-labeled peptides, so thicker shelled QDs exhibited lower FRET efficiencies. It was notable, however, that even the thickest-shell gQDs still exhibited energy transfer and that moderate shell thicknesses (7-10 atomic monolayers of CdS) yielded the brightest FRET sensors that still exhibited significant FRET. The remarkable brightness of gQDs invites the engineering of visible fluorescent sensors with low nanoparticle concentration. Fluorescent sensors with yes/no outputs are valuable in that they do not require special instrumentation or special user knowledge for point-of-care applications. To this end, a test enzymatic cleavage sensor was made with QDs of differing shell thicknesses. We show that thin-shelled QDs were relatively dim by eye and thick-shelled gQDs were very bright, but lacked visible FRET-based modulation, while moderately-shelled gQDs retain enough energy transfer efficiency to show obvious visible changes in the sensor and are bright and distinct for by-eye detection of sensor activity. Our systematic quantification of the advantages and disadvantages of the differently sized CdSe/xCdS/2ZnS QDs for bioimaging and biosensing serve as a guide for optimizing the materials for a given application. The specificity and detailed nature of the measurements for both sensor efficiency and material characterization make for useful reference to materials scientists who wish to further explore the applications of this system.
8:00 PM - NM06.03.07
Enhancement in the Emission Spectra of Gold Nanoparticle Incorporated Indium Oxide Hybrid Nanocomposite Film
Prabal Sen 1 , Durgesh Kar 1 , S Kasiviswanathan 1
1 Department of Physics, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show AbstractPlasmonic metal nanoparticle incorporated semiconductor hybrid nanocomposite has sparked recent interest to study the effect of exciton-plasmon and defect-plasmon coupling over past few years. Gold nanoparticle incorporated indium oxide (AuNP-IO) film exhibits a sharp dip around 575 nm in the transmission spectra due to the localized surface plasmon resonance (LSPR). Photoluminescence of indium oxide (IO) and AuNP-IO nanocomposite has been investigated here. A remarkable red-shift and an enhancement in the emission spectra near LSPR wavelength has been observed in AuNP-IO nanocomposite film over IO film. Both the red-shift and the enhancement in emission spectra are attributed to the defect-plasmon coupling through plasmon induced hot carrier injection.
8:00 PM - NM06.03.08
Wavelength-Dependent Photoresponse at the Metal/Nanostructured TiO2 Interfaces in the Visible Range and Its Persistence
Hyunah Kwon 1 , Ji Ho Sung 1 , Yuna Lee 1 , Moon-Ho Jo 1 , Jong Kyu Kim 1
1 , POSTECH, Pohang Korea (the Republic of)
Show AbstractTiO2 is the most widely used photocatalyst due to its excellent long-term stability, non-toxicity, low cost, and anti-light corrosion. However, the photocatalytic efficiency of TiO2 suffers from its intrinsic properties including the wide band gap limiting available solar irradiation within UV region, and fast recombination rate of photogenerated electron-hole pairs. Therefore, it is crucial to extend light absorption edge to the visible range, and suppress the recombination of electron-hole pairs. Decorating noble metal nanoparticles (NPs) on the surface of TiO2, - noble metal functionalization - is widely used to enhance the photocatalytic activity. The Schottky barrier formed at the metal NPs/TiO2 interface has been reported to make a crucial effect on visible light absorption by either internal photoemission or surface plasmon resonance effect, as well as on suppressing the recombination by an efficient separation of photogenerated carriers. However, non-uniform and discrete distribution of the metal NPs on TiO2 surface makes it difficult to directly investigate and clarify the effect of metal NPs on light absorption, charge separation at the junction, and the factors responsible for improved performances in metal/TiO2 interfaces.
In this study, we investigate the light absorption and the charge separation at the metal/TiO2 Schottky junctions by fabricating and characterizing the unique nanoscale Schottky diodes having hole-patterned Au top and Pt bottom electrodes and a uniformly distributed array of three-dimensional (3D) TiO2 nanohelixes (NHs) between them. Wavelength-dependent photocurrent through Pt/TiO2 NHs/Au structures was obtained under visible light illumination, which gives the direct evidences of the origin of visible light absorption and photogenerated electron-hole separation in the metal/TiO2 interfaces. It is shown that the direction of photocurrent is strongly dependent on the Schottky barrier height formed at the metal/TiO2 interfaces, indicating a great potential for broadband light absorption by various metal functionalization. In addition, huge persistent photoconductivity was observed, indicating that the photogenerated electrons have long lifetime before recombination or surface reaction due to the Schottky barrier which acts as a spatial separator of electron-hole pairs. We believe that the results help the understanding of the origin of the visible light absorption and the separation of the photogenerated electrons at the metal/TiO2 interfaces, which is necessary for the development of highly efficient photocatalysts.
8:00 PM - NM06.03.09
Coherent-Phonon Plasmon Modulation and Deformation Characterization and Applications of Gold Bipyramids and Nanojavelins
Matthew Kirschner 1 2 , Clotilde Letheic 1 , Xiao-Min Lin 2 , Craig Chapman 1 , Yuxiu Li 2 3 , George Schatz 1 , Lin Chen 1 2 , Richard Schaller 1 2
1 , Northwestern University, Evanston, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States, 3 , Wuhan University, Wuhan China
Show AbstractThe ability to tune the localized surface plasmon resonances (LSPRs) of metallic nanoparticles enables a wide range of applications in photocatalysis, photovoltaics, and medical therapeutics. However, optical excitation of LSPRs leads to excitation of particle vibrational modes which can alter the designed optical characteristics. When electron-phonon coupling occurs on a timescale much shorter than the period of a phonon mode, those photo-generated vibrations are in phase resulting in changes in particle size and resultantly LSPR. While previous work in this field has provided insight into phonon dynamics and particle-solvent coupling, there has been relatively little work characterizing the magnitude of the photo induced mechanical or optical changes. We characterize the acoustic phonons for a wide range of gold bipyramids and larger aspect ratio nanojavelins with LSPRs ranging from 670 to 1330 nm. Specifically, we have developed a methodology that relates Finite Difference Time Domain calculations to experimentally observed shifts in LSPR to calculate particle elongation. We found that geometric distortions are linearly related to excitation power and slightly increase with particle size when normalized for photons absorbed. This analysis is then used in the development of a model system that takes advantages of these changes in LSPR to transiently modulate an electronically coupled system. Such information offers the basis to further expand on the potential utility of coherent acoustic phonons for manipulations of higher complexity structures that we have begun to explore and will discuss.
8:00 PM - NM06.03.10
The Role of Electron Delocalization on Exciton-Phonon Coupling in CdSe/CdS Colloidal Nanocrystals
Hendrik Utzat 1 , Igor Coropceanu 1 2 , Jason Yoo 1 , Moungi Bawendi 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemistry, The University of Chicago, Chicago, Illinois, United States
Show AbstractColloidal nanocrystals of II-VI materials (NCs) have found widespread application in display and LED technologies. In these NCs, the exciton-phonon interaction in crucially determines the application relevant emission lineshape. However, the strength and nature of exciton-phonon interaction in NCs remains poorly understood, and has been subject to a multitude of conflicting studies in the past.[1,2] In particular, it has proven difficult to reconcile the narrow (<1 meV) low temperature (~4 K) linewidths and weak phonon sidebands with the broad room temperature emission linewidth (60-100 meV) within the framework of a suitable model. Moreover, clear relationships between exciton-phonon coupling parameters and the architecture of NCs are not yet established.
To elucidate the exciton-phonon interaction in NCs, we have studied a series of CdSe/CdS core/shell NCs with vastly different shell-thicknesses. The quasi type-II band alignment in these materials allows tuning of the excited state electron-hole separation with the shell-thickness.[3,4] Using single NCs emission spectroscopy over a wide temperature range, we have investigated the role of the shell-growth induced carrier separation on the exciton-phonon coupling parameters.
We find that the room temperature single NC lineshape of thin-shell CdSe/CdS and the lineshape at 4 K can be reconciled within the framework of a self-consistent model taking a single set of exciton-phonon coupling parameters into account. For thick-shell CdSe/CdS NCs, we identify an additional broadening mechanism due to enhanced coupling to optical phonon modes. Our study highlights the role of electron-hole separation in exciton-phonon coupling in II-VI NC heterostructres.
[1] M.Salvador et al. J.Chem.Phys. 2006,125,18.
[2] C.Lin et al., ACS Nano, 2015, 9 (8),8131-8141.
[3] J.Cui et al., Nano Lett., 2015, 16, 289-296.
[4] C.Javaux et al., Nat. Nano., 2013, 8, 206-213.
8:00 PM - NM06.03.11
Application of Metamaterial Nano-Engineering for Increasing the Superconducting Critical Temperature
Michael Osofsky 1 , Vera Smolyaninova 2 , Kathryn Zander 2 , Thomas Gresock 2 , Shanta Saha 2 , Bradley Yost 2 , Christopher Jensen 2 , Joseph Prestigiacomo 1 , Heungsoo Kim 1 , Nabil Bassim 5 , Richard Greene 3 , Igor Smolyaninov 4
1 , Naval Research Laboratory, Washington, District of Columbia, United States, 2 Department of Physics Astronomy and Geosciences, Towson University, Towson, Maryland, United States, 5 Materials Science and Engineering Department, McMaster University, Hamilton, Ontario, Canada, 3 Dept of Physics, Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland, United States, 4 Department of Electrical and Computer Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractWe have demonstrated that the metamaterial approach to dielectric response engineering increases the critical temperature of a composite superconductor-dielectric system in the epsilon near zero (ENZ) and hyperbolic regimes. To create such metamaterial superconductors three approaches were implemented. In the first approach, mixtures of tin and barium titanate nanoparticles of varying composition were used [1]. An increase of the critical temperature of the order of 5% compared to bulk tin has been observed for a 40% volume fraction of barium titanate nanoparticles. Similar results were also obtained with compressed mixtures of tin and strontium titanate nanoparticles. In the second approach, we demonstrate the use of Al2O3-coated aluminium nanoparticles to form an ENZ core-shell metamaterial superconductor with a Tc that is three times that of pure aluminium [2]. In the third approach, we demonstrate a similar Tc enhancement in thin Al/Al2O3 heterostructures that form a hyperbolic metamaterial superconductor [3]. IR reflectivity measurements confirm the predicted metamaterial modification of the dielectric. These results open up numerous new possibilities of considerable Tc increase in other superconductors. This work was supported in part by NSF grant DMR-1104676.
References
1. V. N. Smolyaninova, B. Yost, K. Zander, M. S. Osofsky, H. Kim, S. Saha, R. L. Greene, and I. I. Smolyaninov, Scientific Reports 4, 7321 (2014).
2. V. N. Smolyaninova, K. Zander, T. Gresock, C. Jensen, J. C. Prestigiacomo, M. S. Osofsky, and I. I. Smolyaninov, Sci. Rep. 5, 15777 (2015).
3. V. N. Smolyaninova, C. Jensen, W. Zimmerman, J. C. Prestigiacomo, M. S. Osofsky, H. Kim, N. Bassim, Z. Xing, M. M. Qazilbash, I. I. Smolyaninov, Sci. Rep. 6, 34140 (2016).
8:00 PM - NM06.03.12
Surface Chemistry and Electronic Structure of Intermetallic Nanoparticles Studied by X-Ray Photoelectron Spectroscopy
Anna Regoutz 1 , Andres García-Trenco 2 , Edward White 1 , Milo Shaffer 1 , Charlotte Williams 2 , David Payne 1
1 , Imperial College London, London United Kingdom, 2 , University of Oxford, Oxford United Kingdom
Show AbstractX-ray photoelectron spectroscopy (XPS) is a method used widely in the study of solid surfaces. It provides a unique combination of qualitative and quantitative results concerning the chemical environment and elemental atomic ratios whilst being very surface-sensitive and non-destructive. The surface sensitivity of XPS depends on the kinetic energy of the excited photoelectrons which is directly coupled to the X-ray energy being used. This close correlation between information-depth and experimental setup can be exploited to study nanostructures and multi-layered systems.
In this study we use intermetallic Pd-Ga and Pd-In nanoparticles (NPs) to demonstrate how XPS can enable advanced understanding of the surface chemistry and electronic structure of nanostructures in general. In these intermetallic systems the presence of surface oxides, including Ga2O3 and In2O3, as well as of metallic Pd can influence their physical characteristics dramatically.
Core level spectra, including Pd 3d, Ga 2p, In/Ga 3d, and In 4d, as well as the In MNN Auger line, were used to study the oxidation states of the metals and the elemental composition of the samples. The combination of core levels with distinctly different kinetic energies, e.g. Ga 2p and 3d, which lie about 1 keV apart, allows the differentiation of species at the surface and in the bulk of the nanoparticles. This difference in kinetic energy results in significant changes to the information depth (quantified by the inelastic mean free path) which e.g. between Ga 2p and 3d changes from 1.1 to 3.1 nm. Therefore, whilst some core level spectra provide a truly surface sensitive image of the NPs, others are dominated by the bulk of the NPs. Using this analysis, one is able to clearly differentiate between species present on the surface or the bulk.
Furthermore, valence band (VB) spectra are used to study the electronic structure of the NPs. Clear changes in the VB structure, and in particular the VB onset, can be used to directly follow the formation of different phases going from purely metallic to intermetallic to insulating. Whilst metallic Pd shows a high density of states at the Fermi energy EF, the VB maximum shifts away from EF upon formation of the intermetallic phases. However, a small intensity remains leading to the metal-like behaviour of these materials. In contrast, metal oxide NPs have no intensity at EF with a gap opening up between EF and VBmax. In addition, a clear quenching of the overall density of states across these phase changes is a clear indication for alterations in the electronic behaviour.
Ultimately, this work demonstrates the capability of XPS measurements coupled with a detailed analysis to study the chemical and electronic structure of nanostructured systems. In addition, depth sensitive information provides surface to “bulk”-like results, which can be used to identify specific surface species which can influence the overall behaviour of the nanoparticles.
8:00 PM - NM06.03.13
Lead-Free, Blue Emitting Bismuth Halide Perovskite Quantum Dots
Guangda Niu 1 , Meiying Leng 1 , Zhengwu Chen 1 , Ying Yang 1 , Jiang Tang 1
1 , Huazhong University of Science and Technology, Wuhan China
Show AbstractLead halide perovskite quantum dots (QDs) are
promising candidates for future lighting applications, due to
their high quantum yield, narrow full width at half maximum
(FWHM), and wide color gamut. However, the toxicity of lead
represents a potential obstacle to their utilization. Although
tin(II) has been used to replace lead in films and QDs, the high
intrinsic defect density and oxidation vulnerability typically
leads to unsatisfactory material properties. Bismuth, with much
lower toxicity than lead, is promising to constitute lead-free
perovskite materials because Bi3+ is isoelectronic to Pb2+ and
more stable than Sn2+. Herein we report, for the first time, the
synthesis and optical characterization of MA3Bi2Br9 perovskite
QDs with photoluminescence quantum yield (PLQY) up to
12%, which is much higher than Sn-based perovskite nanocrystals.
Furthermore, the photoluminescence (PL) peaks of
MA3Bi2X9 QDs could be easily tuned from 360 to 540 nm
through anion exchange.
8:00 PM - NM06.03.14
Size Dependence of the Photoluminescence Efficiency of CsPbBr3 Nanocrystals
Silvia Motti 1 , Quinten Akkerman 2 , Ajay Kandada 1 , Liberato Manna 2 , Annamaria Petrozza 1
1 , Istituto Italiano di Tecnologia, Milan Italy, 2 , Istituto Italiano di Tecnologia, Genova Italy
Show AbstractLead halide perovskites have attracted great attention as emerging material for photovoltaics, but are also promising for light emitting diodes (LED) and lasing, specially due to their solution processability, tunability of photoluminescence (PL) emission and high PL quantum yields (PLQY). The PL properties of lead halide perovskite polycrystalline thin films is strongly affected by a high defect density. The synthesis of colloidal nanocrystals (NCs) has been reported as an interesting approach for obtaining highly emissive and defect free perovskite crystals. We combine steady-state and time resolved PL, Raman spectroscopy, and femtosecond transient absorption measurements to study the two type of samples. We investigate the size dependence of CsPbBr3 NCs, in the range from 6 to 30 nanometers. We report an interesting dependence of the PLQY on crystal size, where we observe that the larger crystals, although nearly defect free, have lower PLQY. It suggests that apart from competing trapping processes and surface losses, additional factors influence the carrier recombination and limit the efficiency of PL. Our results suggest that stronger lattice strain in larger crystals and the relative phonon distribution and dynamics could be an intrinsic limit for lead halide perovskite PLQY.
8:00 PM - NM06.03.16
Robust Lanthanide Emitters in Polyelectrolyte Thin Films for Photonic and Plasmonic Applications
Andrew Greenspon 1 , Evelyn Hu 1
1 , Harvard University, Cambridge, Massachusetts, United States
Show AbstractNanoscale optical cavities and antennas allow strong spatial localization of electromagnetic fields and the possibility of nonlinear excitation of appropriately matched emitters. In addition to the correct resonance in frequency, such emitters should be robust, long-lived, and easily and controllably integrated into the cavity structure without substantial quenching of their luminescence. Quenching in particular is a critical problem when fabricating plasmonic cavities. We describe a method of forming optically active thin films with typical thicknesses of 10s of nm that contain trivalent lanthanide (Ln3+) emitters whose emission is not quenched even when placed within 10 to 20 nm of the surface of a gold film.
Luminescent thin films ranging from ~9 to 43 nm in thickness were formed on silicon, quartz, and gold substrates through layer-by-layer deposition of positive and negative polyelectrolytes. The Ln emitters, both europium (Eu3+) and terbium (Tb3+) were incorporated into the prepared multilayer films through a charge specific and charge controlled attachment of the organometallic complex Ln-(tris)dipicolinate. Eu-containing films demonstrate principal peak emission at 616 nm with a full-width-half-maximum (FWHM) of 2.35 nm while Tb-containing films show the most intense emission peaks ranging from 539 to 553 nm. The primary variation in Ln emission between samples is the overall emission intensity. The emission linewidths do not change significantly, and the relative intensity between different emission peaks from the same Ln only changes slightly between dielectric and metallic surfaces. The lanthanide emission is not quenched even when the Ln-dipicolinate is brought into close proximity with a metallic gold surface and may in fact be enhanced.
We have found a correlation between Ln emission intensity and the number of polyelectrolyte layers. Although the Ln-complex initially binds to the top of the multilayer structure, micro-photoluminescence experiments combined with preliminary X-ray photoelectron spectroscopy suggest that the Ln-complex diffuses below the surface into the multilayer to some degree. The ease of use of this process also extends to mixtures of Ln-(tris)dipicolinate solutions, allowing us to tune the color output of these Ln-containing films for possible use in lighting, imaging, or bio-sensing. The emission from the lanthanides in these multilayers is robust in intensity, and in durability, with emission intensity and linewidth from some samples preserved over multiple months after the samples are prepared. These results as a whole demonstrate the possibility of using this platform to controllably integrate stable and robust lanthanide emitters within a variety of nanophotonic cavity structures.
8:00 PM - NM06.03.17
Understanding and Manipulating Quantum Dot Photoluminescence Lineshapes—Traps, Defects and Surface States
Justin Caram 1 , Moungi Bawendi 2 , Sophie Bertram 2 , Eric Hansen 2
1 , University of California, Los Angeles, Los Angeles, California, United States, 2 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe ability to manipulate and confine excitons in colloidal QDs allows for their broad range of optoelectronic applications. Exciton properties are measured using ensemble photoluminescence (PL), for which the linewidth and quantum yield presents a rapid analytical tool for determining synthetic qualtiy. However, for this tool to work, we need to fully understand the intrinsic (or single copy) photophysics of a nanocrystal. In particular, in cases where the photoluminescence signatures are partially attributed to trap or defect states, ensemble PL linewidths no longer report on easily controllable synthetic parameters (e.g. size distribution). We present recent measurments of intrinsic nanocrystal linewidths of NIR and IR emitting PbS and CuInS2 QDs, measured using solution photon correlation Fourier spectroscopy (S-PCFS). S-PCFS results demonstrate the effect of heterogeneous traps and defects in governing single molecule linewidths, with broad implications to nanocrystal synthetic preparations and device photophysics.
8:00 PM - NM06.03.18
True Atomistic Level Insights into the Elusive Role of Core-Shell Interfacial Layer on the Optical Properties of Heterostructured Semiconductor Nanocrystals
Somak Majumder 1 , Ajay Singh 1 , Noah Orfield 1 , Han Htoon 1 , Jennifer Hollingsworth 1
1 MPA-CINT, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIn recent years ultra-photostable (non-blinking and non-photobleaching), non-self-reabsorbing and narrowband-emitting core/thick-shell ‘giant’ quantum dots (gQDs) have emerged as promising alternatives to rare-earth phosphors as downconversion materials for solid-state lighting (SSL).1-4 Here, we compare two nominally identical CdSe/CdS gQDs characterized by similarly suppressed blinking and photobleaching behavior at room temperature, but different quantum yields (QYs) and different responses to “stress” conditions. The two were synthesized from the same CdSe cores but using different shell-growth methods to achieve thick, >5 nm CdS shells. One, gQD-X, has a high QY of 75%, while the other, gQD-Y, has a moderate QY of 45%, such that gQD-X would appear to be the superior nanocrystal emitter. Unexpectedly, however, when subjected to LED device lifetime testing, gQD-Y outperforms gQD-X. Furthermore, in single-nanocrystal “stress tests” performed to elucidate the behavior of gQDs at the device level, gQD-Y is revealed to be significantly more stable under conditions of high photon flux (to 10 W/mm2), temperature (to 100 °C), and/or humidity (to 75% relative humidity). In addition, as determined by analysis of condition- and time-dependent fluorescence lifetime-intensity distributions (FLIDs), we find that gQD-X and gQD-Y photobleach by different mechanisms.5 Critically, we characterize for the first time the internal core/shell interface at the atomic scale, explicitly defining the extent of anion mixing (“alloying”) for each type of nanocrystal, and we perform defect-density analysis for the two gQDs. We directly correlate these previously elusive structural properties with the observed differences in device and single-dot behavior, laying the foundation for an intelligent materials-by-design strategy toward bright and truly photostable QD emitters.
References:
Hollingsworth, J. A. et al. U.S. Patent 7,935,419 2011.
Ghosh, Y. et al. J. Am. Chem. Soc. 2012, 134, 9634.
Kundu, J. et al. Nano Lett., 2012, 12, 3031.
Hanson, C. et al. ACS Appl. Mater. Interfaces 2015
Orfield, N. et al. Submitted 2017.
8:00 PM - NM06.03.19
Enhanced Chiral Fields from Magnetic Hotspots in Achiral Dielectric Nanoantennas
Kan Yao 1 , Yongmin Liu 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractAn object is chiral if it is not superimposable to its mirror image. While a pair of chiral molecules, termed enantiomers, share the same scalar physical properties, they could function differently in many biological and chemical processes. Therefore, discriminating between enantiomers is vitally important, especially in pharmacology and life sciences.
Chiral light-matter interactions provide an opportunity to achieve this goal. For example, circular dichroism (CD) spectroscopy that measures the differential absorption of left- and right-circularly polarized (CP) light is widely used to investigate the structural information of chiral molecules. However, CD signals are usually very weak due to the intrinsically weak chirality and low concentrations of the target molecules. In order to enhance CD signals or enantioselectivity, different schemes have been proposed by utilizing standing waves, plasmonic resonances, magnetic resonances, and nano-cavity resonators. Despite improved differential absorption by the chiral molecules, these methods suffer from either strong background absorption by the nanostructures or non-uniform chiral fields that hinder the global CD enhancement. Both issues will restrict the achievable measurement sensitivity. Therefore, new platforms exhibiting low loss and uniform chiral fields are highly desirable.
In this work, we numerically study the generation of chiral fields in a silicon dimer nanoantenna. With experimentally achievable geometric parameters, it is shown that a magnetic hotspot can be created in the gap area, which serves as a favorable constituent to form enhanced and uniform local chiral fields. A volume-averaged chirality enhancement over 15 fold is demonstrated, whereas the dissymmetry factor is not sacrificed as in most existing plasmonic nanostructures. The underlying mechanism is revealed by the mode analysis and inspecting the near field distributions. We further investigate the CD enhancement by attaching a chiral medium to the nanoantenna. Because the antenna is achiral and the loss of silicon is weak in the visible region, very small background absorption will be present. Finally, we compare the dielectric antennas with metallic nanoparticles under linearly polarized excitations. In spite of comparable chirality enhancement, the dielectric nanoantennas are superior in the uniformity of chiral fields, dissymmetry factor and fabrication feasibility. Being able to generate and engineer chiral fields without employing complex nanostructures or lossy materials, we expect that our findings promise a new platform for CD spectroscopy, chiral sensing and photolysis.
8:00 PM - NM06.03.20
Gallium—A Versatile Element for Tuning the Photoluminescence Properties of InP Quantum Dots
Karl Wegner 1 2 3 , Marie Carrière 1 2 , Peter Reiss 1 2 3
1 INAC-SyMMES, Université Grenoble Alpes, Grenoble France, 2 INAC-SyMMES, CEA Grenoble, Grenoble France, 3 , Centre National de la Recherche Scientifique (CNRS), Grenoble France
Show AbstractThe unique optoelectronic properties of colloidal semiconductor quantum dots (QDs) made them to a well-established class of nanomaterials with a wide application range. Although the most investigated types of QDs are cadmium- and lead-based, strict regulations in the EU and in other countries concerning their use in consumer products is severely limiting their commercial utilization. This has drawn the interest to alternative materials with less toxicity but having similar photophysical properties [Reiss et al., Chem. Rev. 2016, 116, 10731-10819].
III-V QDs and in particular InP-based nanocrystals range among the most promising alternatives. With a bulk band gap of 1.35 eV and an exciton Bohr radius of ca. 10 nm the photoluminescence (PL) emission of InP QDs can be tuned from the blue/green to the near-infrared spectral range. In terms of stability the more covalent character of InP compared to the higher ionicity in Cd- and Pb-based QDs is an advantage. However, this feature makes the synthesis of monodisperse QDs with a small PL linewidth more challenging as highly reactive precursors and harsh reaction conditions are required. In order to manipulate the size and shape of InP QDs and tailor their photophysical and optoelectronical properties different strategies were reported. They range from the use of different synthetic parameters such as types and concentrations of precursors and temperatures to post-synthetic treatments like surface etching. Another possibility is the incorporation of other elements within the InP core synthesis like zinc or gallium. In the case of zinc, alloyed In(Zn)P QDs exhibit longer PL decay times, increased Stokes shift and improved QY with respect to pure InP QDs due to enhanced charge carrier confinement induced by lattice fluctuation [Thuy et al., Appl. Phys. Lett. 97, 2010, 193104]. Gallium has been used much less so far even though its beneficial effect on the emission properties in form of a thin GaP interlayer between the In(Zn)P core and an outer ZnS shell has been demonstrated [Kim et al., J. Am. Chem. Soc. 2012, 134, 3804-3809].
In this contribution, we will present novel approaches for the incorporation of Ga into the InP QD. Depending on the nature of the Ga precursor the emission of the InP QDs can be either red- or blue-shifted and allow a PL range from 475 nm to 650 nm with quantum yields up to 70%. The presence of Ga resulted not only in a significant PL enhancement but also a size focusing effect was observed leading to a PL linewidth of 45 nm. Photophysical characterizations (steady-state and PL life-time measurements), transmission electron microscopy, XRD and EDX give insights into structural and photophysical properties of the obtained InGaP nanocrystals. Their use in biological applications like biosensing or bioimaging requires biocompatibility. Therefore we investigated their cytotoxic behavior in terms of cell proliferation, reactive oxygen species (ROS) generation and genotoxicity.
8:00 PM - NM06.03.21
Effects of Radial Grading of the Compositional Profile on Auger Recombination in Semiconductor Quantum Dots
Young-Shin Park 1 2 , Jaehoon Lim 2 , Nikolay Makarov 2 , Victor Klimov 2
1 , University of New Mexico, Albuquerque, New Mexico, United States, 2 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractAuger recombination is a nonradiative three-particle process wherein an energy released during electron-hole recombination is transferred to a third carrier and then dissipated as heat. Auger decay is enhanced in quantum-dot (QD) forms of semiconductor materials compared to their bulk counterparts due to the enhancement in carrier-carrier Coulomb interactions caused by close proximity between interacting charges, effective reduction of dielectric screening, and relaxation of translation momentum conservation. Since this process is detrimental to many prospective QD-based applications including light-emitting diodes (LEDs) and QD lasers, the development of effective approaches for suppressing Auger recombination has been an important goal in the QD field. One such approach involves “smoothing” of the confinement potential, which suppresses the intraband transition involved in the dissipation of the electron-hole recombination energy and can reduce the Auger decay rate by orders of magnitude.
Here we report spectroscopic studies of the effect of a varied shape of the confinement potential on Auger decay employing a series of CdSe/CdS-based QDs wherein the core and the shell are separated by an intermediate layer of a CdSexS1-x alloy. The alloy layer (1.5 - 3 nm thick) is comprised of 1 to 5 sublayers with a radially tuned composition (through varying x) and width. To evaluate the degree of Auger decay suppression, we analyze a biexciton photoluminescence (PL) quantum yields (QYs) of graded-QDs inferred from single-dot photon correlation measurements and compare them to values observed for reference samples with “sharp” core/shell interfaces. Our studies demonstrate that using a five-step grading scheme, we can boost the biexciton PL QY to ~60% for individual dots and ~31% on average. These values are a considerable improvement versus those in reference samples with a similar effective “excitonic volume”, where the biexciton PL QY is less than ~15%. These results provide direct proof that the primary reason for Auger decay suppression in graded structures is the engineered shape of the confinement potential but not a trivial volume-scaling effect. Further, due to nearly identical emissivities of neutral and charged excitons, these QDs exhibit an interesting phenomenon of lifetime blinking, for which random fluctuations of a photoluminescence lifetime occur for a nearly constant emission intensity. The overall conclusion of our studies is that the strategy of “interface-engineering” represents a highly effective approach for suppressing Auger recombination without affecting the degree of quantum confinement and hence the emission wavelength. The developed strategy should help improve the performance of QD-based devices, especially, LEDs and lasers as both of these applications would benefit from highly efficient emission from charged and neutral multicarrier states.
8:00 PM - NM06.03.22
Core/Barrier/Multi-Branch Nanocrystal Heterostructure with Tunable Dual-Band Emission
Sung Jun Lim 1 , Seung Koo Shin 2
1 , Daegu Gyeongbuk Institute of Science and Technology, Daegu Korea (the Republic of), 2 Chemistry, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractColloidal semiconductor nanocrystals displaying dual-band emission are of great interest due to complex multi-carrier interaction and relaxation dynamics in nanostructures having multiple emissive states, which have potential applications in white light generation, multimodal imaging, radiometric sensing, and quantum light source. Numerous dual-emitting nanostructures have been introduced and all have demonstrated some degree of spectral tuning by controlling structure and composition during colloidal growth. Here, we report a new dual-emitting nanostructure whose emission spectrum can be widely and continuously tailored by using a post-growth photoetching process. We synthesized a core/barrier/multi-branch nanocrystal heterostructure (NCH), that is a dual quantum system composed of a single quantum dot core and multiple quantum rod branches. A wide-bandgap barrier that electronically separates the two quantum systems allowed both core and branches to be brightly emissive (total QY up to ~40%) under ambient excitation fluence (1–10 nW/cm2). More importantly, the dual-band spectrum were continuously tuned by controlling the branch emission by applying photoetching. The quantum size-selective photoetching enabled precise tuning of the branch emission in a broad visible range (500–585 nm) while significantly narrowing the bandwidth (FWHM ~20 nm). Time-resolved fluorescence decay and photoluminescence excitation spectroscopy studies respectively confirmed that the dual emissions were from the two distinct quantum systems (dot and rod) and the presence of significant non-radiative energy transfer from the wider-bandgap branches to the narrower-bandgap core were present. Our work suggests a novel and versatile strategy of designing dual-emitting nanocrystals with wide and precise spectral tuning by controlled photoetching.
8:00 PM - NM06.03.24
Amplified Chiroptical Activity and Field Modulated Optical Transmission of Paramagnetic Nanoparticles
Jihyeon Yeom 1 , Mahshid Chekini 1 , André Moura 2 , Nicholas Kotov 1
1 , Univ of Michigan, Ann Arbor, Michigan, United States, 2 , Federal University of São Carlos, Sao Carlos Brazil
Show AbstractChirality is a property unifying both electromagnetic waves and matter. Materials with time- and parity-reversal asymmetries give rise to chiroptical phenomena among which optical rotation dispersion (ORD) and circular dichroism (CD) being the most common and are extensively used in biology. These effects are associated with breakage of left/right symmetry for circularly polarized photons and are primarily associated with the interplay of the electrical field vectors of photons and chiral media. If the media is achiral, the external magnetic field leads to breaking of the time-reversal symmetry of light propagation known as magnetic circular dichroism (MCD). The second order effect that is much more difficult to observe is magneto-chiral dichroism (MChD); it occurs when the magnetic field is applied to chiral magnetic media and both time- and parity-reversal symmetries are broken. MChD manifests as the dependence of absorption or emission of non-polarized light on the directionality of magnetic field.
Chiroptical effects associated with the magnetic component of light are essential for studies of spintronics, skyrmions, magnetochemistry, and Earth’s homochirality. However, it is well known since M. Faraday, that magnetic field of photons are generally much weaker than those based on the electrical component of the electromagnetic waves. Despite the technological appeal of chiromagnetic phenomena as a platform for memory elements, optoelectronic devices, high-speed information processing, and chiral catalysts, the requirements of low temperatures of T=5-7 K and high magnetic fields of B = 1.2-7.5 T complicates their implementation. The difficulties with the molecular design of materials possessing chiral centers with large magnetic moment or exhibiting long-distance spin-coupling that should also be thermally-stable and oxidation-resilient are also well known.
Chiral inorganic nanoparticles (NPs) provide new opportunities for the design of materials and the studies at the nexus of magnetism and chirality. Although subjected to the same requirements of time- and parity-reversal asymmetries, local magnetization of the chiral “centers” (i.e. NP cores) and their interaction with photons are enhanced due to chiral geometries transitioning from the molecular to nanoscale. Here, we demonstrated amplifying the intrinsic chiroptical activity of NPs and field modulation of optical transmission of paramagnetic NPs.
8:00 PM - NM06.03.25
Optical Determination of Crystal Phase in Semiconductor Nanocrystals
Andre Schleife 1 , Sung Jun Lim 2 , Andrew Smith 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 , DGIST, Daegu Korea (the Republic of)
Show AbstractA rapid way of reliably determining crystal phase is essential in order to unequivocally relate electronic and optical properties of a material to the underlying atomic geometry. Accurate techniques, such as X-ray diffraction, have been established to probe bulk materials with high confidence. However, these tend to lead to ambiguous phase signatures when small nanocrystals or polytypic systems are studied. Furthermore, these approaches are oftentimes incompatible with high-throughput experimentation and samples in solution.
We recently combined highly accurate absorption spectroscopy experimentation with cutting-egde first-principles theoretical spectroscopy to study the electronic and optical properties of CdSe nanocrystals [1]. This allowed us to distinguish between the cubic zinc-blende and hexagonal wurtzite crystal phase exclusively based on optical properties, by investigating the spectral range at around 5 eV, i.e., far above the absorption edge (1.76 eV). In this talk we describe the computational work needed and results obtained, which are all based on parameter-free density functional and many-body perturbation theory calculations.
In particular, we show that the influence of excitonic effects on optical absorption spectra of bulk CdSe is negligible due to strong dielectric screening. This justifies using the computationally cheaper density-functional theory with the PBE exchange-correlation functional and a scissors shift. This simplification becomes necessary due to the large number of atoms in a semiconductor nanocrystal, that leads to very high computational cost. We then study optical absorption spectra of pure zinc-blende, pure wurtzite, and mixed nanocrystals in order to demonstrate that focusing on peaks at about 3-4 eV above the absorption onset allows to clearly distinguish between zinc-blende and wurtzite as the crystal phase of the nanocrystal. We show that this is possible even semi-quantitatively in mixed systems. In addition, we are able to explain the origin of the peak structure in this spectral region and compare our results to experiment throughout.
[1] S. Jun Lim, A. Schleife, A. M. Smith, "Optical determination of crystal phase in semiconductor nanocrystals", Nat. Comm. 8, 14849 (2017)
8:00 PM - NM06.03.26
Coupling of Self-Organized InAs Quantum Dots and Ag Nanoparticles
Vladimir Chaldyshev 1 2 3 , Alexander Kosarev 1 3 , Alexey Kondikov 1 2 3 , Nikita Toropov 2 , Igor Gladskikh 2 , Polina Gladskikh 2 , Tigran Vartanyan 2 , Valeriy Preobrazhenskiy 4 , Michail Putyato 4 , Boris Semyagin 4
1 , Ioffe Institute, Saint Petersburg Russian Federation, 2 , ITMO University, St. Petersburg Russian Federation, 3 , Peter the Great Polytechnic University, St. Petersburg Russian Federation, 4 , Institute of Semiconductor Physics, Novosibirsk Russian Federation
Show AbstractNanostructures and metamaterials incorporating semiconductor quantum dots (QDs) and metal nanoparticles (NPs) have been intensively studied. Such hybrid structures take advantage of physical properties of different materials, which can be useful for chemical and biological sensor, solar calls, optical and optoelectronic devices. For instance, self-assembled InAs QDs are excellent light emitters due to localized excitons, suitable for lasing, single photon sources and other applications. At the same time silver NPs can enhance local electromagnetic field and provide good coupling of electro-magnetic waves with localized plasmon excitations.
In this contribution we report on experimental realization of a coupled system of InAs QDs buried in GaAs and Ag NPs on the GaAs surface.
A stack of five layers of epitaxial InAs QDs separated by 10 nm thick GaAs barriers was grown by molecular beam epitaxy using Stranski-Krastanow mechanism. The QDs were vertically self-aligned in the stacks. The upper layer of QDs was capped by 3nm-GaAs/3nm-AlAs/4nm-GaAs layer sequence. Then, a thin silver layer was added via physical vapor deposition in a vacuum chamber. The equivalent thickness of the silver layer was set at 10 nm. Scanning electron microscopy reveals a dense labyrinth structure of silver deposits. After annealing at 200°C for two hours, isolated silver NPs with broad size distribution in the range of 20 to 100 nm were formed above the layer of buried InAs QDs.
Optical reflection, absorption, scattering and photoluminescence spectra were studied to document the optical properties of plasmons in Ag NPs and excitons in InAs QDs and reveal their interaction. The optical plasmon resonances appeared to be centered near 1.1 and 2.1 eV. They showed a large inhomogeneous broadening due to substantial size and shape dispersion in the NP system. The InAs QDs showed a strong photoluminescence (PL) near 1.1 eV with 0.07 eV in width. After the formation of Ag NPs, the PL intensity increased by the factor of 2.4. Our time-resolved PL study showed elongation of the recombination time. For this phenomenon we propose a model, which considers direct carrier exchange between the buried InAs QDs and Ag NPs on the surface.
8:00 PM - NM06.03.27
Exciton in Strained Wurtzite GaN/AlN Core/Shell Spherical Quantum Dot
N. Aghoutane 2 , Elmustapha Feddi 2 , Mohamed El-Yadri 2 , Mostafa Sadoqi 1 , Gen Long 1
2 Group of Optoelectronic of Semiconductors and Nanomaterials, Mohammed V University, Rabat Morocco, 1 , Saint John's University, Jamaica, New York, United States
Show AbstractIn this study, we have investigated the hydrostatic pressure effect on the confined exciton in a spherical core-shell quantum dot. An infinite deep potential has been used to describe the confinement effects. Within the framework of the effective-mass approximation and by using a simple variational approach, we have computed the exciton binding energy as a function of the shell sizes under the influence of the applied hydrostatic pressure. Our results show that the exciton ground state binding energy depends strongly on the shell size, which tends to the 2D well-known limit of 4R*, when the ratio a/b tends to unity. The numerical calculations show, also, that the applied pressure favors the electron-hole attraction; therefore the exciton binding energy increases, when pressure increases. Our results agree with previous theoretical investigations.
8:00 PM - NM06.03.28
Fluorescence Studies of Fe3O4-Au Hybrid Nanoparticles
Gen Long 1 , Mostafa Sadoqi 1 , Raheeb Alsaidi 1 , Blawal Chaudhry 1 , Juhayer Uddin 1 , Arkadiusz Baginski 1 , Andrew Nunez 1
1 , Saint John's University, Jamaica, New York, United States
Show AbstractMagnetic and fluorescent nanoparticles are widely studied in biomedical research such as drug delivery, imaging, etc. Hybrid nanoparticles combining both magnetic and fluorescent properties are particularly interesting. In this presentation, we will report our recent studies on Fe3O4-Au hybrid nanoparticles. Various methods of synthesizing Fe3O4 –Au hybrid nanoparticles via chemical reactions were studied. And the synthesized hybrid nanoparticles were characterized by UV-Vis-NIR spectroscopy and fluorescence spectroscopy, XRD, EDS, TEM, etc. We proposed the optimal synthesis conditions to obtain stable, uniform hybrid nanoparticles without impurities. We studied the correlation between fluorescent life- time and sizes, compositions, shapes of hybrid nanoparticles. Various biomedical applications of synthesized hybrid nanoparticles, utilizing their fluorescent and magnetic properties, were also investigated.
8:00 PM - NM06.03.29
Optical Absorption Associated to Intersubband Transitions of a Single Dopant in Strained AlAs/GaAs Core/Shell Quantum Dot
M. El Houari 2 , A. EL Aouami 2 , Elmustapha Feddi 2 , Mostafa Sadoqi 1 , Gen Long 1 , Sunil Kumar 3 4
2 Group of Optoelectronic of Semiconductors and Nanomaterials, Mohammed V University in Rabat, Rabat Morocco, 1 , Saint John's University, Jamaica, New York, United States, 3 Mechanical and Aerospace Engineering, New York University, Brooklyn, New York, United States, 4 Mechanical Engineering, NYU-ABU DHABI, ABU DHABI United Arab Emirates
Show AbstractThe new optoelectronic devices can associate recently the inclusion of the sigle dopant in nanostructures quantum dots. In this study, we present a theoretical investigation of hydrostatic pressure, donor position and quantum confinement effects on the energies levels, 1s and 1p of single dopant confined in AlAs/GaAs core/shell quantum dot. Within the framework of the effective mass approximation, the Schrödinger equation has numerically solved by using the variational method under the infinite potential barrier. The results show that the energies levels are very affected by the core/shell sizes and by the hydrostatic pressure. It has been shown that the optical absorption associated to the inter-band transition 1s-1p undergo important changes.
