Symposium Organizers
Alexander O. Govorov Ohio University
Andrey L. Rogach Ludwig-Maximilians-Universität München
Zhiming M. Wang University of Arkansas
Juen-Kai Wang National Taiwan University
(and Institute of Atomic and Molecular Sciences
Academia Sinica)
Vladimir M. Shalaev Purdue University
O1: Self Assembled Nanostructures - Magnetic Quantum Dots
Session Chairs
Monday PM, November 30, 2009
Back Bay B (Sheraton)
9:30 AM - **O1.1
Optical Spin Orientation of a Single Manganese Atom in a Quantum Dot.
Henri Mariette 1 , Claire Le Gall 1 , Lucien Besombes 1 , Roman Kolodka 1 , Herve Boukari 1 , David Ferrand 1 , Joel Cibert 1
1 Institut NEEL, CEA-CNRS, Grenoble France
Show AbstractMBE Growth and optical addressing of individual CdTe/ZnTe QDs doped with a single Mn atom were achieved recently (1). Now, the static properties of this system are well understood (2): the photon emitted or absorbed by a Mn-doped QD is directly related to the spin state of the Mn atom localized in the dot. This is due to the exchange interaction of an electron-hole (e-h) pair and the Mn atom: on the Mn point of view, the e-h pair acts as an effective field along the growth axis that lifts up the degeneracy between its six spin states. Depending on the spin projection of the Mn, the recombination of an injected e-h pair emits a photon with a given energy and polarization. In time averaged photoluminescence measurements, this leads to a six line fine structure of the QD emission. It is then possible to probe the spin state of the Mn atom thanks to the intensity of the different lines observed in the emission spectrum.In this communication, we report on the observation of a high degree of spin polarization for a Mn atom in a QD using quasi-resonant or fully-resonant optical excitation at zero magnetic field. Under excitation on an excited state of the dot (quasi-resonant excitation), we were able to optically inject spin polarized e-h pairs. Time-resolved detection of the intensity of a given line of the QD under alternatively sigma+ sigma- trains of light reflects the evolution of the population of the corresponding Mn spin state and shows orientation of the Mn spin in the effective field of an e-h pair. Pump-probe experiments demonstrated that the photo-induced spin orientation was perfectly conserved over a few microseconds. The dynamics and the magnetic field dependence of the optical orientation mechanism shows that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots (3).Using resonant excitation on a given line of the ground exciton-Mn complex, we were able to achieve optical pumping of the Mn spin. Monitoring the time evolution of the resonant fluorescence observed during the optical pumping allows to directly observe the initialisation of the Mn spin. This technique presents the advantage of performing both initialization and measurement of the Mn spin at the same time. All these results can be modelled using a rate equations model valid at low excitation power (4). These experiments demonstrate the possibility to write, read and store information on the spin state of a single magnetic atom in a semi-conductor quantum dot.1. L. Besombes et al, Phys. Rev. Lett. 93, 207403 (2004) 2. Y. Leger et al., Phys. Rev. B 76, 045331 (2007)3. C. Le Gall et al., Phys. Rev. Lett, 102, 127402 (2009)4. A. O. Govorov and A V. Kalameitsev, Phys. Rev. B 71, 035338 (2005)
10:00 AM - **O1.2
Faraday Effect in a Transverse Magnetic Field: An Astonishing Property of Singly Mn-doped InAs/GaAs QDs.
Olivier Krebs 1 , Emile Benjamin 1 , Aristide Lemaitre 1
1 , Laboratoire de Photonique et de Nanostructures-CNRS, Marcoussis France
Show AbstractIn singly Mn-doped InAs/GaAs quantum dots (QDs), the Mn atom is a magnetic impurity of acceptor type which yet remains in its neutral state (A0) at low temperatures. It has been shown that its effective spin is well described by a J=1 spin featuring besides a strong anisotropy related both to its position and to local strains [1]. Here, we show that this effect may lead to a spectacular effect: the splitting of the QD optical transitions into their circularly polarized components (Faraday effect) in a transverse magnetic field.Micro-photoluminescence (µ-PL) spectroscopy was performed on individual Mn-doped quantum dots ( with the magnetic field direction aligned either longitudinally or perpendicularly to the optical axis. For certain quantum dots, we observed that in both field directions the spectral PL lines of a positive trion (X+) are split into strongly circularly polarized components. A theoretical model of the spin interactions which includes (i) the local strain anisotropy experienced by the acceptor level and (ii) the anisotropic exchange due to the out-of-center Mn position provides a very good agreement with these observations. The Faraday effect in a transverse field results from the strong exchange between the ferromagnetic (FM) and anti-ferromagnetic (AFM) configurations of the A0-hole complex which cancels out the mixing of the ↑ and ↓ heavy-hole spins by the field, while the local anisotropy experienced by A0 mixes its |±1> states. As a result these levels are split by the transverse field and drag along the FM states (|↑,1> and |↓,-1>) or AFM states (|↑,-1> and |↓,+1>) into pure heavy-hole states ↑ and ↓ which are still essentially coupled to σ± circularly polarized light. This effect depends yet strongly on the QD anisotropy strength and direction with respect to the applied magnetic field. Our model of spin interaction enables us to reproduce fairly well all encountered situations.
10:30 AM - O1.3
Optically Controlled Nanomagnets.
Sebastian Mackowski 1 , Tak Gurung 2 , Howard Jackson 2 , Leigh Smith 2
1 Institute of Physics, Nicolaus Copernicus University, Torun Poland, 2 Department of Physics, University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractThe results of optical spectroscopy of magnetically doped self-assembled quantum dots will be presented. We find that for such structures resonant excitation of spin polarized excitons leads to robust ferromagnetic alignment of magnetic impurities within CdMnTe quantum dots. Due to strong spatial confinement this optically induced zero-field magnetization is very stable and persists up to 150K. We also propose and demonstrate a way to directly probe the magnetization of magnetic quantum dots by measuring the exciton Zeeman splitting of nonmagnetic CdTe quantum dots placed in the vicinity of ferromagnetically aligned CdMnTe quantum dots. From the dependence of the Zeeman splitting on the polarization of the excitation we estimate the internal magnetic field of spin polarized Mn ions to be of the order of 0.2T. Possible mechanisms responsible for the observed effects will be discussed. Importantly, as the exciton spin relaxation in nonmagnetic CdTe quantum dots depends on the energy level degeneracy (which can be lifted by external magnetic field), this approach can be successfully used to tune the spin dynamics of the excitons confined in semiconductor quantum dots. ReferencesS. Mackowski, T. Gurung, T.A. Nguyen, H.E. Jackson, L.M. Smith, G. Karczewski, J. Kossut, Applied Physics Letters 84, 3337 (2004)S. Mackowski, T. A. Nguyen, H. E. Jackson, L. M. Smith, J. Kossut, G. Karczewski, Applied Physics Letters 83, 5524 (2003)T. Gurung, S. Mackowski, G. Karczewski, H.E. Jackson, L.M. Smith, Applied Physics Letters, 93, 153114/1-3 (2008) S. Mackowski, T. Gurung, H.E. Jackson, L.M. Smith, J. Kossut, G. Karczewski, Applied Physics Letters 87, 072502/1-3 (2005) S. Mackowski, T.A. Nguyen, T. Gurung, K.P. Hewaparakrama, H.E. Jackson, L.M. Smith, J. Wróbel, K. Fronc, J. Kossut, G. Karczewski, Physical Review B 70, 245312/1-9 (2004)
10:45 AM - O1.4
Molecular Beam Epitaxy, Photoluminescence, and Magneto-Optical Studies of Stacked Type-II ZnTe/ZnSe Quantum Dots.
Igor Kuskovsky 1 , Weldon MacDonald 1 , Bidisha Roy 1 , Aidong Shen 2 , Qiang Zhang 2 , Maria Tamargo 2 , Yinyan Gong 3 , Gertrude Neumark 3 , Ian Sellers 4 , Bruce McCombe 4 , Alexander Govorov 5
1 Physics, Queens College of CUNY, Flushing, New York, United States, 2 Chemistry, City College of CUNY, New York, New York, United States, 3 Applied Physics & Applied Mathematics, Columbia University, New York, New York, United States, 4 Physics , University at Buffalo SUNY, New York, New York, United States, 5 Physics & Astronomy, Ohio University, Athens, Ohio, United States
Show AbstractRecently type-II semiconductor nanostructures, in which the bands are staggered, and the charge carriers are spatial separated, have been attracting an increasing interest. In type-II nanostructures carrier lifetimes are relatively long and are dependent on the intensity of excitation, as well as on the external electric and magnetic fields. Moreover, type-II alignment tends to suppress the nonradiative Auger recombination. These properties provide unique opportunities for new and enhanced materials based on type-II heterostructires, including quantum dots (QDs).We show that by manipulating the shutter sequence of the various sources during MBE growth, and incorporating delay times between them, we can fabricate composite nanostructures with sub-monolayer nanoislands of ZnTe embedded in ZnSe (type-II quantum dots). We also discuss how the size and density of QDs can be controlled by adjusting growth parameters including delay times and deposition times or by changing the fluxes and/or flux ratios of the elements forming the QDs. Upon increasing the Te source temperature, the photoluminescence peak positions exhibit red shifts, suggesting the formation of larger nano-islands and/or nano-islands with higher Te fraction. Furthermore, samples grown with longer wait time tall-off exhibit PL spectra with the peak at higher energies, suggesting the formation of smaller dots, due to desorption of Zn. Changing the composition of the well, for example, by adding Mg within the nanoisland, increases the QD bandgap, raising the conduction band and lowering the valence band. The result is the simultaneous reduction of the valence band offset (relative to the surrounding ZnSe barrier) and hole confinement energy. The incorporation of Mg in the dot was accomplished by introducing a Mg flux simultaneously with the Te “on” step of the shuttering sequence.We demonstrate that this method leads to formation of type-II quantum dots QDs vs quantum wells (QW) via studies of magneto-excitons. We show that our samples exhibit optical Aharonov-Bohm (AB) effect, which can be observed only for QDs, since a motion of a charged carrier on a closed orbit is required. Results show strong AB oscillations in both the energy and intensity of the PL from the same structure. This is the only system for which the oscillations in both energy and intensity have been reported. From such oscillations we estimate the lateral size of the nanoislands. We explain the observation by considering the stacked character of the system, which ensures that the electron’s wave-function is “pushed” to the side of the dot due to electron-electron interaction, independent of stress, whereas cylindrical geometry nicely defines the ring-like trajectory for an electron. We thus explain the results as a motion of an electron around an entire stack of QDs, one of which is occupied by a hole.
O2: Self Assembled Nanostructures - Spin in Quantum Dots
Session Chairs
Monday PM, November 30, 2009
Back Bay B (Sheraton)
11:30 AM - **O2.1
A Hole Spin in a Single Quantum Dot.
Richard Warburton 1 , Daniel Brunner 2 , Brian Gerardot 2 , Pierre Petroff 3 , Paul Dalgarno 2
1 Department of Physics, University of Basel, Basel Switzerland, 2 Department of Physics, Heriot-Watt University, Edinburgh United Kingdom, 3 Materials Department, University California, Santa Barbara, Santa Barbara, California, United States
Show AbstractSpin is potentially highly coherent in a semiconductor. By confining an electron to a nano-sized quantum dot, spin dephasing via the phonons can be highly suppressed leading to spin relaxation times up to 1 s. Furthermore, in a self-assembled quantum dot, the spin can be initialized, manipulated and read-out with purely optical techniques. However, despite the long T1 times, the electron spin coherence time is disappointingly small, T2~10 ns. The origin of the fast dephasing is the hyperfine interaction, the coupling of the electron spin to the nuclear spins of the host material. The nuclear spins create an effective magnetic field, the Overhauser field. Electron precession about the randomly fluctuating Overhauser field leads to a rapid loss of electron spin coherence. One possibility is to use not an electron spin but a hole spin. The hole has a p-like atomic Bloch state with a node at the location of the nuclei, conveniently removing the contact part of the hyperfine interaction. The dipole-dipole part of the hyperfine interaction remains however but its effect on the hole spin coherence is largely unknown. We show here that the hole spin is remarkably coherent: we determine a lower limit to the hole spin T2* time of about 1 micro-s at 4.2 K and in an in-plane magnetic field of 3 T.Our experiment involves, first, trapping a single hole in a quantum dot using a vertical charging device with p-type back contact, and, second, probing the hole spin with two coherent lasers. Optical pumping is used to demonstrating that the hole spin T1 is as large as 1 ms. In order to probe T2*, we have exploited a quantum interference, coherent population trapping (CPT), the atomic process which underpins electromagnetically-induced transparency. We couple the two hole spins states to a common exciton state by applying an in-plane magnetic field. A clear CPT ``dip" in the absorption spectrum results, a direct manifestation of the coherent hole spin.
12:00 PM - **O2.2
Injection of Spin-polarized Electrons in InAs QDs.
Athos Petrou 1
1 Physics, University at Buffalo, Buffalo, New York, United States
Show AbstractWe report on electrical injection of spin-polarized electrons from ferromagnetic Fe contacts into InAs QDs embedded in the intrinsic region of n-i-p light emitting diodes. We have concentrated on the role of exchange interactions among parallel spins occupying adjacent shells. The presence of spin down electrons results in the appearance of new spectral features in the emission spectra at energies which fall between the emission intensity peaks. We will also discuss the dramatic decrease in the optical polarization from these LEDs for a narrow range of magnetic fields between 4 and 5 tesla. Possible mechanisms for the decrease in the spin relaxation time are discussed. This work has been supported by NSF and ONR.
12:30 PM - O2.3
Designing Spin Properties in InAs Quantum Dot Molecules.
Weiwen Liu 1 , Shilpa Sanwlani 1 , William Reid 1 , Allan Bracker 2 , Dan Gammon 2 , Matthew Doty 1
1 Materials Science and Engineering, University of Delaware, Newark , Delaware, United States, 2 , US Naval Research Laboratory, Washington , District of Columbia, United States
Show AbstractQuantum dots (QDs) and quantum dot molecules (consisting of two or more coherently coupled QDs) are considered leading candidates for confining and manipulating single spins. [1] Intense research into the architectures and protocols for confining and manipulating the spin states are motivated by potential applications in spintronics, quantum computing and single charge-carrier logic devices. [2] The signatures of coherent coupling and spin interactions of both electrons and holes in quantum dot molecules have been identified in vertically stacked pairs of InAs QDs. [3, 4] Coherent tunneling through the thin barrier separating the QD pair leads to the formation of molecular orbitals with bonding and anti-bonding features. [5] The formation of these molecular states, which can be controlled with an applied electric field, leads to drastic changes in the hole g factor. [6] This effect creates the opportunity to electrically gate spin interactions, but has so far only been demonstrated for holes. We use magneto-photoluminescence spectroscopy to explore the spin properties of quantum dot molecules with a variety of barrier compositions. Varying the barrier composition permits control of the nature and properties of the molecular states that are formed on resonance. This control offers the opportunity to design quantum dot molecules with specific tunable spin properties. For example, utilizing an AlGaAs barrier allows us to design structures in which the electron g factor can be tuned with the applied electric field. We present results on these structures and discuss the implications for the design of quantum dot molecules with tailored spin properties.[1]J.R. Petta et al., Coherent Manipulation of Coupled Electron Spins in Semiconductor Quantum Dots, Science 309, 2180 (2005)[2]M. Bayer et al, Hidden Symmetries in the Energy Levels of Excitonic ‘Artificial Atoms’, Nature 405, 923 (2000)[3]H.J. Krenner et al., Optically Probing Spin and Charge Interactions in a Tunable Artificial Molecule, Phys. Rev. Lett. 97, 076403 (2006)[4] M. Scheibner et al., Spin fine structure of optically excited quantum dot molecules, Phys. Rev. B 75, 245318 (2007)[5]M.F. Doty et al., Antibonding Ground States in InAs Quantum-Dot Molecules, Phys. Rev. Lett 102, 047401 (2009)[6]M.F. Doty et al., Electrically tunable g factors in quantum dot molecular spin states, Phys. Rev. Lett. 97 (19), 197202 (2006)
12:45 PM - O2.4
Time Resolved Resonance Fluorescence Study of QD Spin Dynamics.
Nick Vamivakas 1 , Chao-Yang Lu 1 , Yong Zhao 1 , Clemens Matthiesen 1 , Antonio Badolato 2 , Mete Atature 1
1 , University of Cambridge, Cambridge United Kingdom, 2 , University of Rochester, Rochester, New York, United States
Show AbstractThe spin ground states of a singly charged self-assembled quantum dot (QD) offer one physical realization of a quantum mechanical bit. Further, the transition selective resonant coupling of the spin ground states and the excited (trion) states enables optical control of the confined spin - an attractive feature from the perspective of quantum information science. Here we use time resolved resonance fluorescence to experimentally quantify timescales relevant to the confined spin dynamics. First, we directly determine the time it takes to optically induce a spin-flip when the single electron-trion transition is driven by a resonant laser. Next, we optically measure T1 times of a single quantum dot which can be as long as 18 ms.In this work we study self-assembled InAs/GaAs QDs embedded in a Schottky diode heterostructure under a finite magnetic field applied along the growth direction (the Faraday configuration). The voltage applied to the diode allows precise control of the QD charging state and stabilizes the single electron ground state. Both photoluminescence and differential transmission measurements allow us to spectrally fingerprint the transition of interest. Once the transition is spectrally isolated we use a dark-field microscope to spectrally resolve the QD transition’s resonance fluorescence. In the limit of a laser Rabi frequency on the order of the transition’s spontaneous emission rate we use the time-resolved integrated resonance fluorescence to monitor the spin ground state dynamics.To improve the signal-to-noise ratio of our measurement scheme we employ an N-shot measurement protocol. In measuring the optically induced spin-flip time, or the time it takes to prepare the spin in a particular state, we drive the system resonantly and record photon counts until the transition goes dark. After the transition is dark we recycle the electron by plunging the gate and repeat the sequence. With this approach we directly measure spin pumping times on the order of 1 microsecond. These measurements allow us to identify the state mixing mechanisms to be hyperfine and hole-mixing induced in the low and high magnetic field regimes, respectively, with the turnover around 1 Tesla (T) for these QDs. To measure the spin-flip dynamics (T1 time) unperturbed by the laser, we employ the following sequence: optically pump the spin, let the prepared spin evolve without the resonant laser, turn back on the laser and record photon counts. Finally, we recycle the transition by plunging the gate voltage and repeat the measurement sequence. For a magnetic field of 2.2T we measure a T1 time of 18 ms from a single QD.
O3: Self Assembled Nanostructures - Quantum Manipulation
Session Chairs
Monday PM, November 30, 2009
Back Bay B (Sheraton)
2:30 PM - **O3.1
Fast Coherent Optical Manipulation of Quantum Dots and the Nuclear Servo.
Duncan Steel 1 , Erik Kim 1 , Xiaodong Xu 1 , Katherine Truex 1 , Bo Sun 1 , L. Sham 2 , Allan Bracker 3 , Daniel Gammon 3
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 Physics, University of California - San Diego, San Diego, California, United States, 3 , Naval Research Laboratory, Washington, DC, District of Columbia, United States
Show AbstractOptically driven self-assembled quantum dots provide the opportunity of performing quantum gate operations at high speed (>>GHz) enabling many operation within the quantum coherence time of the electron spin. In this paper, we present the recent results demonstrating high single qubit gate operations including the various steps of a Hadamard gate and a phase gate. Nuclear fluctuations typically result in decoherence times on the order of nanoseconds, but our measurements have discovered a nuclear servo-effect that results from coupling to the hole in the quantum dot that result in suppression of nuclear spin fluctuations, resulting in an increase of 3 orders of magnitude in the electron spin coherence time. This work is supported by NSF, ARO, AFOSR, IARPA, LPS, DARPA and ONR
3:00 PM - **O3.2
Manipulating the Spectrum of an InAs Quantum Dot with a Near-resonant Optical Field.
Glenn Solomon 1
1 , Joint Quantum Institute, NIST & University of Maryland, Gaithersburg, Maryland, United States
Show AbstractWhen a strong monochromatic field is brought through resonance with an optically active transition, such as those in a semiconductor quantum dot, the original transition states become hybridized with the field states. The new states are energy split by an amount determined by the laser field amplitude and the dipole moment (Rabi frequency), and the laser detuning. These composite matter-field states undergo an anti-crossing as a function of detuning. Although these phenomena are well established in atomic systems, experiments in solids have only recently been reported. Using photoluminescence in conjunction with a near-resonant laser field, we show that a set of neutral, optically active InAs single quantum dot states (exciton/biexciton states) can be fully dressed. This allows all-optical control of this system and makes accessible tailored photons. Applications in areas such as the generation of entangled photon will be discussed.
3:30 PM - O3.3
Optical Probes of Coupling Between Laterally Separated InGaAs/GaAs Quantum Dots.
Shilpa Sanwlani 1 , William Reid 1 , Weiwen Liu 1 , Zhiming Wang 2 , Gregory Salamo 2 , Mathew Doty 1
1 Materials Science & Engineering, University of Delaware, Newark, Delaware, United States, 2 Department of Physics, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractOver the past decade, potential device applications have fueled an extensive effort to fabricate lateral arrays of quantum dots (QDs) with specific dot densities, spacings and size distributions [1]. An essential element for the further development of QD devices with new functionalities is the introduction of controllable quantum coupling between two or more QDs in such an array [2]. Tunable quantum coupling between vertically stacked InAs QDs has been demonstrated, with the coupling mediated by coherent tunneling and tunable with a static electric field [3]. While these studies have revealed that the spatial arrangement of QDs can lead to remarkable effects [4], it will be impossible to scale vertical coupling to a large number of QDs. Investigations of lateral quantum coupling have been slower to develop [2], however, because special growth protocols are required [5] and the ability to independently tune the luminescence energy of separate QDs [6] is lost.Spectroscopy of single pairs of laterally separated QDs is required to resolve the signatures of quantum coupling from inhomogeneously broadened ensemble spectra. Laterally-coupled quantum dots require modified sample preparation methods to isolate single pairs of QDs and apply electric fields that tune the relative energies of the two dots. The electric field must be applied along the surface of the sample, perpendicular to the growth direction. To apply this lateral field, we use interdigitated electrodes patterned onto the sample surface with photolithography and metal deposition. Electrical connections are made to each of the interdigitated top contacts as well as to an ohmic back contact. This three-terminal arrangement makes it possible to independently control both the relative energies of the dots and the charging of the QDs. We present photoluminescence spectra of laterally coupled QDs whose coupling and charge states are tuned with this three-terminal arrangement. We further discuss the implications and opportunities for control of quantum coupling in laterally-scalable architectures.References1.B. R. Wang, B. Q. Sun, Y. Ji, M. Dou, Z. Y. Xu, Zh. M. Wang and G. J. Salamo, APL 93,011107(2008)2.G. J. Beirne, C. Hermannstadter, L. Wang, A. Rastelli, O. G. Schmidt, and P. Michler, PRL 96,137401 (2006)3.H. J. Krenner, M. Sabathil, E. C. Clark, A. Kress, D. Schuh, M. Bichler, G. Abstreiter, and J. J. Finley,PRL 94, 057402 (2005)4.M. F. Doty, J. I. Climente, M. Korkusinski, M. Scheibner, A. S. Bracker, P. Hawrylak, and D. Gammon,PRL 102, 047401 (2009)5.L. Wang, A. Rastelli, S. Kiarvittaya, P. Atkinson, F. Ding, C C Bof Bufon, C. Hermannstadter, M. Witzany, G. J. Beirne, P. Michler, and O. G. Schmidt,New Journal of Physics 10 (2008) 0450106.A. S. Bracker, M. Scheibner, M. F. Doty, E. A. Stinaff, I. V. Ponomarev, J. C. Kim, L. J. Whitman, T. L. Reinecke, and D. Gammon, APL 89, 233110 (2006)
3:45 PM - O3.4
A High Efficiency, Purcell-enhanced Microcavity Single Photon Emitting Diode.
David Ellis 1 , Anthony Bennett 1 , Samuel Dewhurst 1 2 , Christine Nicoll 2 , David Ritchie 2 , Andrew Shields 1
1 , Toshiba Research Europe Ltd, Cambridge United Kingdom, 2 Cavendish Laboratory, Cambridge University, Cambridge United Kingdom
Show AbstractAn efficient, high frequency on-demand source of single photons is an essential building block in the development of optical quantum information schemes, such as quantum communication and quantum computing. Self assembled InAs quantum dots (QDs) are excellent candidates to realize high performance devices and, when combined with an optical cavity, enhanced photon collection efficiencies can be achieved [1,2]. To create a practical device, electrical injection is also a necessity in order to avoid the inclusion of a pump laser and associated optics Here we report on the realization of such a high efficiency single photon-emitting diode [3].Lateral confinement of the optical mode in our microcavity structure is achieved by creating an annulus of low refractive index (~ 1.5) aluminum oxide (“AlOx”) within an etched mesa. The AlOx is formed by the wet oxidation of a series of AlGaAs layers, chosen to produce the desired aperture profile. The diameter of the central aperture can be set by controlling the oxidation time. In addition to providing optical confinement, the insulating oxide ring also serves as a current aperture, allowing a simultaneous reduction in the electrically active area of the device. This technique has previously been shown to allow a single quantum dot to be electrically addressed [4].Using this approach, high-Q, small mode volume structures can be produced, leading to Purcell-enhanced QD emission. We report on the enhancement of the radiative decay rate of a quantum dot state coupled to a confined cavity mode in this structure. The measured enhancement corresponds to a Purcell factor of 2.5.Under pulsed electroluminescence, strong antibunching was observed over a wide range of repetition rates. Autocorrelation histograms recorded at 80 MHz and 0.5 GHz demonstrate the flexibility of the device – the repetition rate can be modified by simply adjusting the drive electronics – and results in no degradation in g(2)(0). Furthermore, coupling the QD emission into a single, on-axis optical mode allows a greater fraction of the emitted single photons to be collected and we report on a measured efficiency of 14 ± 1 %, which represents a 28-fold improvement over the theoretical maximum for QDs in bulk GaAs.In conclusion, we have produced an oxide-confined microcavity single-photon-emitting diode in which an enhancement in the radiative decay rate of a coupled quantum dot state can be observed. This device exhibits a 28-fold improvement in photon collection efficiency over a theoretically optimal planar structure. Single photon emission is also demonstrated at repetition rates in excess of 0.5 GHz.References[1] A. J. Shields,Nature Photonics vol 1, pp. 215 - 223, 2007 [2] K. J. Vahala, Nature vol 424, pp 839-846 (2003)[3] D. J. P. Ellis et al New J. Phys. Vol 10 p043035 (2008)[4] D. J. P. Ellis et al Appl. Phys. Lett. Vol 88 pp 133509 (2006)
O4: Self Assembled Nanostructures - Growth and Properties
Session Chairs
Monday PM, November 30, 2009
Back Bay B (Sheraton)
4:30 PM - **O4.1
Design, Growth, and Optical Properties of Charged InAs Quantum Dot Molecules.
Allan Bracker 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractInAs quantum dot molecules are engineered materials that exhibit new physical phenomena and show promise as a way to store and manipulate quantum information through optical control. A major challenge in the development of these quantum dots is to identify the essential tunneling and spin interactions and selection rules that form the basis for spin qubit manipulation, and to engineer them through design, fabrication, and application of electric and magnetic fields. Self-assembly is a natural method for quantum dot growth, although its statistical nature presents considerable experimental challenges. The flexibility provided by molecular beam epitaxy has been pivotal in decoding the optical spectrum. In the simplest system, two or more dots are stacked vertically, with the second nucleated by the strain induced by the first. More complex two- or three-dimensional arrangements are produced with a variety of nucleation techniques. With nearly atomic-scale control of the QD height, we can select whether molecular orbitals form through tunneling of electrons or holes [1]. Natural anisotropies in an MBE machine can be used in a combinatorial manner to explore a range of design parameter space on a single sample. Quantum dots are incorporated into diode heterostructures that allow applied electric fields to inject individual charges and to modify the tunneling rate and spin interactions.Close feedback between research efforts in sample growth and single-molecule optical measurements has been essential to unraveling the seemingly complex optical spectrum of quantum dot molecules [2]. With an understanding of the spectrum and the corresponding selection rules we have identified the elements of a highly versatile quantum bit [3], including techniques to initialize, measure, and rotate individual spins, and the prerequisites for electrically-induced spin manipulation [4]. We are engineering the building blocks of a two-qubit system consisting of two spins in two dots. The composition of the interdot barrier is chosen to optimize the two-electron singlet-triplet fine structure at the edge of the molecular tunneling regime. The interplay between spin and tunneling interactions is observed in very high resolution absorption spectra in a magnetic field.[1] Bracker, et al., Appl. Phys. Lett. 89, 233110 (2006).[2] Scheibner, et al. Phys. Rev. B 75, 245318 (2007).[3] Kim, et al., Phys. Rev. Lett. 101, 236804 (2008).[4] Doty, et al., Phys. Rev. Lett. 102, 047401 (2009).
5:00 PM - O4.2
Shape Control and Emission-wavelength Extension of InP-based InAsSb Nanostructures.
Wen Lei 1 , Hoe Tan 1 , Chennupati Jagadish 1
1 , Department of Electronic Material Engineering, RSPhysSE, The Australian National University, Canberra, Australian Capital Territory, Australia
Show AbstractInP-based InAsSb nanostructures (quantum dots and quantum wires) are promising candidate materials for fabricating mid-infrared (2-3 um) emitters theoretically, which have a wide range of application in military, telecommunications, molecular spectroscopy, biomedical surgery, environmental protection and manufacturing industry, etc.[1] Some effort has been devoted to fabricating InAsSb quantum dots by annealing InAs quantum dots under Sb flux,[2,3] and direct InAsSb growth.[4] However, it still presents a big challenge to grow high quality InAsSb nanostructures with controlled morphology and long emission wavelength due to the large lattice mismatch between InAsSb and InP, surfactant effect of Sb atoms, and low growth temperature requirement for Sb compounds. In this work, we realize the controlled growth of InAsSb nanostructures by using direct growth with metal-organic chemical vapour deposition and successfully extend their emission wavelength to 2.3 um (at 77K). By tuning the growth parameters like growth temperature, growth rate, and V/III ratio, both InAsSb quantum dots and quantum wires can be achieved with homogeneous size. Low growth temperature, high growth rate, and high V/III ratio prefer to induce the formation of InAsSb quantum dots; while high growth temperature, low growth rate, and low V/III ratio prefer to induce the formation of InAsSb quantum wires, which can be mainly explained by the kinetic characteristics of Stranski-Krastanov growth and the surfactant effect of Sb atoms. Furthermore, by using InGaAs and InGaAsSb strain reduced layers the emission wavelength of InAsSb nanostructures can be extended widely (from 1.8 um to 2.3 um at 77 K for InAsSb quantum dots with a nominal composition of 50 percent Sb), which is mainly caused by the reduced confinement barrier and increased height of the nanostructures. [1] C. Cornet, F. Doré, A. Ballestar, J. Even, N. Bertru, A. Le Corre, and S. Loualiche, J. Appl. Phys., 98, 126105 (2005).[2] Y. Qiu, and D. Uhl, Appl. Phys. Lett., 84, 1510 (2004).[3] F. Doré, C. Cornet, P. Caroff, A. Ballestar, J. Even, N. Bertru, O. Dehaese, I. Alghoraibi, H. Folliot, R. Piron, A. Le Corre, and S. Loualiche, phys. stat. sol. (c), 3, 3920 (2006).[4] K. Kawaguchi, M. Ekawa, T. Akiyama, H. Kuwatsuka, and M. Sugawara, J. Cryst. Growth, 291, 154 (2006).
5:15 PM - O4.3
Optical Properties of InAs Quantum Dots Grown by Solid-Source Molecular Beam Epitaxy on InP(001).
Antonio Rivera 1 , David Fuster 1 , Diego Alonso-Alvarez 1 , Benito Alen 1 , Pablo Alonso-Gonzalez 1 , Yolanda Gonzalez 1 , Luisa Gonzalez 1
1 , Instituto de Microelectrónica de Madrid (CNM-CSIC), Tres Cantos, Madrid, Spain
Show AbstractSelf assembled quantum dots (QDs) of InAs on InP are of interest as the active element of optoelectronic devices. The reason is that such devices show good emission properties in the C-band of optical fibers. In particular, the QDs of InAs on InP have been postulated as good candidates to fabricate single photon emitters (SPE) with emission at 1.55 µm necessary for the development of Quantum Information Technologies. The growth of self-assembled InAs QDs on InP(001) is done by molecular beam epitaxy (MBE) using gas-sources [1]. Recently [2], we have directly grown for the first time self-assembled QDs of InAs by solid source MBE on InP(001). Thanks to this method we can use standard solid-source MBE with well established technology for the fabrication of novel optoelectronic devices based on InAs/InP(001) QDs. The growth of InAs/InP QDs by solid source MBE was performed using a two-step cycle: step 1 (In deposition), the typical formation of quantum wires (QWRs) [3] is suppressed and instead nucleation of In droplets over the InAs(4x2) reconstruction takes place; step 2 (As flux), droplets crystallize giving InAs QDs, which get bigger with subsequent cycles. It will be shown in this paper that the emission wavelength of the QDs can be precisely tuned by an appropriate thermal treatment during QD capping leading to an emission peak at 1.5 µm with a width below 70 meV. Rapid thermal annealing (RTA) also allows one to tune the emission wavelength of the QDs, however, with poorer properties. Alternatives to the growth method described above, based on droplet epitaxy at low temperature will be discussed. In order to study the optical properties of the self-assembled InAs/InP QDs, we have fabricated by optical lithography PIN diodes with InAs QDs embedded in the center of the intrinsic layer. One of the advantages of using solid source MBE is the low residual doping that can be achieved for the intrinsic layer, below 1016 cm-3 in our case. The following measurements have been performed: photo-current (PC), (micro-) photoluminescence (PL) and electroluminescence (EL), all of them as a function of temperature and bias. We will discuss the excitonic properties of the QDs and compare them with model predictions. In addition, the results will be compared with those obtained for InAs QWRs embedded in the intrinsic layer of PIN diodes. This study is a basic step to understand the relation between growth conditions and optical properties of individual QDs. The immediate application (underway) is the inclusion of a QD in a photonic crystal to form an efficient SPE at 1.55 µm.[1] C. Paranthoen, N. Bertru, O. Dehaese, A. Le Corre, S. Loualiche, and B. Lambert, Appl. Phys. Lett. 78, 1751 (2001)[2] D. Fuster, A. Rivera, B. Alén, P. Alonso-González, Y. González, and L. González, Appl. Phys. Lett. 94, 133106 (2009)[3] J. M. García, L. González, M. U. González, J. P. Silveira, Y. González, and F. Briones, J. Cryst. Growth 227, 975 (2001)
5:30 PM - O4.4
Photodetectors Fabricated from Strain-free GaAs Coupled Quantum Dots.
