Alexander Govorov, Ohio University
Renaud Bachelot, University of Technolology of Troyes, Charles Delaunay Institute, CNRS
Din Ping Tsai, Academia Sinica
Gary Wiederrecht, Argonne National Laboratory
Tuesday PM, March 29, 2016
PCC North, 100 Level, Room 129 A
2:30 PM - *NT1.1.01
Sustainable Plasmonics and Plasmonics for Sustainability
Naomi Halas 1
1 Rice Univ Houston United States,Show Abstract
The intense research activity of the past two decades focused on the collective electronic oscillations in high-electron-density media, known as surface plasmons, has led to multiple breakthroughs in fields ranging from chemical sensing and catalysis, to active optical devices, solar light harvesting, even nanomedicine. For many of these applications, the original focus on noble metals may ultimately limit their transition from the research laboratory to widely used commercial technologies. We will describe several research directions that, as they point towards more sustainable materials, open up new research opportunities. Aluminum, the most abundant metal on earth, opens the door to new colorimetric sensing applications and opportunities for active devices. Graphene in its smallest form, that of polycyclic aromatic hydrocarbon molecules, can support intense, optical frequency plasmon oscillations with the addition or removal of a single electron from the neutral molecule. In applications that directly address sustainability, we will discuss how plasmonic nanoparticles can be used for solar distillation of liquid mixtures, providing insight into the mechanism of nanoparticle-based distillation that in certain cases allows the distillation fraction to deviate dramatically from conventional thermal distillation processes.
3:00 PM - *NT1.1.02
DNA-Based Plasmonic Metamaterial
George Schatz 1
1 Northwestern Univ Evanston United States,Show Abstract
This talk will emphasize recent theory and experiments in collaboration with Chad Mirkin in which DNA-functionalized nanoparticle superlattice structures are used to generate plasmonic metamaterials with a variety of properties. This involves a bottom-up assembly technique in which DNA hybridization drives the self-assembly of nanoparticle superlattices with exquisite control over the atomic, nano and micron level structure of the materials. We show that the array structures lead to new kinds of hybrid optical modes in which localized surface plasmon resonances in the nanoparticles are coupled with photonic modes of the lattices, including Bragg modes, Fabry-Perot modes and other modes. These hybrid modes are often much narrower than the isolated particle plasmons, and films composed of these superlattices have unusual metamaterials properties related to strong interactions between photonic modes and plasmons, and between excitons and plasmons.
3:30 PM - *NT1.1.03
Designer Nanocavities for Room-Temperature Plasmon Lasing
Teri Odom 1
1 Northwestern Univ Evanston United States,Show Abstract
Plasmon nanolasers, or spasers (surface plasmon amplification by stimulated emission of radiation) are devices based on plasmonic cavities and gain media that can compensate loss and achieve amplification of nano-localized electromagnetic fields. Several nanocavity architectures have been reported for spasers, such as a metal film-dielectric spacer-semiconductor nanowire configuration or arrays of plasmonic cavities, where the unit cells are nanoparticles or nanoholes. Although the array cavities exhibit directional far-field emission normal to the surface, such plasmonic crystals show bi-directional lasing, where half the emitted light is not collected and is essentially wasted. This talk will discuss a platform for unidirectional, tunable lasing from template-stripped 2D plasmonic crystals. 2D plasmonic crystals combine the advantages of a metal film and nanoparticle arrays and can show lasing in a single emission direction. We will describe the design principles for an optimized unidirectional lasing device by examining different plasmonic materials, unit cell shapes, and gain materials.
4:30 PM - *NT1.1.04
Quantum Plasmonics and Hot-Electron Induced Processes
Peter Nordlander 1
1 Rice Univ Houston United States,Show Abstract
Plasmon resonances with their dramatically enhanced cross sections for light harvesting can serve as efficient generators of hot electrons and holes. Such hot carriers can be exploited in a wide range of photophysical and photochemical processes. The physical mechanism for plasmon-induced hot carrier generation is plasmon decay. Plasmons can decay either radiatively or non-radiatively. The branching ratio between these two decay channels can be controlled by tuning the radiance of the plasmon mode. Non-radiative plasmon decay is a quantum mechanical process in which one plasmon quantum is transferred to the conduction electrons of the nanostructure by excitation of an electron below the Fermi level into a state above the Fermi level but below the vacuum level. In my talk I will discuss the basic mechanism of plasmon-induced hot carrier formation, hot carrier relaxation, and how hot carriers can be exploited in a variety of applications ranging from photodetection, photocatalysis, and to dope or induce phase changes in nearby media.
5:00 PM - *NT1.1.05
Aluminum Nanostructures for Plasmonics
Jerome Plain 1
1 Univ de Technologie de Troyes Troyes France,Show Abstract
Progress in nanomedicine will be driven by the ability to detect and manipulate the living matter at the molecular scale in order to cure cancers or fix genetic anomalies. One of the most promising way is the use of confined optical source in the ultra-violet wavelengths to image by self fluorescence, to analyse by enhanced Raman spectroscopy and to repair the wrong molecular sequences by inducing local chemical reaction. Metallic nanoparticles are widely recognized as local sources of energy that resolve the above issues thanks to their optical properties based to the plasmon resonance. To achieve UV plasmonics, aluminum appears as the best candidate . This metal has a negative dielectric constant combined with a low loss coefficient at UV wavelengths down to 100 nm, matching all the criteria to obtain high energy Localized Surface Plasmon Resonances (LSPR) .
UV Localized Surface Plasmon Resonances (LSPRs) are very attracting because their energy matches with most of the electronic transition energies of molecules or solids. In this scope, the development of efficient and low-cost techniques for the synthesis of reproducible Al nanostructures with very good crystalline quality and optical properties has to be investigated [3,4].
In this presentation, we describe various methods for the growth of crystalline Al-NPs. The nanoparticles are made using very reproducible synthesis routes. The first approach is based on the reduction of aluminum ions. The second approach relies on the use of sono-chemistry of aluminum foils. Particles as small as 2nm have been synthesized and characterized with a transmission electron microscope, extinction spectroscopy and other methods. By playing on various the medium of synthesis and the temperature of reaction, it appears to be possible to tune under control the size of the nanoparticles. We completed the characterizations by investigating the optical properties of the synthesized Al NPs.
To summarize, we described in this presentation various chemical method for the growth of aluminum nanoparticle. AL-NPs present a very good homogeneity and reproducibility. They exhibit sharp localized surface plasmon resonances (LSPRs) in the UV region as it has been showed by extinction spectroscopy characterization.
JP acknowledge the Région Champagne-Ardennes, the Conseil général de l'Aube, and the FEDER funds through their support of the regional platform Nanomat. JP thanks the ANR projects NATO for the financial support.
. D. Gerard and S.K. Gray, Journal of Physics D: Applied Physics 48, 184001 (2015).
. J. Martin, M. Kociak, Z. Mahfoud, J. Proust, D. Gerard, and J. Plain, Nano Letters 14, 5517-5523 (2014).
. J. Martin, J. Proust, D. Gerard, and J. Plain, Optical Materials Express 3, 954 (2013).
. J. Martin and J. Plain, Journal of Physics D: Applied Physics 48, 184002 (2015).
5:30 PM - NT1.1.07
Design and Fabrication of a Plasmonic Switching Device
Petra Ivaskovic 2,Atsushi Yamada 1,Renaud Vallee 1,Jean-Baptiste Verlhac 2,Serge Ravine 1,Mireille Blanchard-Desce 2
1 Centre de Recherche Paul Pascal Pessac France,2 Phoenics Institut des Sciences Moléculaires Talence France,1 Centre de Recherche Paul Pascal Pessac France2 Phoenics Institut des Sciences Moléculaires Talence FranceShow Abstract
Over the past decades, significant experimental and theoretical advances were made in the field of light manipulation with hybrid plasmonic nanostructures . In the integrated plasmonic nanodevices, noble metal nanostructures are commonly used as building blocks because they possess geometry-dependent localized plasmon resonances which can be tuned easily .
In this context, we are designing a new path selective plasmonic switching device by combining molecular dipoles with V- or Y-shape gold nanostructures. In such a system, aligned molecules with well-defined dipoles will trigger the selective propagation of a plasmonic signal generated at the entrance of the nanostructure, into one of the nanostructure's branches. Basic designs and predictions of the device's properties have been performed owing to a computational FDTD simulation approach.
The Y-shape nanostructure consists of three gold nanorods linked in a controlled geometry via dedicated nanometric organic assembler. The V-shape nanostructure is a hollow gold triangle synthesized via a two step-method using silver nanoprism as a seed .
In this work, we have designed and fabricated new functional nanodevices and investigated the transport control and routing of the light, thereby establishing an approach to nanoscale plasmonic switching and light manipulation.
 O. L. Berman et al. ACS Nano 2014, 8, 10437–10447.
 H. Wang et al. Nano Lett. 2006, 6, 827–832.
 M. M. Shahjamali et al. Small 2013, 9, 2880-2886.
NT1.2: Poster Session I: Nanomaterials for Optics I
Tuesday PM, March 29, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NT1.2.01
Effect of PEDOT:PSS on Graphene-Oxide/Silver-Nanowire Working Electrodes for Dye-Sensitized Solar Cells
Bo-Tau Liu 1,Jin-Yan Liu 1,Zheng-Tang Wang 1
1 National Yunlin University of Science and Technology Douliou Yunlin Taiwan,Show Abstract
Fossil energy consumption becomes a more and more significant issue because of the limited source in the Earth and the great impact on environment. Photovoltaic technologies have been regarded as a promising route to converting solar energy into electrical power as an alternative energy source. Due to the simple process and low threshold, dye-sensitized solar cells (DSSCs) have received great attentions since they are introduced in 1991. DSSCs mainly consist of several components: a transparent conductive photoanode, a mesoporous oxide layer (typically, TiO2), photo-excitable dye, an electrolyte, a catalyst (typically, Pt), and a conductive photocathode (typically, transparent). For this study, it was the first time to apply electrodes of silver nanowires (AgNWs) as working electrodes for dye-sensitized solar cells (DSSCs). The performance of DSSCs with the AgNW working electrodes has been investigated. To avoid AgNW corrosion by iodine electrolyte, graphene oxide (GO) was used as a protective layer to isolate the AgNWs, revealing effective prevention of corrosion due to the electrostatic interaction between the electrolyte and the charges of the protective layers. With incorporation of 25% PEDOT:PSS into GO, the GO/PEDOT:PSS-AgNW DSSCs showed an 324% improvement of power conversion efficiency. The PEDOT:PSS doping can reduce the work function of GO from 5.63 to 5.24 eV due to alleviating the strength of the C-O dipole moment on GO. As a result, the enhancement on the power conversion efficiency may be attributed to the reduction of Schottky barrier between AgNWs and GO due to the descent of the work function of the GO.
9:00 PM - NT1.2.02
Evaluation of Stress-Grown Carbon Nanotubes for Optically-Active Hybrid Mixtures
Michael Lowry 1
1 NSWC Dahlgren Division Dahlgren United States,Show Abstract
Stress-grown carbon nanotubes (SG-CNTs) are carbon-based nanomaterials that formed in the presence of an external stressor. The stressor creates a unique thermodynamic condition during molecular development and has been shown to manifest itself in the chemical and physical properties of the resulting material. SG-CNTs have not been previously explored as active components in optical mixtures or composite materials, but their similarities to (and differences from) conventional carbon nanotubes (CNTs) suggest that this is an appealing area to pursue. To this end, the interaction of SG-CNTs with electromagnetic radiation in the ultraviolet (UV), visible and near infrared (NIR) regime has been examined. Experimental methodology, material performance and future implications of this work will be presented.
9:00 PM - NT1.2.03
Au-Ag Core-Shell Nanoparticle Array by Block Copolymer Lithography for Synergistic Broadband Plasmonic Properties
Seung Keun Cha 1,Gil Yong Lee 1,Tae Yeong Yun 1,Taewoo Jeon 1,Sang Ouk Kim 1
1 KAIST Daejeon Korea (the Republic of),Show Abstract
Localized surface plasmon resonance of metallic nanostructures receives noticeable attention in photonics, electronics, catalysis and so on. Core-shell nanostructures are particularly attractive owing to the versatile tunability of plasmonic properties along with the independent control of core size, shell thickness and corresponding chemical composition, but commonly suffer from difficult synthetic procedures. We present reliable and controllable route to highly ordered uniform Au@Ag core-shell nanoparticle array via block copolymer lithography and subsequent seeded-shell growth. Size-tunable monodisperse Au nanodot arrays are generated by block copolymer self-assembly and used as seed layers to grow Ag shells with variable thickness. The resultant Au@Ag core-shell nanoparticle arrays exhibit widely tunable broadband enhancement of plasmonic resonance that greatly surpass single element nanoparticle or homogeneous alloy nanoparticle arrays. Surface-enhanced Raman scattering of the core-shell nanoparticle arrays showed an enhancement factor over 270 from Au nanoparticle arrays.
9:00 PM - NT1.2.04
Lithography-Free Oxide Isolation of GaAs Nanowires Using the VLS Growth Method
David Dvorak 1,Ali Darbandi 1,Simon Watkins 1
1 Simon Fraser University Burnaby Canada,Show Abstract
With feature sizes shrinking and established designs reaching their limits, semiconductor nanowires have become one of the main candidates for the next generation of electronic and optoelectronic devices. A staple of the field, selective area growth through the use of pre-patterned oxides is often employed when growing nanowires because of its effectiveness at controlling uniformity and areal density for device applications. Unfortunately, the lithographical processes required for patterning oxides introduce an added layer of cost and complexity that inhibits the rapid study of nanowire device designs during the prototype stage. As a solution to this problem, our group has previously reported on the lithography-free fabrication of radial p-n junction tunnel diodes and the single nanowire characterization of an ensemble of devices without removal from the substrate . Here, we expand our study to the impacts of oxide choice and annealing temperature on this novel nanowire growth technique. Gold seed particles are used to initiate vapor-liquid-solid (VLS) growth of GaAs nanowires. Short GaAs ‘pedestals’ are then coated in thin conformal films of SiO2, Al2O3 or Ga2O3 by means of atomic layer deposition (ALD). These oxides are generally stable at the growth temperature of 400°C, but some will selectively weaken around the gold particle at the tip of the nanowire pedestals, allowing for continued VLS nanowire ‘regrowth’. Additional axial and radial nanowire segments are then electrically isolated from the substrate by the oxide layer which inhibits any planar growth that would result in a parasitic junction. Initially, only Ga2O3–coated wires exhibited regrowth at 400°C, but it was determined that an annealing step before regrowth would also allow Al2O3–coated wires to continue VLS growth. Annealing steps at 580°C and 640°C led to some nanowire regrowth for Al2O3–coated wires, but annealing SiO2–coated wires at 550°C and 640°C resulted in no nanowire regrowth. This suggests that the oxide quality and the oxide bond strength play a role in this process. Nanowire morphology and mechanical deformation of the oxide coating were assessed using transmission electron microscopy. Electrical characterization of individual nanowires and dielectric oxides was carried out using a tungsten probe inside a scanning electron microscope.
 A. Darbandi, K. L. Kavanagh, and S. P.Watkins, Nano Letters, 15 (2015) 5408.
9:00 PM - NT1.2.05
Static and Transient Response of Strongly Coupled Molecular Vibration-Cavity Polariton States
Blake Simpkins 1,Adam Dunkelberger 1,Bryan Spann 1,Walter Dressick 2,Kenan Fears 1,Jeffrey Owrutsky 1
1 Chemistry Naval Research Laboratory Washington United States,2 Center for Bio/Molecular Science and Engineering Naval Research Laboratory Washington United StatesShow Abstract
Coherent coupling between an optical-transition and confined optical mode, when sufficiently strong, gives rise to new modes separated by the vacuum Rabi splitting. Such systems have been investigated for electronic-state transitions, however, only very recently have vibrational transitions been considered. Here, we bring strong polaritonic-coupling in cavities from the visible into the infrared, where a new range of static and dynamic vibrational processes await investigation.
We demonstrate both static and dynamic results for vibrational bands strongly coupled to optical cavities. First, we experimentally and numerically describe coupling between a Fabry-Pérot cavity and carbonyl stretch (~1730 cm-1) in poly-methylmethacrylate. As is requisite for “strong coupling”, the measured vacuum Rabi splitting of 132 cm-1 is much larger than the full width of the cavity (34 cm-1) and the inhomogeneously broadened carbonyl-stretch (24 cm-1). Agreement with classical theories provides evidence that the mixed-states are relatively immune to inhomogeneous broadening. Next, we investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of urethane chromophore. Rabi splittings increase from 0 to ~104 cm-1 with concentrations from 0-74 vol% and are in excellent agreement with an analytical description using no fitting parameters. Ultra-fast pump-probe measurements reveal transient absorption signals over a frequency range well-separated from the vibrational band, as well as drastically modified relaxation rates. We speculate these modified relaxation rates are a consequence of the energy separation between the vibration-cavity polariton modes and excited state transitions.
Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied statically and dynamically.
9:00 PM - NT1.2.06
A Contactless Method to Measure the Doping Concentration of n-type GaAs Nanowires
Shermin Arab 1,Maoqing Yao 1,Chongwu Zhou 1, P Dapkus 1,Stephen Cronin 1
1 University of Southern California Irvine United States,Show Abstract
GaAs nanowires’ direct band gap and large surface-to-volume ratio have attracted considerable attention for their potential use in high efficiency solar cells, energy storage, and lasers. Measuring the concentrations of the dopants in III-V nanowires and specifically GaAs nanowires is an important problem since it governs the mobility, minority carrier diffusion length/lifetime, and conductivity. Previously, both contact and non-contact methods have been employed for estimating carrier concentrations in III-V nanowires. Here, we present a systematic study of the carrier concentration of n-type doped GaAs nanowires grown by MOCVD using low-temperature photoluminescence spectroscopy. The advantage of this method, especially for n-type GaAs nanowires with large diameters is that it is contact-less and does not require complex lithographic processing. Our measurements indicate that an increase in carrier concentration leads to an increase in the complexity of the doping mechanism, which we attribute to the formation of different recombination centers. At high carrier concentrations, we observe a blueshift of the effective band gap energies by up to 25meV due to the Burstein-Moss shift. Based on the FWHM of the photoluminescence peaks, we estimate the carrier concentrations for these nanowires, which varies from 6x1017 cm-3 (lightly doped), to 1.5x1018 cm-3 (moderately doped), to 3.5x1018 cm-3 (heavily doped) as the partial pressure of the disilane is varied from 0.01 sccm to 1 sccm during the growth process.