8:00 PM - NM06.03.30
Continuously Tunable Excitonic Properties of Engineered CdSexS1−x Heteronanoplatelets
Didem Dede 1 , Yusuf Kelestemur 1 , Kivanc Gungor 1 , Can Firat Usanmaz 1 , Onur Erdem 1 , Hilmi Volkan Demir 1 2
1 , Bilkent University, Ankara Turkey, 2 , Nanyang Technological University, Singapore Singapore
Show AbstractSemiconductor nanoplatelets (NPLs), or alternatively known as colloidal quantum wells, have superior optical properties among the solution-processed semiconductor nanocrystals thanks to their magic sized thickness. [1] These favorable excitonic properties stem from their quasi two-dimensional electronic structure resembling epitaxially grown quantum wells. These atomically-flat NPLs show suppressed inhomogeneous broadening, which results in extremely narrow emission bandwidth (<10 nm at room temperature). Moreover, these NPLs exhibit giant oscillator strength, suppressed Auger recombination, extremely large linear and nonlinear absorption cross-sections, high gain coefficient, enabling the achievement of low threshold optical gain and lasing. However, due to pure vertical quantum confinement observed in these quasi two-dimensional NPLs, only discrete emission wavelengths are possible and the spectral tunability is limited.
To overcome these limitations and achieve highly tunable excitonic features, we proposed and synthesized homogenously alloyed CdSexS1-x core NPLs together with their core/crown and core/shell heterostructures. [2] During the synthesis, the composition is precisely tuned by controlling the injected sulfur amount. These carefully designed core-only CdSexS1-x NPLs have blue-shifted excitonic properties and emission behaviour down to 487 nm. With laterally extending CdS crown regions to provide surface passivation of the alloyed core, we achieved enhanced PL-QY up to 60% without changing emission behaviour of the core. Also, with increasing vertical thickness by growing CdS shell on top of the alloyed core, red-shifting in the excitonic features is observed as a result of the relaxation of the quantum confinement. By this way, we observed further extended spectral tunability from 550 to 650 nm. Finally, we studied optical gain performances of these alloyed hetero-NPLs exhibiting reduced reabsorption and highly tunable excitonic features. With these engineered heterostructures of the alloyed CdSexS1-x NPLs, we obtained highly tunable optical gain from these atomically-flat nanocrystals together with very low gain thresholds down to ~ 56 μJ/cm2. By taking all these into account, the heterostructures of CdSexS1-x NPLs have a promising future in lasing and light-emitting diodes applications.
[1] S. Ithurria et al., J. Am. Chem. Soc., 130, 49, 16504–16505 (2008); and Nat. Mat. 10, 12, 936-941 (2011)
[2] Y. Kelestemur, D. Dede et al., Chem. Mater., 29,11, 4857–4865 (2017)
8:00 PM - NM06.03.31
Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions
Peter Sercel 1 , Andrew Shabaev 2 , Alexander Efros 3
1 , California Institute of Technology, Pasadena, California, United States, 2 , George Mason University, Fairfax, Virginia, United States, 3 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractWe have analyzed the effect of symmetry breaking on the optical properties of semiconductor nanocrystals due to doping by Coulomb impurities. Using doped CdSe nanocrystals as an example, we show the effects of a Coulomb impurity on the exciton fine-structure and optical selection rules using symmetry theory and then quantify the effect of symmetry descent on the exciton fine structure by introducing a charged Coulomb impurity in the NCs modelled using a multipole expansion. The descent of the nanocrystal symmetry from spherical to point group Cs, which is characterized by just one mirror plane symmetry element, leads step by step to activation of all five F =2, Fz=±2, ±1, 0 excitons in CdSe NCs. Even the ground exciton becomes optically active, which should be observable in low-temperature photoluminescence measurements. For several intermediate symmetries the band edge exciton fine structure consists of sets of three linearly polarized mutually orthogonal dipoles plus a dark exciton, one of which is always the ground state. The perturbative model shows that the presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through mixing and shifting of the hole spin and parity sublevels. The effect of the Coulomb impurity on the photoluminescence and the absorption spectra are shown, with and without the presence of countercharges on the nanocrystal surface. While absorption spectra of individual nanocrystals are expected to shift and broaden with the introduction of a charged center, ensemble averaging is shown to wash out these effects. The calculations show that the NC symmetry breaking by a Coulomb impurity, particularly a positively charged center, shortens the radiative decay of nanocrystals even at room temperatures in qualitative agreement with the increase in PL efficiency observed in CdSe nanocrystals doped with positive Ag charge centers.
8:00 PM - NM06.03.32
Photoluminescence Stability of Blue Organic Phosphorescent Materials on Silver Plasmonic Nanostructures
Catrice Carter 1 , Zeqing Shen 1 , Kun Zhu 1 , Kelsey Gwynne 2 , Deirdre O'Carroll 1
1 , Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States, 2 , Wagner College, Staten Island, New York, United States
Show AbstractEmerging lighting and display technologies use phosphorescent organic light-emitting diodes (Ph-OLEDs) because they are thinner, more flexible, and less pixelated than their inorganic LED counterparts. While Ph-OLEDs can have an internal quantum efficiency of 100%, on metal electrodes the light-extraction efficiency is 5-30% primarily due to coupling to surface plasmon polariton (SPP) modes and photonic waveguide modes, SPPs, accounting for up to 50% of the loss in light-extraction efficiency. In addition to low light-extraction efficiency, efficiency roll-off in Ph-OLEDs is a significant cause of device degradation at high luminance and is due to triplet-polaron and triplet-triplet quenching processes. One way to address the efficiency roll-off issue is to accelerate the radiative decay rate of phosphorescence in order to reduce triplet quenching processes. Further, efficiency roll-off in blue Ph-OLEDs is very pronounced due to high triplet energies and significant triplet-polaron and triplet-triplet quenching relative to red and green Ph-OLED counterparts.
This study aims to experimentally investigate the use of silver plasmonic nanostructured films with blue organic phosphorescent films to increase the radiative decay rate of triplet emission and, therefore, to minimize triplet quenching processes that cause unstable emission. We use the host poly(N-vinylcarbazole) (PVK) with the blue phosphorescent dopant, bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) which is commonly-used in blue Ph-OLED prototypes. This host-dopant combination has been shown to improve light out coupling and enhance triplet excitation because the host assists in charge transport and excitation energy transfer, while the dopant provides color and increases intersystem crossing which improves the internal quantum efficiency. PVK:FIrpic thin film samples are spin coated onto planar silver, grating (1.6µm and 0.7µm), nanoporous (NPO) silver, and nanoparticle (NPT) silver. In addition PVK, FIrpic, and PVK:FIrpic thin films on glass are used as a reference. The silver plasmonic nanostructures are chosen due to their ability to increase light emission through light scattering. Each silver plasmonic nanostructure is prepared with 50 nm of silver using nanoimprint lithography deposition for grating (1.6µm and 0.7µm) and dewetting deposition for NPO and NPT. The samples are characterized using photoluminescence (PL) stability, PL lifetime, and PL quantum yield measurements to investigate the relationship between silver plasmonic nanostructures and improved phosphorescence stability. Preliminary data has shown a correlation between enhanced PL stability and PL lifetime of silver plasmonic nanostructures relative to a planar silver.
8:00 PM - NM06.03.33
Direct Evidence for Coupled Surface and Concentration Quenching Dynamics in Lanthanide-Doped Nanocrystals
Sha He 1 , Noah Johnson 1 , Shuo Diao 2 , Stefan Fischer 3 , Hongjie Dai 2 , Emory Chan 3 , Adah Almutairi 1
1 , University of California, San Diego, San Diego, California, United States, 2 , Stanford University, Palo Alto, California, United States, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractLuminescence quenching at high dopant concentrations generally limits the dopant concentration to less than 1–5 mol% in lanthanide-doped materials, and this remains a major obstacle in designing materials with enhanced efficiency/brightness. In this work, we provide direct evidence that the major quenching process at high dopant concentrations is the energy migration to the surface (i.e., surface quenching) as opposed to the common misconception of cross-relaxation between dopant ions. We show that after an inert epitaxial shell growth, erbium (Er3+) concentrations as high as 100 mol% in NaY(Er)F4/NaLuF4 core/shell nanocrystals enhance the emission intensity of both upconversion and downshifted luminescence across different excitation wavelengths (980, 800, and 658 nm), with negligible concentration quenching effects. Our results highlight the strong coupling of concentration and surface quenching effects in colloidal lanthanide-doped nanocrystals, and that inert epitaxial shell growth can overcome concentration quenching. These fundamental insights into the photophysical processes in heavily doped nanocrystals will give rise to enhanced properties not previously thought possible with compositions optimized in bulk.
8:00 PM - NM06.03.34
Photogenerated Charge Equilibration in core@shell metal@semiconductor Nanoparticles
Matteo Parente 1 , Andrea Baldi 1
1 , NWO DIFFER, Eindhoven Netherlands
Show AbstractNoble metal nanoparticles strongly absorb and scatter light in the UV, visible, and IR range, thanks to so-called localized surface plasmon resonances (LSPRs)1.
The spectral position of resonances is very sensitive to changes in the surrounding medium of the nanoparticles and in the charge density1,2. For this reason, LSPRs are used as optical sensors for a variety of chemical and physical processes, from CO and H2 oxidation3, to NOx conversion to N23, and biological and biomedical assays4.
Core@shell metal@semiconductor nanostructures are particularly interesting as they combine the high sensitivity of plasmonic metal nanoparticles with optical and surface properties of semiconductors2,5,6.
Such hybrids systems can be used as sensors of charge/equilibration at metal/semiconductor interfaces in nanostructures, a process which is of paramount importance in energy conversion applications2,5,6. For example, it has been shown that Ag@TiO2 nanoparticles can be used to probe the equilibration of photogenerated electrons from TiO2 to Ag, by measuring the shift in the spectral position of their LSPRs2.
However, in order to make efficient use of plasmon resonances for sensing applications, deconvolution of different contributions to their spectral shift is necessary7, as well as a strict control on the surface chemistry of the nanostructures.
Here, we develop a nearly monodisperse synthesis of Ag@TiO2 nanoparticles with tunable Ag core size and characterize their photophysical properties under UV irradiation in inert atmosphere.
Thanks to the accurate control of particles size and shape, we are able to quantitatively asses different contributions to the observed plasmon resonance shifts. We find that the sole electron transfer from TiO2 to Ag cannot account for the whole shift in spectral position of the plasmon resonances, and we discuss additional mechanisms, such as the reduction of the native Ag2O layer at the Ag/TiO2 interface, surface charge accumulation on the metallic cores7, and variations in the dielectric properties of TiO2 due to electron trapping at defects.
Understanding the contributions of different mechanisms to the observed spectral shifts in LSPRs, opens the doors to the design of more efficient and reliable plasmon-based chemical sensors.
References
1. C.F. Bohren, D.R. Huffman, Absorption and Scattering of Light by Small Particles, New York, Wiley, 1983.
2. Hirakawa, T; Kamat P. JACS 2005, 127, 3928-3934.
3. Larsson E.M.; Langhammer C.; Zoric I.; Kasemo B. Science 2009, 326, 1091-1094.
4. Mayer K.M; Hafner J.H. Chem. Rev. 2011, 111, 3828-3857.
5. Hirakawa T.; Kamat P. Langmuir 2004, 14, 5645-5647.
6. Takai A.; Kamat P. ACS Nano 2011, 5, 7369-7376.
7. Brown A.M.; Sheldon M.T.; Atwater H.A. ACS Phot. 2015, 2, 459-464.
8:00 PM - NM06.03.35
Stabilized Self-Assembled Chromophore Antennas J-Aggregates are Able to Enhance NIR QDs Emission
Francesca Freyria 1 2 , Jose Cordero 1 , Justin Caram 1 4 , Sandra Doria 3 , Amro Dodin 1 , Yue Chen 1 , Adam Willard 1 , Moungi Bawendi 1
1 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Applied Science and Technology, Politecnico of Torino, Torino Italy, 4 Department of Chemistry and Biochemistry, California State University, Los Angeles, Los Angeles, California, United States, 3 European Laboratory for Non Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino Italy
Show AbstractHybrid nanomaterials can be applied in several fields, spanning from optoelectronic devices to solar energy and biological imaging. Although the different possibilities of application, the energy transfer between organic and inorganic materials is still not well investigated. We report that self-assembled molecular dye J-aggregates (Light Harvesting Nanotubes or LHNs) can promote the enhancement of PL emission of NIR lead sulfide quantum dots (PbS QDs) more than 8-fold thanks to long-range antenna effect and an efficient Förster resonance energy transfer (FRET) from donor to acceptor either in liquid medium or in solid medium.1,2 As donor, we used amphiphilic cyanine dye (C8S3, 3,3′ -bis(2-sulfopropyl)-5,5′,6,6′-tetrachloro -1,1′ -dioctylbenzimidacarbo cyanine) which is soluble in methanol and aggregate in water into cylindrical double walled nanotubes, which act as powerful light harvesting antennas. These LHNs are formed by two well defined concentric nanotubes, each measuring 12 and 6 nm diameters respectively, and length of several microns.3 LHNs show narrow absorption features and long-range excitation energy migration thanks to the strong interaction between the transition dipole moments of the dye monomers. As acceptor, we synthesized NIR emitting PbS QDs and to make them soluble in water and compatible with LHNs environment, we carried out a ligand substitution directly during the QDs synthesis, followed by a PEG-functionalization reaction using click-chemistry. This method allowed us to preserve the optical and morphological characteristics of the QDs even in water for months. In our composite material, the acceptors, present in low concentration, are weakly physical and energetic coupling with the donors. We compared the enhancement of PbS emission either in presence of LHNs or in presence of the monomer as donor. Experimental measurements and theoretical studies show that both the quantum yield and the long range diffusive exciton (antenna effect) of the donor can promote the energy transfer to the acceptor. Our simple system can be used in a wide photochemical and photoelectrical applications.
1) Freyria, F.S.; Cordero, J. M., Caram, Doria, S.; Dodin, A.; Chen, Y. ,Willard, A.P.; Bawendi, M.G.” NIR-IR Quantum Dot emission enhanced by stabilized self-assembled chromophore antennas” under revision.
2) Caram, J. R.; Doria, S.; Eisele, D. M.; Freyria, F. S.; Sinclair, T. S.; Rebentrost, P.; Lloyd, S.; Bawendi, M. G” Room-Temperature Micron-Scale Exciton Migration in a Stabilized Emissive Molecular Aggregate”. Nano Lett. 2016.
3) Eisele, D. M.; Cone, C. W.; Bloemsma, E. A.; Vlaming, S. M.; van der Kwaak, C. G. F.; Silbey, R. J.; Bawendi, M. G.; KnoesterJ; Rabe, J. P.; Vanden Bout, D. A.:” Utilizing redox-chemistry to elucidate the nature of exciton transitions in supramolecular dye nanotubes” Nat Chem 2012, 4 (8), 655–662.
Symposium Organizers
Matthew Pelton, University of Maryland-Baltimore County
Jennifer Dionne, Stanford University
Alexander Govorov, Ohio University
Maksym Kovalenko, ETH Zurich
Symposium Support
Angstrom Engineering
NNCrystal US Corporation (NN-Labs)
Princeton Instruments
NM06.04: Synthesis
Session Chairs
Maksym Kovalenko
Matthew Pelton
Tuesday AM, November 28, 2017
Hynes, Level 3, Room 311
9:00 AM - NM06.04.01
Plasmon Induced Synthesis of Au@Ag core@shell Nanostructures
Rifat Kamarudheen 1 , Andrea Baldi 1
1 , DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven Netherlands
Show AbstractPlasmonic nanoparticles have interesting applications in a wide range of fields, from photovoltaics, to in-vivo bio-imaging and surface enhanced Raman spectroscopy.1 In the past two decades, a lot of interest has been devoted to the synthesis of anisotropic metal nanoparticles with high yield and precise control over their morphology, using light as a driving force for the reaction.2,3 The growth of these nanostructures has been attributed to the decay of localized surface plasmon resonances, which either result in the ejection of so called “hot” electrons or in localized heating around the nanoparticles. However, open questions remain on the efficiency of generation and injection of hot electrons and on the magnitude of the thermal effects. In particular, depending on the density of nanoparticles and their heat dissipation properties, the plasmon-induced localized heating can give rise to a macroscopic temperature increase in the nanoparticle solution; often orders of magnitude higher than the increase in local temperature at the nanoparticle surface.4 Such collective heating effects could very well contribute to the plasmon-driven growth of nanostructures and need to be taken into proper account when studying plasmon-induced chemical reactions.
Previous studies on collective heating effects have been limited by the difficulty in measuring the local temperature in the nanoparticle solution, during laser irradiation. The aim of our research is to elucidate the temperature profile in irradiated nanoparticle suspensions, by comparing the rate of a temperature-sensitive nanoparticle growth reaction under laser irradiation to the one measured in the dark at different temperatures.
For this reason, we have developed a temperature-dependent chemical reaction for the synthesis of Au@Ag core@shell nanoparticles and used it to benchmark the effect of plasmon-induced collective heating. We estimate the average temperature of the solution under irradiation, by measuring the growth rate of Ag shells and study its dependence on the irradiation power and on the volume of the solution. We interpret our results by modeling the light propagation and heat generation in a highly absorbing and scattering medium, using a combination of Monte-Carlo and numerical techniques. Such studies are relevant for understanding the activation mechanisms of plasmon-induced growth; which in turn is important for the development of controlled new syntheses of metal nanostructures. Furthermore, they are relevant in plasmon-enhanced heterogeneous catalysis, which holds great promise for the development of new selective pathways to chemical and fuel synthesis.5,6
1. Rycenga, M. et al. Chem. Rev. 111, 3669–3712 (2011)
2. Jin, R. et al. Science 294, 1901 LP-1903 (2001)
3. Zhai, Y. et al. Nat. Mater. 15, 889–895 (2016)
4. Richardson, H. H. et al. Nano Lett. 9, 1139–1146 (2009)
5. Marimuthu, A. et al. Science 339, 1590 LP-1593 (2013)
6. Zhang, X. et al. Nat. Commun. 8, 14542 (2017)
9:15 AM - NM06.04.02
Self-Organized Plasmonic Metals Formation in Limited Volume Matrixes
Vladimir Sivakov 1 , Egor Kaniukov 2 , Dzmitry Yakimchuk 2 , Liubov Osminkina 3
1 , Leibniz Institute of Photonic Technology, Jena Germany, 2 , Academy of Sciences of Belarus, Minsk Belarus, 3 , Lomonosov Moscow State, Moscow Russian Federation
Show AbstractThe targeted scientific breakthrough is a study of controlled self-organized process of nanosized structures based on porous silica or alumina on silicon surface systems where dielectric pores are selectively filled by plasmonic metals (silver and gold) for a formation of dimensionally divided plasmonic nanostructures. Swift heavy ion track technology was used for the pre-patterning of porous surfaces with nanoscaled metal particles. Wet-chemical methods of the deposition of noble metals and their combinations in the pores was applied for the formation of the plasmonic nanostructures. The characterization of plasmonic structures was carried out by surface analytic methods like SEM, EDX, EBSD, TEM, etc., which are combined with theoretical modeling of growth processes and plasmonic properties supporting the optimization process of the surface. The Raman scattering measurements were performed at room temperature on a Witec or Horiba based Raman setup (532 nm and 633 nm laser) using Ellman’s reagent or bilirubin. The spatially separated plasmonic nanostructures have been synthesized using heavy ion track technology and self-organization of metal atoms in the closed volumes. The first pre-tests of these nanostructures in Raman scattering spectroscopy have been performed. The first data indicates the possibility of detecting ultra-small concentrations of the Ellman’s reagent on silver dendritic nanostructures, the detection limit of 10-15 M was achieved that corresponds that Raman signal enhanced above 13 orders of magnitude. The detecting ultra-small concentrations of the Bilirubin on gold nanostructures, the detection limit of 10-9 M, was achieved. The foregoing allows us to conclude that spatially separated plasmonic nanostructures in the pores of the SiO2 template on silicon are a new promising effective plasmon active surfaces for SERS, which are of record high sensitivity and can find application in chemo- and biosensorics.
9:30 AM - NM06.04.03
On the Plasmonic Properties of TiN Nanoparticles Produced by a Non-Thermal Plasma Method
Alejandro Alvarez Barragan 1 , Stephen Exarhos 1 , Niranjan Ilawe 1 , Bryan Wong 1 , Lorenzo Mangolini 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractThere is a growing interest towards the potential applications of plasmonic nanoparticles. The high absorption and scattering of light at resonance wavelengths is desired for photothermal therapy. The generation of hot electrons by Landau damping or chemical interface damping is required for several photocatalytic applications, including for water splitting, methanol oxidation, etc. The elastic reemission of photons is ideal for biosensing via surface enhanced Raman spectroscopy (SERS). Gold and silver nanoparticles have been routinely used for these and other plasmonic applications. However, the tuning of their resonance wavelength has proven difficult due to the need to engineer complicated nanostructures. Additionally, both metals are not thermally stable, and their high cost is a major hurdle to develop viable applications. These considerations motivate the interest towards alternative plasmonic materials that show resonance in the visible range. In the last two decades there has been increasing attention towards the use of non-thermal plasmas for nanoparticle synthesis. Herein we present an in-depth study on plasmonic TiN nanoparticles produced by the non-thermal plasma method. Titanium (TiCl4) and nitrogen (NH4) precursor gases are transported into a plasma reactor maintained by a 13.56 MHz (RF) power supply. The reactivity of the plasma environment, the unipolar charging of particles, and nanoparticle heating lead to the formation of cubic ~10 nm nanoparticles with narrow size distribution. We show that the nitrogen-to-titanium ratio plays a crucial role on oxidation. Higher oxide content appears to decrease the plasmonic response of the material by red-shifting its resonance wavelength and significantly reducing the plasmon peak intensity. Real time, time dependent functional tight binding (RT-TDFTB) calculations support experimental results and confirm that surface oxidation is detrimental to the plasmon response, shifting the theoretical peak position from ~615 nm to ~770 nm and decreasing its intensity. This consequently hinders any effort to develop technology based on the localized surface plasmon resonance (LSPR) phenomenon. The introduction of silane (SiH4) gas in a secondary low-power reactor aims to overcome the problem by adding a conformal silicon coating that acts as a diffusion barrier to prevent oxidation of TiN. The resulting extinction spectra of this novel TiN-Si core-shell structure have a sharper peak and are blue-shifted to the visible region (~630nm). The peak intensity increases by more than 50% as the ratio of the extinction measured at the plasmon peak to the extinction at the 400 nm UV band is 1.58 versus the 1.09 ratio obtained for the bare TiN particles. The FWHM of the plasmon peak also decreases from ~520 nm to ~400 nm upon addition of the Si coating. These results highlight the relevance of particle oxidation at the nanoscale and offer plausible solutions driven by a one-step non-thermal plasma process.
10:15 AM - NM06.04.05
Equilibrium Shapes of Large Nanoparticles beyond the Wulff Construction
Magnus Rahm 1 , Paul Erhart 1
1 , Chalmers University of Technology, Gothenburg Sweden
Show AbstractIn the pursuit of complete control over morphology in nanoparticle synthesis, knowledge of the thermodynamic equilibrium shapes is a key ingredient. While the classical Wulff construction provides a solution in the continuum limit, the small particle regime has been studied using global minimum energy search method reaching particle diameters of roughly 1 or 2 nm. The experimentally important intermediate size regime, however, has largely remained elusive. Here, we present an algorithm, based on atomistic simulations in a constrained thermodynamic ensemble, that efficiently predicts equilibrium shapes for any number of atoms in the range from a few tens to 10,000, corresponding to diameters between approximately 1 and 7 nm. We apply the algorithm to Cu, Ag, Au and Pd and reveal an energy landscape that is more intricate than previously suggested. In particular, we demonstrate that, as a result, the transition from icosahedral particles to decahedral and further into FCC particles occurs very gradually. One must thus expect more than one shape in thermodynamic equilibrium and not only for for kinetic reasons.
10:30 AM - NM06.04.06
Colloidal Lead Halide Perovskite Nanocrystals (APbX3, X=Cl, Br and I)—Cesium versus Formamidinium as the A Cation
Loredana Protesescu 1 2 , Maksym Kovalenko 1 2
1 , ETH Zurich, Cambridge, Massachusetts, United States, 2 , Empa-Swiss Federal Laboratories for Materials Science and Technology, Dübendorf Switzerland
Show AbstractColloidal nanocrystals (NCs) of APbX3-type lead halide perovskites [A=Cs+, CH3NH3+ (methylammonium or MA+) or CH(NH2)2+ (formamidinium or FA+); X=Cl-, Br-, I-] have recently emerged as highly versatile photonic sources for applications ranging from simple photoluminescence (PL) down-conversion to light emitting diodes and lasing.
Although CsPbX3 NCs were found to have outstanding emission properties without any passivation shell which is mandatory for the traditional quantum dots such as CdSe/CdS or InP/ZnS, their highly problematic issues such as polymorphs instability (especially for red emitters), and phase separation for mixed halides need to be addressed [1].
The previously inaccessible red to near-infrared (near-IR) region due to the delayed phase-transformation into a non-luminescent wide-bandgap 1D polymorph for CsPbI3 NCs, and the very limited chemical durability of the MAPbI3 is now enabled. Higly monodisperse colloidal FAPbI3 and CsFAPbI3 NCs were proved to enhance the stability of the perovskite structure, therefore the optical properties are retained even under rush conditions. Bright PL with high quantum yield (QY>70%) spanning red (690 nm, FA0.1Cs0.9PbI3 NCs) and near-IR (780 nm, FAPbI3 NCs) regions was obtained and sustained for several months in both the colloidal state and in films. The FAPbI3 and the FA-doped CsPbI3 NCs are uniform in size (10-15 nm), nearly cubic in shape and the peak PL wavelengths can be fine-tuned by using post-synthetic cation- and anion-exchange reactions. Satisfactory chemical durability of these NCs was illustrated by the retention of high QYs (>70%) for months by the successful fabrication of LEDs, with EQEs reaching 2.3%, and by the low-threshold lasing from the compact films of these NCs [2].
Moving to the green region, the “530-535 nm” PL in a solid, polymer-embedded state, is particularly desirable for applications in television displays and related technologies. This emission cannot be delivered by Cs- based perovskite because of the band-gap limitations for CsPbBr3 NCs or segregation issues for the Cs- lead mixed halide NCs. Towards this goal, we have developed a facile synthesis of highly monodisperse, cubic-shaped FAPbBr3 NCs, with perovskite crystal structure, tunable PL in the range of 470-540 nm by adjusting the size (5-12 nm), high QY of up to 85% in films and solutions and PL FWHM of <22 nm. In addition, these films exhibit low thresholds of 14±2 µJ cm-2 for amplified spontaneous emission [3].
[1] Protesescu, L.; Yakunin, S., Bodnarchuk, M. I., Krieg, F., Caputo, R.,Hendon, C. H.,Yang, R. X., Walsh, A., Kovalenko, M. V. Nano Letters 2015, 15, 3692
[2] Protesescu L., Yakunin S., Bodnarchuk M.I., Bertolotti F., Masciocchi N., Guagliardi A., and Kovalenko M.V. J. Am. Chem. Soc., 2016, 138, 14202
[3] Protesescu L., Yakunin S., Kumar S., Bär J., Bertolotti F., Masciocchi N., Guagliardi A., Grotevent M., Shorubalko I., Bodnarchuk M.I., Shih C.-J., and Kovalenko M.V. ACS Nano, 2017, 11, 3119
10:45 AM - NM06.04.07
Formation of Solution-Processed Perovskite Quantum Wells
Rafael Quintero-Bermudez 1 , Aryeh Gold-Parker 2 , Zhenyu Yang 1 , Michael Toney 3 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada, 2 Department of Chemistry, Stanford University, Palo Alto, California, United States, 3 , SLAC, Palo Alto, California, United States
Show AbstractOrganic-inorganic hybrid perovskites quantum wells (PQWs) based on methylammonium lead halides (MAPbX3) have attracted significant attention in recent years due to excellent light harvesting and emissive properties. The addition of large organic cations (such as phenethylammonium and n-butylammonium) during the solution-processed synthesis of perovskite materials has led to the formation of quantum-confined layered structures. Some variations in the perovskite chemical composition, large organic cation and solvent have been explored as means of varying the structure of the resulting materials. A thorough understanding of the morphology and formation of PQWs is lacking, however.
Our studies focus on clarifying the nature of PQW formation and morphology. We find very interesting formation mechanisms which agree with the resulting morphology identified. Furthermore, this morphology is found to vary on the initial precursors such that engineering PQW morphology becomes possible. The results indicate means of controlling the distribution, composition and orientation of PQWs via selection of both the precursors and the solvent as well as control of the stoichiometry. The fine-level of tuning PQWs enabled by this work paves the way for more efficient and stable perovskite-based optoelectronic devices.
11:00 AM - NM06.04.08
Highly Luminescent Lead Halide Perovskite Nanocrystals in Inorganic Matrices
Dmitry Dirin 1 , Bogdan Benin 1 , Sergii Yakunin 1 , Frank Krumeich 1 , Gabriele Raino 3 , Ruggero Frison 2 , Maksym Kovalenko 1 4
1 , ETH Zurich, Zurich Switzerland, 3 , IBM-Research Zurich, Rüschlikon Switzerland, 2 , University of Zurich, Zurich Switzerland, 4 , Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf Switzerland
Show AbstractLead halide perovskite nanocrystals show outstanding photoluminescence (PL) color purity, quantum yields of about 90 % and color tunability across the whole visible range. With such optical properties and relatively cheap and scalable fabrication process these nanocrystals could outperform state-of-the-art emitters for down-conversion displays. However, colloidal lead halide perovskite nanocrystals struggle from the stability issue: these nanocrystals have tendency to merge in compact films, especially in high humidity or at elevated temperatures. This tendency originates from relatively weak bonding of the ligands to nanocrystal surface, high solubility of lead halide perovskites in polar solvents and low melting point. Conventional way to minimize such merging is to isolate nanocrystals from each other by embedding them in robust matrix, for example in polymer film. However, most of known approaches to such composites require postsynthetic treatment of colloidal halide perovskite nanocrystals, which is often rather destructive. Herein, we present a new approach to the synthesis of lead halide perovskite nanocrystals and their in situ embedding into robust inorganic matrices. This method implies direct growth of perovskite nanocrystals on the surface of inorganic carrier without any ligands. Resulting microcrystalline powders resemble all outstanding optical properties of colloidal lead halide perovskite NCs including PL quantum yields approaching 90-100 %, color purity and tunability. At the same time lead halide perovskite nanocrystals embedded into inorganic robust matrixes show significantly improved stability of optical properties in harsh heating and photo-annealing conditions. Accelerated heating tests show stability of PL peak position, width and PL intensity after heating up to 120 °C. Accelerated photo annealing tests show stability of PL peak position and width, and less than 15 % drop of PL intensity after 3 hours under 0.1 W/cm2 flux of 450 nm light.
11:15 AM - NM06.04.09
Quantifying Cation Exchange Kinetics by In Situ X-Ray Diffraction—Insight into Nanoscale Atomic Transport Processes
Andrew Nelson 1 , Richard Robinson 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractThe extent to which the phenomenology of nanoscale diffusion kinetics differs from that inferred from measurements on bulk solids is not known, since nanoscale phase transformations and surface effects are expected to contribute. An unresolved question is whether the primary diffusion mechanism (vacancy, interstitial, kick-out, etc.) might change when the domain in which atoms diffuse is very small. Understanding of these microscopic processes is necessary to develop synthetic strategies to minimize sample heterogeneity arising from transformation processes (e.g. core polydispersity in core-shell nanoparticles), in the same way that understanding nanoparticle nucleation and growth kinetics is necessary to design syntheses of highly monodisperse nanoparticles.
Using the PbS-to-CdS exchange reaction as a model system, we directly characterized the structure of semiconductor nanoparticles undergoing cation exchange at various temperatures (50-200°C) and for various sizes of nanoparticles (3-7 nm) with x-ray diffraction at the Cornell High Energy Synchrotron Source (CHESS). This is in contrast to previous methods that have exclusively used optical spectroscopy. A significant size dependency of the reaction behavior was found; the smallest particles becoming amorphous immediately after starting exchange, but larger particles showed a smooth transformation to core-shell particles with zincblende CdS shells. As determined by peak-fitting analysis of the diffraction pattern, the reaction was found to show clear transitions between qualitatively different solid-state transport processes which arise from sequential surface reactions and reaction-diffusion in the nanoparticles.
At the lowest temperatures and shortest time scales, growth of the CdS shell is limited by the kinetics of Cd adsorption/Pb desorption at the surface, and a very thin shell of either octahedrally coordinated or amorphous CdS develops. Once the shell reaches a temperature-dependent thickness of 0.5-1 nm after several minutes, a crossover to a slower growth process with exponential kinetics takes place, forming the zincblende CdS shell. At even longer time scales (hours), the reaction qualitatively changes behavior for the third time; either the rate constant associated with this process changes, or parabolic (purely diffusive) growth is observed. This transition from exponential to parabolic kinetics is very similar to that seen in oxide scale growth, and indicates that the phenomena responsible for these multiple regimes (field-driven transport versus diffusion) play identical roles in cation exchange reactions.
11:30 AM - NM06.04.10
The Reversible Isomerization of a Cadmium Sulfide Magic-Sized Cluster—Insights into Semiconductor Solid-Solid Transformation
Curtis Williamson 1 , Douglas Nevers 1 , Tobias Hanrath 1 , Richard Robinson 2
1 Chemical Engineering, Cornell University, Ithaca, New York, United States, 2 Material Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractDeveloping new ways to dynamically control phase in solids has relevance to many research areas and applications because the phase can impart significant changes in optical, electronic, and structural properties. When these phase changes occur coherently and without mass addition/subtraction, the transformation can be described as an isomerization. The reversible isomerization of semiconductor magic-size clusters (MSCs) provides fundamental insight into the solid-solid phase transformation of semiconductors. Because MSCs are all identical, the discrete and reversible transitions between two different MSCs create an ideal system to understand the inorganic phase change phenomena at the nanoscale. The discrete transitions are measured with absorption spectroscopy between two cadmium sulfide MSCs in thin films with narrow excitonic peaks at 313 nm (F313) and 324 nm (F324). The x-ray diffraction crystalline phase of these MSCs exhibit zinc blend-like and wurtzite-like phases for the F313 and F324, respectively. Through total scattering and pair distribution analysis we have created model structures that have excellent fits to the experimental data. The model clusters show that transformation between the two species involves a shear deformation with a 4% strain (between the two MSC structures). Fourier transform infrared (FTIR) spectroscopy identifies an equivalent 4% distortion in the oleate ligand binding motif on the surface between the two CdS MSCs. In-situ kinetic analysis of the MSC transformation reveals first order kinetics for the conversion (F324 to F313) and reversion (F313 to F324) processes. The experimental activation energies of the conversion and reversion processes are 1.00 eV and 0.45 eV, respectively, similar to organic-based isomerization energies. We analyze the interplay between surface strain energies and bond energies to experimentally quantify the diffusionless phase change energy of the CdS MSCs as +0.6 meV/atom, which is in close agreement to the theoretical zinc blende-wurtzite transformation. From our comprehension of the CdS MSC reversible isomerization system, we propose critical sizes and limitations to reversibility in solid-solid transformations of other semiconductor materials. This work could lead to colloidal phase control of seeded particle growth and methods for isolation of meta-stable phases at the nanoscale.
11:45 AM - NM06.04.11
Exploiting Surfactant Mesophase Behavior to Stabilize Magic-Sized Cluster Synthesis
Douglas Nevers 1 , Curtis Williamson 1 , Tobias Hanrath 1 , Richard Robinson 2
1 Robert F. Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States, 2 Material Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractTechnologies that aim to exploit the size-dependent properties of nanoparticles (NPs) are faced with a predicament: synthesis sensitivity. This sensitivity is amplified by the inherent increase in process variations at large scales, causing wider NP size distributions and effectively a distribution of different NPs, complicating efforts to isolate precise, uniform-sized NP products. Hence, more reliable synthesis methods (i.e., process intensification) that produce large quantities of high-quality NPs are critical to NP-based technologies. Building on our previous reports of NP synthesis at high concentrations, we extend the synthesis to isolate ultra-small (<2 nm) cadmium sulfide NPs or magic-sized clusters (MSCs), which are identical in size and known to act as crucial intermediates in the formation of colloidal NPs. Access to these MSCs presents unique opportunities to refine our fundamental understanding of the formation of these critical nuclei from which NPs form. In contrast to conventional synthesis, higher precursor concentrations promote the selective formation of a single MSC product. Surprisingly, we found that the MSC nucleation is accompanied by the formation of a large hexagonal mesophase (100's nm grain size), which is comprised of discrete MSCs. Using in-situ SAXS and WAXS at 130○C, we directly tracked the formation of both mesophase assemblies and inorganic MSCs. Despite the continuous formation of MSCs, the extensive and rapid cluster assembly effectively arrests the growth and locks the nuclei in the form of the fibrous assembly, preventing NP growth and minimizing synthesis sensitivity. By changing the ligand length, we can vary the d-spacing of the assembly by up to 0.5 nm, while still forming the same sized MSCs with a hexagonal mesophase. At longer synthesis times (< 2 h) or more dilute conditions (500 mM), NPs form at the expense of the large MSC assemblies, highlighting the stabilizing role of the surfactant mesophase. Whereas surfactant mesophase behavior is well-established for metal-based surfactants (i.e, heavy metal soaps), including many NP precursors, the implications of metal precursor (or surfactant) phase behavior on NP synthesis and assembly have not yet been well-established. Overall, this high concentration approach intensifies the indispensable colloidal interactions that underlie NP synthesis, and showcases inherent concentration-dependent surfactant phase behavior, that is not available in conventional (i.e., dilute) conditions. This work not only provides an insensitive (or robust) synthesis method to produce and characterize identical NP products, but also demonstrates an underappreciated stabilizing role of surfactants in nanoparticle synthesis at high concentrations.
NM06.05: Nanoparticle Assemblies
Session Chairs
Brian Korgel
Delia Milliron
Tuesday PM, November 28, 2017
Hynes, Level 3, Room 311
1:30 PM - *NM06.05.01
Silicon Nanocrystal Assemblies
Yixuan Yu 1 , Adrien Guillaussier 1 , Brian Korgel 1
1 , University of Texas at Austin, Austin, Texas, United States
Show AbstractSilicon nanocrystals can now be made with a high degree of uniformity and assembled into a variety of structures. For example, uniform silicon (Si) nanocrystals with cuboctahedral shape, passivated with 1-dodecene capping ligands assemble into face-centered cubic (FCC) superlattices with orientational order. Transmission electron microscopy (TEM), electron diffraction and grazing incidence wide angle and small angle X-ray scattering (GISAXS and GIWAXS) show that the preferred orientation of these soft cuboctahedra depends on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices. These superlattices exhibit structure-dependent solid-solid phase transitions of the Si nanocrystals under pressure. Application of a quasi-uniaxial pressure was found to induce the formation of a new Si phase with diatomic body-centered cubic (BCC) structure and a lattice constant of 4.08 Å at 9.5 GPa. We have also used Si nanocrystals to create substrate-free self-supporting bubble assemblies, which can be used to study optical phenonmena in the absence of solvent and substrate effects.
2:00 PM - NM06.05.02
Dynamics and Removal Pathway of b= ½ <110> Edge Dislocations in Imperfectly Attached PbTe Nanocrystals—Towards Design Rules for Oriented Attachment
Justin Ondry 1 , A. Paul Alivisatos 1
1 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States
Show AbstractOriented attachment of nanocrystals is a well-known crystal growth process in biological, geologic, and synthetic nanomaterials.[1] Recently, elegant schemes for synthesizing honeycomb and square inorganic structures by epitaxially connecting nanocrystals through oriented attachment have been developed.[2] These structures are theorized to have exotic electronic structures but have not been realized experimentally potentially due to defects formed during nanocrystal attachment. Oriented attachment is not always perfect, and step edges on the attaching surfaces can cause edge dislocations to form in these materials.[3] Using high resolution TEM imaging we observe b=½<110> edge dislocations that result from attachment of the particles on either the {100} or {110} surface facets. For the particles attached on the {110} facets, the glide plane of the dislocation, determined from the burgers vector, is collinear with the attachment direction preventing the dislocation from easily traveling to the surface to be annihilated. For attachment on {100} facets, the glide plane for the dislocation is noncolinear with the attachment direction giving the dislocation a short path to the surface for annihilation.
We observed and tracked the positions of these dislocations as they moved in the structures under modest electron beam irradiation (~3000 e-/Å2s) during high resolution TEM imaging. For particles attached on the {100} facets, the dislocations quickly move along the glide plane to the surface yielding a perfect interface. For particles attached on the {110} facets, the dislocations initially move along the glide plane, but this motion does not get the dislocation any closer to being annihilated at the surface. Instead the dislocation must undergo much slower processes such as climb to move to the surface and be removed from the material. Indeed, analysis of several defect trajectories for {100} and {110} attached nanocrystals, shows that those imperfectly attached on the {110} take an order of magnitude longer to achieve perfect attachment. Based on the defect dynamics observed in rock salt nanocrystals, we believe this reveals an important design rule for preparing defect free epitaxially attached nanocrystal solids. Nanocrystals should be attached on a facet such that, if a dislocation were to form from step edges, the glide plane of that dislocation is not collinear with the attachment direction to facilitate dislocation removal. In the rock salt crystal system specifically, this means that oriented attachment should be performed on the {100} facets rather than the {110} facets to make defect removal easier, potentially leading to better electronic properties.
References:
[1] J. J. De Yoreo et al., Science, 349,aaa6760-1-aaa6760-9(2015).
[2] M. P. Boneschanscher et al., Science. 344, 1377–1380 (2014).
[3] R. L. Penn, J. F. Banfield, Science. 281, 969–971 (1998).
2:15 PM - *NM06.05.03
Disorder, Nonequilibrium Transport and the Origin of Deep Traps in Quantum Dot Solids
William Tisdale 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractUsing a combination of ultrafast spectroscopy, time-resolved optical microscopy, and kinetic Monte Carlo simulation, I will illustrate the effects of structural and energetic disorder on charge and exciton transport in colloidal quantum dot solids. In particular, I will show how analysis of early-time nonequilibrium transport phenomena can yield especially useful insight into fundamental charge and exciton transport processes. Additionally, I will present experimental evidence pointing to an unexpected origin of deep electronic traps in PbS nanocrystal solids.