Jiang Wu 1 , Dali Shao 1 , Omar Manasreh 1 2 , Alvason Li 2 , Zhiming Wang 2 , Vasyl Kunets 2 , Gregory Salamo 2
1 Department of Electrical Engineering, University of Arkansas, Fayetteville, Arkansas, United States, 2 Institute of Nanoscale Science and Engineering, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractInfrared photodetectors based on intersubband transitions in semiconductor quantum structures evolved from the two-dimensional systems (quantum wells) to three-dimensional systems (quantum dots). This evolution was due to several drawbacks encountered in the quantum well systems. The new generation of quantum dot photodetectors was mostly based on InAs and InGaAs quantum dots grown on lattice mismatched GaAs where the growth of the quantum dots is governed by the strain-driven Stranski-Krastanow growth mode, An alternative strain-free growth mode is presented here where GaAs coupled-quantum dots are grown on lattice matched AlGaAs. The coupled quantum dots were grown at 550 °C in a molecular beam epitaxy system. The GaAs quantum dots material system was characterized by using the photoluminescence technique and surface morphology was checked by using an atomic force microscope. Devices were fabricated from silicon doped GaAs coupled quantum dots and tested at both 77 and 300 K. The photoresponse spectra of the detectors were recorded using an FTIR system. Furthermore, the dark current was measured for the photodetectors in the temperature range of 77 – 300 K. The spectra were interpreted as being due to both interband and intersubband transitions cover the mid-infrared spectral range (intersubband transitions) and the visible-near-infrared spectral range (interband or exciton transitions). The photoresponse spectra in mid-infrared spectral range of 1.0 – 6.0 micron were found to exist at temperature lower than 90 K, while the photoresponse spectra in the visible-near-infrared spectral range of 0.4 – 0.9 micron were observed at temperatures as high as 300 K. The observation of the device photoresponse due to the interband transitions at room temperature may be due to the high exciton binging energy in the GaAs coupled quantum dots. The room temperature detectivity was estimated and compared to that of other detection systems. Finally, designs of samples that are taking the reduction of the dark current into account will be presented.
5:45 PM - O4.5
Nanorings of Aluminum Droplet Epitaxy on GaAs Substrate.
Alvason Zhenhua Li 1 , Zhiming M. Wang 1 , Jiang Wu 1 , Gregory J. Salamo 1
1 Institute of Nanoscale Science and Engineering, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractGroup-III metallic droplets are currently of great interest for potential applications in quantum physics because they can be crystallized under a group-V molecular beam into various nanostructures such as quantum dots and rings. However, the detail of crystallization and growth mechanism are poorly understood. In this work, unique Aluminum droplet rings are carried out on GaAs (001) wafer. From basic physics perspective, this investigation will facilitate the development of new insight into the growth processes for self-assembled droplet epitaxy nanostructures. The growth morphology and current understanding on the detail growth mechanism for the nano-rings based on high resolution SEM and TEM studies will be discussed, and a simple model of droplet epitaxy based on crystallization and diffusion will be presented.
Symposium Organizers
Alexander O. Govorov Ohio University
Andrey L. Rogach Ludwig-Maximilians-Universität München
Zhiming M. Wang University of Arkansas
Juen-Kai Wang National Taiwan University
(and Institute of Atomic and Molecular Sciences
Academia Sinica)
Vladimir M. Shalaev Purdue University
O5: Self Assembled Nanostructures - Optical Interaction
Session Chairs
Tuesday AM, December 01, 2009
Back Bay B (Sheraton)
9:30 AM - **O5.1
Signatures of Coherent Tunneling Between Quantum Wells and Quantum Dots.
Yu Mazur 1 , V. Dorogan 1 , E. Marega 1 , P. Vasa 2 , C. Lienau 2 , G. Tarasov 3 , Gregory Salamo 1
1 Physics, University of Arkansas, Fayetteville, Arkansas, United States, 2 Institut fuer Physik, Carl von Ossietzky Universitaet, Oldenburg Germany, 3 Institute of Semiconductor Physics, National Academy of Sciences, Kiev Germany
Show AbstractWe present a spectroscopic manifestation of the intermediate coherent tunneling regime between a quantum dot (QD) and a quantum well (QW) layer. We observe a nontrivial dependence of the resonant QD photoluminescence excitation (PLE) signal as a function of dot-well barrier thickness. For thick barriers and resonant QW excitation, the photogenerated QD carrier density increases exponentially with increasing coupling strength. For separations of a few nm only, however, we observe an anomalous decrease of PLE signal. This behavior is defined by sub-picosecond resonant coherent tunneling dynamics between the QW and QD. Our results shed new light on the intermediate coherent tunneling regime of relevance in a variety of functional nanostructures such as charge- or spin-injectors or photovoltaic devices.
10:00 AM - O5.2
Probing an Optically-generated Electric Field Between Coupled Quantum Wells using Indirect Transitions in Coupled Quantum Dots.
Mauricio Garrido 1 , Kushal C. Wijesundara 1 , Swati Ramanathan 1 , Allan S. Bracker 2 , Daniel Gammon 2 , Eric Stinaff 1
1 , Department of Physics and Astronomy, and Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio, United States, 2 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe generation of a local electric field between the coupled wetting layers (WLs) of a quantum dot molecule system was observed through a shift in its photoluminescence spectra when an optical excitation was applied. Using a coupled quantum dot as a sensitive probe of the optically generated field between the quantum wells we have been able to quantitatively study the properties of this field and demonstrate its potential as a means for local field control. Optical excitation of the WLs was seen to generate a shift of a few tenths of a Volt in the biasmaps of the electric field dependent photoluminescence spectra of coupled quantum dots. The mechanism by which this takes place is attributed to be the creation of electron-hole pairs in the InAs WLs, followed by a charge separation via tunneling through the GaAs barrier. Behaving like a parallel-plate capacitor, the WLs thus generate an optically-controllable effective local electric field that may be of use for fast switching devices. Both laser wavelength and power dependence of this effect were studied, which confirm the proposed mechanism.
10:15 AM - O5.3
Straining Quantum Dot Excitons.
Natalia Malkova 1 , Garnett Bryant 1 , James Sims 2
1 Atomic Physics Division and Joint Quantum Institute, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Mathematical And Computational Sciences Division , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractDynamical control of excitons in quantum dots (QDs) is highly desirable for applications of QD optics. For QDs embedded in nanomechanical structures, dynamical control could be obtained by using externally imposed mechanical strain to reengineer the QD excitons to modify exciton fine structure, polarize optical transitions, induce entanglement, or change coupling between closely spaced dots, all capabilities needed to use dots in optical nanodevices and quantum information processing. To exploit the potential of hybrid nanomechanical/QD devices, one must understand the coupling between internal strain due to lattice mismatch, externally imposed mechanical strain, and the excitons in the QDs in the nanomechanical structure. To identify the effects of mechanical strain, we consider symmetric and asymmetric pyramidal InAs QDs in a GaAs nanomechanical bridge. The bridge is strained by a mechanical bend or an applied surface acoustic wave to reengineer the QD excitons. We use atomistic tight-binding theory and a configuration-interaction approach for the exciton states. Relaxation of local strain due to lattice mismatch and the strain imposed by bending the structure are equally important, so both are included via atomistic valence force field theory. The strain due to flexing a nanomechanical structure acts much like a DC electric field, inducing Stark-like QD level shifts. A bend that is symmetric about the QD modifies the lattice-mismatch induced biaxial deformation of the QD. This strain mimics a vertical electric field which pushes electrons and holes in the same direction, either further into the dot or towards the wetting layer, depending on how the bridge is bent. A shear bend mimics an in-plane electric field that pushes electrons and holes in opposite directions along the bend. As a consequence, applied strain can be used to transfer excitons between vertically or laterally coupled dots. The applied strain can make large changes in the exchange splitting between exciton bright states to modify the exciton fine structure induced by QD asymmetry or atomistic effects, can induce crossing between the bright states for certain strains, and can be used to rotate the polarized response of the bright states. These capabilities should be critical for applications such as entangled photon sources, where the elimination of asymmetric exchange splitting is essential, or cavity-coupled QDs, where control of the exchange-induced dark and bright states is needed. The consequences for the quantum optics of quantum dots and connections to recent experiments will be discussed.
10:30 AM - O5.4
Polarization-correlated Photon Pairs from Charged Biexciton in a Single GaAs Quantum Dot.
Yusuke Arashida 1 , Yoshihiro Ogawa 1 , Fujio Minami 1
1 Department of Physics, Tokyo Institute of Technology, Tokyo Japan
Show AbstractThe atomlike properties of semiconductor quantum dots (QDs), together with the ease of accumulation of many carriers into the discrete energy structures, have been studied in recent years for applications in quantum information. As for fundamental studies, single QD spectroscopy enables direct observation of many-body effect involving few particle states in semiconductor. In particular, the exchange interaction affects not only the energy structure but also the polarization states of the multi-carrier complexes, emerging as rich peaks on the photoluminescence (PL) spectrum of single QD which is excited strongly. We have studied the micro-PL spectra of self-assembled single GaAs/AlGaAs QDs, by using a single photon correlation spectroscopy. The strain-free GaAs QDs employed in this report is embedded in AlGaAs barrier and grown by modified droplet epitaxy using conventional molecular beam epitaxy system. The low density (7×108 cm-2) QDs in conjunction with a confocal optical microscopy enabled to access to a few QDs. The non-resonant optical pulsed excitation was achieved by frequency doubled output of a mode-locked Ti:Sapphire laser, which produced 150 fs pulses of 400 nm in wavelength and 76 MHz repetition rate. In all measurements, the samples were held in closed loop He cryostat kept at 8 K.At high excitation density, we observed multiple peaks on the PL spectrum which reflect the formation of the multi-carrier complexes in the single GaAs QD. These peaks can be assigned to originate from exciton(X), biexciton (XX), negatively charged exciton (X-), positively charged exciton(X+) and positively charged biexciton (XX+) through the excitation density dependence of PL intensities and single photon correlation measurements. In measurements of the single photon correlation, we observed photon pair emission (bunching) from a cascade relaxation of XX+. Analogous to XX, XX+ can emit a photon with the angular momentum ±1. There are, however, two possible final states, and then the XX+-X+ emission shows a doublet structure. The energy difference of this structure is corresponding to the electron-hole exchange energy resulting from the different angular momentum configuration between the two final states. After the XX+-X+ transition, the excitation relaxes into a charged excitonic ground state and photon emission occurs again. In this report, we present the results of the polarization dependent photon correlation measurements for photon pairs from XX+. As mentioned above, the XX+-X+ emission has two peaks. We can thus observe two kinds of polarization-correlated photon pairs in the XX+ related cascadal transition. From these results, we discussed the polarization directions of XX+ in the view of asymmetric crystal structure of the QD.
10:45 AM - O5.5
Photoluminescence Spectroscopy of a 2D Electron-hole Gas Heterostructure.
Eric Gallo 1 , Xia Zhao 1 , Oren Leaffer 2 , Adriano Cola 3 , Bahram Nabet 1 , Jonathan Spanier 2 1
1 Electrical & Computer Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 3 Institute for Microelectronics and Microsystems, National Research Council, Lecce Italy
Show AbstractWe present the results of PL measurements on a heterostructure containing separated electron and hole gases. The electron well is formed at the interface of an AlGaAs barrier layer and a GaAs region. The hole well is formed by an 8 nm psuedomorphic InGaAs layer sandwiched between the GaAs region and an additional AlGaAs barrier layer located 100 nm below the electron well. Measurements using variable temperature (4K < T < 300K) and laser intensities indicate that additional peaks appear at higher powers and lower temperatures. These peaks appear in the range of 900 nm to 850 nm and their behavior is closely tied to the incident power. The peaks are consistent with transitions between the InGaAs conduction band and the GaAs valence band, as well as the GaAs conduction band to the InGaAs valence band. The emergence of these peaks at higher intensities is an indication of band bending within the device and a redistribution of charge concentration within the GaAs region. We use this information to explain two modes of operation of a high speed detector based on the substrate and provide a model to explain the band bending created due to generated carriers. Work supported in part by the NSF under ECCS-0702716 and by DMR-0907381, and by the US Army Research Office under W911NF-08-1-0067.
O6: Self Assembled Nanostructures - Nanowires and Nanorods
Session Chairs
Tuesday PM, December 01, 2009
Back Bay B (Sheraton)
11:30 AM - **O6.1
Quantum Phenomena in Semiconductor Nanowire Heterostructures.
Leigh Smith 1 , Howard Jackson 1 , Jan Yarrison-Rice 2 , Chennupati Jagadish 3 , Jin Zou 4
1 Dept. of Physics, University of Cincinnati, Cincinnati, Ohio, United States, 2 Dept. of Physics, Miami University, Oxford, Ohio, United States, 3 Dept. of Electronic Materials Engineering, Australian National University, Canberra, Australian Capital Territory, Australia, 4 Center for Microscopy and Analysis, University of Queensland, Brisbane, Queensland, Australia
Show AbstractSemiconductor nanowires are one dimensional structures fabricated using gold catalyzed growth from vapor. By varying the constituent gases and growth parameters it is possible to create axial and radial hetero- or homo-structures which can be engineered for particular physics or technological applications. In this talk I will discuss how semiconductor nanowires can be designed to manipulate both the electromagnetic field as well as the electron or hole wavefunctions within semiconductor nanowires, and how these interact to provide interesting quantum phenomena that can be probed using spatially- and temporally-resolved optical experiments. Semiconductor nanowires are cylinders tens of nanometers in diameter and 5 to 10 microns in length. Even when the electron and hole wavefunctions show little effect of quantum confinement, the electromagnetic field is strongly affected by the nanowire resulting in light strongly polarized parallel to the nanowire. This results in a dramatic increase in the radiative lifetime for excitons whose dipoles are aligned perpendicular to the nanowire so that light emission is polarized parallel to the nanowire. We have used both CW and time-resolved photoluminescence measurements in single GaAs/AlGaAs core-shell nanowires to study the spin relaxation dynamics of excitons which are photopumped into nonequilibrium populations. We find that the relaxation time is strongly decreased when excitons are excited non-resonantly at higher energies, or when the exciton density is increased. Under optimal conditions the relaxation time can be as slow as 200 ps or as short as 5 ps.[1] Using axial and radial heterostructures semiconductor nanowires can be constructed which directly manipulate the electron and hole wavefunctions. We demonstrate that axial homostructures of Zincblend and Wurtzite InP layers can be used to strongly quantum confine both the electrons and holes and that the spatially-indirect alignment of the wavefunctions result in a dramatic increase in the radiative lifetime at lower energies.[2] Radial heterostructures of GaAs/AlGaAs nanowires can potentially result in cylindrically symmetric quantum wells which exhibit a true one-dimensional density of states, and for which the orbital angular momentum is quantized. Preliminary efforts to grow and characterize such structures will be discussed. Finally, I will show very preliminary results of adding metallic or plasmonic nanostructures to these semiconductor nanostructures to enhance Raman scattering or two-photon absorption, or to directly manipulate the electron or hole wavefunctions. The ability to fabricate and manipulate semiconductor and metallic nanostructures opens new vistas of both basic physics and new technologies. We acknowledge the support of the NSF through grants 0701703, 0806700 and 0806572, and the Australian Research Council. [1] T.B. Hoang et al., Nano Letters 7, 588-595 (2007). [2] K. Pemasiri et al., Nano Letters 9, 648-654 (2009).
12:00 PM - O6.2
Engineering Optics and Optoelectronics in Semiconductor Nanowires.
Linyou Cao 1 , Joon-Shik Park 1 2 , Pengyu Fan 1 , Justin White 1 , Jon Schuller 1 , Bruce Clemens 1 , Mark Brongersma 1
1 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States, 2 Nanomechatronics Research Center, Korea Electronics Technology Institute, Gyeonggi Korea (the Republic of)
Show AbstractThe use of quantum confinement to tailor the optical properties of semiconductors has enabled a true revolution in the development of high performance semiconductor materials and devices, while it is limited to structures at length-scales comparable to the size of Bohr radii (~1- 10 nm). Here we show exploiting leaky mode resonances (LMRs) to enhance and spectrally engineer optics and optoelectronic properties of semiconductor structures in the size regime of 10 – 500 nm where many practical devices lie in and resonant enhancement effects appeared to be insignificant before. This is experimentally and theoretically illustrated with strong, resonant and tunable light absorption, elastic scattering and emission from individual silicon and germanium nanowire. Following the framework of the LMRs, we fabricated a germanium photodetector with detection efficiency for 1550 nm light significantly enhanced (by 30 folds) and proposed a design for high-efficiency cost-effective solar cell. These results manifest tremendous opportunities for the realization of a wide range of high-performance, nanowire-based optoelectronic devices, including solar cells, photodetectors, optical modulators, and light sources.
12:15 PM - O6.3
Polarized Micro-photoluminescence Imaging of Single GaAs/AlGaAs Core-shell Nanowires with GaAsSb Inserts.
Thang Hoang 1 , Fervin Moses 1 , Hailong Zhou 1 , Dasa Dheeraj 1 , Antonius Van Helvoort 2 , Bjorn-Ove Fimland 1 , Helge Weman 1
1 Department of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim Norway, 2 Department of Physics, Norwegian University of Science and Technology, Trondheim Norway
Show AbstractWe use polarized micro-photoluminescence (micro-PL) imaging technique to probe the electronic structures of single GaAs nanowires with GaAsSb inserts. The nanowires are grown by Au-assisted molecular beam epitaxy (MBE) with zinc blende GaAsSb segments (~20 nm long) inserted in ~ a 20-30 nm diameter dominating wurtzite GaAs nanowire core.[1] A radial AlGaAs shell is added around the core in order to increase the quantum efficiency and to enable a tuning of the amount of strain around the GaAsSb insert. By taking two dimensional (energy vs. spatial) images of the nanowire core-insert (vertically aligned along the entrance slit of a spectrograph) at low temperature (10 K) with a Si-CCD detector we can observe the spatially localized emission from the GaAsSb insert as well as the PL distribution along the GaAs nanowire. We image up to the 4th excited exciton state at the GaAsSb inserts by increasing the laser excitation power. Linear polarized imaging reveals that the PL emission from the zinc-blende GaAsSb inserts is strongly polarized along the nanowire axis while the PL emission from the wurtzite GaAs nanowires is perpendicularly polarized. The results indicate that the crystal structure, through its dipole selection rules, may play an important role in the alignment of the PL polarization of semiconductor nanowires besides the linear polarization effect induced by the nanowire/air dielectric mismatch. The long exciton decay time (up to 6 ns) of the GaAsSb related PL emission indicates a spatial indirect radiative recombination due to a type-II band alignment at the GaAsSb/GaAs interfaces.This GaAs/GaAsSb nanowire core-insert structure promises interesting physics as well as potentials for heterostructure engineering in semiconductor nanowires with a controlled abrupt change of crystal material as well as crystal phase (wurtzite and zinc blende).[1] D. L. Dheeraj, G. Patriarche, H. Zhou, T. B. Hoang, A. F. Moses, S. Grønsberg, A. van Helvoort, B.O. Fimland, and H. Weman, Nano Lett., 8 4459 (2008).
12:30 PM - O6.4
Electron Beam Induced Current Microscopy of Ge Nanowires.
Terrence McGuckin 1 , Eric Gallo 2 , Stephen Nonnenmann 1 , Joan Burger 1 , Jonathan Spanier 1 2
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Electrical & Computer Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractDue in part to their high mobility and narrow gap, nanowires (NWs) composed of Ge have been identified as candidate materials for high-performance transistors and for efficient photodetectors of near infrared and visible radiation[1]. Among important considerations for NWs are the effects of recombination of electronic carriers via surface states and of carrier surface recombination velocity on carrier transport[2]. Scanning probe microscopy has been used to obtain ~μm-scale spatially-resolved information within a variety of optically-active NW devices[3,4], including Ge NWs[1]. Here we report on electron beam induced (EBIC) measurements of Ge NWs possessing metal-semiconductor-metal Schottky-contacts of different selected metals and corresponding barrier heights. At relatively low bias, the highest EBIC current is observed underneath the anode and cathode metal contacts at the Ge NW-metal interfaces; at higher bias where the wire is fully depleted, the highest current is seen in the bulk of the wire. Our results enable unambiguous identification of distinct transport regimes in which carrier generation dominates over recombination. Penetration of electron beam excitation underneath and near the contacts permits highly localized investigation of recombination and generation processes, and of diameter-dependent variations in depletion region that are not possible with proximal probe techniques employing diffraction-limited optical excitation. Work supported in part by the US Army Research Office under W911NF-08-1-0067 and by the NSF under DMR-0907381 and DMR-0722845.[1] Y. H. Ahn and J. Park, Appl. Phys. Lett. 91, 162102 (2007).[2] J. E. Allen, E. R. Hemesath, D. E. Perea, J. L. Lensch-Falk, Z. Li, F. Yin, M. H. Gass, P. Wang, A. L. Bleloch, R. E. Palmer, and L. J. Lauhon, Nature Nanotechnology 3, 168, (2008).[3] Y. Gu, E.-S. Kwak, J. L. Lensch, J. E. Allen, T. W. Odom, and L. J. Lauhon, Appl. Phys. Lett. 87, 043111 (2005).[4] Y. Ahn, J. Dunning, and J. Park, Nano Lett. 5, 1367, (2005).
12:45 PM - O6.5
Exciton Diffusion in MgZnO Nanorods Using ZnO/MgZnO Nanorod Quantum Structures.
Jinkyoung Yoo 1 , Le Si Dang 2 , Gyu-Chul Yi 3 , Bonghwan Chon 4 , Taiha Joo 4
1 National CRI Center for Semiconductor Nanorods, Dept.of Materials Sci. and Eng., POSTECH, Pohang Korea (the Republic of), 2 , Institut Neel, CNRS and Universite Joseph Fourier, Grenoble France, 3 National CRI Center for Semiconductor Nanorods, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 4 Department of Chemistry, POSTECH, Pohang Korea (the Republic of)
Show AbstractIn semiconductors, excitons are bound electron-hole pairs, analogous to positroniums. Their transport properties, which are directly related to material properties, are important subjects for research because they could affect the efficiency of excitonic solar cells, for example in dye-sensitized solar cells, and stimulated emission in nanocrystalline thin films. Because excitons are electrically neutral quasi-particles, optical methods have been usually employed to study excitons in thin films and bulk materials. However, the spatial resolution of optical methods has not been sufficient to observe exciton diffusion quantitatively. Meanwhile, CL measurements using scanning electron microscopy are frequently used to investigate exciton diffusion in thin films and bulk semiconductors, but the spatial resolution can be influenced by the interaction volume within carriers generated through a cascading effect due to elastic and inelastic scattering between the impinging primary electrons and target sample atoms. However, this cascading effect can be avoided by using semiconductor nanorods. Since the nanorod diameter is smaller than the penetration depth of the highly energetic electron beam, excitons are generated in 50-nm volume. Furthermore, we fabricated the nanorod quantum structures specially designed for the detection of CL from the exciton diffusion. Here, we present that exciton diffusion can be quantitatively studied using the CL of semiconductor nanorod quantum structures. The combination of nanorod SQWs and CL spectroscopy is valuable for studying exciton transport in semiconductors. As an example, exciton diffusion in individual MgZnO nanorods was investigated using a SQW on the nanorod tip and CL spectroscopy. Only one SQW emission was observed when an electron beam was focused on spots near the SQW, resulting from exciton diffusion in the MgZnO nanorod. Exciton diffusion length at 5 K was estimated at 100±20 nm for 120-nm-thick MgZnO nanorods with the Mg content of 20 atomic percent. Furthermore, temperature dependence of exciton diffusion behavior will be also discussed.
O7: Self Assembled Nanostructures - Hybrid Applications
Session Chairs
Tuesday PM, December 01, 2009
Back Bay B (Sheraton)
2:45 PM - O7.1
Self-Organization of Semiconductor and Semimetal Quantum Dots in GaAs Matrix by a Combined MBE Process.
Vladimir Chaldyshev 1 , Nikolay Bert 1 , Vladimir Nevedomsky 1 , Valerii Preobrazhenskii 2 , Mikhail Putyato 2 , Boris Semyagin 2
1 , Ioffe Institute, St.Petersburg Russian Federation, 2 , Institute of Semiconductor Physics, Novosibirsk Russian Federation
Show AbstractHybrid nanostructures based on quantum dots (QDs) of metals and semiconductors have attracted constantly increasing attention during the last few years. These objects may have unusual interesting properties due to interaction and hybridization of intrinsic excitations, namely excitons and plasmons. Formation of the hybrid nanostructures is a challenging task since the formation procedures are specific and often inconsistent for the QDs of different origin.In this presentation we first report about possibility of self-organization of semiconductor InAs QDs and semimetal As QDs in a close vicinity to each other in GaAs matrix, utilizing a combined process of the molecular beam epitaxy (MBE).The samples were grown on GaAs substrates with (001) orientation and contained a single layer or stack of coupled InAs QDs. These QDs were self-organized by using the Stranski-Krastanow growth mode. The InAs QDs were overgrown by GaAs at low (200°C) temperature and then annealed in the MBE setup. The self-organization process and resulting structures were studied by transmission electron microscopy (TEM), reflection high energy electron diffraction, atomic force microscopy, x-ray diffraction and optical techniques.The TEM study reveals vertically coupled InAs QDs and an array of As QDs in the top layer. The sizes of InAs QDs were varied by changing in the growth conditions and nominal thickness of InAs layers. The sizes of As QDs were managed by the growth temperature and annealing conditions. An important observation is a higher ripening rate for the As inclusions in a close vicinity of the InAs QDs, when compared to the rest of array. This phenomenon opens a way to the formation of hybrid As-InAs "nanomolecules" in the GaAs matrix. Optical study has been done to reveal specific features of such samples.
3:00 PM - O7.2
Surface Plasmon Coupled Mid-infrared Electroluminescence from InAs Quantum Dots.
Brandon Passmore 1 , Troy Ribaudo 2 , Dan Wasserman 2 , Stephen Lyon 3 , Eric Shaner 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 3 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractThe mid-infrared electroluminescence from surface plasmon modes coupled to intersublevel transitions in self-assembled InAs quantum dots is demonstrated. Subwavelength periodic metal hole arrays with different extraordinary optical transmission designs are patterned on a broadband (9 – 15 μm) mid-infrared emitter and the electroluminescence is measured and compared to devices without a metal hole array. The reflection from various mesh designs is measured to verify plasmonic behavior from the metal/semiconductor interface. As a result, the electroluminescence from the surface plasmon coupled quantum dot emitter can be tuned from 9.5 – 12.0 μm.
3:15 PM - O7.3
Strong Exciton-Photon Coupling in ZnO-based Microresonators.
Helena Hilmer 1 , Chris Sturm 1 , Ruediger Schmidt-Grund 1 , Marius Grundmann 1
1 Inst. f. Exp.Physik II, Universität Leipzig, Leipzig, Sachsen, Germany
Show AbstractMuch effort has been devoted to the investigation of exciton-polaritons in the past decades. These bosonic quasi-particles can be formed in a microresonator, where the interaction of light with matter is strongly enhanced, and can finally form a Bose-Einstein condensate, which allows novel applications such as ultra-low threshold lasers and optical amplifiers. Currently, the limited temperature range for stable exciton-polaritons is the main challenge for these applications.
We report here on the observation of strong coupling between excitons and cavity photons in ZnO-based planar microresonators at temperatures up to 410 K [1]. The resonators were grown by means of pulsed laser deposition (PLD) on c-sapphire substrates and consist of two Bragg reflectors, each made of 10.5 layer pairs yttria stabilized zirconia and Al2O3, surrounding a ZnO-cavity which acts simultaneously as active medium. We use two different types of cavities, first a planar half-wavelength cavity with a large negative detuning, i.e. the difference of the uncoupled cavity-photon mode and exciton mode, in order to study the dispersion behaviour of the exciton-polaritons in a wide temperature range (10 K – 550 K), and secondly a wedge-shaped cavity in order to change the detuning at constant temperature by changing the position on the sample. The advantage of ZnO is its huge exciton oscillator strength and its large exciton binding energy, which renders excitons stable way above room temperature.
Angle-resolved photoluminescence and reflection spectra show the lower polariton branch (LPB) with its typical dispersion, changing from photon-like to exciton-like for increasing angle of emission and reflection, respectively. The upper polariton branch is not observable due to the strong absorption of ZnO in this spectral region [2]. A detailed analysis of the LPB dispersion in its energy and broadening using a 2×2 coupling Hamiltonian, taking into account the complex energies of the uncoupled cavity-photon and the exciton mode, revealed the resonator to be in the strong coupling regime up to 410K. Hereby, a huge coupling strength of 55 meV in maximum for 10 K could be found, slightly reduced to 43 meV at 410K, due to the decrease of the exciton oscillator strength. Above 410 K the obtained coupling strength is similar to the broadening of the LPB and we consider the resonator in this temperature range (410 K – 550 K) to be in the intermediate coupling regime.
[1] C. Sturm, H. Hilmer, R. Schmidt-Grund, and M. Grundmann, New J. Phys., accepted.
[2] S. Faure, T. Guillet, P. Lefebvre, T. Bretagnon, and B. Gil, Phys. Rev. B 78, 235323 (2008).
3:30 PM - O7.4
Nanometer-scale Dielectric Constant Mapping of Ge/Si Quantum Dots.
Yoshihiro Ogawa 1 , Fujio Minami 1 , Yohannes Abate 2 , Stephen Leone 2
1 Department of Physics, Tokyo Institute of Technology, Tokyo Japan, 2 Department of Chemistry and Physics, University of California , and Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractRecently, an alternative form of near-field scanning optical microscopy (NSOM) that utilizes the local field enhancement at the end of an externally illuminated metallic probe (an “apertureless” probe) has also been demonstrated, and various aspects of this new imaging technique, for example, tip-enhanced Raman scattering [1], photo-luminescence [2], Rayleigh scattering [3], coherent anti-Stokes Raman scattering [4], etc, are being explored. The resolution of the so-called tip-enhanced or apertureless NSOM (ANSOM) is only limited by the radius of curvature of the probe, and therefore it promises unprecedented optical resolution (<15 nm) compared with conventional fiber-based NSOM.Tip-enhanced near-field scattering images of Ge quantum dots (QDs) grown on Si substrate have been observed with the spatial resolution of 15 nm. Changing the wavelength of the incidence light the contrast of the images are reversed. It is found that the scattering intensity is caused by the dielectric constants of the materials under the probe, whose main contribution come from E0 direct transition of Si at near ultra violet region and by the E1 transition of Ge at visible region. By changing wavelength of the incident light, we have obtained information about the dielectric constant dispersion of a single Ge QDs. The spectral position of the E1 transition of a single Ge QDs is found to shift to higher energy owing to the quantum confinement effect. [1] A. Hartschuh, et al., Phys. Rev. Lett. 90, pp095503 (2003). [2] J. M. Gerton, et al., Phys. Rev. Lett. 93, pp180801 (2004). [3] B. Knoll and F. Keilmann, Nature 399, pp134 (1999).
3:45 PM - O7.5
Optical and Electrical Properties of Si and Ge Quantum Dots in Silica and Sapphire.
Eric Barbagiovanni 1 , Lyudmila Goncharova 1 , Peter Simpson 1
1 Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
Show AbstractQuantum dot (QD) size and density are key parameters in creating practically efficient nanophotonic devices. The size of a QD, as directly related to the quantum confinement of the states in the system, allows control of the wavelength of emission, while the density of QDs affects the efficiency of devices. In this study, we closely look at QD formation by ion implantation (in the 30-750 keV energy range) into silica and sapphire substrates through a mask and thermal treatment. It is hoped that with the unique arrangement of the Si and Ge QDs produced with the mask we can isolate carrier hopping effects of the excitonic states and the efficiency of individual QDs via a significant peak width narrowing in the emission spectrum. With the implantation energy and dose chosen appropriately we can limit the size and density of the QDs in the substrate, ideally down to a single QD per region. Comprised of silica spheres spun onto the substrate surface in a closed-packed structure, the mask confines the implantation to the region between spheres. The mask allows us to control the density, arrangement and size the QDs, which are isolated from each other through the domain walls of the crystalline substrate. Control samples are used with the same mask preparation technique, and 25keV Au implantation. Unlike Si, gold easily diffuses up to the surface under annealing allowing one to know the effectiveness of the mask directly.Substitution of the substrate material changes the nature of the defects at the QD/matrix interface and should provide information on this mechanism. We examine the structural and optical properties of Si and Ge nanocrystals embedded in silica and in sapphire; further work will look at silicon-oxide and silicon-nitride substrates. Optical properties of these QDs are studied using photoluminescence measurements with a 405 nm exciting laser source, and emission lifetime spectra collected using a photomultiplier tube. Structural and optical properties of the Si and Ge QD arrays will be discussed. These results can be compared with our current theoretical work.
4:00 PM - O7.6
Red-Green-Blue MOSLED Made by PECVD Grown SiOx with Detuning RF Plasma Power.
Chih-Hsien Cheng 1 , Bo-Han Lai 1 , Gong-Ru Lin 1
1 Graduate Institute of Photonics and Optoelectronics, National Taiwan University , Taipei Taiwan
Show AbstractSi nanocrystal formation is one alterative of approaches to overcome the limit of Si indirect bandgap nature which is against efficient lighting for Si-based LED. However, the possibility of Si nanostructure formation is still left a crucial step towards the fabrication of an efficient Si nc-based light emitter. Therefore, versatile solutions have recently been developed to enhance the carrier injection. In this work, the blue-light emitted MOSLEDs made by SiOx grown at different RF powers are investigated.The SiOx films were grown on p-type Si (100) substrate by using PECVD with SiH4/N2O fluence of 33 and 150 sccm, chamber pressure at 67 Pa and substrate temperature of 450oC, and the RF plasma power was controlled at 50 to 70 W. After deposition, the SiOx was annealed with flowing N2 at 1100oC for 10 min. The evaporated Al and sputtered ITO on back and front of samples form the MOSLED structure.The SiOx thickness and the volume density of nc-Si are increased linearly as the deposition time of the SiOx layer linearly increases, while the turn-on electric field of the devices are kept at the constant of 6.6 × 106 V/cm. The power slope and external quantum efficiency are linearly enhanced with increasing thickness. The volume density of the nc-Si embedded in the SiOx grown at RF plasma power of 70 W is maximized to facilitate highest external quantum efficiency for EL. The effect of thermal dissipation is minor for thicker sample, since a higher current is able to tunnel through the thicker SiOx layer. It is found that the EL spectra of the device with thicker SiOx layer slightly red-shifts from 450 nm to 500 nm by means of the relationship between the varied nc-Si size and degraded electron conductivity. It is evident that the EL peak slightly blue-shifts when the biased current increases, which is possibly due to the band filling effect. In more detail, the EL pattern color turns from red to blue as the RF plasma power increases from 50 to 70W. The peak of EL blue-shifts from 760 nm to 420 nm when RF plasma power increases from 50 to 70W. The turn-on voltage increases from 70, 90, 99 V with RF plasma power increasing from 50 to 70 W. The maximum EL power are 270, 300, 469 nW with the power slope of 0.37, 3.24, 115.2 mW/A when RF plasma power increases from 50 to 70 W. The power conversion ratio of the nc-Si based MOSLED fabricated under RF plasma power of 50, 60 and 70 W are 5.29×10-6, 36×10-6 and 466×10-6.