9:00 PM - NT1.2.07
Graphene-Assisted Thermal Stability of Percolative Silver Nanowire Networks
H. Huang 1,Hyeyoung Ahn 1
1 National Chiao Tung Univ Hsinchu Taiwan,Show Abstract
Due to their remarkable physical properties, metallic nanowires emerge as the most promising alternatives to indium tin oxide. Percolatively connected Ag nanowire (AgNW) networks can be spin-coated over nearly any substrate at room temperature and show the potential for realization of cheap and flexible electrodes. Due to the increase of electrical resistivity and the decrease of thermal conductivity related with the size effects on the nanoscale, external heating or self-heating of AgNWs may cause melting of NWs at a much lower temperature than the melting temperature of bulk silver. Indeed, when the AgNW film is annealed at 200 °C for 30 min, some of the NW junctions are fused or broken to form Ag droplets. Then the comprehensive understanding of long-term thermal stability of the AgNW network is a crucial issue for AgNW-based devices. In this work, the thermal stability of AgNW films is investigated through the in situ measurements of sheet resistance and terahertz (THz) conductivity.
Thermal heating of AgNWs at 90–150 °C could remove the polymer protection coating on AgNWs and improve the ohmic contact between NWs. Annealing at 200 °C further reduced the resistance in the AgNW film, but prolonged annealing led to the breakage of NW junctions and the formation of silver droplets. To improve the thermal stability of AgNW film, we fabricated graphene-AgNW (GAgNW) films by stamp transferring a monolayer graphene onto the precoated AgNW film. It was found that when coupled with subpercolative AgNWs, stamp-transferred graphene reduces the resistance of the heated GAgNW film up to ~300 W and dramatically improves the thermal stability. THz spectroscopy showed that near-percolative AgNW network can transit to the percolative network by thermal heating to 200 °C. THz time-domain spectroscopy (THz-TDS) also exhibited that the physical parameters of the GAgNW film show only little variation upon thermal heating and annealing, consistent with the results of two-point probe measurement. Since a single-layer graphene is sufficient to improve the thermal stability in the GAgNW film, optical transparency of the GAgNW film is only 2–3 % lower than that of AgNW films. Our results demonstrate that highly transparent conductive metal NW electrodes with excellent thermal stability can be realized from these graphene-incorporated AgNW hybrid films. Finally, this work provides a full understanding on thermal behavior of metallic films and an easy and effective way to improve thermal and electrical properties of the metal nanostructure networks.
9:00 PM - NT1.2.08
Engineering Transition Metal Dichalcogenides as Efficient Light Absorbers and Catalysts for Solar Energy Conversion
Wei-Ren Wang 1,Jingjie Wu 2,Pulickel Ajayan 2,Isabell Thomann 3
1 Chemistry Rice University Houston United States,2 Materials Science and NanoEngineering Rice University Houston United States1 Chemistry Rice University Houston United States,2 Materials Science and NanoEngineering Rice University Houston United States,3 Electrical and Computer Engineering Rice University Houston United StatesShow Abstract
Transition metal dichalcogenides (TMDs) have drawn much attention as two-dimensional (2D) materials due to their unique properties for solar energy conversion. In particular, the band offsets of monolayer molybdenum and tungsten dichalcogenides are suitable for water-splitting and CO2 reduction in electrocatalysis based on theoretical studies. However, practical applications in solar energy conversion devices using these monolayer materials are hindered by the poor absorption of incident solar illumination. Here, we describe initial demonstrations and future prospects of three-dimensional photoelectrode architectures, which can largely increase absorption within the monolayer . The improved light absorption is achieved by a planar cavity composed of a dielectric spacer and a reflector. Based on our previous studies, NiOx is an excellent candidate as a dielectric spacer layer. These photoelectrode architectures have been shown to achieve enhanced light absorption compared to MoS2 monolayer alone, which should translate into an increased photocurrent for driving the water splitting reaction and CO2 reduction in future work.
 Photon management strategies for monolayer MoS2, Shah Mohammad Bahauddin, Hossein Robatjazi and Isabell Thomann, submitted
9:00 PM - NT1.2.09
Metamirror for Enhancing Light Extraction and Absorption
Majid Esfandyarpour 1,Albeto Curto 1,Mark Brongersma 1
1 Stanford Univ Stanford United States,Show Abstract
The radiative decay of rate of quantum emitters can be significantly enhanced in close proximity to a metal surface. This enhancement in the radiative decay rate arises from a higher local density of optical states due to surface plasmon modes near the metal. Since SPPs are lossy bounded waves, coupling of radiated light to SPPs can degrade the efficiency of thin film emitting devices such as organic light emitting diodes (OLED), which have the emitter layer close to a metallic cathode. It has been shown for OLEDs that SPP coupling losses and waveguide coupling losses have opposite dependence on the distance between the emitter layer and the cathode/mirror. Thus, there is an optimal thickness for the optical spacer layer that is conventionally put between the metal cathode and emitter layer to afford the highest light extraction efficiency. In this work, we illustrate how a metamaterial mirror fabricated with subwavelength periodic structures can be used to suppress the coupling of light to SPPs even when the emitter layer is very close to a metallic back reflector. We have looked at the emission lifetime and extraction efficiency of a 20 nm R6G dye emitter layer for two different structures, one with a flat mirror and one with a metamaterial mirror, and showed that the coupling to SPPs can be significantly reduced for the metamaterial reflector. This type of metamaterial mirror offers a new approach to increase the light extraction/absorption efficiency of thin film light emitting devices.
9:00 PM - NT1.2.10
Low-Temperature Synthesis of Wide Bandgap Semiconductor Nanostructures
Muhammad Sajjad 2,Vladimir Makarov 2,Ali Aldalbahi 3,Peter Feng 1,Gerardo Morell 2,Brad Weiner 2
1 Univ of Puerto Rico San Juan United States,2 Institute of Functional Nanomaterials San Juan United States,3 College of Science, King Saud University Riyadh Saudi Arabia1 Univ of Puerto Rico San Juan United StatesShow Abstract
Coupled with the growing interest in carbon nanotubes (CNT), significant progress has been made in the synthesis of wide bandgap semiconductor boron nitride nanotubes (BNNT) for advanced nanotechnology applications. In spite to CNT, growing quality BNNT up to few atomic walls at low temperature remains a challenge. Here, we report on the low temperature (350 oC) synthesis of BNNT in the presence of nickel and cobalt nanopowder as catalytic support. Synthesis process was carried out by irradiating solid hexagonal boron nitride (h-BN) target with short laser pulses. Entire surface of substrate was covered with large number of BNNT distributed randomly, twisted and scrolled evidenced by SEM and TEM microscopic outcomes. The average diameter of BNNT is estimated ~ 0.25 µm, while due to the complicated geometry, length of nanotubes was unpredictable. Raman together with XRD clearly identified hexagonal structure for BNNT. Due to their wide band-gap, the BNNT could provide bright future of highly efficient deep-UV photo-luminescent device and because of their unique properties; they can play a fundamental role in the rapidly developing field of nanoscience and nanotechnology.
9:00 PM - NT1.2.11
Facile and Scalable Synthesis of TiN Nanoparticles by Using a Non-Thermal Plasma Process
Alejandro Alvarez Barragan 1,Lanlan Zhong 1,Lorenzo Mangolini 1
1 University of California Riverside Riverside United States,Show Abstract
TiN nanoparticles are well-known for their interesting plasmonic properties. They have a localized surface plasmon resonance (LSPR) located at the biological transparency window . They have been proposed as a a substitute of gold nanoparticles for biomedical applications with special focus on laser ablation of carcinogen tissues . TiN also has good chemical stability that enables its use as a catalyst in diverse chemical reactions . Most of the methods involving TiN nanopowder synthesis use effective but complicated chemical routes [4,5]. In this contribution, we will present a one-step method for the production of TiN nanoparticles using a non-thermal plasma process. Ar gas flows into a bubbler system containing TiCl4 and carries the precursor gas into a quartz plasma reactor, where an RF power source with a radiofrequency of 13.56MHz is connected to a cylindrical copper electrode wrapped around the quartz tube. NH3 is then added from an independent gas line at the entrance of the system. The system is operated in the 1-5 Torr pressure range, and the gas residence time in the reactor is of the order of few tens of milliseconds. Under this conditions, TiN particles with a size of 5-10 nm are produced. TEM and XRD confirm the production of crystalline TiN particles with cubic structure. The particle size can be controlled by modifying the NH3 flow rate and the applied power. Higher power and a lower NH3-to-TiCl4 ratio yield larger particles. Absorption measurements of the as-synthesized particles show clear plasmonic resonance in the near-infrared region, between 800 and 1000nm. The role of process parameters on the surface of the particles, which in turn affects their plasmonic properties, will be discussed extensively.
 U. Guler, S. Suslov, A. V. Kildishev, A. Boltasseva, V.M. Shalaev, Colloidal Plasmonic Titanium Nitride Nanoparticles: Properties and Applications, Nanophotonics. 4 (2015).
 I.H. El-Sayed, X. Huang, M. a. El-Sayed, Surface plasmon resonance scattering and absorption of anti-EGFR antibody conjugated gold nanoparticles in cancer diagnostics: Applications in oral cancer, Nano Lett. 5 (2005) 829–834.
 S. Kaskel, K. Schlichte, T. Kratzke, Catalytic properties of high surface area titanium nitride materials, J. Mol. Catal. A Chem. 208 (2004) 291–298.
 F. Liu, Y. Li, Y. Yao, H. Zhang, W. Shao, Y. Kang, et al., Preparation of titanium nitride nanoparticles from a novel refluxing derived precursor, J. Wuhan Univ. Technol. Sci. Ed. 26 (2011) 429–433.
 S. Kaskel, K. Schlichte, G. Chaplais, M. Khanna, Synthesis and characterisation of titanium nitride based nanoparticles, J. Mater. Chem. 13 (2003) 1496.
9:00 PM - NT1.2.12
Synthesis of Bi2S3 Nanocrystals by Microwave Irradiation with Different Reaction Temperature, Pressure and Solution pH
Evelyn B. Diaz-Cruz 1,Claudia Martinez-Alonso 3,Alejandro Baray 1,Concepcion Arenas 2,Hailin Hu 1
1 Instituto de Energias Renovables UNAM Temixco Mexico,1 Instituto de Energias Renovables UNAM Temixco Mexico,3 Facultad de Quimica Universidad Autonoma de Queretaro Queretaro Mexico2 Escuela Nacional de Estudios Superiores UNAM Leon MexicoShow Abstract
As a good semiconducting with a direct energy band gap, bismuth sulfide (Bi2S3) whit band gap of 1.3 eV has received attention of many researchers because of its potential applications in areas of photovoltaic devices, photocatalysis, thermoelectric devices, and so on. On the other hand, the application of microwave (MW) heating in synthesis of materials is a fast growing research area due to its advantages, in comparison to conventional heating methods, of rapid volumetric heating, high reaction rate and selectivity that can reduce reaction time by orders of magnitude and increase yield of products. In recent years, various methods with MW have been developed to synthesize Bi2S3 with different sources of Bi and S, solvents, temperature and reaction time to obtain Bi2S3 with different morphologies. Since the hydrolysis of the sulfur source, thiourea or thioacetamide, depends on the solution pH, the reaction kinetics of Bi2S3 as a function of solution pH has not been analyzed till now. Another factor that influences directly on the synthesis of Bi2S3 is the reaction pressure, which is the result of a combination between the type of solvent, the reaction temperature and the MW power used for synthesis. Many reports on MW synthesis mentioned the numbers of those three parameters without the analysis of the pressure in the solution. In fact, the real experimental conditions change from one MW reactor to another, it is important to know the effect of reaction pressure on the final products. In this work Bi2S3 nanocrystals were prepared by the MW irradiation method with bismuth nitrate (Bi(NO3)35H2O) and thiourea ((NH2)2CS) as raw materials and distilled water as solvent. Different morphologies were obtained by varying the solution pH. The MW power of the reaction was varied from 600 to 800W, and the reaction temperature from 100 to 140°C. The crystal phase, morphology, purity and optical properties of the as-synthesized Bi2S3 products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS), UV–vis diffuse reflection spectroscopy (UV–vis DRS) and photoluminescence (PL) spectroscopy. The XRD results give an orthorhombic phase of Bi2S3 (PDF: 17-320). The SEM results show that at 100°C and 800 W, corresponding to a solution pressure of 20 psi, morphologies of nanorods in form of flowers were obtained with rods of 100-500nm in length. For 140°C and 1000W, a solution pressure of 430 psi, only deformed bars from 100 to 2000 nm in length were obtained. Generating high pressure during synthesis facilitates the crystal growth and separation. The asymmetrical morphology of Bi2S3 nanocrystals may encourage their application in hybrid solar cells.
9:00 PM - NT1.2.13
Preparation of Magnéli Phase Films with Controlled Phase, Grain Size and Morphology
Elham Baktash 1,Clement Sanchez 1,Marco Faustini 1,David Portehault 1
1 College de France, Laboratoire de Chimie de la Matiere Condensee de Paris Sorbonne Universites 75005 Paris France,Show Abstract
Due to the low cost, nontoxicity and special physico-chemical properties of titanium oxides, their application were vastly investigated in areas such as pigments, environmental remediation, photocatalysis and so on.[1,2] These applications rely on wide band-gap semiconductor titanium dioxides TiO2, but those are not the only titanium–oxo compounds of potential wide interest. Recently, a long known family of titanium oxides, namely, TinO2n-1 (4 ≤ n ≤9) phases, has attracted considerable attention due to its surprising electronic and phononic properties. Metal Ti4O7 nanofilaments were evidenced to play a major role in TiO2 resistive switching memory, while light-triggered metal-semiconductor transition was demonstrated for Ti3O5. Different bulk TinO2n-1 phases were also reported as efficient thermoelectric materials. These examples show the potential of these ordered substoichiometric titanium oxides for the design of novel information storage and energy conversion devices. Several techniques were proposed for fabricating TinO2n−1 materials.[6,7] However, processed Magnéli phases generally contain large grains with mixtures of stoichoimetries. As a result, the transport and chemical properties of the separate phases are difficult to evaluate with a high degree of reliability. In this study we present a process for preparing Magnéli phases thin films of optical quality, with efficient control on phase, grain size and morphology. The thickness and properties of the films can be adjusted through chemical and processing conditions. The films were prepared using molecular precursor under reducing environment. The thickness, the optical properties (refractive index) and the porosity of the films were assessed using spectroscopic ellipsometry and suggest that such materials may pave the way toward energy conversion devices.
 B. Louis, N. Krins, M. Faustini, D. Grosso, J. Phys. Chem. C 2011, 115, 3115.
 A. Carretero-Genevrier, C. Boissiere, L. Nicole, D. Grosso, J. Am. Chem. Soc. 2012, 134, 10761.
 D.-H. Kwon, K. M. Kim, J. H. Jang, J. M. Jeon, M. H. Lee, G. H. Kim, X.-S. Li, G.-S. Park, B. Lee, S. Han, M. Kim, C. S. Hwang, Nat. Nanotechnol. 2010, 5, 148.
 S.-I. Ohkoshi, Y. Tsunobuchi, T. Matsuda, K. Hashimoto, A. Namai, F. Hakoe, H. Tokoro, Nat. Chem. 2010, 2, 539.
 D. Portehault, V. Maneeratana, C. Candolfi, N. Oeschler, I. Veremchuk, Y. Grin, C. Sanchez, M. Antonietti, ACS Nano 2011, 5, 9052.
 R. Tu, G. Huo, T. Kimura, T. Goto, Thin Solid Films 2010, 518, 6927.
 F. C. Walsh, R. G. A Wills, Electrochim. Acta 2010, 55, 6342.
9:00 PM - NT1.2.14
A Robust One-Pot Synthesis of Hierarchically Structured Bi2S3/Bi2WO6 Photocatalyst for Highly Efficient Reduction of Cr (VI) Ion
Ali Rauf 1,Selim Sher Shah 1,Pil Jin Yoo 1
1 Sungkyunkwan University Suwon Si Korea (the Republic of),Show Abstract
Porous hierarchically structured microspheres of bismuth sulfide (Bi2S3)/bismuth tungstate (Bi2WO6) have shown promising photocatalytic activity by reducing highly toxic and carcinogenic Cr (VI) in comparison to various heterostructured photocatalysts in different morphologies. Co-synthesis of the composites Bi2S3/Bi2WO6 were carried out in a ternary solvent medium (ethanol/acetic acid/water), ethyl acetate in water acted as soft template for microspheres. Composites were synthesized on basis of different Bi2S3 content and characterized using different spectroscopic, microscopic and surface area analysis techniques. Photoexcitation mechanism of composite materials was explained using photoluminescence spectrometry. Bi2S3/Bi2WO6 heterocatalysts were used to remove toxic Cr(VI) ions via reduction to water insoluble Cr(III) utilizing visible-light irradiation. Similarly, role of citric acid as a hole scavenger in the reduction of Cr(VI) with minimizing the rate of electron-hole recombination during photocatalysis was also investigated. Enhanced activity was observed under appropriate balance between hierarchical structure of catalysts and the amount of hole scavenger, which highlights hierarchically heterostructured materials as a promising photocatalysts.
9:00 PM - NT1.2.15
Particle-on-Film Gap Plasmons on Antireflective ZnO Nanocone Arrays as Ultrasensitive SERS Sensors
Youngoh Lee 1,Jiwon Lee 1,Jonghwa Park 1,Minjeong Ha 1,Hyunhyub Ko 1
1 Ulsan National Inst of Science and Technology Ulsan Korea (the Republic of),Show Abstract
Three-dimensional (3D) semiconducting nanostructured arrays decorated with plasmonic metal nanostructures provide giant surface-enhanced Raman Scattering (SERS) effects due to high density of SERS ‘hot spots’ on large area 3D nanostructures, increased light absorption through the 3D light pathway, and the charge transfer interactions between the semiconductors and noble metals. Here, we introduce 3D SERS sensors based on ultra-sharp ZnO nanocones arrays hybridized with particle-on-film plasmonic systems. In this design, in addition to efficient light trapping and wave-guiding properties of ultra-sharp ZnO nanocones arrays, charge transfer effects between the ZnO and noble metals, and gap plasmons between the metal nanoparticles and the metal film provide large electric field enhancements, resulting in significantly improved SERS effects. To study the effects of various morphologies of ZnO and plasmonic systems, we compared the SERS performance of three different ZnO morphologies (nanocones, nanonails, and nanorods) with Au nanoparticles and Ag film based on the finite-difference time-domain (FDTD) calculation of E-fields and the experimental SERS intensities. Finally, we demonstrated that the multiple field enhancement in optimized SERS sensor can be utilized for the molecular-level detection (100 zeptomole) of target molecules.