3:15 PM - NM06.05.04
Kinetic Modeling of Transient Photoluminescence in Disordered Quantum Dot Films
Nadav Geva 1 , James Shepherd 1 , Lea Nienhaus 1 , Moungi Bawendi 1 , Troy Van Voorhis 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractTransient photoluminescence (PL) measurement can give insight to the electronic processes occurring in many systems. In a molecular system, where all molecules are identical and energetic disorder is low, the result can be fitted to a single exponential per molecular species.
In contrast, quantum dot films are inherently disordered. The processing of quantum dots results in size variation, ligand coverage variation, stoichiometric variation, and more. The resulting PL then cannot be easily fit with a mono-exponential.
We present here a kinetic model using transfer matrices. Using only two fitting parameters, mean and variance of the transfer rate barrier, the multi-exponential character can be captured. The parameters can also give insight to the degree of disorder present. We apply the model to investigate the triplet transfer rate between a quantum dot film and an organic semi-conductor.
The model validates our previous background subtraction method [1,2] used to extract exciton transfer rates. It also explains the role of back-transfer in the observed PL measurement, and quantify the degree of disorder induced by the ligand exchange process. We believe this method has wide applicability as a kinetic fitting procedure where disorder plays an important role.
[1] Wu, M., Congreve, D. N., Wilson, M. W., Jean, J., Geva, N., Welborn, M., Baldo, M. A. (2015). Solid-state infrared-to-visible upconversion sensitized by colloidal nanocrystals. Nature Photonics Nature Photon, 10(1), 31-34. doi:10.1038/nphoton.2015.226 [2] Thompson, N. J., Wilson, M. W., Congreve, D. N., Brown, P. R., Scherer, J. M., Bischof, T., Baldo, M. (2014). Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals. Nature Materials Nat Mater, 13(11), 1039-1043. doi:10.1038/nmat4097
3:30 PM - NM06.05.06
Self-Assembly of Gold Nanorods in Ordered Spherical Clusters
Jessi van der Hoeven 1 , Yang Liu 1 , Maarten Bransen 1 , Marijn van Huis 1 , Petra de Jongh 1 , Alfons van Blaaderen 1
1 Debye Institute for Nanomaterial Science, Utecht University, Utrecht Netherlands
Show AbstractGold nanoparticles exhibit interesting optical properties which arise from their localized surface plasmon resonance. In particular anisotropic Au nanoparticles, such as Au nanorods (NRs), have enhanced and highly tunable plasmonic properties due their longitudinal surface plasmon resonance in the visible and near-infrared range of the spectrum. This makes Au nanorods suitable materials for numerous optical applications such as surface-enhanced Raman spectroscopy (SERS) [1], data storage [2], photo catalysis and medical photo thermal applications. Recently, it has been shown that the plasmonic properties of the AuNRs can be significantly enhanced when placing the NRs in close proximity of each other by self-assembling the rods in large colloidal smectic-like crystal, whereby plasmonic hot spots between the particles were created [3].
In this study we present the synthesis of spherical clusters of silica coated AuNRs with a variable size from 200 nm to 2 µm, and the application of these clusters for SERS. First we show that the degree of order in the orientation of the rods within the spherical clusters depends on their aspect ratio (AR). To this end we synthesized two batches of silica coated AuNRs with either a 18 nm thick mesoporous silica shell or a 4 nm thin silica shell, yielding rods with an aspect ratio of 1.9 and 7.0, respectively. Subsequently, these rods were self-assembled by using a solvent evaporation method [4], whereby an apolar suspension of rods was emulsified in a larger polar phase. By slowly evaporating the apolar phase, the AuNRs in the shrinking droplets self-assembled into spherical clusters. The 3D-structure of the self-assembled clusters was studied in detail with advanced electron microscopy techniques such as 3D high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and focused ion beam scanning electron microscopy (FIB-SEM) slice and view, allowing us to track the precise orientation of the NRs in clusters [5]. We show that the orientation of the rods changes from random to smectic order when increasing the AR of the silica coated Au NRs. Finally, we compared the enhancement of crystal violet in Raman spectroscopy in the presence of non- and self-assembled NRs.
[1] M.N. Sanz-Ortiz, ACS Nano, 9 (2015), 10489–10497
[2] P. Zijlstra et al., Nature, 459, (2009), 410–413
[3] C. Hamon et al., Nanoscale, 8, 2016, 7914
[4] B. de Nijs, S. Dussi, A. van Blaaderen et al., Nature Materials, 14, (2015), 56–60
[5] T. Besseling, A. van Blaaderen et al., J. Phys. Condens. Matter, 27 (2015), 194109
3:45 PM - *NM06.05.07
Synthesis and Assembly of Plasmonic Metal Oxide Nanocrystals
Delia Milliron 1
1 , The University of Texas at Austin, Austin, Texas, United States
Show AbstractSemiconductors can be rendered plasmonic by doping to create high concentrations of free carriers. Degenerately doped wide band gap metal oxides are commonly used as transparent conductive thin films in optoelectronic devices, and these same materials exhibit localized surface plasmon resonance (LSPR) when synthesized as discrete colloidal nanocrystals. I will describe our recent efforts to control the shape of plasmonic metal oxide nanocrystals by tuning synthetic conditions. Highly faceted nanocrystals exhibit distinctive LSPR modes that are evident in their absorption spectra. When assembled into close packed clusters or films, hot spots with amplified near field enhancement factors can result in the spaces between these nanocrystals. These hot spots, which can be predicted by electromagnetic simulations and observed by electron energy loss spectroscopy, facilitate resonant coupling with other oscillators.
4:15 PM - NM06.05.08
Engineering Novel Plasmonic Nanostructures
Mona Treguer-Delapierre 1 , Veronique Many 1 , Cyril Chomette 1 , Sergio Gomez-Grana 1 , Stephane Mornet 1 , Etienne Duguet 1 , Nicholas Shade 2 , Serge Ravaine 3 , Vinothan Manoharan 2
1 Chemistry, ICMCB-Université de Bordeaux, Bordeaux France, 2 , Harvard University, Cambridge, Massachusetts, United States, 3 Chemistry, CRPP-University of Bordeaux, Bordeaux France
Show AbstractA fundamental goal of material science is the design and synthesis of materials with tailored shape and size. There has been tremendous progress over the past decade in the synthesis of plasmonic nanoparticles of various sizes and shapes and with good yield and monodispersity. In this talk we will overview plasmonic nanostructures that can be elaborated by using the concept of patchy nanoparticles, i.e. spherical nanoparticles with a controlled number of patches. The selective functionalization of the patch areas or the inter-patch areas offers the possibility to create complex supracolloids with extraordinaory optical signatures suitable for applications such as (bio-) sensing, metamaterials or catalysis.
4:30 PM - NM06.05.09
The Importance of Ligand Dimensions in the Synthesis, Surface Modification, Property Tuning and the Self-Assembly of Colloidal Nanoparticles
Davit Jishkariani 1 , Christopher Murray 1
1 , Univ of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractSynthesis of colloidal nanoparticles is typically achieved with commercially available ligands, most of which are based on alkyl derivatives of carboxylic and phosphonic acids, amines, phosphines or thiols. While these remain invaluable, the recent advances in custom designed ligands provide enormous opportunities in manipulating the size, self-assembly and physical property of colloidal nanocrystals. Short ligands such as ammonium isothiocyanate (NH4SCN) for example brings nanoparticles close enough and increase the film conductivity while the bulky ligands provide increased interparticle separation allowing the manipulation of the interparticle optical and magnetic coupling. Robust polycatenar ligands, branched molecules bearing diverging chains in which the terminal substitution pattern, functionality, and the surface binding group can be independently modified, offer a versatile platform for the development of ligands suitable for nanoparticle synthesis where the size of nanoparticle inorganic core can be tuned based on the chemical composition of the ligand.
Our research lab designs diverse libraries of polycatenary and dendritic ligands derived from polyalkylbenzoates and bis-MPA with a variety of alkyl chains and surface anchoring properties where the ligand size, number and the nature of the end-group, and the nature of the surface binding group can be independently tuned. To demonstrate their utility and identify the key structural components, we carried out the synthesis of a broad range of nanocrystals NCs including CdSe, CdS, PbSe, PbS, ZnO, Fe2O3, InP, and Au. Monodisperse nanocrystals coated with these ligands self-assemble to form single component and binary self-assembled superlattices that show large solid state interparticle spacings. The large, programmable interparticle separations obtained using such ligands controls the self-assembly which is tunable from hard sphere to soft sphere behavior.
The synthetic design of dendritic and polycatenar molecules of various sizes, as well as their use in the synthesis and tuning of optical, magnetic and the self-assembly properties of the nanoparticles, will be presented with the special focus on the importance of the ligand dimensions.
NM06.06: Poster Session II: Synthesis, Assembly and Structure
Session Chairs
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - NM06.06.01
Correlating Solvent Environment with Nanoparticle Coating Thickness and Aggregation Tendency
Albert Kwansa 1 , Danielle Stallings 1 , Yaroslava Yingling 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractGold nanoparticles (AuNPs) have been sought for medical diagnostics, drug and gene delivery, biological and chemical sensors, catalysis, and electronics, due to their optical, electronic, and surface properties. AuNPs are often functionalized and exposed to various solvents during their preparation and use; however, several factors can complicate solvent environment selection and influence AuNP properties. Such factors can include the surrounding solvent, AuNP coating chemistry and thickness, AuNP size and shape, and AuNP concentration. Thus, we are using all-atom molecular dynamics (MD) to (1) establish predictive mathematical models (2D or 3D functions) that relate different solvent properties to AuNP properties and (2) gain mechanistic insights into NP aggregation tendency.
To our knowledge, only a few solvent environments have been investigated for this purpose using MD, namely, decane, ethane, saline, and water. In the present work, we explored a 2D (2-factor) space of eight solvents and six AuNP coating thicknesses, leading to a total of 48 simulated systems. Each system consisted of two AuNPs in one of eight solvents (acetic acid, acetone, acetonitrile, chloroform, dimethyl sulfoxide, methanol, and water) at an AuNP concentration of 12.9±0.7% (g/mL). Each AuNP included a 1.5-nm-diameter gold core coated with 60 ligands (-S(CH2)nC6H4OH) representing one of six different lengths (number of CH2 groups, n = 4, 8, 12, 16, 20, 24); AuNPs of a similar size and coating chemistry (phenol-terminated alkanethiol) have been sought for drug delivery applications, where the phenol group aids the linking of the drug to the NP. The Amber 14 simulation package was used (300 K, 1 atm, 100 ns, 2-fs timestep) with the General Amber Force field (GAFF), TIP3P water model, and other published solvent models.
The aggregation tendency of the AuNPs was quantified with metrics such as NP-NP core separation, NP-NP surface separation, and NP-NP non-bonded interaction energy. Non-linear relationships were observed for these aggregation metrics; solvent total Hansen Solubility Parameter (HSP) and molar volume were found to be the strongest predictors of the solvent properties considered. NP aggregation tendency was minimal (acetic acid, acetonitrile, and dimethyl sulfoxide), moderate (toluene, chloroform, acetone, and methanol), or strong (water); aggregation was minimized in acetic acid and maximized in water. These relationships could be described by two sigmoidal functions that form a peak near acetic acid; these results also suggest that the total HSP of this particular functionalized AuNP is close to that of acetic acid. The accuracy with which solvent models are able to reproduce experimentally determined solvent properties is also being investigated and can influence relationships gleaned from these AuNP-solvent simulations. Future work may incorporate factors such as AuNP concentration and ligand chemistry to provide a more complete predictive model.
8:00 PM - NM06.06.02
Writing on Nanocrystals—Enhancing Stability and Patterning of Cesium Lead Halide Nanocrystal Films through Irradiation-Induced Chemical Transformations of Surface Ligands
Mirko Prato 1 , Francisco Palazon 1 , Quinten Akkerman 1 , Liberato Manna 1
1 , Istituto Italiano di Tecnologia - IIT, Genova Italy
Show AbstractDespite the outstanding optoelectronic properties of halide perovskite thin films [1] and nanocrystals (NCs),[2] their widespread implementation in optoelectronic devices is severely hindered by their poor stability. Indeed, different factors such as high temperature and moisture have demonstrated to degrade perovskite materials.[3] Such material degradation has a double negative consequence: (i) loss of optoelectronic properties eventually leading to non-functional devices and (ii) possible release of environmentally-harmful species such as lead ions.
In this communication, we will show that X-ray exposure can induce intermolecular C=C bonding on the thin (< 2 nm) ligand shell surrounding cesium lead halide NCs deposited as a film on a silicon substrate, thus dramatically increase their stability.[4]
This transformation resulted in several interesting features as:
1) Insolubility of the exposed regions in organic solvents which caused instead complete dissolution of the unexposed regions. This enabled the fabrication of stable and strongly fluorescent patterns over millimeter scale areas;
2) Resistance of the films to degradation caused by exposure to air and moisture;
3) Stability of the film in water and biological buffer. Indeed, CsPbI3 NC films could retain their photoluminescence after being fully immersed in water for several weeks, while non-treated NCs rapidly degraded in (moist) air. In turn, this means that no toxic elements were released in the water environment.
Importantly, we demonstrated that the same approach is also highly efficient in blocking chemical transformations, such as anion exchange reactions, that are instead known to proceed very fast in not-X-rays exposed nanocrystals and in solution. This finding allowed us to realize an efficient UV-to-white color-conversion layer based on cesium lead halide nanocrystals of different chemical composition, preserving the emission properties on each of the chosen stoichiometries.[5]
Moreover, we demonstrated that X-ray irradiation is able to transform the ligand shell in an effective shield able to block gases (e.g. butylamine gas) that could induce structural and optical transformation in CsPbBr3 NCs. Indeed, we recently shown that reaction of these NCs with amines can result in the partial leaching of PbBr2 from the structure, eventually leading to the transformation into the so-called 0D Cs4PbBr6 phase.[6] By exploiting this phenomenon and a masked X-ray irradiation, we were able to fabricate patterns of luminescent CsPbBr3 surrounded by non-luminescent Cs4PbBr6.
[1] S. D. Stranks et al., Science (2013), 342, 341-344.
[2] L. Protesescu et al., Nano Lett. (2015), 15, 3692-3696.
[3] J. S. Manser et al., Acc. Chem. Res. (2016), 49, 330.
[4] F. Palazon et al., ACS Nano (2016), 10, 1224-1230.
[5] F. Palazon et al., Chem. Mater. 2016, 28, 2902−2906
[6] F. Palazon et al., Chem. Mater. 2017, 29, 4167−4171
8:00 PM - NM06.06.03
Reshaping Colloidal Metal Chalcogenide Nanostructures via Selective Etching
Andrew Nelson 1 , Don-Hyung Ha 1 2 , Richard Robinson 1
1 , Cornell University, Ithaca, New York, United States, 2 School of Integrative Engineering, Chung-Ang University, Seoul Korea (the Republic of)
Show AbstractResearch into ligand-surface interactions in colloidal nanoparticles has led to profound advances in researchers’ ability to control particle size, shape, structure, and functional properties. Synthetic strategies for nanoparticles primarily utilize their protective or capping properties (or lack thereof), with such factors as ligand size, binding strength, and facet selectivity serving to dictate their impact on the growing particle. In this regard trialkylphosphines (“phosphines”) have served a particularly prominent role. However, reports have uncovered decidedly “non-innocent” behaviors in this reactive, air-sensitive class of ligands, such as the ability to serve as a phosphorus source during the synthesis or to dramatically change the stoichiometry of nanoparticles. Here we demonstrate another aspect of this vigorous participation by a “passivating” ligand in nanoparticle synthesis and transformation: a reaction in which phosphines attack and dissolve nanoparticles of copper sulfide, Cu2-xS, under oxidizing conditions at room temperature. The presence of small amounts of phosphine leads to anisotropic etching behavior which crosses over to purely isotropic etching as phosphine concentration is increased and the particle surface becomes saturated with phosphine. Importantly, this etching reaction is capable of removing Cu2-xS from Cu2-xS-ZnS epitaxial nanostructures with perfect selectivity. X-ray diffraction shows that etching is preceded by destabilization of the ordered-vacancy roxbyite (Cu1.81S) phase, which immediately transforms to the more copper-rich djurleite (Cu31S16) phase; when the Cu2-xS is strained by epitaxial ZnS, this transformation is suppressed due to severe lattice mismatch of djurleite to ZnS. In air, Cu2-xS is dissolved into a mixture of phosphine sulfides, as confirmed by infrared spectroscopy, and Cu2+ coordinated by phosphine oxidation products, as shown by electron paramagnetic resonance. By using an electron acceptor, Ce4+, as a more controllable etching promoter, we establish that etching is driven by redox of the particle itself and, by consideration of the reaction stoichiometry, that complete dissolution of the particles requires that sulfide S2- must be oxidized to S- or S0, after which it is extracted by reduction of the particle with phosphine. The use of combined oxidizing and reducing conditions to control carrier concentration, in conjunction with chemically and structurally selective nanomachining, could allow access to novel semiconductor heterostructures by combining the “bottom-up” particle growth techniques with “top-down” etching methods.
8:00 PM - NM06.06.04
Connection of Magnetic Properties to Defect Structure in Synthetic Iron Pyrite
Dennice Roberts 1
1 , University of Colorado at Boulder, Boulder, Colorado, United States
Show AbstractUnderstanding the nature and consequences of defect structure in iron pyrite (FeS2) is central to bridging the divide between the material’s desirable theoretical properties and its lackluster experimental performance. We assess the impact of surfaces on the magnetic and electronic properties of synthetic iron pyrite by comparing the response of 20 nm particles to 1 um particles in attempt to deconvolute surface effects from bulk response. A comprehensive array of magnetometry measurements of iron pyrite nano- and micro-particles from 1.8 to 300 K were obtained using a superconducting quantum interference device (SQUID) magnetometer in collaboration with NIST-Boulder. Structural refinement of high-quality x-ray diffraction data collected from the BM-11 beamline at Argonne National Laboratory were used to ascertain sulfur occupancy of samples in order to determine the role of defects on magnetic properties. In addition to reporting the first known magnetic measurements on particles in the 1 um size regime, we discuss for the first time a quantitative relationship between defect population and magnetic properties. Additionally, we present a comprehensive analysis of the magnetic properties of synthetic FeS2 and discuss how the electron environment elucidated from these results correlated with a reduced band gap.
8:00 PM - NM06.06.05
Surface Instabilities in Silicon Nanocrystal Thin Films—Finite Bending
Alborz Izadi 1 , Mayank Sinha 1 , Sara Roccabianca 1 , Rebecca Anthony 1
1 , Michigan State University, East Lansing, Michigan, United States
Show AbstractNonthermal plasmas are powerful reaction tools for synthesizing high-quality semiconductor nanocrystals – but their non-equilibrium nature makes them even more attractive. While the electrons gain significant energy and the nanocrystals spike to high temperatures, the overall gas flow is near room temperature and the nanocrystals equilibrate to this temperature by the time they exit the reactor. This means that these vapor-phase-entrained nanocrystals can be deposited directly onto substrates with low thermal budget or solvent susceptibility, such as flexible/stretchable elastomers.
This capability opens the door to exploring the creation of bilayered structures on stretchable substrates, and to understanding formation and control of wrinkles and surface instabilities in the nanocrystal layers depending on the compression or tension of the nanocrystal layer. These instabilities can be used as tunable electromagnetic gratings, possible pressure/strain sensors, and in creation of flexible displays and electronic skins. Here, we discuss controlling and modeling the wrinkling instabilities formed by inertially impacting plasma-produced silicon nanocrystals (SiNCs) on polydimethylsiloxane (PDMS) substrates. In this work, we employed a finite-bending approach to creating surface instabilities in the SiNC layers. To create the instabilities, we began with PDMS slabs and created cylindrical or semi-cylindrical forms with varying bending angle. Then, we used orifice-based inertial impaction of the SiNCs to deposit thin layers of luminescent SiNCs onto the PDMS forms directly from the plasma reactor. Next, we unwrapped the PDMS cylinders to form flat bilayers, therefore introducing compression in the SiNC layer. We analyzed the wrinkling instabilities that form in the bilayers using SEM and optical microscopy, mapping the instability properties (“wavelength” of wrinkles, amplitude, direction) to the bilayer parameters such as bending angle during deposition, SiNC layer thickness, and SiNC size. We also performed uniaxial tensile testing and nanoindentation to estimate the mechanical properties of PDMS and the bilayers. PDMS is generally defined as an isotropic, homogeneous, hyperelastic and incompressible material, and is characterized by strain energy functions defined for rubber-like materials. For silicon NCs, we propose to adopt different strain energy functions which have proven to be descriptive of elasto-plastic materials to fit the results obtained from the nanoindentation and uniaxial tensile tests. We will incorporate these findings into constitutive models of the bilayer materials. When completed, the model will be used to predict and control the formation of these instabilities, moving towards future applications in stretchable electronics and more.
8:00 PM - NM06.06.07
Semiconductive Cellulose Nanocrystals Synthesized by Sonogashira Grafting of Poly (ethynylene 9,9-dihexyl fluorene)
Allen Chang 1 , Sandra Chen 1 , Kenneth Carter 1
1 Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractIn this work, we demonstrate the ability to synthesize organic, semiconductive nanoparticles based on an abundant, renewable, and natural feedstock. Semiconducting poly (2-acetylene-9,9-dihexyl fluorene) was grafted from the surface of functionalized cellulose nanocrystals (CNCs) via Sonogashira cross coupling chemistry. CNCs were first surface functionalized with 4-bromo benzoyl chloride via an acid chloride esterification. This functionalization was characterized by FTIR and XPS to provide confidence in the effectiveness of the esterification reaction and to quantify the potential grafting density. Poly (ethynylene fluorene) was grafted from the active bromine sites with the aid of Pd and Cu catalysts. The end product was characterized by XPS, showing expected trends in the C1s curve deconvolution. A portion of the grafted polymer was cleaved by acid hydrolysis of the ester linkage, regenerating some surface hydroxyl groups, and yielding uniquely end-capped polymer that could be analyzed by MALDI-ToF MS. The combined analysis provides confidence in the synthesis of a covalently bound, solution dispersable, organic semiconductor/CNC nanoparticulate material.
8:00 PM - NM06.06.08
Carge Carriers Modulate the Bonding of Dopants in Semiconductor Quantum Dots
Asra Hassan 1 , Xiaoyi Zhang 2 , Richard Schaller 3 4 , Preston Snee 1
1 , University of Illinois at Chicago, Chicago, Illinois, United States, 2 X-Ray Sciences Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 4 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractOur group recently discovered that the interaction of a charge carrier (electron or hole) with a semicondutor dopant can change the bonding of the guest ion to the host matrix. This phenomenon was observed by monitoring the electronic dynamics of a dopant in a semiconductor quantum dot matrix using time resolved X-ray absorption spectroscopy. Specifically, photoexcitation of copper-doped cadmium sulfide quantum dots resulted in a shift of the Cu K-edge XANES absorption to higher energy due to hole capture by the dopant. This in turn instigated a stronger bonding interaction of copper with sulfur within the semiconductor host as revealed by the excited state EXAFS spectrum. X-ray analyses also revealed two types of surface-bound copper ions that display different dynamics in the excited state. These observations are supported by large-scale DFT calculations, which attest to the generality of the conclusions made with this system. Overall, the modulation of dopant bonding by electrons and holes represents a new dynamic that has implications for understanding the mobility of charge carriers in semiconductor hosts.
8:00 PM - NM06.06.09
A New Electrochemical Approach to Convert Thin Metal Film into Nanocrystals
Chang Liu 1 , Shien Ping Feng 1
1 , University of Hong Kong, Hong Kong China
Show AbstractMetal and semiconductor nanocrystals have attracted great attention due to their fascinating size- and shape-dependent properties for various applications, such as catalysis, sensing, drug delivery, and bioimaging. Particularly, the synthesis of functional nanocrystals with high surface-to-volume ratios and high-index planes is of significance to achieve enhanced catalytic activities or optical properties. Scientists and engineers have devised hundreds of methods to synthesize a variety of nanocrystals with fine-tailored sizes and shapes. Most common synthetic methods, seed-mediated growth methods and polyol processes, are time-consuming and susceptible to the use of adsorbates and reaction temperature. In this work, a new electrochemical approach, named as cyclic scanning electrodeposition (CSE) method, is presented to convert thin metal films into metal nanocrystals, or semiconductor nanocrystals. The core of this process is a specific electrolyte consisting of CH3COONa, NiSO4, and Na2SO4, and this technique deals with potential waveform, the population of adion, and foreign ions in a methodical manner to effectively synthesize Ag nanocrystals in shapes such as nanoflower, nanorods, dendrites, decahedrons, and icosahedrons. The Ag nanoflowers show a remarkably improved catalytic activity for electro-oxidation of glucose with one order of magnitude improvement in detection limit as well as the highest sensitivity achieved to date. An instructional knob has been proposed to precisely control nucleation and growth of nanocrystals with different shapes, which can be extended to various metal or bimetallic systems. Here, cuprous oxide nanocrystals are produced by converting Cu thin film via CSE in the similar system. The flower-like Cu2O nanocrystals with a high surface-to-volume ratio and high-index faceted Cu2O microcrystals are synthesized in a high yield. A novel type of semiconductor substrates for high-performance SERS is demonstrated based on three-dimensional flower-like Cu2O nanocrystals. The photocatalytic activity of high-index faceted Cu2O microcrystals is reformed by constructing high-index facets and show an enhanced photocatalytic activity in photoelectrochemical hydrogen production.
8:00 PM - NM06.06.10
Molybdenum and Tungsten Sulfide Ligands for Versatile Functionalization of All-Inorganic Nanocrystals
Hyeong Woo Ban 1 , Sangmin Park 1 , Hyewon Jeong 1 , Da Hwi Gu 1 , Seungki Jo 1 , Jae Sung Son 1
1 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractWe report a strategy toward the synthesis of colloidal nanocrystals capped with inorganic molybdenum and tungsten sulfide ligands. MoS42– and WS42– thiometalates were utilized to replace organic ligands capping a wide range of nanocrystals such as metals, semiconductors, and well-conserved primary properties of nanocrystals in polar media. Especially, MoS42–- and WS42–-capped CdSe nanocryatals showed the dramatic enhancement of photoluminescence properties by the photo-oxidation treatment, which originated from the preferential formation of MoSxOy layers on the CdSe surface. The highest quantum yield reached up to 51%. Furthermore, we studied the charge-transport properties of MoS42–-capped PbS nanocryatals by the fabrication of a field-effect transistor and photodetectors. Finally, MoS42–- and WS42–-capped nanocrystals were used for the production of two-dimensional MoS2 and WS2 thin layers on nanostructures by heat treatment. Such versatility of these thiometalate ligands offers an additional degree of control over the functionality of nanocrystals for optoelectronic and catalytic applications.
8:00 PM - NM06.06.11
New Insights into the Thermodynamics and Experimental Control of Twin Defects in Metal Nanocrystals
Kyle Gilroy 1 , Joël Puibasset 2 , Madeline Vara 3 , Younan Xia 1 3 , Shan Zhou 1
1 The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States, 2 Interfaces, Confinement, Materiaux et Nanostructures, CNRS et Universite d’Orleans, Orleans France, 3 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractMetal nanocrystals have found use in a wide variety of applications, with ample examples in plasmonics, catalysis, sensing, and biomedicine. It is well established that the performance of metal nanocrystals towards a specific application strongly depends on their shape and symmetry. More recently, it was further demonstrated that the value of metal nanocrystals could be greatly augmented by introducing twin defects into the crystal lattice. When present in a nanocrystal, the number and orientation of twin defects define the underlying symmetry, but more importantly, they also control the degree of lattice strain, packing geometry of surface atoms, and the corresponding surface-energy landscape. However, while the excitement for twin defects continues to grow, the true mechanism that guides twin-defect formation in nanocrystals is still unknown and perplexing. This presents an urgent need to develop synthetic strategies, while at the same time working towards determining how and why atoms assemble into a particular configuration. At the moment, the generation of nanocrystals with a particular twin-defect structure relies on what is referred to as kinetically controlled wet-chemistry. In essence, this approach exploits the strong correlation between the rate at which a solution-phase metal-salt precursor is reduced and the twinning expressed in the resultant nanocrystals. While this offers a viable route to the generation of specific twinned nanocrystals, the pathways are unpredictable and extremely sensitive to slight changes in experimental condition. Herein, we demonstrate how, and then offer computational insights to explain why, metal nanocrystals with well-defined twin defects can be rationally engineered by simply following the guidelines defined by thermodynamics. For a face-centered cubic (fcc) metal nanocrystals, theory predicts that the most stable arrangement of atoms, and thus the geometric shape, trends with the number of atoms contained in the particle, with large, medium, and small sizes favoring the formation of single-crystal, decahedral, and icosahedral structures, respectively. To experimentally validate this theoretical trend, we devised a protocol that involves heating size-controlled Ag nanoparticles to 600 oC, followed by slow cooling. When cooled down slowly from an elevated temperature, we show with high-resolution transmission electron microscopy that the atoms contained in each particle would arrange such that the individual structure reached an equilibrium state in terms of internal defect structure (i.e., the number and orientation of twin defects) and external structure (i.e., facet expression).
8:00 PM - NM06.06.12
Transition Metal Sulfide Ligands for All-Inorganic Nanocrystals
Hyewon Jeong 1 , Seung Hwae Heo 1 , Da Hwi Gu 1 , Hyeong Woo Ban 1 , Sangmin Park 1 , Jae Sung Son 1
1 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractInorganic ligands for nanocrystals capping have been intensively studied for providing new robust functionalities to all-inorganic forms of colloidal nanocrystals. In this work, we developed a new type of inorganic ligands that contained transition metal sulfides (Fe, Co, Ni and Pt based thiometallates) for nanocrystals capping and examined the catalytic performance of these ligands-capped all-inorganic nanocrystals. Thiometallates anionic compounds were synthesized in a solution batch system and their optical, structural properties, and thermal behaviors were systematically characterized. All these compounds were transformed into crystalline phases at temperature higher than 300 °C by thermal decomposition. Furthermore, the generality of these compounds as inorganic ligands was demonstrated for a wide range of nanocrystals such as semiconductors, metals, and ceramics. These inorganic ligands fulfilled all expected functions of ligands capping nanocrystals, where colloidal stability as well as preservation of original structural and electronic properties of nanocrystals were demonstrated. Combining the structural changes of the thiometallates ligands at high temperatures, we attempted to form hybrid nanostructures for synergistic catalytic functionalities. For example, the PtS thiometallates ligands capping oxide nanocrystals were annealed at temperatures higher than 300 oC, generating pure Pt particles-decorated oxide nanostructures by the evaporation of sulfur. We utilized these hybrid nanostructures as heterogeneous catalysts, exhibiting the significantly enhanced activity compared with bare nanostructures. The currently developed chemical route will pave a new way to provide the catalytic functionality to all-inorganic nanocrystals.
8:00 PM - NM06.06.13
Self-Organized Freestanding One-Dimensional Plasmonic Au Nanoparticle Arrays
Myungkoo Kang 1 , Yu Yuwen 2 , Wenchong Hu 2 , Seokho Yun 2 , Krishnamurthy Mahalingam 3 , Bin Jiang 4 , Kurt Eyink 3 , Ekaterina Poutrina 3 , Kathleen Richardson 1 , Theresa Mayer 2
1 , University of Central Florida, Orlando, Florida, United States, 2 , The Pennsylvania State University, University Park, Pennsylvania, United States, 3 , Air Force Research Laboratory (AFRL), Dayton, Ohio, United States, 4 , FEI Company, Hillsboro, Oregon, United States
Show AbstractPlasmonic nanoparticle arrays are promising for a broad range of applications, including biosensors, surface enhanced Raman spectroscopy, waveguides, nanoantennas, and negative index materials. The array properties are based on electromagnetic field enhancement at the metal-nanoparticle surface, which is controlled by the nanoparticle array material and geometry, the dielectric constant of the surrounding media, and the wave polarization and direction. This work reports a versatile method to synthesize self-organized one-dimensional Au nanoparticle arrays encapsulated within freestanding silicon dioxide nanowires.1 This process provides independent and precise control of nanoparticle diameter and interparticle spacing along the length of the wire. This is achieved by thermal oxidation of Au-coated Si nanowires with highly tailorable and reproducible diameter and surface modulation created by deep reactive ion etching. The nanoparticle diameters are determined by the volume of the deposited Au film on the surface of the wire, and their interparticle spacing is defined by the surface modulation wavelength of the starting Si nanowire. Optical absorption measurements of a suspension of randomly oriented SiO2-encapsulated Au nanoparticle arrays with 80 nm diameter particles and 230 nm interparticle spacing showed a plasmonic response with an intense peak at 550 nm. Scanning transmission electron microscopy-electron energy loss spectra of individual nanoparticle array wires confirmed the same plasmonic response and high uniformity in the Au nanoparticle properties. Additional energy filtered transmission electron microscopy analysis showed optical coupling between adjacent Au nanoparticles in the array. These results demonstrate that this fabrication method provides a cost-effective and scalable approach to create free-standing one-dimensional nanoparticle array building blocks with increased flexibility for future plasmonic devices.
1. Kang, M.; Yuwen, Y.; Hu, W.; Yun, S.; Mahalingam, K.; Jiang, B.; Eyink, K.; Poutrina, E.; Richardson, K.; Mayer, T. S. Self-Organized Freestanding One-Dimensional Au Nanoparticle Arrays. (accepted in ACS Nano)
8:00 PM - NM06.06.14
Synthesis and Characterization of Ternary Intermetallic Fe2CoAl Inverse Heusler Alloy Nanoparticles
Aquil Ahmad 1 , Sanjeev Kumar Srivastava 1 , Amal Kumar Das 1
1 Physics, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India
Show AbstractThe ternary intermetallic compounds with 2:1:1 stoichiometry is called full Heusler alloy, which always fascinated to the researchers due to their unique properties like high magnetic moment, high Curie temperature, and Half-metallicity. These materials have great potential to achieve half-metallicity at room temperature and predicted to exhibit 100% spin polarization at the Fermi level (Ef), also suitable for spintronic devices. Substantial efforts have been made to synthesize Heusler alloy, but studies are limited to bulk and the thin film only since phase separation easily occurs due to lattice mismatch, immiscibility in the case of ternary alloy. There have been few studies available in nano-metric Heusler alloy.
In this study, Fe2CoAl Heusler Alloy was chemically synthesized and characterized, which forms inverse Heusler Alloy (Y2XZ, where Y and X are transition metals and Z is main group element) type structure under F-43m space group with space group no-216. X-ray diffraction (XRD) analysis was performed to confirm the phase and the diffraction peaks appeared at 2θ = 44.46°, 65.10° and 82.41° corresponding to the plane of (220), (400), (422) under fundamental diffraction satisfying the relation h+k+l = 4n, with lattice parameter a=5.71 A°. It can also be predicted from the XRD results, the synthesized alloy had A2 type disordering depending upon the availability of the atom at three crystallographic lattice sites viz. (0, 0, 0) and (0.25, 0.25, 0.25) for Fe, (0.50, 0.50, 0.50) for Co and (0.75, 0.75, 0.75) for Al, confirmed from the absence of superlattice peaks (100) and (200). High-resolution transmission electron microscopy (HRTEM) analysis was performed and indexed ring pattern as (220), (400) and (422) also confirmed the phase and suggested polycrystalline nature of the sample. Average particle size of 80 nm obtained from HRTEM analysis was found to be consistent with the average crystallite size of Dv ~ 21 nm for characteristic (220) peak using Scherer Relation Dv = (K×λ)/β cosθ, where K=0.89 and β is full width at half maximum (FWHM), λ is the wavelength of the X-ray source (of CuKα; λ =1.54 A°, in our case) and θ is the Bragg angle. The results obtained from EDAX analysis attached with TEM facility revealed the atomic ratio of 2:1:1 for the as-synthesized alloy. Magnetic characterization has been carried out in physical properties measurement system (PPMS) and from magnetization data total magnetic moment at-300 K ~118.60 emu/gm, is in good agreement with the value of bulk material according to Slater-Pauling rule, which suggests that the half-metallic properties are conserved even in particles on the nanometer scale. In addition, high-temperature measurement also carried out in vibrating sample magnetometer (VSM), and after analysis of moment vs temperature data, Curie temperature (Tc) of around ~1000K was obtained for the alloy.
8:00 PM - NM06.06.15
Nanoprinted Nanoarrays of Gold Nanoparticles and/or Semiconducting Oxide Nanocrystals on the Originally-Developed 0.3 nm-High Atomically Stepped Ultra-Flat Polymer Sheets
Mamoru Yoshimoto 1 , Risa Goto 1 , Taichiro Kinoshita 1 , Shiori Yamada 1 , Satoru Kaneko 2 , Akifumi Matsuda 1
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Kanagawa Institute of Industrial Science and Technology, Ebina Japan
Show AbstractIn fabrication of semiconductor and/or plasmonic nanostructures arrays on the flexible polymer sheets, atomic-scale surface flattening of polymers is critically important from the point of advances in nanoscience and photonic technology. The nanoimprint or nanocontact printing technique may play a future role in polymer surface patterning as a replacement for projection type photolithography because of its advantages of simple, low-cost, and high-throughput production. The resolution limit of nanoimprinting has attracted much attention from both scientific and industrial field. In this work, we presents the following exciting results on nanoprinted fabrication of nanoarrays of gold nanoparticles and/or semiconducting ZnO nanocrystals on the originally-developed 0.3 nm-high atomically stepped ultra-flat polymer sheets [1-5].
(1) The sub-nanoscale surface patterning was performed on the thermostable polyimide sheets as well as poly(methyl methacrylate) (PMMA) polymer sheets by thermal nanoimprinting using an atomically stepped sapphire template (α-Al2O3 single crystal). The present 0.3 nm-high atomic step & terrace surface morphology of the polymer sheets was stable for over a year.
(2) Large area gold and/or ZnO nanoparticles nanoarrays of dot or mesh were produced onto the 0.3 nm-high stepped ultra-smooth PMMA sheets by applying a nanocontact-print technique using the Au-film coated pillar or mesh molds. The optical properties of these plasmonic nanoparticles, semiconductor nanocrystals, and metal-hybrid array structures were characterized, and also the thermal stability and the influence of the nanoprint conditions on the pattern transfer were investigated.
(3) The smooth and atomically stepped indium tin oxide (ITO) transparent conducting thin films could be deposited on the 0.3 nm-high atomic step-and-terrace surface of the flexible and transparent polyimide sheet, leading to development of the nanostructured flexible polymer electrodes for the new-generation photonic devices.
[1] G. Tan et al., Appl. Phys. Express 7 (2014) 055202.
[2] M. Yoshimoto, Applied Physics A 121 (2015) 321
[3] G. Tan et al., Polymer Journal 48 (2016) 225.
[4] K. Shimada et al., Jpn. J. Appl. Phys. 55 (2016) 098002
[5] G. Tan et al., Nanotechnology 27 (2016) 295603
8:00 PM - NM06.06.16
Single-Particle Resolution Quantum Dot Self-Assembly and Subsequent Nanotransfer Printing of the Quantum Dot Array
Tae Won Nam 1 , Geonyeong Kim 1 , Hunhee Lim 1 , Yeon Sik Jung 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractDirected self-assembly of nanoparticles (NPs) provides versatile functionalities beneficial for many different fields including device miniaturization, optical applications, sensors and quantum devices. While certain applications require close-packed arrays of NPs, specific positional or orientational control of NPs is necessary for practical design of many devices. However, in order to utilize the extrinsic properties of NPs, the resolution of positional control of NP arrays must keep up with the NP size of actual significance; that is, at least higher than sub-10 nm, or even up to sub-5 nm for those of quantum dots (QDs), the semiconducting elements. For an example, the fluorescence resonance energy transfer (FRET) efficiency of QDs is best understood by the positional interaction between adjacent QDs within the array; hence, delicate positional control of QDs in single-particle resolution is crucial to manipulate not only such FRET behavior but also other near-field communication of QDs. However, positional and orientational control of sub-5 nm NPs are limited due to the resolution limit of a directing template itself. Among very limited candidates of guiding template with ultra-high resolution as well as ordering quality, block copolymers (BCPs) stand out as a promising media which proposes diverse template morphology, high ordering quality and sub-10 nm pattern resolution, commensurable to that of QDs. Here, we report ultra-high resolution directed self-assembly of 5 nm sized CdSe QDs by inexpensive and facile approach via capillary force self-assembly on topographical BCP template. A high-chi (χ), silicon containing BCP, poly(dimethylsiloxane)-b-poly(styrene) (PDMS-b-PS) is selected due to high template resolution of up to sub-10 nm scale. However, mere delicately controlled QD array is limited in its application at diverse device environment due to its difficulty in delivery on various substrates. Here, we not only induce the positional control of QDs but also successfully deliver the assembled QDs while maintaining their array information via nanotransfer printing method. Abovementioned assembly and printing of sub-10 nm scale NPs are expected to narrow down the gap between feasibility and the actual utilization of NPs with unique material properties.
8:00 PM - NM06.06.17
Synthesis, Formation Mechanism and Magnetic Properties of Monodisperse Semiconducting Spinel CdCr2S4 Nanocrystals
Chao Pang 1 2 , Ningzhong Bao 2 , Arunava Gupta 1
1 , University of Alabama, Tuscaloosa, Alabama, United States, 2 , Nanjing Tech University, Nanjing China
Show AbstractMagnetic spinel CdCr2S4 nanocrystals have been synthesized using a high-temperature solvothermal method and a facile and mild one-step “seed-mediated” growth procedure. The high-temperature solvothermal synthesis process involves the reaction of excess 1-dodecanethiol (1-DDT) with CdCl2 and CrCl3●6H2O in 1-octadecene (ODE) solution carried out in a sealed titanium alloy autoclave. In an alternative facile and mild one-step solution-based synthesis procedure, we use cubic phase CdS, which has similar face-centered cubic crystal structure as spinel CdCr2S4, as “seed” to react with CrCl3●6H2O in a solution mixture of 1-DDT and ODE. Monodisperse CdCr2S4 spinel nanocrystals are obtained. The possible formation mechanism of CdCr2S4 spinel nanocrystals using both methods will be presented, along with detailed structural and magnetic properties of the synthesized CdCr2S4 nanocrystals.