O8: Colloidal Nanocrystals I: Sensing and Optical Properties
Session Chairs
Tuesday PM, December 01, 2009
Back Bay B (Sheraton)
4:30 PM - **O8.1
Nanoparticle-Bioconjugates: Characterization and Use for Sensing and Imaging.
Hedi Mattoussi 1 , Michael Stewart 1 , Igor Medintz 2 , Kimihiro Susumu 1
1 Optical Sciences Division, Code 5611, Naval Research Laboratory, Washington, District of Columbia, United States, 2 Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractInorganic nanocrystals, such as those made of semiconductor materials (QDs), exhibit unique size-dependent photophysical properties. They can also be highly sensitive to interactions with proximal dyes and metal complexes, via resonance energy transfer or charge transfer mechanisms. This makes them very attractive for use in sensor design and live cell imaging. Interfacing these inorganic nanoparticles with biology involves the combination of basic chemistry with biomolecular engineering. We have developed approaches based on cap exchange of the native capping shell with modular ligands to promote their dispersion in a wide range of buffers. These ligands are based on bi-dentate and multidentate dihydrolipoic acid (DHLA) motifs, and each is made of a strong anchoring head, a tunable poly(ethylene glycol) segment and a terminal functional group, which promotes biocompatibility of the nanocrystals. We have also developed conjugation strategies based on non-covalent self-assembly or covalent chemistry to couple CdSe-ZnS core-shell QDs and AuNPs to a variety of biomolecules. We start with a brief characterization of the ligand design along with the newly functionalized nanoparticles; we will provide examples including QDs and Au nanparticles. We then provide a few specific examples where these hybrid bioconjugates have been employed in sensor design based on external control of the QD emission via, for example, fluorescence resonance energy transfer or redox-induced quenching.
5:00 PM - O8.2
Spectral Dependence of Emission Enhancement Factors for Quantum Dots Near Single Silver Nanoprisms.
Keiko Munechika 1 , Andreas Tillack 1 , Yeechi Chen 1 , Abhishek Kulkarni 1 , David S. Ginger 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractMetal nanoparticles possess localized surface plasmon resonance which act as nanoscopic antennae that can harvest light absorption as well as change the quantum yield of nearby fluorophores by altering their radiative and non radiative decay rates. This makes nanoparticles appealing for many applications ranging from biosensing to optoelectronics. The improved optical performance of the fluorophores near metal nanoparticles can arise from two different contributions; changes in light absorption (excitation enhancement) and changes in decay rates (emission enhancement). The ability to engineer metal nanoparticle-fluorophore structures for optimal fluorophore performance in specific applications relies un a detailed understanding on the metal near field effects on both excitation and emission enhancement. Here we isolate the spectral dependence of emission enhancement factors by measuring the photoluminescence (PL) lifetimes and corresponding radiative rate enhancements of quantum dots near single plasmon resonant silver nanoparticles when excited far from the plasmon resonance. We show that both the total brightness and radiative rate enhancement of the quantum dots closely track the overlap of their emission with the plasmon resonance spectra of the metal nanoparticles, and we provide guidelines for tailoring emission enhancement factors independently of excitation enhancement using colloidal nanoparticles.
5:15 PM - O8.3
Plasmon Interactions of Closely-Spaced Au Nanoparticle Dimers and Trimers.
Alison Funston 1 , Carolina Novo 1 , Tim Davis 2 , Paul Mulvaney 1
1 The School of Chemistry, The University of Melbourne, The University of Melbourne, Victoria, Australia, 2 CSIRO Materials Science and Engineering, CSIRO, Clayton SOuth, Victoria, Australia
Show AbstractThe collective oscillation of the conduction electrons in metal nanoparticles gives rise to the localised surface plasmon resonance (LSPR) and consequently the intense colours of such particles. A direct consequence of the LSPR is an enhancement of the nanoparticle near field. When two particles are located close to one another, the near-fields of the two particles interact. The LSPR interaction between nanoparticles is highly distance dependent and near-field coupling of particles spaced less than one diameter apart allows the transmission of light energy through an array or down the nanoparticle chain. Whilst there have been many theoretical investigations of the nanoparticle interactions when the nanoparticles are less than 2 nm apart, experimental fabrication and investigation of such particle pairs has remained a challenge.We report our investigation into the coupling between nanoparticles, specifically gold nanorods, with interparticle distances smaller than 2 nm and in different orientations. The particles were chemically synthesized and are single crystals. The investigation was carried out utilizing the recently reported Focussed Ion Beam Registration Method [1,2], allowing correlation of the SEM image of the particle pairs with their scattering spectrum [3]. The experimentally determined scattering spectra of discrete, crystalline, gold nanorod dimers arranged side-to-side, end-to-end, at right angles and with longitudinal offsets will be reported along with the electron micrographs of the individual dimers. The spectra exhibit both red- and blue-shifted surface plasmon resonances, consistent with the plasmon hybridization model. However, the plasmon coupling constant for gold dimers with less than a few nanometers separation between the particles does not obey the exponential dependence predicted by the Universal Plasmon Ruler equation, which does not hold for s/D ratios less than 0.09.The experimentally determined spectra are compared with electrodynamic calculations. Small changes in the rod orientation lead to relatively large changes in the plasmon interaction. Dimers arranged in both "L" and "T" geometries are models for T junctions in optical circuits, for these geometries to act as T-junctions strong coupling between the two rods must occur. Our results show that the degree of coupling between the two geometries is significantly different and is maximized for the L geometry with transmission of the plasmon resonance throughout the full structure. The discussion will also be extended to nanoparticle trimers. These results highlight the importance of orientation on the coupling of anisotropic nanoparticles such as rods.1) Novo, C., Funston, A. M., Pastoriza-Santos, I., Liz-Marzán, L. M., Mulvaney, P., Angew. Chemie. Int. Ed., 2007, 46, 3517-3520.2) Novo, C., Funston, A. M., Mulvaney, P., Nature Nanotech., 2008, 3(10), 598-602.3) Funston, A. M., Novo, C., Davis, T. J., Mulvaney, P., Nano Lett., 2009, 9(4), 1651-1658.
5:30 PM - O8.4
SPR Tuning of Silver-Copper Alloy Nanoparticles: Application in Metal Enhanced Luminescence.
Sanchari Chowdhury 1 , Venkat Bhethanabotla 1 , Rajan Sen 2
1 Chemical and Biomedical Engineering Department, University of South Florida, Tampa, Florida, United States, 2 Civil and Environmental Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractLuminescence techniques have increasingly found promising applications in biological research including single molecule detection, cellular imaging, gene profiling, proteomics, drug discovery and disease diagnostic. Strong luminescence intensity is one of the most important desired properties for luminophores for these applications. Nearby conducting metallic particles, colloids, or surfaces are known to significantly influence the emission of vicinal luminophores( 1). Surface plasmon resonance (SPR) wavelength, one of the most important properties of nanostructures, dictates the choice of materials to be used for luminescence enhancement. Tam et al.( 2) found that the enhancement is optimal when the plasmon resonance of the nanoparticles is tuned to the emission wavelength of the low quantum yield luminophores. Recently, some theoretical and experimental studies have suggested that luminescence enhancement is largest when emission wavelength is slightly red-shifted from the plasmon resonance(3,4). One can expect that by tuning the position of the SPR peak of the nanoparticles over a wide range of wavelengths, metal enhanced luminescence can be extended for a wide range of luminophores. Metal alloys offer additional degrees of freedom for tuning their optical properties by altering atomic composition and atomic arrangement. This motivates us to study alloy nanostructured platforms for metal enhanced luminescence (MEL). Due to their interesting optical properties, we have chosen to study silver-copper alloy nanoparticles5 for MEL application. SPR wavelengths of these Ag-Cu nanoparticles were tuned in the visible and near infrared region by changing annealing temperature. We observed strong emission enhancement of luminophores (141.48+/-19.20 times for Alexa Fluor 488 and 23.91 +/-12.37 times for Alexa Fluor 594) at the vicinity of Ag-Cu nanoparticles when SPR spectrum was tuned to produce maximum spectral overlap. This study suggests that as SPR spectrum of Ag-Cu alloy nanoparticles can easily be tailored, this platform can be effectively used to enhance luminescence of different luminophores. This finding opens new avenue for the utilization of metal alloy nanoparticles in MEL applications. We will also present theoretical calculations using the corrected Gersten-Nitzan (GN)(6) model and the Kümmerlen et al(7) model to provide insights into these experimental findings. Reference:1C. D. Geddes and J. R. Lakowicz, J. Fluoresc. 12, 121 (2002).2F. Tam, G. P. Goodrich, B. R. Johnson, and N. J. Halas, Nano Lett. 7, 496 (2007).3Y. Chen, K. Munechika, and D. S. Ginger, Nano Lett. 7, 690 (2007).4M. Thomas, J.-J. Greffet, and R. Carminati, Appl. Phys. Lett. 85, 3863 (2004).5M. Hirai and A. Kumar, J. Appl. Phys. 100, 014309 (2006).6H. Mertens, A. F. Koenderink, and A. Polman, Phys. Rev. B 76, 115123 (2007).7J. Kümmerlen, A. Leitner, H. A Brunner, F. R. A Aussenegg, and A Wokaun, Mol. Phys. 80, 1031 (1993).
5:45 PM - O8.5
Investigations of Localized Surface Plasmons in Silver Nanoparticles Using Electron Energy Loss Spectroscopy.
David McComb 1 , Stefan Maier 2 , Ai Leen Koh 1 , Kui Bao 3 , Peter Nordlander 3
1 Materials, Imperial College London, London United Kingdom, 2 Physics, Imperial College London, London United Kingdom, 3 Physics, Rice University, Houston, Texas, United States
Show AbstractLocalized surface plasmons (LSPs) are oscillations of the conduction electrons in metallic nanostructures coupled to the electromagnetic field [1,2]. They can be generated by the electric field component of an externally irradiating electromagnetic wave or by high energy electrons. To realize the potential applications in LSPs such as optics, sensing and single-molecule spectroscopy [3-6], it is essential to understand their associated near-field electromagnetic interactions, correlate them with geometry and then tailor their dimensions accordingly. A scanning transmission electron microscope (STEM) equipped with an electron energy-loss (EEL) spectrometer and monochromator is a powerful method to study surface plasmons in noble metal nanoparticles because of its high spatial (~ 0.2 nm) and energy (~ 0.2 eV) resolution. Excitation via electron impact also constitutes a particularly promising way for the investigation of inherently dark modes, which only weakly couple to the radiation continuum [7-8].This paper investigates the plasmonic mode spectra in various silver nanoparticle geometries using an FEI-Titan operated at 300 kV equipped with a monochromator. All experimental data are verified using theoretical modeling. A critical assessment of the radiation damage and its effects on the plasmon spectra will also be discussed.Funding for this work has been provided by the Engineering and Physical Sciences Research Council (EPSRC) in the UK.References:[1] R. Ritchie, Phys. Rev. 106, 874-881 (1957).[2] E. Stern and R. Ferrell, Phys. Rev. 120, 130-136 (1960)[3] K. Kneipp et al., J. Phys.: Condens. Matter 14, R597 (2002)[4] J. Nelayah et al., Nature Phys. 3, 348 (2007).[5] L.R. Hirsch et al., Proc. Natl Acad. Sci. USA 100, 13549 (2003).[6] W.L. Barnes et al., Nature 424, 824-830 (2004).[7] M-W. Chu et al., Nano Lett. 9(1), 399 (2009).[8] P.Nordlander et al., Nano Lett. 4(5), 899 (2004).
O9: Poster Session: Quantum Dots and Nanocrystals
Session Chairs
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - O9.1
Silica-coated Silver Nanoparticles.
Georgios Sotiriou 1 , Sotiris Pratsinis 1
1 Mechanical and Process Engineering, Particle Technology Laboratory, Zurich Switzerland
Show AbstractSilver (Ag) nanoparticles dispersed on an amorphous silica (SiO2) matrix or coated by a SiO2 layer were synthesized by flame spray pyrolysis (FSP) of silver benzoate followed by in-situ SiO2 coating from hexamethylsiloxane (HMDSO) vapor injected downstream of the FSP burner. The coated nanoparticles were produced by using a modified enclosed FSP setup, in which the SiO2 precursor was injected through a ring above the FSP nozzle at various burner-ring-distances (BRDs), after the core Ag nanoparticles had been formed. The produced nanoparticles were characterized by XRD, BET, TEM and UV/vis analysis. The Ag particle size was possible to be controlled by tuning the FSP parameters. For the SiO2 coated nanoparticles, larger Ag core sizes were obtained for higher BRDs. All the produced nanoparticles exhibited the characteristic plasmon resonance frequency of Ag nanoparticles.
9:00 PM - O9.10
Wavelength-Dependent Refractive Indices of Plasmonic Nanoparticles: Live-Cell Imaging with Differential Interference Contrast (DIC) Microscopy.
Gufeng Wang 1 2 , Wei Sun 1 2 , Ning Fang 1 2
1 Chemistry, Iowa State University, Ames, Iowa, United States, 2 , Ames Laboratory-USDOE , Ames, Iowa, United States
Show AbstractGold and silver nanoparticles display extraordinarily large refractive indices near their localized surface plasmon resonance (LSPR) wavelengths. This leads to a good detectability of these nanoparticles as small as 5-10 nm in diameter in a narrow band in differential interference contrast (DIC) microscopy. The wavelength-dependence of DIC contrast of gold/silver nanoparticles is demonstrated to have potential in multiplexed DNA binding assays and live-cell imaging. A commercial DIC microscope was modified to enable high-contrast, real-time imaging of live cells with and without gold nanoparticle probes simultaneously, providing definite evidence for probe identification. Live-cell uptake of single 40-nm gold nanoparticles functionalized with a cell-penetrating peptide was recorded at 32 frames per second, shedding new light in CPP-mediated endocytosis.
9:00 PM - O9.11
Structural and Optical Characterization of a Single ZnO Tetrapod Crystallite.
Tadaaki Nagao 1 2 , Wei Yi 2 , Venkatesh Narayanamurti 2
1 WPI MANA, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractWe report the characterization of the structure and luminescence properties of individual ZnO tetrapod crystallites grown upright on the sapphire (0001) substrate. The EBSD measurements for these 3D objects can provide us the crystallographic information such as the angles between the four legs and the epitaxial relationship between these segments. Position dependent vibrational spectroscopy of a ZnO tetrapod by micro Raman spectroscopy shows pronounced intentisty and a new phonon mode form the tiptoes with respect to that from the central hub of the tetrapod. A detailed micro photoluminescence measurement with 325nm CW laser is also carried out to investigate the pump power dependence and the temperature dependence of the sharp excitonic feature around 369 nm. This feature is actually compsed of two sharp peaks at 368.8 nm and 369.2 nm and we tentatively assigned them to the Donor bound exciton (DoX) and the Surface exciton (SX) at the tips. Possibility of lasing action is also discussed.
9:00 PM - O9.12
Structure and Optical Properties of Boron Nitride Capped Silver Nanoparticles Grown by Magnetron Sputtering.
Gyoergy Kovacs 1 , Gintautas Abrasonis 1 , Thomas Oates 2 , Helfried Reuther 1 , Matthias Krause 1 , Arndt Muecklich 1 , Andreas Kolitsch 1 , Wolfhard Moeller 1
1 Nanostructures, Forschungszentrum Dresden-Rossendorf, Dresden OT Rossendorf Germany, 2 Thin Films Physics, University of Linkoping, Linkoping Sweden
Show AbstractNanostructured silver films have demonstrated plasmonic functionality but suffer from the effects of environmental degradation. We aim to overcome this issue by encapsulating the silver in hard transparent ceramics. Silver nanoparticles were grown on Si and borosilicate glass substrates by magnetron sputtering in the temperature range of RT-200oC. Subsequently the Ag nanoparticles were capped in-situ by a boron nitride layer. The film composition and depth profile were determined by Auger electron spectroscopy. The morphology and structure was investigated by transmission electron microscopy and Fourier transform infrared spectroscopy, while the optical properties were determined by spectroscopic ellipsometry and optical absorption spectroscopy. The results demonstrate that a dense BN capping layer prevents the Ag segregation to the surface, thus exposure to the atmosphere. The films have a composite structure with nanosized silver particles separated by the amorphous boron nitride matrix. In addition, the BN matrix prevents the coalescence of the supported Ag islands, which is observed for non-capped Ag films. In films with a nominal silver thickness below 10 nm the optical properties can be tuned by adjusting the growth and post-growth annealing parameters (nominal thickness, temperature, annealing duration). The structure-optical property relationship is discussed on the basis of plasmon-polariton resonance and the film morphology.
9:00 PM - O9.13
Efficient Energy Transfer Between CdS Quantum Dots in Layer-by-layer Self-assembled Films.
Kunio Shimura 1 , DaeGwi Kim 1 , Masaaki Nakayama 1
1 , Osaka City University, Osaka Japan
Show AbstractOptical properties of semiconductor quantum dots (QDs) have been intensively investigated in the past two decades. Randomly dispersed QDs have been major target in most of the studies so far. The dynamical process of resonant energy transfer (ET) between CdSe and CdTe QDs was reported in recent years. This opened up a new aspect in photophysics of semiconductor QDs and stimulated studies on QD-based ET processes employing QDs as energy donors in QD-bioconjugate system and QD-organic dye system as well as ET between QDs. In this work, we have investigated efficient ET between CdS QDs measuring photoluminescence dynamics in layer-by-layer (LBL) self-assembled films. LBL assembly is a simple and convenient method for preparing highly-homogeneous QD/polymer multilayers: The assembly of negatively charged colloidal QDs and positively charged poly(diallyldimethylammonium chloride) (PDDA) results in QD/polymer multilayers. As a control sample, we measured PL dynamics of CdS QDs which were dispersed in a polyvinyl alcohol (PVA) film. Since a mean distance between QDs in the PVA film is more than 50 nm due to a dilute concentration of QDs, ET between QDs can be ignored. The decay profile in the multilayer structure is faster than that in the PVA film sample. This result obviously shows the occurrence of ET between QDs in the multilayer structure. To reveal how the ET rate depends on the distance between CdS QDs, we fabricated bilayer structures consisting of differently sized CdS QDs. In this structure, efficient "vertical" ET from smaller QDs to larger QDs is realized like a donor-acceptor system. Our key idea is that the distance between two QD monolayers in the bilayer structure can be controlled by the spacer-layer thickness with nanometer accuracy by using LBL assembly of oppositely charged polyelectrolytes. The spacer layer was deposited by LBL assembly of positively charged PDDA and negatively charged poly(acrylic acid) (PAA). The thickness of the spacer layer was controlled by number of PAA-PDDA bilayers. The bilayer structure enabled us to systematically measure the spacer layer dependence of photoluminescence dynamics reflecting the ET process between QDs. The decay profiles in the bilayer structures are faster than that in the PVA film sample and become slower with increasing the spacer-layer thickness. The above results demonstrate a successful control of ET from the D-QDs to the A-QDs by changing the spacer-layer thickness with nanometer accuracy. It is found that ET between the donor and acceptor QDs is conclusively dominated by the dipole-dipole interaction, which verifies the appropriateness of the Förster model.
9:00 PM - O9.14
Controlling the Electronic Coupling in Quantum Dot Solids –Making Photoluminescence Temperature Independent.
Jianhong Zhang 1 , Andrey A. Lutich 1 , Andrei S. Susha 1 , Markus Doeblinger 2 , Alexander O. Govorov 3 , Andrey L. Rogach 1 , Frank Jaeckel 1 , Jochen Feldmann 1
1 Department of Physics and CeNS, Photonics and Optoelectronics Group, Munich Germany, 2 , Department of Chemistry, Munich Germany, 3 Department of Physics and Astronomy, Clippinger research Lab, Athens, Ohio, United States
Show AbstractWe report on the temperature dependence of the photoluminescence from quantum dot solids prepared from colloidal CdTe semiconductor nanocrystals with varying degrees of electronic coupling between the constituting particles. In the strongest coupling regime, controlled by the preparation method, we observe practically identical photoluminescence at room and liquid helium temperature. This is in sharp contrast to situations with weaker electronic coupling in which strong, well known blue shifts of the photoluminescence are observed. The observation is explained by a temperature dependent exchange interaction between the semiconductor nanocrystals constituting the quantum dot solid. This opens new avenues in the control of the photophysical properties of semiconductor nanocrystal quantum dot solids.
9:00 PM - O9.15
Concentration Dependence of Inter-dot Coupling in CdSe Quantum Dot Assembly.
Akira Sugimura 1 2 , Kohei Tai 1 , Wei Lu 2 , Ikuro Umezu 1 2
1 Department of Physics, Konan University, Kobe Japan, 2 Quantum Nanotechnology Laboratory, Konan University, Kobe Japan
Show AbstractCoherently coupled quantum dot (QD) structure is the basis for designing novel functional devices applicable to modern nanotechnology such as quantum information processing. Although independent CdSe QDs show excellent optical properties, only incoherent coupling has been studied so far[1]. This is because the lowest exciton state is the dark state while the second lowest one the bright state, so that the resonant energy transfer (RET) from the dark state of a QD to the bright state of the larger QD becomes dominant process. However, since the coupling between the lowest exciton states of the same sized QDs is important to achieve the coherent coupling, we study, in the present paper, the inter-dot couplings by examining the dependence of the PL properties of the CdSe QD assembly on the QD concentration.Two kinds of colloidal CdSe QDs in toluene solvent having diameters of 2.6 nm (donor) and 4.0 nm (acceptor) were used in this work. The mixed solutions and pure donor and acceptor solutions were put in quartz cell and evaporated under the same condition to study the QD concentration dependence. As we concentrate the pure donor and acceptor samples, their PL intensities decrease monotonously. Since these results can be reproduced by re-diluting the samples, the PL decrease is called as a concentration quenching. The PL spectrum of the mixed solution is composed of two peaks corresponding to donor and acceptor QD emissions. The PL intensity ratio of donors to acceptors also decreases monotonously as the QD concentration is increased. This is attributed to the resonant energy transfer (RET) from donors to acceptors [2], in which the RET rate is proportional to D^(-6), D being the inter-dot distance. Since this concentration dependence is almost the same as those of PL intensity quenching of the pure donor and acceptor samples, we may conclude that the quenching here is originated from the coupling between the same sized QDs through dipole-dipole interaction. We studied time dependent PL spectra for different QD concentrations. We observed PL decay times for independent QDs as well as for coupled systems. We adopted rate equation analysis, in which both the RET process to the different sized QDs and the PL quenching from the same sized QDs are also taken into account, in order to obtain quantitative values for inter-dot coupling rates. The result shows that RET rate is 0.13(1/ns) and the quenching rate is 0.08(1/ns) for the sample with the highest concentration. In conclusion, we studied the concentration dependence of the inter-dot coupling in CdSe QD assembly and estimated the effective coupling rate between the same sized dots. The results suggest that the coherent coupling between the quantum dots is not unrealistic. Reference[1] S. A. Crooker et.al., Phys. Rev. Lett. 89 (2002) 186802.[2] D. L. Dexter, J. Chem. Phys. 21(5) (1953) 836.
9:00 PM - O9.16
Study of Tb-doped Li2O-LaF3-Al2O3-SiO2 Glasses Containing Silver Nanoparticles.
Zhengda Pan 1 , Olanrewaju Obadina 1 , Alexis Crosby 1 , Akira Ueda 1 , Roberto Aga Jr 1 , Richard Mu 1 , Steven Morgan 1
1 , Fisk University, Nashville, Tennessee, United States
Show AbstractTb-doped Li2O-LaF3-Al2O3-SiO2 (LLASOF) glasses were previously reported to have good photoluminescence (PL) and β-induced luminescence light-yield. In this study, the Tb-doped LLASOF glasses containing silver nanoparticles (NPs) were investigated. Raman scattering, UV-visible absorption, PL, and PLE were performed on glass samples. A broad absorption band due to surface Plasmon resonance (SPR) of the silver NPs was observed. This SPR absorption band of silver NPs is peaked at about 420 nm, and the absorbance increases with the silver concentration and heat treatment of the glass samples that controls the nucleation of the silver NPs. Four major emission bands of Tb3+ at 489, 542, 585, and 662 nm were observed. The emission of Tb3+ ions is enhanced in the glass containing silver NPs due to the presence of SPR of silver NPs compared to that in the glass without silver NPs. PLE results indicate that the enhancement of Tb3+ emission due to SPR is excitation wavelength dependent, and is correlated to the density and size of silver NPs in the glass matrix. This enhancement effect due to SPR of silver NPs is attributed to the local field enhancement and a possible energy transfer between silver NPs and Tb3+ ions.This research is supported by US National Science Foundation NSF-CREST HRD-0420516, NSF-REU DMR0453562, and US Department of Defense (DOD)/ARO contracts W911NF-05-1-0453.
9:00 PM - O9.18
Polyelectrolyte Multilayers Stabilized Plasmonic Nanosensors.
Chaoming Wang 1 , Anindarupa Chunder 2 , Lei Zhai 2 , Ming Su 1
1 Department of Mechanical, Materials, and Aerospace Engineering, University of Central Florida, Orlando, Florida, United States, 2 Department of Chemistry, University of Central Florida, Orlando, Florida, United States
Show AbstractSurface plasmon nanosensors based on noble metal nanoparticles can detect trace amounts of chemicals and biomolecules at low concentrations without labeling. Shifts in the resonance peaks are sensitive to changes in local dielectric constants due to large surface areas of nanoparticles. But, the structural changes of nanoparticles after preparation can also shift the resonance peaks, which bring the stability issue of such sensors and need an additional annealing process. In order to eliminate the annealing process of plasmonic nanosensors, polyelectrolyte multilayers are layer-by-layer deposited on an ordered array of silver nanoparticles generated by nanosphere lithography. The polymer multilayers stabilize the plasmonic resonance peaks of nanoparticles in air and liquid, and resonance peaks shift towards long wavelength upon further attachments of polyelectrolyte films, exposures to chemical vapor or protein solution. We have used optical, electron and scanning probe microscopy study the morphology and property of the nanoparticle array and polyelectrolyte multilayers, and used optical spectroscopy to monitor optical responses of the nanosensors. The effects of the multilayer on plasmonic signals have been simulated and the result is consistent with the experimental results. The optic transparency, easy deposition and quantitative response character of the polyelectrolyte multilayer will enhance the applicability of nanoparticle array based nanosensors in chemical and biological sensing.
9:00 PM - O9.19
Dynamics of the Coupling between InGaAs Quantum Well and InAs Quantum Dots.
Nicola Pavarelli 1 2 , Tomasz Ochalski 1 , Baolai Liang 3 , Guillaume Huyet 1 2 , Diana Huffaker 3
1 Photonic Device Dynamics Group, Tyndall National Institute, Cork Ireland, 2 Applied Physics and Insrumentation, Cork Institute of Technology, Cork Ireland, 3 California NanoSystems Institute, Electrical Engineering, University of California, Los Angeles, California, United States
Show AbstractQuantum dots (QDs) are very attractive nanostructures for the development of the next generation optoelectronic devices and semiconductor lasers. The fast injection of carriers from the continuum of states of the optical confinement layer into the discrete levels of the dots is thus becoming a basic requirement to increase the global efficiency of such devices. One of the widely used methods to achieve this purpose is to place an auxiliary structure, for example a quantum well (QW), in proximity to the QD layer. This structure, acting as a carrier reservoir, collects carriers and transfers them directly into the quantum dots, either by tunnelling or lateral diffusion transport. Such innovative systems not only allow the enhancement of the performance and the optimization of the stability of the device, but also offer an additional degree of freedom in the design of the active region, since the injector (QW) and the emitter (QDs) are now two separated entities.In this work, the study of the carrier transfer dynamics between a single InGaAs QW and a single layer of InAs QDs in tunnel injection structures has been investigated using a time-resolved photo-luminescence (TRPL) technique. The investigated structures consist of a single InGaAs quantum well and a single layer of InAs quantum dots separated by a GaAs barrier. The thickness of the barrier is 100 nm for the uncoupled sample and 4 nm for the coupled one. TRPL measurements have been performed at 7 K, exciting the samples with a 780 nm, 75.6 MHz pulsed laser diode and detecting the optical response with the photocathode of a streak camera.Experimental results show that the quantum well decay time decreases from 0.7 ns in the uncoupled structure to 0.2 ns for the coupled one, indicating a fast transfer of carriers from the injector to the emitter in case of the 4 nm barrier. This behaviour is reflected in the emission dynamics of the quantum dots. In fact, by thinning the GaAs layer, the injection of carriers from the quantum well promotes the filling of the highest energy states inside the dots, improving the brightness of the emitting process. As a consequence, the third quantum dot excited state at 980 nm becomes visible for the coupled sample.The fast transfer of carriers from the quantum well to the quantum dots through the 4 nm GaAs barrier alters the emission of the coupled structure in terms of intensity and timescale. Experimentally, a reduction in the QW decay time transition and a global enhancement of the QDs radiative recombination have been measured. These properties can be employed in the realization of high performance and high speed optoelectronic devices.
9:00 PM - O9.2
Si/SiO2 Quantum Dots: Electronic Properties.
Igor Filikhin 1 , Sergei Matinyan 1 , Branislav Vlahovic 1
1 Physics, North Carolina Central University, Durham, North Carolina, United States
Show AbstractSpherical shaped Si quantum dots embedded into SiO2 substrate are considered under single sub-band effective mass approach. In this model the electron and heavy hole sub-bands are taken into account. The energy dependence electron effective mass [1] is especially applied for case of QD with small size. Calculations of low-lying single electron and hole energy levels are performed. For QD having small sizes (diameter d<6nm) there is a strong confinement regime when the number confinement levels is restricted by several levels. We used first order of perturbation theory to calculated neutral exciton recombination energy taking into account the Coulomb force between electron and heavy hole. For the Si/SiO2 QDs the PL experimental data [2,3] are available for comparison with the theoretical consideration. The PL exciton data are reproduced well by our model calculations. We also compare the results with those obtained within the more sophisticate model given in [2]. The comparison shows that inter-band interaction taken in to account in [2] has character of second order term and cannot be defined by the PL data. We have found the Coulomb shift of exciton energy is larger than one evaluated in [2]. For weak confinement regime (QD diameter d>10 nm), when the number of confinement levels is limited by several hundred, we considered the statistical properties of the confinement. Evidence of chaotic properties [4] of the electron spectrum is demonstrated and reason of this effect is discussed. [1] I. Filikhin, V. M. Suslov and B. Vlahovic, Phys. Rev. B 73, 205332 (2006). [2] A. S. Moskalenko et al. PR B 76, 085427 (2007). [3] Y. Kanzawa et al. Solid State Comm. 102, 533 (1997). [4] T.S. Biro, S.G. Matinyan, B. Muller, Chaos and Gaude Field Thory, Wold Science (Singapure) 1994.
9:00 PM - O9.20
Comparison of MISLEDs Made on Si-rich SiOx and SiNx.
Chun-Chieh Chen 1 , Cheng-Tao Lin 1 , Yi-Hao Pai 1 , Gong-Ru Lin 1
1 Graduate Institute of Photonics and Optoelectronics, National Taiwan University , Taipei Taiwan
Show AbstractThe research of Si-based light-emitting materials has attracted much attention because of their low cost manufacturing and potential applications in optoelectronic devices based on Si integrated circuits. One of these structures is Si/Si3N4-based thin multilayer structure with Frenkel-Poole tunneling based carrier injection mechanism reported by Tan et al. Jamei et al. also fabricated the nano-crystalline Si LED with Si-ncs buried in TiO2 by plasma-enhanced hydrogenation. The other structure is producing Si nanoclusters (Si-ncs) in Si-rich SiNx film by high-temperature annealing. However, there were few literatures indicating the optical power of SiNx based LEDs and the comparison on emission efficiency of Si-rich SiOx and SiNx LEDs. In this work, we compare the turn-on voltage, P-I, and EL responses between the MISLEDs made by Si-rich SiNx and SiOx films. The SiNx films studied in this experiment were deposited on (100)-oriented p-type Si substrate by PECVD. In contrast to the SiOx deposited using SiH4 and N2O mixture, the SiH4 and NH3 are used as the reactant gases with corresponding fluencies of 250 and 150 sccm, respectively. Active layer thickness enlarged from 120 to 360 nm is achieved by lengthening deposition time from 10 to 30 min, which inevitably increases the forward turn-on voltage from 3 to 41 V. The separation of the nano-crystallite Si and Si3N4 phases is induced by post annealing. To form the MISLEDs, a 1000-Å ITO film layer was deposited on the top of Si-rich SiNx or SiOx and a 5000-Å Al contact electrode was coated on the bottom of the Si substrate. We observe that the forward turn-on voltage of SiNx based MISLED is only 10 V and that of SiOx based one is 69 V with the same film thickness of 100 nm. The tunneling-based carrier transport mechanism is dominated due to the exponential like V-I behavior, while the tunneling probability is strongly dependent on the height of the barriers between metal/dielectric and dielectric/nc-Si matrices. The P-I slope of SiNx and SiOx based MISLEDs are 1.6 and 2.6 μW/A, respectively. The SiNx MISLED reveals threshold current and voltage of only 4 mA and 12 V due to lower barrier height of both ITO/SiNx and SiNx/nc-Si, whereas the threshold current and voltage of SiOx based MISLED are 0.4 mA and 78 V, respectively. In comparison, the higher tunneling current through the SiNx MISLED fails to promote the larger external quantum efficiency of the MISLED, indicating that such lower barriers are not beneficial to the confinement of tunneling carriers and the enhancement of light-emission efficiency.
9:00 PM - O9.21
Superfluorescent Pulsed Emission from Biexcitons in an Ensemble of CuCl Quantum Dots.