9:00 PM - NT1.2.16
Flexible and Transparent Photodetector Arrays with Highly Enhanced Optical Properties by Using Embedded AgNW Electrodes
Doo-Seung Um 1,Seongdong Lim 1,Youngsu Lee 1,Hyunhyub Ko 1
1 Ulsan National Institute of Science and Technology (UNIST) Ulsan Korea (the Republic of),Show Abstract
Flexible and transparent photodetectors have recently attracted great attentions for various potential applications. Silver nanowires (AgNWs) can provide a high optical transparency and an outstanding mechanical flexibility for the electrodes in flexible and transparent photodetectors, but the high-resolution patterning of AgNWs electrodes is a great challenge for applications in photodetector arrays. In this study, we introduce a simple solution-based technique for the high-resolution AgNWs patterning based on the filtration of AgNWs solution on the patterned polyimide shadow mask. In this method, the pattern size of AgNWs network can be easily controllable via the pattern size of polyimide mask and can be reduced down to 5 μm width. We also demonstrate the highly flexible and transparent ZnO-based UV photodetector arrays based on the patterned AgNWs electrodes. Here, the AgNWs electrodes can be embedded in ZnO film to enhance the photocurrent by light scattering and plasmon resonance effects. The optical performances of ZnO UV photodetector embedded with AgNWs electrode were greatly enhanced about 800% for photocurrent and over 1000% for On/Off ratio compared to the stacked AgNWs electrode type. In addition, the flexible photodetectors can be operated under extremely bent state (bending radius of ~770 μm) with slight decrease of performances. The patterning technique of AgNWs electrodes can be potentially employed for applications in photodetectors and thin-film transistor arrays.
9:00 PM - NT1.2.18
Platinum-Decorated Cadmium Chalcogenide Hybrid Nanocrystals with Different Shapes for Photocatalytic Hydrogen Generation
Younghun Sung 2,Jaehoon Lim 5,Jai Hyun Koh 3,Lawrence Hill 4,Byoung Koun Min 3,Jeffrey Pyun 2,Kookheon Char 2
1 The National Creative Research Initiative (CRI) Center for Intelligent Hybrids Seoul National University Seoul Korea (the Republic of),2 The World Class University (WCU) Program of Chemical Convergence for Energy amp; Environment, School of Chemical amp; Biological Engineering Seoul National University Seoul Korea (the Republic of),5 Chemistry Division Los Alamos National Laboratory Los Alamos United States3 Clean Energy Research Center Korea Institute of Science and Technology (KIST) Seoul Korea (the Republic of)4 Department of Chemistry amp; Biochemistry University of Arizona Tucson United States4 Department of Chemistry amp; Biochemistry University of Arizona Tucson United States,2 The World Class University (WCU) Program of Chemical Convergence for Energy amp; Environment, School of Chemical amp; Biological Engineering Seoul National University Seoul Korea (the Republic of)Show Abstract
Colloidal metal-semiconductor hybrid nanomaterials have recently gained much attention due to synergistic properties originating from different combinations of metal and semiconductor within a single nanocrystal structure. Particularly, platinum-incorporated cadmium chalcogenide hybrid nanocrystals have extensively been studied for photocatalytic hydrogen generation due to semiconductors as light absorbers and metals serving as cocatalysts. Here, we report on the direct decoration of Pt nanoparticles on cadmium chalcogenide (CdX) nanocrystals with different shapes (i.e., rods and tetrapods) and their effects on the photocatalytic hydrogen generation. In the presence of alkyl halide ligands at CdSe or CdSe@CdS semiconductor nanorods and tetrapods, we noted that Pt nanoparticles directly nucleated and grew uniformly at the surface of semiconductor nanocrystals. Controlled size of Pt nanoparticles decorated on the CdX nanocrystals showed different photocatalytic hydrogen generation efficiency, which is believed to be due to the controlled reduction potential of Pt clusters. Detailed structural analysis and carrier dynamics are also discussed.
9:00 PM - NT1.2.19
Three Dimensional Sculpturing of Vertical Nanowire Arrays by Conventional Photolithography
Chun Cheng 1,Yuan Shi 1,Shuhan Bao 1,Xianglong Bai 1,Dawen Li 1,Yi Zhang 1,Xinghao Fan 1,Dongyong Wang 1
1 SUSTC Shenzhen China,Show Abstract
Ordered nanoarchitectures have attracted an intense research interest recently because of their promising device applications. They are always fabricated by self-assembling building blocks such as nanowires, nanodots. This kind of bottom up approaches is limited in poor control over height, lateral resolution, aspect ratio, and patterning. Here, we break these limits and realize 3D sculpturing of vertical ZnO nanowire arrays (NAs) based on the conventional photolithography approach. These are achieved by immersing nanowire NAs in thick PR layers, which enable the cutting and patterning of ZnO NAs as well as the tailoring of NAs. Our strategy of 3D sculpturing of NAs promisingly paves the way for designing novel NAs-based nanoarchitectures.
9:00 PM - NT1.2.20
Studies on Immobilization of Au Nanoparticles on ZnO Using Self-Assembled Monolayer (SAM) for Plasmonic Organic Solar Cell
Bo-Cong Gong 1,Yian Tai 1
1 National Taiwan University of Science and Technology Taipei Taiwan,Show Abstract
Organic thin film solar cells is one of the solar device which are light in weight, thin and flexible. However, it showed the poor power conversion efficiency (PCE). Recently, many researcher are focusing on to improve the PCE of organic thin film solar cell. It has been widely reported that plasmonic effect of metallic nanoparticles can enhance the photon absorption in polymer solar cells (PSCs). Herein, we demonstrated the immobilization of gold nanoparticles on the self-assembled monolayer (SAM) modified ZnO electron transport layer. The amount of gold nanoparticles can be easily controlled by fixing the immersion time and concentration of Au nanoparticle solution and it was confirmed by absorption and scanning electron microscope. Moreover, the electron generated from the active layer could pass through the surfactant-capped gold nanoparticles to the ZnO surface with the help of SAM whereas the electrons were trapped in the Au nanoparticles for without using SAM modified Au/ZnO due to the physisorption of surfactant-capped Au nanoparticles on the surface of ZnO. As a result, the short circuit current density could be enhanced effectively for the Au nanoparticles incorporated SAM modified ZnO device when comparing the without SAM modified An/ZnO device.
9:00 PM - NT1.2.21
Fabricating Large-Area Multicolored Photopatterns via Targeted Recovery of Selected QD Emission Peaks in Mixed QD Films
Sidney Malak 1,Jaehan Jung 1,Young Jun Yoon 1,Chun Hao Lin 1,Marcus Smith 1,Zhiqun Lin 1,Vladimir Tsukruk 1
1 Georgia Inst of Technology Atlanta United States,Show Abstract
This work demonstrates approaches to fabricate multicolored photopatterns in mixed QD-polymer films which significantly extend previous photopatterning approaches that utilized only a single QD component. Two approaches are presented that allow for either selective or collective modification of specific QD photoluminescent (PL) peaks during photopattern development, yielding novel photopatterns and unprecedented control over how the color of the photopattern evolves. Applying selective or collective modification of selected QDs makes it possible to change or maintain the color of the photopattern as it is developed. These results demonstrate that the evolution of the PL spectrum of a multicolor QD film during pattern development can be controlled either by careful consideration of the development wavelength or through combinations of unstable and stable QDs. The flexibility and capability of the selective or collective modification approaches greatly expand the capabilities of photopatterns, particularly in the areas of sensing, imaging, and lighting systems where it is important to have control over the intensity of selected colors within specific spatial regions.
9:00 PM - NT1.2.22
Improving Photostability of Self-Assembled Quantum Dot Ensembles by Ligand Exchange with a Liquid Crystal-Like Molecule
Jose Amaral 1,Linda Hirst 1,Sayantani Ghosh 1
1 University of California, Merced Merced United States,Show Abstract
Embedding or dispersing quantum dots (QDs) in photovoltaic devices is a continuing challenge where there is a need to have high concentration of QDs to facilitate efficient solar absorption. However, if they are too closely packed, increased Forester resonant energy transfer (FRET) can serve to destabilize QD ensembles by enhancing photo-degradation. We aim to reduce this photo-degradation by performing a ligand exchange with a custom made molecule that demonstrates liquid crystalline (LC) behavior. During self-assembly of the QDs, the LC-like ligand increases the inter-particle distance between the dots, thereby reducing FRET efficiency. To determine if the close-packing with the new ligands is optimal with respect to photo-stability, we study photo-induced static and dynamic spectral changes in self-assembled CdSe/ZnS core-shell QD thin films under ambient conditions. We observe that photoluminescence (PL) quenching of a QD ensemble is arrested by up to 25% when the red-shift due to FRET is limited to approximately 5 nm, corresponding to an inter-particle spacing of approximately 10.5 nm. With the octadecylamine (ODA) ligands, the observed red-shift is 8 nm and the inter-particle separation is approximately 9.4 nm, which decreases photo-stability. These inter-particle distances were obtained by performing small angle X-ray scattering experiments. TEM images indicate that the LC-like molecules form a loose 3-D network comprised of quasi-linear chains, reducing average nearest neighbor distances. Dynamically, the radiative lifetime of the QD ensembles is measured using time-resolved spectroscopy. As the ensembles are photo-excited, the radiative lifetime of the larger (acceptor) QDs increase until the ensemble PL quenches, at which point the radiative lifetime begins to decrease, indicative of preferential photo-oxidization. This process allows for uniform, macroscopic self-assembly of QDs and may provide an inexpensive option for improving the stability of QD-based photovoltaic devices.
This work was funded by NSF DMR 1056860.
9:00 PM - NT1.2.23
Graphene Quantum Dot: Titania Nanoparticle Composite Materials for Photocatalytic Water Splitting Application
Ravneet Kaur 1,Sowbaranigha Chinnusamy Jayanthi 1,Folarin Erogbogbo 1
1 San Jose State University San Jose United States,Show Abstract
Titania (TiO2) is a wide band gap semiconductor that exhibits photocatalytic activity, high resistance to photocorrosion, and stability when exposed to light. The appropriate valence and conduction band energies of TiO2 are best suited to overcome the thermodynamic and the electrochemical potential required for photoelectrolysis of water. However, TiO2 as a photo anode material faces some significant challenges such as poor absorption of visible light, high carrier recombination, and limited charge-carrier transport. To overcome these limitations, we propose the synthesis of a composite material using carbon based graphene quantum dots (GQDs) and TiO2 nano particles. The GQDs are synthesized by an inexpensive wet chemical method using bird charcoal as a precursor. GQD nanostructures exhibit band gap tunability based on their size and has the potential to enhance the photo absorption in TiO2. In particular, the hybrid combination of the nano materials is expected to decrease the recombination of charge carriers, increase charge carrier mobility and aids to improve the overall photo-conversion efficiency. The synthesized composite is characterized using scanning electron microscope (SEM) image, atomic force microscope (AFM) and dynamic light scattering (DLS). Electrical/electronic performance of the composite is investigated by photocurrent density measurements. Further, optoelectronic properties are studied using photoluminescence (PL) spectrum and UV-visible transmission spectrum. The use of this combination of nano materials is non-toxic, inexpensive, and novel for photo electrochemical (PEC) water splitting application and has implications for cost effective solar fuel cell developments.
Alexander Govorov, Ohio University
Renaud Bachelot, University of Technolology of Troyes, Charles Delaunay Institute, CNRS
Din Ping Tsai, Academia Sinica
Gary Wiederrecht, Argonne National Laboratory
NT1.3: Hybrid Nanomaterials for Energy and Optics
Wednesday AM, March 30, 2016
PCC North, 100 Level, Room 129 A
9:30 AM - *NT1.3.01
On Blue-Emitting Nanoplatelets and Carbon Dots
Jochen Feldmann 2
1 University of Munich (LMU) Munich Germany,2 Nanosystems Initiative Munich (NIM) Munich Germany,Show Abstract
The photophysics of two types of nanoparticles with intense optical emission in the blue and green spectral region will be discussed. Nanoplatelets made of organometal halide perovskites show high quantum efficiencies, pronounced quantum size effects and strong excitonic characteristics . We have also addressed the striking optical properties of blue/green-emitting carbon dots. Their properties can be understood as a consequence of a unique fluorescent cocktail of polycyclic aromatic hydrocarbons .
J. Sichert, Y. Tong, N. Mutz, M. Vollmer, S. Fischer, K. Milowska, R. Cortadella, B. Nickel, C. Cardenas-Daw, J. Stolarczyk, A. Urban and J. Feldmann, Nano Letters 15, 6521 (2015)
M. Fu, F. Ehrat, Y. Wang, K. Milowska, C. Reckmeier, A. Rogach, J. Stolarczyk, A. Urban and J. Feldmann, Nano Letters 15, 6030 (2015)
10:00 AM - *NT1.3.02
Glutathione Capped Gold Clusters for Light Energy Conversion
Prashant Kamat 1
1 Univ of Notre Dame Notre Dame United States,Show Abstract
Glutathione stabilized few atom gold clusters (Au-GSH) exhibit red emission with a 5-10 % quantum efficiency. The excited state lifetime of ~1ms arises from ligand-metal charge transfer state. These clusters are capable of sensitizing TiO2 and deliver a photoconversion efficiency of 2% when employed in the DSSC mode. The high open circuit voltage (0.9 V) observed in these cells makes them interesting candidate as sensitizers and cosensitizers. Their relatively high reduction and oxidation potential also makes them suitable for water splitting reaction. Furthermore we have also evaluated the metal cluster-plasmonic Ag (or Au) nanoparticle interactions by coupling glutathione protected gold clusters (Au-GSH) with larger size Ag nanoparticles. By employing transient absorption spectroscopy we have succeeded in demonstrating the synergy arising from optical interactions (i.e. plasmon enhancement) between the two coupled systems. The role of metal clusters in light harvesting systems will be discussed.
10:30 AM - *NT1.3.03
Multifunctional Materials for Electronics and Photonics
Federico Rosei 1
1 INRS Varennes Canada,Show Abstract
The bottom–up approach is considered a potential alternative for low cost manufacturing of nanostructured materials . It is based on the concept of self–assembly of nanostructures on a substrate, and is emerging as an alternative paradigm for traditional top down fabrication used in the semiconductor industry. We demonstrate various strategies to control nanostructure assembly (both organic and inorganic) at the nanoscale. We study, in particular, multifunctional materials, namely materials that exhibit more than one functionality, and structure/property relationships in such systems, including for example: (i) control of size and luminescence properties of semiconductor nanostructures, synthesized by reactive laser ablation ; (ii) we developed new experimental tools and comparison with simulations are presented to gain atomic scale insight into the surface processes that govern nucleation, growth and assembly [3-7]; (iii) we devised new strategies for synthesizing multifunctional nanoscale materials to be used for electronics and photovoltaics [8-25].
 F. Rosei, J. Phys. Cond. Matt. 16, S1373 (2004);  D. Riabinina et al., Phys. Rev. B 74, 075334 (2006);  K. Dunn et al., Phys. Rev. B 80, 035330 (2009);  F. Ratto et al., Small 2, 401 (2006);  F. Ratto et al., Phys. Rev. Lett. 96, 096193 (2006);  F. Ratto et al., Nanotechnology 19, 265703 (2008);  F. Ratto et al., Surf. Sci., 602, 249 (2008);  C. Yan et al., Adv. Mater. 22, 1741 (2010);  C. Yan et al., J. Am. Chem. Soc. 132, 8868 (2010);  R. Nechache et al., Adv. Mater. 23, 1724–1729 (2011);  R. Nechache et al., Appl. Phys. Lett. 98, 202902 (2011);  G. Chen et al., Chem. Comm. 48, 8009–8011 (2012);  G. Chen et al., Adv. Func. Mater. 22, 3914–3920 (2012);  R. Nechache et al., Nanoscale 4, 5588–5592 (2012);  J. Toster et al., Nanoscale 5, 873–876 (2013);  T. Dembele et al., J. Power Sources 233, 93–97 (2013);  S. Li et al., Chem. Comm. 49, 5856–5858 (2013);  T. Dembele et al., J. Phys. Chem. C 117, 14510–14517 (2013);  R. Nechache et al., Nature Photonics 9, 61 (2015).
11:30 AM - *NT1.3.04
Hot Electron Photodetectors Based on Bulk and 2D Semiconductors
Jason Valentine 1,Wei Li 1,Wenyi Wang 1,Andrey Klots 1,Dhiraj Prasai 1,Zachary Coppens 1,Kirill Bolotin 1
1 Vanderbilt Univ Nashville United States,Show Abstract
While the non-radiative decay of surface plasmons was once thought to be only a parasitic process which limits the performance of plasmonic devices, it has recently been shown that it can be harnessed in the form of hot electrons for use in photocatalysis, photovoltaics, and photodetectors. Here, we will discuss metamaterials and plasmonic antennas that have been specifically designed to maximize and harness hot electron injection at near-infrared wavelengths in both traditional semiconductors such as silicon as well as 2D semiconductors such as MoS2. We will first discuss metamaterial perfect absorbers that allow one to achieve near-unity optical absorption in metal films that are thinner than the hot electron diffusion length. The metamaterials are integrated with a silicon substrate forming a Schottky barrier with a height that is smaller than the silicon band gap, allowing electrons with sub-band gap energy to be collected. This configuration was used to experimentally demonstrate a broadband and omnidirectional hot electron photodetector with a photoresponsivity >3mA/W at wavelengths >1200 nm. We also show how metamaterial perfect absorbers can be utilized to realize hot electron photodetectors that are sensitive to circularly polarized light. The detectors have among the highest polarization discrimination that has been demonstrated to date in an integrated detector. Lastly, we will discuss hot electron injection in bilayer MoS2. One of the unique features of MoS2 is the presence of traps that in turn lead to photoamplifaction. The amplification allows the realization of photoresponsivities in excess of 1 A/W.
12:00 PM - *NT1.3.05
Excitonic Properties of Inorganic-Organic Hybrid Perovskites and Nanophotonic Devices
Qihua Xiong 1
1 Nanyang Technological Univ Singapore Singapore,Show Abstract
In this talk, we present investigations of vapor phase synthesis of purely inorganic or organic-inorganic perovskites nanoplatelets by a van der Waals epitaxy mechanism, and their excitoic properties. Those crystals exhibit 2D well-faceted triangular, hexagonal or square geometry with thickness range of tens to hundreds of nanometers. Optical spectroscopy investigations suggest that the crystals have large exciton binding energy, high external quantum efficiency and long diffusion lengths. The naturally formed high-quality planar whispering-gallery mode cavities ensure adequate gain and efficient optical feedback for low-threshold optically pumped in-plane nanolasers ranging from ultraviolet and near-infrared, with a very high quality factor (>4000) in purely inorganic perovskite square-shaped crystals. Our findings open up a new class of wavelength tunable nanomaterials potentially suitable for on-chip integration and flexible optoelectronic devices. Progress in light-emitting diode and waveguiding will also be discussed.
 Q. Zhang, S.T. Ha, X.F. Liu, T.C. Sum* and Q.H. Xiong*, "Room-Temperature Near-Infrared High-Q Perovskite Whispering-Gallery Planar Nanolasers", Nano Lett. 14, 5995–6001 (2014)
 S.T. Ha, X.F. Liu, Q. Zhang, D. Giovanni, T. C. Sum and Q.H. Xiong*, "Synthesis of Organic–Inorganic Lead Halide Perovskite Nanoplatelets: Towards High-Performance Perovskite Solar Cells and Optoelectronic Devices”, Adv. Opt. Mater. 2, 838-844 (2014)
 J. Xing, X. F. Liu, Q. Zhang and Q. H. Xiong*, “Vapor Phase Synthesis of Organometal Halide Perovskite Nanowires for Tunable Room-Temperature Nanolasers”, Nano Lett. 15, 4571 - 4577 (2015).