8:00 PM - NM06.06.18
Morphological Analysis of Sequential Cation Exchange in Chalcogenide Nanocrystals
Savannah Benjamin 1 , Xyan Aguilar 1 , Jonathan Campbell 1 , P. Greg Van Patten 1
1 , Middle Tennessee State University, Murfreesboro, Tennessee, United States
Show AbstractNanoparticle technology has emerged in recent years with expansive applications ranging from photovoltaics to biomedical imaging. Our lab focuses on the synthesis of chalcogenide nanocrystals and cation exchange reactions. We have conducted experiments on partial cation exchange with Ag+ in CdSe, PbS, and CdS nanocrystals in order to determine the particle morphologies and cation distributions within the product nanocrystals. We have combined this partial cation exchange with sequential cation exchange experiments in which we follow the Ag exchange with a second exchange with another cation of interest (Cd, Pb, Zn, Mn, Cu) in order to understand how the cation distribution in the first (Ag-containing) product influences the cation distribution in the final product (after the second exchange process). Optical spectroscopy, electron microscopy, and x-ray elemental analysis have been used to characterize the products and correlate structural and compositional changes with the optical properties of the product nanocrystals.
8:00 PM - NM06.06.19
Direct Synthesis of Platinum Nanodots in ZIF-8 Coated Fe3O4 Nanoparticles
Sanghee Lee 1 , Changyong Yim 1 , Sangmin Jeon 1
1 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractA novel method was developed for synthesizing platinum nanoparticles into zeolitic imidazolate framework nanostructures without using additional reducing agents or additives. Fe3O4 magnetic nanoparticle clusters (MNCs) were synthesized and coated with ZIF-8 (ZIF) shells. Upon addition of ZIF/MNC hybrid nanoparticles into a platinum precursor (K2PtCl4) solution, platinum ions were reduced to metallic platinum nanodots by the 2-methyl imidazolate groups. Synthesized platinum nanodots were ~2 nm in diameter and uniformly distributed in the pores of the ZIF-8 shell. The catalytic activity of the platinum nanodots was examined by using Pt/ZIF/MNCs for the reduction of 4-nitrophenol using NaBH4. The resulting high catalytic activity was attributed to the high surface area of the platinum nanodots and the absence of capping layers. Furthermore, the hybrid nanoparticles were collected using a permanent magnet and were found to maintain their catalytic activity after multiple cycles.
8:00 PM - NM06.06.20
Developing a Nanoscale Understanding of the Growth Mechanism of III-V Quantum Dots
Qing Zhao 1 , Jeong Yun Kim 2 , Heather Kulik 2
1 Chemical Engineering/Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractColloidal semiconductors nanocrystals (i.e., quantum dots or QDs) have a wide range of applications due to their unique size- and shape-dependent electronic and optical properties, motivating extensive experimental and theoretical work. Indium phosphide (InP) QDs, in particular, represent promising alternatives to more toxic II-VI (i.e., CdSe) QDs, but recipes for controlled III-V InP QD growth mechanism lags behindmore established II-VI synthesis approaches. Some insight has come from ab initio molecular dynamics modeling of the earliest stages of quantum dot growth that revealed In-O bond cleavage in typical indium carboxylate precursors to be essential to the formation of the In-P bond in InP QDs. Experimentally, magic-sized nanocluster intermediates have been characterized by spectroscopy, including X-ray diffraction. We use these available experimental models of intermediate structures in large scale electronic structure calculations to identify mechanisms by which continued QD growth occurs. In this first-principles study, we identify simple structural descriptors as a determinant of the thermodynamic favorability of continued growth at sites on the QD surface. We also identify how this structural descriptor can explain the termination of further growth in InP QDs. Our work provide nanoscale insights into the mechanisms of QD formation fully from first-principles and offers motivation for continued development of synthesis techniques to control QD growth.
8:00 PM - NM06.06.21
Knowledge-Based Design of Nanoparticle Surfaces via Resolving Ligand Adsorption in Colloids on A Molecular Level
Wei Lin 1 , Michael Mahler 1 , Jochen Schmidt 1 , Johannes Walter 1 , Alexandra Burger 2 , Harald Maid 2 , Andreas Hirsch 2 , Wolfgang Peukert 1 , Doris Segets 1
1 , Institute of Particle Technology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Germany, 2 , Institute of Organic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg , Erlangen Germany
Show AbstractAlthough being of major importance for various semiconductor nanocrystals based applications, the characterization of nanoparticle (NP) surfaces in colloids especially with respect to ligand exchange reaction is still an open and highly challenging question. Therefore, a general strategy to study the thermodynamics of ligand adsorption to colloidal surfaces was established by means of catechol (ethyl-3,4-dihydroxybenzoate, esterCAT) binding to ZnO NPs.[1] The derived toolbox was applied to tailor the ZnO surface by CAT derivatives with different functionalities.
First, isothermal titration calorimetry (ITC) was used to extract all relevant thermodynamic parameters, namely association constant, enthalpy, entropy and free energy of the ligand binding. To confirm the characterization of ligand binding by measuring the heat of adsorption, the free energy was cross-validated by mass-based adsorption isotherms. To close the mass balance, analytical ultracentrifugation (AUC) was applied to detect the amount of free, unbound catechol in solution. Then, Raman spectroscopy and nuclear magnetic resonance spectroscopy (NMR) were performed to quantify the replaced amount of acetate which is the ligand from synthesis with esterCAT (65 wt %) and to distinguish bound (chemisorbed) and unbound (physisorbed) esterCAT. Finally, based on a collection of all our results, the in-depth picture of ligand binding to the ZnO colloid was obtained.
In a follow up study, the toolbox was applied to tailor the ZnO surface by CAT derivatives with different functionalities namely hydrogen (pyroCAT), t-butyl group (tertCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The results showed that the binding enthalpies of the CAT molecules follow the order of tertCAT < pyroCAT < naphCAT < esterCAT < nitroCAT, which is in agreement with the electronegativity of tail groups (keeping in mind the superimposed steric effects of tertCAT). Moreover, the visible emission induced by defect sites on ZnO NPs surfaces was quenched by the binding of CAT molecules. The efficiency of quenching is in the same order as binding enthalpy. Thus, the correlations between electronegativity of molecules, binding enthalpies to NP surfaces, and the photoluminescence properties of NP are unraveled.
In conclusion, first, a widely-applicable strategy to study the thermodynamics of ligand adsorption to colloidal surfaces was established. Then, the toolbox was applied to tailor colloidal ZnO NP surfaces by CAT derivatives with different electronegativity. Finally, the electronegativity of ligands is linked with the binding enthalpy and photoluminescence quenching of NPs. We believe that such correlation is an important step towards a more general way of selecting and designing ligand molecules for surface functionalization. This allows establishing strategies for tailored colloidal NP surfaces beyond formulation on a case by case basis.
[1] W. Lin, et al. Chem. Mater, 2015, 27, 358.
8:00 PM - NM06.06.23
The Birth of a Nanocrystalline Supraparticle—Crystallization Kinetics of Nanocrystals in Spherical Confinement Studied with In Situ X-Ray Scattering
Federico Montanarella 1 , Jaco Gecuhies 1 , Tim Prins 1 , Carlo van Overbeek 1 , Rajeev Dattani 2 , Andrei Petoukhov 1 , Patrick Baesjou 1 , Alfons van Blaaderen 1 , Daniel Vanmaekelbergh 1
1 , Utrecht University, Utrecht Netherlands, 2 , ESRF, Grenoble France
Show AbstractWe have recently introduced a new class of three dimensional superstructures, named supraparticles (SPs), formed from the self-assembly of nanocrystals in an oil-in-water emulsion through spherical confinement [1]. In the SPs the nanocrystals arrange in different crystalline structures depending only on the number of nanocrystals present during the spherical confinement. SPs have attracted more and more interest as they can exhibit optical, magnetic and catalytic properties that differ from the individual nanoparticles and their bulk assembly. It has been shown recently that SPs composed of quantum dots show whispering gallery mode emission due to the strong difference in refractive index from the SP material and the surrounding environment, thus making the SPs good candidate for their use as lasing cavities [2]. In addition, SPs composed of a different mixture of red, green and blue emitting quantum dots have been shown to emit tunable light with high control in a wide range of the visible spectrum [3].
Although the use of SPs in different applications is growing, the self-organization process of the nanocrystals in spherical confinement, is poorly understood. In order to shed more light on the NC crystallization, we performed synchrotron based time-resolved in-situ small- and wide-angle X-ray scattering (SAXS & WAXS). The wide q-range allowed us to study not only the crystallization kinetics of the NCs inside the emulsion, but also follow the shrinking of the spherical oil droplets over time. The scattering patterns are combined to give full description of the self-assembly process: from the individual NCs inside the spherical droplets to the SPs in which the NCs are ordered into a FCC lattice.
[1] de Nijs et al., Nat. Mat., 2015,14, pp 56-60
[2] Vanmaekelbergh et al., ACS Nano, 2015, 9 (4), pp 3942–3950.
[3] F.Montanarella, submitted (2017)
8:00 PM - NM06.06.24
Antisolvent Precipitation from Supercritical Fluids—Effective Method of Synthesis of Functional Materials Based on Oxides of d-block Elements
Ilya Sokolov 1 , Valery Fomichev 1 , Ruslan Zakalyukin 1 , Igor Konovalov 1 , Dmitriy Drobot 1 , Zoya Kudryshova 1 , Kseniya Smirnova 1 , Vladimir Mahinov 1
1 , Moscow Technological University (MITHT), Moscow Russian Federation
Show AbstractIn this study nanoparticles of oxides of rare earth elements and aluminum as well as their solid solutions were prepared by precipitation from supercritical CO2.
The particle syntheses were performed using a SuperParticle SAS 50 system manufactured by Waters Corp. The experimental conditions during the syntheses of nanoparticles of TiO2, ZrO2, HfO2, Al2O3 and nanoparticles of solid solutions in the systems TiO2 - ZrO2 and TiO2 - Al2O3 were varied in the following ranges: pressure from 7 to 25 MPa, temperature from 40 to 70 °C, rate of CO2 addition from 35 to 50 g/min and rate of the precursor solution addition from 0.25 to 1.0 mL/min. Solutions of metal isopropoxides in isopropanol were used as precursors. In case of HfO2 solution of hafnium butoxide in butanol was used.
The prepared samples were characterized by X-ray powder diffraction, DSC, Raman and FT-IR spectroscopy, and TEM. Particle size was measured using dynamic light scattering. Nitrogen adsorption at -196 °C was measured using the static volumetric method (BET).
Obtained results demonstrate that in all instances amorphous nanoparticles form first. Particle size varies in the range between 10 and 100 nm and is controlled by the process conditions. In the systems TiO2 - ZrO2 and TiO2 - Al2O3 solid solutions form in the whole range of oxide concentrations.
Annealing of the prepared materials leads to formation of crystalline products. At temperatures above 450 °C, the solid solutions decompose forming products which are in accordance with the known equilibria in the corresponding T-X diagrams. We found that nature of the starting material influences the sequence of thermal transformations and phase composition of the final product. For instance, zirconium dioxide obtained upon annealing of the corresponding alkoxide crystallizes according to the following sequence: α-ZrO2→ t-ZrO2→ t-ZrO2 + m-ZrO2 (at temperature >600 °C), while when zirconium acetylacetonate is used as a starting material the sequence is different: α-ZrO2→ c-ZrO2 + α-ZrO2 (at 540 °C) and α-ZrO2→ m-ZrO2 (at 700 °C).
Methods of synthesis of nanopowders of Nb2O5 with particle size in the range between 180 and 200 nm and Ta2O5 with particle size in the range between 60 and 80 nm using the SCF process will be also reported.
The SCF method described in this study allows to obtain inorganic high quality precursors for electronic equipment.
This work was conducted with financial support from the Russian Federation Fund for Fundamental Research, grant 15-03 04436.
8:00 PM - NM06.06.25
Novel Routes To Europium Sulphide
Asma Alenad 1
1 , University of Manchester, Manchester United Kingdom
Show AbstractEuropium chalcogenide nanocrystals exhibit significant changes in their magnetic and luminescent properties as compared to bulk. EuS microcrystals have been shown to display a remarkably large Faraday effect which suggests possible optoelectronic applications. EuS has also exhibited a variety of magnetic ordering, and magneto-optic effects which potentially enables it to be used in spintronics, functioning as a spin filter. EuS nanoparticles have been synthesized by the colloidal route, ultraviolet irradiation, liquid ammonia reduction reactions and decomposition of single source precursors. The magneto-optical properties of these materials are strongly dependent on their shape, size, and surface conditions.
Recent years have witnessed the syntheses of nanomaterials from single source precursors. The use of these precursors offers numerous advantages over the multiple route counterparts. Some of these are the existence of preformed bonds which lead to the formation of metal chalcogenide nanomaterials with fewer defects and better stoichiometry. They are also air-stable and are therefore easier to handle and characterize. O’Brien et al., have pioneered the preparation of many single source precursors as efficient routes to high quality, crystalline and monodispersed nanoparticles with semiconducting properties.
This work presents the synthesis of two new europium complexes teraphenylphosphonium tetrakis (ethylxanthato)europium(III) and teraphenylphosphonium tetrakis (diethylcarbamato)europium(III) and eheir use as single source precursors for the deposition of EuS NCs using a colloidal method. The nanoparticles were characterised by powder X-ray diffraction, transmission electron microscopy and UV-Visible spectroscopy and the band gaps were determined.. X-ray structures of both complexes have been determined. The structure of (a) Teraphenylphosphonium tetrakis (ethylxanthato)europium(III) and (b) Teraphenylphosphonium tetrakis (diethylcarbamato)europium(III) is shown in the Figure 1.
8:00 PM - NM06.06.26
Growth of Small Palladium Particles in the Gap of Gold Plasmon Rulers
Sarah Lerch 1 , Bjoern Reinhard 1
1 , Boston University, Boston, Massachusetts, United States
Show AbstractPlasmon coupling between Au nanoparticles localizes a strong electric field to the gap between the particles and dramatically shifts the plasmon resonance in a uniquely distance-dependent manner. This relationship is easily observable in the scattered far-field spectra, where the bonding dipolar plasmon (BDP) mode red-shifts with decreasing gap size until the classical coupling model deteriorates at separations smaller than 1 nm due to nonlocal and quantum tunneling effects. This so-called “quantum regime” results in a blue-shift of the BDP resonance from the classical models due to the depolarization of the BDP mode. Interest in expanding and analyzing this quantum regime results from the desire to control coherent energy and charge transfer in plasmonic assemblies and to develop a complete description of plasmon coupling on all relevant length scales. When plasmonic dimers are synthesized through a linker-based, self-assembly method, it is possible to incorporate linker materials, such as DNA, which extend the coherent tunneling of the electrons between the particles, expanding the quantum regime to separations of ~ 3 nm. To further increase the separations at which the effects of coherent tunneling are notable, we grew small Pd particles in the gaps of the Au dimers. This growth, isolated through the initial binding of Pd2+ cations to DNA and the subsequent reduction to Pd particles, results in three distinct configurations observable through the shift and broadness of the BDP mode. The first configuration occure when there is an excess of DNA on the particles, resulting in a large deposition of Pd in the gap of the dimers. This results in a broad, red-shifted BDP mode due to the conductive contact between the particles established by the Pd particles, creating a lossy, bimetallic nanorod structure. The second configuration occurs when the gap is large and not filled by Pd nanoparticles. In this case, a slight red-shift of the resonance, consistent with a change in the refractive index but not indicating any conductive contact, is detected. The final configuration occurs when the gap is below 10 nm and a limited number of Pd nanoparticles are located in the gap. Preliminary data indicates a spectral blue-shift for this configuration. This presentation will investigate the coupling mechanisms underlying the three different configurations and present models that account for classic and quantum mechanical coupling mechanisms.
8:00 PM - NM06.06.27
Systematic Search for Luminescent Quantum Dot/Insulator Systems via Ion Implantation
James Gaudet 1 , Lyudmila Goncharova 1 , Peter Simpson 1
1 , University of Western Ontario, London, Ontario, Canada
Show AbstractIon implantation is a widely used industrial technique for introducing dopants to semiconductor material, creating silicon on oxide devices (SIMOX) and wafer separation via H/He implantation. Medium energy (up to 1 MeV) ion beam accelerators have found a niche in the academic environment for materials characterization techniques (RBS, MEIS, etc) and the synthesis of novel materials systems. Systems of luminescent quantum dots (QD) embedded in insulator can be formed via ion implantation and have several advantages over systems forms by other techniques: more control over initial distribution of implanted ions, lower concentration of elemental impurities in the as-implanted system and a final product that has both greater uniformity (within a plane parallel to the sample surface) and is more robust. Offsetting this is a greater cost of production. Together, these facts suggest that the optimal role of medium-energy ion implantation in QD research is as a search technique for new QD and insulator host matrix compounds. Combinatorial samples were prepared using variable-dose Si implantation into (thermal) SiO2, Si implanted into other insulators or semiconductors and other QD compounds implanted into SiO2. Composition and structure of samples were characterized using Rutherford Backscatter Spectroscopy (RBS) and micro-XRD. Photoluminescence (PL) spectroscopy and time-resolved PL (TRPL) data were gathered with 50µm or 100µm lateral resolution using a confocal microscope. This presentation will discuss these samples as well as more detailed studies of promising compositions found thereby.
8:00 PM - NM06.06.28
Tunable Conductance and Application in Metal-Doped Quantum Dots Made by One-Pot Microwave Synthesis
Donovan Thomas 1
1 Center for Materials Research, Norfolk State Univ, Norfolk, Virginia, United States
Show AbstractThe effects that metal doping have on the optical & electronic properties of Bulk Quantum Dots (QDs) for eventual device implementation have been briefly studied. Optoelectronic changes in fluorescence intensity/shifting and absorption, by way of Photoluminescence (PL) and UV-VIS respectively, are of interest. Leakage current, capacitance and frequency dispersion data has been examined to observe the electronic behavior of QD’s. X-Ray photoelectron spectroscopy (XPS) and Energy-dispersive X-ray spectroscopy (EDX) characterization confirm the elemental composition of each device, including all materials used. QD thin films were created by drop-casting and film thickness is obtained by X-Ray Reflectivity (XRR). Transmission Electron Microscopy (TEM) will confirm film thickness and individual QD size on a more accurate level. Surface property effects due to doping will be examined using Atomic Force Microscopy (AFM). Preliminary results show that doping Cadmium Selenide (CdSe) QD’s with Gold (III) Acetate does indeed have effects on fluorescence shifting and absorbance. An increase in Gold (III) Acetate concentration causes an increase in red-shifting for PL data. A quick study was done to observe the effects that each concentration of doped CdSe had on MOSCAP structures. Gathered data showed a slight decrease in leakage current as you increase the concentration of Gold (III) Acetate, compared to using HfO2 or undoped CdSe on GaAs solely. This data also indicates that the CdSe:Au layer is more insulating than both GaAs by itself and HfO2 on GaAs. Rare Earth Metals, which are known to have high electrical conductivity and great fluorescence, have also briefly been studied. Doping with Europium (III) Acetate Hydrate has been tested and PL shifting is once again present. A Europium presence at approximately 618 nm was observed. This suggests that there is possible electronic application tunability which is dependent on the metal dopant that is used. Further studies using a combination of various quantum dot systems, metal dopants and semiconductor materials will be conducted to determine the effects that each combination have on optical and electronic properties. Eventual MOSCAP implementation is one of a few end goals, as MOSFET device implementation will be tested if time permits.
8:00 PM - NM06.06.29
Microwave-Assisted Hydrothermal Synthesis of ZnO and Zn-Terephthalate Hybrid Nanoparticles Employing Benzene Dicarboxylic Acids
Yuji Hirai 1 , Koji Furukawa 1 , He Sun 1 , Yuta Matsushima 1 , Keiji Shito 1 , Akito Masuhara 1 , Ryouma Ono 2 , Yuma Shimbori 2 , Hidenobu Shiroishi 2 , Matthew White 3 , Ajit Khosla 1 , Tsukasa Yoshida 1
1 , Yamagata University, Yonezawa Japan, 2 , National Institute of Technology, Tokyo College, Hachioji Japan, 3 , The University of Vermont, Burlington, Vermont, United States
Show AbstractNano-/micro-sized particles of zinc oxide (ZnO) have versatile functions represented in their applications as white pigments, photocatalysts, light-emitting materials and electron transport materials (ETM) for photovoltaics.
Control of their structure and size is the key to maximize their functionalities.
In our precedent work, we have succeeded to synthesize differently structured ZnO nanoparticles with well-defined preferentially exposed facets through the microwave assisted hydrothermal reaction and employing structure directing agents (SDAs).
In this study, three isomers of benzene dicarboxylic acids, phthalic acid (PA), isophthalic acid (IPA) and terephthalic acid (TPA) were employed as SDAs. ZnO nanoparticles with a variety of shape and size were obtained to reveal their strength in the order of TPA > PA > IPA when the solution pH > 10.
However, TPA behaved differently from the others when pH of the precursor solution was reduced. ZnO was no longer formed but Zn-TPA metal-organic frameworks (MOFs) were formed, in which layered double hydroxide of Zn2+ (Zn LDH) was stabilized by the intercalation of TPA dianion. Zn-TPA MOFs in four different structures and compositions were depending on pH. Three of them could be isolated to identify their compositions as Zn3(OH)4(TPA)●6H2O, Zn4(OH)6(TPA) and Zn2(OH)2(TPA)●H2O, with their interlayer distances of 14.4, 10.8 and 9.03 Å under pH 7.0, 5.9 and 5.3, respectively, as revealed by XRD, TG-DTA and FT-IR analyses. Although such discrete change of the composition and structure should usually result from the difference of their thermodynamic stability under different pH, these Zn-TPA MOFs are hitherto unknown in their synthesis by slow hydrothermal reaction. These unique structures could kinetically be chosen in the rapid crystallization under microwave radiation.
DOI: 10.1007/s00542-017-3392-y
8:00 PM - NM06.06.30
Two-Step Nucleation of Magic-Sized Clusters from “Liquid-Like” Intermediates in the Induction Period
Kui Yu 1 2 , Shuo Han 1 , Tingting Zhu 1 , Mingyang Liu 1 , Baowei Zhang 1 , Kun Wang 1 , Linxi Wang 1 , Hongsong Fan 3 , Nelson Rowell 4 , John Ripmeester 4 , Romain Renoud 4 , Fenggang Bian 5 , Jianrong Zeng 5
1 College of Physics, Sichuan University, Chengdu China, 2 School of Chemical Engineering, Sichuan University, Chengdu, Sichuan, China, 3 Engineering Research Center in Biomaterials, Sichuan University, Chengdu China, 4 , National Research Council of Canada, Ottawa, Ontario, Canada, 5 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai China
Show AbstractColloidal semiconductor quantum dots (QDs), with various potential applications such as in bio-imaging, light emitting diodes (LEDs), and solar cells, have been the focus of our laboratories. Particularly, we have been interested in the “induction period”, which takes place prior to nucleation and growth of the compound QDs (M2En, M = Cu, Cd, Zn, Ge, Pb, and In; E = S, Se, and Te). Here, we will present our fundamental understanding of the two step nucleation of magic-size clusters (MSCs) from “liquid-like” intermediates which form in the induction period. For the formation of colloidal QDs including MSCs, we have concluded a general mechanism; the detailed pathway, which is proton-mediated ligand exchange (of HY molecules with Y = OR, OOCR, SR, PPh2, and NRH), has been demonstrated for the evolution of monomers M2En.1 When cationic (M, such as Cd2+) and anionic (E, such as Te2-) precursors were mixed with each other, “micellar-like” aggregates of ~ 1 nm in size were formed firstly followed by M-E covalent bonds. The resulting aggregates were “liquid-like” without a crystalline structure but a similar size of ~ 1 nm.2 We studied the evolution of CdS MSC-311 (which exhibiting absorption peaked at 311 nm) from its immediate precursor IP311 which has Cd-S bonds and is “liquid-like”.3 With a first order kinetics, IP311 developed into MSC-311 via surface-induced intra-molecular re-organization, the mechanism of which was supported by the effect of the presence of a small amount of MeOH, which accelerated the kinetics. Our study opens a new setting that broadens the fundamental understanding of a two-step nucleation pathway of MSCs, in addition to the low reaction yield of QD products and the relation between MSCs and QD products.
References
1. Kui Yu, Xiangyang Liu, Ting Qi, Huaqing Yang, Dennis M. Whitfield, Changwei Hu “General low temperature reaction pathway from precursors to monomers before nucleation of compound semiconductor nanocrystals” Nat. Commun. 2016, 7, 12223.
2. Mingyang Liu, Kun Wang, Linxi Wang, Shuo Han, Hongsong Fan, Nelson Rowell, John A. Ripmeester, Romain Renoud, Fenggang Bian, Jianrong Zeng, Kui Yu “Probing Intermediates of the Induction Period Prior to Nucleation and Growth of Semiconductor Quantum Dots” Nature Commun. 2017, 8, 15467.
3. Tingting Zhu, Baowei Zhang, Jing Zhang, Jiao Lu, Hongsong Fan, Nelson Rowell, John A. Ripmeester, Shuo Han, Kui Yu “Two-Step Nucleation of CdS Magic-Size Nanocluster MSC-311”. Chem. Mater. 2017, 29, accepted.
8:00 PM - NM06.06.31
Fabrication of Ag/CuAgS/CuInS2 Hetero-Nanostructure by Cation Exchange Method
Toshihiro Kuzuya 1 , Takahiko Kuwada 2 , Yasushi Hamanaka 2 , Shinji Hirai 1
1 , Muroran Institute of Technology, Muroran Japan, 2 , Nagoya institute of technology, Nagoya Japan
Show AbstractNobel metal – semiconductor hetero-nanostructure have recently attracted more attention, because of their applications such a catalysis, and a quantum dot sensitized solar cell (QDSSC). Hetero-nanostructure can be categorized by their morphology as open-type, such as dumbbell- and Janus- like NPs, or closed core-shell type. Nan et al. reported the synthesis and tunable optical properties of Ag2S-coated Au nanorods (Au@Ag2S nanorods), where the plasmon resonance and local field confinements could be controlled by the shell morphology. Consequently, an appropriate shell structure was able to enhance the nonlinear and saturable intensity of the Au-nanorods. In our previous work, Ag-core / CuInS2-shell nanoparticles (Ag@CuInS2 NPs) were synthesized. FDTD simulation revealed that Ag core served as the light collector to enhance the electric field in CuInS2 shell and its surface. In an open-type hetero-nanostructure, a metal or a chalcogenide phase is not perfectly surrounded by other phases. Because of good electron and heat conductivities of metal phase, a metal phase of hetero-nanostructure serves as a migration pathway of excited-electron and phonon between semiconductor phase and outer side of hetero-nanostructure. Therefore, open-type metal/semiconductor hetero-nanostructure is a strong candidate for a light harvesting material.
In this study, we demonstrate that cation exchange (CE) method is an effective path way for fabrication of Ag / chalcopyrite hetero-nanostructure. Chalcopyrite has relatively large absorption coefficient, optimum band gap for solar cell and tolerance for cosmic ray. And Ag metal NP is considered to serve as the light collector due to its surface plasmon resonance effect. Therefore, Ag / chalcopyrite hetero-nanostructure is believed to be an excellent light absorbing material for QDSSC.
CuAgS host NPs were synthesized by the thermal decomposition of Cu and Ag thiol complexes. And then, CuAgS host NPs were annealed in In-thiol complex solution. The bond dissociation energy of In-S (287.9 kJ) is larger than those of Cu-S (274.5 kJ) and Ag-S (216.7 kJ). Therefore, Ag+ ion was selectively exchanged by In3+ ion. This selective CE reaction provided Ag / orthorhombic – CuAgS (o-CuAgS) / tetragonal - CuInS2 ( t - CuInS2) hetero-nanostructure. To our best knowledge, CE method can provide only NPs with a sulfur sub-lattice identical to that of a host NP. In this procedure, o - CuAgS NPs with a low phase transition temperature were employed as host NPs and a phase transition of cubic to orthorhombic gives the unique combination of o – CuAgS / t – CuInS2 to the hetero - nanostructure. Furthermore, the selective formation of Ag+ defect was achieved by the direct reduction of Ag+ in CuAgS. Replaced Ag+ was reduced to Ag and Ag metal phase was deposited on the surface of CuAgS phase. High Resolution (HR) TEM and STEM images revealed that (1 1 2) plane of CuInS2 was attached to (0 1 0) plane of CuAgS.
8:00 PM - NM06.06.32
Janus Heterodimers—Synthesis, Selective Surface Modification and Self-Assembly
Davit Jishkariani 1 , Yaoting Wu 1 , Da Wang 2 , Yang Liu 2 , Alfons van Blaaderen 2 , Christopher Murray 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Utrecht University, Utrecht Netherlands
Show AbstractJanus nanoparticles (NPs) often referred to as nano-sized analogs of molecular surfactants are amphiphilic structures with potential applications in materials science, biomedicine and catalysis and their synthesis and self-assembly into complex architectures remain challenging. We have recently demonstrated the preparation of Janus heterodimers via asymmetric functionalization of Fe3O4-Pt and Fe3O4-Au heterodimeric NPs. The hydrophobic and hydrophilic dendritic ligands that have phosphonic acid and disulfide surface binding groups selectively coat the iron oxide and platinum (or gold) parts of the heterodimer, respectively. Such approach allows simple and efficient preparation of amphiphilic structures. Moreover, liquid-air interface self-assembly studies of each ligand exchange step revealed a drastic improvement in film crystallinity suggesting the dendronization induced improvement of the whole particle polydispersity.
8:00 PM - NM06.06.33
Controlling Anisotropy and Quantum Confinement in Cesium Lead Halide Perovskite Nanocrystals via Controlled Halide Activation
Yitong Dong 1 , Tian Qiao 1 , Dong Hee Son 1
1 , Texas A&M University, College Station, Texas, United States
Show AbstractCesium lead halide (CsPbX3) perovskite semiconductor nanocrystals have emerged as new materials useful for photonic and photovoltaic applications due to their remarkable optical and charge transport properties, and facile post-synthesis anion exchange readily broadening the accessible range of bandgap. Because of the highly symmetric cubic lattice structure, typical hot-injection synthesis of CsPbX3 nanocrystals forms symmetric nanocubes. While anisotropic morphology provides unique functionalities, such as the directional flow of charge carriers or directional photon emission, it has been difficult to obtain anisotropic structures of CsPbX3 nanocrystals with sufficient controllability and uniformity of shape and size to harvest the well-defined anisotropic properties. The control of the size in quantum confinement regime determining the energetics and dynamics of exciton also remains as a major challenge regardless of the morphological anisotropy. Here, we present a new approach based on controlling the halide activation enabling the synthesis of CsPbBr3 nanocrystals with systematically controlled anisotropic morphology and size in quantum-confined dimension with very high ensemble uniformity. The elegance of the new approach is that the tight control of the morphological anisotropy and size in quantum-confined dimension is obtained by controlling only the rate and amount of halide released in the reacting system. In particular, the size in the shortest, quantum-confined dimension exhibits a direct correlation with the amount of halide available during the reaction. 1-dimensional (1D) structures exhibiting strong linear optical polarization anisotropy and controlled quantum confinement as well as quantum dots with widely tunable quantum confinement were produced with previously unachievable ensemble uniformity. The unique control capability of halide is presumably obtained from the combined action of the kinetic control of anisotropic growth and stoichiometric selection of the size facilitated by the highly mobile halide in the lattice and size-dependent halide/metal composition of CsPbBr3 nanocrystals. Further microscopic understanding of the role of halide in controlling the morphology and size will broaden the applicability of this unique approach for the larger-scale synthesis of morphology- and size-controlled anisotropic CsPbX3 nanostructure important for the practical applications of this new family of nanomaterials.
8:00 PM - NM06.06.35
Synthesis and Properties of Boron-Hyperdoped Silicon Nanoparticles
Parham Rohani 1 , Mark Swihart 1
1 , State University of New York at Buffalo, Buffalo, New York, United States
Show AbstractSilicon, the most important semiconductor in electronics and photovoltaics, must be doped to tune its electronic structure and properties. Doped silicon nanoparticles and nanostructures have applications in optoelectronics, photovoltaics, electronics, energy storage, and bioimaging. Boron is the most common p-type dopant (acceptor) for silicon, and is the only acceptor with sufficient solubility for applications requiring extremely high dopant concentrations. Conventional doping of bulk silicon occurs under near-equilibrium conditions, which means that the dopant concentration is limited by the solid solubility limit at a given temperature. However, the ability to dope silicon at concentrations higher than the solid-solubility limit (hyperdoping) could open up a new range of interesting properties, such as localized surface plasmon resonance, and related applications. Hyperdoping is a non-equilibrium process that must be carried out by rapid thermal processes under conditions where the composition is determined by kinetics, not thermodynamics. In this study, we created nanoparticles of boron hyperdoped silicon via laser-induced pyrolysis of silane and diborane. The unique design of the reactor enables rapid thermal initiation of particle formation and rapid quenching of the gas mixtures in the reaction zone leading to the formation of boron doped silicon nanoparticles with up to 31% boron concentration. The primary particle size in the nanoparticle aggregates is 17-25 nm. Interstitial doping with boron was confirmed by Raman spectroscopy, and LSPR was observed by FTIR spectroscopy. Further studies of the detailed nanoparticle structure and electronic properties are underway and will be reported.
8:00 PM - NM06.06.37
Synthesis and Characterization of Metal Doped-InP Clusters and Nanostructures
Yongju Kwon 1 , Gyuhyun Bang 1 , Sungjee Kim 1
1 , Postech, Pohang, SE, Korea (the Republic of)
Show AbstractUnderstanding and controlling the nucleation stage before the continuous growth is important for nanoparticle science. In semiconductor nanocrystal quantum dot (QD) syntheses, 1-2 nm sized preliminary clusters(PCs) are often formed before the continuous growth of nanostructures. InP QDs attract great interest because they do not have heavy metals and the band gap can be tuned to visible range and thus can be well suited for display materials. We report synthesis and applications of metal doped InP PCs. The PCs exhibit sharp excitonic absorption in UV-Vis region and have ~1.6 nm diameters. The exciton dynamics was investigated by using transient absorption spectroscopy. Their mass was elucidated using matrix-assisted laser desorption/ionization time-of-flight spectroscopy. Their chemical composition and dopant position was determined by angle-resolved x-ray photoelectron spectroscopy. Various InP nanostructures that included branched InP nanostructures were synthesized using the metal doped InP PCs as a precursor. TEM investigations revealed branches diameters of the lateral dimension of 2-4 nm and the length of 5-20 nm. X-ray diffraction patterns of branched nanostructures match the zinc blende structure of InP. The reactions between InP PCs and molecular monomers were also studied. Growth mechanism of InP branched nanostructure will be discussed.
Symposium Organizers
Matthew Pelton, University of Maryland-Baltimore County
Jennifer Dionne, Stanford University
Alexander Govorov, Ohio University
Maksym Kovalenko, ETH Zurich
Symposium Support
Angstrom Engineering
NNCrystal US Corporation (NN-Labs)
Princeton Instruments
NM06.07: Metal-Nanoparticle Hybrids
Session Chairs
Alexander Govorov
Christopher Murray
Wednesday AM, November 29, 2017
Hynes, Level 3, Room 311
8:30 AM - *NM06.07.01
Building Modular Semiconductor-Plasmonic Hybrid Materials through Semiconductor Nanocrystal Assembly and Surface Exchange
Christopher Murray 1 2 , Yaoting Wu 1 , Siming Li 3 , Stan Najmr 1 , Natalie Gogotsi 2 , Cherie Kagan 4 2 1 , Jason Baxter 3
1 Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Chemical and Biochemical Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 4 Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractColloidal nanocrystals (NCs) with controlled composition, size, and shape and surface functionalization provide ideal building blocks for the assembly of new multicomponent materials and devices. Monodisperse colloidal NCs serve as "artificial atoms" with tunable electronic, and optical properties that can be assembled on the “Mesoscale” to yield properties that combine the best attributes of the isolated quantum systems, localized resonances and the extended electronic transport of traditional semiconductor thin films. In this talk, we will briefly outline progress in synthesis, purification, and integration of size and shape controlled single phase NCs as well as core-shell and heterostructure NCs combining quantum confined and plasmonic properties Routes to 2D arrays and 3D materials through liquid air interfacial assembly and scalable dip-coating processes. Chemical tailoring of NC shape and ligand structure can program the binary NC thin films. The coupling between the NC building blocks can be modified further by exchange of the surface stabilizing ligands to direct the orientation and linking of neighboring NCs. The modular assembly of these NCs allows the desirable features of their underlying quantum character to be retained, or even enhanced by the interactions between the NCs and the hybridization drives the emergence of new delocalized properties and local plasmonic fields interact with the polarizable semiconductor NC states. The electronic and optical properties of these coupled systems will be probed through a combination of direct electrical and non-contact optical techniques.
9:00 AM - NM06.07.02
Monitoring Ag-Semiconductor Janus Nanoparticle Formation Using In Situ Reactive High Resolution TEM
Joel van Embden 1 , Laure Bourgeois 2 , Lynne Waddington 3 , Enrico Della Gaspera 1 , Jacek Jasieniak 2 , Anthony Chesman 3
1 Applied Chemistry, RMIT University, Melbourne, Victoria, Australia, 2 Engineering, Monash University, Melbourne, Victoria, Australia, 3 Manufacturing, CSIRO, Melbourne, Victoria, Australia
Show AbstractJanus nanoparticles are a subclass of heteronanostructures that specifically comprise two material types (and regions) that are bonded adjacently into a single nanoparticle.[1] The combination of the two materials in these nanostructures can be tailored to give rise to a synergistic effect, resulting in a substantial increase in their desired efficacy compared to the use of their individual component materials without such intimate physical contact. In light of this, Janus nanoparticles have found use in a broad range of areas, including energy-based applications,[2] plasmonics,[3] and catalysis.[4]
In spite of these myriad applications very little direct evidence exists on the mechanism of Janus nanostructure formation. This is borne out of the fact that specific synthetic methods are required to to be able to slow down and capture the otherwise rapid transformation steps that lead to Janus nanostructures, as well as the difficulty in physically monotoring phase separation at the nanoscale. The high ionic mobility and chemical reactivity of Ag enables the self-regulated formation of Janus nanostructures in optimized single step “heat up” reactions – a phenomenon that is almost unique to silver-based systems. As such, silver-based systems are ideal candidates to study the formation of Janus nanostructures.
Herein we present both a method for synthesising novel colloidal Janus silver–semiconductor nanoparticles (Ag–Ag8GeS6) and an elucidation their formation mechanism.[1] Using an optimized "heat up" reaction,[5] as opposed to the classical "hot-injection" technique, we were able to reliably isolate and analyse the particles at various key points during their growth and transformation and gain valuable insights into Janus nanoparticle evolution. Furthermore, using high resolution in situ reactive high resolution TEM, HAADF-STEM, and XEDS mapping, the formation of the nanostructures was directly observed.[1] The formation is discovered to occur in three stages comprising (i) nucleation; (ii) phase separation of the metal and semiconductor components; (iii) segregation of the metal and semiconductor components to form the Janus nanostructure. The details of these three stages will be presented and discussed.
[1] van Embden, J.; Bourgeois, L.; Della Gaspera, E.; Waddington, L.; Yin, Y.; Medhekar, N.V.; Jasieniak, J.J.; Chesman, A.S.R. J. Mater. Chem. A., 2016, 4, 7060-7070.
[2] M. Lattuada and T. A. Hatton, Nano Today, 2011, 6, 286–308.
[3] R. Jiang, B. Li, C. Fang and J. Wang, Adv. Mater., 2014, 26, 5274–5309.
[4] A. Kudo and Y. Miseki, Chem. Soc. Rev., 2009, 38, 253–278.
[5] van Embden, J.; Chesman, A.S.R.; Jasieniak, J.J. Chem. Mater., 2015, 27 (7), 2246-2285
9:15 AM - *NM06.07.03
Metal-Polymer Hybrid Nanostructures
Renaud Bachelot 1
1 , Univ of Technology-Troyes, Troyes France
Show AbstractHybrid nanomaterials are targeted by a rapidly growing group of nanooptics researchers, due to the promise of optical behavior that is difficult or even impossible to create with nanostructures of homogeneous composition. Examples of important areas of interest include coherent coupling, Fano resonances, optical gain, solar energy conversion, photocatalysis, and nonlinear optical interactions. In addition to the coupling interactions, the strong dependence of optical resonances and damping on the size, shape, and composition of the building blocks provides promise that the coupling interactions of hybrid nanomaterials can be controlled and manipulated for a desired outcome. Great challenges remain in reliably synthesizing and characterizing hybrid nanomaterials for nanooptics.
We review and describe the synthesis, characterization, and applications of new hybrid plasmonic nanomaterials that are created through plasmon-induced photopolymerization. Involved polymer can contain active species, resulting in advanced hybrid nano-emitters
The work is placed within the broader context of hybrid nanomaterials involving plasmonic metal nanoparticles and molecular materials placed within the length scale of the evanescent field from the metal surface. We specifically review three important applications of free radical photopolymerization to create hybrid nanoparticles: local field probing, photoinduced synthesis of advanced hybrid nanoparticles (including light-emitting nanosystems), and nanophotochemistry.
10:15 AM - *NM06.07.04
Quantum Dots in Plasmonic Systems—From Optical Transparencies and Nonlinearities to Entanglement
Stephen Gray 1
1 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractQuantum mechanical models of semiconductor nanocrystals or quantum dots interacting with plasmonic systems are discussed. Calculations show that just one quantum dot interacting with a plasmonic system can lead to interesting optical effects, including optical transparencies and more general Fano resonance features that can be tailored with ultrafast laser pulses. In cases with two or more quantum dots within a plasmonic system, the possibility of quantum entanglement mediated through the dissipative plasmonic structure arises.
10:45 AM - NM06.07.05
Temperature Tuning of Surface Plasmon-Exciton Interaction in Hybrid MoSe2@Au Nanodisk Array
Ines Abid 2 , Arash Bohloul 1 , Jiangtan Yuan 1 , Weibing Chen 1 , Renaud Péchou 2 , Adnen Mlayah 2 , Jun Lou 1
2 Centre d'Elaboration de Matériaux et d'Etudes Structurales, CNRS-Université de Toulouse, Toulouse France, 1 Department of Material Science and Nanoengineering, Rice University, Houston, Texas, United States
Show Abstract
Transition metal dichalcogenide materials (TMDs) are increasingly gaining attention, due to their unique optical, spintronic, and electronic properties [1]. These properties result from the ultimate confinement in 2D monolayers of the excitons of a direct band-gap semiconductor and the lack of inversion symmetry in the crystallographic structure [2]. To control and enhance the optical response of these materials, it is interesting to integrate them with plasmonic nano-resonators, known by their ability to strongly boost the light absorption and emission of nano-objects located in the vicinity of their surface [3-4].