Kensuke Miyajima 1 2 , Shingo Saito 3 , Masaaki Ashida 1 , Tadashi Itoh 1
1 Graduate School of Engineering Science, Osaka University, Toyonaka Japan, 2 , PRRESTO - JST, Kawaguchi Japan, 3 , National Institute of Information and Communications Technology, Kobe Japan
Show AbstractSince a cooperative spontaneous emission from many two-level systems was theoretically reported by R. H. Dicke in 1954, the experimental researches have been performed mainly for atoms and molecules, and those embedded in the solid states. For these systems, the cooperative emissions were observed as “superfluorescence” (SF) that emerges with a time profile of a pulse under a complete population inversion.The semiconductor quantum dots (QDs) are expected to be plausible systems to realize the cooperative emission since they have discrete energy levels and long dephasing time caused by the quantum confinement effect. In 2007, the superradiance from CdSe QDs was reported; the radiative time of the exciton becomes shorter with increasing the number of the QDs. In the present paper, on the other hand, we will report the SF from an ensemble of the QDs. It is difficult to prepare the complete population inversion in single exciton systems because the excitons are generated in QDs following Poisson distribution. Here, we have noticed a biexciton state since two-photon resonant excitation of biexcitons provides the complete population inversion between them at the initial stage of the excitation. CuCl has a large biexciton binding energy of ~32 meV in bulk crystal which increases in the QDs. Therefore, CuCl QDs are appropriate for the study on the biexciton dynamics under resonant two-photon excitation of biexcitons.We used the sample of the CuCl QDs embedded in NaCl matrices fabricated by a transverse Bridgman method and a successive heat treatment. The nominal concentration of CuCl was about 1 mol%. The average radius of the dots estimated by photoluminescence (PL) peak energy was ~5.5 nm. To clarify the existence of superfluorescence, time-resolved PL measurements were performed by means of an optical Kerr gate method using a regenerative amplifier and an optical parametric amplifier. Two measurement systems were constructed for ps pulse (pulse width of ~2 ps, spectral width of ~3 meV) and fs pulse (~200 fs, ~12 meV) laser systems, respectively. The excitation pulse irradiates on the sample with the stripe shape by using a cylindrical lens, and the PL emitted from an edge of the sample was collected. With ps pulsed excitation, the time-profile of the biexcitons changed from an exponential decay to a pulse shape with the time width of ~20 ps, when the excitation density or the length of the excitation stripe were increased. These results indicate a transition from an amplified spontaneous emission to the SF. When fs pulse was used, in addition to the abovementioned phenomena, a new ultrafast pulsed emission (time width of sub-ps) of the biexciton emerged. This pulsed emission shows clearly a nature of the SF for the dependence of PL peak intensity on the excitation density.
9:00 PM - O9.22
Optically Pumped NIR to UV Nanolasers by Composition Tuning: Towards CW Operation in a Single Chip.
Juan Zapien 1 , Yingkai Liu 2 , Ting Fung Chung 1 , Igor Bello 1 , Shuit-Tong Lee 1
1 Physics and Materials Science, City University of Hong Kong, Hong Kong, Hong Kong, China, 2 Department of Physics, Yunnan Normal University, Kunming China
Show AbstractPreviously1, we shown that self-assembled nanostructures can provide efficient lasing at any predetermined wavelength in the complete NIR to UV spectral range. This is accomplished by simply using nanoribbons of two ternary compositions, namely, CdSXSe1-X and ZnYCd1-YS. Under optical pumping, using the pulsed (6 ns) 4th harmonic (266 nm) emission of a Nd:YAG laser, CdSXSe1-X nanoribbons lase from NIR (710 nm) to green (510 nm) as X changes from 0 to 1, while ZnYCd1-YS nanoribbons lase from green (510 nm) to UV (340 nm) as Y varies from 0 to 1. It is relevant to emphasize that for each ternary compound (ZnCdS or CdSSe) it is possible to prepare nanoribbons spanning the complete composition range and capable of support lasing action with low lasing threshold (35-100 kW/cm2) and high quality factor Q > 1000 (and as high as Q>3000, FWHM ~ 0.1 nm for lasing emission at 340 nm). In addition, it is possible to select the adequate composition for any pre-selected wavelength with a precision greater than 0.1 nm. This fine tuning capability overlaps thermally induced tuning and clearly demonstrates the means to select any arbitrary lasing wavelength in the 710-340 nm spectral range. Single devices fabricated with such nanolasers could, in principle, be fabricated with multiple and precisely controlled lasing wavelengths. The possibility to simultaneously address many technologically important wavelength regions from a single device can provide numerous advantages in communication, data storage, sensing and biological applications. Many of theses applications will benefit from efficient integration of large number of such structures into small devices as well as operation in continuous wavelength (CW) mode. In this presentation we will review some schemes we have explored to achieve the orderly growth of optically pumped nanolasers with wide composition tuning capabilities as well as some steps towards the development of CW mode of operation.1 J. A. Zapien, Y. K. Liu, Y. Y. Shan, H. Tang, C. S. Lee, and S. T. Lee, “Continuous near-infrared-to-ultraviolet lasing from II-VI nanoribbons” Appl. Phys. Lett. 90 (2007) 213114.
9:00 PM - O9.23
Excitons in Negative-band-gap Quantum Dots: Effect of Surface States.
Natalia Malkova 1 , Garnett Bryant 1
1 Atomic Physics Division, NIST, Gaithersburg, Maryland, United States
Show AbstractHgS quantum dots (QD) are very attractive both for fundamental interest in quantum confinement effects in QDs with negative (inverted) band gap and for their promising applicability in tunable IR devices. Bulk HgS is interesting because its band gap is so narrow that the energy of the elementary excitations, such as phonons and plasmons, excitonic binding are close to the gap energy. On the other hand, in the strong confinement regime, the spectrum of HgS QDs changes from negative-gap through the gapless state to positive-gap with decreasing size. If the excitonic binding energy becomes larger than the band gap, the normal state of the system becomes unstable against the formation of the electron-hole pairs, so-called the “excitonic insulator” phase (even though this has not been observed yet). As a result, the entire range of the sizes of HgS QDs can be divided into three regions: the region of the negative band gap, the region of the “excitonic insulator”, and the region of the positive gap. Furthermore, intrinsic surface states (which are not caused by the dangling bonds) appear under the negative-gap – positive-gap transition. In this presentation, we investigate the evolution of the optical response of the HgS QDs with decreasing size. We identify how states evolve from a negative gap to a positive gap as the confinement is increased. We determine the origin of the surface states and analyze their effect on optical response of the HgS QDs. We first study the single-particle spectrum in the empirical tight-binding model and use these states to determine the exciton states by incorporating Coulomb and exchange interaction. We investigate the Coulomb shift, exchange splitting, and identify the three confinement regimes for the QDs. Finally, we calculate the optical response of the QDs as a function of size. We demonstrate non monotonic behavior on size of the lowest optical excitations. We correlate this effect with negative gap – positive gap transition followed by appearance of the surface states.
9:00 PM - O9.24
Quantum Ring Infrared Photodetector Based On Droplet Epitaxy Technique.
Dali Shao 1 , Jiang Wu 1 , Zhenhua Li 2 , Omar Manasreh 1 2 , Vasyl P Kunets 2 , Zhiming M Wang 2 , Gregory J Salamo 2
1 Electrical Engineering, University of Arkansas, Fayetteville, Arkansas, United States, 2 Nanoscale Science and Engineering, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractInfrared photodetectors have been evolving from two-dimensional systems to three-dimensional systems due to the inherent advantages for three-dimensional confinement. Strain-driven Stranski-Krastanow growth mode has dominated the three-dimensional nanostructures, such as quantum dots and quantum rings. In this work, we reported a quantum ring infrared photodetector based on lattice-matched GaAs/AlGaAs. By using droplet epitaxy growth technique, three dimensional nanostructure with zero strain was realized. The GaAs quantum rings were grown by a molecular beam epitaxy system. The GaAs rings/AlGaAs barrier structure was repeated ten times to form the active region of the photodetector. The morphology and optical property of the quantum rings have been characterized by atomic force microscopy (AFM) and photoluminescence spectroscopy respectively. The photoresponse was measured by using Bruker IFS 125HR Fourier-transform infrared spectrometer. Dual band photoresponse was observed in the visible-near-infrared band and middle infrared band as a result of interband and intersubband transitions. The dark current was measured from 77 K to 300 K and the detectivity D* was estimated for both the visible-near-infrared band and midinfrared band.
9:00 PM - O9.25
Full Color Printing Using Single Ink: Flexible Photonic Crystal Based on Magnetic Assembly of Superparamagnetic Nanoparticles and Photochemical Fixation of Its Periodic Arrangement.
Hyoki Kim 1 , Jianping Ge 2 , Junhoi Kim 1 , Sung-Eun Choi 1 , Hosuk Lee 1 , Wook Park 1 , Yadong Yin 2 , Sunghoon Kwon 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 Department of Chemistry, University of California, Riverside, Riverside, California, United States
Show AbstractMany creatures in nature, such as butterflies and peacocks display unique brilliant colors, known as "structural colors", which result from the light interaction with periodic nanostructures on their surface. Unlike chemical dyes, structural color originating from the physical structures shows iridescent, metallic, and free from photobleaching. Mimicking such nanostructures found in nature, however, requires state-of-the-art nanofabrication techniques that are expensive and not scalable. Especially, productions of multicolors and high resolution patterning of such structures were hard to achieve. Here in this report, we demonstrate high resolution patterning of multiple structural colors within seconds, based on successive tuning and fixing of color using a single material along with a special instrumentation. Also, we demonstrate flexible photonic crystal for a realizable possibility of structural color printing using a single material. With the superior simplicity, controllability, and scalability, our structural color printing scheme is believed to show realizable possibilities of full color printing with single material.Material system we developed here is three-phase system, M-Ink, which is composed of superparamagnetic colloidal nanocrystal clusters (CNCs), solvation liquid, and photocurable resin. Under external magnetic field, the superparamagnetic CNCs are assembled to form chain-like structures along the magnetic field lines. Attractive magnetic force due to the superparamagnetic core is balanced with repulsive electrostatic and solvation force, both of which determine the inter-particle distance. The inter-particle distance in a chain determines the diffracted color from the chain. Thus, the color can be tuned by simply varying the interparticle distance using external magnetic fields. Once the desired color is obtained, it can be fixed by solidifying the photocurable resin through instantaneous UV exposure with spatial light modulator. The particle chains can be frozen in the solidified polymer network without distorting its periodic arrangements, thus retaining the structural color. High resolution patterning of structural color with single material was demonstrated by sequential process involving cooperative actions of magnetic field modulation and spatially controlled UV exposure. Fast production (<100ms) of structural color and high resolution color patterning (~10µm, 1500DPI) was achieved. For the proof-of-concept demonstration, we reproduced Mona-Lisa by structural color printing. Unique optical characteristic dependent on incident angle and direction of chain was investigated using generalized Mie theory and finite element analysis based near-field calculation. We believe that the M-Ink based system opens a door to the wide use of structural color for various potential applications including design material and color printing.
9:00 PM - O9.3
Synthesis and Structural Characterization of Lead Europium Sulfide (Pb1-xEuxS) Nanocrystals.
Suseela Somarajan 1 2 , Melissa Harrison 3 2 , Dmitry Koktysh 2 4 , Jed Ziegler 1 2 , Richard Haglund 1 2 , Edward Payzant 5 , James Dickerson 1 2
1 Department of Physics & Astronomy, Vanderbilt University, Nashville, Tennessee, United States, 2 Institute of Nanoscale Science & Engineering, Vanderbilt University, Nashville, Tennessee, United States, 3 Interdisciplinary Program in Material Science, Vanderbilt University, Nashville, Tennessee, United States, 4 Department of Chemistry, Vanderbilt University, Nashville, Tennessee, United States, 5 Centre for Nanophase Material Science Division , Oak Ridge national laboratory, Oak Ridge, Tennessee, United States
Show AbstractAdvancements in nanoscale engineering may be realized with novel, alloyed nanocrystals, which allow for customized physical properties with variations in size and composition. Lead europium chalcogenides (Pb1-xEuxX, X = S, Se, Te) have been studied for many years, as these materials are useful for infrared diode lasers and spintronics devices due to their tunable optical and semi-magnetic properties[1,2]. Among the Pb1-xEuxX ternary compounds, lead europium sulfide (Pb1-xEuxS) is likely to be most suitable for applications that call for dilute magnetic semiconductors because they can form a completely miscible alloy system with tunable energy band gaps over a wide range [2]. Both lead sulfide (PbS) and europium sulfide (EuS) crystallize in the NaCl crystal structure formation; the lattice mismatch between the two materials is only 0.5%. Here we report the first synthesis and characterization of nanocrystalline Pb1-xEuxS materials. Mixed precursors of a 1,10 phenanthroline, europium diethyldithiocarbamate complex [Eu(dedtc)3phen] and a 1,10 phenanthroline, lead diethyldithiocarbamate complex [Pb(dedtc)3phen] were used in a facile thermolysis technique to produce Pb1-xEuxS nanocrystals. The decomposition temperatures of the mixed precursors were analyzed via thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to investigate the size and morphology. The structure of the alloy Pb1-xEuxS nanocrystals was verified by X-ray diffraction (XRD). The diffraction peaks successively shifted toward shorter angles with a corresponding increase of the Eu2+ molar ratio in the material. Micro-Raman measurements were performed to study the influence of Eu2+ doping on the lattice dynamic properties of the host PbS. References[1] D. L. Partin, Ieee Journal of Quantum Electronics 24 (1988) 1716-1726.[2] A. Ishida, N. Nakahara, T. Okamura, Y. Sase, H. Fujiyasu, Applied Physics Letters 53 (1988) 274-275.
9:00 PM - O9.4
Shape-controlled Syntheses of Ag Nanoparticles via High Throughput Experimentation.
I-Chen Chiang 1 , Ren-Jye Wu 1 , Fang-Ching Chang 1
1 , Industrial Technology Research Institute, Hsinchu Taiwan
Show AbstractThe shape-controlled Ag nanoparticles have been highlighted recently due to their unusual optical properties result from different shapes. They have been attracting intensive interest because of their potential applications in the areas of optoelectronic devices, innovative biosensors, bioimaging and so on. Therefore, to investigate the growth mechanism of shape-controlled Ag nanoparticles is important. In this study, the growth mechanism has been explored for a more thorough understanding. Herein, Ag nanoparticles with different shapes were synthesized by seed-mediated growth method [1] via the reduction of silver nitrate in the presence of stabilizers trisodium citrate and poly(vinylpyrrolidone). In addition, we used high throughput experimentation (HTE) to accelerate synthesis and characterization of Ag nanomaterials. The workflow of HTE appears more reproducibility than batch to batch experiment. The results of UV-vis spectra showed the plasmon resonance bands of these particles are quite different from 400 to 850 nm under various synthesis conditions. The growth mechanism was discussed as follows. The elemental silver was formed due to moderate reduction of silver nitrate. Then, the silver complex appeared with the addition of an amount of hydrogen peroxide as an oxidant. In the subsequent growth process, silver atoms generated on the surface of silver complex by adding NaBH4. The major product of the Ag nanoparticles was notably changed into triangular nanoprisms in the presence of citrate ions, which adsorbed on silver complex to promote the two-dimensional growth.Although little works have been done on the study of nanoparticles via HTE approach until now, the HTE was proved to be a powerful tool for the development of nanoparticles in the future.
9:00 PM - O9.5
Instant Formation of Cyanine H- and J-aggregates during Phase Separation.
Jakob Heier 1 , Rolf Steiger 2 , Frank Nueesch 1 , Roland Hany 1
1 , EMPA (Swiss Federal Laboratories for Materials Testing and Research), Duebendorf Switzerland, 2 , Emeritius, Le Mouret Switzerland
Show AbstractDye molecules that are capable of self-assembling into aggregates show interesting collective optical properties, and numerous new applications are under discussion. All thin film systems described so far have shortcomings either in terms of reproducibility, stability or the rate of aggregate formation. A new, fast and reproducible method for the bottom-up construction of well defined and highly organized J- and H-aggregates in organic blend films of cyanine dyes and a nucleation agent is reported. Aggregates form spontaneously during phase separation and their formation can be controlled through the various parameters that influence the film formation. We map the optimal processing conditions and investigate the role of the nucleation sites. Aggregates formed that way are characterized by unusual attenuance properties and show enhanced reflectance and resonance light scattering.
9:00 PM - O9.6
Evolution of Gold Nanoparticles Through Catalan, Archimedean, and Platonic Solids.
Do Youb Kim 1 , Sang Hyuk Im 2 , O Ok Park 1 , Yong Taik Lim 3
1 Chemical and Biomolecular Engineering, KAIST(Korea Advanced Institute of Science and Technology), Daejeon Korea (the Republic of), 2 Device Materials Research Center, KRICT(Korea Research Institute of Chemical Technology), Daejeon Korea (the Republic of), 3 Division of Bioconvergence Technology, KRIBB(Korea Institute of Bioscience and Biotechnology), Daejeon Korea (the Republic of)
Show AbstractThe control of the shape and morphology of metal nanocrystals has been intensively studied in recent years in order to investigate the strong correlation between their shapes and their optical, electronic, chemical, physical, and catalytic properties. In particular, gold nanocrystals have attracted considerable attention because of their numerous applications, such as in surface plasmonics, surface-enhanced Raman scattering (SERS), photo-thermal therapy, as well as in chemical and biological sensing. Various synthetic methods based on colloidal chemistry have already provided routes for the production of shape-controlled gold nanoparticles such as Platonic solids, decahedra, rods, plates, and multipods. The seed-mediated growth of gold nanoparticles has recently been used to demonstrate transformations between nanoparticles with various shapes such as rod to octahedron and cube to cuboctahedron to octahedron; this latter transformation shows the possibilities for nanocrystals with octahedral symmetry (Oh). However, rhombic dodecahedral nanoparticles composed of twelve {110} facets have been difficult to achieve even though they have the same Oh symmetry as cubes and octahedra, because the surfaces of gold nanocrystals tend to exhibit facets in the order {111} > {100} > {110} among the lowest index planes to minimize their surface energies. Here we report that a rhombic dodecahedron can be directly transformed to an octahedron through two different pathways depending on the water content. At low water contents, the rhombic dodecahedron is transformed into a rhombicuboctahedron to a truncated octahedron and then to an octahedron, while at higher water contents, the rhombic dodecahedron is transformed into a rhombicuboctahedron and then to a cube or a truncated cube and then to a cuboctahedron and on to a truncated octahedron. In addition, we demonstrated cell imaging by using the truncated octahedral, rhombic dodecahedral and octahedral gold nanoparticles as a contrast agent.
9:00 PM - O9.7
Characterization of Charge Exchange and Oxygen Ion Formation by Localized Surface Plasmon Resonance Shifts in Au-Yttria-Stabilized Zirconia Nanocomposites.
Phillip Rogers 1 , Nicholas Joy 1 , Michael Carpenter 1
1 College of Nanoscale Science and Engineering, University at Albany, State University of New York, Albany, New York, United States
Show AbstractThe localized surface plasmon resonance (LSPR) of noble metal nanoparticles embedded in dielectric matrices is an optical response that can be extremely sensitive to many environmental parameters. Nanocomposites of Au nanoparticles embedded in yttria-stabilized zirconia (Au-YSZ) are an ideal case study for these plasmonic materials. Using a metal oxide matrix with oxygen ion vacancies, such as YSZ, allows one to finely tune the local environmental charge of the embedded metal nanoparticles upon varying the oxygen and hydrogen content of the gas exposure mixture. After exposure data is collected, the absorption spectra due to the Au nanoparticles are fit to the Drude model for spherical metal nanoparticles. These titration experiments have been performed for Au-YSZ nanocomposites and equilibrium data has been acquired for both the average charge per Au nanoparticle and the scattering frequency of the plasmons in a variety of exposure conditions. In comparing the charge exchange observed using both the Drude model fit data and an electrochemical model, insight into reaction energies pertaining to metal nanoparticle induced catalytic reactions can be gained. The electron scattering frequency, also known as the dampening parameter (γ), within the Drude model, is modeled as arising directly from inelastic scattering from electron states within the YSZ matrix, and the magnitude of which can be used as a measure of the number of filled oxygen vacancies. Characterization of these nanocomposite films using this multivariable method utilizing both the Au nanoparticle charge and γ to probe the catalytic processes occurring at nanocomposites containing noble metal nanoparticles shows promise as a valuable form of plasmon-based in-situ materials analysis and sensing method.
9:00 PM - O9.8
MOF-Templated Growth of Small Matrix-Supported Ag-Clusters for Raman Enhancement and Gas-Phase Small Molecule Sensing.
Ronald Houk 1 , Benjamin Jacobs 1 , Alec Talin 3 2 , Mark Allendorf 1
1 Energy Nanomaterials, Sandia National Laboratories, Livermore, California, United States, 3 Materials Physics, Sandia National Laboratories, Livermore, California, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThree non-related metal-organic frameworks (MOF) have been infiltrated with silver via solution immersion for the purpose of generating enhanced Raman scattering for both MOF characterization and subsequent small molecule sensing. The MOFs used were HKUST-1, also known as Cu(BTC), MOF-508, and MIL-68(In). The as-synthesized Ag@MOFs gave little to no Raman enhancement indicating that the clusters were too small generate efficient plasmons. TEM analysis of the as-synthesized materials also supports this hypothesis as well as the discovery of the extreme sensitivity of these soft hybrid materials to high-energy electron beam irradiation. Even under extremely gentle conditions, the MOFs quickly degraded and the coalescence of large (2-7nm) Ag-clusters was observed. Electron beam induced Ag agglomeration is concomitant with framework degradation; however thermal (250 °C) and/or chemical (DMF@80 °C 16h) annealing allows for Ag coalescence without long-range destruction of the MOF as indicated by PXRD. These annealed samples give much greater Raman enhancement indicating the presence of significant population of clusters large enough to generate plasmonic resonance. Initial results also indicate that the annealed samples can be used as a selective sensor for vapor phase reactive oxygen species such as hydrogen peroxide in the presence of water.
9:00 PM - O9.9
Saturation of Luminescence from Si Nanocrystals Embedded in SiO2.
Dolf Timmerman 1 , Tom Gregorkiewicz 1
1 Van der Waals - Zeeman institute, University of Amsterdam, Amsterdam Netherlands
Show AbstractIn this contribution we present results of a photoluminescence excitation study on silicon nanocrystals embedded in a SiO2 matrix. We show that while the excitation cross-section is wavelength-dependent and increases for shorter excitation wavelengths, the maximum time-integrated photoluminescence signal for a given sample saturates at the same level independent of excitation wavelength. By comparing the results from this study with linear absorption measurements, and analyzing the absorption with a statistical method, we demonstrate explicitly that saturation is achieved when every nanocrystal has absorbed at least one photon. In nanocrystals where several electron-hole pairs have been created during the excitation pulse, fast non-radiative recombinations reduce their number, leading to the situation that effectively only a single electron-hole pair per nanocrystal can recombine radiatively, producing a photon and contributing to the photoluminescence. In this way a natural limit is set for photoluminescence intensity from an ensemble of Si nanocrystals excited by a laser pulse with a short duration in comparison with the radiative recombination time. We will also present the most recent result concerning exciton generation upon absorption of multiple photons in a single nanocrystal using two photons of the same or different energies. The limits of this process will be explored.
Symposium Organizers
Alexander O. Govorov Ohio University
Andrey L. Rogach Ludwig-Maximilians-Universität München
Zhiming M. Wang University of Arkansas
Juen-Kai Wang National Taiwan University
(and Institute of Atomic and Molecular Sciences
Academia Sinica)
Vladimir M. Shalaev Purdue University
O10: Colloidal Nanocrystals II: Plasmons and Excitons
Session Chairs
Wednesday AM, December 02, 2009
Back Bay B (Sheraton)
9:30 AM - **O10.1
Plasmon Rulers for Single Molecule Imaging of Cell Signaling Events In Vivo.
Young-wook Jun 2 , Paul Alivisatos 1 2
2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 1 Chemistry Department, University of California, Berkeley, Berkeley, California, United States
Show AbstractThe use of plasmon coupling in metal nanoparticles has shown great potential forthe optical characterization of many biological processes. Recently, we havedemonstrated the use of “plasmon rulers” to observe conformational changes ofsingle biomolecules in vitro. Plasmon rulers provide robust signals withoutphotobleaching. These properties suggest that the rulers will be useful to observevery long trajectories (no limit has yet been observed) of single biomolecules in livecells. Here, we present a new type of plasmon ruler comprised of peptide-linkedgold nanoparticle satellites around a core particle, and utilized them as probes tooptically follow cell signaling pathways in vivo at the single molecule level. These“crown nanoparticle plasmon rulers” allowed us to continuously monitortrajectories of caspase-3 activity in live cells for over 2 hours, providing sufficienttime to observe early-stage caspase-3 activation and cell-by-cell heterogeneity,which was not possible by conventional ensemble analyses.
10:00 AM - O10.2
Effect of Nanoparticle Size and Shape on Localized Surface Plasmon Resonance Frequency: A Single Particle Approach Applied to Silver Bipyramids and Gold Nanocubes.
Emilie Ringe 1 , Anne-Isabelle Henry 1 , Marc Langille 1 , Jian Zhang 1 , Kwon Nam Sohn 2 , Claire Cobley 3 , Younan Xia 3 , Chad Mirkin 1 , Huang Jiaxing 2 , Laurence Marks 2 , Richard Van Duyne 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Materials Sciences and Engineering, Northwestern University, Evanston, Illinois, United States, 3 Biomedical Engineering, Washington University, St. Louis, Missouri, United States
Show AbstractLocalized surface plasmon resonances (LSPR), collective electron oscillations in nanoparticles, are being heavily scrutinized for applications in chemical and biological sensing, as well as in prototype devices. This phenomenon exhibits an acute dependence on the particle’s shape and size. The characterization of structures and properties of nanoparticles is blurred by ensemble averaging, such that single-particle data must be obtained to extract useful information from polydisperse reaction mixtures. Recently, a correlated LSPR-transmission electron microscopy (TEM) technique has been developed and applied to silver nanocubes [1,2]. We report here a second generation of experiments using this correlation technique, in which statistical analysis is performed on a large number of single particles. Silver bipyramids, a structure presenting a (111) twin and (100) faces, and gold nanocubes, single crystals presenting (100) faces, were studied. The dependence of LSPR peak on size for silver bipyramids was found to vary with the extent of corner rounding for a large range of sizes. A thorough study of gold nanocubes has been made, including the effect of substrate refractive index, corner rounding, and size. [1] J. M. McMahon, Y. Wang, L. J. Sherry, R. P. Van Duyne, L. D. Marks, S. K. Gray, and G. C. Schatz, J. Phys. Chem. C, 113, 2731-2735 (2009) [2] Y. Wang, S. K. Eswaramoorthy, L. J. Sherry, J. A. Dieringer, J. P. Camden, G. C. Schatz, R. P Van Duyne, and L. D. Marks, Ultramicroscopy, doi:10.1016/j.ultramic.2009.04.003 (2009)
10:15 AM - O10.3
Engineering Single-walled Carbon Nanotube Excitonic Antennas That Funnel Nearly All Their Near-infrared Photoluminescence into the Smallest Bandgap Nanotubes.
Jae-Hee Han 1 , Geraldine Paulus 1 , Ryuichiro Maruyama 1 2 , Woo-Jae Kim 1 , Paul Barone 1 , Daniel Heller 1 , Chang Young Lee 1 , Moon-Ho Ham 1 , Wonjoon Choi 1 , Jong Hyun Choi 1 3 , Michael Strano 1
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Advanced Material Laboratories, Sony Corporation, Kanagawa Japan, 3 School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractWhile there has been much investigation on both carrier transport and optical properties of single single-walled carbon nanotube (SWNT), their aggregates or bundles have received less attention, even though for many applications, such as transparent conducting films and thin film transistors, the properties of the latter are dominant. To realize the useful devices utilizing the bundles, one needs to understand how to decouple orthogonal carrier transport and couple optical properties of constituent nanotubes within the bundle. In this work, we use a recently developed separation method to purify semiconducting SWNTs, dielectrophoretically form bundles in the solid form, and explore two categories of their nature: i) electrical transport with a significantly inherent carrier scattering and ii) optical properties ensuring the unprecedented nano-scale excitonic antenna. For the former, we compare carrier transport in the bundles at 298 K to un-separated counterparts. We find that for 36- to 110-nm-diamter bundles produced, estimated transmission probabilities of 0.017 to 0.004 are approximately 1 to 2 orders of magnitude lower than single nanotube counterparts, suggesting a significant amount of carrier scattering in the bundled state. This is also reflected in the room temperature electronic mean free paths of 4.3 to 18.6 nm. For the latter, we first investigate the exciton energy transfer (EET) within the bundle as a function of environmental temperature (277 to 357 K) between donors (larger bandgap tubes) and acceptors (smaller bandgap ones) in the proximity, and spatially resolve the EET behavior using the home-built dual-channel microscopy. Then we eventually engineer excitonic antennas at the nanoscale, where most of their near-Infrared photoluminescence occurred upon the entire range of incident light (400 to 800 nm in wavelength) funnels into the longest wavelength regime. These artificial excitonic antennas could be exploited as critical components in solar energy harvesting system.
10:30 AM - O10.4
Electrical Control of Plasmon Resonance of Gold Nanoparticles using Electrochemical Oxidation.
Takashi Miyazaki 1 , Ray Hasegawa 1 , Hajime Yamaguchi 1 , Haruhi Oh-oka 1 , Hitoshi Nagato 1 , Isao Amemiya 1 , Shuichi Uchikoga 2
1 Corporate Research & Development Center, Toshiba Corporation, Kawasaki Japan, 2 Toshiba Research Europe Limited, Toshiba Corporation, Cambridge United Kingdom
Show Abstract[Introduction] Surface plasmon resonance (SPR) is a charge-density oscillation that may exist at the interface of two media with dielectric constants of opposite signs, for instance, a metal and a dielectric. Many industrial applications such as light-emitting devices and molecular sensors have been proposed and actively developed. These applications are referred to as plasmonics. Another possible application is considered to be spatial light modulators. Localized surface plasmon resonance (LSPR) excited on nanoparticle surface results in wavelength-selective absorption with extremely large molar extinction coefficients. If the resonance wavelength can be electrically modulated over a wide range, spatial light modulators with large tunable range will be realized and attractive applications such as reflective displays and optical communications can be expected. Moreover, condition of incident angle is not severe and no polarizers are required for LSPR excitation, which is also favorable to practical use.[Results and discussions] In this study, LSPR spectrum of gold nanoparticles was shifted by electrochemical oxidation of the nanoparticle surface. This oxidation occurred in a cell consisting of a pair of indium tin oxide (ITO) electrodes and water medium between the electrodes. On the one side of the ITO electrode, the gold nanoparticles (diameter: 40 nm) were adsorbed. The LSPR spectrum was moved consecutively to the red by increasing the applied positive voltage. By the application of 5 V voltage to the cell, the spectrum shift as large as 68 nm was obtained. This large shift due to electrochemical oxidation resulted from the large refractive index of Au-O. The electrochemical oxidation was confirmed by XPS analysis of the gold nanoparticles with the LSPR spectrum shift. The upper limit of the LSPR spectrum shift was estimated to be 138 nm by fitting the experimental data into the theoretical formula of the resonance wavelength. According to the results of SEM measurement etc., other possible mechanisms of the shift such as charge localization, aggregation and adsorption of charged materials have no effect. This large shift of the resonance spectrum can be expected to lead to further development of spatial light modulators for next-generation optical communications and displays.[Originality] Large shift of LSPR spectrum of gold nanoparticles (68nm) was attained by electrochemical oxidation of the nanoparticle surface. The amount of the spectrum shift was about six times larger than that observed by changing liquid crystal (LC) orientation surrounding gold nanoparticles (11nm). That was because the variation of the effective refractive index of LC was rather small. Our large shift due to electrochemical oxidation resulted from the large refractive index of Au-O.
10:45 AM - O10.5
Role of the ``Dark” State in the Fate of Excitons in PbSe Nanocrystals.
Richard Schaller 1 , David Bussian 1 , Scott Crooker 1 , Jin Joo 1 , Jeffrey Pietryga 1 , Victor Klimov 1
1 Chemistry Division, Los Alamos National Lab, Los Alamos, New Mexico, United States
Show Abstract Colloidal semiconductor nanocrystals (NCs) offer a size-tunable energy gap and unique physical processes that are of interest for a wide variety of optoelectronic applications (LEDs, lasers, photovoltaics). Lead salt NCs are of particular interest due to their potential utility in generation-III photovoltaic devices. Interestingly, studies of single electron-hole pairs in PbSe NCs at room temperature have revealed that the excited state lifetime is unusually long (hundreds of nanoseconds) relative to more well-studied materials such as CdSe NCs (20ns). The origin of this long lifetime has been debated in the literature. The role of an optically passive (“dark”) exciton state in PbSe NCs has received consideration, but calculations also indicate that large dielectric screening effects may be important. Recent theoretical work has provided an estimated of the band-edge exciton fine structure and offers that the lowest energy state is optically passive, with a significant dark-bright energy splitting of 17 and 2 meV for 1.5 and 3.0 nm radius PbSe NCs, respectively. We report the excited state lifetime of single excitons in multiple sizes of PbSe NCs as a function of temperature (from 298 to 1.6 K) and magnetic field (0 to 15 T) in an attempt to understand the detailed electronic structure. Our measurements indicate that the single exciton lifetime increases from ~800 ns at 298 K to ~5 μs at 1.6 K whereas application of magnetic fields at low temperature reduces it. Such behavior is indicative of thermally activated emission from a lower-energy dark state with an exchange splitting of order 1 to 10 meV. Based upon this splitting energy, we conclude that the slow relaxation in PbSe NCs at room temperature is mainly an effect of dielectric screening as opposed to involvement of the optically passive state.
O11: Colloidal Nanocrystals III: Coupled Dots and Excitons
Session Chairs
Wednesday PM, December 02, 2009
Back Bay B (Sheraton)
11:30 AM - **O11.1
Coupling Nanocrystals in Solids and Wires.
Jochen Feldmann 1
1 Photonics and Optoelectronics Group, Ludwig-Maximilians-Universität München, Munich Germany
Show AbstractNanocrystal multilayers with type I and type II band alignment can exhibit cascaded energy transfer or charge separation upon optical excitation. Accordingly, such systems have a potential for photovoltaic applications. The transport of charged carriers is still a drawback concerning optoelectronic applications in general. Wires with densely packed CdTe nanocrystals show strong coupling effects between the electronic states of the constituent nanocrystals and give some insights how to improve the transport properties of nanocrystal solids.