12:30 PM - NT1.3.06
Photoinduced Spontaneous Free-Carrier Generation in Chirality-Pure Semiconducting Single-Walled Carbon Nanotube in a Low Dielectric Solvent
Jaehong Park 1,Obadiah Reid 1,Jeffrey Blackburn 1,Garry Rumbles 3
1 National Renewable Energy Laboratory Golden United States,2 Renewable and Sustainable Energy Institute, University of Colorado at Boulder Boulder United States,1 National Renewable Energy Laboratory Golden United States1 National Renewable Energy Laboratory Golden United States,3 Department of Chemistry and Biochemistry, and Renewable and Sustainable Energy Institute University of Colorado at Boulder Boulder United StatesShow Abstract
Photoinduced free-carrier generation in semiconducting single-walled carbon nanotubes has been controversial because of the substantial exciton binding energy (hundreds of meV). Here, we report the direct measurement of long-lived free-carrier generation in a chirality-pure single-walled carbon nanotube in a low dielectric solvent. Frequency-resolved solution-phase flash-photolysis time-resolved microwave conductivity (fp-TRMC) provides a contactless and quantitative measurement of the real and imaginary photoconductance of individually suspended nanotubes. This solution-phase fp-TRMC as well as low excitation fluences, allow us to avoid complications from tube-tube/tube-electrode contact, dielectric screening by nearby-excitons or many-body interactions. Even under these mild conditions, we unambiguously probe a photoconductance.
12:45 PM - NT1.3.07
Directly Metering Light Absorption and Heat Transfer in Single Nanowires Using Metal-Insulator Transition in VO2
Chun Cheng 1,Run Shi 1,Chengzi Huang 1,Yuan Shi 1,Shuhan Bao 1
1 SUSTC Shenzhen China,Show Abstract
Absorption and propagation of light at the sub-wavelength length scale is the key process for many technologies such as light management in modern photovoltaics. Similarly, heat exchange and transfer at length scales shorter than the phonon mean free path is critically important for nanoscale thermal management. For such near-field energy conversion and transfer, gauging the energy flow has been either indirect or requires complicated tools.[1, 2] Here we demonstrate a multi-functional powermeter that directly quantifies light absorption and heat transfer at the near-field length scales, such as in a single nanowire. The mechanism is based on the metal-insulator phase transition (MIT) in single-crystal vanadium dioxide (VO2) microbeams, where the domain wall moves free of kinetic obstruction and exhibits distinct optical contrast between the two phases. The powermeter is contactless and optically readable, allowing quick determination of local temperature, optical absorbance, thermal conductivity, and contact thermal resistance of single nanostructures.
 L. Cao, J. S. White, J. Park, J. A. Schuller, B. M. Clemens, M. L. Brongersma, Nat. Mater. 2009, 8, 643.
 P. Kim, L. Shi, A. Majumdar, P. McEuen, Phys. Rev. Lett. 2001, 87, 215502.
 J. Wu, Q. Gu, B. S. Guiton, L. Ouyang, N. de Leon, H. Park, Nano Lett. 2006, 6, 2313.
NT1.4: Semiconductor Nanomaterials for Energy and Optics—Nanowires, Quantum Dots, Plasmonic Emitters
Wednesday PM, March 30, 2016
PCC North, 100 Level, Room 129 A
2:30 PM - *NT1.4.01
Resonant Cavities for III-V Semiconductor Nanowire Device Applications
Chennupati Jagadish 1
1 Australian National Univ Canberra Australia,Show Abstract
III-V semiconductor nanowires offer the possibility of high density/three dimensional optoelectronic device integration and growth of III-V semiconductors on cheap substrates. The shape anisotropy of nanowires that makes the above applications possible also means that nanowires have a large free surface area. The free surface area of nanowires increases the probability of surface states assisted non-radiative recombination processes, especially in materials like GaAs that have very large surface recombination velocity (~106 cm/s). High non-radiative recombination rates result in low radiative efficiency in nanowires, defined as, where and are the probability of radiative recombination and non-radiative recombination event, respectively, compromising the performance of optoelectronic devices fabricated from these nanowires.
Combating the detrimental effects of surface states on the radiative efficiency of nanowires is thus essential for device applications. The conventional approach for enhancing the radiative efficiency in semiconductors involves reducing the surface state assisted non-radiative recombination probability by employing surface passivation. AlGaAs is widely used for passivating the surface of GaAs, and with this approach we have demonstrated radiative efficiency of ~2% in GaAs nanowires.
An alternative approach to increase the radiative efficiency of nanowires is to enhance the probability of radiative recombination processes. This can be achieved by coupling the nanowires to resonant cavities. We have recently demonstrated ten-fold increase in the radiative efficiency of surface passivated GaAs nanowires using this approach. In my presentation, I will discuss the challenges of this approach, design and characteristics of different resonant cavities for enhancing the radiative efficiency of nanowires, the effect of these cavities on the emission properties of nanowires and its implications for nanowire based optoelectronic devices.
3:00 PM - NT1.4.02
Scalable Epitaxy-Free Synthesis of Broadband, Super-Absorbing III-V Nanowire Arrays
Wen-Hui Cheng 1,Katherine Fountaine 2,Colton Bukowsky 1,Harry Atwater 1
1 California Institute of Technology Pasadena United States,2 Northrop Grumman Aerospace Systems Redondo Beach United StatesShow Abstract
Group III-V compound semiconductor nanowire arrays are promising candidates for energy harvesting and sensing applications, including photovoltaics, solar fuels, and photodetectors, due to their high volumetric absorption. Nevertheless, like many resonant optical structures, scalability is a prominent concern. Widely-practiced nanowire array fabrication methods include e-beam lithography and MOCVD, making them prohibitively expensive and time-intensive for large-scale applications in, e.g., photovoltaics, large-area detectors or thermal management layers.
We report here a scalable and economic fabrication procedure for achieving broadband near-unity absorption in sparse arrays of InP nanowires that function by strong coupling into resonant waveguide modes. Large area nanowire arrays are fabricated without epitaxy, but instead from bulk InP substrates by mechanical exfoliation of InP nanowire arrays, defined via nanoimprint and ICP-RIE.
Uniform nanowire arrays exhibit high absorption at certain wavelengths due to strong coupling into resonant waveguide modes. Simulations indicate that it is possible to achieve near-unity broadband absorption in sparse semiconductor nanowire arrays. Multi-radii nanowire arrays and tapered nanowire arrays were predicted to achieve near-unity broadband absorption in sparse arrays (<5% fill fraction) and exhibited ~25% absorption enhancements compared to arrays with uniform wire radius .
In this work, we experimentally demonstrate scalable, epitaxy-free fabrication of InP nanowire arrays using nanoimprint lithography for pattern transfer and inductively-coupled plasma, reactive-ion etching to define nanowire arrays in bulk InP wafers. Polymer-embedded wires are removed from the bulk InP substrate by a mechanical method that facilitates extensive reuse of a single bulk InP wafer to synthesize many polymer-embedded nanowire array thin films. In addition to mask pattern definition (wire radius and spacing) and etch chemistry (wire taper), appropriate selection of a hard mask material and thickness for the InP etch is found to be critical to attaining precise dimension control and reproducibility. After embedding in PDMS and peeling-off the substrate, the resulting arrays achieve ~80% broadband absorption (λ=400-900 nm) in less than 100 nm planar equivalence of InP. Depositing a silver back reflector increases this broadband absorption to ~90%. The repeatable process of imprinting, etching and peeling to obtain many nanowire arrays from one single wafer represents an economical manufacturing route for high efficiency III-V photovoltaics and photodetectors.
 K.T. Fountaine, C.G. Kendall, Harry A. Atwater, “Near-unity broadband absorption designs for semiconducting nanowire arrays via localized radial mode excitation,” Opt. Exp. (2014).
3:15 PM - *NT1.4.03
Probing the Carrier Dynamics of Mid-Infrared Semiconductor Nanowires
Howard Jackson 1,Leigh Smith 1
1 Univ of Cincinnati Cincinnati United States,Show Abstract
Exploring semiconductor nanowires with mid-infrared band gaps has received much less attention than the prototypical III-V nanowires with band gaps in the visible range like GaAs. One reason is that the mid-infrared poses certain technical challenges. We demonstrate that the recent technique of transient Rayleigh scattering (TRS) can be utilized to probe these materials in fruitful ways. Recently, high quality growth of InGaAs and GsAsSb nanowires whose band gaps are in the mid-infrared range has been carried out [1,2]. Here we present Raman spectroscopy and (TRS) spectroscopy results to characterize the energy structure, strain, and carrier dynamics of individual InGaAs and GaAsSb and individual core/shell nanowires with an InP shell. Specifically, individual wurtzite In0.65 Ga0.35 As nanowires and In0.65 Ga0.35 As/InP core/shell nanowires as well as zincblende GaAs0.70 Sb0.30 nanowires and GaAs0.70 Sb0.30/InP core/shell nanowires were investigated.
Raman measurements indicate that in the core/shell structures the InGaAs core is under compressive strain. TRS measurements on single nanowires at room temperature show a clear resonance at 1440 nm or 0.86 eV for the unstrained InGaAs that shifts up in energy in the core/shell structure to 1400 nm or 0.886 eV. At room temperature, the time decay is found to be quite long, ~500 ps in the core/shell structure in contrast to the bare InGaAs core where the response is weak suggesting a much larger nonradiative recombination rate.
For the GaAsSb core/shell nanowires, Raman scattering suggests that the GaAsSb core is under tensile strain. TRS measurements on the bare GaAsSb again find recombination times of less than the instrument response of 50 ps at all temperatures. In sharp contrast, lifetimes from the core/shell structures are measure to be 130 ps at room temperature and 820 ps at 10K. A shift in the bandgap between bare and core/shell nanowires is also observed.
These measurements demonstrate that the TRS technique is suitable for probing mid-infrared optical properties including band gaps and carrier dynamics of single nanowires.
We acknowledge the support of NSF through DMR-1507841, DMR 1531373, and ECCS-1509706. We also acknowledge the support of the Australian Research Council (ARC) and the Australian National Fabrication Facility.
 A. Ameruddin, H.A. Fonseka, P. Caroff, J. Wong-Leung, R.L.M. Veld, J. Boland, M.B. Johnston, H.H. Tan, and C. Jagadish, Nanotechnology 26, 205604 (2015).
 X. M. Yuan, P. Caroff, F. Wang, Y.N. Guo. Y.D. Wang. H.E. Jackson, L. M. Smith, H.H. Tan, and C. Jagadish, Advanced Functional Materials 24, 5300 (2015).
3:45 PM - NT1.4.04
Two-Color Single Hybrid Plasmonic Nano-Emitters
Xuan Zhou 1,Gerard Colas des Francs 3,Gary Wiederrecht 4,Hilmi Demir 2,Jerome Plain 1,Xiao Wei Sun 2,Renaud Bachelot 1
1 University of Technology of Troyes Troyes France,3 Université de Bourgogne Franche Comté Dijon France4 Argonne National Laboratory Argonne United States2 Nanyang Technological University Singapore SingaporeShow Abstract
Modern information and communication technologies require higher bandwidth and greater energy efficiency in order to face the challenge of the increasing amount of data traffic. In this context, optical data is the key: the fast development of integrated optics and nanophotonics has steadily produced more optical functionality in a small chip. This continued development of nanophotonics requires integration of efficient optical nanosources (including multicolor sources for future nanoscale multiplexing) that are able to address and activate specific parts of the circuit. In this regard, hybrid plasmonic nanosources, including plasmon lasers, are a recent promising solution.
We introduce a new type of hybrid plasmonic nano-emitter. We demonstrate two-color nano-emitters that enable the selection of the dominant emitting wavelength by varying the polarization of excitation light. The nano-emitters were fabricated via surface plasmon-triggered two-photon polymerization. By using two polymerizable solutions with different quantum dots, emitters of different colors can be positioned selectively in different orientations in the close vicinity of the metal nanoparticles. The dominant emission wavelength of the metal/polymer anisotropic hybrid nano-emitter can thus be selected by altering the incident polarization.
NT1.5: Semiconductor Nanomaterials for Energy and Optics—Excitons and Plasmons
Wednesday PM, March 30, 2016
PCC North, 100 Level, Room 129 A
4:30 PM - *NT1.5.01
Engineered Quantum Dots for Luminescent Solar Concentrators
Victor Klimov 1
1 Los Alamos National Laboratory Los Alamos United States,Show Abstract
Luminescent solar concentrators (LSCs) could become an important element of future net zero-energy-consumption buildings as semitransparent photovoltaic windows. Colloidal quantum dots (QDs) are promising materials for LSCs, as in addition to a tunable emission wavelength they can be engineered in such a way as to provide strong absorption across much of the solar spectrum while having a negligibly small re-absorption at the emission wavelength. This is important for suppressing losses for wave-guided light in large-area devices. Here, we study LSCs utilizing two types of QDs. The first is based on II-VI core/shell heterostructures (e.g., CdSe/CdS and CdSe/CdZnS), in which the absorption and emission functions are separated between a wider-gap shell and a narrower-gap core. This allows for almost independent control of absorption cross-sections responsible for light harvesting and re-absorption losses. The second system, ternary I-III-VI2 semiconductors (CuInE2, where E = S or Se or their mixture), provides a heavy-metal-free alternative to Cd-based QDs. In these materials, re-absorption losses are considerably reduced compared to II-VI counterparts due to the involvement of an intra-gap hole state in the emission process, which leads to the spectral displacement of the photoluminescence with respect to the onset of inter-band absorption. Using QD-solution-based LSCs, we investigate the dependence of the light collection efficiency on micro-structural parameters of the QDs, their concentration, and LSC dimensions. To analyze the experimental data, we develop an analytical model (validated by Monte Carlo simulations), which allows us to predict the LSC performance based on the QD optical spectra and device geometry. In addition, we demonstrate prototype solid-state devices by incorporating QDs into polymeric matrices, which results in freestanding, almost scattering-free slabs with negligible reabsorption losses over distances of a few tens of centimeters. Measurements under simulated solar illumination indicate high light-collection efficiencies of more than 3% with semi-transparent devices that transmit 80 to 90% of incident radiation. These studies demonstrate the significant promise of engineered QDs for applications in solar window technologies.
5:00 PM - *NT1.5.02
All-Colloidal Lasers of Solution-Processed Quantum Dots and Wells
Hilmi Demir 2
1 Bilkent University Ankara Turkey,2 LUMINOUS! NTU Singapore Singapore,Show Abstract
Solution-processed semiconductor nanocrystals have attracted great interest in photonics including color conversion and enrichment in quality lighting and display backlighting . Optical properties of these colloidal nanocrystals can be conveniently tuned and controlled by tailoring the dimensionality, size, and composition of these nanostructures in an effort to realize high performance in light generation and lasing . These span different types and heterostructures of colloidal semiconductors in the form of quantum dots and rods to more recently emerging quantum wells. Based on the rational design and control of excitonic processes in these nanocrystals, it is possible to achieve highly efficient light-emitting diodes  and optically pumped lasers [4,5]. In this talk, we will present all-colloidal solid lasers developed by incorporating nanocrystal emitters as the optical gain media in a fully colloidal cavity for the first time . As an extreme case of solution-processed highly-confined quasi-2D colloids, we showed that the atomically flat heteronanoplatelets uniquely combine ultra-low threshold stimulated emission and record high optical gain coefficients. In addition, the controlled stacking of these nanoplatelets further allows us to tune their excitonic properties . The recent progress in the colloidal optoelectronics suggests that solution-processed quantum materials hold great promise to challenge epitaxial counterparts in the near future.
 H. V. Demir et al., Nano Today 6, 632 (2011); T. Erdem and H. V. Demir, Nature Photonics 5, 126 (2011).
 B. Guzelturk et al., Laser & Photonics Reviews 8, 73 (2014); and J. Phys. Chem. Lett. 5, 2214 (2014).
 X. Yang et al., Advanced Materials 24, 4180 (2012); Advanced Functional Materials 24, 5977 (2014); ACS Nano 8, 8224 (2014); and Small 10, 246 (2014).
 Y. Wang et al., Advanced Materials 27, 169 (2015).
 B. Guzelturk et al., Advanced Materials 27, 2678 (2015).
 B. Guzelturk et al. ACS Nano 8, 6599 (2014); and ACS Nano 8, 12524 (2014).
5:30 PM - NT1.5.04
Plasmon-Exciton Interactions Probed Using Spatial Co-Entrapment of Nanoparticles by Topological Singularities
Paul Ackerman 2,Ivan Smalyukh 3,Haridas Mundoor 1,Jao van de Lagemaat 1
1 Department of Physics University of Colorado Boulder United States,2 Department of Electrical, Computer and Energy Engineering University of Colorado Boulder United States,1 Department of Physics University of Colorado Boulder United States,2 Department of Electrical, Computer and Energy Engineering University of Colorado Boulder United States,3 Department of Physics Liquid Crystal Materials Research Center and Materials Science and Engineering Program Boulder United States1 Department of Physics University of Colorado Boulder United States4 National Renewable Energy Laboratory Golden United States,1 Department of Physics University of Colorado Boulder United StatesShow Abstract
We study plasmon-exciton interaction by using topological singularities to spatially confine, selectively deliver, co-trap and optically probe colloidal semiconductor and plasmonic nanoparticles. The interaction is monitored in a single quantum system in the bulk of a liquid crystal medium where nanoparticles are manipulated and nanoconfined far from dielectric interfaces using laser tweezers and topological configurations containing singularities. When quantum dot-in-a-rod particles are spatially co-located with a plasmonic gold nanoburst particle in a topological singularity core, its fluorescence increases because blinking is significantly suppressed and the radiative decay rate increases by nearly an order of magnitude owing to the Purcell effect. We argue that the blinking suppression is the result of the radiative rate change that mitigates Auger recombination and quantum dot ionization, consequently reducing nonradiative recombination. Our work demonstrates that topological singularities are an effective platform for studying and controlling plasmon-exciton interactions.
NT1.6: Poster Session II: Nanomaterials for Optics II
Wednesday PM, March 30, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NT1.6.02
High Density Quantum Dots by Direct Laser Fabrication
Anahita Haghizadeh 1,Nikhil Pokharel 1,Haeyeon Yang 1
1 South Dakota School of Mines and Technology Rapid City United States,Show Abstract
For photovoltaic and solar cell applications, it is desirable for quantum dots to have a high density in order to increase the absorption of light. Epitaxial nanodots are typically fabricated by the so-called Stranski-Krastanov (S-K) growth method, which is an energy minimization process driven by the relaxation of accumulated strain energy. The quantum dots by the S-K technique have been studied for their application of solar cells such as intermediate band solar cells. High density quantum dots were sought because it is crucial to have high absorption of light for photovoltaics and other optoelectronic device applications. However, large cluster defects begin to show up as the dot density is increased over the certain value, a critical density of about 7x1010 dots/cm2, over which the increase in dot density does not increase the performance of solar cells. We report that direct laser fabrication produce quantum dots with their density higher than the critical density without appearance of large clumps. Atomic force microscopy is used to image GaAs(001) surfaces that are irradiated by high power laser pulses interferentially, while the stoichiometric analysis indicate that their composition is the same as that of the substrate. The formation mechanism of high density quantum dots will be discussed along with their optical properties, examined by photoluminescence.