In this context, we investigated the interaction between the surface plasmons of gold nanodisks and the 2D excitons confined in MoSe2 monolayers. The MoSe2 layers were grown by Chemical Vapor Deposition (CVD) and then transferred to the gold nanodisks array. The latter were synthesized by nano-sphere lithography and designed in such a way that their surface plasmon resonance falls in the spectral range of the excitonic transition of MoSe2 . Optical measurements revealed the presence of transparency dips, typical of Fano spectral lineshapes, thus proving the interference between the plasmonic and excitonic resonances. Fano-type coupling regime was evidenced by a quantitative analysis of the optical extinction spectra based on an analytical model of two coupled oscillators [5] . This analysis was complemented by numerical simulations of the optical spectra and of the electric near-field distribution. We found that the surface plasmon-exciton interaction is mainly localized in the gap region between the nanodisks. Moreover, by changing the temperature, we were able to fine tune the excitonic transition to the plasmonic resonance, which allows to investigate the Fano-lineshape dependence on excitonic energy and broadening. In addition, using a fitting of the experimental data by an analytical model, we were able to extract the temperature dependence of the plasmonic-excitonic coupling strength. Our results contribute to the understanding of the near-field interaction between strongly localized surface plasmons and excitons and paves the way to the development of new applications in the field of hybrid plasmonics.
[1] Z.Weijie et al., Accounts of Chemical Research 48, 91 ( 2015)
[2] W. Q. Hua et al., Nature Nanotechnology 7, 699 (2012)
[3]E. Petryayeva et al., Anal. Chim. Acta 706, 8 (2011)
[4] S. Najmaei et al., ACS Nano, 8, 12, 12682 (2014)
[5] I. Abid et al., Nanoscale 8, 8151 (2016)
[6] X. Wu et al., Opt. Express, 18, 23, 23633 (2010)
11:00 AM - NM06.07.06
A Customizable Class of Colloidal-Quantum-Dot Spasers and Plasmonic Amplifiers for Fundamental Studies and On-Chip Use
Jian Cui 1 , Stephan Kress 1 , Patrik Rohner 1 , Robert Keitel 1 , David Kim 1 , Felipe Antolinez 1 , Karl-Augustin Zaininger 1 , Kevin McPeak 1 , Dimos Poulikakos 1 , David Norris 1
1 , ETH Zurich, Zurich Switzerland
Show AbstractWhen the spaser—a laser-like source of high-intensity, narrow-band surface plasmons—was first proposed, colloidal quantum dots were specified as the ideal plasmonic gain medium for overcoming the significant intrinsic losses of plasmons. Many subsequent spasers, however, have required a single material to simultaneously provide gain and define the plasmonic cavity, a design unable to accommodate quantum dots and other colloidal nanomaterials. Additionally, these and other designs have been ill-suited for integration with elements in a larger plasmonic circuit, limiting their use.
Here, we develop a more open architecture that decouples the gain medium from the cavity, leading to a versatile class of quantum-dot-based spasers for controlled generation, extraction, and manipulation of plasmons. We first create high-quality-factor, aberration-corrected, plasmonic cavities at desired locations on an ultrasmooth silver substrate. We then incorporate quantum dots into these cavities via electrohydrodynamic printing or drop-casting. Photoexcitation under ambient conditions generates monochromatic plasmons (0.65 nm linewidth at 630 nm, Q ~ 1000) above threshold at defined cavity modes. We observe spasing modes that coincide with gain from the conventional excitons and biexcitons, as well as triexcitons and higher-order excitons of greater energy. This signal is then extracted from the cavity, directed through an integrated amplifier, and focused at a nearby nanoscale tip, generating intense electromagnetic fields.
The customizability and open-cavity nature of our spaser architecture enables exploration of a vast design parameter space. Generally, our device platform can be deployed over different wavelengths, size scales, and geometries on large-area plasmonic chips. Through systematic changes of the cavity geometry and controlled excitation over defined areas, we characterize the full range of longitudinal and transverse modes of the spaser. This understanding allows us to work toward engineering the optimal cavity geometries for on-chip applications while minimizing device footprint.
11:15 AM - *NM06.07.07
Hybrid Nanostructures Based on Rare Earth Doped Nanoparticles
Fiorenzo Vetrone 1
1 Centre Énergie, Matériaux et Télécommunications, INRS, Université du Québec, Varennes, Quebec, Canada
Show AbstractThe ability to stimulate luminescent inorganic nanoparticles with near-infrared (NIR) light has made possible their potential use in a plethora of applications. In fact, the biggest impact of such materials would be in the field of disease diagnostics and therapeutics, now commonly referred to as theranostics. The use of NIR light for excitation mitigates some of the drawbacks associated with high-energy light (UV or blue) excitation, for example, little to no background autofluorescence from the specimen under investigation as well as no incurred photodamage. Moreover, one of the biggest limitations is of course, that of penetration. As such, NIR light can penetrate tissues much better than high-energy light especially when these wavelengths lie within the three so-called biological windows. Rare earth (RE3+) doped nanoparticles (RENPs) are at the vanguard since they posses multiple absorption (and emissions) in these optically transparent windows. Here, we present various NIR excited (and emitting) RENPs and demonstrate how new functionality can be achieved through the rational combination of RENPs with other optically active nanostructures such as plasmonic nanostructures. Furthermore, we will show how these hybrid nanostructures can be used as building blocks in the development of multifunctional nanoplatforms for simultaneous detection and therapy of disease.
NM06.08: Plasmonics
Session Chairs
Peter Nordlander
Matthew Pelton
Wednesday PM, November 29, 2017
Hynes, Level 3, Room 311
1:30 PM - *NM06.08.01
Quantum Plasmonics
Peter Nordlander 1
1 , Rice University, Houston, Texas, United States
Show Abstract
Plasmon resonances with their dramatically enhanced cross sections for light harvesting have found numerous applications in a variety of applications such as single particle spectroscopies, chemical and biosensing, subwavelength waveguiding and optical devices. Recently it has been demonstrated that quantum mechanical effects can have a pronounced influence on the physical properties of plasmons. Examples of such effects is the charge transfer plasmon enabled by conductive coupling (tunneling) between two nearby nanoparticles, tunable molecular plasmons in small graphene-like molecules, and plasmon-induced hot carrier generation. These discoveries have stimulated the growth of Quantum Plasmonics as a new and vibrant subfield of plasmonics. In my talk, I will briefly review the field of quantum plasmonics and highlight a few important recent applications such as active tuning of the charge transfer plasmon, active tuning of molecular plasmons, and hot carrier generation for photodetection and photocatalysis.
2:00 PM - *NM06.08.02
Understanding Plasmonics Using Silver and Gold Clusters
George Schatz 1
1 , Northwestern University, Evanston, Illinois, United States
Show Abstract
Silver and gold clusters with 10-200 atoms provide a wealth of opportunities for studying the fundamental properties of plasmonic materials, both from the perspective of the optical properties of the clusters themselves, and in their use as models for the properties of much larger (10-200 nm) nanoparticles.. In this talk I describe several recent theory studies, often coupled with experiment, where the properties of these clusters have been explored.
Silver clusters are especially useful for plasmonics, as silver clusters exhibit strong plasmonic excitations even for 20 atom clusters. This has led to models for SERS, both for electromagnetic enhancements and for chemical enhancements. However a limitation in density functional theory studies has concerned self-interaction errors, which leads to spurious charge transfer states. Recently my group has developed an INDO/S method for describing silver cluster optical properties that are free from self-interaction errors. This has enabled a number of studies, including the characterization of quadrupole plasmons, and the use of silver clusters for modeling single-molecule electrochemistry.
Another issue concerns the role of ligands in influencing plasmon excitations. Here we use density functional theory to relate bare and ligand-protected silver clusters, showing how adding ligands leads to energy shifts and splittings in spectra, making the electronic excitations less plasmonic, but in a systematic way.
Clusters can also be used as models for the excitation of acoustic modes by ultrafast lasers. Here we show that the numerous experiments that have been used to characterize acoustic modes in 10-100 nm particles, and the correlation of plasmon excitation with oscillating structure, can be translated to 10-100 atom clusters, which provides atomic level understanding of the variation of electronic structure with acoustic excitation.
3:30 PM - NM06.08.03
The Birth of Atomic-Scale Quantum Plasmons
Emily Townsend 1 , Tomas Neuman 2 , Javier Aizpurua 2 , Garnett Bryant 1
1 , NIST, Gaithersburg, Maryland, United States, 2 , Center for Materials Physics, San Sebastian Spain
Show AbstractLinear atomic chains, such as atom chains on surfaces, linear arrays of dopant atoms in semiconductors, or linear molecules, provide ideal testbeds for studying collective, plasmonic excitations in the quantum limit. We use exact diagonalization to find the many-body spectra of finite (4-26) atom chains. This allows us to identify the plasmonic excitations of these atomic-scale systems and reveal their quantum character.
Highly correlated, multi-excitonic states, strongly dependent on the electron-electron interaction strength λee, dominate the exact spectral response of these short 1D atomic chains. The ubiquitous presence of excitonic many-body states in the spectra makes it hard to identify plasmonic excitations. A combination of criteria involving the many-body state transition dipole moment, balance, transfer charge, dynamical response and induced transition charge density do strongly suggest which many-body states are plasmonic. For small λee, the lowest excitations are single-particle-like. For large λee, local correlations are dominant and a few plasmonic many-body excitations are hidden in a dense spectrum of excitonic-like states. In this regime, plasmon-like excitations are sliding excitations of Wigner crystal states. Low energy excitations similar to plasmons in nanoparticles are best seen for intermediate λee. In this interaction regime, the lowest excitation is a hybridization of the lowest single-particle response and a plasmonic response. For short chains (less than 15 atoms), the plasmonic response is out of phase with the single particle response, providing a depolarization of the single-particle response. For longer chains, the plasmonic response becomes increasingly important, in-phase with the single-particle response. This signals the onset of plasmonic behavior in these atomic-scale systems. Because of the hybridization, the plasmonic response is a resonance rather than an excitation. We separate the plasmonic response from the single-particle response to define a plasmonic wave function. Using this wave function we can determine the width of the plasmonic resonance. As the chain length increases, the plasmonic resonance becomes a sharper excitation with a longer dephasing time. The quantum statistics of the plasmon are studied using this plasmon wave function.
For one-dimensional systems, Pauli blockade plays a critical role in defining the excitations for all electron-electron interaction strengths λee. At the same time, Coulomb blockade and strong, local correlations become increasingly important for large λee. Blockade effects are reduced in systems with spin and for systems with higher dimensionality. Results for systems extended to include spin and for quasi-one-dimensional chains (ie dimer chains) are discussed to show the reduced effects of Pauli and Coulomb blockade on quantum plasmons.
3:45 PM - NM06.08.04
A New Take on Gold Nanostars—Synthesis, Characterization and Modeling
Ted Tsoulos 1 , Supriya Atta 1 , Kholud Dardir 1 , Ashley Pennington 1 , Fuat Celik 1 , Laura Fabris 1
1 , Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States
Show AbstractGold nanostars have the potential to impact several areas of research where field enhancement effects or hot carriers are involved, for instance surface enhanced Raman scattering or photocatalysis. However, synthetic protocols ensuring sample monodispersity and batch-to batch reproducibility, and detailed, shape-dependent characterization still appear to elude us. As a consequence, the enthusiasm for this nanomaterial of both industry and the scientific community have been lukewarm at best. To address this important problem, we have initiated a combined effort involving synthesis, characterization, and modeling to develop monodispersed and reproducible nanostars, for which we can understand and predict both physical and optical properties. For instance, we have recently implemented a novel experimental/computational method to determine volume, surface area, and shape-dependent extinction coefficient of nanostars (and in principle of any non-spherical nanoparticle) by collecting 3D STEM tomograms and employing the reconstructed 3D topography in finite element modeling to calculate intensity and distribution of local scattered electric fields for the experimentally synthesized nanostars. Furthermore, we have devised a novel synthetic strategy that allows us to obtain nanostars with finely tunable spike lengths and narrow plasmonic resonance bands that can be exactly reproduced with our 3D models. The ability to exactly reproduce computationally the plasmonic properties of the nanostars affords us the opportunity to use them as test beds to understand how plasmonic resonances in highly anisotropic nanoparticles may differ from those of their more characterized and understood spherical counterparts. Finally, we have developed a new method to coat the nanostars with a conformal and uniform layer of crystalline TiO2 for applications in photocatalytic studies. Taken together, these results may be important to exploit the exceptional features of these nanoparticles and increase their attractiveness for industrial applications.
4:00 PM - NM06.08.05
Enabling the Rational Design of Chiral Light
Lisa Poulikakos 1 , Prachi Thureja 1 , Alexia Stollmann 1 , Eva De Leo 1 , David Norris 1
1 , ETH Zurich, Zurich Switzerland
Show AbstractChirality, the phenomenon of handedness, is a distinctive property of living matter.1 Molecules of opposite handedness drastically differ biochemically, potentially causing severe side effects in pharmaceuticals. Hence, developing techniques for the selective detection and separation of molecules with respect to their chirality is of great interest. Chiral light, found e.g. in circularly polarized plane waves, offers a versatile and non-invasive platform to achieve this goal, as molecules respond selectively to chiral light based on their handedness. Yet to date, such detection techniques lack the necessary sensitivity for high-throughput applications.2
Advancements in nanotechnology have enabled the fabrication of chiral metallic nanostructures such as helices, spirals or chiral pyramids.3 When optically excited, these structures generate evanescent near fields which exceed the chirality of circularly polarized light, thus potentially increasing the detection sensitivity of chiral molecules by orders of magnitude.4,5 However, moving beyond initial demonstrations for highly chiral light, the criteria to effectively design chiral nanostructures with respect to the chirality of their evanescent fields are not well understood. The rapid decay and limited accessibility of evanescent fields has rendered this task particularly challenging. An appropriate far-field technique providing information on chiral near fields would bridge this essential gap towards the efficient optimization of chiral optical biosensors.
Recently, the optical chirality flux was identified as a measurable far-field quantity which provides useful information on nanoantenna-mediated chiral near fields, unobtainable from conventional spectroscopic methods.6 Here, we introduce an experimental technique to measure the optical chirality flux. The power of this technique is demonstrated with chiral metallic nanorod dimers. We show that both the optical chirality flux, detected in the far field, and the local chirality of the evanescent fields are controlled by the chiral near-field coupling between two nanorods. Thus, our technique for optical chirality flux detection provides vital information on chiral near fields with unprecedented accessibility in the far field. This enables the rational design of chiral nanostructures with respect to the chirality of their evanescent fields and opens the door to specifically tailored chiral sensing applications and the optimal utilization of highly chiral light.
References:
[1] L. Pasteur, Bull. Soc. Chim. Fr., 41, 219 (1884).
[2] S. M. Kelly et al., Biochim. Biophys. Acta, 1751, 119–139 (2005).
[3] M. Hentschel et al., Sci. Adv., 3, e1602735 (2017).
[4] E. Hendry et al., Nature Nanotechnol., 5, 783-787, (2010).
[5] Y. Tang and A. E. Cohen, Science, 332, 333 (2011).
[6] L. V. Poulikakos et al., ACS Photonics, 3, 1619−1625 (2016).
4:15 PM - NM06.08.06
Bending Nanorods—Tuning the Resonance Frequency and Polarization of Plasmonic Modes as a Gateway to Enhancing Non-Linear Effects
Oded Rabin 1 , Andrew Lawson 1 , Chase Ellis 2 , Joseph Tischler 2
1 , University of Maryland, College Park, Maryland, United States, 2 , U.S. Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe tunability of the frequency and polarization of surface plasmon resonances of nanostructures is crucial for their implementation in nanophotonics applications. We report FTIR spectroscopic data of gold and aluminum plasmonic nanorods and nanoarcs with resonance frequencies spanning the mid-infrared regime (2-10 microns). The dependence of the frequency on the nanorod/nanoarc material and dimensions as well as substrate material are explained with a model based on the properties of plasmon-polaritons in confined geometries. The tunability is key to engineering structures for the manipulation of the propagation, polarization and frequency of photons.
4:30 PM - NM06.08.07
Bending and Splitting Gold Nanorods with Light
Christoph Maier 1 , Anastasia Babynina 1 , Verena Hintermayr 1 , Theobald Lohmüller 1 2
1 Chair for Photonics and Optoelectronics, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München, Munich Germany, 2 , Nanosystems Initiative Munich (NIM), Schellingstraße 4, 80799 Munich, Germany, Munich, Bavaria, Germany
Show AbstractPlasmonic nanoantennas and nanoantenna arrays are prominent building blocks for the rational design of flat metamaterials and optical devices. Yet, the fabrication of such materials is not a simple task. E-beam lithography is widely used, but shows limitations when it comes to the fabrication of very small gold nanostructures with high crystallinity and purity. Here, we report on the possibility of transforming and patterning nanoparticles with light as an intriguing alternative to conventional nanofabrication approaches.
First, we show that laser manipulation can be applied to controllably bend single gold nanorods in solution. Optical forces, which emerge during the bending process, can be utilized to optically pattern the re-shaped particles onto an underlying substrate. By taking advantage of both optical forces and plasmonic heating, we devised a mechanism how both the bending angle and the alignment of the bent nanorods can be controlled with respect to each other by tuning the laser conditions [1]. In a second step, we demonstrate that the optical transformation of a gold nanorod can eventually result in the formation of a nanoparticle dimer. In this experiment, merely laser light is used to split a single gold nanorod into two spherical nanoparticles of equal size. Scanning electron and transmission electron microscopy images reveal that the particles are separated at distances of less than 3 nm with the smallest gaps being in the sub-nanometer regime. As the mechanism for this dimer formation we suggest a combination of Rayleigh instability in the presence of strong optical and hydrodynamic forces. Plasmonically coupled nanostructures with nanometer-sized gaps feature intriguing properties due to the very strong field confinement in the gap region. By conventional means, however, they are extremely challenging to produce. Nanorod splitting by means of light thus represents a promising alternative for the synthesis of nanoparticle dimers to take advantage of strong plasmonic coupling and quantum plasmonic effects.
[1] Babynina, A., Fedoruk, M., Kühler, P., Meledin, A., Döblinger, M. and Lohmüller, T. Nano Lett., 2016, 16 (10), pp 6485–6490
4:45 PM - NM06.08.08
Dramatic Modification of Coupled-Plasmon Resonances Following Exposure to Electron Beams
Haixu Leng 1 , Brian Szychowski 1 , Marie-Christine Daniel 1 , Matthew Pelton 1
1 , University of Maryland, Baltimore County, Baltimore, Maryland, United States
Show AbstractStudies of the plasmon resonances in individual and coupled metal nanoparticles often involves imaging of the nanostructures of interest in an electron microscope. Here, we show that the scattering spectrum of a coupled gold-nanorod / gold-nanosphere dimer is dramatically modified after the nanoparticle pair is imaged in a scanning electron microscope (SEM). Exposure to the high-energy electron beam in the SEM modifies the nature of coupling between the nanoparticles, which can be explained by the deposition of a thin, partially conductive carbonaceous layer on the particles. In the case of isolated gold nanorods, exposure to electron beams shifts the plasmon resonances to lower energies. Our findings can be used to selectively fine-tune the plasmonic response of individual synthesized nanostructures, and can explain discrepancies in the literature between predicted and measured optical spectra.
NM06.09: Poster Session III: Plasmonics
Session Chairs
Thursday AM, November 30, 2017
Hynes, Level 1, Hall B
8:00 PM - NM06.09.01
Facile Synthesis of Silver Nanoparticles Film by Spark Method and Its Application as a Highly Active SERS Substrate
Mohamed Abdelhamid 1 , Takafumi Seto 1 , Yoshio Otani 1
1 Faculty of Natural Systems, Kanazawa University, Kanazawa Japan
Show AbstractHighly sensitive Surface-Enhanced Raman Scattering (SERS) substrate composed of silver nanoparticles was fabricated via a spark discharge method in the gas phase. The spark-ablated species were directly deposited on copper or glass substrates at ambient conditions (air or N2 flow). The FE-SEM showed that the fabricated substrates were composed of spherical Ag particles with size range from 25 to 100 nm. The HRTEM also revealed the existence of quantum sized Ag dots (<10 nm). The EDX results indicated that the surface of Ag nanoparticles was partially oxidized when the substrate was prepared without flow (air). The sharp and reproducible SERS peaks from Rhodamine B (Rh B), as a model molecule, were observed from both surface oxidized and non-oxidized Ag substrates. By optimizing the deposition conditions, the detection limit of Rh B reached single molecular level (10-16 M), with an enhancement factor of 3.9 x 1012. High SERS signal from adenine were also detected from the Ag substrates prepared in N2 atmosphere with the detection limit of 10-6 M. However, no SERS peaks from adenine were detected from the surface-oxidized Ag substrates, indicating that the control of surface-oxidation is important to detect biomolecules.
8:00 PM - NM06.09.02
Processing and Fabrication of Semiconductor Nanostructures by Multiphoton Lithography in Arsenic Sulfide and Germanium-Doped Arsenic Selenide as a Route to Functional Plasmonic Devices
Casey Schwarz 1 , Chris Grabill 2 , Gerald Richardson 2 , Shreya Labh 2 , Anna Young 2 , Aadit Vyas 2 , Benn Gleason 3 , Clara Rivero-Baleine 4 , Kathleen Richardson 3 , Alexej Pogrebnyakov 5 , Theresa Mayer 5 , Stephen Kuebler 2 3 6
1 , Ursinus College, Collegeville, Pennsylvania, United States, 2 Chemistry, University of Central Florida, Orlando, Florida, United States, 3 CREOL, The College of Optics & Photonics, University of Central Florida, Orlando, Florida, United States, 4 , Lockheed Martin, Orlando, Florida, United States, 5 Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 6 Physics, University of Central Florida, Orlando, Florida, United States
Show AbstractThis work reports a detailed study of the processing and multi-photon lithography (MPL) of the semiconductor chalcogenide glasses (ChGs) arsenic trisulfide (As2S3) and germanium-doped arsenic triselenide Ge5(As2Se3)95 and Ge5(As3Se7)95 and how the nano-structure morphology, chemical networking, and appearance of the resulting features are affected by the chemical composition, deposition rate, etch processing, and the inclusion of an anti-reflection (AR) layer of As2Se3 between the substrate and the photo-patternable As2S3 layer. ChGs have excellent infrared (IR) transparency, large index of refraction, low coefficient of thermal expansion, and low change in refractive index with temperature2-5. These features make them applicable for a wide range of commercial and industrial applications including periodic plasmonic structures, waveguides, optical sensors based on plasmon resonance, photonics, and active plasmonic switching devices1-5. Their properties may also be tuned through compositional variation5. Photo-patternable films of As2S3 and Ge5(As2Se3)95 were prepared by thermally depositing the ChGs onto silicon substrates2-5. The ChG films were photo-patterned by MPL and then chemically etched to remove the unexposed material, leaving free-standing structures. The resulting nano-structure morphology and chemical composition were characterized and correlated with the film compositions, conditions of thermal deposition, patterned irradiation, and chemical etch processing. Large area functional nano-structured arrays and gratings are fabricated in the As2S3-on-As2Se3 film. The addition of germanium and selenium into the composition stabilizes the film and decreases the degradation effects typical of arsenic sulfide (As2S3) films. The photo-patterned nano-structures have a tailorable shapes which are useful for anti-reflective coatings and meta-optics. This work provides a route to the use of novel materials and processing techniques for creating nanostructures with precise control over size/shape that support plasmonic resonances.
References:
1. Z. L. Samson, et al., “Chalcogenide glasses in active plasmonics.” Phys. Stat. Sol. (RRL), 4, 274-276, 2010.
2. C. M. Schwarz, C. N. Grabill, G. D. Richardson, S. Labh, A. M. Lewis, A. Vyas, B. Gleason, C. Rivero-Baleine, K. Richardson, A. Pogrebnyakov, T. S. Mayer, C. Drake, S. M. Kuebler, "Fabrication and characterization of direct laser written 3D micro-structures in arsenic trisulfide chalcogenide glasses for optical applications." (2017). (Accepted in Journal of Micro/Nanolithography, MEMS, and MOEMS)
4. C. M. Schwarz, et al., "Fabrication and characterization of micro-structures created by direct laser writing in multi-layered chalcogenide glasses," Proc. SPIE 9374, 937403-1 - 937403-9, (2015).
5. C. M. Schwarz, et al., “Multi-photon lithography of 3D micro-structures in As2S3 and Ge5(As2Se3)95 chalcogenide glasses,” Proc. SPIE 9759, 975916-1 - 975916-8, (2016).
8:00 PM - NM06.09.03
Continuous Fabrication of Plasmonic Broadband IR Absorber Film via Photo-Roll Lithography Process
Minsu Kim 1 , Moonkyu Kwak 1
1 , Kyungpook National University, Daegu Korea (the Republic of)
Show AbstractFor decades, metamaterials utilizing plasmonic phenomena have been drawing considerable attention owing to their extraordinary optical characteristics; furthermore, some of them have been fabricated and explored in a laboratory scale recently. Metal-insulator-metal (MIM) structure, a metamaterial exploiting localized surface plasmon resonances (LSPRs), has been theoretically expected and experimentally proved to be able to almost perfectly absorb an electromagnetic wave of a certain wavelength depending on the size of the structure. Still, due to the poor productivity of conventional fabrication techniques, commercialization of the material has been severely limited in regards to its cost performance. In this work, we introduce continuous fabrication of plasmonic broadband infrared (IR) absorber film via photo-roll lithography (PRL) process. It is experimentally confirmed that continuous fabrication of the metamaterial is possible and it has greatly improved productivity while maintaining the IR absorbing performance. Disk-shaped MIM structure having 4 different diameters was continuously fabricated using Al and SiO2 as a metal and insulating layer, respectively. The productivity is compared to the conventional fabrication methods in regards to the time and cost. IR absorbing properties of the fabricated structure are shown by measuring the IR transmittance spectra using FT-IR spectroscopy. It is expected to contribute to the commercialization of the plasmonic IR absorber film by using the continuous fabrication process shown in this work.
8:00 PM - NM06.09.04
Synthesis and Characterization of Plasmonic Hierarchical Systems by Integration of TiO2 Nanostructured Films with Au Nanoparticles for Photocatalytic Applications
Matteo Ghidelli 1 , Luca Mascaretti 1 , Tarek Afifi Afifi 1 , Beatrice Bricchi 1 , Valeria Russo 1 , Carlo Casari 1 , Roberto Matarrese 1 , Isabella Nova 1 , Andrea Li Bassi 1
1 , Politecnico di Milano, Milan Italy
Show AbstractPlasmonic nanoparticles (NPs) have recently attracted attention of the scientific community for the possibility to enhance light harvesting and quantum efficiency in photoconversion processes; possible applications range in the field of thin film photovoltaics, solar fuel (e.g. hydrogen) production, photocatalysis, chemical sensing and spectroscopy [1]. Specifically – by embedding plasmonic metal NPs within a wide band gap semiconductor (TiO2, ZnO) – it has been reported an increase of light harvesting beyond the ultraviolet region combined with enhanced light scattering effects improving photoconversion [2].
Nevertheless, the coupling mechanisms between plasmons and light within metal-semiconductor nanostructures is still subject of research, while key questions involving the effect of size distribution of plasmonic NPs to develop high-efficiency devices still require thorough studies [1,2]. Furthermore, the plasmonic NPs are often produced using liquid phase techniques followed by an embedding phase within the semiconductor film deposited by vapor phase techniques, thus hindering possible scaling up to industrial technology [1].
Here, vapor phase Pulsed Laser Deposition (PLD) technique is used to produce both plasmonic Au NPs and nanostructured TiO2 films and to integrate them within a single deposition step. A wide range of PLD process parameters – including background gas pressure, the number of laser shots as well as post-deposition annealing treatments – has been investigated to control the growth of Au NPs and percolating films providing a precise control of the optical behavior and surface plasmon characteristics [3]. In parallel, forest-like nanostructured TiO2 films have been deposited by the same PLD setup tuning the thickness and porosity. Then, optimized Au plasmonic NPs are coupled with TiO2, involving deposition of Plasmonic NPs at the bottom or at the top of the TiO2 as well as co-deposition of integrated, hierarchical TiO2/Au-NPs assemblies or multilayers.
For the different morphologies, we show that the Au NPs affect the TiO2 optical behavior inducing light absorption in the visible range depending on the size distribution and plasmonic response of the NPs, while promoting multiple-reflections as well as light scattering. In the case of co-deposition, we show that the TiO2 growth, morphology and optical properties are affected by the embedded Au NPs. For the best-optimized systems, we discuss the results of the water splitting photocatalytic performance under solar simulator illumination. On-going testing reports interesting results, suggesting the potentiality of this approach for the synthesis of novel plasmonic-based devices.
[1] H. A. Atwater & A. Polman. Nature Materials 9, 205-2013 (2000).
[2] S. Mubeen et al. Nano Letters 11, 5548-5552 (2011).
[3] M. Ghidelli et al. submitted to Materials & Design (2017).
8:00 PM - NM06.09.06
Synthesis, Interconversion, Alloying and Applications of Plasmonic Copper Sulfide-Based Nanomaterials
Yang Liu 1 , Mark Swihart 1
1 , State University of New York at Buffalo, Buffalo, New York, United States
Show AbstractPlasmonic copper sulfide-based nanocrystals (NCs) have attracted considerable attention due to their unique and versatile optical and electronic properties. Localized surface plasmon resonance (LSPR) is an especially important optical phenomenon with rapidly growing applications in theranostics, nanophotonics, and nanoelectronics. These applications involve not only diverse phases of copper sulfides, but also various ternary and quaternary copper sulfide-based NCs, such as copper indium sulfide (CIS) and copper zinc tin sulfide (CZTS). In this contribution, we will summarize some of the recent progress that our group has made on the synthesis and interconversion of these materials. We recently developed a novel synthesis of covellite CuS nanoplatelets (NPls) by reacting ammonium sulfide with a Cu-oleylamine precursor in toluene. The diameter of hexagonal CuS NPls are controllable over a wide range (7-100 nm), while maintaining a constant thickness of 4 nm. We further generalized this method to achieve rapid, room-temperature synthesis of various metal sulfides (e.g., Ag2S, PbS, CdS). The CuS NPls were tested for electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline solution. ORR activity increased with increasing size of CuS NPls, due to anisotropy of electron mobility and of electrochemical activity of 2-dimensional NPls. Moreover, we explored reversible phase interconversion between two stoichiometric limits (CuS and Cu2S), using 1-dodecanethiol as reducing agent and oleic acid-S as sulfur donor. We have also shown that ternary CIS and copper tin sulfide (CTS) NPls can be prepared using binary CuS NPls as the template. Two distinct CTS crystal phases were obtained by different combinations of oxidation state of Sn sources and reducing agents. On the other hand, CIS NPls can be converted to biconcave (red blood cell like) djurleite Cu31S16 NCs via cation exchange. Both ternary CIS and CTS NPls were converted to quaternary CZIS and CZTS by zinc incorporation. All of the projects above provide not only a better fundamental understanding of colloidal copper sulfide-based nanomaterials, but also new insight into the design of these nanostructures.
8:00 PM - NM06.09.07
Progress in the One-Pot, Polyol Synthesis Method of Uniform Silver Nanorods for Plasmonic Nanostructure Applications
Jill Tracey 1 , Deirdre O'Carroll 1 2
1 Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey, United States, 2 Materials Science and Engineering, Rutgers, The State University of New Jersey, New Brunswick, New Jersey, United States
Show AbstractThe implementation of plasmonic nanostructures has led to a multitude of new applications and device designs for energy conversion and energy storage, optoelectronic devices, lasers, sensing, and displays. There has been a lot of progress towards control of the structure of nanoparticles of certain metals, such as gold. Controlling the structure of metal nanoparticles is important since nanoparticles that support plasmon resonances can effectively confine light into nanoscale volumes and tuning the shape and size effects how that light is confined. For plasmonic nanorods, gold tends to be the material most commonly employed due to facile bottom-up synthesis, good stability, and reproducibility. Silver nanorods are not as commonly utilized due to the lack of well-developed or reproducible synthesis methods and due to changes in their structure and size over time. However, silver nanorods have more advantageous optical properties, such as lower parasitic absorption losses and surface plasmon resonances that can be tuned to span the entire visible range.
In this presentation our progress towards the synthesis of silver nanorods will be discussed. The one-pot, polyol method, an established method, was chosen for its claimed ease of reproducibility and controllability of shape, size, and aspect ratios of nanoparticles; however, we find that these claims have not always proven to be true. Many aspects of the synthesis were investigated to determine their effect on the morphology of the nanoparticles, including: varying the viscosity of the solvent, heating conditions, salts added, strength of reducing agents, and time over which the synthesis proceeds. Throughout the synthesis of nanoparticles the reaction is monitored qualitatively and quantitatively, by visual color changes, and UV/Visible extinction spectroscopy. Scanning electron microscopy is used after the reaction to observe the final morphology of the nanoparticles. This presentation will discuss our results thus far, which include synthesis of nanospheres of various sizes, synthesis of nanowires of various lengths, as well as synthesis of mixtures of nanospheres, nanowires, and nanorods.
8:00 PM - NM06.09.08
Plasmon Enhanced Emission of Perovskite Quantum Dot Films
Evren Mutlugun 1 , Seyma Dadi 1 , Yemliha Altintas 1 , Emre Beskazak 1
1 , Abdullah Gul University, Kayseri Turkey
Show AbstractAll inorganic halide perovskite quantum dots have gained great attention in recent years owing to their high photoluminescence quantum yield and narrow emission bandwidth (1). On the other hand, colloidal metallic nanoparticles have been used for long, in conjunction with the semiconductor quantum dots for plasmonic applications. Localized in optimal distances with the quantum dots, metallic nanoparticles have been shown to enhance the local electric field and increase the photoluminescence intensity of the semiconductor quantum dots (2). In this work, for the first time, we propose and demonstrate the enhancement of the in film photoluminescence of the perovskite quantum dots, possessing the photoluminescence enhancement up to 57%. High quality green emitting CsPbBr3 perovskite quantum dots have been synthesized with 85% quantum yield and emission full width at half maximum of as narrow as 18 nm. Au nanoparticles synthesized in organic phase with 10 nm average sizes (diameter) and perovskite quantum dots has been blended into polystyrene, and the control of the particle-particle distance within the spin coated film was achieved by tuning the concentrations of perovskite quantum dot-Au nanoparticles. Plasmon coupled perovskite quantum dots has been monitored further using time resolved photoluminescence spectroscopy. Plasmon enhanced emission of perovskite quantum dots will open up new possibilities for future optoelectronic devices.
This work was supported by TUBITAK 114E107.
1. L. Protesescu, S. Yakunin, M. I. Bodnarchuk, F. Krieg, R. Caputo, C. H. Hendon, R. X. Yang, A. Walsh, M. V. Kovalenko Nano Letters, 15, 6, 3692-3696 (2015).
2. . T. Ozel, P. L. Hernandez-Martinez, E. Mutlugun, O. Akin, S. Nizamoglu, I.O.Ozel, Q. Zhang, Q.Xiong, H. V. Demir, Nano Letters, 13, 7, 3065-3072 (2013).
8:00 PM - NM06.09.09
ZnO-Au Heterojunction Enhanced the Photoluminescence of ZnO Nanocrystals
Suzanna Akil 1 , Jean Gaumet 1 , Aotmane En Naciri 1 , Hervé Rinnert 2 , Pierre Magri 1 , Issraa Shahine 1
1 Laboratoire de Chimie et Physique, Universit de Lorraine, Metz France, 2 UMR CNRS, Université de Lorraine, Vandœuvre-lès-Nancy France
Show AbstractZnO-Au heterojunction enhanced the photoluminescence of ZnO nanocrytalsI. Shahine
1, J-J. Gaumet
1, A. En-Naciri
1, H. Rinnert
2, P. Magri
1 and S. Akil
11 Laboratoire de Chimie et Physique; Université de Lorraine
1 Bd. Arago, 57070 Metz (France)
2 Université de Lorraine, UMR CNRS 7198, Institut Jean Lamour, BP 70239, 54506 Vandœuvre-lès-Nancy, France
Corresponding author:
[email protected]Abstract
The construction of a semiconductor heterojunction has attracted a lot of attention due to its perfect effectiveness in improving the sensing, luminescence and photocatalytic activity of a wide range of nanomaterials.
1-3In particular, hybrid nanostructures composed of semiconductor (SC) and metallic nanoparticles (MNP) have received growing interest due to the high confinement associated to the plasmonic resonances of MNP. This phenomenon enables strong interactions with other photonic elements such as quantum emitters.
4The resulting plasmon-exciton interaction gave benefits to a wide range of applications such as gas and vapor sensing, hydrogen storage, electro-optics, and catalysis.
In this context, we develop a metal-semiconductor nanomaterial (Au-ZnO and Ag-ZnO) using a new synthesis method which is green, simple and exhibiting high quantum yield and good stability nanomaterials.
The first step was the synthesis of ZnO nanoparticles by a hydrothermal process in order to tune their photo-luminescence properties based on optical and structural characterization using UV-Visible spectroscopy, Differential scanning calorimetry (DSC), photoluminescence (PL) and Transmission electron microscopy (TEM). In this communication, we show results about the synthesis of ZnO nanocrystals and some ones about the hybrid nanoparticles.
References1 Jiang, R., Li, B., Fang, C., & Wang, J. (2014). Advanced Materials, 26(31), 5274-5309.
2 Wang, X., Chen, X., Thomas, A., Fu, X., & Antonietti, M. (2009). Advanced Materials, 21(16), 1609-1612.
3 Zhang, L., Wong, K. H., Chen, Z., Jimmy, C. Y., Zhao, J., Hu, C. & Wong, P. K. (2009). Applied Catalysis A: General, 363(1), 221-229.
4 Alvarez-Puebla, R., Liz-Marzan, L. M., & Garcia de Abajo, F. J. (2010). The Journal of Physical Chemistry Letters, 1(16), 2428-2434.
8:00 PM - NM06.09.10
Plasmonic Optical Nonlineartities of Copper Sulfide Nanoparticles
Yasushi Hamanaka 1 , Tatsunori Hirose 1 , Kaoru Yamada 1 , Kazuki Miyagawa 1 , Toshihiro Kuzuya 2
1 , Nagoya Institute of Technology, Nagoya Japan, 2 , Muroran Institute of Technology, Muroran Japan
Show AbstractLocalized surface plasmon resonance (LSPR) of heavily-doped semiconductor nanoparticles (NPs) have attracted significant attention as a strong candidate of the plasmonics devices which are responsible to near-infrared (NIR) light and possess tunable LSPR frequencies by carrier doping. Most important feature of the LSPR to be noted is an electric field enhancement near the NPs’ surface (near-field enhancement: NFE) induced by optical excitation of the LSPR which can improve the efficiency of light-matter interaction. Among various semiconductor NPs, LSPRs of copper chalcogenide NPs such as CuxS, CuxSe, and CuxTe have been most actively studied. However, development of a technique evaluating the magnitude of NFE has not been presented for plasmonic semiconductor NPs. We noticed that the nonlinear optical spectroscopy can be an accurate analysis method of NFE because the nonlinear optical response is excessively sensitive to the electric field compared with the linear optical response. In this study, we present the synthesis of CuxS NPs and their third-order nonlinear optical susceptibilities (χ(3)) which are resonantly enhanced due to the LSPR. The magnitude of NFE from CuxS NPs and correlation between NFE and free-carrier concentrations were examined through the analysis of χ(3) values.
Spherical CuxS NPs (x = 1.8 - 2) with average diameters of 4 - 5 nm were synthesized via the chemical reaction in the solution phase between copper-alkylamine complexes and a sulfur source. By changing the alkylamine species used in the synthesis process, absorption peaks of the LSPRs of the CuxS NPs varied between 0.7 - 1.0 eV. Carrier concentrations were estimated by analyzing the LSPR bands which were in the 1021 cm−3 range and controllable by the selection of the alkylamine species. Simultaneously with the spectral changes in the LSPR bands, optical bandgap energies of the CuxS NPs exhibited an apparent shift from 2.0 to 2.5 eV. Such blue-shifts have been ascribed to the Burstein-Moss effect and can be corroborative evidence of an increase in the carrier concentrations.
Imaginary part of χ(3) of the CuxS NPs dispersed in hexane was the maximum −3×10−15 esu at the LSPR frequency which is comparable to that of the typical plasmonic NPs, Au NPs, with the same dimensions and concentrations, indicating that the CuxS NPs can be used for nonlinear optical devices operating in the NIR region. Such large optical nonlinearities are caused by the local-field enhancement inside the NPs induced by the LSPR excitation. However, χ(3) measurements suggest that the local-field enhancement effect is weaker (≒1/2) in CuxS NPs than in Au NPs. Therefore, it is estimated that the NFE around the CuxS NPs was also weaker than that of Au NPs. Such weak NFE is presumably due to lower carrier concentrations of the semiconductor NPs compared to those of the metallic NPs.
8:00 PM - NM06.09.11
Plasmon-Induced Charge Separation in Ag Nanoparticles Decorated Single Polypyrrole Nanowire
Seung-Hoon Lee 1 , Seung Woo Lee 2 , Jae-Won Jang 1
1 , Pukyong National University, Busan Korea (the Republic of), 2 Chemical Engineering, Yeungnam University, Gyeongsan Korea (the Republic of)
Show AbstractAmong hybrid nanostructures, semiconductor with metal nanomaterial has been more exploited because metal and semiconductor have different properties that, in combination, result in unique electrical and optical properties. Localized surface plasmon resonance (LSPR), which is one of novel properties of metal nanoparticles (NPs), has been used as a good strategy for increasing an opto-electric performance in semiconductors. In this presentation, improvement of the opto-electronic properties of non-single crystallized nanowire (NW) devices with space charges generated by LSPR is demon-strated. The photocurrent and spectral response of single polypyrrole
(PPy) NW devices are increased by electrostatically attached Ag NPs. In particular, it is also proved the space charge generation by LSPR of Ag NPs by means of characterizing current-voltage (J-V) dependence and finite differential time domain (FDTD) simulation on the NW devices. Moreover, semiconductor type dependent role of metal NP in metal NPs decorated semiconductor NW is demonstrated by using light irradiated Kevin probe force microscopy.