12:00 PM - O11.2
Coupled Quantum Dot / Quantum Shell Systems: Optical Gain, Ultrafast Charge Transport, and Single Particle Blinking.
Eva Dias 1 , Patanjali Kambhampati 1
1 Chemistry, McGill University, Montreal, Quebec, Canada
Show AbstractThe CdSe/ZnS/CdSe core/barrier/shell nanostructure forms an electronically coupled quantum system that is a spherical analog to the quantum well superlattice. The core’s brightness is enhanced via light harvesting by the shell. This material offers an opportunity to study charge transport in spherical nanoscale materials. Here, we present new results on the femtosecond dynamics of radial charge transport in these materials. With a combination of excitonic state selectivity and femtosecond time resolution, we monitor the ultrafast relaxation dynamics of either the core or the shell, having optically excited either phase. The femtosecond experiments reveal strong optical gain as well as evidence of spatially separated biexcitons, and coupling between phases. Finally, we present single dot data on the two-color blinking kinetics of these coupled quantum dot quantum shell systems. The blinking of each phase is cross-correlated to provided insight into the mechanism of the blinking process.[1] “Single dot spectroscopy of core/barrier/shell nanocrystals”, E.A. Dias, A. Petrik, D.S. English, and P. Kambhampati, J. Phys. Chem. C, 112, 14229 (2008)[2]“Light Harvesting and Carrier Transport in Core/Barrier/Shell Semiconductor Nanocrystals”, E.A. Dias, S.L. Sewall, and P. Kambhampati, J. Phys. Chem. C, 111, 708 (2007).
12:15 PM - O11.3
Effect of Quantum Confinement on Radiative and Nonradiative Decay Rates in Germanium Nanocrystals.
Istvan Robel 1 , Doh Lee 1 , Scott Crooker 2 , Jeffrey Pietryga 1 , Han Htoon 1 3 , Richard Schaller 1 , Victor Klimov 1 3
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIn its bulk phase, germanium is an indirect-gap semiconductor and therefore, a poor light emitter. Strong spatial confinement, however, can lead to mixing between electronic states with different translational momenta, making phononless recombination events possible and thus leading to a quasi-direct-gap behavior. Here, we study the effects of quantum confinement on radiative and nonradiative Auger recombination in colloidal germanium nanocrystals (NCs). NC sizes are in the 3-4 nm range with corresponding emission wavelengths from 0.9 to 1.2 μm. The maximum room-temperature photoluminescence (PL) quantum yield is 8% [1]. A notable blue-shift of both the absorption onset and the emission peak with decreasing nanocrystal size indicates that band-edge optical properties are dominated by optical transitions involving intrinsic quantized states of NCs. In order to investigate the nature of the lowest-energy emitting states, we have performed time-resolved PL measurements as a function of temperature (1.7-300 K) and magnetic field (0-15 T). The observed temperature- and magnetic field-dependence of the PL lifetimes indicate the presence of an optically dark (dipole-forbidden) lowest excited state closely separated from an optically active bright state. Independent measurements of thermal activation of the bright state and magnetic-field-induced mixing of the dark and bright states yield a consistent energy scale of the splitting of about 1 meV. We further analyze our results by considering the magnitude of this splitting in comparison to the lowest acoustic phonon energies available for thermal activation and relaxation between the dark and bright states. We also investigate the effect of spatial confinement on decay rates due to multiexciton nonradiative Auger recombination [2]. An interesting result of these studies is that Auger decay rates in Ge NCs are close to those in similarly sized NCs of direct gap semiconductors despite a large (orders of magnitude) difference in respective bulk Auger constants. This observation indicates that, as in the case of radiative decay, spatial confinement eliminates the need for the momentum-conserving phonon in the Auger recombination. This effect increases the likelihood of Auger transitions, and as a result, the Auger decay rates observed for Ge NCs approach those in direct gap NCs.References:[1] D. C. Lee, J. M. Pietryga, I. Robel, D. J. Werder, R. D. Schaller, and V. I. Klimov, J. Am. Chem. Soc. 131, 3436 (2009)[2] I. Robel, R. Gresback, U. Kortshagen, R. D. Schaller, and V. I. Klimov, Phys. Rev. Lett. 102, 177404 (2009)
12:30 PM - O11.4
Efficient Direct Bandgap Emission in Silicon Nanocrystals.
Wieteke de Boer 1 , Tom Gregorkiewicz 1
1 Van der Waals-Zeeman Institute, University of Amsterdam, Amsterdam Netherlands
Show AbstractIt is well-known that quantum confinement (QC) induces relaxation of the momentum conservation restriction in silicon nanocrystals (SiNCs), leading to enhancement of radiative electron-hole recombination. However (despite some theoretical predictions) the indirect character of the bandgap remains preserved. QC effects on the indirect bandgap in SiNCs are thoroughly investigated and reasonably well understood; upon decrease of NC diameter, QC induces a blueshift of the emission (photoluminescence – PL) maximum from ~1.1 eV (bulk Si) towards the visible. A limitation on the blueshift of the PL occurs for SiNCs in a SiO2-matrix, due to formation of an inter-bandgap O-related energy level, which for NC smaller than ~3 nm stabilizes PL energy at around ~2.5 eV [1]. Next to the indirect bandgap-related PL, another emission band is frequently observed, both in solid state and colloidal NCs-dispersions. It is characterized by higher photon energies and faster decay times (nano- vs. microseconds for the indirect bandgap recombination time). Controversy remains however on the microscopic nature of this emission band – whether it arises due to O-related surface state recombinations or transitions between NC core levels. Based on results obtained with time-resolved PL experiments conducted on SiNCs embedded in a SiO2-matrix combined with a theoretical model on the QC effects at the Γ-point [2], we postulate to identify this band with radiative recombinations of electron-hole pairs across the direct bandgap. The theoretical model predicts a QC induced redshift of the direct bandgap value upon NC size decrease, from the 3.32 eV value of bulk Si, covering the entire visible spectral range. We demonstrate that experimental results indeed reveal efficient PL band, tunable into the visible, and are therefore in good agreement with the proposed model. The proposed identification yields far-reaching consequences both on the fundamental side – understanding of QC effects in SiNCs, and application-wise, where use could be made of the enhanced absorption/emission cross-section tunable in the visible.
1.M.V. Wolkin et al., Phys. Rev. Lett. 82, 197 (1999)
2.A. A. Prokofiev et al., Phys. Rev. Lett., under submission
12:45 PM - O11.5
Size Dependence of the Spontaneous Emission Rate and Absorption Cross Section of CdTe and CdSe Quantum Dots.
Celso de Mello Donega 1
1 Chemistry, Debye Institute for Nanomaterials Science - Utrecht University, Utrecht Netherlands
Show AbstractUnderstanding the size dependence of the absorption cross section and of the exciton radiative lifetime of quantum dots (QDs) is important from both fundamental and applied viewpoints. This has motivated several groups to investigate the extinction coefficient of colloidal QDs for a number of materials, but large discrepancies are observed between the size-dependent trends reported by different groups, even for the same material. Reports on the exciton radiative lifetime of QDs are scarcer, probably due to the difficulty of synthesizing QDs yielding purely radiative decay. The emission transition of a QD is in first approximation the reverse of the lowest energy exciton absorption transition. Therefore, it can be expected that the size dependence of the oscillator strengths of the emission transition and of the lowest absorption transition of a QD will be similar. In this contribution the size dependence of the band gap, of the spontaneous emission rate and of the absorption cross section of Quantum Dots is systematically investigated over a wide size range, using colloidal CdSe and CdTe QDs as model systems (diameters ranging from 1.2 to 8 nm and from 2 to 9.5 nm, respectively). The size-dependence of the band gap is well described by theoretical models, and is dominated by the quantum confinement contribution. The spontaneous emission rate increases linearly with the emission frequency for both CdSe and CdTe QDs, in good agreement with theoretical predictions. By extrapolating the frequency dependence of the emission rates to the bulk band gap values, the exciton radiative lifetime in bulk CdSe and CdTe was estimated for the first time. Comparison between the empirical trends and theoretical predictions provides new fundamental insights into the size dependence of the 1S-1S oscillator strengths of QDs, both for emission and absorption. The results highlight the importance of the balance between quantum confinement and coulomb interaction contributions to the size-dependence of the exciton properties in QDs, and offer an explanation to the long-standing discrepancies observed between the empirical size-dependent trends and the theoretical predictions. The difference between the size-dependence of the radiative decay rates and of the absorption cross sections is shown to be due to the fundamental differences between the emission and absorption transitions (viz., spontaneous versus stimulated). The results are also relevant from a practical viewpoint, since they show that the molar extinction coefficients at energies far above the band-gap are better suited for analytical purposes. Moreover, the size- and temperature-dependence of the exciton lifetimes of CdSe and CdTe QDs in the 1.5 to 300 K is analysed.
O12: Colloidal Nanocrystals IV: Superstructures, Hybrids, and Optical Properties
Session Chairs
Wednesday PM, December 02, 2009
Back Bay B (Sheraton)
2:30 PM - **O12.1
Understanding Self-Assembly of Colloidal Nanoparticles into Complex Superstructures.
Maryna Bodnarchuk 1 , Sara Rupich 1 , Maksym Kovalenko 1 , Elena Shevchenko 2 , Dmitri Talapin 1 2
1 Deparment of Chemistry, The University of Chicago, Chicago, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractNanoparticles of different metals, semiconductors and magnetic materials can self-assemble from colloidal solutions into long range ordered periodic structures (superlattices). Combining two types of nanoparticles yields binary nanoparticle superlattices (BNSLs) exhibiting very rich phase diagrams with a multitude of close-packed and non-close-packed phases. Through a series of systematic studies of self-assembly phenomena in single- and multicomponent nanoparticle assemblies we demonstrate that observed structural diversity is a result of the intricate interplay of entropy-driven crystallization with isotropic and anisotropic interparticle interactions, such as van der Waals, Coulombic and dipolar forces. We found that neither nanoparticle size ratio nor relative concentrations play dominant role in self-assembly. Instead, many additional factors, such as solvent and temperature can dramatically affect relative stabilities of different BNSL phases. Moreover, proper design of nanoparticles and experimental conditions allowed us achieving unprecedented palette of complex phases including superlattices isostructural with the Archimedean tilings and dodecagonal quasicrystals.
3:00 PM - O12.2
Energy Transfer in Type II Hybrid Organic-inorganic Nanocomposites.
Andrey Lutich 1 , Guoxin Jiang 1 , Andrei Susha 1 , Andrey Rogach 1 , Fernando Stefani 1 , Jochen Feldmann 1
1 Department of Physics and CeNS, Ludwig-Maximilians-Universitaet Muenchen, Munich Germany
Show AbstractEffective design of tailored optoelectronic properties of hybrid materials consisting of semiconductor nanocrystals and conjugated polymers requires a deep understanding of the related photophysics, which includes charge separation as well as Dexter and Förster energy transfer (FRET). We performed a detailed and quantitative spectroscopic investigation of a type II aligned hybrid system consisting of a blue emitting conducting polymer and CdTe nanocrystals. Although charge separation is expected from the type II alignment, we find a dominant (70% efficiency) energy transfer process. We discuss all possible de-excitation pathways for the excitons in terms of the alignment of energy levels, time scales and physical geometry of the system. This allows us to conclude that energy transfer occurs via the Förster mechanism and provides a clear guideline for the design of novel hybrid materials. As an example, we demonstrate that water soluble organic-inorganic nanocomposites of a fluorescent conjugated polymer and CdTe nanocrystals provide a simple and reliable signal-on sensing platform for DNA hybridization detection. The sensor relies on a two-step FRET process from the conjugated polymer to CdTe nanocrystals and further to an infrared-emitting dye labeled on the probe DNA.
3:15 PM - O12.3
Direct Observation of the Two Lowest Exciton Zero-Phonon Lines in Single CdSe/ZnS Nanocrystals.
Brahim Lounis 1 , Louis Biadala 1 , Yann Louyer 1 , Philippe Tamarat 1
1 , CNRS & Université Bordeaux, Bordeaux France
Show AbstractWe report a spectroscopic study of highly photostable individual CdSe/ZnS colloidal nanocrystals. At low temperature, photoluminescence spectra display two sharp zero-phonon lines which we attribute to the radiative recombination from the two lowest levels of the band-edge exciton fine structure. For the first time, resonant photoluminescence excitation spectra of these lines is performed, and spectral diffusion broadening of 10 µeV is measured over integration times of 100 ms, corresponding to an optical coherence lifetime longer than 100 ps.Reference:Biadala et al, to appear in Phys Rev Lett 2009
3:30 PM - O12.4
Polyurethane Gold Nnanorod Chiral Nanocomposites.
Ashish Agarwal 1 , Nicholas Kotov 1
1 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractNegative Index Materials (NIMs) because of their ability to refract light on the opposite side of the normal have the most intriguing optical properties which may find application in construction of perfect lens and cloaking devices. The two most actively pursued approaches to NIMs are via using resonating metallic nanostructures and photonic crystals. Recent theoretical investigations have showed that NIMs can also be realized through chiral materials if the chirality is sufficiently strong. The current work is an effort to realize chiral negative index materials by using resonating metallic nanorods in polymers to create highly chiral nanocomposites. Anisotropic gold nanorods are aligned inside stretched thin polymer films to create strong polarizer’s owing to the longitudinal plasmon resonance. The stretched films are then piled on at a rotating angle and hot pressed into one composite film. The dependence of chirality on the concentration of gold nanorods, piling angle and thickness of the composite will be discussed. One of the biggest advantages of this system is that a chiraly active material can be achieved over a large range of wavelength simply by tuning the absorption of the rods.
3:45 PM - O12.5
Charge Storage and Optical Response of Hybrid Nanodots Floating Gate For Functional Memories.
Seiichi Miyazaki 1 , Naoya Morisawa 1 , Sho Nakanishi 1 , Akira Kawanami 1 , Mitsuhisa Ikeda 1 , Katsunori Makihara 1
1 , Hiroshima Univ., Higashi-Hiroshima Japan
Show AbstractWe have proposed and fabricated a hybrid nanodots floating gate (FG), in which Si quantum dots (QDs) as charge injection/emission nodes and NiSi nanodots as charge storage nodes are stacked with an ultrathin SiO2 interlayer, to satisfy both large memory window and multivalued capability. In this work, we demonstrated stable storage of many charges in the deep potential well of NiSi nanodot and stepwise charge injection to and emission from NiSi nanodots through discrete energy states in Si-QDs. Also, we report optical response caused by the redistribution of stored charges in the hybrid FG under infrared light irradiation. Hemispherical Si-QDs with a dot density of ~3x1011cm-2 and an average dot height of 6nm were firstly formed on ultrathin thermally-grown SiO2 by controlling the early stages of LPCVD of pure SiH4. To form NiSi nanodots, the silicidation of pre-grown Si-QDs was conducted by evaporation of an ultrathin Ni layer and subsequent exposure to remote H2 plasma without external heating. In the fabrication of a hybrid nanodots FG consisting of NiSi nanodots and Si-QDs, after the surface oxidation of firstly formed Si-QDs on the tunnel oxide, the 2nd formation of Si-QDs was preformed and followed by Ni evaporation and silicidation with the remote H2-plasma exposure. We also prepared a stack structure with additional Si-QDs after the formation of an ultrathin SiO2 interlayer by inductively-coupled remote plasma CVD with SiH4 and excited O2/Ar. For MOS capacitors, a ~22-nm-thick SiO2 was grown as a control oxide at 350°C by the inductively-coupled remote plasma CVD, and finally Al gates with 1 mm in diameter were fabricated by thermal evaporation through a stencil mask.The formation of NiSi nanodots was confirmed from the photoemission spectra of core lines and the valence band. Also, the electrical separation among NiSi nanodots on SiO2 was verified from the surface potential changes due to electron charging to and discharging from the dots by using a non-contact AFM/Kelvin probe technique. Capacitance-voltage(C-V) characteristics of MOS capacitors with a NiSi nanodots/Si-QDs hybrid FG shows a fairly large flat-band voltage (Vfb) shift in comparison with the case with a doubly stacked Si-QDs FG fabricated with the same process except silicidation, which is attributed to charge storage in the deep potential well of NiSi nanodots. In applying pulsed gate biases for electron injection to and emission from the hybrid nanodots FG, the increase rate of the Vfb shift was decreased with increasing pulse width in a stepwise manner. This suggests that discrete energy states of the Si-QDs work as an energy filter to control of charges stored in NiSi nanodots. In addition, by 1310nm (~0.95eV) light irradiation, a distinct optical response in C-V characteristics was detected, which can be interpreted in terms of the shift of charge centroid in the hybrid FG stack due to transfer of photoexcited electrons from NiSi-nanodots to the Si-QDs.
4:00 PM - O12: CN-IV
Break
O13: Nanostructures and Nanomaterials
Session Chairs
Wednesday PM, December 02, 2009
Back Bay B (Sheraton)
4:15 PM - **O13.1
Studies of Surface Exciton Polaritons in Nano-Materials by Electron Energy-Loss Spectroscopy.
Cheng-Hsuan Chen 1 , Chien-Ting Wu 1 2 , Ming-Wen Chu 1 , Li-Chyong Chen 1 , Chun-Wei Chen 2
1 Center for Condensed Matter Sciences, National Taiwan University , Taipei Taiwan, 2 Materials Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractSurface plasmon polaritons (SPPs), which normally occur in the optically metallic spectral regime, are collective charge density oscillations of conduction electrons at the surface of metals. In sharp contrast to SPPs, the excitations of surface exciton polaritons (SEPs), which are collective oscillations of delocalized excitons at the surface of semiconductors or insulators, have been shown to be correlated with sharp excitonic onsets (interband transitions) in these materials. Electron energy-loss spectroscopy (EELS) in conjunction with scanning transmission electron microscopy (STEM) has been widely used for studies of surface excitations with a spatial resolution unmatched by any optical methods. In this talk, we shall report our STEM-EELS studies of SEP excitations in GaN and ZnO nanorods. SEP excitations near interband transitions are observed near bandgap and also far above bandgap in the deep UV spectral regime. Compared to SPPs, SEPs have been shown to exhibit a much smaller decaying constant. Using electron energy-loss spectroscopy (EELS) with a 2-Å electron probe in aloof (near-field) geometry and energy-filtered imaging in real space, we firmly establish the exponentailly decaying charateristics of the wavefields of the surface excitations. It is noted that most recent interest in the applications of palsmonics is concentrated in the visible spectral regime. We think SEPs could lead to new applications of plasmonics in UV and deep UV beyond the visible spectral regime.
4:45 PM - O13.2
Enhancement of Photovoltaic Device Performance in Close-Packed Nanowire Excitonic Solar Cells by Foerster Resonance Energy Transfer.
Karthik Shankar 1 , Sanghoon Kim 2 , Xinjian Feng 2 , Craig Grimes 3 2
1 Electrical & Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 The Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractOur ability to fabricate close-packed single crystal rutile TiO2 nanowire arrays with average inter-wire distances of 5-10 nm allows us to create and control FRET-induced coupling effects, which can occur in this distance regime. The objective of this work was to explore the use of such coupling to boost the performance of nanowire excitonic solar cells.The poor spectral match of organic dyes and organic semiconductor absorbers to the AM 1.5 solar spectrum results in inadequate light harvesting and limits the achievable efficiencies in excitonic solar cells. In particular, both dye sensitized solar cells and bulk heterojunction solar cells exhibit poor quantum yields for red photons and near-negligible response for near-IR photons. The conventional route to overcome the limitation of poor spectral matching consists of synthesizing low-bandgap polymers and near-IR absorbing dyes, which are then used either in isolation or together with existing dyes or polymers in cocktails. This approach has not improved device efficiencies significantly. Several low band-gap dyes have been reported to catalyze recombination processes on the host electrode, which may account for why no dye with significant absorption beyond 750 nm has functioned properly. Our approach uses FRET to increase the harvesting of red and near-IR photons in dye sensitized solar cells. In configuration A, fluorescent donors (tetra t-butyl substituted Zinc Phthalocyanine) were combined with broadly absorbing triplet acceptors (N719 and Black dye). Despite the smaller donor-acceptor spectral overlap in configuration A, the selection rules for FRET prohibit energy transfer from a triplet excited state to a singlet ground state and ensure unidirectional energy transfer to triplet dye acceptors. In configuration B, highly fluorescent Nile Red donors were used with unsymmetrical Squaraine acceptors to obtain large spectral overlap. In all our devices, the acceptor dye molecule was anchored to the surface of the nanowires while donor molecules were introduced directly into the tri-iodide redox electrolyte. Due to the confinement of the liquid electrolyte in the inter-wire spaces of the electrode a large number of donor dye molecules dissolved in solution were effectively within a Förster radius of the acceptor molecules-thus facilitating energy transfer between donor and acceptor molecules. FRET induced increases in the quantum yield were observed for both configurations, but the increase was more dramatic for configuration A (four fold increase in the spectral range 680-700 nm) compared to B (~60% increase at 530 nm).Our results indicate that the population of monomer and partial overlap excimer species of fluorescent donors is relatively higher in the inter-nanowire spaces than in the bulk. We also develop fundamental design principles for increasing the efficiency of solar cells using FRET in nanotube and nanowire array architectures.
5:00 PM - O13.3
Carbon Nanotube / CdSe Nanoparticle Hybrid Materials: Synthesis and Optical Properties.
Austin Akey 1 , Chenguang Lu 1 , Wei Wang 2 , Irving Herman 1
1 Applied Physics and Applied Mathematics, Columbia University, New York, New York, United States, 2 Chemistry, Columbia University, New York, New York, United States
Show AbstractCarbon nanotubes present remarkable opportunities as a base for construction of advanced nanomaterials with uniques properties, for use in sensors and optoelectronic device applications. Chemical attachment of nanoparticles to nanotubes has thus far resulted in low loading efficiency and low coverage, and direct nucleation of particles on the tube sidewalls leads to a loss of control over particle size and monodispersity. We report the synthesis of novel heterostructures composed of single-walled carbon nanotubes and chemically attached, monodisperse cadmium selenide nanoparticles that form after treatment with pyridine. The resulting hybrid material is stable and resists aggregation; TEM and SEM characterization shows the nanotubes to be densely covered in nanoparticles. The nanoparticles used range in size from 3.5 to 6 nm in diameter, and exhibit strong quantum confinement. The optical properties of the hybrid material differ significantly from those of the raw nanoparticles and nanotubes, pointing to the existence of strong electronic/optical interaction effects between the two. Specific differences in absorption/emission behavior and the photoluminscence Stokes shift in the nanoparticles will be presented. This work is primarily supported by the Nanoscale Science and Engineering Center at Columbia University, which is supported by the Nanoscale Science and Engineering Initiative of the NSF under Award Number CHE-0641523.
5:15 PM - **O13.4
Room-temperature Polariton Lasing in an Organic Single Crystal Microcavity.
Stephane Kena-Cohen 1 2 , Stephen Forrest 2
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Electrical Engineering and Computer Science and Physics, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWhen a material possessing a strong excitonic resonance is placed inside a microcavity, it can result in a new excitation termed a cavity polariton. Due to the bosonic nature of these quasiparticles, coherent nonlinear emission occurs if the ground state occupation reaches unity. This phenomenon, which is analogous to Bose-Einstein condensation, is called polariton lasing and has recently been demonstrated in inorganic microcavities. Strongly-coupled organic microcavities possessing giant Rabi splittings at room temperature (>200 meV) were first demonstrated 10 years ago, yet to date, there has been no report of nonlinear emission from these structures.Here, we report on the first observation of polariton lasing in an organic microcavity. The microcavity is composed of a 120 nm-thick single crystal of anthracene enclosed between two dielectric Bragg reflectors. Upon reaching threshold, superlinear emission is observed, accompanied by a collapse of the emission lifetime (<40 ps) and a thermalization of the polariton distribution function. Significant changes are also observed in the spatial mode profile beyond threshold. Conventional photon lasing has never been observed in crystalline anthracene. Nevertheless, we have directly measured the gain in this structure and the observed threshold for polariton lasing (430 uJ/cm2) is found to be lower than our best case estimate for the photon lasing threshold in anthracene (320 uJ/cm2).
5:45 PM - O13.5
Photoluminescence in Nanotube Bundles Due to Exciton Energy Transfer from Excitonic Phonon Sidebands.
Francesco Bonaccorso 1 , PingHeng Tan 1 2 , Tawfique Hasan 1 , Andrea Ferrari 1
1 Engineering, Cambridge University, Cambridge, Cambridgeshire, United Kingdom, 2 Institute of Semiconductors, Chinese Academy of Science, Beijing China
Show AbstractExciton-exciton resonances are the main features in Photoluminescence excitation (PLE) maps of Single Wall Carbon Nanotube (SWNT) suspensions. We suggested that exciton energy transfer (EET) can happen from large bandgap semiconducting SWNTs (donor tubes) to smaller bandgap semiconducting SWNTs (acceptor tubes) [1]. Excitons are generated in donor nanotubes and then non-radiatively transfer their energy to acceptor nanotubes via Förster interaction. Recent works validated our initial observations [1, 2, 3]. EET can be a major non-radiative relaxation channel for large gap tubes in nanotube bundles, lowering their photoluminescence (PL) quantum efficiency [1,2]. The exciton-phonon interaction is very strong in nanotubes [4]. This can mix an exciton with phonons and form an exciton sideband above the main absorption peak[4]. Here, we investigate the PL excitation spectroscopy of chirality sorted CoMoCAT suspensions after the first iteration of density gradient ultracentrifugation [5]. We argue that EET can aslo occur from excitonic phonon sidebands to acceptor nanotubes. This can enhance PL emission from small gap semiconducting nanotubes, while phonon sidebands of larger gap tubes act as photon absorbers for energy transfer. The transfer efficiency of this process is at least 30% for specific donor-acceptor couples [5]. Bright phonon sidebands of dark K-momentum eh11 exciton of (6,5) tubes are observed in isolated nanotubes. The enrichment of single chirality in such suspensions permits us to point out the difference amongst energy-transfer-related features and bright phonon sidebands of dark K-momentum eh11 excitons. They are different in peak position and intensity [5]. [1] Tan, P. H.; Rozhin, A. G.; et al., Phys. Rev. Lett. 2007, 99, 137402.[2] Qian, H.; Georgi, C.; Anderson, N.; et al., Nano Lett. 2008, 8, 1363.[3] Lefebvre, J.; Finnie, P. J. Phys. Chem. C 2009, 113, 7536.[4] Perebeinos, V.; Tersoff, J.; Avouris, P. Phys. Rev. Lett. 2005, 94, 027402.[5] Tan, P. H. et al., submitted, 2009.
Symposium Organizers
Alexander O. Govorov Ohio University
Andrey L. Rogach Ludwig-Maximilians-Universität München
Zhiming M. Wang University of Arkansas
Juen-Kai Wang National Taiwan University
(and Institute of Atomic and Molecular Sciences
Academia Sinica)
Vladimir M. Shalaev Purdue University
O14: Optical Properties of Emitters in the Presence of Plasmons
Session Chairs
Thursday AM, December 03, 2009
Back Bay B (Sheraton)
9:15 AM - **O14.1
Metal-Enhanced Fluorescence of Chlorophylls in Single Light-Harvesting Complexes.
Sebastian Mackowski 1
1 Institute of Physics, Nicolaus Copernicus University, Torun Poland
Show AbstractToday nanotechnology offers various ways to externally tune the optical properties of biomolecules and as a result extend the possibilities developed by the Nature. In this work we apply plasmon excitations in metal nanoparticles to study the influence of electromagnetic field enhancement on the optical properties of a photosynthetic antenna. The results of ensemble and single-molecule spectroscopy demonstrate for the first time that both emission and absorption of peridinin-chlorophyll-protein (PCP) photosynthetic antennae can be dramatically enhanced through plasmonic interactions. On average, we observe 7-fold increase of the fluorescence intensity of PCP complexes placed in the vicinity of silver nanoparticle layer with maximum enhancement reaching factor of 18. This enhancement, which leaves no measurable effects on the protein structure, is observed when exciting either chlorophyll or carotenoid molecules. The experimental findings are supported by model calculations of the electric field enhancement of both absorption and emission, which outweigh any fluorescence quenching due to the Ag nanoparticles. This observation is an important step toward applying plasmonic nanostructures for controlling the optical response of complex biomolecules. Particularly appealing is the prospect of using advanced biochemical techniques to control the morphology of hybrid structures, thereby optimizing the interactions between biomolecules and metal nanoparticles. Initial results show that combination of CdTe nanocrystals with light-harvesting complexes further improves light collection efficiency by extending the spectral range and taking advantage of huge absorption coefficients typical for the nanocrystals.ReferencesS. Mackowski, S. Wörmke, A.J. Maier, T.H.P. Brotosudarmo, H. Harutyunyan, A. Hartschuh, A.O. Govorov, H. Scheer, C. Bräuchle, Nano Letters 8, 558-564 (2008) S. Mackowski, S. Wörmke, T H.P. Brotosudarmo, H. Scheer, C. Bräuchle, Photosynthesis Research 95, 253-260 (2008)S. Mackowski, S. Wörmke, T.H.P. Brotosudarmo, C. Jung, R.G. Hiller, H. Scheer, C. Bräuchle, Biophysical Journal 93, 3249-3258 (2007)S. Wörmke, S. Mackowski, C. Jung, M. Ehrl, A. Zumbusch, T.H.P. Brotosudarmo, H. Scheer, E. Hofmann, R.G. Hiller, C. Bräuchle, Biochimica et Biophysica Acta - Bioenergetics 1767, 956-964 (2007)T.H.P. Brotosudarmo, E. Hofmann, R.G. Hiller, S. Wörmke, S. Mackowski, A. Zumbusch, C. Bräuchle, H. Scheer, FEBS Letters 580, 5257-5262 (2006)
9:45 AM - O14.2
Strongly Enhanced Er3+ Excitation and Emission Rates at 1500 nm in Plasmonic Nanocavities.
Ewold Verhagen 1 , Erwin Kroekenstoel 1 , Robert Walters 1 , L. (Kobus) Kuipers 1 , Albert Polman 1
1 Center for Nanophotonics, FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractThe enhanced fields associated with the excitation of resonances in plasmonic nanostructures can strongly influence the dynamics of nearby emitters. The coupling of surface plasmon resonances to optical emitters is of interest for application in photovoltaics, LEDs, and sensors. We experimentally demonstrate a strong alteration of both the excitation and emission rates of erbium ions placed in close vicinity to arrays of subwavelength apertures in a metal film. Suitably shaped apertures act as plasmonic nanocavities. They enhance infrared pump intensity leading to a strong increase in upconversion emission emitted by the Er ions, and strongly increase the radiative emission rate of Er at 1.5 µm through the Purcell effect.Erbium ions are implanted in a sapphire substrate at a depth of 35 nm below a Au film containing arrays of subwavelength apertures. The Er ions can convert 1480 nm incident radiation to 980 nm emission in a nonlinear upconversion process. The upconversion luminescence is used as a probe for the strength of the enhanced excitation field near the apertures. Resonant plasmonic field enhancement in aperture arrays can have two origins: the excitation of surface plasmon polaritons (SPPs) propagating on the film surface through resonant grating diffraction, or the excitation of localized modes in individual apertures acting as nanocavities.We demonstrate that by tuning a resonance associated to the excitation of propagating SPPs on a subwavelength hole array to the excitation wavelength, the upconversion emission from Er ions can be enhanced by a factor 500. The optimum hole size yielding maximum field enhancement balances SPP coupling strength and resonance linewidth. We show that the array periodicity giving maximum field enhancement is significantly shifted from that for which the far-field transmission is maximal due to the Fano effect.In contrast to regular holes, annular apertures can support a strong localized plasmon resonance at the cutoff frequency for surface plasmons propagating in the aperture. By studying upconversion enhancement in annular aperture arrays we show that the field enhancement due to the excitation of these localized modes is independent of the incident angle. Because annular apertures act as nanocavities, they can also strongly enhance the decay rate of Er ions through the Purcell effect. The ultrasmall mode volumes of these cavities can lead to a strong increase of the radiative rate of Er ions placed inside the cavities. As the plasmon resonance is tuned to the 1.5 μm emission wavelength by changing the aperture dimensions, we observe a 10-fold increase of the emitted luminescence intensity. Time-resolved measurements show that this increase goes in conjunction with a strong increase of the Er decay rate, proving that the Purcell effect is responsible for the observed photoluminescence enhancement.
10:00 AM - O14.3
Plasmon Enhanced Decay for Lanthanides in Au-nanoparticle Model Systems.
Timon van Wijngaarden 1 , Matti M. van Schooneveld 1 , Celso de Mello Donega 1 , Andries Meijerink 1
1 Debye Institute for NanoMaterials Science, Utrecht University, Utrecht Netherlands
Show AbstractLanthanides are an interesting class of emitters because of their rich energy level structure. This makes them promising candidates for spectral up- and down conversion in solar cells. In this (and other) applications control over the transition rates between specific energy levels is highly desirable to be able to tune the emission output and the absorption strength. One method to achieve this is by bringing lanthanide ions close to a metal (nano)particle and use plasmon coupling to modify transition rates. In this contribution we present careful studies on a model system consisting of silica coated gold nanoparticles for which lanthanide complexes have been incorporated in the amphiphilic coating surrounding the silica using a newly developed coating procedure for silica nanoparticles[1]. The resulting model system comprises a gold nanoparticle core (for which the size and shape can be varied to tune the plasmon resonance), a silica spacer layer (of a well-controlled and variable thickness) and an amphiphilic layer (consisting of octadecanol covalently attached to the silica surface and intercalated with a lanthanide complex and pegylated lipids) and can be dissolved in water. The system will be shown to serve as a model system to study plasmon enhanced transition probabilities and to test theoretical models describing the influence of plasmon coupling as a function of plasmon resonance frequency and distance. For example, we did experiments with 60 nm gold particles, surrounded by silica shell varying in thickness between 7 and 20 nm, and coated with an amphiphilic layer including the Eu(TTA)3 complex. For the 5D0 emission of Eu3+ we measured almost no decay rate enhancement with a 20 nm silica shell surrounding the Au particle, while for the thinnest shells we measured a decay rate enhancement up to a factor of five.Comparison with classical electromagnetic calculations [2] shows good qualitative agreement between our experiments and theory.References:1.M. M. van Schooneveld, E. Vucic, R. Koole, Y. Zhou, J. Stocks, D.P. Cormode, C.Y. Tang, R.E. Gordon, K. Nicolay, A. Meijerink, Z.A. Fayad, and W.J.M. Mulder, Nano Lett., 8, (2008), 25172.H. Mertens, A.F. Koenderink, and A. Polman, Phys. Rev. B., 76, (2007), 115123
10:15 AM - O14.4
Quantum Dot-Metal Nanoparticle Hybrid Exciton Systems: Exciton Induced Transparency, Bistability, Chaos and Entangled Response.