9:00 PM - NT1.6.03
Quantum Wires by Direct Laser Fabrication
Anahita Haghizadeh 1,Nikhil Pokharel 1,Haeyeon Yang 1
1 South Dakota School of Mines and Technology Rapid City United States,Show Abstract
For optoelectronic applications, quantum wires may provide unique physical properties. However, conventional approaches such as the self-assembly via the Stranski-Krastanov (S-K) technique have a limited success in their applications toward optoelectronic devices including photovoltaics and solar cells. A novel mechanism for quality quantum wires will be been discovered. The laser fabricated nanowires on the GaAs(001) surfaces has that the width and height of nanowire can be as small as 30 and 5 nm, respectively while the density is one per 200 nm as indicated in atomic force microscope (AFM) images. The examinations by low voltage of 3kV, electron energy dispersive X-ray spectroscopy (EDS), suggest that their chemical composition is the same as that of substrate. The formation mechanism of nanowires fabricated directly by laser will be discussed along with their optical properties, examined by photoluminescence.
9:00 PM - NT1.6.04
Efficient Photo-Reduction of Bi-Carbonate to Formate Catalyzed by TiO2 Nanocatalysts in the Presence of Ag Nanoparticles- A Different Mechanism
Hanqing Pan 1,Alynna Do 1,Alexzander Steiniger 1,Michael Heagy 1,Sanchari Chowdhury 1
1 New Mexico Tech Socorro United States,Show Abstract
In this study, a new CO2 utilization strategy is developed via the hydrogenation of CO2 derived bicarbonate to produce value-added chemicals such as formate. A high yield of formate (production rate 160 micromol/gm TiO2.hr.), was achieved after reducing sodium bicarbonate in glycerol–water solution at room temperature with the TiO2 nano-catalyst (
9:00 PM - NT1.6.05
Strong Plexcitonic Coupling between Metallic Nanoparticles and Fluorophores for Bio-Sensing Applications
Andrea Rodarte 1,Andrea Tao 1
1 University of California, San Diego La Jolla United States,Show Abstract
Metallic nanostructures can be paired with fluorescent molecules or nanoparticles in order to create a plexcitonic device in which the localized surface plasmon resonance (LSPR) of the metallic nanoparticle couples with the exciton of a fluorescent material. Many applications have been demonstrated in which the LSPR of the metallic nanoparticle is perturbed by the presence of the fluorescent molecule. This interaction is considered weak coupling between the particles. We investigate the strong coupling regime in which the coupling between the exciton and plasmonic cavity result in two hybrid energy states.
A donor/acceptor pair of plasmonic nanoparticle/fluorophore is designed so that the localized surface plasmon resonance (LSPR) band of the plasmonic nanoparticle and the absorption band of the fluorophore overlap. Acceptors are then conjugated to the plasmonic nanoparticles via a chemical linker molecule. When the plasmon and exciton couple we observe a hybrid state where the extinction of the hybrid system is significantly changed, showing two split peaks. We investigate the dependence of donor/acceptor separation distance on coupling as well as the spectral overlap by varying the LSPR of the donor nanoparticles. The versatility of these donor/acceptor pairs make them prime candidates for new solid state optical bio-sensors.
9:00 PM - NT1.6.06
Characterization of InN-In0.25Ga0.75N Quantum Well Laser with In0.4Al0.6N Layers for 1300 nm Band
Md. Mobarak Polash 2,Kamruzzaman Khan 1
2 Electrical and Electronic Engineering (EEE) University of Asia Pacific (UAP) Dhaka Bangladesh,1 Electrical Engineering amp; Computer Science (EECS) University of Toledo Toledo United StatesShow Abstract
Group-III nitrides have recently opened the door for devices like lasers and light-emitting diodes (LEDs), power electronics and high frequency electronic devices with exciting performances. Nitride lasers and LEDs have higher lifetimes than previously used II-VI devices. Quite recently nitride quantum wells are studied in the spectral range over 1100nm due to the prospect of their applications in optical communication. For optical communication, 1330nm and 1550nm wavelengths are most important for short distance and long distance communication respectively. At 1330nm, dispersion of a signal is lowest when at 1550nm path loss of a signal is the lowest. As a result, III-nitride semiconductors and their alloys are attracting much interest for optoelectronic devices particularly at around 1300nm band. For designing nitride semiconductor lasers in 1300nm band, generally intersubband optoelectronic devices are studied due to the large conduction band offset of the III-nitride heterostructures. In this range, design of interband structures are hardly proposed in recent works. For attaining these wavelength band, InN has been proposed as well material while In0.25Ga0.75N as barrier material. In0.4Al0.6N has been used as separate confinement heterostructure (SCH) to provide better optical and carrier confinement in the active region. For the analysis, the calculation of the band structures and wave functions has been performed by using a self-consistent model where Schrodinger equation has been solved with Poisson’s equation. For conduction band calculation, Schrodinger equation has been formed with single-band Hamiltonian with effective mass approximation and parabolic band nature consideration. Valence band Hamiltonian has been formed with 6-band k.p formalism with valence band mixing effect, strain effect and polarization effect. Analysis of optical properties including interband momentum matrix elements, spontaneous emission spectrum and optical gain have been carried out after solving the electronic properties of the structure. In previous works, GaN layer has been suggested instead of InAlN layer to attain the communication wavelength. GaN layer introduced a significant strain in well layer which make the structure less suitable for fabrication. Using InAlN layer reduces the strain in well region. Characterization has been performed for 12Å InN QW with 17Å In0.25Ga0.75N barrier. Amount of the compressive strain is 7.33% and the internal electric field is -9.74 MVcm-1 in well layer. C1-HH1, C1-LH1, C2-HH1 and C2-LH1 are the most dominant transitions which made the structure TE polarized. At 3×1019 cm−3 carrier density, the spontaneous emission spectrum gives peak amplitude of 4×1027 s−1cm−3eV−1 at 1308.6nm and the peak optical gain of 251.63 cm−1 occurs at 1336.7nm. At 6×1019 cm−3, the peak amplitude of spontaneous emission spectrum of 9.89×1027 s−1cm−3eV−1 occurs at 1301.7nm and the peak optical gain of 6850.65 cm−1 occurs at 1308.6nm wavelength.
9:00 PM - NT1.6.07
Stable and Highly Loaded CdSe/Cd1-xZnxSe1-ySy Crosslinked Quantum Dot Films with High Gain in the Quasi-Continuous Wave Region
Chun Hao Lin 1,Evan Lafalce 2,Jaehan Jung 1,Marcus Smith 1,Sidney Malak 1,Zhiqun Lin 1,Z. Vardeny 2,Vladimir Tsukruk 1
1 Materials Science and Engineering Georgia Institute of Technology Atlanta United States,2 Physics and Astronomy University of UTAH Salt Lake City United StatesShow Abstract
This work demonstrates an effective ligand modification approach that can increase the net gain value of CdSe/Cd1-xZnxSe1-ySy quantum dot (QD) films to 500±100 cm-1, which is many fold higher than values typically reported in literature for cast Cd based QD films, while preserving the photoluminescence stability. Two strategies were implemented to improve the gain performance and achieve high QD loading, including the replacement of the long ligand oleic acid with the short ligand butylamine, and the appropriate selection of a stabilizing bifunctional crosslinker (1,7 diaminoheptane) that has much higher melting and boiling point as well as the lower vapor pressure than those of butylamine. Results indicate that a higher QD loading of the film increases the net gain value significantly while the thermodynamic properties of the ligand are crucial to maintain the gain performance. In addition, we demonstrate free-floating crosslinked QD films on the original solvent used to dissolve the QDs, indicating the crosslinked QD film is much more chemically and mechanically stable than the conventional cast QD film. The high net gain and improved chemical and mechanical stability make these films promising candidates for the fabrication of new photonic systems like parity-time symmetric devices that require stable net gain, an ability to control the ratio between gain and loss, and resilience to the environment.
9:00 PM - NT1.6.08
Dynamic Radiative Thermal Management with Switchable Vanadium Dioxide Based Fabry-Perot Thermal Emitters
Sydney Taylor 1,Yue Yang 1,Liping Wang 1
1 SEMTE Arizona State University Tempe United States,Show Abstract
Radiative cooling and heating are topics of recent interest due to their applications in energy conservation, solar power, and thermal management. Thermal emitters can reduce the surface temperature by selectively radiating thermal energy in the mid-infrared region through the atmospheric window into outer space. Radiative cooling is desired during the daytime when the surface temperature is high but should be minimized during the night when there is no solar heating to prevent the temperature from dropping significantly. Therefore this work seeks to develop a dynamic thermal emitter whose emissivity can respond to temperature changes. A well-performing thermal emitter should be highly reflective in the mid-infrared region when its temperature is lower than the desired temperature, and should exhibit large infrared emissivity when the temperature is higher.
Vanadium dioxide (VO2) is an insulator-to-metal phase transition material, which undergoes a dramatic shift in optical properties during phase transition. This study considers an asymmetric Fabry-Perot cavity with a lossless dielectric spacer sandwiched between a VO2 thin film and an opaque aluminum substrate. Below the phase transition temperature (341 K), the VO2 is insulating and the proposed structure is highly reflective with low emissivity in the mid-infrared region. When the temperature increases beyond 341 K the VO2 top layer becomes metallic and forms a Fabry-Perot resonator to exhibit high emissivity in a broad spectral range around 10 μm. As a result, the surface could cool down due to enhanced radiative cooling with much higher thermal emission loss. The large contrast in the emissivity of the dynamic VO2-based thermal emitter could lead to smaller temperature variations between daytime and nighttime, thus saving energy in cooling and heating.
We have developed a uniaxial transfer matrix method to calculate the radiative properties of VO2 multilayer thin films as a function of temperature. The optical constants of VO2 during phase transition are modelled via Bruggeman effective medium theory. The preliminary results show that the emissive power is increased by a factor of nearly 7 when VO2 changes from insulator to metal between 341 K and 345 K. At a wavelength of 10 μm, the emissivity of the dynamic radiative thermal emitter is about unity with metallic VO2 but as small as 0.1 with insulating VO2. The radiative properties are shown to be insensitive to incidence angle. Fabrication of the designed multilayer structures is in progress, and temperature-dependent spectrometric measurements will be carried out to experimentally verify the dynamic infrared emissivity at different VO2 phases. The ability of the emitter to self-regulate its temperature near the phase transition temperature will also be investigated. The proposed structure could be useful for applications such as building cooling and spacecraft thermal management.
9:00 PM - NT1.6.09
Near-Field Thermal Radiation between Dual Uniaxial Electromagnetic Metamaterials
Jui-Yung Chang 1,Yue Yang 1,Liping Wang 1
1 Arizona State University Tempe United States,Show Abstract
Recently, near-field thermal radiation has attracted much attention since it can exceed the Planck blackbody limit through the coupling of evanescent waves. Numerous studies have been conducted in near-field radiation during the past few years for applications such as thermophotovoltaic and thermal management. Among these researches, the magnetic responses which correspond to s polarized waves are mostly neglected due to the non-magnetic behavior (i.e., permeability μ = 1) of naturally existing materials. However, magnetic resonance has been demonstrated in nanostructured metamaterials to selectively control far-field optical and radiative properties. However, the effect of magnetic response in near-field radiative transfer is little studied and understood.
In this work, the near-field radiative heat transfer between two semi-infinite dual uniaxial electromagnetic metamaterials is theoretically analyzed. The considered metamaterials exhibit both the magnetic and electrical responses with homogeneous uniaxial permeability and permittivity. Hypothesized homogeneous uniaxial properties are chosen over isotropic properties since isotropic magnetic materials do not exist naturally and nanostructured metamaterials can usually be homogenized to uniaxial media via effective medium theory. The near-field radiative heat transfer is calculated by the fluctuational electrodynamics at both s and p polarized waves. Besides the mechanisms such as electrical hyperbolic mode, electrical surface polariton, and epsilon-near-pole which can only occur for p polarized waves, new mechanisms such as magnetic hyperbolic mode, magnetic surface polariton, and mu-near-pole with s polarized waves, will be thoroughly investigated by the contour of transmission coefficient and spectral heat flux. Moreover, the total heat fluxes at different wave polarizations will be studied under different vacuum gap distances as well. The fundamental understandings and insights obtained here could facilitate and enrich the near-field thermal radiation applications through the resonance mechanisms at both s and p polarized waves.
9:00 PM - NT1.6.10
Fe Contacts to GaAs Nanowires
Mingze Yang 1,Ali Darbandi 1,Simon Watkins 1,Karen Kavanagh 1
1 Physics Simon Fraser University Burnaby Canada,Show Abstract
Epitaxial Fe contacts have been selectively fabricated onto the top half of free-standing, Te-doped ((13 ± 7) x 1016 cm-3) (111) GaAs nanowires (NWs) via electrodeposition. The NWs were grown via Au catalyzed metal-organic chemical vapour deposition (MOCVD) using tertiarybutylarsine (TBAs) and trimethylgallium (TMGa) as precursors. The doping concentration was determined using direct probing of the Au/GaAs Schottky interface using a W probe in situ within a scanning electron microscope (SEM). A current density of 0.1 mA/mm2 was used in the electrodeposition, resulting in the growth rate of Fe of 0.8 ± 0.3 nm/s as measured by scanning transmission electron microscopy (STEM). Top views of the Fe films via both SEM and TEM showed them to be hexagonal, even though the shape of the underlying GaAs NWs was found to be triangular. The deposited Fe was shown to be (110) oriented via TEM, epitaxially aligned with the (110) GaAs NW side facets. An insulating polymer (SU-8) was used to fill in between the nanowires preventing deposition directly onto the GaAs substrate, which enabled the measurement of electrical transport through individual wires. Plasma cleaning was used for 2 minutes to remove the residual SU-8 before the electrodeposition, which damaged the nanowire surface. This resulted in a broad variation (4 orders of magnitude) in the current at high bias (> 1 V) indicative in changes in the NW bulk resistivity. But the experimental current-voltage characteristics were highly rectifying with a linear log-current voltage range of 7 orders of magnitude. Combining these results with transport simulations the effective three-dimensional contact area was determined giving an average Fe-GaAs diode barrier height of 0.64 ± 0.02 eV (ideality factor 1.48 ± 0.02).
9:00 PM - NT1.6.11
Electron Beam Induced Current Measurement of Carrier Diffusion Lengths in GaAs Nanowires Studied by the Nanoprobe Method
Ali Darbandi 1,Simon Watkins 1
1 Simon Fraser Univ Burnaby Canada,Show Abstract
In the last decade there have been numerous attempts to develop nanowire-based semiconductor devices including solar cells, lasers and light emitting diodes. However there are still challenges inherent to NW structures that are not fully understood. This includes the effect and control of the NW sidewall surface states. Due to the large surface-to-volume ratio in NWs the surface states play a major role in limiting the electronic properties of NW devices. The latter translates into the reduction of the minority carrier diffusion length (Ld) in semiconductor NWs since the surface states act as recombination sites.
Here we present the study of electron and hole diffusion lengths in p-type and n-type GaAs NWs using the electron beam induced current (EBIC) method. EBIC measurements were carried out on free standing NWs using a nanoprobe technique implemented inside a scanning electron microscope, without the need for lithographic processing. NWs were grown by the vapor-liquid-solid method using metalorganic precursors at at a growth temperature of 400°C, and using diethyltellurium and diethylzinc as the n- and p-type dopants. Two types of structures were fabricated: (1) single carrier type structures where the depletion region under the Au catalyst particle was used to collect minority carriers, and (2) n-p axial homojunction structures where the EBIC signal was measured separately on either side of the junction. It was observed that for both types of minority carriers Ld reaches a maximum of approximately 170 nm for NWs with radius greater than 400 nm. The obtained results are lower than the reported Ld for GaAs thin films with values larger than 1 µm. Also we observed that the diffusion lengths strongly decrease with NW diameter below 400 nm, indicating the dominant effect of surface states at smaller diameters. In order to improve the electrical properties of GaAs NWs an InGaP shell was grown radially around the GaAs core. The InGaP shell enhances the minority carrier lifetime somewhat, however this process needs further optimization. The key finding of this work is the ability of the nanoprobe technique to provide rapid characterization of an ensemble of NWs without lithographic processing in order to screen potential passivation methods rapidly and accurately.
9:00 PM - NT1.6.12
Enhancement of Sensitivity of the Solution-Phase Localized Surface Plasmon by a Nanostructured Substrate
Shengjie Zhai 1,Hui Zhao 1
1 Dept. of Mechanical Engineering University of Nevada, Las Vegas Las Vegas United States,Show Abstract
There is a need to design a sensitive and low-cost plasmonic biosensing technique which own biocompatibility and optical stability to detect the low level of analytes in biological samples. In this study, we describe a simple and inexpensive method to enhance the sensitivity or improve the detection limit of solution-phase localized surface plasmon (LSPR) sensors of metallic nanoparticles, which has been entrapped in a thin silicon shells and can be successfully used as versatile plasmonic probe for molecular sensing in solution phase. Furthermore, the substrate surface that supports the LSPR detection contains metallic nanostructures which are replicated from commercial optic disks via the standard soft lithography. As the proof of the concept, by mixing BSA molecules with nanoparticle solution, we demonstrate that the wavelength shift due to the absorption of BSA molecules on nanoparticle surfaces is amplified by more than an order of magnitude in comparison to that over a smooth flat surface. It would be very attractive for investigation of analytes in biological fluids.
9:00 PM - NT1.6.13
Oxidative Photocatalysis at TiO2 Aerogels Driven by Surface Plasmon Resonance of Non–Precious Metal Nanoparticles
Jeremy Pietron 1,Paul DeSario 1,Todd Brintlinger 2,Rhonda Stroud 2,Debra Rolison 1
1 Chemistry Division Naval Research Laboratory Washington United States,2 Material Science amp; Technology Division Naval Research Laboratory Washington United StatesShow Abstract
In the present study, we describe the incorporation of surface plasmon resonance (SPR)-active, non–precious metal nanoparticles into TiO2 aerogels. Titanium dioxide (TiO2) aerogels feature inherent design flexibilty that make them superior design platforms for composite photocatalysts. The sol–gel-derived nanoscale titania networks of the aerogel act as an interconnected system of covalently bonded nanowires with readily modifiable structure, enabling efficient transfer of electrons to reactive catalytic sites.1 Additionally, plasmonic metal nanoparticulate guests can be readily incorporated into the mesoporous host, sensitizing the metal-modified aerogels to visible light and enabling visible light–driven photocatalytic oxidation of water and alcohols.2,3 The composite aerogels feature clear optical SPR signatures, and drive the photoelectrochemical oxidation of methanol in aqeuous base. We will also describe some of the specific advantages inherent to TiO2 aerogels for supporting plasmonic nanoparticles derived from non-precious metals.
This work was supported by the Office of Naval Research.