8:00 PM - NM06.09.13
Gold-Coated Macroporous Silicon for Highly Sensitive SERS-Spectroscopy
Sergey Zavatski 1 , Hanna Bandarenka 1 , Ksenia Girel 1 , Nadia Khinevich 1 , Vitaly Bondarenko 1
1 Micro- and Nanoelectronics, Belarusian State University of Informatics and Radioelectronics, Minsk Belarus
Show AbstractGold nanoparticles (Au NPs) demonstrate surface plasmon resonance (SPR) and are widely used in high sensitive optical sensors based on the Surface Enhanced Raman Scattering effect (SERS). For such sensors, both NPs dimensions and distance between NPs are of importance. Dimensions of plasmonic Au NPs determine the frequency of SPR. When the certain distance between Au NPs is reached, so-called “hot spots” are formed. These hot spots provide strong localization of electromagnetic field which exhibits the SERS effect. For high sensitivity of SERS sensors it is very important to increase a number of hot spots. This is possible by controlling the size and shape of the Au NPs. Recently it was shown [1] that the fabrication of macropores at the surface of Si substrate followed by the Au NPs deposition allowed increasing the number of hot spots in 2-3 times. For further progress in the design of these plasmonic nanostructures it is necessary to study the influence of pore and Au NPs sizes on the optical properties. For optical characterization of plasmonic nanoparticles the extinction spectra are usually used. However, in the case of Au NPs deposited on Si substrate, there is no chance to get the extinction spectra due to the strong absorption of visible light by Si. The reflectance spectra can be measured but unfortunately these spectra are very weak due to the roughness of the Si substrate containing macropores.
In this work the reflection spectroscopy with special detection module in the form of integration sphere was used to measure the reflectance spectra of the Au NPs deposited on macroporous silicon. Application of this method provided information about spectral position of SPR depending on size and surface distribution of Au NPs. Reflection spectroscopy was carried out in the spectral range from 300 to 700 nm. Au NPs were deposited on the top of 1 µm thick macroporous silicon with pore diameter of 1-2 µm. Au was deposited chemically from the aqueous solution of potassium dicyanoaurate (II) (KAu(CN)2) and hydrofluoric acid for 30, 40, 60, 70 and 80 min. It was found that SPR bands are located in the spectral range from 480 to 485 nm. Histograms of Au NPs diameters and spaces between Au NPs were obtained by analysis of SEM images with the program ImageJ. The SEM study showed that the Au NPs have the spherical shape with diameters ranging from a few tens to less than 100 nm while spaces between Au NPs are several nanometers. The variation of the Au deposition time was demonstrated to cause various enhancement of the Raman signal. Obtained results are useful for further development of the novel high sensitive SERS-based optical sensors.
Reference
S. Zavatski et al., Structure and SERS activity of Gold Nanoparticles Formed by Chemical Deposition on Porous Silicon. Physics, chemistry and applications of nanostructures: Nanomeeting-2017, Minsk, Belarus, 30 May - 02 June 2017, pp. 240-243.
8:00 PM - NM06.09.14
Designing 0D/2D Hybrid Structures for Visible and Near-Infrared Plasmonics
Kaci Kuntz 1 , Adam Woomer 1 , Daniel Druffel 1 , Scott Warren 1 2
1 Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractLayered electrides, such as Ca2N, are an exotic class of materials. These ionic crystals have layers of cationic slabs (Ca2N+) and anionic free electron gas (e-), formally written as [Ca2N]+ e-. As a result of these alternating layers, Ca2N is a metallic crystal with highly mobility and a low work function (Nature, 494, 336-340 (2013)). Recently, we exfoliated Ca2N into a two-dimensional (2D) material (J. Am Chem. Soc., 138, 16089-16094, (2016)). As a 2D material, Ca2N remains metallic, crystalline, and interestingly, becomes relatively transparent. With application as a transparent conductor, this 2D material also shows potential as a catalyst, reducing agent, and near-infrared plasmonic material (Scientific Reports, 5, 12285 (2015)). Despite the prediction of these interesting properties, experimental studies on 2D Ca2N as a reducing agent or plasmonic material have yet to be performed. To address these challenges, here, we synthesize and characterize a 0D/2D hybrid plasmonic structure composed of silver nanoparticles and 2D Ca2N.
Through a facile wet-synthesis, silver nitrate in N-methyl-2-pyrrolidone was added to a liquid exfoliated suspension of 2D Ca2N in propylene carbonate with stirring. The solution changes from black to dark purple, indicating that the silver ions are reduced by the Ca2N. Interestingly, in transmission electron microscopy images, we observed that silver nanoparticles (5-10 nm) adhere to the 2D sheets, creating a 0D/2D hybrid structure. Through selected area electron diffraction, we confirm that the Ca2N remains crystalline with an anti-CdCl2-type structure. Furthermore, we modeled the phonon dispersions of Ca2N through density functional theory and identified the out-of-plane (A1g) and in-plane (Eg) Raman-active modes. Experimentally, we find good agreement between the measured and calculated Raman active modes of Ca2N. In the hybrid structure, we find that the A1g mode remains at 300 cm-1, further confirming the crystallinity of the Ca2N. In addition, we characterize the surface composition of assemblies of the silver nanoparticle/2D Ca2N material through X-ray photoemission spectroscopy (XPS). Since XPS is sensitive to local chemical environments, the atomic composition of different oxidation states can be quantified. We found that the silver is reduced to Ag0 and Ca2N remains unchanged by the silver nanoparticles. Based on these characterizations, we successfully synthesized a metallic 0D/2D hybrid structure. Finally, we investigate the optical properties of this coupled plasmonic structure. We examine the broadening of the Ag0 plasmon resonance to elucidate the electron transfer in the 0D/2D structure. An understanding of the electron transfer between the silver nanoparticle and 2D electride may create opportunities to catalyze or drive chemical reactions using the 2D electron gas. This metallic 0D/2D hybrid structure shows potential for photochemistry, photocatalysis, photovoltaics, and photodetectors.
8:00 PM - NM06.09.15
Concurrent Activation of Localized Surface Plasmons and Polarons in Tungsten Oxide Nanoparticles
Shota Yamanaka 1 , Tadashi Saitoh 1 , Shinnosuke Yamazaki 1 , Hiromitsu Kozuka 1 , Mitsuru Inada 1
1 , Kansai University, Osaka Japan
Show AbstractWe prepare metallic tungsten oxide nanoparticles by RF sputtering without doping, and investigate optical properties of the nanoparticles. Optical absorption spectra show clear two independent absorption species in near-infrared region, which are originated from localized surface plasmon resonance and polaron. This concurrent activation property not only provides a stage for understanding the fundamental physics of plasmon and polaron of tungsten oxide nanoparticles, but also shows that the nanoparticles are interesting candidates for device application.
Tungsten oxide nanoparticles are prepared by RF sputtering in the mixture of argon and oxygen gas atmosphere at various substrate temperatures. From AFM observation, mean diameter of the nanoparticles is about 20 nm. XRD patterns reveal that the nanoparticle have crystalline nature above 350 °C deposition. From Hall measurements, carrier concentration of the deposited sample increases with increasing deposition temperature (1.5×1020 cm-3 for room temperaure and 1.3×1024 cm-3 for 350 °C). It is widely understood that the origin of the free carrier is oxigen vacacies, and the higher deposition temperature enhance to create the oxgen vacancies. UV-vis-NIR absorption spectra of the tungsten nanoparticles show clear two species located at around 1.0 eV and at 1.7 eV. The peak position of former spectra slightly red shifts with increasing the carrier density. Comparing these results with the reported results1,2, the former is considered to be localized surface plasmon absorption of free carriers and the latter is polaron absorption. Details of sample preparation and optical, structural and electric transport properties will be presented and discussed in the meeting.
1) Karthish Manthiram and A. Paul Alivisatos, J. Am. Chem. Soc. 134, 3995-3998, (2012).
2) Kenji Adachi and Tsuyoshi Asahi, J. Materials Research, 27, 965-970, (2012).
8:00 PM - NM06.09.16
Strong Coupling between Supramolecular Excitons and Plasmonic Surface Lattice Resonances
Robert Collison 1 2 3 , Rahul Deshmukh 4 , Jacob Trevino 3 , Vinod Menon 4 , Stephen O'Brien 2 , Adam Braunschweig 5 3
1 Chemistry, City University of New York, Graduate Center, New York, New York, United States, 2 Chemistry, City College of New York, CUNY, New York, New York, United States, 3 , Advanced Science Research Center, CUNY, New York, New York, United States, 4 Physics, City College of New York, CUNY, New York, New York, United States, 5 Chemistry, Hunter College, CUNY, New York, New York, United States
Show AbstractWe report on the fabrication and spectral characterization of films of self-assembling supramolecular dye aggregates deposited on top of 2D periodic arrays of gold nanoparticles. Coupling between the excitons of the supramolecular dye aggregates and the plasmonic surface lattice resonances (SLRs) of the gold particle arrays is investigated by measurement of k-space images and transmission, reflection, and photoluminescence spectra of the dye-conjugated arrays. These data are analyzed to determine the degree of coupling and to elucidate the nature of the hybrid states, including their energy and dispersion relation. Using pump probe techniques, the effects of the exciton-plasmon coupling on the energy, diffusion length, lifetime, and decay pathways of the supramolecular dye excitons are assessed. From these results, the potential for SLR-supporting arrays to enhance the performance of thin film solar cells based on supramolecular organic dye aggregates is discussed.
8:00 PM - NM06.09.17
Programmable Three-Dimensional Plasmonic Helicoid Nanoparticles with Giant Optical Activity
Hye-Eun Lee 1 , Hyo-Yong Ahn 1 , Yoon Young Lee 1 , Jungho Mun 2 , Junsuk Rho 2 , Ki Tae Nam 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractPlasmonic chiral structure has attracted significant attention at it provides a new route to intriguing optical properties such as negative refractive index, light polarization filters, and phase modulation. However, the fabrication regarding with limited resolution in conventional synthesis and complexity of asymmetric synthesis pose a major hindrance for further development. In this study, a new class of three dimensional chiral plasmonic nanostructures was successfully fabricated using molecular shape modifiers and crystallographic control of nanoparticle. Previously, we discovered a novel system that characteristic of molecule is transformed into distinctive gold nanoparticle shape.1,2 On the basis of this system, chirality transfer between molecular modifier and gold surface allow us to achieve numerous chiral morphologies of gold nanoparticle, named plasmonic helicoids. Particularly, enantiospecific interaction of molecule and high index plane plays pivotal role to provide asymmetric structuring process on the gold surface, forming distinct chiral morphology in single nanoparticle level. One of the representative shape of helicoid structure showed gammadion-like structure, consisting of four highly curved arms of increasing width, in all six faces of cubic geometry. The unprecedented chiral morphology of plasmonic helicoid has remarkable optical activity (dissymmetry factor ~ 0.2 at 622 nm) even in a randomly dispersed solution, substantiated by direct visualization of macroscopic color transformation. Changes in molecular recognition and growth parameter led to different morphological evolution, and structural alterations provided a straightforward means of tailoring optical response, such as optical activity, handedness, and resonance wavelength. Also, our aqueous phase synthesis is readily scalable without losing exquisite chiral structure at nanoscale. In these aspects, our approach, chirality evolved in single nanoparticle, provide a truly new paradigm and valuable insight for chiral metamaterial fabrication.
1. Lee, H.-E.; Yang, K. D.; Yoon, S. M.; Ahn, H.-Y.; Lee, Y. Y.; Chang, H.; Jeong, D. H.; Lee, Y.-S.; Kim, M. Y.; Nam, K. T. “Concave Rhombic Dodecahedral Au Nanocatalyst with Multiple High-Index Facets for CO2 Reduction” ACS Nano, 9, 8384-8393, 2015.
2. Ahn, H.-Y.; Lee, H.-E.; Jin, K.; Nam, K. T. “Extended gold nano-morphology diagram: synthesis of rhombic dodecahedra using CTAB and ascorbic acid” J. Mater. Chem. C 1, 6861-6868, 2013.
8:00 PM - NM06.09.18
Optically Active Transitions in a Chiral Metamaterial Onset by Intensity Modulation
Sean Rodrigues 1 , Shoufeng Lan 1 , Mohammad Taghinejad 1 , Lei Kang 1 , Yonghao Cui 1 , Augustine Urbas 2 , Wenshan Cai 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , Air Force Research Laboratory (AFRL), Dayton, Ohio, United States
Show AbstractThe reciprocal optical responses exhibited by chiral materials of opposite handedness offer an exciting avenue for switching activities that could lead to utility in optical communications and memory storage. The first step to seizing this potential is to instigate active control over these optical responses. Chiral metamaterials transcend traditional chiral structures by providing enormous chiroptical signals that surpass naturally occurring media, by engineering metal-dielectric components on the subwavelength scale to react differently when interacting with left and right circular polarizations of light. Here, we spectrally modify two absorptive resonances by exposing a chiral metamaterial to modest intensities beyond its linear optical regime. In addition, our study exhibits an exceptionally large nonlinear optical rotation, achieving an intensity-induced change of 14° in the polarization rotation from a metamaterial with a thickness of λ/7. The spectral shifts in the absorption resonances and the induced transition in the rotation of the optical polarization at higher intensities demonstrates the functionality of nonlinear, chiral metamaterials.
8:00 PM - NM06.09.19
Sub-10-nm-Pitch Plasmonic Helical Nanoparticles with Chiroptical Activity Engineerable in the UV-Visible Region
Zhifeng Huang 1
1 , Hong Kong Baptist University, Kowloon Tong Hong Kong
Show AbstractThe geometrical prerequisite to form a helix is P (helical pitch) > d (wire diameter). Limited by the current development of nano-fabrication techniques, it is difficult to minimize d and consequently P to the sub-10-nm molecule-comparable scale, preventing the study of chiroptically active nanoplasmonics at dimensions approaching the physical limit. In this presentation, glancing angle deposition (GLAD) at high speed of substrate rotation will be introduced to generate plasmonic helical nanoparticles (PhNPs) with nominal P < d. The deposited PhNPs exhibit intrinsic chiroptical activity characterized by circular dichroism (CD), originating from the hidden helicity. PhNPs are made from Al, Ag and Cu, such that the chiroptical activity can be flexibly tailored in the UV-visible region. With increasing P from 3 to 66 nm, the plasmonic mode of Ag PhNPs barely shifts but shows a logarithmic increase in CD amplitude. When an achiral Al thin film is deposited on a host of Cu PhNPs, the helical structures are duplicated from the chiral host to the achiral guest of Al nanocappings. The host@guest helicity duplication is a new GLAD methodology to generate chiroptically active nanoplasmons, which can be generally adapted to diverse plasmonic metals for tailoring plasmonic chiroptical activity flexibly in the UV-visible region. This presentation introduces a cost-effective, facile approach to minimize P to sub-10-nm at a regular substrate temperature, paving the way to study chiroptically active nanoplasmonics approaching the physical limit and exploit chirality-related biological phenomena.
8:00 PM - NM06.09.20
Mechanisms of the Fluorescence Enhancement from Semiconducting Polymer Thin-Films on Silver Nanomembranes
Zeqing Shen 1 , Kun Zhu 1 , Deirdre O'Carroll 1
1 , Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States
Show AbstractSurface plasmons at metal electrode surfaces have been found to be both a problem and a benefit to thin-film organic optoelectronics, and, therefore, there is considerable disagreement on whether or not they are useful in practice. Semiconducting polymers are versatile optoelectronic materials that are beginning to displace more traditional semiconductors for thin-film lighting, display and laser applications. Because of the variety of possible polymer chain orientations in thin films, an understanding of the influence of semiconducting polymer chain alignment on the mechanisms of metal-mediated fluorescence at metal surfaces is needed to provide information about when metallic nanostructures can be used to improve device performance.
In this study, we identify the mechanisms of metal-mediated polymer fluorescence by planar Ag (plAg) and random nanoporous Ag nanomembranes (NPAg) (~100 nm thick) in detail. Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), regio-random and regio-regular poly(3-hexylthiophene-2,5-diyl) (rra-P3HT and rr-P3HT, respectively), who have similar absorption (400 - 600 nm) and emission wavelengths (600 - 800 nm), but different chain morphology are applied. By comparing local- and large-area emission intensity and quantum efficiency (ηloc and η) enhancements and by varying viewing angle, we unravel the influences of semiconducting conjugated polymer chain orientation on the excitation modification, emission angle modification, and emission quantum efficiency modification by which their fluorescence can be mediated by metallic surfaces.
We show that the excitation of conjugated polymer thin films is largely dependent on polymer chain alignment and extinction coefficient. Up to 65 times local excitation enhancement (Eex) is experimentally observed for polymers with more out-of-plane chains and low extinction coefficients (rra-P3HT) on NPAg compared to plAg. There is virtually no Eex for polymers with dominant in-plane chain alignment and high extinction coefficient (rr-P3HT and MEH-PPV). We also show that the emission angles of conjugated polymer thin films can be affected differently by plAg and NPAg, and this is also dependent largely on polymer chain orientation. Moreover, we show that the emission quantum efficiency can be enhanced for polymer thin-films with greater fractions of out-of-plane polymer chains by extracting plasmonic surface waves and through the Purcell Effect at nanostructured metal surfaces. The η and ηloc of polymers with significant fractions of out-of-plane polymer chains can be increased by up to 53% and 414%, respectively, by NPAg. In contrast, only subtle changes in η exist in polymer thin-films in which in-plane polymer chains predominate.
8:00 PM - NM06.09.21
Experimental Detection of Thermal Effects in Sensors Based on Surface Plasmon Resonance
Jose Vicent 1 2 , Fernando Galvez 1 , Miguel A. Garcia 3 4 , Jorge Spottorno 1 4 , David Perez de Lara 2
1 Departamento Fisica Materiales, Universidad Complutense, Madrid Spain, 2 , IMDEA-Nanociencia, Madrid Spain, 3 , ICV-CSIC, Madrid Spain, 4 , Instituto Magnetismo Aplicado, Madrid Spain
Show AbstractSurface Plasmon Resonance (SPR) is the relevant effect used for chemical sensors which are fabricated to discriminate different gas or molecular samples on a functionalized surface. Heating (1) may alter processes leading to erroneous results since the gas and molecular absorption/desorption rates on a functionalized surface depend on the local temperature. We present a straightforward experimental method (2) to determine the local increase of temperature upon SPR excitation. This method allows estimating the local increase of temperature when exciting SPR on Au films with low-power sources. From experimental data and simulations, we found that local increase of temperature at the laser spot position are below 0.1 K and 1 K for laser power flux of the order of 1.5 mW/mm2 and 15 mW/mm2 respectively, for sensors working in air.
(1) L. Röntzsch, K. H. Heinig, J. A. Schuller, M. L. Brongersma, Applied Physics Letters 90 044105 (2007).
(2) Galvez, D. Pérez de Lara, J. Spottorno, M. A. García and J. L. Vicent Sensors and Actuators B: Chemical 243, 806 (2017)
8:00 PM - NM06.09.23
Plasmonic Coupling Mechanism behind UV Enhancement of Au-Coated ZnO Nanorods
Saskia Fiedler 1 , Laurent Lee Cheong Lem 1 , Cuong Ton-That 1 , Matthew Phillips 1
1 Science, University of Technology Sydney, Sydney, New South Wales, Australia
Show AbstractThe light extraction of ZnO-based devices such as LEDs and lasers and light injection in solar cells can be enhanced via Localized Surface Plasmons (LSPs) using metal nanoparticles (NPs). Significant UV emission enhancement factors have been achieved in ZnO by applying a surface coating of Au NPs despite their plasma resonance frequency being in the green spectral range. Although the enhancement mechanism is not fully understood as yet, two different models have been put forward to explain the increased light emission; one involving exciton-LSP coupling and the other charge transfer of hot carriers from LSP decay.
In this work, the coupling between ZnO nanorods (NRs) and LSPs in Au NPs is systematically investigated using optical, cathodoluminescence (CL) and photoluminescence (PL) spectroscopy as well as a novel concurrent CL-PL technique. ZnO NRs have been hydrothermally grown at 90°C resulting in a dense film of NRs with an average diameter of 40 nm and a length of 700 nm. A simple post-growth sputtering and annealing process produced a continuous, uniformly distributed 5 nm Au NP coating onto the NRs. Optical spectroscopy of the Au NP-coated ZnO exhibited a broad absorption centred at 550 nm (2.25 eV) characteristic of the plasma resonance frequency of spherical 5 nm Au NPs. Depth- and temperature-resolved CL and PL were performed on bare and Au NP-coated ZnO NRs. Both techniques showed a relatively sharp, intense UV emission at 3.36 eV from excitonic recombination, and a broad deep level (DL) emission centred at 1.76 eV attributed to native point defects. Compared with bare ZnO NRs, a 5-fold enhanced UV emission of the Au NP-coated NRs was observed while the DL emission was unchanged. Time-resolved PL at a fixed wavelength of 370 nm (3.35 eV) was carried out resulting in a 40 ps decreased excitonic life time of the ZnO NRs decorated with Au NPs. This result can be explained by the creation of an additional, faster recombination channel through LSPs enhancing the spontaneous emission rate of Au NP-coated ZnO. A concurrent CL-PL technique was developed to investigate a possible charge transfer process involving hot electrons in the Au NPs into the conduction band of ZnO, increasing the UV emission. Simultaneous excitation with a green laser (λ = 532 nm) and the electron beam induced UV CL from ZnO NRs and LSPs in the Au NPs. The intensity of the UV emission under concurrent e-beam and green laser irradiation is identical to e-beam excitation alone, indicating that while LSPs are created in the Au, hot electrons are not injected into the conduction band of ZnO NRs. This result confirms that direct exciton-LSP coupling leads to the observed five times enhancement of the UV emission with 5nm Au NP film.
8:00 PM - NM06.09.24
Magneto-Optics at the Atomic Limit with Optical Nanoantenna Surfaces
Chatdanai Lumdee 1 , Peter Oppeneer 2 , Alexandre Dmitriev 1
1 , University of Gothenburg, Gothenburg Sweden, 2 Department of Physics and Astronomy, Uppsala University, Uppsala Sweden
Show AbstractEnhanced optical fields, molded at the nanoscale by optical nanoantennas, prompt the creation of a strong interaction with the surrounding medium and enable exciting possibilities in diverse areas, such as molecular sensing, energy conversion, and active nanophotonic circuitry. The combination of optical antennas with magnetic nanostructures, termed magnetoplasmonics, unveils magnetically-controlled optical surfaces and allows strongly enhanced magneto-optical effects.1-5 However, the ultimate limit for such enhancement has not been fully explored. Here we devise magnetoplasmonic optical antennas that enable magneto-optical detection in ambient conditions of the equivalent of less than 5% atomic monolayer of Fe, otherwise typically only available with x-ray spectroscopy at large synchrotron radiation facilities. This is done by engineering the enhanced near-field of the nanoplasmonic antennas and by the precise positioning of the magneto-optically-active material in the hot-spots with large-scale highly parallel bottom-up nanofabrication. We characterize the limits of the nanoantenna-enabled magneto-optical enhancement experimentally, numerically and by ab initio calculations. We further propose a highly sensitive detection scheme for monitoring the changes in the Fe oxidation state in ferromagnetic oxide at ambient conditions.
References
1. Liu, M.; Zhang, X. Nat Photonics 2013, 7, (6), 430-431.
2. Gonzalez-Diaz, J. B.; Garcia-Martin, A.; Garcia-Martin, J. M.; Cebollada, A.; Armelles, G.; Sepulveda, B.; Alaverdyan, Y.; Kall, M. Small 2008, 4, (2), 202-205.
3. Sepulveda, B.; Gonzalez-Diaz, J. B.; Garcia-Martin, A.; Lechuga, L. M.; Armelles, G. Phys Rev Lett 2010, 104, (14).
4. Maccaferri, N.; Berger, A.; Bonetti, S.; Bonanni, V.; Kataja, M.; Qin, Q. H.; van Dijken, S.; Pirzadeh, Z.; Dmitriev, A.; Nogues, J.; Akerman, J.; Vavassori, P. Phys Rev Lett 2013, 111, (16).
5. Maccaferri, N.; Bergamini, L.; Pancaldi, M.; Schmidt, M. K.; Kataja, M.; van Dijken, S.; Zabala, N.; Aizpurua, J.; Vavassori, P. Nano Lett 2016, 16, (4), 2533-2542.
8:00 PM - NM06.09.25
Plasmonic, Electronic and Magnetic Properties of the Quantum Height MnGa Islands and Atomic Chains Hetero-Epitaxially Grown on the Ga-Rich N-GaN(000-1) Surface
Zakia Alhashem 1 , Joseph Corbett 1 , Arthur Smith 1 , James Gallagher 2 , Fengyuan Yang 2
1 Department of Physics and Astronomy, Ohio University, Nanoscale and Quantum Phenomena Institute, Athens, Ohio, United States, 2 Department of Physics, The Ohio State University, Colombus, Ohio, United States
Show AbstractThe Heusler MnGa alloy grown on the N- GaN(000-1) surface leads to the formation of the quantum-height metallic islands, which are induced by sub-monolayer deposition of Mn on the GaN surface under Ga-rich conditions. Only two discrete height values of the MnGa quantum-height islands was reported including 9.3 Å for the 5-monolayer meta-stable islands, and 11.3 Å for the 6-monolayer stable islands.[1] Possible surface models for these islands were provided by considering them to be an intermediate phase that can transition to the δ-MnGa/GaN magnetic system.[2] The purpose of the present study is to investigate the role of the quantum size effect in the surface plasmon excitations corresponding to the electrons and their spins of the quantum-height MnGa islands spontaneously formed on the Ga-rich N-GaN(000-1) surface. Because the propagation length of the charge spillage can be controlled by adjusting the size of the islands, these results can give important insights for designing quantum-sized plasmonic and spintronic based devises.
Molecular Beam Epitaxy approach is used for preparing the samples. Highly ordered crystalline N-GaN(000-1) films are first grown on c-plane sapphire(0001) substrates followed by sub-monolayers of Mn deposition at ~ 250 degree C. The crystalline growth is monitored in real time using RHEED system. EELS is utilized to study surface plasmon excitations at RT. Fresh prepared samples are transferred in situ to an adjacent ultra-high vacuum analysis chamber, where surfaces are probed using RT-STM with Fe coated W tip. Also, magnetic properties of the quantum-height MnGa islands with atomic chains are characterized based on ex situ Superconducting Quantum Interference Device (SQUID) measurements.
Upon Mn deposition, dotted 2× streak is clearly observed in RHEED results. EELS spectra clearly show a sharp peak that corresponds to the surface plasmon excitation at ~ 13.77 eV for the atomically smooth MnGa islands revealed by STM results. RT-STM measurements reveal characteristic structure represented by fall lines on the surface of the 5 ML islands with noticeable correlation with the atomic chains formed on the surface of 6 ML islands. These distinctive structural lines may due to strain effect and/or interface dislocations. Also, spin polarized STM results show different contrast between atoms in the atomic chains formed on the 6-monolayer islands; possibly it is a magnetic contrast. Moreover, dI/dV mappings show different contrast between the atomic chains and the surface of the 6 ML islands due to different local density of states. Based on the SQUID results, the quantum quasi-particles contributed in the surface plasmon excitations of the quantum-height MnGa islands formed on the N-GaN surface may correspond to both electrons and their spins, namely plasmons and magnons, respectively.
References:
[1] A. Chinchore et al., Appl. Phys. Lett. 100, 061602 (2012).
[2] J. Pak et al., App. Phys. A 120, 1027 (2015).
8:00 PM - NM06.09.26
A Tunable Plasmonic Metamaterial Based on Au-Ag Bimetallic Nanoparticle Using a Galvanic Replacement Reaction
Soo-Jung Kim 1 , Mingi Seong 1 , Hye-Won Yun 1 , Heon Lee 1 , Soong Ju Oh 1 , Sung-Hoon Hong 2
1 , Korea University, Seoul Korea (the Republic of), 2 , ETRI, Daejeon Korea (the Republic of)
Show AbstractSurface plasmon excitation causes resonance due to dielectric constant, geometry and size of metal and dielectric materials. When the light of the resonance wavelength comes in, strong scattering and absorption of the light and focusing of the electromagnetic wave occur. Using this phenomenon, it can be applied to various wavelength fields such as biomolecular sensing, imaging, and energy harvesting. Therefore, many researches are being conducted to control plasmon resonance property by controlling geometric factors such as hybridized metal nanostructures and 3-dimensional nanostructures for their various application fields. However, since a conventional plasmonic nanostructure is usually made of metal thin films which have fixed optical properties, it is not easy to control the plasmonic properties in a wide range and in an accurate manner, limiting the practical applications.
In this study, the optical properties of Ag nanoparticle materials were controlled through a solution based Au coating process and the Au coated Ag nanoparticles were applied to plasmonic metamaterial for a tunable plasmon resonance. Firstly, the plasmonic nanostructure composed of Ag nanoparticles was formed through a nanoimprint process and the nanoparticles were linked by a short ligand for coupling between nanoparticles. Then, the nanoparticle based plasmonic structure was coated with gold chloride trihydrate (HAuCl4*3H2O) solution with a concentration and time. As a result, it was confirmed that the permittivity property changes according to the degree of coating of Au, and the resonance characteristics of a 300 nm Ag nanoparticle based plasmonic metamaterial were changed from 1025nm 1370 nm wavelength. We also confirmed that the plasmonic properties of Au coated Ag nanoparticle are thermally or chemically stable, so It is expected to be used in various applications.
8:00 PM - NM06.09.27
The Interplay of Shape and Crystalline Anisotropies in Plasmonic Semiconductor Nanocrystals
Jongwook Kim 1 2 , Ankit Agrawal 2 , Franziska Krieg 2 , Amy Bergerud 2 , Delia Milliron 2
1 , Ecole Polytechnique, Palaiseau France, 2 , University of Texas at Austin, Austin, Texas, United States
Show AbstractDoped semiconductor nanocrystals are an emerging class of materials hosting localized surface plasmon resonance (LSPR) over a wide optical range. Studies so far have focused on tuning LSPR frequency by controlling the dopant and carrier concentrations in diverse semiconductor materials. However, the influence of anisotropic nanocrystal shape and of intrinsic crystal structure on LSPR remain poorly explored. We illustrate how these two factors collaborate to determine LSPR characteristics in hexagonal cesium-doped tungsten oxide nanocrystals. The effect of shape anisotropy is systematically analyzed via synthetic control of nanocrystal aspect ratio, from disks to nanorods. We demonstrate the dominant influence of crystalline anisotropy, which uniquely causes strong LSPR band-splitting into two distinct peaks with comparable intensities [1]. Modeling typically used to rationalize particle shape effects is refined by taking into account the anisotropic dielectric function due to crystalline anisotropy, thus fully accounting for the aspect ratio-dependent evolution of multiband LSPR spectra [1]. This finding highlights the limitations of conventional treatments of LSPR that assume isotropic dielectric constants and attribute multimodal peaks uniquely to shape anisotropy effects. It also extends our insight to exquisitely tune LSPR lineshape and near-field enhancement via synthetic control of shape and crystalline anisotropies of semiconductor nanocrystals.
[1] J Kim*, A Agrawal, F Krieg, A Bergerud, D J Milliron*, Nano Lett. 16, 3879-3884 (2016)
Symposium Organizers
Matthew Pelton, University of Maryland-Baltimore County
Jennifer Dionne, Stanford University
Alexander Govorov, Ohio University
Maksym Kovalenko, ETH Zurich
Symposium Support
Angstrom Engineering
NNCrystal US Corporation (NN-Labs)
Princeton Instruments
NM06.10: Energy Applications
Session Chairs
Maksym Kovalenko
MingLee Tang
Thursday AM, November 30, 2017
Hynes, Level 3, Room 311
8:45 AM - NM06.10.01
Linking Indirect Carrier Excitation in Nanoparticles to an Enhanced Catalytic Activity
Sarah Wieghold 1 2 3 , Lea Nienhaus 1 3 , James Shepherd 1 , Ueli Heiz 2 , Martin Gruebele 3 , Friedrich Esch 2
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Technical University of Munich, Garching Germany, 3 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractDue to the rising cost of catalytically active noble metals, it is of interest to minimize the amount of material while maximize their efficiency. Understanding their light-matter interaction at the nanoscale is crucial when engineering new approaches in photoactivated catalysis.
Here we present the plasmonic activation of high surface-to-volume ratio Pt nanoclusters for use in photoactivated catalysis. Due to their high optical bandgap it is not possible to directly optically excite these nanoparticles, and the excitation commonly occurs through a support-mediated process. We deposit the Pt clusters onto an optically active gold support, which has a plasmon resonance in the visible spectrum. Due to the direct contact between the two metals, the plasmonic excitation of the gold support results in indirect excitation of carriers in the Pt clusters.
We perform two experiments to link the carrier excitation in Pt clusters initiated by plasmon excitation of the gold surface with enhanced catalytic activity. The optically induced activity of the Pt clusters is demonstrated on the model system of the decomposition of methylene blue. To study the underlying mechanism of the activation, single molecule optical absorption spectroscopy detected by scanning tunneling microscopy (SMA-STM) is performed to map the change in the local density of states (LDOS) under illumination. Based on our results, we propose a mechanism whereby electron migration from Au to Pt, due to the different work functions, is enhanced by surface plasmon excitation of the gold film support, leading to a d-s,p excitation-based LSPR in the Pt clusters.
9:00 AM - *NM06.10.02
Nanocatalysts for Energy Applications
Congjun Wang 1 2
1 , National Energy Technology Laboratory, Pittsburgh, Pennsylvania, United States, 2 , AECOM, South Park, Pennsylvania, United States
Show AbstractCatalysis is crucial to modern society and it is indispensable in such diverse fields as energy, chemical and pharmaceutical industry, transportation, and so on. Breakthroughs in catalysis can also open up tremendous new opportunities to shape and advance energy production and utilization in an era when technology drives the progress in energy resources extraction and consumption. Semiconductor and plasmonic nanoparticles offer interesting opportunities to enhance the performance of a wide variety of catalysts. In this talk, I will discuss the use of different nanocatalysts developed in our laboratory for energy applications. I will describe semiconductor and plasmonic nanoparticle based catalysts for CO2 reduction. Small, atomically-precise electrocatalysts will also be presented. Moreover, new Fischer-Tropsch catalysts for converting gas to industrially important olefins will be discussed. To rationally improve the performance of these diverse catalyst materials, an in-depth understanding of the property-structure relationship is essential. To this end, I will analyze the characterization of our catalysts using a wide range of techniques, such as both labortory- and synchrotron-based X-ray spectroscopy, advanced electron microscopy, optical spectroscopy, Mössbauer spectroscopy, X-ray diffraction, and so on. Additional in situ and/or operando characterization results that can help unveil the properties of catalysts under realistic reaction conditions will be presented. Finally, combining experimental with theoretical results can offer insights and provide guidance for future catalyst design.
9:30 AM - NM06.10.03
Upconversion and Plasmon-Enhanced Photocatalysis for Broadband Solar Harvesting
Qingzhe Zhang 1 , Mohamed Chaker 1 , Dongling Ma 1
1 , INRS, Varennes, Quebec, Canada
Show AbstractPhotocatalysis is considered to be one of the most promising technologies for tackling the energy crisis and environmental pollution by directly harvesting and utilizing solar energy. However, most of the photocatalysts are only able to efficiently capture photons in the ultraviolet (UV) and visible ranges, with a large portion of energy in solar light remaining unutilized. Plasmonic Au nanoparticles (NPs) have been extensively incorporated with semiconductor photocatalysts for efficient photocatalysis, benefiting from their unique size-tunable localized surface plasmon resonance effect, which is characterized by the improved light scattering, strong near field effect and/or hot electron injection. Herein, we will present some of our recent development in Au plasmonic nanostructures and their applications in photocatalysis. One example is about our recent synthesized nanocomposites based on plasmonic Au NPs, in-situ synthesized lanthanide-doped NaYF4 (NYF) on g-C3N4 with high NYF yield and coupling efficiency between NYF and g-C3N4, excellent stability, and enhanced UV-, visible- and near infrared-light photocatalytic activity. In addition to yielding novel and interesting materials and properties, the current work also provides physical insights that can contribute to the future development of plasmon-enhanced broadband photocatalysts.
9:45 AM - NM06.10.04
A Speed Limit in Solid-State Infrared Upconversion
Lea Nienhaus 1 , Mengfei Wu 1 , Nadav Geva 1 , James Shepherd 1 , Mark Wilson 1 2 , Vladimir Bulovic 1 , Troy Van Voorhis 1 , Marc Baldo 1 , Moungi Bawendi 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , University of Toronto, Toronto, Ontario, Canada
Show AbstractUnderstanding the mechanism of energy transfer across hybrid interfaces combining inorganic and organic materials is crucial to advance the development of optoelectronic devices. The exact transfer mechanism between the inorganic and organic materials remains obscure, particularly when both the macroscopic donor and acceptor materials consist of many separately interacting molecules.
Here, we investigate the mechanism of exchange-mediated spin-triplet exciton transfer from semiconducting nanocrystals (NCs) to the triplet state of rubrene. This process enables the efficient upconversion of incoherent infrared light to visible wavelengths via diffusion mediated triplet-triplet annihilation.
By reducing the ligand shell thickness of the NCs from 13 to 6 Å, we are able to show an increase in the characteristic rate of triplet energy transfer by an order of magnitude. Interestingly, we observe a saturation of the transfer rate, which we attribute to a reduced Dexter coupling brought on by an increase in the effective dielectric constant of the solid-state NC films for short ligands.
Shorter ligands, combined with an improved solid-state device structure [4] have boosted the measured upconversion efficiency from previously reported (1.2 ± 0.2) % [1] to (7 ± 1) % upconverted photons per pair of absorbed infrared photons. By tailoring the NCs and the ligands used, a further enhancement in the upconversion efficiency is possible and is subject of current investigation. This technology has the potential to extend the capabilities of silicon optoelectronics beyond the limitations of the silicon bandgap. [1, 2, 3]
[1] Wu, Congreve, Wilson et al. Nature Photonics 10, 31–34 (2016)
[2] Huang et al. Nano Lett., 15, 5552–5557 (2015)
[3] Mongin et al., Science, 351, 369-372 (2016)
[4] Wu et al. Applied Physics Letters, 110, 211101 (2017)
10:30 AM - *NM06.10.05
Directing Triplet Excitons in a Hybrid Molecular-Nanocrystal Platform for Energy Harvesting
MingLee Tang 1 , Zhiyuan Huang 1 , Xin Li 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractThird generation photovoltaics are inexpensive modules that promise power conversion efficiencies (PCEs) exceeding the thermodynamic Shockley-Queisser limit, perhaps by using up- or down-converters, intermediate band solar cells, tandem cells, hot carrier devices, or multi-exciton generation (MEG). Here, I discuss a hybrid platform comprised of semiconductor nanocrystals and organic semiconductor molecules that can efficiently upconvert light of visible and infrared wavelengths, at excitation densities below the solar flux. For example, colloidally synthesized core-shell lead sulfide -cadmium sulfide nanocrystals (NCs), in combination with tetracene derivatives, absorb near infrared (NIR) light and emit visible light at 560 nm with an upconversion quantum yield (QY) of 8.4 ± 1.0 %. This is achieved with 808 nm cw excitation at 3.2 mW/cm2, approximately three times lower than the available solar flux. The molecular and nanocrystal engineering here paves the way towards utilizing this hybrid upconversion platform in photovoltaics, photodetectors and photocatalysis.
11:00 AM - NM06.10.06
Luminescent Solar Concentrators Made of Copper-Doped Near-Unity Emitting Atomically-Flat Nanocrystals
Kivanc Gungor 1 , Manoj Sharma 1 , Aydan Yeltik 1 , Murat Olutas 1 , Burak Guzelturk 1 , Yusuf Kelestemur 1 , Talha Erdem 1 , Savas Delikanli 1 2 , James McBride 3 , Hilmi Volkan Demir 1 2
1 Department of Electrical and Electronics Engineering, Department of Physics, UNAM--Institute of Materials Science and Nanotechnology and Nanotechnology Research Center, Bilkent University, Ankara Turkey, 2 Luminous! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronics Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore Singapore, 3 Department of Chemistry and Vanderbilt Institute for Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee, United States
Show AbstractLuminescent solar concentrators (LSCs) are cost-effective light-harvesting devices for solar conversion. [1–2] Reemitted light by fluorophores embedded in LSCs is guided through total internal reflection and concentrated toward their thin edges where photovoltaic (PV) cells are applied. Increasing the light collection area in LSCs enables additional concentration of incident solar flux onto PV cells increasing the photogenerated power. Increasing the efficiency of LSCs is possible further through spectrally matching the photoluminescence emission of their fluorophores with the peak efficiency of a desired PV device. [3] In this respect, colloidal semiconductor nanocrystals (NC) could possibly make excellent LSC fluorophores because of their well-known emission tunability. [4] Among various loss mechanisms reducing the LSC performance, optical reabsorption losses are the most significant, preventing the practical applications of LSCs. To overcome the reabsorption losses for NCs, highly Stokes-shifted emission is key. For this purpose, copper doping in CdSe nanocrystals of colloidal quantum dots (CQDs) offers a promising approach with their relatively high performance as compared to other colloidal NC heterostructures. However, their limited absorption cross-section, relatively low PL QE and absorption tail coinciding with the emission spectrum reduce their performance. Ideal LSC fluorophores should feature step-like absorption profile along with a large Stokes shift. To address this need, thanks to their exceptionally tight one-dimensional confinement, colloidal quantum wells (CQWs) potentially offer superior optical properties including giant absorption cross-section and inherently step-like absorption features essential to making high-performance LSCs. In this study, we proposed and demonstrated the copper doping of CdSe colloidal quantum wells. [5] Here we show that these copper-doped CQWs outperform all other NCs as LSC fluorophores. The synthesized Cu-doped CQWs achieve near-unity PL QEs (up to ≈97%). Using a one-dimensional waveguide setup, we experimentally characterized reabsorption losses and numerically modeled the performance of these CQW luminophores exhibiting the largest flux gain. We successfully incorporated these CQWs in a polymer matrix as proof-of-concept LSC devices that surpass the performance of Cu-doped CQDs. The resulting high performance of these Cu-doped CQWs in LSCs is enabled by the combination of their large Stokes-shifted and tunable dopant induced photoluminescence emission in visible-to-NIR region and extraordinarily large absorption cross-section, in conjunction with their distinctly sharp absorption profile.
[1] A. Goetzberger, et al., Appl. Phys. 14, 123 1977
[2] F. Meinardi, et al., Nat. Photonics 8, 392, 2014.
[3] F. Meinardi, et al., Nat. Nanotechnol. 10, 878, 2015.