Garnett Bryant 1 , Ryan Artuso 1 2
1 Atomic Physics Division and Joint Quantum Institute, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Joint Quantum Institute, University of Maryland, College Park, Maryland, United States
Show AbstractHybrid structures consisting of semiconductor quantum dots (QD) and metal nanoparticles (MNP) joined by biolinkers have been assembled and studied. Such structures allow the study of physics at the classical/quantum interface that could provide technology for a number of quantum information devices. These structures should allow the transport of excitations as well as the transport of coherent states. Experiments have already demonstrated the plausibility for such transport. We study theoretically the optical response of excitons in QDs coupled with plasmons in an MNP. Exciton dynamics is treated quantum mechanically via a density matrix approach. Coupling to the plasmons is via a classical dipole-dipole interaction. The entire system is driven by a classical light field [1,2]. For hybrid structures with one QD and one MNP, three regimes of behavior occur in the strong field limit. In the first regime, the energy absorption spectrum displays an asymmetric Fano shape (as in [1]). This results from interference between the applied field and the field induced by the QD at the MNP. When the QD/MNP dipole coupling is increased by increasing the QD size, an exciton induced transparency (EXIT) dip appears in the plasmon absoption. The EXIT dip occurs when the induced interparticle field becomes stronger than the external field. As the coupling is further increased by increasing the sizes of both the QD and the MNP, a regime of bistability appears in which QD states with different initial conditions evolve to different steady states with different level populations. This originates when the self-interaction of the QD exciton, which is induced by coupling with the plasmons, becomes significant, making the exciton response strongly nonlinear. We explore these three regimes in detail and define a phase diagram. When a second QD is added to the QD/MNP system, the effective strength of the coupling is increased and features from the single QD case are accessible at lower fields. More importantly, a new regime of bistability, characterized by different steady states having different polarizations, emerges. Finally, a regime of chaotic response appears as the coupling is further increased. These new regimes originate from the mutual interaction between the two QDs. The same model used to study two QDs coupled to an MNP is extended to study a single QD coupled to the MNP with two bright excitions in the QD. This allows us to investigate plasmonic coupling to biexciton states and to determine the effect of this coupling on exciton cascade from the biexciton state. We investigate how this coupling can be used to modify exciton fine-structure splitting and polarization, and induce entangled photon generation.References[1] W. Zhang, A. O. Govorov, and G. W. Bryant, Phys. Rev. Lett. 97, 146804 (2006).[2] R. D. Artuso, and G. W. Bryant, Nano Lett. 8, 2106 (2008).
10:30 AM - O14.5
Light-Emitting Conjugated Polymer/Metal Nanowire Heterostructure Plasmonic Antennas.
Deirdre O'Carroll 1 , Carrie Hofmann 1 , Harry Atwater 1
1 Thomas J. Watson Sr. Laboratory of Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractPlasmonic nanoantennas can significantly modify the direction and rate of spontaneous emission from nanoscale light emitters due to their intense, highly localized surface plasmon resonances. Only a few examples of direct near-field coupling of linear plasmonic nanoantennas to local nanoemitters have been experimentally demonstrated and, typically, the light-emitting nanostructure is either randomly dispersed relative to the nanoantenna or it acts as a nucleation point for chemical growth of the antenna. In this work, individual gold nanowire antennas and conjugated polymer (poly(3-hexylthiophene), P3HT) excitonic light emitters are self-aligned into axial nanowire heterostructures by template-directed sequential electrodeposition. Using this approach P3HT nanoemitters are positioned at the end of gold nanowire antennas, where highly-localized, longitudinal surface plasmon mode fields are strongest. Comprehensive optical characterization and theoretical modeling are employed to demonstrate plasmonic nanoantenna-mediated light emission from individual nanowire heterostructures - as identified by pronounced modifications to the excitonic emission spectrum, polarization direction and emission lifetime of the P3HT nanoemitter. The excitonic photoluminescence (PL) intensity from gold-P3HT nanowires is shown to be enhanced by a factor of 1.8 compared to that of neat P3HT and the full-width-at-half-maximum of the PL spectrum is reduced to just 68 nm - compared to 130 nm for neat P3HT. In addition, excitonic emission is preferentially polarized along the longitudinal axis of individual gold-P3HT nanowires due to near-field proximity of the P3HT nanoemitter to the end of the gold nanowire antenna. In contrast, the PL spectrum from neat P3HT nanowire emitters does not change with emission polarization angle. Using PL lifetime measurements, the total decay rate, Γtot, of P3HT nanoemitters is found to increase by a factor of 1.7 upon coupling to the end of gold nanowire antennas.Full-field electromagnetic simulations show that Γtot strongly depends on the distance, d, of P3HT dipole emitters from the gold nanowire end due to variations in the degree to which light emitted from the P3HT segment is either absorbed non-radiatively by the metal near the gold-P3HT interface (d < 10 nm) or couples to far-field radiation farther away from the interface (d = 10 - 50 nm) due to strong local field enhancement at the gold nanowire end. For d > 50 nm dipole emission from P3HT is largely unaffected by the presence of the gold nanowire. Radiative decay rate can be enhanced by a factor of up to 7 (d = 10 nm) at the full-wave resonance wavelength of the gold nanowire antenna, while quantum efficiency can be increased by a factor of up to 2.4. This work presents a simple route to fabricate optical nanoemitter/nanoantenna heterostructures with controlled dimensions and composition and with precise placement of the nanoemitter relative to the plasmonic nanoantenna.
10:45 AM - O14.6
Decay-rate Engineering of Silicon Nanocrystals in MOS Waveguides: Toward a Plasmon-enhanced On-chip Light Source for Silicon Photonics.
Aaron Hryciw 1 , Mark Brongersma 1
1 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States
Show AbstractThe absence of a CMOS-compatible on-chip light source capable of high-frequency direct modulation and exhibiting high power efficiency continues to hinder the realization of a monolithic Si photonics technology, despite favorable advances in Si-based waveguides, modulators, and detectors. Attractive candidate light-emitting materials such as silicon nanostructures (e.g., quantum dots, wires) and rare-earth-doped Si nanocomposites—although CMOS compatible—can suffer from long radiative recombination lifetimes and low internal quantum efficiencies. However, by placing the emitters within a sufficiently thin dielectric layer of a planar metal–oxide–semiconductor (MOS) structure, semi-classical spontaneous emission rate calculations predict substantial radiative rate enhancements across a broad, non-resonant wavelength range, with a concomitant increase in internal quantum efficiency, due to the large density of optical states afforded by coupling to propagating surface plasmon polariton (SPP) modes. While the MOS architecture has been well-characterized as regards its electrical properties, its intrinsic photonic behavior has so far been largely overlooked. To evaluate the MOS structure thus as a photonic component, we use time-resolved photoluminescence (PL) spectroscopy of a 20-nm-thick oxide film containing silicon nanocrystals (Si NCs) incorporated into a planar Ag/Si NC/Si geometry. At the peak Si-NC PL wavelength of 743 nm, we observe a 70× increase in the total decay rate compared with a film on a quartz substrate. We also model the behavior of emitters in a Ag/SiO2/Si/SiO2 structure, in which the emission exhibits strong preferential coupling to a single well-defined Si waveguide mode, as well as radiative rate enhancement similar to the MOS case. We therefore propose a new class of power-efficient, high-modulation-speed, CMOS-compatible optical sources based on this effect, exploiting both the excellent electrical properties and plasmon-enhanced optical properties of MOS devices.
O15: Exciton-plasmon Systems and Surface-enhanced Raman Scattering
Session Chairs
Thursday PM, December 03, 2009
Back Bay B (Sheraton)
11:30 AM - O15.1
Gap Plasmon Coupled Light Emission of Semiconductor Quantum Dots in Metal Nanoslits.
Young Chul Jun 1 , Ragip Pala 1 , Mark Brongersma 1
1 Geballe Laboratory for Advanced Materials, Stanford university, Stanford, California, United States
Show AbstractA metal-dielectric-metal (MDM) structure with a nanoscale gap supports highly confined surface plasmon modes (called gap plasmons). The spontaneous light emission (SE) in such a metal nanogap is expected to be strongly modified due to coupling to gap plasmons. We investigate the light emission properties of semiconductor quantum dots (QD) in a metal nanoslit, which is a lateral MDM structure that provides a natural way for light coupling into and out-of a nanoscale gap. We measure lifetime and polarization of the out-coupled QD emission from a metal nanoslit. We observe clear lifetime and polarization changes of QD emission. As the slit width gets smaller, the QD exciton lifetime gradually decreases and its emission becomes polarized normal to the slit, as expected for gap plasmon coupled light emission. We also find that the polarization of the collected QD emission is flipped (i.e. becomes parallel to a slit), when emitters are excited just outside of the slit. We have conducted dipole emission calculations in metal nanoslits, and these explain the experimentally observed lifetime and polarization changes well. We further analyze the effect of a finite metal film thickness. While reflections from slit terminations cause a MDM resonance peak of the SE rate at a certain metal thickness, the SE rate is also strongly enhanced in a very thin metal layer limit, due to the enhanced waveguide mode excitations along a slit groove. This thickness dependence suggests that we can control QD light emission direction as well as its SE rate in a metal nanoslit, via optimizing metal film thicknesses. The enhanced SE rate can result in the enhancement of an emitter quantum efficiency and response time, and it may have applications in nanoscale optical sources and sensors. Because a nanoslit is also ideal for applying the electric field across the slit and isolating single emitters, it may be useful for electro-optic active devices, single QD spectroscopy, and a variety of quantum optics experiments.
11:45 AM - O15.2
Dynamic Control of Plasmon-exciton Coupling in Au Nanodisk–J-aggregate Hybrid Nanostructure Arrays.
Yue Bing Zheng 1 , Bala Krishna Juluri 1 , Linlin Jensen 1 , Lasse Jensen 1 , Tony Jun Huang 1
1 , The Pennsylvania State University, State College, Pennsylvania, United States
Show AbstractWe report the formation of plasmon-exciton states with dynamic in-situ control of the coupling strength in Au nanodisk arrays surrounded by J-aggregate molecules. The angle-resolved spectra of an array of bare Au nanodisks exhibit continuous shifting of localized surface plasmon resonances. This characteristic enables the production of real-time, controllable spectral overlaps between molecular and plasmonic resonances and thus the efficient measurements of the plasmon-exciton coupling as a function of wavelength without the need to fabricate new nanopartice arrays for individual wavelengths. Experimental observations of varying resonant coupling strength due to the incident angle of probe light match with coupled dipole approximation calculations.
12:00 PM - O15.3
Bacterial SERS Sensing Using Aperiodic Plasmonic Nanogalaxies.
Ashwin Gopinath 1 , Svetlana Boriskina 1 , Luca Dal Negro 1
1 ECE, Boston University, Boston, Massachusetts, United States
Show AbstractThe accurate and reproducible control of intense electromagnetic fields localized on the nanoscale is essential for the engineering of optical sensors based on the Surface Enhanced Raman Scattering (SERS) effect. In this work, SERS substrates consisting of periodic and aperiodic arrays of electromagnetically coupled Au nanoparticles were fabricated using electron beam lithography (EBL). The Raman enhancement factors for the periodic and aperiodic nanoparticle arrays with controlled inter-particle separations ranging from 20nm to 100nm were experimentally measured using pMA (p-mercapto aniline) molecular monolayers as the SERS reporter and compared with accurate electrodynamical calculations based on the Generalized Mie Theory. Spatially-averaged reproducible SERS enhancement factors of the order of 10^5 and 10^7 have been obtained with DA arrays of Au nano-cylinders and nano-triangles, respectively. The design and optimization rules for SERS detection in aperiodic plasmonic arrays have also been developed experimentally and theoretically resulting in the demonstration of significantly higher SERS signals in the deterministic aperiodic structures than in their periodic counterparts.To obtain even higher field enhancement necessary for measuring SERS spectra of live bacteria, we combine top-down (EBL) and bottom-up (selective in-situ Au reduction) nanofabrication approaches to fabricate novel multi-scale plasmonic nanostructures. These nanostructures, termed “Plasmonic Nanogalaxies”, feature a cascade electromagnetic field enhancement effect leading to experimental demonstration of ~10^8 spatially-averaged, reproducible SERS enhancement. The potential of plasmonic nanogalaxies for bio-sensing applications is demonstrated by acquisition of highly reproducible SERS spectra from E-coli and Staphylococcus bacteria. Our results demonstrate for the first time that lithographic fabrication (assisted by a simple chemical reduction step) of deterministic aperiodic arrays results in SERS enhancement comparable to traditional SERS substrates obtained by chemical synthesis. The perspectives for low-cost wafer-size device scaling using nano-imprint lithography of these novel SERS substrates will also be discussed.
12:15 PM - O15.4
Blinking in the Surface-enhanced Second-harmonic Generation of Rough Silver Films: Implications for Single Molecule SERS.
Nicholas Borys 1 , Manfred Walter 1 , John Lupton 1
1 Physics, University of Utah, Salt Lake City, Utah, United States
Show AbstractRough silver films grown following the Tollens silver mirror reaction are uniquely suited for high resolution single molecule surface-enhanced Raman (SERS) spectroscopy. Using this methodology, we have succeeded in relating over a dozen vibronic modes of a single conjugated polymer chain, as used in organic electronic devices, in combined fluorescence and Raman measurements [1].Silver nanoparticle films also exhibit a variety of remarkable non-linear optical effects, such as white light emission and second harmonic generation. Surprisingly, we find that while the white light continuum emitted from plasmonic hot spots is stable in time, second harmonic generation is not. In fact, the second harmonic radiation from silver films displays blinking reminiscent of the luminescence of single molecules and quantum dots, which we attribute to random fluctuations of the χ(2) tensor. Tempting as it is to relate such fluctuations to temporal variations in single molecule SERS intensity, careful experimentation reveals precisely the opposite: SERS hot spots are spatially anti-correlated with non-linear optical hot spots [2].Although continuum emission from SERS substrates is often viewed as detrimental to spectroscopy, we demonstrate that non-linear light emission from nanoparticle films can serve its own purpose. In a new type of transmission microscopy in which silver nanobeacons serve as broad-band light sources, we succeed in probing the transmission of near-opaque optical materials such as biological photonic crystals [3]. [1] Walter et al. Phys. Rev. Lett. 98, 137401 (2007).[2] Walter et al. J. Am. Chem. Soc. 130, 16830 (2008).[3] Chaudhuri et al. Nano Lett. 9, 952 (2009).
12:30 PM - O15.5
Anomalous Raman Enhancement of Longitudinal Optical Phonons on Ag-nanoparticle-covered GaN and ZnO.
Chih-Yi Liu 1 , Mykhaylo Dvoynenko 2 , Ming-Yu Lai 2 , Tsu-Shin Chan 2 3 , Ya-Rong Lee 2 , Juen-Kai Wang 2 4 , Yuh-Lin Wang 2 5
1 Institute of Innovations and Advanced Studies, National Cheng Kung University, Tainan Taiwan, 2 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan, 3 Department of Chemistry, National Taiwan University, Taipei Taiwan, 4 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 5 Department of Physics, National Taiwan University, Taipei Taiwan
Show AbstractSurface-enhanced Raman scattering (SERS) has been attractive in the past three decades, because it provides potential in utilizing Raman scattering as a diagnostic technique to detect an extremely small quantity of chemical and biological molecules [1]. Understanding and controlling the two enhancement mechanisms (electromagnetic and chemical enhancements) are the most important issues in the development of SERS. A lot of progresses in controlling the electromagnetic enhancement have been used to fabricate delicate SERS substrates with uniformly high Raman enhancement [2]. Although several theoretical models have been proposed to understand the nature of the chemical enhancement mechanism, the corresponding experimental endeavor to identify its origin however lags behind, owing to extremely poor understanding and control in molecular adhesion on the surface of metal nanostructures. In comparison with molecular species that have been commonly used in SERS studies, semiconductors can benefit the investigation of the chemical enhancement because of their well-defined phonon structures, cleanly prepared and characterized metal-semiconductor interfaces, and a vast amount of successful research efforts in metal-semiconductor interfaces. Here, we report a systematic experimental study of SERS on wurtzite-type GaN and ZnO crystalline samples covered by Ag-nanoparticles. The longitudinal optical (LO) phonons, including A1-LO and E1-LO modes, exhibit unusually large Raman enhancing factors in comparison to other phonon modes. The anomaly is interpreted by a proposed model based on a resonant Raman scattering process assisted by metal-induced gap states located at the Ag/GaN and Ag/ZnO interfaces, on the basis of the fact that the interaction strength of electron with LO phonons is much larger than that with other phonons [3]. This study suggests that the enhancing factor of SERS is sensitive to the propagation nature of the corresponding phonon, opening up a new perspective view on the electron-mediated enhanced Raman scattering. [1] K. Kneipp, M. Moskovits, and H. Kneipp, eds. Surface-Enhanced Raman Scattering: Physics and Applications (Springer, Berlin, 2006).[2] H.-H. Wang et al., Adv. Mater. 18, 491 (2006).[3] C. Chen et al., Phys. Rev. B 70, 075316 (2004).
O16: Nanomaterials and Thermal Effects
Session Chairs
Thursday PM, December 03, 2009
Back Bay B (Sheraton)
2:30 PM - O16.1
One-, Two-, and Three-Dimensional Plasmonic and Excitonic Structures Fabricated by Nanoskiving.
Darren Lipomi 1 , Benjamin Wiley 1 , Mikhail Kats 2 , Romain Blanchard 2 , Sung Kang 2 , Joanna Aizenberg 2 1 , Federico Capasso 2 , George Whitesides 1
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractNanoskiving is the re-purposing of the ultramicrotome from a tool that generates thin sections for electron microscopy to a tool that fabricates nanostructures. This paper describes the use of nanoskiving to produce one-, two-, and three-dimensional nanostructures for photonic applications. An ultramicrotome equipped with a diamond knife can section patterned or stacked thin films embedded in a polymeric matrix into structures as thin as 30 nm. After sectioning, the structures remain embedded in a polymeric slab—a macroscopic object that can be manipulated by hand or with magnetic forces and placed on arbitrary substrates. We describe three applications of nanoskiving: (1D) the fabrication of single-crystalline Au plasmonic waveguides by sectioning chemically synthesized Au microplates; (2D) the fabrication of metallic split-ring resonators by sectioning metalized epoxy posts molded by soft lithography; and (3D) the fabrication of a heterojunction of conjugated polymers for photovoltaics by sectioning a laminated film of electron-donating and electron-accepting materials.
2:45 PM - O16.2
Surface Plasmon Enhanced Radiative Decay Engineering of Direct Bandgap in Ion-implanted Polarized Silicon Quantum Dots.
A. Singh 1 , K. Gryczynski 1 , M. Dhoubadel 1 , B. Rout 1 , F. McDaniel 1 , A. Neogi 1
1 , University of North Texas, Denton, Texas, United States
Show AbstractSi nanocrystal (NC) in SiO2 matrix normally exhibit quasi-direct interband transitions due to band mixing of direct and indirect gaps in a nanoscale environment. Compared to direct bandgap III-V or II-VI semiconductor nano-particles, the radiative recombination coefficient of Si is rather low at room temperature B ≈ 1e-14 cc/s. Therefore, even considering the defect mediated recombination and Auger assisted non-radiative transitions to be suppressed due to spatial localization of carriers in Si nanoparticles, the electron-hole recombination lifetime is observed to be in the range of ms to microsecond. Ion implantation provides a route for synthesis of Silicon based nanocrystals for VLSI compatible nanophotonic emitters. Crystalline silicon quantum dots have been synthesized in an amorphous Silicon matrix using implantation of keV Ag ions. For studying the effect of surface plasmon polariton on the exciton dissociation, we compare the emission from quantum dots synthesized by Si ion induced implantation. High resolution transmission electron microscopy shows quantum dots of 2 nm which emits at 3.3 eV at room temperature with a linewidth of 40-60 meV. The broad emission spectrum shows fine structure at low temperature due to contribution from the confined excitons as well as the interface states of the quantum dots. The recombination of carriers in Si quantum dot is mediated by transverse optical phonon due to the polarization of the surface of the quantum dots. The low energy side of emission spectrum at low temperature is dominated by Ist and 2nd order phonon replica showing the high quality of the quantum dots. Quantum confined emission in the ultraviolet region can be enhanced at room temperature due to exciton plasmon coupling induced by the Ag induced surface plasmon polaritons at the surface of the quantum dots.The modification of the surface recombination rate due to the silver plasmons is estimated from the Purcell enhancement factor. The Purcell factor is obtained from the ratio of the luminescence decay time in the absence and presence of silver ion implantation. The enhancement in luminescence due to implantation of silver ions at the ground state of the confined exciton transition is observed to be four. The recombination life time of the electron-hole pair as estimated from the time resolved PL measurement changes from ~ 2 ns to 400 ps in the presence of silver ion induced surface plasmon polariton. This is the first report of sub-nanosecond recombination dynamics in silicon quantum dots which can be further modified by resonant surface plasmon coupling.
3:00 PM - O16.3
Nanoscale Thermal Imaging of Optically-Excited Nanostructures on AlGaN Doped with Erbium.
Hugh Richardson 1 , Alexander Govorov 2 , Michael Carlson 1 , Pedro Hernandez 2
1 Chemistry and Biochemistry, Ohio University, Athens, Ohio, United States, 2 Physics and Astronomy, Ohio University, Athens, Ohio, United States
Show AbstractUnderstanding heat transfer at the nanoscale is essential to predict and control the thermal energy balance in nanodevices and other nanostructures. As device dimensions continue to be reduced and number densities increase, heat dissipation becomes an increasingly serious problem. We have recently shown that a single isolated metal nanoparticle can generate sufficient heat upon irradiation to induce readily observable phase changes in ice and water1-4. The amount of phase change can serve as the basis for sensitive nanocalorimetry experiment in which the temperature profile around a nanoparticle heat source can be measured as a function of optical energy input. We extend our nanocalorimetry experiments by constructing a sensitive nanoscale thermometer made from the photoluminescence properties of Erbium doped in AlGaN. This thermometer can be used to image the temperature profile around optically-excited nanostructures. First we immobilized gold nanoparticles, single-walled carbon nanotubes, or CdSe/ZnS quantum dots on a AlGaN surface and characterized them with confocal Raman, photoluminescence and dark-field microscopy. The nanostructures have also been characterized externally with atomic force microscopy and then located with photoluminescence and dark-field microscopy. Once the single NP complexes are located, a temperature image around the NP complex during optical excitation is collected by measuring the relative intensities of the Erbium photoluminescence. The relative intensities of the photoluminescent peaks from Er3+ ions in the AlGaN matrix depend upon temperature, and we use this temperature dependence to measure the nanoscale surface temperature around the nanostructures. The temperature images are then compared to theoretical calculations to determine a quantitative measure of the amount of heat generation. 1.Richardson, H. H.; Hickman, Z. N.; Govorov, A. O.; Thomas, A. C.; Zhang, W.; Kordesch, M. E. Nano Letters 2006, 6, (4), 783-788.2.Richardson, H. H.; Thomas, A. C.; Carlson, M. T.; Kordesch, M. E.; Govorov, A. O. Journal Of Electronic Materials 2007, 36, (12), 1587-1593.3.Govorov, A. O.; Zhang, W.; Skeini, T.; Richardson, H.; Lee, J.; Kotov, N. A. Nanoscale Research Letters 2006, 1, (1), 84-90.4.Govorov, A. O.; Richardson, H. H. Nano Today 2007, 2, (1), 30-38.
3:15 PM - O16.4
Photothermal Measurements in Photo-Excited Nanoparticles.
Shin Chou 1 , Hyeong Gon Kang 1 , Matthew Clarke 1 , Jeeseong Hwang 1
1 Optical Technologies Division, Physics Laboratory, NIST, Gaithersburg, Maryland, United States
Show AbstractIn this study, we present an optical metrology developed to measure the spatial distribution of heat dissipation from photo-excited plasmonic nanoparticles embedded in polymer matrix at the single particle level, using photothermal heterodyne imagine technique and optical spectroscopy. The thermal distribution around the photo-excited nanoparticles is probed using a combination of Raman microscopy and ratiometric imaging. The physical insight gained by the study allows a better heat transfer model to be built for a localized heat source embedded in complex media. The optical metrology also enables detailed studies of localized, heat activated biological and chemical reactions.
3:30 PM - O16.5
Size Dependent Joule Heating of Gold Nanoparticles and Nanoshells Using Shortwave Radiofrequency Fields.
Paul Cherukuri 1 2
1 , The University of Texas MD Anderson Cancer Center, Houston, Texas, United States, 2 , Rice University, Houston, Texas, United States
Show AbstractCapacitively coupled RF fields (13.56 MHz) rapidly heat low concentrations (~1 ppm) of gold nanoparticles with a thermal power dissipation of ~380 kW/g of gold. We have found that smaller diameter gold nanoparticles (< 50 nm) heat at nearly twice the rate of larger diameter gold (≥50 nm). This size dependence is attributed to the higher resistivity of smaller metallic nanostructures. A Joule heating model has been developed which should provide critical insights into the rational design and engineering of nanoscale metals for noninvasive thermal elimination of cancer.
3:45 PM - O16.6
Theromophotovoltaic Enhancement: 2D Photonic Crystals to Increase TPV Efficiencies.
Corey Shemelya 1 , Dante DeMeo 1 , Thomas Vandervelde 1
1 Electrical Engineering , Tufts University, Medford , Massachusetts, United States
Show AbstractFor many years researchers have attempted to efficiently harvest waste heat and transform it into a usable energy via thermophotovoltics (TPVs). The low quantum efficiency (QE; i.e. the probability that a photon will be absorbed) in most TPV cells is probably the biggest limiting factor in achieving an economically viable device and directly affects the conversion efficiency (CE; i.e. the probability that a photon will be converted into a carrier that is collected). In many cases, top of the line TPV cells might only have a CE of 20%. Recent advances in micro-/nano-fabrication techniques have enabled the creation of novel structures to enhance the absorption and, therefore, the conversion of the incident thermal photons. In particular, photonic crystals (PhC) and surface plasmon (SP) interface enhancements have been shown to increase the efficiency of photon to current conversions for infrared photodetectors. Here, we report on the enhancement of photon conversion by integration of PhC and SP structures into the TPV cells. To this end, photonic crystals consisting of rods of either air or dielectric surface-passivation material are placed into the base semiconductor TPV cells to increase duration of thermal photon absorption, resulting in significantly enhanced QE and CE. The use of photonic crystals in augmenting the conversion efficiency of TPV cells is applicable for most IR wavelengths, making this a widely useful technology. The ability to harvest waste heat for energy will help make many processes and/or systems more energy efficient, which will be a critical component in ushering to USA into an era of energy independence.
4:00 PM - O16: HSTE
Break
O17: Plasmons in Nanostructures I
Session Chairs
Thursday PM, December 03, 2009
Back Bay B (Sheraton)
4:15 PM - **O17.1
Quantum Description of Plasmons in Strongly Coupled Nanostructures.
Peter Nordlander 1
1 Physics, Rice University, Houston, Texas, United States
Show AbstractThe optical properties of closely coupled plasmonic or excitonic nanoparticles depend strongly on nanoparticle shape and separation. For excitonic particles coupled to plasmonic particles, bonding and antibonding resonances (Plexcitons) are formed with energies that can depend sensitively on the coupling strength and detuning of the individual resonances.[1] In plasmonic dimers, the couplings between adjacent nanoparticles can induce extraordinary large electric field enhancements in the junctions between the particles of relevance for surface enhanced spectroscopies. For an accurate description of the optical response of closely spaced nanoparticles it is necessary to include quantum mechanical effects such as electron tunneling between the particles and screening due to the finite electron density in the junction. In his talk a fully quantum mechanical investigation of the plasmonic response of two coupled metallic nanoparticles as a function of interparticle separation is presented.[2] We identify three distinct regimes of interaction. In the classical regime for separations larger than 1 nm, the nanoparticles remain neutral and the plasmonic response is well described using classical theory. In the cross-over regime for separations between 0.5 and 1nm, electrons begin to tunnel between the nanoparticles and a reduction of the plasmonic couplings and field enhancements result. In the conductive regime for separations smaller than 0.5nm, a large conductive overlap is established between the two particles and a Charge Transfer Plasmon (CTP) emerges.[3,4] [1] N.T. Fofang, T.-H. Park, O. Neumann, N.A. Mirin, P. Nordlander, and N.J. Halas, Nano Lett. 8(2008)3481[2] J. Zuloaga, E. Prodan, and P. Nordlander, Nano Lett. 9(2009)887[3] J.B. Lassiter et al., Nano Lett. 8(2008)1812[4] D.R. Ward et al., Nano Lett. 8(2008)919
4:45 PM - O17.2
Single Plasmonic Nanocavities with Designed Subradiant, Superradiant, and Fano-type Modes.
Yannick Sonnefraud 1 , Niels Verellen 2 3 , Heidar Sobhani 4 , Feng Hao 4 , Victor Moshchalkov 3 , Pol Van Dorpe 2 , Peter Nordlander 4 , Stefan Maier 1
1 Physics Department, Imperial College, London United Kingdom, 2 , IMEC, Leuven Belgium, 3 INPAC-Institute for Nanoscale Physics and Chemistry, K.U. Leuven, Leuven Belgium, 4 Department of Physics and Astronomy, Rice University, Houston, Texas, United States
Show AbstractPlasmonic nanocavities constitute classical physical oscillator systems on the nanoscale. In this talk we show that control over plasmon lineshapes is possible in a cavity consisting of a concentric arrangement of a disk and a ring. Hybridization of the parent dipolar plasmon modes leads to the emergence of sub- and superradiant modes. Breaking the symmetry of the structure further leads to the appearance of Fano resonances within the superradiant lineshape. Such coherent processes can be employed for plasmonic lineshape design to tailor light/matter interactions, particularly in a context of optical sensing. Investigations of single cavities using supercontinuum confocal spectroscopy confirms our theoretical modelling, and lead to proof-of-concept sensing studies.
5:00 PM - O17.3
Mapping the Dispersion Relation and Emission Rates of Isolated Plasmonic Coaxial Waveguide Resonators.
Stanley Burgos 1 , Rene De Waele 2 , Albert Polman 2 , Harry Atwater 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States, 2 Center of Nanophotonics, AMOLF, Amsterdam Netherlands
Show AbstractPlasmonic coaxial resonators are attractive as ultrasmall resonators for dispersion engineering and enhancement of spontaneous emission since they support modes with extremely small volumes (~ 0.001 cubic microns) and have polarization independent and angle-insensitive in-coupling characteristics. We have experimentally mapped the dispersion relations of isolated coaxial waveguides by comparing transmission measurements of variable length coaxial structures with the analytically calculated dispersion relation of an infinitely long coaxial waveguide of the same average cross-sectional dimensions. The isolated coaxial structures considered here consist of ~300 nm diameter ~20 and ~100 nm thick annular channels FIB milled onto an Ag film, ranging from 250-500 nm in thickness, evaporated over a quartz slide. Transmission measurements were done in the frequency spectrum ranging from 400-1100 nm for both air and spin-on-glass in-filled coaxial channel structures. In transmission, we observe resonance peaks that red-shift with increasing coax length – a characteristic attributed to the Fabry Perot resonances within the coaxial waveguide. By fitting the freespace wavelength corresponding to the transmission peak maximum for a given coax length, we were able to fit standing surface plasmon waveguide modes to a given coax length, allowing us to plot them as discrete points onto an omega-k dispersion plot. Next, we analytically calculated the dispersion relation of an infinitely long equal cross-sectional dimension coaxial structure by solving Maxwell’s equations for a three-layer metal-insulator-metal system in cylindrical coordinates. By considering the lowest order linearly polarized modes of the coaxial structure, we are able to map the discrete measured transmission dispersion points directly onto the dispersion relation of the infinitely long coaxial structure. Finally, we also explore enhancement of spontaneous emission rates in these subwavelength coaxial resonators by experimentally measuring the radiative emission rate and Q/V (quality factor/mode volume) by infilling the coaxial channels with CdSe quantum dots whose emission wavelength corresponds to the transmission resonance wavelength of a given length coaxial structure and measuring photoluminescence decay rates.
5:15 PM - O17.4
From Plasmonic Disk Resonators to Coupled Nanoparticles.
Martin Kuttge 1 , Javier Garcia de Abajo 2 , Albert Polman 1
1 Center for Nanophotonics, FOM-Institute AMOLF, Amsterdam Netherlands, 2 Instituto de Óptica, CSIC, Madrid Spain
Show AbstractConfining electromagnetic energy in metal-insulator-metal MIM structures using plasmons has raised a lot of interest in the field of plasmonics. While the limit of the insulator layer thickness has been explored, the in-plane confinement of MIM plasmons has not been studied in detail. We present a detailed study, based on experiment and calculations, of nanoscale disk resonator cavities for MIM plasmons. For large disks we find multiple modes similar to dielectric disk resonators, for small resonators only a single mode is found which resembles the mode found for coupled metal nanoparticles.Multilayer films consisting of 100nm silver, 10 or 50nm silica, and 100nm silver were deposited on silicon substrates. The layers were capped with a 10nm chromium layer to damp out surface plasmons propagating on the outer silver interface. We used focussed-ion-beam milling to structure disk resonators into the stack by milling away 1mu wide rings. MIM plasmons were then excited inside the disk cavities using the 30 keV electron beam of a scanning electron microscope. By detecting the optical radiation in the far field, we were able to determine spatially and spectrally resolved plasmonic eigenmodes inside the disk resonators. For large disks with a diameter of 2mu and a silica layer thickness of 50nm the spatially resolved CL signal shows a periodic modulation as a function of radial position. From the integrated spectrum a multitude of modes are observed with peaks in the spectrum. We have successfully assigned radial and azimuthal mode numbers to the resonances using a model for dielectric disk resonators using the effective mode index of the MIM mode. We find radial mode numbers up to n=8 and azimuthal mode numbers up to m=2. Calculations of the CL emission spectrum using a boundary element method to solve Maxwell's equations are in good agreement with measurements. The calculated CL emission patterns at the resonance wavelengths show the symmetry as expected from the determined mode numbers.If the disk diameter is reduced below 150nm only a single mode is observed in the CL measurements for MIM structures with 10nm silica layer thickness. The mode shifts to shorter wavelength for decreasing disk diameter and can be identified as a (1,1) mode. The measured spectra are similar to coupled nanoparticles spaced by a thin silica layer. Additional calculations of the near-field pattern show that for small resonator sizes a transition from dielectric-like disk resonators towards the regime of coupled metal nanoparticles takes place.