1. P. A. Desario, J. J. Pietron et al., J. Phys. Chem. C 119 (2015) 17529
2. P. A. Desario, J. J. Pietron et al., Nanoscale 5 (2013) 8073.
3. D. A. Panayotov, P. A. DeSario et al., J. Phys. Chem. C 117 (2013) 15035.
9:00 PM - NT1.6.14
Probing Radiative Heat Transfer in the Extreme Near-Field
Bai Song 1
1 University of Michigan, Ann Arbor Ann Arbor United States,Show Abstract
Bai Song1, Kyeongtae Kim1, Víctor Fernández-Hurtado2, Woochul Lee1, Wonho Jeong1, Longji Cui1,
Dakotah Thompson1, Johannes Feist2, M. T. Homer Reid3, Francisco J. Garcia Vidal2, 4,
Juan Carlos Cuevas2, Edgar Meyhofer1 and Pramod Reddy1, 5
1Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
2Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, 28049, Spain
3Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
4Donostia International Physics Center (DIPC), Donostia/San Sebastián, 20018, Spain
5Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
Fluctuational electrodynamics computations have long predicted dramatic enhancements of radiative energy flow across nanometer gaps. Such phenomenon is expected to be of great importance to diverse novel technologies including near-field thermophotovoltaics and lithography. While experimental advances have enabled exploration of near-field radiative heat transfer in gaps as small as 20 to 30 nm, quantitative analysis in the extreme near-field (<10 nm) has been greatly limited by a range of challenges. Further, pioneering measurements reported results that differ from theoretical predictions by orders of magnitude. In our study1, we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with novel suspended microdevices capable of periodic temperature modulation, to systematically measure radiative heat transfer in gaps as small as 2 nm. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica–silica, silicon nitride–silicon nitride and gold–gold surfaces to reveal dramatic, gap size-dependent enhancements of radiative heat transfer. Furthermore, our boundary-element-method calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results providing unambiguous evidence that confirms the validity of this theory for modeling radiative heat transfer in the extreme near-field. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale thermal radiative heat transfer.
 K. Kim*, B. Song*, V. Fernández-Hurtado*, W. Lee, W. Jeong, L. Cui, D. Thompson, J. Feist, M.T.H. Reid, F. J. García-Vidal, J. C. Cuevas, E. Meyhofer and P. Reddy, Radiative heat transfer in the extreme near-field, Nature, In Press.
9:00 PM - NT1.6.15
Decoding Supercrystal Structure by "Supercrystallography"
Ruipeng Li 1,Zhongwu Wang 1
1 Cornell Univ Ithaca United States,Show Abstract
Nanocrystals (NCs) behave like atoms, functionalize with surface-coating molecules, and self-assemble into periodically ordered superlattice (SL). Recent advances on synthesis and assembly of NCs have been witnessed by fast growth of NC-assembled superlattices, made up of single, binary or ternary components over control of NC size, shape and composition. However, programmable design of supercrystals with expected structure for desirable applications is still constrained by limited understanding NC−ligand interactions in solvent-mediated NC assembly processes. Meanwhile, low penetration of electron beam used for structural characterization in electron microscopy provides information of only very thin layers, which differs significantly from large assembled samples.
We have grown large single supercrystals and developed ‘supercrystallography’ as a synchrotron-based Small/Wide Angle X-ray Scattering (SAXS/WAXS) approach for single supercrystal to overcome the low in-depth penetrating ability and resolve the structure of nanocrystal assembly from atomic to mesoscale. We collected a series of SAXS/WAXS images of supercrystal, which allow us to accurately reconstruct the shape orientations of NCs at various crystallographic sites and explore the inter-particle packing configurations. In situ SAXS measurements under high pressure offer additional insights into surface ligand density and nature of ligand–NC interactions, as well as the correlations between strain and lattice distortion, which present a primary image of various superlattice polymorphs to elucidate the superlattice transformations and associated developing pathways. These results provide detailed structural information towards controlled design and efficient materials-processing for fabrication of nano-based functional materials with tailored structures and desired properties
9:00 PM - NT1.6.16
Effect of Nanostructure Embedding on the Light Matter Interactions at Metal/Polymer Interface
Binxing Yu 3,Martin Vacha 2,Deirdre O'Carroll 3
3 Department of Chemistry and Chemical Biology Rutgers Univ. Piscataway United States,2 Tokyo Institute of Technology Tokyo Japan1 Department of Materials Science amp; Engineering Rutgers Univ Piscataway United States,3 Department of Chemistry and Chemical Biology Rutgers Univ. Piscataway United StatesShow Abstract
It is well known that exciton quenching can be significant at metal-semiconductor spacings of a few nanometers due to very efficient dipole-dipole energy transfer between the conjugated polymer materials and the metal. However, certain nanoantenna designs can mitigate the effects of dipole-dipole interactions by having high radiative nanoantenna efficiency and a large local density of optical states in the nanoantenna near field. Optical response in a structure with ultra-thin conjugated polymer film sandwiched between metal nanostructure and metal thin film was identified and manipulated. Single-particle dark-field scattering spectra showed distinct resonance features assigned to four different modes: a horizontal image dipole coupling mode, a vertical image dipole coupling mode and horizontal and vertical coupling modes between localized surface plasmon resonances (LSPRs) and surface plasmon polariton (SPPs). We found that Au nanostructure with sufficient size can result in partial embedding when positioned on top of conjugated thin films such as P3HT and MEHPPV. Simultaneous dark-field and photoluminescence measurements was conducted to investigate whether the significantly enhanced electric fields in this “sphere on plane” system can outpace the metal quenching and result in the enhancement of emission efficiency in the embedded system. Through multi-beam defocused imaging, a full 3D orientation of the scattering dipole moment can be extracted. Compared with polymers that exhibit no embedding, we found that not only does embedding situation show a more complex electromagnetic interaction, but also proved that the strong field enhancement in the gap region not only compensates the quenching of emission brought by the metallic ground plane, but also increases the emission efficiency.
9:00 PM - NT1.6.17
A Kinetic Investigation of Charge Transfer Characteristics of Hyperbolic Metamaterials
Olivia Penrose 1,Carl Bonner 1
1 Center for Materials Research Norfolk State University Norfolk United States,Show Abstract
The motivation of the research is to understand the quantum phenomena of charge transfer characteristics of hyperbolic metamaterials, specifically materials in which the dielectric constant is different in different directions and negative in one direction. The metamaterials are alternating layers of Au and MgF2 with a metal-like negative dielectric constant perpendicular to the stack and a positive dielectric constant in the plane of the stack. The research will observe the enhancement kinetic rate of electron transfer, which cannot be fully explained by the distance dependence of Marcus theory.
We have used Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) to study the rate of electron transfer (ET) at the surface of the electrode in our electrochemical cell. Our system consists of a SCE reference electrode, a Pt counter electrode, and Au on In-doped SnO2 (ITO) working electrode with a range of materials between the ITO and exterior Au surface. The redox couple is K3Fe(CN)6 , a stable, reversible, well characterized one-electron redox couple. The interior materials in the working electrode included, thick (~200 nm) and thin (25 nm) Au layers, thick and thin MgF2 layers, a 20 nm Au - 20 nm alkanethiol self-assembled monolayer (SAM) as well as multilayer stacks of alternating Au-MgF2, which formed our metamaterial.
As expected, the electron transfer rates of our redox couple on bare Au, Au layers coated with self-assembled monolayers (SAM) followed the usual distance dependence. Further, the ET rate for layer of MgF2 were slower than our SAM in accordance with the difference in the dielectric constants of MgF2 and the SAM. The observed ET rate for our electrode with the metamaterial was competitive with the thin and thick Au layers. We compare our rates to the variable directional dielectric constants. CV data and EIS measurements are used to understand the mechanism of reduction of the redox couple and to extrapolate ET kinetic and carrier diffusion coefficients.
9:00 PM - NT1.6.18
Photothermal Response of Gold Nanorods Prepared in the Presence of Salicylic Acid Derivatives
Iris Guo 1,Michael Wang 1,Idah Pekcevik 1,Byron Gates 1
1 Simon Fraser University Burnaby Canada,Show Abstract
Anisotropic metal plasmonic nanomaterials, such as gold nanorods, are attractive for a variety of applications that utilize localized heating effects that result from photothermal processes. Through photothermal processes, the gold nanorods can be used as a platform to trigger small molecule release and/or localized cell death. These nanomaterials have an advantage that their localized surface plasmon resonance properties are coupled to both their shape and aspect ratio; tuning the physical features of gold nanorods during their synthesis is a simple means to control their optical properties and, thus, photothermal efficiencies over a variety of electromagnetic energies. The second component of utilizing gold nanorods as vehicles for photothermal triggered events is to understand (and control) the evolution of their size and shape under photothermal conditions. High photon fluxes during photothermal processes are known to induce structural and morphological changes to gold nanorods, but these changes are dependent on a number of factors that include the surface chemistry of these materials. Understanding the potential instability of gold nanorods is vital to retain their plasmonic properties for prolonged or repeated use in photothermally triggered processes. The study discussed here introduces the photothermal response of gold nanorods prepared by a modified seed mediated synthesis that uses a mixture of surfactants to control and direct the growth of the nanorods. One class of surfactants, salicylic acid derivatives, have been recently introduced for high yield, controlled synthesis of gold nanorods, and their photothermal response will be discussed based on the results of a combined analysis from extinction spectroscopy, dynamic light scattering, and electron microscopy techniques (e.g., STEM, EDS, and HR-TEM).
9:00 PM - NT1.6.19
Highly Uniform Self-Assembled Metasurfaces for Enhanced Emission
Matthew Rozin 1,Eric Brown 1,Andrea Tao 1
1 NanoEngineering Univ of California-San Diego San Diego United States,Show Abstract
Towards realization of nanoscale opto-electronic devices, nanocube-on-metal metasurfaces show particular promise in large spontaneous emission rate and fluorescence enhancement. Previously reported emission enhancement using film-coupled nanocubes varies widely based on the degree of spatial control of the emitter in the nanocube cavity. Here, we demonstrate an optimized structure where a dense-packed layer of CdSe/ZnS quantum dots is precisely positioned in the cavity formed by the film-coupled Ag nanocubes. The quantum dot layer—electromagnetically isolated from the metal film and nanocubes—provides a uniform spacer layer for maintaining a precise nanocube-film gap. We observe uniform fluorescent and radiative rate enhancement of the quantum dots as a function of the plasmon gap-mode resonance.
9:00 PM - NT1.6.20
Solar Steam Generation by Concentrating Heat
Fatih Canbazoglu 1,Prabhakar Bandaru 1
1 UCSD La Jolla United States,Show Abstract
Recent solar steam generation technologies require high solar concentration to be able to heat the bulk liquid to high temperatures which has drawbacks such as high optical loss, surface heat loss and high system cost. We are working on a one layer porous structure which stays on top of the water and enhance the evaporation rate and solar-thermal efficiencies rapidly. The main characteristic of the structure is localizing heat in the top region of the water while wicking the water through the porous structure. Four main characteristic of the structure helps to have the heat localization and high efficiencies which are high solar absorption, insulating behaviour of the porous structure to keep the heat on the top hot region, hydrophilic surfaces to promote wicking and interconnected porosity for fluid flow movement through the structure. We achieved almost four times more steam generation with carbon structure (1.56 kg/m2) than pure water case ( 0.392 kg/m2) under 1 Sun ( 1000W/m2) situation. Right now, we are working on new materials to improve the efficiencies of the system. This new way of comparatively cheap steam generation will have many applications.
9:00 PM - NT1.6.21
High-Density 2D Homo- and Hetero- Plasmonic Dimers with Universal sub-10-nm Gaps
Mingliang Zhang 3,Nicolas Large 4,Ai Leen Koh 3,Yang Cao 4,Alejandro Manjavacas 4,Robert Sinclair 3,Peter Nordlander 4,Shan Wang 3
1 University of Pennsylvania Philadelphia United States,3 Stanford University Stanford United States,2 Northwestern University Evanston United States,4 Rice University Houston United States3 Stanford University Stanford United States4 Rice University Houston United StatesShow Abstract
Fabrication of high-density plasmonic dimers on a large (wafer) scale is crucial for applications in surface-enhanced spectroscopy, bio- and molecular sensing, and optoelectronics. Here, we present an experimental approach based on nanoimprint lithography and shadow evaporation that allows for the fabrication of high-density, large-scale homo- (Au�Au and Ag�Ag) and hetero- (Au�Ag) dimer substrates with precise and consistent sub-10-nm gaps. We performed scanning electron, scanning transmission electron, and atomic force microscopy studies along with a complete electron energy-loss spectroscopy (EELS) characterization. We observed distinct plasmonic modes on these dimers, which are well interpreted by finitedifference time-domain (FDTD) and plasmon hybridization calculations.
9:00 PM - NT1.6.22
Azopolymer-Based Nanofabrication Method for Fluorescence-Enhancing Plasmonic Nanostructures
Ville Pale 1,Jorma Selin 1,Christoffer Kauppinen 1,Markku Sopanen 1,Ilkka Tittonen 1
1 Department of Micro and Nanosciences Aalto University Espoo Finland,Show Abstract
Fluorescence-based measurement techniques are fundamentally limited in terms of performance by the intrinsic quantum yield of a fluorophore. The fluorescence emission of a fluorophore can be significantly improved with radiative decay engineering enabled by metallic nanostructures. Especially, periodic arrays of metallic nanostructures have the advantage of exhibiting a strong and prescribed optical response, which is beneficial for improving sensitivity in surface enhanced spectroscopic techniques
Usually, these arrays are fabricated using electron beam lithography (EBL), in which the size of the array typically lies in the order of 100 x 100 µm2. Due to its serial nature, EBL is not particularly suitable for high-throughput, large-scale fabrication. In this work we present a variant of interfencence lithographic method to create periodic plasmonic nanoparticle arrays for fluorescence enhancement that utilizes azobenzene-containing polymers (azopolymers) as the resist material. This approach allows us to circumvent the generation of a standing wave pattern within the resist when performing the exposure on a reflective surface and substantially mitigates the processing requirements. Hence, this enables a cost-effective and large-scale fabrication scheme for plasmonic arrays with tunable response.
We demonstrate the creation of periodic arrays of symmetrical metallic nanostructures that exhibit a good long-range order. Furthermore, the dimensions of the array and the structures can be tuned by changing the exposure or process parameters. The optical properties of the fabricated structures was studied both experimentally and theoretically. The fluorescence enhancement performance was verified by using Rhodamine 6G and Cascade Blue as the fluorophores for blue and green wavelength regions. We expect that this fabrication approach could be advantageous for other application areas of plasmonics, such as SERS or sensing.
9:00 PM - NT1.6.23
pH Imaging of Multiphase Systems in Microfluidic Channels Using an Embedded Silica-Shell Nanoparticle with Plasmonic Enhancement
Mazeyar Gashti 1,Jeremie Asselin 1,Denis Boudreau 1,Jesse Greener 1
1 Chemistry Laval University Québec Canada,Show Abstract
We demonstrate a nanoparticle-based pH sensing surface embedded in a microfluidic device for in situ chemical mapping of heterogeneous systems relevant to chemical biology and environmental science. A planar glass substrate is covalently grafted with core-shell nanoparticles, comprised of a spherical silver core covered by a pH-sensitive fluorescent indicator encased in a uniform silica shell. By allowing the conducting electrons in the metal core to couple to the fluorophores, this nanoarchitecture provides improved brightness and robustness with regards to photobleaching. In addition, the immobilized fluorophores within the silica shell are protected from shear-force driven detachment and diffusion into the surrounding media. The resulting sensing system was used for quantitative, spatially-resolved pH measurements in multiphase systems at high frame rates with standard epifluorescence microscopes. A variety of validation and proof-of-concept measurements were conducted. These included spatially resolved pH mapping of co-flowing streams, monitoring proton diffusion across flowing liquid-liquid interfaces, monitoring the acidification of an aqueous environment by CO2 gas bubbles and observing time- and spatially-dependent extracellular acidification by oral biofilms.
9:00 PM - NT1.6.24
Strong Chiroptical Response of Biomolecule-Coupled Plasmonic Nanostructure: Ultrasensitive Detection of Chiral Molecules
Hyo-Yong Ahn 1,Hye-Eun Lee 1,Ki Tae Nam 1
1 Material Science and Engineering Seoul National University Seoul Korea (the Republic of),Show Abstract
The chirality of organic and biomolecules is exhibited by molecular structures, which is one of the crucial determinants for many biological reactions. Though diverse methods are used to probe the chirality of molecules, chiroptical spectroscopic methods such as optical rotation dispersion(ORD), circular dichroism(CD) and Raman optical activity(ROA) are mainly used to analyze the chirality and conformational information of molecules. However, the optical transitions of molecules are generally in ultraviolet(UV) region, and the intensity of their chiroptical signal is very weak. To detect the chiroptical signal in practice, the amount of molecules is limited to microgram level. Meanwhile, noble metal nanostructure has strong absorption band in visible region, corresponding to localized surface plasmon resonance(LSPR) phenomenon, and plasmon resonance effect can be utilized to amplify molecular signals such as surface enhanced Raman scattering(SERS) and enhanced fluorescence. Recently it was theoretically and experimentally demonstrated that the coupling of plasmonic structure and chiral molecule can generate new plasmon induced chiroptical signal in visible range, which has enhanced intensity in comparison with weak molecular signal in UV region. Here we demonstrate strong chiroptical responses in plasmon resonance using various plasmonic nanostructures coupled with chiral molecules. Using nanofabrication techniques such as colloidal synthesis, nanosphere lithography and e-beam lithography, we fabricated novel plasmonic nanostructures including chiral and achiral geometries. Those nanostructures are coupled with various biomolecules such as amino acid, peptide assembly, protein and DNA, so we constructed combinations of achiral structure-chiral biomolecule and chiral structure-chiral biomolecules with different scale and directionality. Using those biomolecule-coupled plasmonic nanostructures, we observed strong chiroptical responses originated from interaction of biomolecule and plasmon at nanogram level. We expect that this research will provide ultrasensitive probing of chiral molecules and further understanding of plasmon induced chiroptical phenomenon.
9:00 PM - NT1.6.25
Brookite TiO2 Nanorods as Ideal Building Blocks for Photoelectrochemical Water Oxidation: Bulk versus Surface Plasmonic Decoration
Alberto Naldoni 1,Francesco Malara 1,Marta Mroz 2,Alessandro Beltram 3,Tersilla Virgili 2,Marcello Marelli 1,Tiziano Montini 3,Vladimiro Dal Santo 1,Paolo Fornasiero 3
1 CNR-Istituto di Scienze e Tecnologie Molecolari Milan Italy,2 Dipartimento di Fisica CNR - Istituto di Fotonica e Nanotecnologie (IFN) and Politecnico di Milano Milan Italy3 Dipartimento di Scienze Chimiche e Farmaceutiche e Unità di Ricerca ICCOM-CNR Università degli Studi di Trieste Trieste ItalyShow Abstract
A promising strategy to extend the harvested solar light by TiO2 to the visible/NIR wavelength range consists in its sensitization with plasmonic metal nanostructures (e.g., Au).  By acting as an antenna that localizes the optical energy by localized surface plasmon resonance (LSPR), Au sensitizes TiO2 to light with energy below the bandgap generating additional charge carriers for water oxidation. [2,3] Moreover, plasmonic metallic centers can generate increased light absorption through radiative scattering. In order to build efficient plasmonic PEC devices, one of the key design issues to be still clearly defined is the effect of the location of plasmonic component with respect to both the semiconductor and the electrolyte. [4-6] In this contribution we show that brookite TiO2 nanorods are the ideal building blocks for addressing these unanswered questions on plasmonic geometry.  Through a precise control of Au nanoparticles deposition, we show that the bulk (TiO2/Au-bulk) versus preferential surface (TiO2/Au-surface) Au decoration generates profound difference in PEC activity and photoinduced charge separation processes occurring in the photoelectrodes.