[4] L. R. Bradshaw, et al., Nano Lett. 15, 1315, 2015.
[5] M. Sharma, K. Gungor, et al., Adv. Mater. (DOI: 10.1002/adma.201700821).
11:15 AM - NM06.10.07
Origin of Excess Stokes Shift in Colloidal Quantum Dots and its Effect on Open-Circuit Voltage in Solar Cells
Oleksandr Voznyy 1 , Fengjia Fan 1 , Grant Walters 1 , James Fan 1 , Larissa Levina 1 , Amirreza Kiani 1 , Alex Ip 1 , Edward (Ted) Sargent 1
1 , University of Toronto, Toronto, Ontario, Canada
Show AbstractColloidal quantum dots has just reached 12% certified photovoltaic performance by using solution-based ligand exchange that reduces
defect densities and improves carrier extraction. Open circuit voltage deficit (Voc=0.65 V, significantly lower than a theoretical value of 0.95 V for a bandgap of 1.3 eV) remains the final frontier that has not yet been addressed.
PbS QDs are known for their excess Stokes shift (up to 150 meV), a strong contributor to Voc deficit, however, the origin of this large Stokes
shift and broad PL emission remain unresolved. Stokes shift due to traps, symmetry forbidden core states, and Franck-Condon shift have been speculated, yet none has guided a resolution of the problem.
Here we show that the Stokes shift originates from energy transfer between the QDs in a polydisperse ensemble even in solution phase, exaggerated by the long radiative lifetime. Following this guidance, we eliminate the Stokes shift completely using strategies based on concentration and solvent engineering. We also show that excess Stokes shift in other nanomaterials, e.g. CuInS2, CdHgTe, has the same origin.
Our findings reveal that ensemble polydispersity and aggregation cause a major portion of Stokes shift. They show that efforts should be focused on improving synthetic control over nanocrystal growth and monodispersity. The Stokes shift itself can be used as the most sensitive metric for estimating ensemble size distribution.
Following these prescriptions, we employ machine learning algorithms on thousands of QD syntheses performed in our group to devise the improved synthetic conditions and achieve record ensemble monodispersities for PbS QDs, and analyze the role of various parameters to generalize our findings to other materials.
Keywords: quantum dots, Stokes shift, energy transfer, monodispersity, machine learning, solar cells
11:30 AM - NM06.10.08
Radiative Efficiency Limit with Band Tailing Exceeds 30% for Quantum Dot Solar Cells
Joel Jean 1 , Thomas Mahony 1 , Deniz Bozyigit 1 , Melany Sponseller 1 , Jakub Holovský 2 , Moungi Bawendi 1 , Vladimir Bulovic 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Czech Academy of Sciences, Prague Czechia
Show AbstractColloidal quantum dot (QD) solids have improved rapidly as solar photovoltaic (PV) absorbers in spite of their disordered nature. Disordered PV materials face a radiative efficiency limit lower than the ideal Shockley-Queisser bound due to increased recombination through band tail states. However, previous investigations of band tailing in QD films have been limited by indirect measurement techniques, leading to uncertainty in the ultimate efficiency of QD solar cells. Here we use photothermal deflection spectroscopy (PDS) to characterize disorder-induced absorption band tailing in PbS QD films across different QD sizes, ligands, and processing conditions. Materials used in the highest-performing devices today exhibit sharp band tails, with Urbach energies of 22±1 meV for iodide-treated films and 24±1 meV for ethanedithiol (EDT)-treated films, comparable to commercial polycrystalline thin-film PV absorbers such as CdTe and CIGS. For solar cells based on these films, we calculate semi-empirical radiative efficiency limits of 31%, not far from the ideal detailed-balance limit. These results suggest that disorder does not severely constrain the long-term potential of PbS QD solar cells.
NM06.11: Hot Electrons and Photocatalysis
Session Chairs
Martin Moskovits
Matthew Sheldon
Thursday PM, November 30, 2017
Hynes, Level 3, Room 311
1:30 PM - *NM06.11.01
Colloidal Chemistry to Advance Energy Storage in Chemical Bonds
Raffaella Buonsanti 1
1 , EPFL, Sion Switzerland
Show AbstractThe design of stable visible-light absorbers and catalysts for converting H2O and CO2 into value-added chemicals poses new challenges for chemists and material scientists. Here, the ability to tailor-make material platforms with tunable morphological characteristics in an unrestricted compositional range is critical for providing understanding of the performance sensitivities to different structural parameters.
Our work highlights how colloidal chemistry can aid to construct materials and to develop new concepts for storing energy in chemical bonds.1-5 We are tackling three different classes of nanocrystals: visible light absorbing metal oxides, quantum dots and metals. Metal oxides and quantum dots are studied as light absorbers to convert sun light into chemically active charges. The main challenges for metal oxides are the synthetic control and their usually poor ability to generate and separate charge carriers following photon absorption. While quantum dots do not suffer from these issues, they are often unstable in the harsh environment required to reduce or oxidize water. Metal nanoparticles are being explored as electrocatalysts for CO2 conversion. In this talk, I will discuss our recent work on copper nanocrystals as CO2 reduction catalysts3 and on the development of a protection scheme to stabilize thin films of perovskite quantum dots in water.5
1. A. Loiudice, J. Ma, W. S. Drisdell, T. M. Mattox, J. K. Cooper, T. Thao, C. Giannini, J. Yano, L.-W. Wang, I. D. Sharp, R. Buonsanti Adv. Mater. 2015, 27, 6733.
2. A. Loiudice, J.K. Cooper, Lucas H. Hess, T.M. Mattox, I.D. Sharp, R. Buonsanti Nano. Lett. 2015, 15, 7347.
3. A. Loiudice, P. Lobaccaro, E.A. Kamali, T. Thao, B.H. Hung, J.W. Ager, R. Buonsanti Angew. Chem. Int. Ed. 2016, 55, 5789
4. C. Gadiyar, A. Loiudice, R. Buonsanti, J. Appl. Phys. D 2017, 50, 074006.
5. A. Loiudice+, S. Saris+, E. Oviesi, D. Alexander, R. Buonsanti, Angew. Chem. Int. Ed. 2017, 56, 10696
2:00 PM - *NM06.11.02
Dynamics of Charge Transfer between Semiconductor Nanocrystals and Redox Catalysts
Gordana Dukovic 1
1 , University of Colorado Boulder, Boulder, Colorado, United States
Show AbstractThis presentation will focus on the coupling of semiconductor nanocrystals as light absorbers with redox catalysts for multi-electron transfer reactions to drive solar photochemistry. Reactions of interest include H2 generation, CO2 reduction, N2 fixation, and water oxidation. We have demonstrated that nanocrystal excited state behavior, charge transfer dynamics, and surface chemistry play a governing role in the overall photochemistry. This presentation will describe our most recent findings about how the reactions of interest can be driven and controlled through manipulation of nanocrystal excited state dynamics.
2:30 PM - *NM06.11.03
Plasmon-Accelerated Electrochemical Synthesis
Martin Moskovits 1
1 , University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractIn the intermediate future, when we have weaned ourselves off fossil fuels as our primary source of energy, solar electricity will undoubtedly become a dominant and abundant energy source. If so, the price of electricity will be especially low during daylight hours when supply outpaces demand. Such circumstances will almost certainly elevate the utility of electrochemical syntheses for producing valuable chemical products including fuels from such abundant precursors as CO2 and naturally occurring nitrates. Recently we showed [Wu et al., Adv. Phot. Mater. 2016, 4, 1041–1046] that plasmon-mediated photocatalysis can radically increase the rate of redox chemistry on Pd nanoparticles, presumably as a result of the generation of a large concentration of energetic electrons (and holes) that participate in some of the elementary steps of the reaction.
By judiciously shaping metal nanoparticles, one can create plasmonic systems that absorb sunlight over much of the UV-Visible spectrum. Moreover, (as has been known for many years) almost any nanostructured metal has plasmonic properties, including such earth-abundant species as Ni and Cu that can function both as efficient plasmonic absorbers and electrocatalysts. Using these strategies we show that solar energy could be harnessed in two ways: by creating abundant low-cost electrical power to drive electrochemical syntheses of valuable organic chemicals; and as a catalytic strategy whereby thermally-driven chemical processes can be accelerated through the intermediacy of plasmon-mediated hot electrons and holes
3:30 PM - *NM06.11.04
Hot Carrier Up-Conversion Luminescence in Nanocrystal Heterostructures
Matthew Sheldon 1
1 , Texas A&M University, College Station, Texas, United States
Show AbstractPlasmonic enhancement of non-thermalized, ‘hot’ carrier phenomena in metal nanostructures has prompted significant interest in the fundamental properties and applications of these short-lived, ballistic charge carriers. Here we report our studies on new classes of Cd-chalcogenide and all-inorganic Cs-Pb-Halide perovskite metal-semiconductor nanocrystal heterostructures with several ideal compositional and optical properties for probing hot carrier generation and transport. We have optimized synthetic protocols for more complex level alignments in Cd-based chalcogenide semiconductor-metal heterostructure nanoparticles in order to promote hot carrier transport and collection. We also report our recent success designing all-inorganic CsPbX (X = Cl, Br, I) perovskite nanoparticles with Au metal deposited on the particle surface. Importantly these new hybrid perovskite materials maintain quantum fluorescence yield > than 75%, which is especially remarkable when compared with the near-complete quenching of photoluminescence observed in similar Au-chalcogenide nanocrystals.
In combination with full-wave optical modeling (FDTD method), we have characterized samples using photoluminescence excitation (PLE) spectroscopy and dark field microcopy. By systematically mapping the potential landscape that defines the charge transfer dynamics, these optical studies provide fundamental insights into non-equilibrium charge phenomena across nanoscale electronic interfaces, crucial for identifying strategies that best optimize photocatalysis and photoelectrochemical reactions.
In particular, we report nanocrystal morphologies that exhibit a new mechanism of up-conversion luminescence (UCL), whereby the photo-induced transfer of hot electrical carriers from the metal region over the interfacial Schottky barrier can produce band-edge luminescence in the semiconductor, with energy greater than the incident light. This novel mechanism could have potentially significant advantages in applications that benefit from UCL, such as biological imaging, optical energy conversion, and optoelectronic signal processing and data storage. This behavior also informs fundamental thermodynamic issues related to energy conversion.
4:00 PM - NM06.11.05
Hot Carrier Generation in Nanoscale Optical Coatings for Near-Infrared Photodetection
Lisa Krayer 1 2 , Jeremy Munday 1 2
1 Electrical and Computer Engineering, University of Maryland, College Park, Maryland, United States, 2 , Institute for Research in Electronics and Applied Physics, College Park, Maryland, United States
Show AbstractOptical confinement in nanometer scale films through excitation of zeroth order Fabry-Perot (FP) modes has recently been utilized to obtain tunable, high absorption in ultra-thin semiconductor films on metal substrates. Here we propose and experimentally demonstrate an alternative material system that enables hot carrier generation and photon detection in the near-infrared based on this phenomenon. We extend the bandwidth of traditional semiconductor devices through absorption and hot carrier generation in nanoscale metal contacts. While plasmonic nanostructures have been shown to enable sub-bandgap photodetection in semiconductors, their fabrication often requires costly lithography processes and are difficult to incorporate into commercial devices. Our proposed device is enabled by simple, lithography free fabrication and is compatible with commercial processes. By selecting metals with approximately equal real and imaginary components of their refractive index (n ~ k for m = n + ik), it is possible to absorb ~80% of the broadband, sub-bandgap radiation in planar films as thin as 10 nm. The absorbed photons excite hot carriers that are injected into the semiconductor, enabling photocurrent generation from light with energy below the semiconductor bandgap energy. Applications for imaging detectors will also be discussed.
4:15 PM - NM06.11.06
Hot Electrons Generated by Nano-Gap Plasmons in the Near-Infrared Spectral Interval
Xiang-Tian Kong 1 2 , Zhiming Wang 1 , Alexander Govorov 2
1 , University of Electronic Science and Technology of China, Chengdu China, 2 , Ohio University, Athens, Ohio, United States
Show AbstractPlasmonic hot electrons generated by metal nanocrystals (NCs) have attracted a great deal of interest in the fields of photochemistry and photophysics. Here we report that hybrid plasmonic structures with nanogaps can generate very large numbers of hot electrons in the near-infrared spectral interval. Such plasmonic structures are composed of a plasmonic NC and a metal substrate. The generation rate of hot electrons is directly determined by the normal-to-surface electric field component inside the metal components, and strongly depends on the material and shape of the plasmonic NCs and on the nanogap thickness. The nanogaps can support a strong dipolar plasmon mode, whose resonance wavelength can be tuned in the near-infrared from 700nm to 2000nm by changing the shape and size of the nanogap. In particular, the gap plasmons supported by a gold or silver nanocube and a gold substrate create a new strong absorption peak in the near-infrared spectral interval. Thus, the hot electron generation rate associated with the decay of the gap plasmons becomes strongly enhanced as compared with the case of single metal NCs. Moreover, we show that the hot electron generation process in the near-IR spectral interval with the nanogap plasmons has comparable quantum efficiencies with the similar process in the UV-visible spectral interval for single metal NCs. The systems containing silver NCs and substrates show greater quantum efficiencies as compared with the case of Au nanostructures. Overall, we show that large populations of hot electrons and high quantum efficiencies can be achieved using plasmonic IR nanostructures with narrow gaps. Our results can be useful for plasmon-assisted photochemistry and photophysics.
4:30 PM - NM06.11.07
Energy Dependent Hot Carrier Generation via Surface Plasmon Polaritons
Wonmi Ahn 1 , Igor Vurgaftman 2 , Daniel Ratchford 3 , Pehr Pehrsson 3 , Blake Simpkins 3
1 National Research Council Postdoctoral Associate, U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 2 Optical Science Division, U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 3 Chemistry Division, U.S. Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractHot carriers generated by surface plasmon decay in noble metals can be injected into a semiconductor to drive useful chemical reactions such as photocatalytic energy conversion and degradation of organic compounds. Among many parameters in plasmonically-induced chemical reactions, energy tunability is critical for revealing fundamental mechanisms of charge transport. Recently, we have shown that surface plasmon polaritons (SPPs) generated at the interface between a noble metal / titanium dioxide heterostructure film and aqueous solution can drive methanol oxidation and water splitting with SPP resonances continuously tuned via incident excitation angle [1]. Here, we further investigated carrier energy dependent photocatalytic processes using seven different light sources with energies ranging from 1.6 to 2.4 eV. A strong excitation angle dependence in the photocurrents confirmed that electrochemical reactions were SPP-driven, and the energy dependence in the photon-to-carrier conversion efficiency allowed us to establish an accurate energy diagram of the metal / semiconductor heterostructure system. The hot-carrier generation, transport, and transmission efficiencies were also calculated as a function of photon energy, and the resulting injection efficiency was in good agreement with the measured values. Our study demonstrates that by tuning the energy of a SPP system, generation and injection of hot carriers can be optimized for a specific chemical reaction, which makes the SPP system an excellent platform for plasmon-induced photocatalysis.
[1] Ahn, W., Ratchford, D. C., Pehrsson, P. E., and Simpkins, B. S. “Surface plasmon polariton-induced hot carrier generation for photocatalysis” Nanoscale, 2017, 9, 3010 - 3022.
4:45 PM - NM06.11.08
Nonthermal Hot-Electron Generation and Relaxation in Plasmonic Metasurfaces
Matthew Sykes 1 , Jon Stewart 2 , Gleb Akselrod 2 , Xiang-Tian Kong 3 4 , Zhiming Wang 3 , David Gosztola 1 , Alex Martinson 5 , Daniel Rosenmann 1 , Maiken Mikkelsen 2 6 , Alexander Govorov 4 , Gary Wiederrecht 1
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 2 Electrical and Computer Engineering, Duke University, Durham, North Carolina, United States, 3 Institute of Fundamental and Frontier Sciences and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu China, 4 Physics and Astronomy, Ohio University, Athens, Ohio, United States, 5 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 6 Physics, Duke University, Durham, North Carolina, United States
Show AbstractUpon photoexcitation in plasmonic metallic nanostructures, surface plasmons rapidly decay to produce hot electrons near the metal’s surface. These charge carriers can initially possess a nonthermal energy distribution that subsequently thermalizes through electron-electron scattering. Using a metasurface of substrate-coupled silver nanocubes in a nanopatch antenna geometry, we demonstrate the enhanced generation of nonthermal hot electrons through both modeling and experiment. Due to the optical field hot spots within the gap of the antennas and their low plasmon resonance frequencies, nonthermal electrons with energies up to the photon energy are created through quantum optical transitions with non-conservation of linear momentum. Using ultrafast transient absorption spectroscopy, we then resolve the spectral and temporal response of nonthermal carriers on the femtosecond timescale. Due to the perturbation of multiple plasmonic modes and interband transitions within the metasurface, we are able to probe the optical response over 1000 nm from the ultraviolet to near-infrared. We find evidence for three different subpopulations of nonthermal carriers with distinct spectral and kinetic signatures. We propose these arise from anisotropic electron-electron scattering within the band structure of the metal.
NM06.12: Poster Session IV: Devices and Applications
Session Chairs
Friday AM, December 01, 2017
Hynes, Level 1, Hall B
8:00 PM - NM06.12.01
Synthesis of MoTe2O7 Nanowires and Carbon Composite with High Catalytic Performance for Hydrogen Evolution Reaction
Sang Hwa Lee 1 , Jung Eun Lee 1 , Min Hyung Lee 1
1 Applied Chemistry, KyungHee University, Yongin, Gyeonggi, Korea (the Republic of)
Show AbstractVarious transition-metal dichalcogenide (TMD) groups have been studied extensively due to their special catalytic performance in hydrogen evolution reaction (HER). One of the challenges to enhance the catalytic performance of TMD materials is an improvement of long-term stability in the electrolytes. In this study, we synthesized MoTe2O7 nanowires using simple hydrothermal synthesis and applied those nanowires as HER catalyst. Pristine MoTe2O7 nanowires show a tafel slope of 95 mV/dec. and further improved up to 55 mV/dec. by forming composite with carbon. Furthermore, growth mechanism of MoTe2O7 nanowire from MoOx basal structure are studied to understand relation of material composition and HER acitivty.
8:00 PM - NM06.12.02
Plasmonic Periodic Nanodot Arrays for Organic Photovoltaic Cells with >10% Efficiency via Laser Interference Lithography
Ju Won Lim 1 , Yulin Oh 2 , Yu Jin Jang 1 , June Sang Lee 1 , Byeong-Kwon Ju 2 , Dong Ha Kim 1
1 Chemistry and Nano Science, Ewha Womans University, Seoul Korea (the Republic of), 2 Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractIn this study, we demonstrate a viable optical engineering technique enabling the development of high-performance plasmonic organic photovoltaic devices. Laser interference lithography was explored to fabricate metal nanodot (MND) arrays with elaborately controlled dot size as well as periodicity, allowing spectral overlap between the absorption range of the active layers and the surface plasmon band of MND arrays. Incorporation of MND arrays with ∼91 nm dot size and ∼202 nm periodicity embedded in a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer remarkably enhanced the average power conversion efficiency (PCE) from 7.52 up to 10.11%, representing one of the highest PCE and degree of enhancement (∼34.4%) levels compared to the pristine device among plasmonic organic photovoltaics reported to date. To clarify the efficiency enhancement, we investigated three mechanisms by both optical and electrical analyses using finite difference time domain (FDTD) simulation and conductive atomic force microscopy study. The MND arrays located between the HTL and bottom electrode induced both light scattering and a strong localized surface plasmon resonance (LSPR) effect in the photovoltaic devices, thus enhancing the light absorption at the photoactive layer. In addition to the LSPR effect of MND arrays, we also analyze the advantages in terms of electrical properties, facilitating the charge transport and extraction through the MND arrays. In conclusion, we propose that configuration-adjusted plasmonic MND arrays fabricated by the laser interference lithography process can be a powerful method, paving the way for development of addressable, advanced, and large-scale photovoltaic and optoelectronic devices.
8:00 PM - NM06.12.03
Synthesis of Composition-Controllable Ternary Nanoparticles as Highly Active and Stable Catalysts
Hannah Cronk 1 , Daniel Adrion 1 , Zakiya Skeete 1 , Fangfang Chang 1 , Jin Luo 1 , Valeri Petkov 2 , Chuan-Jian Zhong 1
1 Chemistry, State University of New York at Binghamton, Binghamton, New York, United States, 2 Physics, Central Michigan University, Mount Pleasant , Michigan, United States
Show AbstractThe improvement in quality living and environmental sustainability is dependent on the advancement in green energy conversion systems such as fuel cells. One issue with most existing fuel cells is the need of catalysts which involve high cost of materials due to use of high loading of noble metals and their propensity to CO poisoning over time. Platinum and palladium have the best electrocatalytic activities but are scarce and therefore expensive. From industrial perspective, one important pathway to the reduction of the cost of the catalyst is alloying them with earth abundant transition metals such as nickel, copper, etc. It has been found that by alloying the metals, not only the cost is reduced but the stability and the activity could be significantly enhanced. These alloys can outperform the pure platinum or palladium catalysts. A key challenge with the alloy nanoparticles is controllability of their synthesis in terms of the size, shape, structure and composition of the nanoparticles. This presentation will report on recent findings of our investigation of the synthesis of platinum-nickel-cobalt nanoalloys, focusing on the size, shape, and composition controllability. Our results show that the rational manipulation of the synthetic parameters produces ternary nanoparticles produces with narrow size distribution and controllable compositions. The detailed morphological and structural characterizations of the ternary nanoalloys will also be discussed, attempting to better understand the nanostructural correlation with the catalytic properties.
8:00 PM - NM06.12.04
Synthesis and Application of Cobalt Oxide Nanocrystals of Different Phases and Morphologies in Electrocatalysis
X Yiliguma 1 , Gengfeng Zheng 1 , Yun Tang 2
1 Laboratory of Advanced Materials, Fudan University, Shanghai China, 2 Department of Chemistry, Fudan University, Shanghai China
Show AbstractOur demand for green and sustainable energy has been on a rise. Electrochemical energy conversion and storage is one of the approaches to this issue. While noble metal-based materials are well known with the promising performance their practical application is hindered by their high price and low abundance. In this regard, transition metal oxide (TMO) materials has attarcted lots of research interest, due to their relatively high performance, lower cost and easy access, in electrochemical catalysis, lithium ion batteries, supercapacitors, etc.1 Cobalt oxide, one of the widely studied TMO, has shown high electrocatalytic activity for oxygen evolution (OER) 2, oxygen reduction (ORR) 3 and CO2 redcution (CO2RR) reactions 4.
Herein, we present the synthesis of cobalt oxide nanocrystals (NCs) with different phases (rock salt and wurtzite) and morphologies (bridged-multi-octahedral 5, stacking-sheets-like, nanosheet, rods-grown-on-plate) through a similar method previously developed by Hyeon group 6. We studied the crystal growth mechanisms of each morphology to identify the improtant factors such as the oriented attachment, crystal-structure assymetry, and the valence state of the cobalt in the precursor for the formation of the specific phase and morphology. The electrocatalytic OER and ORR performance of these different cobalt oxide NCs was further studied. Our work could help better understand the sturcture - performance relation to rationally tune the electrocatalytic activity through NC crystal-structure engineering.
Reference
[1] C. Yuan, et al., Angew. Chem. Int. Ed., 2014, 53, 1488-1504.
[2] Y. Wang, et al., Adv. Science, 2015, 2: 1500003.
[3] T. Ling, et al., Nature Commun., 2016, 7: 12876.
[4] S. Gao, et al., Nature Commun., 2017, 8: 14503.
[5] Yiliguma, et al., J. Mater. Chem. A, 2017, 5, 7416-7422.
[6] J. Park, et al., Nat. Mater., 2004, 3, 891-895.
8:00 PM - NM06.12.05
Gold Nanosphere-Embedded Silver Cubic Nanomesh Using Partially Sacrificial AgCl Templates for Environmenral Applications
Jae-Seung Lee 1 , Jangho Joo 1
1 , Korea University, Seoul Korea (the Republic of)
Show AbstractWe present a novel synthesis for gold nanosphere-embedded silver cubic nanomesh materials using AgCl templates via a template-assisted co-reduction method in aqueous media. The AgCl nanocubes are first prepared, combined with gold and silver precursors, and finally co-reduced to lead to the reduction of gold precursor into gold nanoparticles on the surface of AgCl templates, followed by the reduction of AgCl and silver precursor into silver cubic nanomesh structures. The delicately designed silver nanomesh structures embedded with gold nanospheres are demonstrated by removing the AgCl template. We investigate the synthetic mechanism, structural properties, and surface functionalization using spectroscopic methods. We further examine the environmental applications of the cubic nanomesh structures based on their plasmon-photocatalytic properties for the degradation of organic pollutants and removal of highly toxic metal ions. The photocatalytic activity of the cubic nanomesh structures is superior to those of conventional TiO2 catalysts owing to their high surface area and excellent chemical stability. We also confirm that their catalytic functionality even in natural water. The synthetic development presented in this study could exploited for the highly elaborate yet facile design of other nanomaterials with outstanding chemical and physical properties.
8:00 PM - NM06.12.06
Large-Scale Synthesis of Freestanding Layer-Structured PbI2 and MAPbI3 Nanosheets for High-Performance Photodetection
Ziyao Zhou 1 , Changyong Lan 1 , Johnny Ho 1 , Lei Shu 1 , Dapan Li 1 , Sen Po Yip 1 , Dong Ruoting 1
1 , City University of Hong Kong, Hong Kong China
Show AbstractAbstract: Due to the possibility to be thin down to the atomic thickness, exhibiting fascinating chemical and physical properties, layered materials have attracted extensive amounts of attentions. In particular, PbI2, a kind of layered material, and its perovskite derivatives, CH3NH3PbI3 (i.e. MAPbI3), have been demonstrated with excellent photoresponsivities for efficient photodetection as well as photovoltaic devices. In this work, we report the successful synthesis of large-scale, highly-dense and freestanding PbI2 nanosheets by manipulating the local surface reaction kinetics during the growth by physical vapor deposition. As contrasted to the conventional 2D growth along the substrate surface, we synthesize the nanosheets via effective nucleation of micro-planes with different angles relative to the in-plane direction of underlying rough-surfaced substrates. This results in freestanding nanosheets with high-density. Meanwhile, the synthesized PbI2 nanosheets are highly crystalline with superior photosensing characteristics. When configured into photodetectors, the fabricated photodetector exhibits a photoresponsivity of 410 mA/W, a detectivity of 3.1×1011 Jones, and a fast response with the rise and decay time constants of 86 ms and 150 ms, respectively, under a wavelength of 405 nm. In addition, these PbI2 nanosheets can also be completely converted into MAPbI3 materials via chemical
vapor deposition with a strong photoluminescence and an improved photoresponsivity up to 40 A/W. The impressive performance parameters of the PbI2 nanosheet are competitive to those of state-of-the-art layered materials based photodetectors, revealing the technological potency of these freestanding nanosheets for next-generation high-performance optoelectronics.
8:00 PM - NM06.12.07
Engineering Biomimetic Supraparticle Assemblies for Catalysis
Naomi Ramesar 1 , Nicholas Kotov 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractNature has developed highly specific and efficient catalysts capable of synthesizing complex organic compounds, such as the synthesis of sugars in photosynthesis. Due to the efficiency of these reactions, considerable effort has been geared towards the development of artificial reaction schemes that can replicate the complexity found in nature. The success of producing these biomimetic systems can lead to an improved understanding of biological systems in nature, which often translates to better engineering of catalysts in the form of enhanced stability and reduced cost.
The use of inorganic nanoparticles (NPs) for developing biomimetic systems presents a favorable choice due to its similarities with proteins. Advancement in the synthesis of NPs has allowed for tunable size, shape, charge, and surface functionality to be achieved, thus, allowing NPs to self-assemble into terminal superstructures similar to biological components. These superstructures, known as supraparticles (SPs), have shown to improve the functionality over their NP constituents due to collective and synergistic interactions between subunits. The tight structural integration of components in SPs present the capacity to enhance the stability of catalysts and mitigate the aggregation of individual constituents by offering separation while remaining immobilized. As a result, SPs are a key tool in the advancement of artificial reaction schemes.
The formation of SPs are not limited to the self-organization of inorganic NPs; hybrid assemblies, containing biological components, such as proteins, are also possible. Although there is evidence that suggests SPs have a positive impact on catalysis, there is limited research in the literature regarding SP catalysis, highlighting the need for improved understanding and engineering of such assemblies.
This work focuses on the formation, characterization, and application of both hybrid and inorganic SP assemblies. Hybrid SPs composed of cadmium telluride NPs, cytochrome C, and formate dehydrogenase are explored for the reduction of CO2 to formic acid in the presences of a co-factor enzyme. While inorganic metal-sulfide SPs are investigated as a potential photocatalyst for self-replication reactions.
8:00 PM - NM06.12.08
Doped ZnO Semiconductor Nanocrystals for Magnetic Sensing Applications
Eugene Chubenko 1 , Vitaly Bondarenko 1
1 Micro- and Nanoelectronnics, Belarusian State University of Informatics and Radioelectronics, Minsk Belarus
Show AbstractSemiconductor ZnO nanocrystals are the very attractive material for numerous applications since the several simple routes of their fabrication exist. Low temperature CVD, sol-gel, chemical and hydrothermal deposition are among them. The main advantages of hydrothermal deposition are the low process temperature, high crystalline product quality and possibility to dope the ZnO semiconductor nanocrystals directly during deposition. ZnO nanocrystals doped with transitional metals are considered as a candidates for fabrication of diluted magnetic semiconductors. In this work we have investigated the influence of the deposition parameters on the size- and shape-dependent properties of ZnO nanocrystals fabricated by chemical hydrothermal method and doped with nickel and cobalt. Aqueous equimolar solution of zinc nitrate with hexamethylenetetramine additive was used for hydrothermal deposition. Doping of ZnO with nickel and cobalt was carried out during the deposition by addition of appropriate additives to the deposition bath. The concentration of the precursors, temperature and process duration varied during the experiments. Concentration of transitional metals varied from one fiftieth part to one five hundredth of the zinc nitrate concentration. Deposition solution temperature varied in the range 80 – 90 °C. The duration of ZnO deposition process was from 2 to 4 hours. It has been found that optimal conditions for the deposition of doped ZnO are 80 °C, pH = 6 and duration – 3 h. In these regimes self-assembly of ZnO nanocrystals were formed. According to the XPS analysis the concentration of transitional metals in the ZnO nanocrystals is 0,03 – 0,04 at.%. Introduction of nickel and cobalt drastically reduced the efficiency of photoluminescence. However, the formation of magnetic metal clusters in the ZnO crystalline lattice led to the ferromagnetic behavior which was confirmed by the ponderomotoric measurements in the temperature range 77 – 650 K. Applications of the magnetic ZnO nanocrystals for spin transistors, spin-polarized LED and magnetic sensors will be discussed.
This work was partially supported by the Belarus Government Research Programs “Photonics, opto- and microelectronics” (Grant 2.1.02) and “Physical materials science, novel materials and technologies” (Grant 1.15).
8:00 PM - NM06.12.09
Hydrothermal Synthesis and Investigation of Sunlight Driven Catalytic Activity of La Doped CuO Nanostructures
Cosmas Muiva 2 , Lucia Lepodise 2 , Albert Juma 2 , Romang Bosigo 2 , Pearson Luhanga 1
2 Physics, Botswana International University of Science and Technology, Palapye Botswana, 1 Physics, University of Botswana, Gaborone Botswana
Show AbstractNanostructured semiconducting transition metal oxides have been the subject of relentless research pursuit due to their useful intrinsic and size dependent properties. Among them sunlight driven photocatalysis is seen as one of the potential green and environmentally friendly processes for environmental pollution mitigation and water treatment. Cupric oxide (CuO) is a p-type semiconductor material with diverse applications in photovoltaic and photo-thermal energy conversion, catalysis, gas sensing, dye sensitised solar cells, lithium ion battery technologies and magnetic storage. In this work, a series of La (La = 0, 2, 3, 6, 10, 12 at.%) doped CuO nanostructures were synthesised by a simple, low cost and facile hydrothermal method. Ethylene glycol (EG) was used as a surface assisting agent. The structural, optical and photocatalytic properties of the products were investigated. X-ray diffraction (XRD), Raman spectroscopy and Energy dispersive spectroscopy (EDS) confirmed formation of CuO. For doping concentertion of 0 – 6 at.%, all the XRD peaks observed were indexed to pure monoclinic phase of CuO with strong orientation towards the (002) crystallographic direction. No peaks corresponding to other crystalline phases or Cu and Cu(OH)2 impurities were observed. Higher doping was accompanied by formation of a secondary less known La(3+);O(2-);carbonate (CLa2O5). Scanning electron microscopy revealed nanoshrimps like structures for the undoped sample and nanostructures of various shapes and aspect ratios for the doped samples including rice shaped, rods, ellipses and spheres. Optical absorption spectra pointed to absorption mainly in the UV and Vis spectral regions. The photocatalytic efficiency of the nanostructures was investigated by monitoring the degradation of methylene blue (MB) as a model compound under UV-Vis light (450 - 800 nm) and it was observed that the degradation rate was influenced by the dopant concentration.
8:00 PM - NM06.12.10
Nanostructured Spinel Ferrite Materials for Photoelectrochemical Water Splitting
Kristin Kirchberg 1 , Anna Becker 1 , Christian Suchomski 1 , Roland Marschall 1
1 , Justus-Liebig-Univ Giessen, Giessen Germany
Show AbstractWe have developed a straightforward microwave synthesis protocol using acetylacetonate and acetate precursors to produce nanocrystals of the earth-abundant cubic spinel ferrites MgFe2O4 and ZnFe2O4[1], which are promising materials for both photoelectrochemical and photocatalytic water splitting under visible light irradiation due to their narrow band gaps (~ 2.0 eV) and matching band positions. The crystallite size can be tailored by post-synthetic heat treatment or seed-mediated growth method. Samples were characterized employing transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), Raman spectroscopy and N2 physisorption, indicating highly-crystalline, single phase nanoparticles with specific surface areas of around 200 m2/g and good colloidal stability in non-polar solvents. Phase transfer into aqueous medium has been performed using different organic capping ligands, resulting in stable dispersions with a narrow size distribution. First results of photocatalytic experiments will be presented.
In addition, well-ordered mesoporous ZnFe2O4 thin films were fabricated by sol-gel synthesis, using a polymer-templating approach previously reported by Haetge et al.[2]. By means of the amphiphilic diblockcopolymer poly(isobutylene)-block-poly(ethylene oxide) (PIB50-b-PEO45), ordered mesopores are obtained after dip-coating by evaporation-induced self-assembly [3] followed by heat treatment. Scanning electron microscopy (SEM) confirms the porous morphology with average pore diameters of 12-15 nm. Raman spectroscopy and XRD Rietveld analysis revealed phase pure ZnFe2O4 with a crystallite size of 15 nm of. Furthermore,photocurrent and Mott-Schottky measurements were performed at different pH values to determine the flat band potential and photocurrent density of the thin film electrodes calcined at various temperatures.
References
[1] C. Suchomski, B. Breitung, R. Witte, M. Knapp, S. Bauer, T. Baumbach, C. Reitz, T. Brezesinski, Beilstein J. Nanotechnol. 2016, 7, 1350.
[2] J. Haetge, C. Suchomski, T. Brezesinski, Inorg. Chem. 2010, 49, 11619.
[3] C. J. Brinker et al., Adv. Mater. 1999, 11, 579.
8:00 PM - NM06.12.11
Metal-Semiconductor Heteronanorystals with Desired Configurations for Plasmonic Photocatalysis
Dae Han Wi 1 , Sang Woo Han 1
1 Chemistry, KAIST, Daejeon, South Korea, Korea (the Republic of)
Show AbstractPrecise control over the topology of plasmonic metal-semiconductor heteronanostructures is essential for fully harnessing their plasmonic function and hence for designing innovative solar energy conversion platforms. Here, we present a rational synthesis strategy for the realization of plasmonic metal-semiconductor heteronanocrystals (HNCs) with intended configurations through the site-selective overgrowth of semiconductor Cu2O on desired sites of anisotropic Au NCs. Hexoctahedral (HOH) Au NCs enclosed by 48 triangular high-index {321} facets were chosen as a plasmonic NC component, due to their highly anisotropic structural characteristics imparted by a high-density of vertices with distinctively different curvatures. Through exploitation of the inherent structural features of HOH Au NCs, the growth mode of Cu2O on the HOH Au NCs could be manipulated with the assistance of relevant stabilizing agents. As a consequence, HNCs with explicitly different coupling manners between the HOH Au NCs and Cu2O were selectively generated: 1) Auvertex-Cu2O HNCs formed by the overgrowth of Cu2O exclusively on the 8 vertices of the HOH Au NCs pointing toward the <111> direction (vertices<111>), 2) Auvertex-exp-Cu2O HNCs formed by the growth of Cu2O on the HOH Au NCs apart from the regions of the vertices<111>, and 3) AuHOH@Cu2O HNCs formed by the isotropic growth of Cu2O on the entire surface of the HOH Au NCs. Both the exploitation of structural characteristics of Au NCs and the selective stabilization of their surfaces are keys to the construction of HNCs with a specific configuration. Our approach can provide an opportunity to precisely explore the link between the solar energy conversion efficiency and the structure of HNCs as well as to obtain important insights into the underpinning mechanism. HNCs produced by Cu2O overgrowth preferentially on the multiple high-curvature sites of Au NCs exhibited prominent photocatalytic hydrogen production activity due to efficient charge separation by strong plasmon excitation at the Au-Cu2O interface and subsequent sustainable hot electron transfer from Au to Cu2O.
8:00 PM - NM06.12.12
Solution-Processed Short-Wave Infrared PbS Colloidal Quantum Dot/ZnO Nanowire Solar Cells with High Open Circuit Voltage
Takaya Kubo 1 , Haibin Wang 1 , Jotaro Nakazaki 1 , Hiroshi Segawa 1
1 , The University of Tokyo, Tokyo Japan
Show AbstractEfficient utilization of the solar energy in the near infrared (NIR) and short-wave infrared (SWIR) regions is one of the keys to achieve ultra-high efficiency solar cells such as multi-junction solar cells. PbS colloidal quantum dots (CQDs) have been gaining much attention as promising constituent materials for the solar cells because the absorption band of PbS QD can be tuned from the visible to infrared regions. However, short exciton and/or carrier diffusion lengths of PbS QD films limit the PbS QD active layer thickness, therefore limiting light harvesting efficiency. There is then a trade-off between carrier transport efficiency and light harvesting efficiency. In the light of this situation, we have developed PbS CQD-based solar cells with ZnO nanowires (NWs) to achieve good carrier pathways and high light harvesting efficiency simultaneously [1, 2].
In this paper, a systematic investigation into the performance of PbS QD/ZnO NW solar cells in the NIR and SWIR regions was carried out. The solar cells were confirmed to convert a wide range of solar energy (3.54–0.62 eV, corresponding to 0.35–2.0 μm). We found that the solar cells working in the SWIR region had a high open-circuit voltage (Voc). A relatively high Voc of 0.25 V was achieved even in solar cells whose photocurrent onsets were at approximately 0.64 eV (1.9 μm); this Voc is as high as that of Ge solar cells, which have been used for III-V compound semiconductor triple-junction solar cells. These results indicate that solution-processed colloidal QD solar cells with ZnO NWs are promising candidates for the middle and/or bottom subcells of multijunction solar cells.
“PbS-Quantum-Dot-Based Heterojunction Solar Cells Utilizing ZnO Nanowires for High External Quantum Efficiency in the Near-Infrared Region”, H. Wang, T. Kubo, J. Nakazaki, T. Kinoshita, and H. Segawa, J. Phys. Chem. Lett., 4, 2455 (2013).
“Enhanced carrier transportation distance in colloidal PbS QD-based solar cells using ZnO nanowires”, H. Wang, V. Gonzalez-Pedro, T. Kubo, F. Fabregat-Santiago, J. Bisquert, Y. Sanehira, J. Nakazaki, and H. Segawa, J. Phys. Chem. C, 119, 27265 (2015).
8:00 PM - NM06.12.13
High-Throughput Development of CdS-CdSe Quantum Dots with Graded Alloy Interfaces for Solid State Lighting
Haoran Yang 1 , Michael Campos 2 , Leslie Hamachi 2 , Iva Rreza 2 , Jonathan Owen 2 , Emory Chan 1
1 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Chemistry, Columbia University, New York, New York, United States
Show AbstractCadmium chalcogenide quantum dots are emerging optical materials for solid state lighting due to their narrow photoluminescence spectra that are tunable across the visible spectrum. Manufacturing these nanomaterials is a synthetic challenge since sophisticated core-shell structures are necessary for achieving high photoluminescence quantum yield (PLQY) and environmental stability. Recent studies have suggested that a large passivating shell and a graded alloy interface between the core of a nanoparticle and its shell reduce Auger recombination in these nanoparticles and enhance their PLQY. Although the structural control necessary to synthesize such complex heterostructures has been demonstrated using repeated sequential reactions, such as successive ionic layer adsorption and reaction (SILAR), these multi-step reactions are tedious and time-consuming.
Here, we utilize high-throughput theoretical and synthetic techniques to develop an alternate approach for producing graded-alloy CdS-CdSe nanoparticles for solid state lighting applications. Our approach leverages a mixture of sulfur and selenium precursors with precisely tunable decomposition kinetics. As the sulfur and selenium precursors decompose with different rates, heterostructures with either abrupt or graded interface can be achieved. The parameter space of the synthesis can be exceedingly large since temperature, reaction time, reagent concentration, and precursor conversion rate constants all have a profound impact on the reaction pathway and the final structures. To narrow down the parameter space, we first developed kinetics models to predict the radial elemental distribution of the resulting heterostructures. These models were further validated by using the high-throughput automated robotic techniques developed at the Molecular Foundry to screen a library of chalcogenide precursor mixtures and optimize the optical properties of the resulting heterostructures. Our modeling reveals, and our high-throughput experiments confirm, that the desired structures and optical properties can only be achieved within a narrow range of reaction parameters within this multidimensional parameter space. We show that by our high-throughput approach, the optimized structures with tunable emission wavelength, and narrow emission linewidth can be obtained, which, upon shelling with another CdS layer, are suitable for solid state lighting. Furthermore, our high-throughput approach can be generalized for optimization of the synthesis of the other metal chalcogenide heterostructures.