5:30 PM - O17.5
Study of Point Spread Function in Double Negative Metamaterial.
Jun Xu 1 , Hyungjin Ma 2 , Nicholas Fang 1
1 Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show Abstract A Metal(Ag)-dielectric(Si)-metal(Ag) “fishnet” structure which has double negative property in near IR range was demonstrated as a good candidate of optical modulator in high speed optical communication. The image resolution study of the fishnet structure will point out the spatial limitation of multi-channel modulator. In this report, we studied the point spread function(PSF) in a fishnet modulator theoretically and experimentally. The broadening of probe and pump signal (modulation beam) originating from a 900nm x 900nm rectangular aperture upon passing through the fishnet modulator was simulated and measured. The estimated FWHMs of PSF in simulation and experiment were 2.9um and 6.95um, respectively. Assuming that the input beam has a width of 5um, widths of output beam become 5.8um and 8.9um, respectively. Therefore, the minimum size of the individual fishnet modulator or channel can be as small as 4~6 times of probe wavelength. In a theoretical study, since the dimensions of Ag-Si-Ag fishnet structure are small compared to the wavelength, it can be treated as a homogeneous medium. A slab of negative index material (NIM) with effective permittivity and permeability is used in the simulation. Also, since our actual configuration for the measurements used a finite sized aperture rather than an ideal point source, we have performed full wave simulations with a finite aperture size and then extract the PSF from the result by assuming Gaussian profile for both beam and aperture. At the negative refraction index region (the index of the fishnet structure is assumed to be -1.26 +0.95i by reference), the simulated FWHM of line profile was 670nm, which demonstrated the focusing effect of NIM. Interestingly, we observed a broadening of line profile when index reaches zero even compared to the off-resonance case where index is positive. The estimated FWHM of PSF at 1550nm was 2.9um, which is almost 2 times larger than the wavelength when the FWHM for off-resonance wavelength is maintained at around half of the wavelength. Experimentally, near-field scanning optical microscope(NSOM) was employed to measure the PSF of light transmitting through the aperture. The measurements were done at both visible (off-resonance) and IR (on-resonance) wavelengths. At off-resonance wavelength, FWHM of the beam is around 1.4um which is calculated from the measured data with the assumption of Gaussian profile of beam and aperture. Also, at the resonance wavelength, we have performed the measurements with two different polarizations. Here one polarization excites the fishnet mode while the other one cannot and serves as a control experiment. As expected from the simulation, we clearly see the beam broadening when exciting the fishnet mode (when E-field is along the thinner wire). The calculated FWHMs of PSF for each case are 3.4um and 6.9um, respectively.
O18: Poster Session: Plasmons and Excitons: Applications
Session Chairs
Friday AM, December 04, 2009
Exhibit Hall D (Hynes)
9:00 PM - O18.1
SERS in Hierarchical Structures of Au Formed using Templates by Site-controlled Tunnel Etching of Al.
Toshiaki Kondo 2 , Tatsuro Fukushima 1 , Kazuyuki Nishio 1 2 , Hideki Masuda 1 2
2 , KAST, Sagamihara Japan, 1 , Tokyo Metropolitan Univ., Hachioji Japan
Show AbstractThe fabrication of ordered fine structures of noble metals has attracted much interest because of their utilization as various types of functional optical devices based on localized surface plasmon (LSP). To optimize the performance of the obtained optical devices, the achievement of accurately controlled geometrical structures of noble metals is essential. When compared with two-dimensional (2D) metal structures, three-dimensional (3D) structures are advantageous for enhancing the efficiency of nonlinear optical effects owing to their large surface area. To fabricate 3D structures that are effective for enhancing the electric field, it is necessary to increase the surface area without decreasing the degree of ordering of the structures. A hierarchical structure composed of ordered units with different dimensions is promising for effectively enhancing the electric field of incident light, because it has both a precisely controlled fine structure and a large surface area. In the present report, we describe the fabrication of hierarchical structures of Au composed of micrometer-scale quadrangular prisms and a nanometer-scale fine pillar array. Such structures were prepared using a template formed by the site-controlled tunnel etching of Al and its subsequent anodization and the electrodeposition of Au. After the preparation of the 3D Au structure, the SERS properties of pyridine were examined. The process described in the present work enables the preparation of highly ordered fine metal structures with a high surface area that are expected to be used for various types of functional optical devices based on LSP.
9:00 PM - O18.10
Surface Plasmon-enhanced Raman Scattering on Gold-coated Biogenic Silica.
Anna Zarow 1 , Kai-Chun Lin 2 , B. Ramakrishna 2 , Zafar Iqbal 1
1 Chemistry, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 School of Materials, Arizona State University, Tempe, Arizona, United States
Show AbstractBiogenic silica derived from diatoms possess several unique properties including, highly ordered porous hierarchical nanostructures that facilitate transport, the ability to undergo a variety of surface modifications through well-established chemistries for the tethering of molecular species and flexibility of design through the availability of a variety of shapes, sizes, and symmetries, from more than a 100,000 species of diatoms. In addition, micro- and meso-pores provide size and/or shape selectivity for a guest molecule, while macropores reduce transport limitations.Surface-plasmon enhanced Raman scattering from the ionic energetic compound ammonium nitrate and organics, such Rhodamine 6G dye, have been carried out after deposition from solutions on gold coated biogenic silica. While enhanced Raman detection is observed down to 10-6 M concentrations of Rhodamine 6G in water and alcohol, only small enhancements of the Raman signal are seen for ammonium nitrate. However, it is observed that the Raman line frequencies in ammonium nitrate are shifted to different values (relative to bulk crystals) on adsorption on the gold-coated diatoms. Details of these results with respect to surface-enhanced Raman scattering on these novel biogenic substrates will be discussed.
9:00 PM - O18.11
Organic Emitter-plasmon Coupling in a Thin Film using Thermally-evaporated Ag Nanocluster Layer and its Application to Organic Light-emitting Devices.
Ki Youl Yang 1 , Kyung Cheol Choi 1 , Chi Won Ahn 2
1 Department of Electrical Engineering and Computer Science, KAIST, Daejeon Korea (the Republic of), 2 , National Nanofab Center, Daejeon Korea (the Republic of)
Show AbstractIn line with the recent trend of various metal/ dielectric interfacial nano-structures being used as light radiators, which convert surface plasmon (SP) waves into radiative emission, to reduce energy loss from SP-related heat dissipation [1-3], we study the effect of insertion of an LiF-capped Ag cluster layer on the photoluminescence characteristics of organic emitter based on tris-(8-hydrooxyquinolinato) aluminum (Alq3); Ag clusters were thermally deposited on a 2-nm-thick LiF layer, which is an interfacial layer between the organic layer and the Al cathode layer. While a large portion of the SP excitation energy is coupled to the nonpropagating evanescent wave, as opposed to direct emission in the plane metal/ dielectric interface, a few tens of nanometer-sized metal clusters can cause the light to scatter, lose momentum, and become coupled to light radiation [4]; metal nanoclusters in an organic light-emitting device (OLED) structure increase the spontaneous emission rate of the organic emitter, and the photoluminescence efficiency. Experimental results show that the insertion of a thermally evaporated Ag cluster layer between the organic layer and the Al cathode layer renders continuous wave photoluminescence intensity of the Alq3 layer, a significant 3.5-fold improvement over that of Ag cluster-deficient organic emitters [5]. Time-resolved photoluminescence results consistently indicate that the Alq3 layer coupled with the Ag cluster layers have a higher spontaneous emission rate than those without the LiF-Ag cluster-LiF interfacial layer; as the SP resonance wavelengths become closer to the wavelength of the organic emitter, continuous wave photoluminescence intensity and exciton lifetime become greater and shorter. Such differences in photoluminescence behavior are discussed such that Ag nanoclusters, which are the resonators of SPs, not only shorten the spontaneous emission rate of the organic emitter, but also convert a large portion of the excitation energy into light radiation. Moreover, the Ag nanocluster layer overcomes the large contact barrier between the organic layer and the LiF/ Al cathode layer, by minimizing the conduction area. Finally, we demonstrate the feasibility of the Ag nanocluster layer by presenting Ag nanocluster deposited OLEDs that employ a multilayer electrode in which the Ag nanocluster layer plays a key role in terms of both optical and electrical characteristics.[1] K. Okamoto, I. Niki, A. Shvartser, Y. Narukawa, T. Mukai, and A. Scherer, Nat. Mat. 3, 601 (2004).[2] T. D. Neal, K. Okamoto, and A. Scherer, Opt. Express 13, 5522 (2005).[3] M. K. Kwon, J. Y. Kim, B. H. Kim, I. K. Park, C. Y. Cho, C. C. Byeon, and S. J. Park, Adv. Mater. 20, 1253 (2008).[4] K. Okamoto, I. Niki, A. Schrer, Y. Narukawa, T. Mukai, and Y. Kawakami, Appl. Phys. Lett. 87, 071102 (2005).[5] K. Y. Yang, K. C. Choi, C. W. Ahn, Appl. Phys. Lett., 94, 173301 (2009).
9:00 PM - O18.12
Grating Coupled Surface Plasmon Resonance Enhanced Fluorescence and Its Application for Cell Observation.
Xiaoqiang Cui 1 , Keiko Tawa 1 , Junji Nishii 2
1 Research Institute for Cell Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka Japan, 2 Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka Japan
Show AbstractFluorescence spectroscopy is rapidly becoming a leading methodology in life science and has been widely used in biological and medical research. Improving its sensitivity, to get lower detection limit for analytical and biological science, remains a great challenge. The efforts to do this lead to a new area so called surface enhanced fluorescence (SEF) [1]. Up to now, most of the efforts for surface enhanced fluorescence were focused on metal nanoparticle based localized surface plasmon resonance, in which assembled nanoparticles or deposited nano islands were adopted. However, nanoparticle method is greatly suffering from the poor reproducibility. Propagated surface plasmon resonance (SPR) is another way to get fluorescence enhancement. In this strategy, the Kretschmann geometry was used to get prism-coupled SPR by attenuated total internal reflection setup. However, complicated optical setups such as prism and a large resonance angle around 60 degree at 630nm wavelength in water ambience are barrier in the view of utilizing a commercial microscope. Fluorescence excited by the electric field of grating-coupled surface plasmon resonance (GC-SPR), which can be obtained at grating surface on the same side of the incident light, becomes an ideal candidate to upright fluorescence microscopic observation. By adjusting the grating pitch, the coupling between surface plasmon polaritons (SPP) and radiation for excitation was obtained at a quite small incident angle, which will greatly benefit the observation of fluorescence under microscope without high numerical aperture (NA) objective lens. In this work, surface relief gratings with 400 nm pitch were fabricated and applied for enhanced fluorescence detection and microscopic observation [2]. Investigation of the effect of grating depth and its duty ratio on the fluorescence intensity showed that a 40-times enhanced fluorescence was obtained under optimal condition of 20nm-depth and 0.43-duty ratio. The observation of dye-labeled transfected cells exemplified that this facile grating substrate has the potential for application to highly sensitive fluorescence microscopy using general epi-fluorescence microscope without any additional accessories .Reference1.E. Fort and S. Gresillon, J. Phys. D: Appl. Phys., 41, 0313001 (2008).2.K. Tawa, H. Hori, K. Kintaka, K. Kiyosue, Y. Tatsu and J. Nishii, Opt. Express, 16, 9781 (2008)
9:00 PM - O18.13
Surface Plasmon Enhanced Photoluminescence from Silver Nanoparticles.
Anatoliy Pinchuk 1 , Oleg Yeshchenko 2 , Igor Dmitruk 2 , Alexandr Alexeenko 3 , Andriy Kotko 4
1 Physics and Energy, University of Colorado at Colorado Springs, Colorado Springs, Colorado, United States, 2 Physics, National Taras Shevchenko Kyiv University, Kyiv Ukraine, 3 , Gomel State Technical University, Gomel Belarus, 4 , Frantsevich Institute for Problems of Materials Science , Kyiv Ukraine
Show AbstractWe report the size dependence of the photoluminescence spectra from silver nanoparticles embedded in a silica host medium. The quantum yield of the photoluminescence increased when the size of the nanoparticles was decreased. The quantum yield for 8 nm silver nanoparticle was estimated to be on the order of 10^-2 which is 10^8 times higher than the one observed for bulk silver. The two photoluminescence bands observed from silver nanoparticles were rationalized as the radiative electron interband transitions and radiative decay of the surface plasmons in silver nanoparticles. The strong local electric field induced by the surface plasmon resonance in silver nanoparticles enhances the exciting and emitted photons and increases the quantum yield of the photoluminescence.
9:00 PM - O18.14
Nanoscale Temperature Imaging of Gold Nanoparticles Using Optical Properties of Rare-Earth Metals.
Michael Carlson 1 , Hugh Richardson 1 , Pedro Hernandez 2 , Alexander Govorov 2
1 Chemistry and Biochemistry, Ohio University, Athens, Ohio, United States, 2 Physics and Astronomy, Ohio University, Athens, Ohio, United States
Show AbstractNanoparticle research has gained considerable momentum over the past few years, particularly within the realm of heat generation of metal and semiconducting nanocrystals under optical illumination. As the fields of science and technology approach smaller and smaller size scales, it becomes increasingly vital to fully understand the heating effects at the nanoscale. For the continued construction and success of nanodevices and nanostructures, thermal transport and heat dissipation on a single-particle level must be fully characterized. Our current work focuses on studying the nanoscale heating effects of single gold nanoparticles optically excited at their plasmon resonance frequency. We have developed a novel nanoscale temperature sensor using erbium ions in a III-V semiconductor thin film host matrix on a silicon substrate to study the resulting temperature gradient surrounding the optically excited metal nanoparticle. The relative intensities from the photoluminescence peaks of the Er3+ ions are used to create a temperature map with high spatial resolution of the nanoparticles on the thin film. A linear temperature profile across the nanoparticle was constructed with a resulting Gaussian line shape. A histogram was constructed of the profile maximum from different nanoparticles, and a wide variability in temperature was observed. Polarization studies were conducted, showing a 10% variation in temperature, which does not account for the large variation observed from the histogram. We believe that changes in the effective dielectric constant for different nanoparticles cause large variability on the local temperature. Theoretical calculations are matched to experiment to determine the microscopic parameters (effective dielectric constant, effective thermal conductivity) of the system.
9:00 PM - O18.15
Transmission Efficiency Across Gaps in a Surface Plasmon Waveguide.
Richard Flynn 1 , Konrad Bussmann 1 , Igor Vurgaftman 1 , Blake Simpkins 1 , Chul Soo Kim 1 , James Long 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractNanoplasmonic circuitry requires the coupling of energy to and from plasmonic waveguides, which presently is accomplished by converting between photons and surface plasmon polaritons (SPPs). One common approach employs end coupling, which may be achieved by co-linearly aligning an optical fiber against the end of a plasmonic guide. One can also imagine plasmonic circuitry where end-coupling conversions among plasmonic modes is desirable, such as in the recently proposed MEMS-based switch which requires plasmon to plasmon coupling across an air gap between stripe waveguides [1]. A gap cut through a planar-film plasmonic guide by a focused ion beam provides a straightforward geometry with which to explore the physics of plasmon to photon to plasmon conversion in plasmonic waveguides.Here we introduce a convenient optical technique that measures SPP energy transmission efficiency across such gaps. Rather than apply a near-field scanning probe technique or a leakage radiation approach, we measure the ratio of far-field radiation emitted by two probe gaps that bracket the gap under test. In optically thick (110 nm) stripe waveguides 5 μm across, we measure transmission values from nearly 100% down to the noise floor of ~5%, for gaps ranging, respectively, from 30 nm to 10 μm wide. Transmission efficiencies of 50% occur for gaps as wide as 2 μm. To our knowledge, this is the first quantitative measurement of SPP coupling across gaps in a waveguide structure as opposed to a planar film structure. Our data exhibits excellent agreement with finite-element simulations of the gap coupling. It is shown that the coupling efficiency cannot be accurately estimated from an overlap integral of the SPP mode and the diffracted wave in the gap, especially for micron-sized gaps.[1] Zhang XM, Zhu WM, Cai H, Liu AQ, MEMS 2008: 21st IEEE International Conference on Micro Electro Mechanical Systems, Technical Digest, 778-781 (2008)
9:00 PM - O18.16
Polarization Tuning of Surface Plasmon Resonance in Metallic Structures using Liquid Crystal.
Masayoshi Ojima 1 , Yasuhiro Ogawa 1 , Naoki Numata 1 , Koji Murata 1 , Yasumasa Fujiwara 1 , Hitoshi Kubo 1 , Hiroyuki Yoshida 1 , Akihiko Fujii 1 , Masanori Ozaki 1
1 Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show AbstractSurface plasmons are transverse magnetic (TM) electromagnetic waves that propagate along to the surface of a metal. They can be excited on metallic surfaces with TM-polarized light by using a prism in the Otto and Kretschmann-Raether configurations or grating configuration. Such excitations of surface plasmons by light are called surface plasmon resonance (SPR). SPR is employed color-based biosensors, since the propagation constant of the SPR depends on the refractive index of the material placed on the metallic surface. Although the application of tunable SPR devices using liquid crystals (LCs) to RGB displays has already been reported, these devices either employ the Kretschmann-Raether configuration or use polymer dispersed LCs. In these previous reports, the tunability of the SPRs was achieved by modulating the refractive index of the material placed on the metallic surface. In this study, we propose another approach to realize the tunability of the SPRs based on the control of the polarization direction of the SPRs. Tunable SPR devices are realized using a grating coupling configuration and a twisted nematic (TN)-LC layer. The metallic grating was fabricated using the photolithography, and 200-nm Au was deposited on it using thermal evaporation. The holographic exposure of grating pattern was realized using a Lloyd-mirror setup with a frequency-tripled Nd:YAG laser system at 355 nm. From the SEM image of the metallic grating structure, the step and space structure having a periodicity of 370 nm were confirmed. The TN-LC layer was formed by placing nematic LC into a sandwiched cell comprising substrates with a metallic grating and a rubbed polymer alignment layer. The dip in reflection spectra due to the SPR appears only in the case of the TE-mode incident light. The polarization direction of the TE-mode incident light is perpendicular to the grating vector at the counter substrate. However it is rotated along the direction of the short axis of the LC. The polarization direction at the surface of the metallic grating is in the same direction of the grating vector; hence, SPR occurred in the case of the TE-mode incident light for the metallic grating with TN-LC. From the applied voltage dependence of the reflection spectra, the SPR depends on the applied voltage. When the electric field was applied normal to the substrate, the LC molecules gradually aligned along the electric field with increasing applied voltage. This is because the rotation of the polarization direction with the TN-LC layer could be controlled by varying the electric field. This TE-mode plasmonic absorption was simulated with FDTD, and the results of the simulation were well agreed well with the experimental results.
9:00 PM - O18.19
Nanoscale Optical Imaging of Au Nano-structure by Using Apertureless Near-field Scanning Optical Microscopy.
Satoshi Takahashi 1 , Yoshihiro Ogawa 1 , Fujio Minami 1 , Kenji Todori 2
1 Department of Physics, Tokyo Institute of Technology, Tokyo Japan, 2 , TOSHIBA, Tokyo Japan
Show AbstractApertureless scanning near-field optical microscopy is an extremely powerful technique capable of 10 nm spatial resolution to probe the local fields around single nanoobjects such as metallic particles [1].In this study, we report tip-enhanced photoluminescence (PL) from a fluorescence film deposited on an Au holographic grating. A 532 nm cw Nd:YAG laser line is used to excite photoluminescence. A notch interference filter is inserted in appropriate place to remove the scattered laser light signal. The PL signals are recorded by an avalanche photo-diode (APD). We attached a single Au nano-particle with the diameter of 100 nm to a commercial AFM tip produced from a single mode glass fiber. A film of tris(8-hydroxyquinoline)aluminium (Alq3) (thickness of 40 nm) were deposited on an Au holographic grating (pitch and height are 560 nm and 100 nm, respectively). By inserting a 600 nm high pass filter in front of the APD, we observed integrated emission signal of the Alq3 film at room temperature. The approach of the tip to the film surface results in a drastic enhancement of the PL signal. The fluorescence intensity is enhanced by a factor of 20-60. The tip and illumination are fixed while the sample is scanned in two directions by piezoelectric elements. We observed the spatial distribution of the local fields on the film with the resolution of 100 nm. When the incidence light filed is parallel (perpendicular) to the grating, the local fields distribute on the top and bottom (slope) of the structure, which is corresponding well to the numerical calculations by the FDTD method.Furthermore, we demonstrate a near-field scattering imaging of Au nanoparticles with the diameter of 80-200 nm on Si substrate by using the tip-enhanced scattering technique with the spatial resolution of 15 nm.This paper belongs to "Innovative nanophotonics components development project" which OITDA contracted with The New Energy and Industrial Technology Development Organization (NEDO) since 2006.[1] Lukas Novotny and Bert Hecht, "Principles of Nano-Optics" (Cambridge University Press, Cambridge, 2006).
9:00 PM - O18.2
Au-Fullerene: A Tunable Localized Surface Plasmonic Nanocomposite Thin Film.
Rahul Singhal 1 , Jean Pivin 2 , Ramesh Chandra 3 , Devesh Avaasthi 1
1 Material Science, Inter University Accelerator Centre, New Delhi, Delhi, India, 2 , CSNSM, IN2P3-CNRS, Orsay France, 3 , IIC, Indian Institute of Technology Roorkee, Roorkee, Uttaranchal, India
Show AbstractCarbon based nanocomposite materials containing noble metal nanoparticles (NPs) have attracted the researchers due to their applications in chemical and biological sensors, optical waveguides, photonic devices and surface enhanced spectroscopies. Fullerene, an allotrope of carbon, is a functional material having applications in various fields such as electronic devices, memory devices, drug delivery, catalysis, coatings and especially in biology due to its biocompatibility. By embedding the Au nanoparticles in fullerenes, the optical properties of noble metal nanoparticles as well as the properties of fullerene co-exist and therefore the dual properties can be effectively used. Noble metal nanoparticles are of interest due to their localized surface plasmon resonance (LSPR) resulting in a strong absorption of light at a particular wavelength in visible region. The transparency of C60 and C70 in the visible region and their immiscibility with noble metals make nanocomposite of fullerenes and noble metals interesting particularly for plasmonic integrated devices. In this work, nanocomposite thin films containing Au nanoparticles in different carbon based matrices such as fullerenes (C60 and C70) and amorphous carbon (a-C) were synthesized by thermal co-evaporation and atom beam co-sputtering techniques respectively. Au with different concentrations (10 to 30 %) was deposited in each case. The metal atomic fraction in the films was quantified by Rutherford Backscattering Spectroscopy. Transmission electron microscopy (TEM) confirms the spherical shape of Au nanoparticles and average size of Au nanoparticles varies from 3 to 6.5 nm. The particle size is also measured by x-ray diffraction (111) peak of Au and was found in good agreement with that of TEM results. The visible absorption measurements reveal that the tuning of LSPR wavelength from 563 to 764 nm is achieved in these nanocomposites, making them very interesting for plasmonic devices.
9:00 PM - O18.20
Surface Plasmon Resonance Responses of Au-SnO2 Nanocomposite Films.
Dongfang Yang 1
1 IMI-London, National Research Council of Canada, London, Ontario, Canada
Show AbstractMetal-dielectric composite thin films formed by noble metal nanoparticles embedded in a dielectric matrix show attractive SPR phenomenon due to collective excitations of conduction electrons in metal nanoparticles when photons are coupled to the metal particle–dielectric interface. SPR responses of those composite thin films have many interesting applications such as surface enhanced spectroscopes, biological and chemical sensing. In this article, Au-SnO2 composite films of various Au content and thickness were prepared by the pulsed laser deposition technique, and their crystal structures, morphology and chemical compositions were evaluated using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and x-ray photoelectron spectroscopy (XPS), respectively. The SPR responses of the composite films of various Au percentage and film thickness were investigated in the Kretschmann geometry of attenuated total reflection using a polarized light beam at 633 nm wavelength. Theoretical calculation of SPR responses based on Bruggeman or Maxwell-Garnett models with MacLeod general characteristic matrix method was compared with experimental measurement. The simulated results are able to predict the trend on the dependence of SPR responses with Au content and thickness of Au-SnO2 films although obvious discrepancies with experimental measurements existed. The potential of using the SPR responses of Au-SnO2 composite films for gas sensing was also discussed.
9:00 PM - O18.21
Dynamic Hot Spots: Magnetically Controllable Plasmonic Nanoparticles.
Lily Kim 1 , Sung-Eun Choi 1 , Sunghoon Kwon 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show Abstract Nanoparticles, consisting of a dielectric core and a metallic shell of nanometer thickness have remarkable optical properties. Although the plasmon coupling properties of gold and silver nanoparticles have been extensively studied, formation of metal nanoparticle pairs and control of interparticle spacing are still very difficult. To overcome the problems, we developed magnetically tunable plasmonic nanoparticles by synthesizing superparamagnetic core/metal nanoshell structured materials and studied their optical properties. The average diameter of magnetic core, Fe3O4/silica nanoparticles was 120 ± 10 nm and the thicknesses of gold and silver nanoshells were varied from 5 to 30 nm. The monodisperse magnetic core/metal nanoshell colloids were aligned and formed magnetic particle chains when a magnetic field was applied. Plasmon couplings of metal nanoshells in a particle chain were monitored by a dark-field microscope. Some scattering particles changed colors due to particle chain formation by a magnetic field. The particle chains disappeared and colors were recovered when a magnetic field was removed. The plasmon coupling of the magnetic core/metal nanoshells can be changed dynamically and reversibly by a magnetic field and interparticle spacings of gold and silver nanoshells can be controlled by strength of an applied magnetic field. These materials serve as a surface-enhanced Raman scattering (SERS) substrate. Hot spots for SERS can be easily generated by applying a magnetic field and the enhancement factor can be tuned by strength of magnetic field. When a magnetic field is applied on the superparamagnetic core/ metal nanoshells which are used as SERS substrates, enhancement can be observed due to particle chain formation. The enhancement can be recovered when a magnetic field is revomed. Plasmon coupling of closely spaced magnetic core/metal nanoshells form magnetically controllable 'dynamic hot spots'. The dynamic hot spots can contribute to control the enhancement of Raman signal.
9:00 PM - O18.23
Key Role of Aspect Ratio in Optimising Local Surface Plasmon Sensitivities of Solution Phase Triangular Silver Nanoplates.
Denise Charles 1 , Damian Aherne 2 , Deirdre Ledwith 3 , Yurii Gun'ko 2 , John Kelly 2 , Werner Blau 1 , Margaret Brennan-Fournet 3
1 School of Physics, Trinity College, Dublin Ireland, 2 School of Chemistry, Trinity College , Dublin Ireland, 3 School of Physics, National University of Ireland, Galway Ireland
Show AbstractRefractive index sensitivity of localized surface plasmon resonances (LSPR) of plasmonic nanostructures is recognized as having considerable potential in many biomolecular recognition applications. To date the majority of LSPR sensitivity studies have been performed on single substrate bound nanostructures despite the clear advantages of solution phase nanostructure ensembles being homogeneously in phase with the biomolecular target. Solution phase triangular silver nanoplate (TSNP) ensembles are herein presented as tunable, highly sensitive, LSPR sensors with excellent potential for versatile highly responsive biosensing. The recorded LSPR sensitivities for the highest aspect ratio TSNPs examined exceed those reported to date for various other nanostructures with values of up to 1070 nm/RIU at a LSPR peak wavelength of 1093 nm. Aspect ratio is identified as a key parameter in controlling the LSPR sensitivity of the TSNP. Theoretical studies indicate that high aspect ratio contributes to the dominance of electron scattering contributions over radiation damping. Calculations demonstrate that sensitivities of the TSNP sols, as high as the theoretical upper limit, are achieved by tuning the aspect ratio parameter, without any significant diminution observed due to ensemble averaging.
9:00 PM - O18.24
Fabrication of Gold Shell Covered Nanopatterns with Polymeric Cores for Optical Sensing Application.
Youn-Kyoung Baek 1 , Hwan-Jin Jeon 1 , Hee-Tae Jung 1
1 Chemical and Biomolecular Engineering , KAIST, Daejeon Korea (the Republic of)
Show AbstractThe plasmonic nanostructures have attracted great interest in the wide range of applications such as surface enhanced spectroscopies, biosensors, chemical sensors and optical devices since the structures enable to manipulate light at small wavelength scale. Surface plasmon resonance (SPR) of metal nanostructure can be tailored by controlling the composition of metal, shape, size and dielectric environment. Gold nanostructures generally represent maximum absorption bands in visible wavelength region. Gold nanoshell recently reported shows, however, very unique properties to tune the resonance frequency by varying the relative dimensions of the silica core and gold shell, resulting in optical resonance up to NIR region. Thus, the gold nanoshell array shows great promise in the optical sensing application such as surface enhanced Raman scattering (SERS) and surface enhanced infrared absorption (SEIRA). However, the additional procedures such as surfactant decoration and solution evaporation are usually required to fabricate ordered assemblies of the gold nanoshells. In this work, we developed a simple process to fabricate ordered gold shell pattern by employing polymeric pattern. For the fabrication of polymeric core, we first prepared chitosan hydrogel solution using acetic acid and fabricated the chitosan pattern by using nanoimprint lithography (NIL) technique. The resulting patterns have uniform array of nanoscale pillars (avg. 350 nm dia. × 300nm height) over the large area (7mm × 7mm). Prior to fabricating chitosan mediated gold pattern, the chitosan pattern was etched by reactive ion etching which enables to control geometrical condition of pattern as well as to remove residual layer. For the fabrication of gold shell pattern, the isolated chitosan pattern was immersed in gold nanoparticle solution, followed by reduction of the gold nanoparicles onto the surface of chitosan pattern. Finally, we determined the optimal conditions such as concentration of reduction agent, amount of gold source and reduction time to produce well-ordered gold shell covered patterns. Especially, by controlling the geometrical condition of chitosan patterns, we found that the unique SPR characteristics of gold patterns with chitosan cores can be modulated from visible to NIR wavelength region. Based on the advantages such as ordered geometry and tunability of SPR properties, the gold shell patterns with chitosan cores are expected to show great potential to serve as a sensitive optical sensor.
9:00 PM - O18.25
Systematic Study of Plasmonic Interactions in Nano-Sructured Voids.
Jatin Sinha 1 , Fumin Huang 2 , Jeremy Baumberg 2 , Philip Bartlett 1
1 School Of Chemistry, University Of Southampton, Southampton United Kingdom, 2 Cavendish Laboratory, University Of Cambridge, Cambridge United Kingdom
Show AbstractPlasmons are electromagnetic modes tethered to metal surfaces. Despite common perceptions that they exist only on specific metals, they can also be induced & controlled by nanostructure geometry [1]. The deep sub wavelength spatial decay of their modes provides strong nano-scale field enhancements. This can be exploited, for instance in extracting light from nano-emitters, or funnelling energy into molecules providing surface-enhanced Raman scattering (SERS). Traditionally two sorts of modes are studied: propagating surface-plasmon-polaritons (SPPs) and nanoparticle plasmons. We have discovered that voids in a metal (‘anti-nanoparticles’) support plasmons in radically different ways to nano-particles. Voids are more strongly coupled to light, they can be embedded in films without floating off, and have widely tuneable properties that can be combined with other layers such as semiconductors, or used to make unusual metals support plasmons. In this ongoing work, Nano-structured voids of different metals or combination of metals (e.g. Au, Ag) with different thickness were obtained by electrochemical deposition through a templated closed hexagonal packed polystyrene latex spheres (of diameter 100-1000 nm) on evaporated gold surfaces and subsequent removal of the spheres from the surfaces. The void diameters can be varied by controlled electrochemical deposition through the closed hexagonal packed array of spheres from shallow dishes to completely encapsulated voids.[1]M. E. Abdelsalam, S. Mahajan, P. N. Bartlett, J. J. Baumberg, and A. E. Russell, J. Am. Chem. Soc. FIELD Full Journal Title:Journal of the American Chemical Society 129:7399 (2007).
9:00 PM - O18.26
A Plasmonic-photonic Nanodevice for Label-free Few Molecule Detection.
Giorgio Guizzetti 1 , Francesco De Angelis 2 , Gobind Das 2 , Patrizio Candeloro 2 , Maddalena Patrini 1 , Matteo Galli 1 , Alpan Bek 3 , Marco Lazzarino 3 4 , Ivan Maksymov 1 , Carlo Liberale 2 , Enzo Di Fabrizio 2 4
1 Dept. of Physics "Volta", University of Pavia, Pavia Italy, 2 BIONEM lab, University of Magna Graecia, Germaneto Italy, 3 CBM scrl, Area Science Park, Trieste Italy, 4 TASC National Laboratory, CNR-INFM Area Science Park , Trieste Italy
Show AbstractThe interest in knowing the spectroscopic signature of nanostructured materials is wide and spans from physics, chemistry and biology, where fast and efficient single-molecule spectroscopy is highly desirable. In this work we report on the design and fabrication of a novel nano-optical device for sensing of a few nanometric entities, and we demonstrate its detection capabilities on SiOx nanoparticles, on a single CdSe quantum dot, and on monolayers of organic compounds (1). In all cases, the number of molecules involved covers a range between 10 and 200. The detection is accomplished by far-field Raman scattering spectroscopy operating in the subdiffraction regime. The working principle combines the light harvesting capabilities of a dielectric photonic crystal cavity with the extraordinary confining properties of a metallic nanowaveguide. This leads to efficient optical excitation of target samples through surface plasmon polariton modes localized at nanoscale, as demonstrated by Raman scattering measurements, in confocal configuration, and confirmed by numerical calculations. Furthermore, by fabricating a tapered metallic waveguide directly on atomic-force microscopy cantilever, we demonstrate the capability of performing simultaneous topographic and Raman scattering mapping of silicon nanostructures with very high spatial resolution. The present results, demonstrating label-free detection of a few or even single nano-sized entities in subwavelength regime and in far-field configuration, opens up new perspectives toward efficient spectroscopic characterizations at a nano-scale level in different areas of research. (1) F. De Angelis et al., Nano Letters 8, 2321 (2008).
9:00 PM - O18.28
Optical Transmission through Optically Thin and Thick Sub-wavelength Hole Arrays.