Brookite nanorods photoanodes showed a maximum photocurrent of 0.14 mA/cm2 and a record onset potential of -0.2 V (RHE). Au-decorated samples showed no change in onset potential. However, the photocurrent of TiO2/Au-surface was almost doubled if compared to reference TiO2 and TiO2/Au-bulk. Electrochemical impedance measurements showed that TiO2/Au-surface had lower charge transfer resistance and higher donor density than both pure TiO2 and TiO2/Au-bulk. Femtosecond ultrafast pump-probe spectroscopy revealed that in both samples containing Au nanoparticles, plasmonic hot electrons injection occurred in ~150 fs. Most importantly, in TiO2/Au-bulk all excited carriers recombine on the same timescale of plasmonic injection, whereas in TiO2/Au-surface we detected two and four orders magnitude longer charge decay times (ps and ns). These results are in agreement with the photocurrent trend. When Au nanoparticles are homogeneously dispersed in the film of brookite nanocrystals (TiO2/Au-bulk), they act as recombination centres. Differently, if Au is preferentially deposited close to the electrode/electrolyte interface (TiO2/Au-surface) the plasmonic sensitization is effective providing extra charges for water oxidation.
 M .L. Brongersma et al. Nat Photonics 2015, 10, 25–34.  Y. C. et al. Nano Lett 2013, 13, 3817–23.  L. Amidani et al. Angew Chemie Int Ed 2015, 54, 5413–6.  E. Thimsen et al. Nano Lett 2011, 11, 35–43.  I. Thomann et al. Nano Lett 2011, 11, 3440–6.  Z. Zhan ACS Appl. Mater. Interfaces 2014, 6, 1139−44.  A. Beltram et al. Appl. Catal. A 2015, doi:10.1016/j.apcata.2015.09.022.
9:00 PM - NT1.6.26
Revealing Self-Induced InAlN Core-Shell Nanorod Formation Mechanism and Their Unique Optical Properties
Justinas Palisaitis 1,Ching-Lien Hsiao 1,Lars Hultman 1,Jens Birch 1,Per Persson 1
1 Linkoping University Linkoping Sweden,Show Abstract
Semiconductor materials fabricated in the form of nanorods (NRs) offer fascinating physical properties and engineering capabilities in future nanoscale functional units . In particular, group-III nitride semiconductor NRs based on AlN, GaN, InN and their ternary alloys are attractive due to the widely tunable direct bandgap (0.64-6.2 eV), high crystal quality and improved light extraction efficiency. The implementation of heterostructures inside ternary NRs (e.g., core-shell InAlN) drastically extends their optical performance together with advantages of the 1D geometry. Recently, self-induced ternary nitride core-shell NRs have been demonstrated [2-4]. However, the understanding of the formation mechanism and optical properties remains debated.
We have examined the magnetron sputter expitaxy grown self-induced InAlN core-shell NR formation processs by means of transmission electron microscopy methods. The results show that the grown structure phase separates during the initial moments of deposition into AlN-rich (majority) and InN-rich islands. The islands possess polygonal shapes and are mainly c-axis oriented. The growth proceeds with densification and coalescences of the InN-rich islands, resulting in a base for the InN-rich NR cores with shape transformation to hexagonal. The AlN-rich shell formation around such early cores is observed at this stage. The matured core-shell structure grows axially and radially, eventually reaching a steady growth state which is dominated by the axial NR growth. To account for the present observations we consider a number of factors affecting the NRs evolution, including: adatom (In, Al, and N) surface kinetics (adsorption, desorption and surface diffusion), chemical potential of islands, surface energy, thermal stability, and incoming flux (shadowing effect). Herein we provide direct atomic scale experimental observations of core-shell NRs nucleation, coalescence and growth, through which we present a growth model.
In parallel, we explored the optical properties of self-induced InAlN core-shell NR. We will demonstrate how implementation of curved-lattice epitaxial growth (CLEG)  could be used for synthesizing chiral InAlN core-shell NRs and tailor their optical properties. CLEG growth induces curved lattice and composition grading along the lateral direction of NRs. The reflected lights exhibit very high degree of circular polarization of around 80%, indicating nearly circular polarization with opposite right- and left-handed polarization, respectively, from the two opposite chirality NR samples.
 C. R. Eddy Jr., et al., J. Vac. Sci. Technol. A 31, 058501 (2013).
 C.-L. Hsiao, et al., Appl. Phys. Exp. 4, 115002 (2011).
 M. Gómez-Gómez, et al., Nanotechnology. 25, 075705 (2014).
 R. F. Webster, et al., Phys. Status Solidi C 11, 417–420 (2014).
 G. Z. Radnóczi et al., Phys. Stat. Sol. (a) 202, R76 (2005).
9:00 PM - NT1.6.27
Nickel Electrodeposition on Anodized Aluminum Oxide Films as Selective Absorbing Coating Made by AC Voltage with Variable Frequency
Samuel Santiago 2,Arturo Fernandez Madrigal 2,Julio Rodriguez Gonzalez 1,Eduardo Mercado Aguilar 1,Ogilver Teniza Garcia 1
1 Universidad Tecnologica de Huejotzingo Huejotzingo Mexico,2 Solar Materials UNAM Temixco Mexico,2 Solar Materials UNAM Temixco Mexico1 Universidad Tecnologica de Huejotzingo Huejotzingo MexicoShow Abstract
Anodized aluminum oxide films (Al2O3) on aluminum substrates 1050 (99.5% w Al) was impregnated with nickel (Al2O3-Ni) by electrodeposition technique with alternating current (AC) voltage with variable frequency. In this paper, we report the synthesis of Ni using the galvanostat mode, as well as some experimental variations in the frequency and intensity of AC voltage in order to optimize the amount of nickel in the oxide aluminum substrates. EDS, XRD, SEM and UV-VIS spectrophotometry techniques was used to analyses the atomic composition, structural morphology and optical properties of the samples. Additionally, an emissometer was used to measure the hemispherical thermal emissivity. Data values of the total reflectance for the visible solar spectrum (VIS) and near infrared (NIR) as a function of voltage and frequency for fixed times nickel impregnation were analyzed, several experiments were performed with in order to correlate these parameters with the nickel content in the bottom of the pores of the films and their optical properties. Absorptance values between 0.09 to 0,15 and emittance values of 0.09 to 0.15 were obtained, the pores of the films developed to 11 Vrms and 60 Hz are filled with nickel 30% by volume pore and optical properties αs= 0.83, ET(80oC) = 0.11 that make them good prospects for application in solar collectors.
9:00 PM - NT1.6.28
Aligned Epitaxial Titanium Nitride (TiN) and Titanium Oxynitirde (TiNO) Nanowires for Solar Energy and Optical Applications
Chandra Shekar Reddy Nannuri 1,Mayur Singh 1,Rahul Goud Ponnam 1,Svitlana Fialkova 1,Sergey Yarmolenko 1,Zhigang Xu 1
1 North Carolina Aamp;T State Univ Greensboro United States,Show Abstract
This paper reports a first-hand fabrication of single crystalline titanium nitride (TiN) nanowires using a bottom-up method on sapphire (single crystal Al2O3) by catalyst-assisted pulsed laser deposition. The growth strategy involves depositing ultra-thin gold films and subjecting them to in-situ annealing in high vacuum for 10 min at 800 °C to form gold nanodots. This is followed by TiN nanowire deposition by ablating TiN target in 200 mtorr of nitrogen ambient. After deposition the samples were cooled down to room temperature in same ambient pressure. By this simple growth strategy we fabricated highly oriented and epitaxial TiN nanowires. The influence of the deposition pressure, seed-particle, temperature, and annealing time on the composition, structure and internal stress was studied systematically. As the deposition pressure is increased from (100 mtorr-350 mtorr), the nanowires evolves from mixture of α-TiN0.30 (002) and pure TiN (200) to stoichiometric pure TiN (200), and finally to overstoichiometric TiN. At a critical pressure of 200 mtorr, vertically aligned, highly oriented, and epitaxial TiN1+x (x≥0) (200) nanowires possess a cubic structure with diameter of (20-30) nm, length (500-550) nm. We found that in-situ gold annealing time plays a major role in TiN phase formation, crystal growth direction and morphology. In addition we investigated how growth parameters mainly substrate temperatures (600- 800 °C), laser fluence (2-5 J/cm2), growth time (5-60 min), particle size (20-60nm) and nanowires length (500-600nm) affect typical growth characteristics such as morphology, crystal growth direction, nucleation, crystal structure, and growth rate. The study of electrical resistance as a function of temperature shows that these nanowires have semiconducting behavior. Mainly the effect of deposition pressure, temperature and catalyst on structural and electrical properties of nanowires has been studied by transport measurements for tuning electrical properties. Further the metallic TiN nanowires were converted to TiN1-xOx (TNO) oxinitride nanowires that have potential application in water splitting and hydrogen generation using visible solar light. The band gap of TNO was tailored to be in the visible range (λ > 415 nm) by controlling the oxygen content in TNO. In brief we demonstrate the growth phenomenon of high crystalline quality of the TiN nanowires on single crystal Al2O3. The epitaxial growth of semiconductor nanowires with high structural quality has major importance in device applications in electronics, photonics, optical, and solar cells.
9:00 PM - NT1.6.29
Fabrication of Defect-Rich TiO2, and ZrO2 and SnO2 Nanostructured Devices for Enhanced Solar Energy Conversion
Md Anisur Rahman 1
1 WATLab, Dept of Chemistry Univ of Waterloo Waterloo Canada,Show Abstract
Engineering the defects in wide-band gap transparent conductive oxide semiconductors are crucial in governing the physical and chemical properties of these oxides. Enormous efforts have been made to narrow the band gap and to extend the working spectrum to the visible light region. Unfortunately, all of these efforts provides two to three orders less photoactivity when ultraviolet light (<430 nm) is filtered out from the AM 1.5 G spectrum. Compared to other type of defects (such as those introduced by doping, hydrogen treatment), oxygen vacancy defects are desirable for wide band gap semiconductors because the oxygen vacancies act as electron donors and could therefore significantly enhance light absorption and electrical conductivity. The dependence of photoelectrochemical activity on the surface morphology of and the amount of oxygen vacancy defects in the 1D nanostructures are also not well understood.
We have succeeded in synthesizing several defect-rich 1D nanostructures of TiO2, SnO, and ZrO2 for the first time by by an efficient vapour deposition approach, with the goal to reduce cost, to simplify the process and to greatly improve the performance and stability. Photoelectrochemical measurement of TiO2 nanowires under simulated sunlight shows that the observed photocurrent densities in AM 1.5G light were found to reduce by nearly 50% when ultraviolet light was filtered out (>430 nm), we observe only a 13% reduction with just the visible light component in the present work.1 Similarly, the defect-rich p-type hierarchical ZrO2 nanowires also showed high photoelectrochemical activity in the longer wavelength visible light. A remarkable improvement in the solar cell performance, including open circuit voltage, short circuit current density, fill factor, and photoconversion efficiency is observed for the hierarchical SnO2 nanostructured photoanode.2 More importantly, precisely controlled deposition of size-selected TiO2 NCs produced by gas-phase aggregation in a special magnetron sputtering system exhibit remarkable photoelectrochemical water splitting performance in spite of a small amount of material loading.3
We expect these results (and precisely defect-rich decorated 1D nanostructured materials) to have a significant impact in the design of efficient and low-cost photoanodes working in visible light for green energy applications.
1. Md Anisur Rahman et al.,, “Defect-rich decorated TiO2 nanowires for super-efficient photoelectrochemical water splitting driven by visible light.” 2015, Energy & Environmental Science (DOI: 10.1039/C5EE01615K).
2. M. Abd-Ellah, Md Anisur Rahman, et al., “Hierarchical Tin Oxide Nanostructures for Dye-Sensitized Solar Cell Application.” 2015, Advanced Electronic Materials, 1, 9.
3. S. Srivastava, Md. Anisur Rahman, et al., “Size-Selected TiO2 Nanocluster Catalysts for Efficient Photoelectrochemical Water Splitting.” 2014, ACS Nano, 8(11), 11891-11898.
Alexander Govorov, Ohio University
Renaud Bachelot, University of Technolology of Troyes, Charles Delaunay Institute, CNRS
Din Ping Tsai, Academia Sinica
Gary Wiederrecht, Argonne National Laboratory
NT1.7: Photovoltaics with Advanced Nanomaterials
Thursday AM, March 31, 2016
PCC North, 100 Level, Room 129 A
9:30 AM - *NT1.7.01
Multiple Exciton Generation in Semiconductor Quantum Dots and Rods, Arrays, Buried Junctions, and Novel Molecules: Applications to Future Generation Solar Photon Conversion to Photovoltaics and Solar Fuels
Arthur Nozik 2
1 Department of Chemistry University of Colorado Boulder United States,2 NREL Golden United States,Show Abstract
In order to utilize solar power for the production of solar electricity and solar fuels on a global scale, it will be necessary to develop solar photon conversion systems that have an appropriate combination of high efficiency (delivered watts/m2) and low capital cost ($/m2). One potential, long-term approach to attain high conversion efficiencies above the well-known Shockley-Queisser thermodynamic limit of 32% is to utilize the unique properties of quantum dot/rod (QD/QR) nanostructures to control the relaxation dynamics of photogenerated carriers to produce either enhanced photocurrent through efficient photogenerated electron-hole pair multiplication or enhanced photopotential through hot electron transport and transfer processes. To achieve these desirable effects it is necessary to understand and control the dynamics of hot electron and hole relaxation, cooling, charge transport, and interfacial charge transfer of the photogenerated carriers. These fundamental dynamics in various bulk and nanoscale semiconductors have been studied for many years using transient absorption, photoluminescence, photocurrent, and THz spectroscopy with fs to ns time resolution The prediction that the generation of more than one electron-hole pair (which exist as excitons in size-quantized nanostructures) per absorbed photon would be an efficient process in QDs and QRs has been confirmed over the past several years in different classes of materials and their architectures. Very efficient and ultrafast multiple exciton generation (MEG), also called Carrier Multiplication (CM), from absorbed single high energy photons has been reported in Group IV-VI and Group IV semiconductors and associated solar photon conversion devices for solar electricity and solar fuels (e.g. H2) production. Selected aspects of this work will be summarized and recent advances will be discussed. Finally, the analogous MEG effect in molecules (called singlet fission) and its use in molecular-based solar cells will also be discussed
10:00 AM - NT1.7.02
Electrocatalysis in Photovoltaics:#xD;
Research on Counter Electrode in Dye-Sensitized Solar Cells
Yantao Shi 1,Suxia Liang 1,Jiahao Guo 1,Huawei Zhou 1,Chunyu Zhao 1,Tingli Ma 1
1 State Key laboratory of Fine Chemicals, School of Chemistry, Dalian University of Technology Dalian China,Show Abstract
Among various photovoltaics, some require electrolyte to serves as “shuttles” for charge transmission, e.g. dye-sensitized solar cells (DSCs). As one key component in DSCs, counter electrode is responsible for collection of electrons from external circuit and reduction of the redox couple, e. g. triiodide (I3–) and iodide (I–). Generally, CE can be prepared by sputtering of platinum (Pt) on conductive glass. However, there are many limitations in terms of using Pt as CEs, like resource scarcity. Consequently, minimizing the use of Pt or replacing Pt with inexpensive but efficient catalyst is meaningful and has become one of the priorities in this field. Recent years, we have developed dozens of inorganic materials that proved very efficient and nearly approached Pt when fabricated into CE for DSCs. These non-Pt materials include oxides, sulfides, selenides, and tellurides. In our work, the structure-effect relationships at multiscale were revealed systematically, for example, the dependence of catalytic activity and selectivity on crystallinity, microscopic morphology, surface structure, and so on.
Single-atom catalysts (SACs) currently is a new frontier in the fields of catalytic science. SACs can be regarded as one extreme case because the particle size reaches the limit. In our work, we for the first time demonstrated the use of SAC of FeOx-supported Pt single atoms (Pt/FeOx-SAC) as counter electrode (CE) in dye-sensitized solar cells (DSCs). The electrocatalytic and photovoltaic behaviors of such SACs in mesoporous photovoltaic device, and the remarkable atom utility were well illustrated. Compared with conventional Pt CE, the SAC-based CE exhibited a much better activity and reversibility for catalytic reduction of triiodide into iodide. Pt/FeOx-SAC with an extremely Pt loading (only 0.08%) exhibited the most effective atom utilitzation and doubled the power conversion efficiency (PCE) of the DSCs based on bare FeOx. Using such Pt/FeOx-SACs, high PCEs were achieved while the consumption of Pt in DSCs would be reduced significantly. We ascribed the superior catalytic performance of Pt/FeOx-SAC to the unsaturated coordination environment of Pt single atom. Besides, the Pt/FeOx-SAC also exhibited good stability in the electrolyte solution because Pt single atoms were chemically and tightly bonded on the support. Finally, we proposed some effective strategies to further improve the performance of SAC in DSCs.