8:00 PM - NM06.12.14
Production of Efficient PbS Quantum Dot Solar Cells via Inkjet Printing
Ella Wassweiler 1 , Giovanni Azzellino 1 , Nicole Moody 2 , Moungi Bawendi 2 , Vladimir Bulovic 1
1 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractSolution processing is a promising route for the manufacture of large-area, flexible, lightweight and inexpensive solar cells with short energy payback time and high specific power. With record power conversion efficiencies of lead sulfide (PbS) quantum dot (QD) solar cells increasing beyond 11% [1], colloidal PbS QD solutions are viable candidates as starting materials for solution-processed photovoltaics (PVs). Indeed, QD PVs show a superior stability as compared to organic or perovskite solar cells [2] and can be engineered with proper ligands to optimize the energy band alignment needed to maximize the power conversion efficiency.
In this work we address the challenge of large area manufacturing of PbS QD PVs, which is presently hampered by the use of spin coating deposition, where QDs are dispersed in a solution and spun over a substrate, then quickly treated in a solid state ligand exchange process to boost efficiency. Rather than relying on the spin coating deposition, which poorly utilizes solutions of photo-active materials through a lack of patterning and a large solution runoff during deposition, we adopt piezoelectric inkjet printing to manufacture our solar cells. We develop a PbS ink, where we exchange QD ligands in solution, leading to a practical one step manufacturing of PbS thin films. Through the precise control of the droplet formation and drying characteristics of our PbS QD solutions, we demonstrate how different printing conditions impact the power conversion efficiency of the final solar cell. In addition, by depositing the remaining layers using tools common to industrial production, we are able to create PbS QD solar cells compatible with large-scale manufacturing and in line with the current state-of-the-art spin coated PbS photovoltaics.
[1] Liu M., et al. Nat. Mater. 2017, 16, 258-263.
[2] Chuang C. H. M. , Brown P. R., Bulović V., Bawendi M. G, Nat. Mater. 2014, 13, 796-801.
8:00 PM - NM06.12.15
Adsorption and Photocatalytic Removal of MB Dyes by WO3 Nanorods
Chunghee Nam 1 , Sung-Myung Ryu 1
1 , Hannam University, Daejeon Korea (the Republic of)
Show AbstractTungsten oxides have attracted much interest not only due to their fundamental scientific issues but also their various technological applications such as environment-, energy- and electronic- materials. Among them, dye-adsorption and photo-catalyst properties of WO3 nanomaterials have been independently studied due to their large surface area and low-band gap.[1,2] In this presentation, WO3 nanorods have been synthesized by hydrothermal methods at various temperatures using sodium tungstate (Na2WO42H2O) as a precursor material. In order to obtain one-dimensional nanostructures, we have added a directional capping agent of citric acid during the preparation of solution. The morphology and structure of synthesized WO3 samples were characterized by scanning electron microscopy, x-ray diffraction technique, transmission electron microscopy, and BET methods for surface area measurements. Dye adsorption properties were investigated by using a series of MB solutions with a specific amount of WO3 powders in a dark room, where duration time was changed to monitor adsorption capacities. In addition, pH-dependences of adsorption were studied to understand relations between the surface charges of WO3 powders and the cationic dye. Finally, photocatalytic properties were examined by simple UV-absorption methods depending on UV exposure times after saturated adsorption time of MB dyes on the WO3 surfaces. The results will be presented in detail.
References
1. J. Y. Luo, Y. R. Lin, B. W. Liang, Y. D. Li, X. W. Mo, and Q. G. Zeng, RSC advances, 5, 100898 (2015)
2. A. A. Ashkarran, A. I. Zad, M. M. Ahadian, and S. A. M. Ardakani, Nanotechnology, 2008, 19, 0957 (2008)
8:00 PM - NM06.12.16
Beyond the Nanoparticle—Memory Devices Using Near Atomic Structures
Febin Paul 1 , Shashi Paul 1
1 , De Montfort University, Leicester United Kingdom
Show AbstractThe rise of the flash memory technology has completely revolutionized modern electronics by radically increasing the storage capacity per unit area [1]. Not very long ago people used to boast of their Commodore 64s that had a 64 kb RAM. But in the shadow of the magnificent success we have gained all that seems to be a chapter from the ancient history. The ITRS roadmap last year dubbed the memory technologies to be the ‘driving force’ of Moore’s law [2]. With the rise of better performing devices, the horizontal device area has been shrinking at a consistent pace. But the shrinking hasn’t been without flaws. Many problems like the leakage of the charges due to insulator layer defects still affect the device performance and charge retention [3].
This work explains the working of a memory device using a thin film consisting of particles of conducting and/or semiconducting materials in the quantum realm. Such nano-bits exhibit exotic properties which are greatly desirable for memory application. A thin film of such an active material acts as a quantum traps for charges. It is these traps that we employ to store information. Many quantum phenomena like the quantum confinement is experienced in a significant manner in such quantum scales. Due to this, the scale and size of the material being used in the fabrication of the device remain consistent with the small device area without compromising on the performance. Moreover, the fabrication process is also designed to be easily scalable and can result in a 3D architecture for memory devices.
Current-Voltage (I-V), data retention time (Current-Time), write-read-erase-read (W-R-E-R) measurements were conducted using HP 4140B pico-ammeter and Capacitance-Voltage (C-V) measurements of memory devices were conducted using an LCR bridge HP 4192A. All the electrical measurements were conducted in an electromagnetic shielded dark box.
REFERENCE:
[1] Galatsis, K. et al. "Emerging Memory Devices". IEEE Circuits and Devices Magazine 22.3 (2006): 12-21.
[2] International Technology Roadmap for Semiconductors 2.0, 2015 ed. Executive Report: 2015.
[3] Prime, D., S. Paul, and P. W. Josephs-Franks. "Gold Nanoparticle Charge Trapping And Relation To Organic Polymer Memory Devices". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 367.1905 (2009): 4215-4225.
8:00 PM - NM06.12.17
Quantifying the Effects of Charging on the Performance of Quantum Dot Light-Emitting Diodes
Han Zhu 2 , Giovanni Azzellino 1 , Jason Yoo 3 , Michel Nasilowski 3 , Moungi Bawendi 3 , Vladimir Bulovic 4
2 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe distribution of charges and their dynamics in a colloidal quantum dot light-emitting diode (QD-LED) strongly influences device performance. In the inverted QD-LED architecture, large imbalance between electron and hole injection can lead to low quantum efficiency, and is usually associated with a loss through non-radiative Auger recombination and current leakage due to insufficient charge blocking. Various approaches to remedy this include material engineering to reduce the rate of Auger-related exciton loss and device architecture modifications to improve injected charge balance at the QD film. However, excess charge accumulation within a QD-LED is still inevitable when operating at high brightness. Furthermore, the effects of charging at various bias levels and the interplay between free and trapped charges has not been well studied due to the complex energy landscape of quantum dots embedded within the semiconducting charge transport layers.
In order to systematically characterize how charging affects device operation, we fabricated QD-LEDs with one to two monolayers of highly luminescent CdSe/CdS core-shell dots to access regimes of low through very high degrees of charging. By simultaneously measuring the electroluminescence, photoluminescence, and time-resolved photoluminescence of the devices under bias, we identify distinct regimes where either Auger recombination or leakage current dominate the loss. A significant hysteresis which we observe under certain voltage sweeping conditions can be attributed to modification of the distribution of free charges and electric field by interfacial trapped charges. Spectroscopic signatures show that Coulombic interactions lead to the preferential formation of excitons on a subset of charged QDs at low bias. The demonstrated ability to quantitatively characterize multiple effects of charging in a QD-LED under various bias regimes suggests the design for highly bright and efficient QD-LEDs that can maintain high efficiency over a wider range of brightnesses.
8:00 PM - NM06.12.18
Laser Operation By Kesterite Chalcogenide Nanocrystals
Katarzyna Ozga 1 , Iwan Kityk 1
1 , Czestochowa University of Technology, Czestochowa Poland
Show AbstractLaser Operation By Kesterite Chalcogenide Nanocrystals
K.Ozga, I.V.Kityk
Institute of Optoelectronics and Measuring Systems, Faculty of Electrical Engineering, Czestochowa University of Technology, Armii Krajowej 17, 42-200, Czestochowa, Poland
e-mail:
[email protected]We demonstrate a possibility to change optoelectronics parameters for kesterite Cu
2ZnSnS
4 nanocrystalline films using external laser beams at 1540 nm, 532 nm, 1064 nm, 337 nm wavlengths. It is shown a possibility to vary the electronic features of the nanocrystallites with sizes varying within the 10 nm…70 nm. The different power densities (up to 800 MW/cm
2), light polarizations and polarizations of illuminations were used to operate by principal optoelectronics parameters: photo-carrier mobilities, nonlinear optical functions, photovoltaics efficiencies etc. The principal changes were observed for energy gaps (up to 15 %), carrier mobility (about 35 %), optical constants (13 %), reflection and transparency spectra. The energy of the fundamental laser beams was continuously tuned up to 800 MW/cm
2. The role of photo-thermal and electron-phonon contributions is discussed. The performed molecular dynamics and quantum chemical evaluations within the DFT approach have shown that the crucial role here belongs to near-the-surface sheet with thickness about 2…5 nm. The maximal changes of the carrier motilities and effective masses were achieved during simultaneous illumination by bicolor coherent 1540 nm/770 nm Er: glass laser beams. The regime of the treatment was carried out at 10 ns…30 ns pulses.
One of specific features for the such kind of compounds is a huge degree of phonon anharmonicitiy. The latter is described by a third rank polar tensor similarly to many space non-centrosymmetry compounds. The photoinduced treatment in this case favors an enhanced number of anharmonic phonons which are closely related to the formation of the local acentricity and varying the principal effective masses. The effects are studied both for particular nanocrystalline films as well for the films doped additionally by Se and Te. The role of the coherent laser light was to operate by the particular ground state and first excited dipole moments playing a crucial role for all the mentioned optoelectronic features. After switching off of the external light the particular dipole moment magnitudes were decreased leading to disappearance of the effect. The additional coating by thin polymer layer of PMMA favored an enhanced fixation of the effect. The presented studies open a new approach of production the chalcogenide photovoltaics materials operated by external light treatment. It may be also used for application of one synthesized material during multi-color coherent laser treatment.
8:00 PM - NM06.12.19
Plasmonics-Enhanced All-Optical Magnetic Recording at the Nanoscale
Feng Cheng 1 , Yihao Xu 1 , Yongmin Liu 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractThe rapid development of plasmonics has triggered a variety of research areas, such as photochemical transformations, plasmon-induced hot carriers, plasmonic metamaterials, and heat-assist magnetic recording(HAMR). HAMR technology utilizes a strongly localized optical field at the nanoscale to heat up magnetic recording medium, which allows the information to be recorded with areal density ~Pb/m^2. However, in such a process the recording won't happen in time scale shorter than 2 picoseconds due to the utilization of traditional writing poles. Over the last decade, researchers discovered the all-optical helicity-dependent switching(AO-HDS) phenomenon, which can potentially remove traditional writing poles and improve the storage speed by three orders of magnitude.
In this poster, we propose plasmonics-enhanced all-optical magnetic recording(PE-AOMR) that takes advantage of both plasmon-enhancement and AO-HDS phenomena. This technique promises high speed, low power consumption and high density magnetic recording. PE-AOMR can be realized by integrating plasmonic nanostructures on the magnetic recording media. Such an approach requires plasmon-enhanced circularly polarized field inside the recording media. One plasmonic structure that meets both requirements is the plasmonic cross-dipole antenna, which is constituted by two pairs of dipole antennas that are perpendicularly aligned. Based on the special designs of both cross-dipole antennas, we are able to achieve two field components with pi/2 phase difference and near unity amplitude ratio, which dilivers localized circularly polarized field to the recording media. To simulate the PE-AOMR phenomenon, we constructed a multi-physics model built up with two steps. Firstly, the nanoscale plasmonic enhancement is modelled with COMSOL multiphysics. Our results demonstrate well-defined locally-enhanced circularly polarized fields at specific wavelength. Secondly, we theoretically calculate the plasmonics-enhanced all-optical magnetic recording behaviors for left-handed and right-handed polarizations. The laser takes both heating and magnetic effects on the magnetic material. The heating effects is modelled with three-temperature model. And the magnetic effect is modelled as an external magnetic pulse calculated from the Inverse Faraday effect. Our model predicts plasmonics-enhanced all-optical magnetic recording phenomenon at the nanoscale.
In conclusion, we have proposed a multi-physics model for the PE-AOMR technique. With a pragmatically designed plasmonic cross-dipole antenna, we are able to obtain strongly localized laser fields with well-defined circularly polarization. Nanoscale magnetic switching behaviors are further modelled with the macroscopic three-temperature model.
8:00 PM - NM06.12.20
Fabrication of Green and Red InP/ZnSeS/ZnS QDs Multi-Layered Films for Display Backlight System
Sohee Kim 1 , Soyoung Lee 1 , Soyeon Yoon 1 , Young Rag Do 1
1 , Kookmin University, Seoul Korea (the Republic of)
Show AbstractWe synthesized green and red emitting InP/ZnSeS/ZnS quantum dots (QDs) using a colloidal hot injection method and fabricated multi-layered green and red InP/ZnSeS/ZnS QD films in order to realize the display backlight. The green and red InP/ZnSeS/ZnS QDs were synthesized with different indium precursors and core growth time. To increase the photoluminescence quantum yield (PLQY), we adopted multi-shelling steps by injecting anion and cation shells alternately. The peak wavelength of green and red QDs are 519nm and 599nm, and full-width at half maximum (FWHM) is 50nm and 63nm, respectively. Also, the PLQYs of QDs are more than 75%. Finally, we fabricated the green and red QD films with NOA that is UV curable binder and realized white backlight combined with multi-layered green and red QDs film and blue LED. We measured the optical properties such as luminous efficacy (LE), correlated color temperature (CCT), national television system committee (NTSC) and the color coordinates of above structures by an electroluminescence (EL) spectrophotometer.
8:00 PM - NM06.12.21
Plasmonic Metal-Hybrid Hydrogen Sensor Based on Semiconductor Nanocrystal Micro Ring Resonator
Ya Sha Yi 1 , Dachuan Wu 1 , Mao Ye 1
1 , University of Michigan, Dearborn, Michigan, United States
Show AbstractSemiconductor nanocrystals that support plasmon resonances can effectively confine light into nanoscale volumes, whereas semiconductor nanostructures that exhibit quantum confinement show unique size- and shape-dependent properties. Controlling the nanoscale structures utilizing metal-hybrid plasmonics opens promising opportunities to manipulate the semiconductor nanostructure properties with great precision and flexibility. In this work, we have proposed and demonstrated an ultrasmall plasmonic metal-hybrid hydrogen sensor based on a semiconductor nanocrystal microring resonator coated with a hydrogen-sensitive Pd/Pt layer. The device is very sensitive to low hydrogen concentration variation (0% to 1%), with nm resonance wavelength shift due to the excitation of plasmonic modes, which is at least an order of magnitude higher than the fiber based optical hydrogen sensor. We have also investigated the tradeoff between the portion coverage of the Pd/Pt metal-hybrid layer and the sensitivity. The width of the hydrogen-sensitive layer is also studied, and the minimum feature width is determined to be the length of the metal-hybrid waveguide evanescent wave. The ultra small size of the plasmonic metal-hybrid hydrogen sensor (4 × 4 μm2) will have the potential to be applied in integrated nanophotonic circuits with large integration capability and portability.
These plasmonic and quantum-confined semiconductor nanocrystal structures have important implications for tailoring electromagnetic radiation in various other applications like solar energy conversion, light-emitting devices, sensors, therapeutics, and information technology.
8:00 PM - NM06.12.22
Electrically Stable Ag Nanowire Electrode Passivated by Transparent Carbon Films for High Performance Flexible Thin-Film Heaters
Hae-Jun Seok 1 , Jae-Gyeong Kim 1 , Hyeong-Jin Seo 1 , Han-Ki Kim 1 , Jong-Kook Kim 2
1 , Kyung Hee University, Yongin-si Korea (the Republic of), 2 , Korea Institute of Materials Science, Changwon Korea (the Republic of)
Show AbstractWe developed highly stable Ag nanowire electrode passivated by transparent conducting carbon thin film for flexible and transparent thin film heaters (TFHs). Combining slot-die coating and filtered cathodic vacuum arc coating technologies, we fabricated flexible carbon/Ag NW/PET samples as a function of thickness of transparent carbon passivation layer to apply as a transparent electrode for flexible TFHs. Although the optical transmittance of the Ag NW electrode passivated carbon layer slightly decrased with increasing a thickness of carbon passivation layer, the sheet resistance of carbon/Ag NW/PET samples decreased from 8 to 14 Ohm/square due to bridge effect of conductive carbon passivation layer. At an optimized thickness (10 nm) of the carbon passivation layer, the carbon/Ag NW/PET sample showed a sheet resistance of 36.83 Ohm/square and optical transmittance of 79.61 %, which is acceptable in fabrication of flexible TFHs. In addition, the effects of carbon thickness on the mechanical properties of the carbon/Ag NW/PET samples were investigated in detail using specially designed inner/outer bending test, twisting test, rolling test, and dynamic fatigue test. To investigate the feasibility of carbon/Ag NW/PET samples, we fabricated flexible TFHs on the carbon/Ag NW/PET samples. The time-temperature profiles and heat distribution analysis demonstrated that the performance of the TFHs with the carbon/Ag NW/PET is better than that of a TFHs with Ag NW/PET electrodes. In particular, the TFHs fabricated on carbon/Ag NW/PET exhibited better stability and reliability than the TFHs on a Ag NW/PET due to the effective current spreading through the carbon layer and passivation of carbon layer. Successful operation of flexible and transparent TFHs on carbon/Ag NW/PET samples demonstrated the possibility of carbon passivated Ag NW film as a flexible electrode for high performant flexible and transparent TFHs.
8:00 PM - NM06.12.23
Drastic Performance Enhancement in AZO Photodetector by Incorporating AgNPs and CdSe Quantum Dots
Eunji Song 1 , Jieun Park 1 , Manjeet Kumar 1 , Vishwa Bhatt 1 , Ju-Hyung Yun 1
1 , Incheon National University, Incheon Korea (the Republic of)
Show AbstractIn recent years, a drastic increase in the demands of transparent electrodes have been witnessed because of its applications in most of the optoelectronic and photovoltaic devices such as solar cells, photodetectors, phototransistors, thin film transistors (TFTs), flat panel display, etc. In order to achieve high performance along with the transparent features of the material, it is necessary to examine the other important parameters such as cost of the material, stability, need of fabrication techniques, photoresponse etc. In recent years, many transparent metal oxide semiconductors have been investigated to fulfil the demands in various day today life applications. Among them, ZnO has been one of the most fascinating oxide semiconductor having transparency along with low cost, ease of fabrication, non-toxicity, stability and abundant availability on the earth. Many researchers have tried to investigate and utilize ZnO in various device applications in efficient ways. But in order to achieve further enhanced performance of ZnO based devices, researchers have carried out different kinds of studies by doping ZnO material with other metal oxides such as Ga, Al, In, Sn and so on. Till date, effect of doping of different kinds of material has been well studied but still there is a lack of high performance to fulfil the requirement of latest technologies. Photodetectors are one of the most important optoelectronic devices which has been investigated since many years. Among them ZnO based photodetectors have been a very important area of research and development.
In this article, Al doped ZnO photodetectors have been fabricated over p-type silicon substrates and photodetection has been examined. Since, the goal of this framework is to optimise the photodetection of AZO thin films. So, authors have fabricated different types of device architectures i.e. (a) AgNPs/AZO/Si (b) QDs/AZO/Si and (c) QDs/AgNPs/AZO/Si and examined the photoresponse of the device structures. After investigating the light absorbance phenomenon in the fabricated devices, photodetection mechanism has been studied and the drastic enhancement in photoresponse has been realized. Such extreme increase in photoresponse has been observed because of the plasmonic effect introduced in the device due to depositions of AgNPs and CdSe QDs which reflects in the performance parameters of the devices. It has been revealed that there is a drastic increase by 6.5 times in case of introducing AgNPs in device b even at the applied bias of -3V. Hence, it can be a promising approach to further enhance the photodetection by introducing plasmonic effect due to CdSe QDs and AgNPs in a same device structure.
8:00 PM - NM06.12.24
Highly Transparent, Conductive and Flexible Electrodes with Chemically Treated Ag Nanocrystals
Min Su Kang 1 , Hyungmok Joh 1 , Seung-Wook Lee 2 , Mingi Seong 1 , Woo Seok Lee 1 , Haneun Kim 1 , Soong Ju Oh 1
1 Materials Science and Engineering, Korea University, Seoul Korea (the Republic of), 2 Semiconductor Systems Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractFor the better performance of optoelectronic devices, highly transparent and conductive electrodes are essential. Furthermore, to be used as a wearable and flexible device, flexibility and low temperature fabrication process is also required because flexible substrates might be ruptured at over 200 degrees celcius. While ITO electrodes have low resistance and high optical transmittance; they involve high-temperature processes and are too brittle. Here, we design highly conductive, transparent, flexible and electromechanically stable electrodes using Ag nanoparticles, fabricated by all solution process at room temperature. For optical transparency enhancement, we used photolithography to create an Ag grid on a flexible PET film. In this research, we treated various ligand exchange to Ag grid and investigated the effect of post chemical treatment on their performance. Optical, structural, chemical, electronic and mechanical analysis are characterized. With the optimal design of Ag grid, we obtained a very low sheet resistance (~18 Ω/square) and high optical transmittance (~92 %), with highest figure of merits (FOM). Simulations based on fill factor shows similar tendency regarding FOM.
8:00 PM - NM06.12.25
Pt Nano-Dot Photonic Crystal Thermal Emitter for Thermophotovoltaic System with Simple Method and Oxidation Resistance Using Metal Thin Layer Dewetting Process
KeumHwan Park 1 , Jong-Moo Kim 1 3 , Da-Som Kim 1 2 , Sun-Kyung Kim 2 , Byeong-Kwon Ju 3 , Youngseok Kim 1
1 , KETI, Sungnam-si Korea (the Republic of), 3 , Korea University, Seoul Korea (the Republic of), 2 , Kyunghee University, YongIn-si Korea (the Republic of)
Show AbstractThe thermophotovoltaic (TPV) system is a portable generator which can directly converts the radiant energy produced by the combustion of the fuel into electrical energy. In order to fabricate an emitter for effective TPV system, it has been studied to control optical properties by using photonic crystal (PhC) structures. Since the PhC structure composed of metallic materials such as W and Ta can greatly improve the emissivity of the effective wavelength region, lots of studies have been actively made to manufacture and apply these structures to TPV emitter. Unfortunately, most metals are easily oxidized at high temperatures where the TPV system operates, and metal emitters are being limitedly applied in an inert ambient.
In this study, we propose a new method for fabricating Pt nano dot patterned emitter which has oxidation resistance through the Pt thin film dewetting technology on a templated substrate. Pt nano dot periodic array with 350nm diameter and 250nm height was fabricated by annealing at 1300K atmosphere after deposited 20nm of Pt on 2D patterned Si substrate. Due to the excellent oxidation resistance of Pt, it can be used stably at high temperature, and it can be produced economically by using a very thin layer. In addition, it is capable to control the position and size of the Pt nanoparticles by substrate morphology and optical characteristics could be controlled. Also, it confirmed the formation of a periodic Pt nano-particles array with a single-crystal (FCC structured) structure and oxidation resistance by using TEM-energy dispersive spectroscopy (EDS). The fabricated Pt PhC emitter was able to exhibit high emissivity as a result of high absorption in corresponding to the bandgap of the GaSb PV cell.
8:00 PM - NM06.12.26
Nanoparticle Chains for High-Resolution Sensing and Catalytic Applications
Long Pu 1 , Vivek Maheshwari 1
1 , University of Waterloo, Waterloo, Ontario, Canada
Show AbstractWith the recent advances in technology, the market for electrochemical sensing applications is growing rapidly to meet the requirements for today’s society. Nanoscale electrodes are promising candidates for applications in low-power and size-limiting systems. Compared to conventional electrodes, they offer significant advantages by improving the signal to noise ratio, having low diffusional resistance and low sample volumes. Self-assembled chains of metal nanoparticles, in particular, have drawn interest for fabrication of nanoelectrodes because of their unique properties and geometric morphology. In our study, Au nanoparticle chains are assembled by multivalent ionic linkers, and then the in situ reaction takes place to synthesize functional layers on the surface of the nanoparticle chains. With such chains, better performance arises from both increase in electroactive area and analyte mass transport. The size, morphology and the composition of the assembled chains can be controlled by use of appropriate linkers and the ratio of linkers to nanoparticles. Multifunctionality can also be easily achieved by involving multiple linkers in the assembling process. This further leads to control over the spatial distribution of the linkers in the assembled structures, which ranges from a random distribution of the linkers to discreet domains of with various domain sizes. Their feasibility as electrochemical sensors has been demonstrated by the synthesis of Pt-Au chains which has a good glucose sensitivity and a short response time. Nanoscale electrodes that can catalyze various reaction were also fabricated, e.g. Pt-Ru alloy towards ethanol oxidation and CoO towards water splitting. The strategy will be of significant interest to further advance new applications, such as nanoscale electrode-optical devices, biosensors, and diverse catalytic systems.
8:00 PM - NM06.12.27
Photoxidation of Benzyl Alcohol with CdS QDs—The Complex Interplay with the Autoxidative Reaction
Taleb Mokari 1
1 , Ben-Gurion University of the Negev, Beer-sheva Israel
Show AbstractHeterogeneous photocatalysis is an efficient route for the synthesis of a diverse number of chemicals. When developing a new oxidation photocatalyst, evaluating the relevance of the non-catalyzed autoxidation reaction under irradiation by means of control experiments is crucial. Usually, the autoxidation is disregarded when its yield is close to zero. However, in the ubiquitous case of aromatic aldehydes’ synthesis such as benzaldehyde, irradiating with UV light may lead to a more complex mechanism than previously thought. Herein, we show that benzaldehyde enhances its own production from benzyl alcohol through an autocatalytic reaction when irradiated with UV-A light. This suggests a relevant parallel pathway to the heterogeneous catalysis mechanism which is commonly ignored. Therefore, we show here that autoxidation of benzyl alcohol can occur in presence of a heterogeneous catalyst, CdS, even when the typical control experiments yielded no appreciable product.
8:00 PM - NM06.12.28
Dependency of Image Contrast on Optical Properties of Blue-Light Emitting Quantum Dots in Quantum-Dot UV Camera
Jun-Seong Park 1 , Il-Hwan Kim 1 , Hyeon-Ju Shin 1 , Ji-Ho Choi 1 , Tae-Hun Shim 1 , Jea-Gun Park 1
1 , Hanyang University, Seoul, SE, Korea (the Republic of)
Show AbstractMany researchers have studied highly-sensitive ultra-violet (UV) sensors such as photodiode based on silicon-on-insulator, ZnO and quantum-dots (QDs) because UV light may cause skin aging and skin cancer. Most commercial and studied UV sensors could measure only UV index. however, an image sensor displaying the UV amount has not been reported yet. Thus, we designed QD UV camera implemented with 3M pixels C-MOS image sensor (CIS) using QD filter. The QD filter absorbs UV light and emits blue light on CIS via energy-down-shift. As a result, the amount of the absorbed blue light in blue pixels of CIS is remarkably enhanced while the amount of the absorbed green and red light in green and red pixels of CIS almost does not change. The difference of output voltage contrast (i.e., image) between the blue pixels of CIS with and without using the QD filter could make the UV amount images.
To realize a QD UV camera, there are critical concepts; i.e., i) sufficient high quantum yield (QY) of QDs (>80%), narrow full-width at half-maximum (FWHM) of QDs (<30 nm), iii) accurate alignment between the peaked wavelength of the emitted blue light from QDs and the transmitted-light peak wavelength of blue color filter.
In previous our work, we used Cd0.5Zn0.5S/ZnS core/shell QDs performing the peaked photoluminescence (PL) wavelength of 461 nm, the QY of 78%, and FWHM of 36.60 nm. The QD filter was made by spin-coating QD on quartz glass. We confirmed that the photo-responsivity of the Si photodiode implemented with the 0.5-wt% QDs was 0.778 A/W and the output voltage sensing margin (Vout, dark-state – Vout, photo-state) of CIS pixels increased 195% at 365-nm-wavelength compared to the CIS without implementing QDs. In particular, the QD UV camera implemented with the QD filter demonstrated a clear UV contrast image for various environment, which depended on the absorbed UV light flux.
In our presentation, we developed the QD UV camera using the perovskite CsPbCl3-xBrx QDs (PeQDs) filter. The PeQDs showed the QY of 52% and the FWHM of 20.2 nm, and the peaked PL wavelength of 440 nm. Although the QY of the PeQDs (52%) was lower than Cd0.5Zn0.5S/ZnS core/shell QDs (78%), the FWHM of the PeQDs (20.2 nm) was narrower than core/shell QDs (36.6 nm), meaning that the emitting blue-light amount of the PeQDs could be considerably higher than that of core/shell QDs. Remind that the FWHM of QDs determines the voltage sensing margin of CIS pixel implemented with the QD filter and the emitting blue-light amount of the PeQDs could be enhanced by increasing the QD concentration. We will present the dependency of the UV image-contrast enhancement on the concentration of the perovskite CsPbCl3-xBrx QDs and the UV image contrast comparison between the perovskite CsPbCl3-xBrx QD UV camera and Cd0.5Zn0.5S/ZnS core/shell QD UV camera in detail.
*This work was financially supported by the Brain Korea 21 Plus Program in 2017. We thank HyVISION SYSTEM for implementation of the camera module.
8:00 PM - NM06.12.29
RGB Color-Gamut Comparison between Perovskite and Cd Based Quantum-Dots Functional-Color-Filters for Ultra High Resolution LCD
Seung-Jae Lee 1 , Yun-Hyuk Ko 1 , Jalalah Mohammed 1 , Jea-Gun Park 1
1 , Han-Yang University, Seoul Korea (the Republic of)
Show AbstractRecently, the quantum-dot enhancement film (QDEF) has been introduced to improve the color gamut for LCD technology. Although this QDEF achieves approximately zero cross-talk among the main three RGB colors, it leads to the loss in the light power of back light unit due to the resin and barrier sheets. We, therefore, introduce a new, simple and cost-effect structure for conventional white LED (wLED) LCD having no QDEF but higher resolution and wider color gamut by mixing perovskite QDs directly into the color filter. This structure is called quantum dot-functional color-filter (QDCF).
To apply this proposed structure of QD-functional CFs to an ultra-high resolution LCD application, the color gamut performance of the LCD-like micro-displays using blue, green, and red CFs were estimated by using the CIE 1931 color space with Rec. 2020 and NTSC 1953 standards. Then it compared with that of the conventional LCD like micro displays using the wLED BLU and conventional CFs. The CIE coordinates of three types of micro-displays using blue, green and red PrQD color filters were calculated by using the PL spectrum information and the Matlab-based CIE coordinate calculator software. Furthermore, blue, green and red PrQD emit a light at the wavelengths of 448.0, 510.7, and 626.5 nm having narrow PL-FWHM of 20.2, 20.4, and 43.5 nm and high PL-QY of about 52.5, 61, and 90.2%, respectively. The RGB color gamut of the conventional LCD-like micro-displays using the wLED BLU and conventional CFs showed only 73.7 % (NTSC) and 55.1 % (Rec. 2020). On the other hand, the RGB color gamut of the proposed LCD-like micro-displays using the fabricated PrQD function CFs presented a higher value of 128.1 % (NTSC) and 95.7 % (Rec. 2020) due to the zero cross-talk among PL spectrums of RGB colors. As comparison, we produced three types of micro-displays using blue, green and red Cd based QD color filters. Furthermore, blue, green and red Cd based QD emit a light at the wavelengths of 449, 483, and 629 nm having narrow PL-FWHM of 27, 26, and 29 nm and high PL-QY of about 92, 82, and 85 %, respectively. the RGB color gamut of the proposed LCD-like micro-displays using the fabricated Cd based QD function CFs presented a higher value of 122.1 % (NTSC) and 91.3 % (Rec. 2020). We will present the detail the RGB color gamut between Pr and Cd based QD color filters in view of optical properties of QDs and LCD display operation.
8:00 PM - NM06.12.30
High Performance Nanostructured ZnO UV Photodetector—Effect of Aspect Ratio and Defect Chemistry
Manjeet Kumar 1 , Vishwa Bhatt 1 , Jieun Park 1 , Eunji Song 1 , Ju-Hyung Yun 1
1 , Incheon National University, Incheon Korea (the Republic of)
Show AbstractZinc oxide (ZnO) nanostructures have been considered as a promising material for the fabrication of optical, optoelectronic, and energy harvesting devices due to its environment-friendly features along with low cost and attractive optical and electrical properties [1]. Selectively, detection of UV light finds applications in many important areas of environmental monitoring, space to space communication, defense sector and many more. In recent years, UV photodetectors based on wide bandgap metal oxide nanostructures such as ZnO, SnO2, Ga2O3, Nb2O5, WO3 etc., have attracted major research and commercial interest and have been utilized to fulfill different purposes [2-3]. The UV detection can be mainly enhanced by modifying the device structure or by synthesizing the nanostructures. Till date, much research work is carried out on different kinds of device engineering but still there is a lack of progress in optimizing material nanostructures. Hence, there is a scope to further enhance UV detection by modifying the nanostructures itself and try to fulfill the increasing demand of high performance and highly efficient devices. ZnO has been considered as one of the most important technological materials due to their unique advantages, such a robustness, and transparency, wide bandgap of 3.37 eV and low UV detection limits.
In this work, we demonstrate the fabrication of a UV photodetector based on ZnO nanostructures with three different aspect ratios. The nanostructures have been synthesized by a simple and single step direct thermal decomposition of zinc acetate dihydrate at different temperatures ranging from 350°C to 550°C. From XRD patterns, it has been confirmed that all obtained ZnO nanostructures were highly crystalline in nature and have hexagonal wurtzite structure. It is observed that the average particle size has been increased with an increase in decomposition temperature. The UV detection of the fabricated devices has been performed and the photodetection performance parameters have been evaluated from the photoresponse at 365nm (power intensity of 3W/m2) and a fast response with a transit time of 99ms is obtained. Thus, ZnO nanorods with a higher aspect ratio display considerably higher photo response of 58µA at 5V and detectivity has been increased by 4 times and obtained to be 5.3×1010 Jones. Similarly, spectral responsivity is increased by 3.5 times and obtained to be 185 A/W respectively.
Reference
1. Walia, Sumeet, et al. Progress in Materials Science 58.8 (2013): 1443-1489.
2. Tian, Wei, et al. Nano Research 8.2 (2015): 382-405.
3. Zhang, Yuzhu, et al. ACS applied materials & interfaces 8.34 (2016): 22647-22657.
8:00 PM - NM06.12.31
Whispering Gallery Mode Lasing in Supraparticles of Luminescent Nanocrystals
Federico Montanarella 1 , Darius Urbonas 2 , Michael Becker 2 , Thilo Stoeferle 2 , Rainer Mahrt 2 , Patrick Baesjou 1 , Alfons van Blaaderen 1 , Daniel Vanmaekelbergh 1
1 , Utrecht University, Utrecht Netherlands, 2 , IBM Research, Zurich Switzerland
Show AbstractSemiconductor nanocrystals (NCs) have recently attracted a lot of interest in the scientific community due to their unique size-dependent optical properties: NCs show very sharp photoluminescence emission due to quantum confinement of the exciton in all three dimensions. Thanks to the confinement, NCs show a much higher density of states at the band edge and their emission profile is concentrated in a much narrower spectral region compared to the corresponding bulk material. All these properties make NC quantum dots promising for lasing applications. In some cases, NCs have already shown lower lasing thresholds compared to corresponding bulk gain media [1]. Similarly, NCs can be absorbed onto the surface of silica spheres, which act in this case as ring resonators, obtaining coherent lasing from whispering gallery modes [2].
Here we show whispering gallery mode lasing from spherical supraparticles (SPs), composed of luminescent NCs. The supraparticles are formed through an oil-in-water micro emulsion synthesis [3] and they have a size that can be adjusted between a few hundreds of nanometers to some micrometers. Due to the large difference in refractive index of the supraparticles with air, the electromagnetic light modes become confined in the supraparticles, acting as gain medium and cavity, as well. Whispering gallery modes have been observed in these systems [4], we show for the first time coherent lasing from a single SP. The sharp lasing peaks at the blue end of the spectrum are associated with emission from the core and from shell of the CdSe/CdS NCs.
[1] V.I. Klimov et al., Science, 2000, 290, 5490, pp. 314-317.
[2] S. Yakunin et al., Nat. Comm., 2015, 6, 8056
[3] de Nijs et al., Nat. Mat., 2015,14, pp 56-60
[4] Vanmaekelbergh et al., ACS Nano, 2015, 9 (4), pp. 3942–3950.
8:00 PM - NM06.12.32
Reversibly Wavelength Tunable Laser Based on Single Band-Gap-Graded Semiconductor Nanowires
Minghua Zhuge 1 , Zongyin Yang 2 , Chenlei Pang 1 , Pengfei Xu 1 , Xu Liu 1 , Haifeng Li 1 , Tawfique Hasan 2 , Qing Yang 1
1 College of Optical Science and Engineering, Zhejiang University, Hangzhou, Zhejiang, China, 2 Cambridge Graphene Centre, University of Cambridge, Cambridge United Kingdom
Show AbstractSemiconductor nanowire (NW) lasers have huge potential applications in a lot of fields such as photonic circuits, biology, medicine and environmental monitoring etc. Wavelength tuning of NW lasers is extremely important for their practical applications and caused a lot of interests in recent years.
Utilizing AEA effect, combined with cutting the NWs step-by-step, continuously wavelength variation reaches up to 40 nm has been obtained on pure CdSe NWs. And in single band-gap-graded CdSSe nanowires, the range of wavelength variation could extend to more than 119 nm. Though this approach enables controlling wavelength in an easy way, the nanowire laser can be only used once as the homemade fiber taper has cut them off and the lasing wavelength can’t reverse to longer direction. Up to now, wavelength reversibly tuning lasers still stay a big challenge.
In this work, A reversibly wavelength tunable laser has been achieved on a single band-gap-graded CdSSe NW by introducing effective scattering points to form new oscillating FP cavity. The emitting laser wavelength of this kind of semiconductor NWs is strictly defined by the narrowest band-gap end rather than the wider band-gap. According to this rule, by the touching between the CdSSe NW and another semiconductor NW, the forming scattering point which scatters enough strongly combines the wide band-gap-end face to emerge the new FP oscillating cavity. The fiber probe sticking with the semiconductor NWs is fixed to the 3D-movable PZT modulator can be micro-manipulated automatically so that the lasing wavelength can be tuned reversibly and automatically over a wide visible range.The lasing wavelength from this new FP cavity is totally defined by the center wavelength of photoluminescence (PL) from the renewed scattering point. The reversibly tuning range of the lasing wavelengths from a single NW could cover more than 40 nm, which is limited by the range of photoluminescence (PL) from the nanowires’ band-gap’s variation. With further optimization of material growth and synthesizing condition, the wavelength tuning range can be expected to extend to more than 100 nm.
This reversibly wavelength tunable laser could be expected to have a big application in next-generation of optics intergraded field, multicolor display, optical communication, and so on.
8:00 PM - NM06.12.33
Plasmonic Excitation-Assisted Photovoltaic Enhancement in MoOx/c-Si Solar Cells by Air Brush Spray Deposited Au Nano-Particles
Seda Kayra Güllü 1 2 3 , Hisham Nasser 3 , Emir Aydin 4 , Hasan Güllü 5 , Alpan Bek 2 3 4
1 , TÜBITAK Space Technologies Research Institute, Ankara Turkey, 2 , Department of Physics, Middle East Technical University, Ankara Turkey, 3 , Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, Ankara Turkey, 4 , Micro and Nanotechnology, Middle East Technical University, Ankara Turkey, 5 , Central Laboratory, Middle East Technical University, Ankara Turkey
Show AbstractOne of the plasmonic enhancement mechanisms in photovoltaic solar cells (SCs) is based on increased light absorption due to increased optical path length of incident photons in the active region. Plasmonic enhancement interfaces for SCs are thin but strong light scattering layers of a few nanometers that redirect incident photons in to the plane of p-n junction. In this study, gold nanoparticles (Au NPs) are produced by the seed-mediated growth method and the decoration of Au NPs by the air brush spray coating technique is utilized as a suitable method for plasmonic interface integration to MoOx/n-cSi SC devices. Reflection measurements are performed on Si SCs in order to investigate the local plasmonic resonances of the Au NPs. The variations of particle size and surface coverage are investigated. The effect of introducing plasmonic layer on the overall performance of the cell is studied in terms of the morphology, optical absorption and reflection, I-V characteristics. An enhancement in the photocurrent is observed in MoOx/Au NPs/n-cSi compared to MoOx/n-cSi from I-V measurements under AM 1.5 illumination by the help of solar simulator. Under consideration of plasmonic effect of Au nanoparticles, this enhancement can be resulted in change in absorption within the junction and so that increase in photocurrent response of heterojunction device. The findings on the most suitable nanoparticle system production parameters by this method, depends on the applied substrate properties which are expected to guide further applications of plasmonic interfaces and also to the other kinds of device structures in the ultimate quest for attaining affordable high efficiency SCs.
Financial support from METU under BAP-08-11-2017-022 is gratefully acknowledged.
8:00 PM - NM06.12.34
PbS Quantum Dots Layer Effect on Ag/n-Si/p-CIGS/PbS QDs/In Heterojunction Diode
Idris Candan 1 , A. Cigdem Ercelebi 2
1 Physics Department, Kocaeli University, Kocaeli Turkey, 2 Physics Department, Middle East Technical University, Ankara Turkey
Show AbstractBroadband absorption is critical point to harvest solar energy in wide spectrum to increase the efficiency value of light converter devices. The aim of study to alternate of this problem via quantum dot (QDs) layer addition at photon to electron charge transportation structure. In this study, we discussed the contribution of lead sulfide quantum dot (PbS QD) layer inside Ag/n-Si/p-CIGS/In (ASCI) heterojunction diode systems. Detailed of characterizations of thin film layers were performed by using XRD, Raman spectroscopy and transmittance measurement. Electrical properties of CIGS thin film with and without QD layer were carried out via temperature dependent photoconductivity measurements. The effects of QD layer on the diode parameters of ASCI heterojunction diode system were investigated via using temperature dependent current-voltage (I-V) measurements and capacitance–voltage (C-V) measurements under the dark and illuminated conditions. Our results exhibit a new approach to improve device parameters of heterojunction diodes and the solar cells structure as well by incorporating QD thin film layer.