10:15 AM - NT1.7.03
The Grass is Always Greener: Lawn-Like TiO2 Nanofiber-Carbon Nanotube-Composite Dye-Sensitized Solar Cells
Thomas Macdonald 1,Ivan Parkin 1,Joseph Shapter 2,Thomas Nann 3
1 Department of Chemistry University College London London United Kingdom,2 Centre for Nanoscale Science and Technology Flinders University Bedford Park Australia3 MacDiarmid Institute for Advanced Materials and Nanotechnology Victoria University of Wellington Wellington New ZealandShow Abstract
Electrospun titanium dioxide nanofibers (TiO2-NFs) and single-walled carbon nanotubes (SWCNTs) were combined to form a nanocomposite light-scattering layer for dye-sensitized solar cells (DSSCs). No nanoparticulates were present in the light-scattering layer and the combination of TiO2-NFs and SWCNTs and formed a fibrous lawn-like nanoarchitecture. The integration of SWCNTs to the TiO2-NFs DSSCs increased the power conversion efficiency (PCE) from 2.90 % to 4.83 % under 1 sun illumination. Furthermore, TiO2-NF and TiO2- NF/SWCNT-based DSSCs reached PCE values of up to 3.7 % and 6.6 % under reduced light intensities (0.25 sun). We hypothesize that the addition of SWCNTs provides additional charge-transport channels, which contributes to an increase in the diffusion coefficient and significant improvement in device performance.1
(1) Macdonald, T. J.; Tune, D. D.; Dewi, M. R.; Gibson, C. T.; Shapter, J. G.; Nann, T. ChemSusChem 2015, n/a – n/a
10:30 AM - NT1.7.04
Multiple Plasmonic Effect on Organic Thin Film Solar Cells
Akira Baba 1,Supeera Nootchanat 2,Apichat Pangdam 2,Sanong Ekgasit 2,Chutiparn Lertvachirapaiboon 1,Kazunari Shinbo 1,Keizo Kato 1,Futao Kaneko 1
1 Niigata Univ Niigata Japan,1 Niigata Univ Niigata Japan,2 Chulalongkorn University Bangkok Thailand2 Chulalongkorn University Bangkok ThailandShow Abstract
The use of plasmonic structures have been a great deal of interest in fabricating electric-field enhanced organic device applications such as biosensors and photovoltaic devices. Especially, the plasmonic solar cell is a promissing approach to create additional light traping layer facilitating the improvement light absorption capability and efficiency of the solar cells without increase of the active layer thickness. In this work, we studied the effect of grating-coupling surface plasmon excitation on organic thin film solar cells. The solar cell Al/P3HT:PCBM/PEDOT:PSS/ITO/glass was fabricated. The subwavelength diffraction grating pattern was transferred form a master template to the active layer of the solar cell using PDMS mold. The formation of the grating structure in the surface of the blended polymer was studied. The effect of two different diffraction gratings, in particular periodic (BD-R) and non-periodic (BD) were studied. The use of used-BD-R and BD can be an alternative way to reduce electronic wastes yet benefit the energy industrial. The SPR reflectivity results reveal the increase of trapped light as a broad band absorption from 400 nm to 650 nm in the device with grating structure which is originated from the effect of light scattering. The increase of the absorption at the wavelength long than 650 nm can be observed and assigned to the GCSPR of Al grating as the present of red-shifted dip when increase the incident angle. Introducing BD and BDR diffraction grating patterns as the additional light trapping layer could increase the short-circuit photocurrent and the efficiency of the solar cells. Furthermore, gold nanoparticles were added in the devices to study the mutiple plasmonic effext, i.e. both garting-coupled propagating plasmon and gold nanoparticles localized surface plasmon., on the perfoemance of organic thin film solar cells.
10:45 AM - NT1.7.05
Enhanced Absorption and Charge Photogeneration in Polymer: Fullerene Thin-Films with MoS2-Metasurface Heterostructures for Photovoltaics
Christopher Petoukhoff 2,M. Bala Murali Krishna 2,Damien Voiry 1,Ibrahim Bozkurt 1,Skylar Deckoff-Jones 2,Manish Chhowalla 1,Deirdre O'Carroll 3,Keshav Dani 2
1 Materials Science and Engineering Rutgers University Piscataway United States,2 Femtosecond Spectroscopy Unit Okinawa Institute of Science and Technology Onna Japan,2 Femtosecond Spectroscopy Unit Okinawa Institute of Science and Technology Onna Japan1 Materials Science and Engineering Rutgers University Piscataway United States1 Materials Science and Engineering Rutgers University Piscataway United States,3 Chemistry and Chemical Biology Rutgers University Piscataway United StatesShow Abstract
Polymer:fullerene-based photovoltaics have shown great promise as third-generation solar cells due to their solution-processability, low toxicity, earth-abundant elemental constituents, and short energy payback times. Although polymer:fullerene-based photovoltaic efficiency has recently exceeded 10 %, the efficiency is still limited for two primary reasons: 1) the competing constraints on the thickness of the polymer:fullerene active layer, in that it must be kept thin enough to minimize charge recombination while simultaneously being thick enough to absorb all of the incident light; and 2) conjugated polymers typically have narrow absorption bandwidths, preventing absorption of the full solar spectrum. Here, we simultaneously offer solutions to both efficiency limitations by employing plasmonic metasurfaces modified by MoS2 thin-film coatings. We demonstrate through integrating sphere reflectance measurements that the plasmonic metasurface improves absorption within thin-films of P3HT:PCBM, one of the most widely-studied polymer:fullerene active layers. Using electromagnetic simulations, we show that the absorption enhancement arises from excitation of both localized and propagating surface plasmon modes, in addition to electromagnetic coupling between surface plasmons from the metasurface and the optical transitions of the P3HT:PCBM. To address the narrow absorption bandwidth of typical polymer:fullerene active layers, we employed MoS2-metasurface heterostructures, and we show that the MoS2 plays an active role in the charge carrier photogeneration in P3HT:PCBM, resulting in a 6-fold increase in the P3HT polaron population. Using microscope-coupled reflectance measurements and electromagnetic simulations, we show that active layer absorption is broadened by 170 nm for P3HT:PCBM using MoS2-metasurface heterostructures as substrates. We show that the broadened and enhanced absorption spectrum and enhanced polaron population can only be achieved through the combined synergistic effect of the MoS2 and the plasmonic metasurface. Future work includes employing MoS2-metasurface heterostructures as electrodes in polymer:fullerene photovoltaics.
11:30 AM - *NT1.7.06
Coherent Light-Trapping in Nanostructured Solar Cells: New Limits, New Challenges
Stephane Collin 1,Andrea Cattoni 1,Nicolas Vandamme 1,Julie Goffard 1,Alexandre Gaucher 1,Jean-Francois Guillemoles 3
1 LPN-CNRS Marcoussis France,2 LIA NEXT-PV, RCAST Tokyo Japan,3 IRDEP-CNRS Chatou FranceShow Abstract
Conventional light trapping in solar cells is based on incoherent light scattering achieved with rough interfaces. However, this approach is not suitable for thin-film solar cells with thicknesses below 1µm.
We propose a new paradigm for light trapping. It is based on multi-resonant absorption in periodically nanostructured absorbers. Broadband absorption is achieved with a series of overlapping resonant modes in the critical coupling regime. We have developed a simple theoretical model and derived a closed-form expression for the absorption limit. We demonstrate that this multi-resonant critical coupling limit exceeds the conventional lambertian limit (4n2) for any absorber thickness (Jsc).
These results could allow a drastic reduction of the absorber thickness in thin-film photovoltaics. We provide numerical and experimental examples of multi-resonant absorption in ultra-thin semiconductor layers. We also present our latest experimental results of ultra-thin solar cells made of various semiconductor materials (GaAs, CIGS, c-Si). We will discuss the record short-circuit currents achieved in ultra-thin photovoltaic devices, and the technological challenges that should be addressed to reach the theoretical limits.
12:00 PM - NT1.7.07
Downscaling Diameter of Self-Organized TiO2 Nanotube towards Higher Efficiency of Hybrid Photochemical Solar Cells
Milos Krbal 1,Hanna Sopha 1,Jan Macak 1
1 Center of Materials and Nanotechnologies (CEMNAT) University of Pardubice Pardubice Czech Republic,Show Abstract
Today, there is a clear worldwide consensus regarding the need for the long-term replacement of fossil fuels by low-cost, high-efficient, renewable and environmentally friendly sources of energy. The solar cell technology becomes tremendously developing field of research which can meet the target. While the single crystal silicon solar cells possess high efficiency ~25 % , the initial cost and their fragility motivated researchers to focus on the new type thin film-based devices, such as amorphous silicon , CdTe  or CuGa1-xInxSe2 (CIGS) , dye-sensitized cells (DSSC) , organic cells  and perovskites  which can be deposited on any substrates. Still, there is a reason why thin film solar panels have not replaced older types yet. They are just not as efficient. Additionally, some thin film materials have shown degradation of performance over time and can be toxic (CdTe). However, the hybrid photocells employing TiO2 oxide/chromophore interface have potential to improve the functionality of the new solar cells .
For instance, tailoring the TiO2 anode chromophore interface can increase the efficiency of the cells, such as DSSC and perovskite-based solar cells. The enhancement can be achieved by increasing the interfacial surface area between the chromophore and the TiO2 oxide in order to facilitate charge separation. Unlike randomly ordered mesoporous TiO2 support, ordered nanostructures, such as self-organized TiO2 nanotubes with high aspect ratio or TiO2 nanowires, offer the advantage of directed charge transport and controlled phase separation between donor and acceptor materials and thus they seem to be one of the most promising nanoscale solar hybrid technologies .
Here, we will present initial photo-electrochemical results for anodic TiO2 nanotubes grown with different diameter sizes utilized as highly ordered n-type conductive scaffold for inorganic chromophores [10, 11]. Downscaling the nanotube diameter significantly increases the number of nanotubes per square unit and thus the active surface area increases as well. The photo-chemical cells were fabricated using the solvent solution method, when TiO2 nanotubes were infilled with inorganic chromophores dissolved in appropriate solvents by soaking or spin-coating. The possible improvement of such hybrid solar cells will be discussed.
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12:15 PM - *NT1.7.08
Plasmon-Induced Resonance Energy Transfer and Hot Electron Injection for Solar Energy Conversion
Nianqiang Wu 1
1 West Virginia Univ Morgantown United States,Show Abstract
For plasmonic metal-semiconductor heterojunctions, plasmon can induce the charge carries in semiconductors via two near-field mechanisms, that is, the plasmon-induced resonance energy transfer (PIRET) and the hot electron injection. This presentation will discuss the difference between the two mechanisms. PIRET proceeds via the dipole-dipole interaction between the metal and the semiconductor. It depends on the gap and the spectra overlap between the metal and the semiconductor. The hot electron injection from the metal to the semiconductor depends on the Schottky barrier at the metal-semiconductor interface. The occurrence of two mechanisms in a metal-semiconductor heterojunction is controlled by some factors such as the physical contact and the spectral overlap.
12:45 PM - NT1.7.09
Ultrafast Dynamics of Electron-Hole Pairs in Two-Dimensional InSe Layers
Jannika Lauth 1,Frank Spoor 1,Aditya Kulkarni 1,Arjan Houtepen 1,Juleon Schins 1,Sachin Kinge 2,Laurens Siebbeles 1
1 Delft University of Technology Delft Netherlands,2 Toyota Motor Europe Materials Research amp; Development Zaventem BelgiumShow Abstract
Graphene-like two-dimensional (2D) crystals with non-zero band gaps exhibit highly interesting anisotropic dimensionality-dependent properties and bear high potential for ultrathin electronics. Amongst the most investigated 2D semiconductors, one material recently moved into focus: Exfoliated InSe, a van-der-Waals layered III-VI metal chalcogenide with an atomically smooth surface. It has proven its highly promising (opto-)electronic properties as high mobility field-effect transistor  and even outperformed other 2D crystal-based compounds like MoS2 and GaSe as high responsivity (visible to NIR) photodetector [2, 3].
We have synthesized ultrathin 2D InSe layers (<6 nm with organic ligands) by a ligand templated colloidal method and have fully characterized the 2D structures with electron and atomic force microscopy, X-ray photoelectron spectroscopy and scattering methods . By applying ultrafast transient absorption spectroscopy, we evaluate the charge carrier and recombination dynamics in atomically thin InSe and extract (intrinsic) mobilities of ~30 cm2/Vs by using time-resolved terahertz spectroscopy. The combination of colloidal synthesis and pump-probe spectroscopy allows us to assess the potential of solution-processed atomic InSe layers for next generation electronics.
 Sucharitakul, S.; Goble, N. J.; Kumar, U. R.; Sankar, R.; Bogorad, Z. A.; Chou, F.-C.; Chen, Y.-T.; Gao, X. P. A., Nano Lett. 2015, DOI:10.1021/acs.nanolett.5b00493.
 Tamalampudi, S. R.; Lu, Y.-Y.; Kumar, R. U.; Sankar, R.; Liao, C.-D.; Moorthy, K. B., Karukanara; Cheng, C.-H.; Chou, F. C.; Chen, Y.-T., Nano Lett. 2014, 14, 2800-2806.
 Lei, S.; Ge, L.; Najmaei, S.; George, A.; Kappera, R.; and Lou, J.; Chhowalla, M.; Yamaguchi, H.; Gupta, G.; Vajtai, R.; Mohite, A. D.; Ajayan, P. M.; ACS Nano 2014, 8, 1263-1272.
 ] Lauth, J.; Gorris, F. E. S.; Samadi Khoshkhoo, M.; Chassé, T.; Wiebke Friedrich, W.; Lebedeva, V.; Meyer, A.; Klinke, C.; Kornowski, A.; Scheele, M.; Weller, H., submitted.
NT1.8/EE3.8: Joint Session: Recent Developments in Optoelectronics and Photovoltaics
Thursday PM, March 31, 2016
PCC North, 100 Level, Room 129 A
2:45 PM - *NT1.8.01/EE3.8.01
Optoelectronics: Is There Anything It Cannot Do; Can Opto-Electronics Provide the Motive Power for Future Vehicles
Vidya Ganapati 1,T. Xiao 1,Eli Yablonovitch 1
1 Electrical Engineering and Computer Sciences Dept. University of California, Berkeley Berkeley United States,Show Abstract
A new scientific principle[i] has produced record-breaking solar cells. This is exemplified by the mantra: “A great solar cell also needs to be a great LED”. It is essential to remove the original semiconductor substrate, which absorbs luminescence, and to replace it with a high reflectivity mirror.
In thermo-photovoltaics, high energy photons from a thermal source are converted to electricity. The question is what to do about the majority of low energy infrared photons? It was recognized that the semiconductor band-edge itself can provide excellent spectral filtering for thermophotovoltaics, efficiently reflecting the unused infrared radiation back to the heat source. Exactly those low energy photons that fail to produce an electron-hole pair, are the photons that need to be recycled.
Thus the effort to reflect band-edge luminescence in solar cells has serendipitously created the technology to reflect all infrared wavelengths, which can revolutionize thermo-photovoltaics. We have never before had such high rear reflectivity for sub-bandgap radiation, permitting step-function spectral control of the unused infrared photons for the first time. This enables conversion from heat[ii] to electricity with >50% efficiency. Such a lightweight “engine” can provide power to electric cars, aerial vehicles, spacecraft, homes, and stationary power plants.
[i] O. D. Miller, Eli Yablonovitch, and S. R. Kurtz, “Strong Internal and External Luminescence as Solar Cells Approach the Shockley–Queisser Limit”, IEEE J. Photovoltaics, vol. 2, pp. 303-311 (2012). DOI: 10.1109/JPHOTOV.2012.2198434
[ii] The heat source can be combustion, radio-activity, or solar thermal.
3:15 PM - *NT1.8.02/EE3.8.02
Controlling both Solar and Thermal Spectra for Solar Cell Applications
Shanhui Fan 1
1 Stanford Univ Stanford United States,Show Abstract
We show that the use of photonic structures, which allows control of both solar and thermal radiation spectra, has important implications for various aspects of solar energy conversion, including voltage, current and cooling considerations.
3:45 PM - NT1.8.03/EE3.8.03
Highly Conductive Ag Nanowire Meta-Electrodes Improve Silicon Heterojunction Solar Cells
Mark Knight 1,Jorik Van De Groep 1,Paula Bronsveld 2,Wim Sinke 1,Albert Polman 1
1 FOM Institute AMOLF Amsterdam Netherlands,2 Energy research Centre of the Netherlands Petten Netherlands2 Energy research Centre of the Netherlands Petten Netherlands,1 FOM Institute AMOLF Amsterdam NetherlandsShow Abstract
Silicon heterojunction (SHJ) solar cells, where the crystalline Si is passivated by thin layers of a-Si:H, have attracted significant interest due to their record voltages. However, reflection from macroscopic metallic ‘fingers’ has constrained current generation – and efficiency – in front contacted cells. These fingers are essential for harvesting electrons due to poor lateral transport in indium tin oxide (ITO), which is both the most common transparent conductive electrode (TCE) and limited by a fundamental tradeoff between transmission and conductance. Since the optimal finger spacing depends on TCE conductivity, the efficiency of SHJ cells is married to the quality of the TCE layer.
In this presentation we introduce a hybrid TCE which decouples the optical and electrical functionalities, and enables the independent optimization of each function. The geometry consists of Ag nanowires (80 nm wide, 120 nm tall) arranged in a sparse square grid, fabricated on top of an ultrathin ITO layer to transport charge in the interstitial regions. The nanowires are conformally coated with Si3N4, providing both environmental stability and an antireflection coating free from the interband and free carrier losses in ITO. For cells with fingers spaced by the standard 2 mm, replacing ITO with Si3N4 reduces optical loss by 1.1 mA cm-2.
We apply this nanostructured hybrid electrode to large-area (4 cm2) untextured SHJ solar cells using substrate-conformal imprint lithography (SCIL), a fabrication method that enables rapid, wafer-scale fabrication of nanowire (NW) arrays with full geometric control. The SCIL fabrication process does not damage the passivating a-Si:H layer, with consistent values for Voc measured on cells with and without nanowire modification. Optically, the nanowire networks exhibit broadband anomalous transmission due to detuning of the plasmonic nanowire resonances from the solar spectrum, shading 30% less light than the NW area coverage. Electrically, the square grids of nanowires have measured sheet resistances of 4.0, 7.2, and 15.0 Ω/sq. for pitches of 1, 2, and 4 µm, respectively. This is a significant (10x) improvement relative to an industrially processed ITO electrode with a measured 150 Ω/sq. sheet resistance. Due to the improved transmission and conductivity, the hybrid electrode enables an increase in finger pitch from 2 to 5 mm, reducing shading. For the champion hybrid electrode SHJ cell we measure a Jsc enhancement of 1.4 mA cm-2 (32.7 to 34.1 mA cm-2) with a simultaneous increase in FF (0.622 to 0.670), yielding an absolute efficiency enhancement of 2.2% (13.8% to 16.0%).
This demonstration of an engineered ‘meta-electrode’ within the electrical and optical environment of high performance SHJ solar cells shows that large-area nanostructuring provides practical pathway to increased performance and a reduced dependence on rare metals, especially indium.
NT1.9: Hybrid Nanomaterials for Energy and Optics
Thursday PM, March 31, 2016
PCC North, 100 Level, Room 129 A
4:30 PM - *NT1.9.01
Functional Nanostructures and Their Applications in Catalysis, Sensing and Color Conversion
Alexander Eychmueller 1
1 Physical Chemistry TU Dresden Dresden Germany,Show Abstract
Gels and aerogels manufactured from a variety of nanoparticles available in colloidal solutions have recently proven to provide an opportunity to marry the nanoscale world with that of materials of macro dimensions which can be easily manipulated and processed, whilst maintaining most of the nanoscale properties . The materials carry an enormous potential for applications. This is largely related to their extremely low density and high porosity providing access to the capacious inner surface of the interconnected nanoobjects they consist of. The aerogel materials may be further processed in order to achieve improvements in their properties relevant to applications in optical sensing and catalysis.
The commercialization of polymer electrolyte fuel cells (PEFC) is still hindered by the cathode electrocatalyst for the oxygen reduction reaction (ORR) not fulfilling the criteria of low cost, high performance, and high durability. We recently developed a facile strategy for the controllable synthesis of nanoparticle-based b