Serap Aksu 1 , Hatice Altug 2
1 Materials Science and Engineering, Boston University, Boston, Massachusetts, United States, 2 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractLight transmission through subwavelength holes in metal films has received significant attention after the seminal paper of Ebbesen. They have showed that at specific resonances metal can be “transparent” and transmit light extraordinary in contrast to the predictions of classical aperture theory of Bethe. Recently nanosphere lithography has also received significant attention for fabrication of subwavelength plasmonic nanostructures. It is capable of covering nano-patterns over large areas, at high resolution, inexpensively and much faster than the conventional electron and ion-beam lithography techniques. In this work we have studied transmission and scattering of light through randomly distributed and hexagonally packed circular subwavelength holes in optically thin and thick metallic film. The gold nanohole arrays are fabricated on glass substrates by combining nanosphere lithography with dry-etching technique. We observed that the transmission resonances of the thin films are significantly different than that of the thick films due to the coupling of plasmons at metal/air and metal/glass interfaces. We also investigated the effect of the diameter and the periodicity on the transmission resonance by controlling the dry-etching time and the bead size used in lithography, respectively. Finally, we have looked at the spectral response of the fabricated structures in media with different refractive indexes for bio-sensing application. In this talk, we will present our experimental results and give physical interpretation by performing numerical simulations and introducing analytical models.
9:00 PM - O18.29
Radiative Engineering with Aperiodic Plasmonic Nanostructures.
Ashwin Gopinath 1 , Rui Li 1 , Svetlana Boriskina 1 , Selcuk Yerci 1 , Luca Dal Negro 1
1 ECE, Boston University, Boston, Massachusetts, United States
Show AbstractIn this work, we demonstrate controlled nanofabrication of novel optical devices based on the engineered deterministic aperiodic nanostructures (DANS) that provide nanoscale electromagnetic localization and enhancement. These devices consist of aperiodic arrays of metal nanoparticles fabricated by electron-beam lithography on non-conductive light-emitting amorphous silicon nitride (SiNx) thin films deposited by reactive magnetron sputtering followed by rapid thermal annealing at 800°C for 6 minutes to facilitate efficient broad-band emission centered at 700nm. Electron-beam nanofabrication is performed on SiNx thin films and results in 100x100 microns size arrays of 30nm-thick Au nano-cylinders with 50 nm-250 nm radii and 20 nm – 500 nm controlled inter-particle separations. Semi-analytical scattering simulations based on the Generalized Mie Theory (GMT) provide the physical insights into the complex electromagnetic scattering response of metal-nanoparticles DANS. Our GMT calculations combined with experimental dark-field microscopy measurements reveal characteristic electromagnetic resonances in DANS due to the excitation of characteristic plasmonic modes with strong field enhancement. We demonstrate that the resonant coupling of light-emitting localized states in SiNx with plasmonic modes in aperiodic metal nanoparticles arrays provides significant enhancement in the photoluminescence intensity over a broad spectral range (across the visible and near-IR?). We also study the effect of the metal nanoparticle shapes on the radiative enhancement in aperiodic plasmonic arrays. Various shapes, including circular cylinders, elliptical and triangles are investigated, and the engineering design rules for the optimization and control of broadband emission from SiNx are discussed. Our results demonstrate that top-down nano-patterning of aperiodic metal nanostructures on Si-based light emitting surfaces can open new pathways for the radiative engineering.
9:00 PM - O18.30
UV Nanoantennas Array for Refractive Index Sensing.
Liangcheng Zhou 1 , Volkmar Dierolf 1
1 Physics, Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractStudy of Ultraviolet Surface Plasmon Polariton (UV-SPP) is of special interest because of UV light’s wide applications in biology and medical research. It has been shown that dipole and bowtie optical nanoantennas not only squeeze the optical field in a volume well below the diffraction limit, but also enhance the optical field intensity in the gap area. We investigated in detail the sensitivity of the UV nanoantennas to index change using both numerical simulations and optical experiments. FDTD simulations predicted that there exist several resonant wavelengths for dipole antennas and the resonant wavelength will shift as a function of antenna length. In this work, by optimizing the geometric shape of metallic aluminum nanoantennas, we experimentally determined the sensitivity of a nanoantenna array by monitoring the optical intensity change at its resonant input wavelength in the UV domain. Index sensing using metallic nanoantennas opens new possibilities to cost-effective integrated biosensors on a chip.
9:00 PM - O18.31
A Chemical Approach for the Fabrication of Sub-wavelength Hole Arrays in Metallic Films.
Stefan Quint 1 2 , Claudia Pacholski 1
1 , Max-Planck-Institute for Metals Research, Stuttgart Germany, 2 , University of Heidelberg, Heidelberg Germany
Show AbstractSub-wavelength hole arrays support the unusual phenomenon of extraordinary optical transmission (EOT) and can find applications in several fields such as chemical as well as biochemical sensing, device fabrication, and enhanced spectroscopy. A method to fabricate sub-wavelength hole arrays in metallic films solely based on chemical techniques will be presented. Hole arrays are prepared by using the self-assembling ability of poly(N-isopropylacrylamide) microspheres to generate a highly ordered array of discs with defined spacing on a glass substrate which serves as a mask for the chemical growth of a gold film by selective electroless plating. The obtained nanostructure shows the desired optical properties and has successfully been tested as sensor. The introduced method is fast, inexpensive and suitable for any standard chemical laboratory.
9:00 PM - O18.32
Plasmon Spectra at Wurtzite Aluminium Gallium Nitride / Silicon Carbide Heterojunctions.
Choudhury Praharaj 1
1 Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah, United States
Show AbstractWe present theoretical calculations of electron plasmon excitation spectra at hetero-interfaces between wurtzite Aluminium Gallium Nitride and Silicon Carbide. AlGaN/SiC heterojunctions are of interest for a variety of electronic applications like Heterojunction Bipolar Transistors and also for optoelectronic applications, due to a unique combination of properties found in these materials like wide band-gap and low impact ionization coefficients. The wurtzite crystal structure permits the presence of spontaneous polarizations in the absence of externally applied electric fields. Further, strained wurtzite semiconductors have piezoelectric polarizations. The interface charges caused by polarization discontinuities at AlGaN/SiC heterointerfaces are of the order of 1e13 electrons per cm^2. The band-bending due to the electrostatic effect of these charges is often sufficient to induce two-dimensional electron or hole gases, since they need to be compensated by a large amount of depletion and accumulation charge to maintain overall charge neutrality in the device structures. We calculate the plasmon spectra of polarization-induced electron gases at AlGaN/SiC heterojunctions for different alloy compositions of AlGaN. The electronic sub-band wave-functions are significantly affected by the amount of polarization-induced charge at the interface. This manifests itself in the screening properties and the collective excitations of the two-dimensional electron gas. Our calculations are relevant to device structures involving nitride / silicon carbide heterojunctions, and will be useful for understanding the limits of electron mobility in these structures.
9:00 PM - O18.33
Transparent Conducting Oxides for Active Plasmonics.
Kenneth Diest 1 2 , Eyal Feigenbaum 2 , Harry Atwater 2 1
1 Materials Science, Caltech, Pasadena, California, United States, 2 Applied Physics, Caltech, Pasadena, California, United States
Show AbstractActive plasmonics is an emerging field that enables light compression into nano-structures based on plasmon resonances at a metal-dielectric interface and active modulation of the of these plasmons with an applied external field. One area of active plasmonics has focused on replacing the dielectric layer in these waveguides with an electro-optic material and designing the resulting structures in such a way that the transmitted light can be modulated.In this talk we will look at using transparent conducting oxides (TCOs) as the dielectric layer within a metal-insulator-metal (MIM) plasmonic waveguide. Hall probe measurements show that these materials are capable of obtaining carrier concentrations between 1x10^19 and 2x10^21 cm^-3. In this regime, the plasma frequency of these materials can be tuned across the mid to near infrared frequencies. By utilizing these structures in an MOS configuration within the MIM waveguide, the properties of the plasmonic mode confined at the metal-oxide interface of the waveguide can be significantly tuned with an applied field. Structures were fabricated with 300nm of Au as the top and bottom cladding layers and a layer of TCO and silicon dioxide were deposited between the metal layers. Spectroscopic ellipsometry was used to measure the complex indicies of refraction within the multi-layer stack and the effective index of TCO-Si02 interface layer shifts from 2.0 to 1.2 for certain regions of the visible and IR spectrum. Measurements of active MIM geometries will also be presented.
9:00 PM - O18.34
Plasmonic Nano-resonators Based on Periodic and Aperiodic Order.
Svetlana Boriskina 1 , Carlo Forestiere 1 , Gary Walsh 1 , Ashwin Gopinath 1 , Luca Dal Negro 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractWe theoretically investigate and compare spectral and spatial localization properties of photonic-plasmonic modes in periodic and aperiodic finite-size arrays of noble-metal nanoparticles. Our simulations, based on the coupled-dipole method and the generalized multi-particle Mie theory reveal the differences in the electromagnetic near-field intensity distribution in plasmonic arrays of different complexity. We demonstrate how subtle interplay between diffractive and near-field coupling in metal nanoparticles arrays with complex, yet deterministic, morphologies can be exploited to achieve efficient light localization and electromagnetic hot-spots formation. For example, our results indicate that the control of diffraction coupling and multiple scattering offers the possibility to increase the hot-spots intensities by scaling the size of the plasmonic arrays, potentially providing orders of magnitudes larger enhancement with respect to isolated nanoparticle dimer or periodic structures. Additional step of the plasmonic arrays performance optimization is based on accurate tuning the radii of individual nanoparticles, and nanoparticle shapes. The ability of aperiodic plasmonic arrays to generate highly localized intense hot-spots can be exploited in the design of robust and efficient substrates for Surface Enhanced Raman Scattering. Furthermore, intense localized electromagnetic fields in aperiodic plasmonic structures can be used to enhance the efficiency of light emission from low-quantum yield systems such as fluorescent molecules, silicon quantum dots and erbium doped silicon structures. The plasmonic resonator morphology can be engineered to provide strong field enhancement and focusing in sub-wavelength hot spots at several pre-defined wavelengths paving the way for the design of multi-wavelength broadband nano-antennas.
9:00 PM - O18.35
Real-time Monitored Wet Chemical Preparation of Plasmonic Nanostructures for Surface Enhanced IR Absorption Spectroscopy.
Dominik Enders 1 , Tadaaki Nagao 1 , Osamu Saito 1
1 WPI MANA, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
Show AbstractThe effect of Surface Enhanced Infrared Absorption (SEIRA) has become a meaningful tool in chemo- and biosensing [1]. As for the preparation of SEIRA active substrates wet chemical preparation methods have gained much interest in the last years because of their easiness, the low time consumption, and the low cost compared to the known ultra high vacuum based methods. For a routine production of SEIRA substrates, it is necessary to develop not only an easy but also a reproducible procedure of fabrication, to ensure a precise control of the film morphology.Here we demonstrate that optical in situ monitoring of the film preparation process can be of valuable use, utilizing SEIRA of the surrounding molecules as well as the effect of a film morphology dependent shift and change of shape of the surface plasmon absorption band. A two-step wet-chemical preparation method of plasmonic SEIRA active nanostructures for surface enhanced infrared absorption spectroscopy (SEIRAS) is shown. Au nanoparticles are deposited on SiO2/Si and grown to form a network of densely packed tabular islands close to the 2D percolation threshold. In situ IR spectroscopy is utilized to monitor the growth of the Au islands, which enables the termination at a well defined state of the morphology. The SEIRA activity of the resulting films is analysed by measuring IR spectra of octadecanethiol (ODT) monolayers on the respective film. For the antisymmetric CH2 stretching vibration peak heights of up to 16% were measured, which can be assigned to a SEIRA enhancement of three orders of magnitude compared to flat Au films [2].Reference:[1] A. Hartstein, J. R. Kirtley, and J. C. Tsang, Phys. Rev. Lett. 45, 201 (1980).[2] D. Enders, T. Nagao, T. Nakayama, M. Aono, Jpn. J. Appl. Phys. 46, L1222 (2007).
9:00 PM - O18.36
Fabry-Perot Nanocavities in Multi-Layered Plasmonic Crystals for Enhanced Biosensing.
Alp Artar 1 , Ahmet Yanik 1 , Hatice Altug 1
1 Electrical and Computer Engineering , Boston University, Boston, Massachusetts, United States
Show AbstractAbility to confine electromagnetic waves on metallic surfaces in the form of localized and propagating surface plasmons (SPP) have opened up new possibilities reshaping the photonics field, Orders of magnitude stronger extraordinary light transmissions through subwavelength nano-apertures are shown in defiance to Bethe’s predictions. So far studies are focused on two-dimensional (2D) arrangement of plasmonic nanostructures. However, engineering of materials in three-dimensions (3D) by integrating different kinds of plasmonic resonances in muti-layers offers additional degrees of freedom in our design space.In this work, extra-ordinary light transmission effect in multi-layered plasmonic crystals formed by coupling of two physically separated metal nanohole and nanodisk array layers is demonstrated. We show that this multi-layered plasmonic structures support Fabry-Perot (FP) resonances in addition to the grating based SPP modes of conventional nanohole arrays with optical transmission efficiencies greater than predicted by Bethe’s theory. Electromagnetic fields of these FP resonances are confined in the dielectric region instead of the metallic surfaces enabling superior field-medium overlap. As a result, we show that they are highly sensitive to the refractive index changes within the media. The large field-medium overlap makes these structures an ideal candidate for biosensing applications. Their physical shape allows a natural trapping geometry for bio-particles. Furthermore, simplicity of the fabrication scheme used here conveniently eliminates the use of more specialized focused ion beam tool and enables nanohole array fabrication in a single step with more widely available e-beam lithography.
9:00 PM - O18.5
Strong and Weak Coupling in Plasmon-exciton Systems.
Bala Krishna Juluri 1 , Mengqian Lu 1 , Yue Bing Zheng 1 , Lasse Jensen 2 , Jun Huang 1
1 Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractPlasmon-exciton systems consisting of an inorganic metallic nanoparticle covered with a monolayer of resonant organic molecules have been recently investigated. Experiments using various types of nanoparticles and resonant molecules have resulted into two general types of observations: 1) formation of two peaks in the extinction spectra, called hybrid states, that closely follow Rabi splitting behavior and 2) a single peak in extinction spectra and the localized surface plasmon resonant (LSPR) shift follows the real part of the refractive index of resonant molecules. By evoking the interaction of plasmon resonance with molecular resonance, both the set of experiments have shown control over the landscape of plasmonic extinction spectra. Such control over LSPR is very important and will open novel applications of plasmon-exciton systems in tunable nanophotonic devices and molecular sensing. However, the nature of the experimental results in these two important sets of works remains different and the question of which conditions give rise to a certain set of experimental results remains unanswered. In this work, first, we show that the magnitude of absorbance of the molecular layer controls the amount of Rabi splitting in plasmon-exciton systems and therefore the strength of resonant coupling between molecular and plasmonic resonances is controlled by absorbance. Second, we show that the two observations mentioned above are closely related with each other and the magnitude of absorbance decides the nature of experimental results. This understanding opens up knowledge for better design of plasmon-exciton systems for developing molecular sensing and nanophotonic devices.
9:00 PM - O18.6
Photon Statistics in Enhanced Fluorescence from a Single CdSe/ZnS Quantum Dot in the Vicinity of Metal Nanostructures.
Sadahiro Masuo 1 2 , Hiroyuki Naiki 1 , Shinjiro Machida 1 , Akira Itaya 1
1 , Kyoto Institute of Technology, Kyoto Japan, 2 , PRESTO-JST, Kawaguchi Japan
Show Abstract One of the interesting optical properties of colloidal quantum dots (QDs) is their single-photon emission behavior at room temperature. Single-photon sources capable of emitting only one photon at any point in time have been intensively investigated for quantum information processing. However, single QDs show strong fluorescence blinking. It has been reported that this blinking behavior is strikingly suppressed by localized surface plasmon resonance (LSPR) in metal nanostructures and/or by interacting merely with metals. LSPR is also reported to give rise to an increase in the fluorescence intensity and a shortening of the lifetime, which is known as fluorescence enhancement. In this study, we investigated single-photon emission behavior in the enhanced fluorescence from single QDs near metal nanostructures using a single molecule fluorescence spectroscopy technique. By simultaneously measuring time traces of fluorescence intensity, lifetime, fluorescence spectra, and photon correlations of single QDs, we have found a strong relationship between the degree of enhancement, the lifetime, and the probability of single-photon emission. CdSe/ZnS core/shell QDs were used. As the metal nanostructures, silver nanoparticles (AgNPs) were prepared by the conventional reduction method. In order to enhance the fluorescence from the single QDs, a AgNPs/QD in PMMA/coverslip sample structure was prepared by drop-casting AgNPs-dispersed aqueous solution onto a PMMA thin film in which isolated QDs were embedded. The fluorescence behavior of single QDs was measured using a Hanbury-Brown and Twiss type photon correlation set-up in combination with pulsed laser excitation at 411 nm under a sample-scanning confocal microscope consisting of a spectrograph with a cooled CCD camera, two avalanche single photon counting modules, and a time-correlated single photon counting module. As results of measurements for single QDs near AgNPs, it was found that the degree of fluorescence enhancement from single QDs increased with decrease in the lifetime and the probability of single-photon emission, that is, highly enhanced fluorescence with a shortened lifetime exhibited a low probability of single-photon emission, and such single QDs exhibited less blinking behavior. We suggest that one possible mechanism is that the enhanced radiative and nonradiative rates caused by LSPR can compete with the Auger process, resulting in enhanced multiphoton emission, suppression of blinking, and a reduction in lifetime. Another possibility is that multiple excitations due to enhanced electromagnetic field occur within a single excitation pulse if the shortened exciton lifetime is smaller than the pulse width, while the Auger process can be suppressed by fast nonradiative decay. The present results yield new insights into fundamentals of QD-metal nanostructure interactions, and are also important to understand the mechanism of the fluorescence enhancement by LSPR of metal nanostructures.
9:00 PM - O18.8
Polarization Behaviour of the Exciton-polariton Emission in ZnO Based Microresonators.
Chris Sturm 1 , Helena Hilmer 1 , Ruediger Schmidt-Grund 1 , Marius Grundmann 1
1 Inst. f. Exp. Physik II, Universität Leipzig, Leipzig Germany
Show AbstractThe properties of exciton-polaritons in microresonators have been intensively investigated in the last years. These bosonic quasi particles, composed of an exciton and a cavity-photon, can form a Bose-Einstein condensate (BEC) at elevated temperatures. Of special interest are ZnO based microresonators. Due to the large exciton oscillator strength and exciton binding energy of ZnO, excitons are well stable and can easily couple to a cavity-photon in order to achieve the strong coupling regime at elevated temperatures [1]. In this work we study the polarization behaviour of the exciton-polariton emission from ZnO based microresonators and derive properties of the relaxation processes of the exciton-polaritons into their ground state, which are of particular interest with respect to a possible BEC in such resonators.
The microresonators were made by pulsed laser deposition and consist of a ZnO cavity embedded between two Bragg reflectors made of 10.5 pairs of yttria stabilized zirconia (YSZ) and Al2O3. We studied the microresonators by photoluminescence (PL) measurements for emission angles 0° – 50° as function of temperature and detuning. The last one was changed by varying the temperature as well as the lateral position on the sample due to the intentionally graded resonator thickness.
The recorded PL data show clearly the signature of a lower polariton branch (LPB) whose dispersion behaviour differs slightly for light polarized perpendicular (s) and parallel (p) with respect to the plane of incidence. A splitting of about 2 meV between s- and p-polarization was obtained at an emission angle of 38°, caused by the splitting of the s- and p-polarized uncoupled cavity-photon mode. At larger angles, the LPB energy converges to the energy of the uncoupled exciton mode for both polarizations. The recorded PL intensity, which is connected to the exciton-polariton density, shows a strong polarization dependence with respect to the emission angle. In contrast to the s-polarization, the p-polarization shows a bottleneck effect, this means the PL intensity reaches a maximum at an emission angle of about 28°. For larger emission angles the PL intensity decreases for both polarizations similarly. Comparing the observed occupation behaviour with numerical simulations [2] it follows that the polariton-polariton scattering mechanism should contribute stronger to the relaxation into the ground state for the s- than for the p-polarization. With increasing temperature the bottleneck effect becomes weaker and vanishes for temperatures larger than 190 K. We relate this finding to the increase of the polariton-polariton scattering rate with increasing temperature and its saturation at high temperatures [3].
1. C. Sturm et al. New. J. Phys., accepted.
2. A. Kavokin, G. Malpuech, Cavity polaritons, Elsevier, 2003.
3. F. Tassone et al. Phys. Rev. B. 59, 10830 (1999).
9:00 PM - O18.9
Recombination Rates for Single Colloidal Quantum Dots Near a Smooth Metal Film.
Xiaohua Wu 1 , Matthew Pelton 1 , Yugang Sun 1
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe investigate the intrinsic recombination rates for single quantum dots (QDs) in nanometer proximity to a smooth metal film. By making time-resolved measurements of decay kinetics, we remove the effects of non-radiative rate fluctuations associated with blinking and determine intrinsic decay rates for a number of individual QDs. Most previous studies of QD-metal coupling have considered only fluorescence intensity; in this case, though, several competing mechanisms contribute to the measured signal, including enhanced absorption of the excitation light, changes in the spatial pattern of emission, and changes in radiative and non-radiative recombination rates. Recombination rates provide a more direct measure of the QD–metal coupling, and have been investigated for both ensembles and individual QDs near metal nanostructures. However, both inhomogeneous broadening in QD ensembles and emission “blinking” in single QDs make it difficult to extract meaningful decay rates from such measurements. By doing a time-tagged time-resolved fluorescence measurement, and isolating photons emitted when the dot is in a high-intensity state, we eliminate the effects of time-fluctuating non-radiative processes. The delay time histogram of those photons shows a single exponential decay behavior and thus defines the “intrinsic” recombination rate, which is the sum of radiative decay to free space and non-radiative energy transfer to the metal. The measured decay-rate distributions broaden and their averages shift to larger values as the dot–metal separation decreases. The experimental distributions are well described by an analytical model that takes into account the random orientation of the two-dimensional QD dipole. This simple system thus demonstrates an important framework that can be used to investigate the coupling of QDs to more complex metal structures. Any quantitative characterization of QD–metal coupling will require going beyond ensemble averaging and time averaging and making time-resolved kinetic measurements on individual quantum dots.
Symposium Organizers
Alexander O. Govorov Ohio University
Andrey L. Rogach Ludwig-Maximilians-Universität München
Zhiming M. Wang University of Arkansas
Juen-Kai Wang National Taiwan University
(and Institute of Atomic and Molecular Sciences
Academia Sinica)
Vladimir M. Shalaev Purdue University
O19: Plasmons in Nanostructures II
Session Chairs
Friday AM, December 04, 2009
Back Bay B (Sheraton)
9:30 AM - **O19.1
Profiled and Nanostructured Metal Surfaces as Plasmonic Components.
Alexandra Boltasseva 1 2 , Paul West 1 , Gururaj Naik 1 , Rasmus B. Nielsen 2 , Claus Jeppesen 2
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Technical University of Denmark, Lyngby Denmark
Show AbstractDifferent fabrication approaches for realization of plasmonic components will be discussed. For applications in integrated optical systems, fabrication and performance of low-loss long-range surface plasmon polariton (SPP) waveguides and waveguide components will be considered. Profiled metal surfaces (V-grooves and wedges) used as plasmonic waveguides with subwa-velength confinement will also be discussed. For plasmonic waveguides, nanoimprint-based fabrication techniques that offer mass-production compatibility and wafer-scale parallel fabrication of plasmonic components will be presented. Nanofabrication of different arrangements of surface nanoscatterers for efficient in-plane manipulation of SPPs will also be mentioned. Moving one step further toward ‘’active plasmonics’’, controlled fabrication of metal nanoparticles will be discussed for optical nanoantennae realization. Finally, fabrication approaches for making optical metamaterials will be discussed.
10:00 AM - O19.2
Functional Plasmonic Antenna Scanning Probes Fabricated by Induced Deposition Mask Lithography.
Alexander Weber-Bargioni 1 , Adam Schwartzberg 1 , Martin Schmidt 1 , D. Frank Ogltree 1 , P. Jim Schuck 1 , Stefano Cabrini 1
1 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractIn this work we present the successful fabrication of a well-defined functional plasmonic antenna on a SPM tip with a novel nanofabrication method, showing a Raman enhancement factor on the order of 5*10^5. Research and Development of plasmonic/optical antennae is a topic of high interest since these antennae allow manipulating light in the visible regime on the nm scale. Much work has been published on the basic characterization of metal nano particles as optical antennae. Presently much effort is invested into the next R&D phase, that is the implementation of well-defined optical antennae into actual devices to employ properties such as optical near fields localized on the order of 10nm and 3 orders of magnitude near field enhancements. A significant application for localized optical Near Fields is Tip Enhanced Raman Spectroscopy (TERS) , which enables the imaging of single proteins and can potentially be used for chemical mapping with a resolution down to individual molecules. With our novel nanofabrication method Induce Deposition Mask Lithography (IDML) we were able to address the lack of a nano fabrication method for the reproducible, well-defined fabrication and flexible placement of optical antennae, which is a key problem for the implementation of optical antennae into devices. Here we present IDML by fabricating bowtie optical antennae and the instrumentation used. Furthermore the functionality of the optical antenna is demonstrated via dark field spectroscopy, the local field enhancement shown for a well-defined functional dipolar optical antenna placed on a SPM tip as well as the first employment of these Tips for TERS.
10:15 AM - O19.3
Correlated Optical Spectroscopy and Transmission Electron Microscopy of Individual Hollow Nanoparticles and their Dimers.
Linglu Yang 1 , Bo Yan 1 , Bjoern Reinhard 1
1 , Boston University, Boston, Massachusetts, United States
Show AbstractThe optical spectra of individual Ag-Au alloy hollow particles were correlated with the particles’ structures obtained by transmission electron microscopy (TEM). The TEM provided direct experimental access to the dimension of the cavity, thickness of the metal shell, and the interparticle distance of hollow particle dimers with high spatial resolution. The analysis of correlated spectral and structural information enabled the quantification of the influence of the core-shell structure on the resonance wavelength, plasmon lifetime, and plasmon coupling efficiency. Electron beam exposure during TEM inspection was observed to affect plasmon wavelength and lifetime, making optical inspection prior to structural characterization mandatory.
10:30 AM - O19.4
Resonant Behavior of Plasmonic Nanowire and Nanostrip Antennas.
Edward Barnard 1 , Ana Brown 1 , Mark Brongersma 1
1 , Stanford University, Stanford, California, United States
Show AbstractA combined theoretical and experimental study of the optical properties of wavelength-scale plasmonic resonator antennas is presented. These antennas support standing surface plasmon-polariton (SPP) waves that enable substantial concentration of light at a set of well-defined resonant frequencies. From experiments and full-field simulations, it is now well-established that the resonant frequencies critically depends on the exact antenna geometry (size and shape) and the optical properties of the metal. Using full-field electromagnetic simulations and analytical optical antenna models, we are able to derive simple and intuitive design rules to achieve antennas with a desired set of optical properties (field enhancement, scattering cross section, absorption cross section, and resonant frequency) based on their geometric properties. With these design rules, we provide resonance maps that allow a designer to choose an antenna structure that provides these desired resonant parameters. In order to verify our design rules, noble metal nanowires and stripes of varying shape and length were fabricated using a template-assisted electrochemical process and using electron-beam lithography. Dark-field and near-field optical microscopy techniques were used to determine the resonant properties of the structures and theory is compared against experiment. The results of this study enable optical engineers to more easily design a myriad of plasmonic devices that employ optical antenna structures, including nanoscale photodetectors, light sources, sensors, and modulators.
10:45 AM - O19.5
Resonance-based Plasmonic Modulators: Design and Analysis.
Wenshan Cai 1 , Mark Brongersma 1
1 Materials Science And Engineering, Stanford University, Stanford, California, United States
Show AbstractThe nanoscale control of photons is known to be one of the major obstacles towards a seamless integration of electronic circuits and optical functionalities. Recent advances in plasmonics have revealed its great potential to overcome this challenge. Among all externally controllable, active plasmonic devices, electrooptic plasmonic modulators stand out as a key element in that they load carrier waves with on-chip information, mostly in the form of voltage signals. In this work we explore the possibility of realizing a compact plasmonic modulator that combines low power consumption and high modulation speed with a reasonable modulation depth and optical throughput. In particular, we avoid using interference-based structures as they usually require a large index change or a long interaction channel necessary for the interference to happen efficiently. Instead, we propose several resonance-based plasmonic modulators where light-matter interactions can be substantially boosted due to engineered field confinement and enhancement.We present detailed optimization protocol for plasmonic modulators and show that devices with an overall transmittance of over 50% and a 3dB modulation depth can be realized with a very modest change of Δn”=0.004 or Δn’=0.008 in the cavity index. With a swing voltage of ~1V, the magnitude of such changes is well within the reach of available electrooptic effects, including electroabsorption in semiconductors, quantum-confined Stark effect in quantum wells, and electrorefractive effect in nonlinear polymers. We also show that such structures are capable of ultra-high-speed operation and are suitable for low-loss on-chip integration with conventional dielectric waveguides.
O20: Plasmons in Nanostructures III
Session Chairs
Friday PM, December 04, 2009
Back Bay B (Sheraton)
11:30 AM - **O20.1
High-speed Monitoring of Bacteria’s Response to Antibiotic Treatments using Raman Scattering Enhanced by Ordered Arrays of Nanoparticles.
Yu Chen 1 , You-Hsuan Lin 1 , Chia-Shui Huang 1 , Ting-Ting Liu 1 , Chi-Hung Lin 1 , Juen-Kai Wang 2 3 , Huai-Hsien Wang 3 4 , Yuh-Lin Wang 3 4
1 Institute of Microbiology and Immunology, National Yang-Ming University, Taipei Taiwan, 2 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan, 4 Department of Physics, National Taiwan University, Taipei Taiwan
Show AbstractSilver nanoparticles are grown on anodic aluminum oxide (AAO) template to form substrates that exhibit extraordinarily large, uniform, and stable surface-enhanced Raman scattering (SERS) property [1,2]. The successful preparation of such AAO-based substrates has dramatically improved the sensitivity and reproducibility of SERS and facilitated its applications in many fields including the detection and identification of a single bacterium. Since SERS provides non-destructive molecular information about an object brought near to the substrate surface, it is also an important spectroscopic method for probing the structure and dynamics the cell walls of microbes. The SERS spectra evolution of various bacteria in response to atibiotic treatments will be discussed.1. “Highly Raman Enhancing Substrates Made of Ag-Nanoparticle Array with Tunable Sub-10 nm Gaps”, Huai-Hsien Wang, Chih-Yu Liu, Shr-Bin Wu, Nai-Wei Liu, Cheng-Yi. Peng, Tsu-Hsin Chan, Chen-Feng Hsu, Juen-Kai Wang, and Yuh-Lin Wang, Advanced Materials 18, 491-495(2006).2. “A High Speed Detection Platform Based on Surface-Enhanced Raman Scattering for Monitoring Antibiotic-Induced Chemical Changes in Bacteria Cell Wall“ Ting-Ting Liu, You-Hsuan Lin, Chia-Sui Hung, Tian-Jiun Liu, Yu Chen, Yung-Ching Huang, Tsung-Heng Tsai, Huai-Hsien Wang, Da-Wei Wang, Juen-Kai Wang, Yuh-Lin Wang, Chi-Hung Lin, PLoS ONE 4(5), e5470 (2009).
12:00 PM - O20.2
Plasmonic Coupling of a Gold Colloid and a Thin Gold Film.
Albert Chang 1 , Fei Le 1 , Tamer Ali 1 , Felicia Tam 1 , Naomi Halas 1 , Peter Nordlander 1 , Kevin Kelly 1
1 , Rice University, Houston, Texas, United States
Show AbstractA wide variety of geometries of metal nanoparticles have been created to extend tunability across the electromagnetic spectrum. An alternative strategy, however, is to tune the plasmon of the simple spherical nanoparticle by controlling the surrounding geometry. The key feature in our system is the coupling of the plasmon of a nanoparticle and a thin gold film separated by a thin dielectric spacer. As we show, this mixing allows for a great deal of control in generating a strong and localized enhancement of the incident electric field. Using confocal Raman microscopy and additional structural characterization through scanning electron and atomic force microscopy, we explore this coupling phenomenon and compare the resulting enhancement to their equivalent finite element models. The results of these studies yield a clearer picture about the subtle role of both scale and geometry towards utilizing these trends for various applications.
12:15 PM - O20.3
Surface Plasmon Resonance Enhanced Magneto-Optics (SuPREMO) in a Composite Magnetic/Plasmonic Nanostructure.
Prashant Jain 1 , Yanhong Xiao 2 , Ronald Walsworth 2 3 , Adam Cohen 4 3
1 Dept. of Chemistry and Miller Institute for Basic Research in Science, University of California Berkeley, Berkeley, California, United States, 2 Harvard-Smithsonian Center for Astrophysics, Harvard University , Cambridge, Massachusetts, United States, 3 Department of Physics, Harvard University , Cambridge, Massachusetts, United States, 4 Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts, United States
Show AbstractThe ability to detect and manipulate magnetic fields using light relies on the magnetic optical (MO) properties of a material, such as Faraday rotation and the Kerr effect; however, these phenomena are typically weak. I will talk about how the intrinsic MO properties of a material can be enhanced by employing the optical resonances (also known as plasmons) of noble metal nanostructures. We recently demonstrated MO enhancement in a composite magnetic/plasmonic nanostructure consisting of a superparamagnetic iron oxide nanoparticle coated with a shell of gold, with a plasmon resonance around 560 nm. The gold-coated iron oxide nanocrystals exhibit a sharp peak in their Faraday rotation spectrum around 530 nm, which is indiscernible in uncoated gold nanocrystals. Plasmon resonances excited in the gold shell generate strong near-fields and field gradients that enhance a spectrally and spatially nearby weakly allowed electron pair transition (ca. 510 nm) in the iron oxide, resulting in a magneto-optical enhancement in this narrow spectral region. This demonstration of surface plasmon resonance-enhanced magneto-optics (SuPREMO) in a composite magnetic/plasmonic nanosystem may enable the design of nanostructures for remote sensing and imaging of magnetic fields, magneto-optical data storage, and miniaturized magneto-optical devices.
12:30 PM - O20.4
A Q/V Design Approach to Enhancing Spontaneous Emission With Plasmonic Devices.
Carrie Hofmann 1 , Deirdre O'Carroll 1 , Anna Hiszpanski 1 , F. Javier Garcia de Abajo 2 , Harry Atwater 1
1 Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, California, United States, 2 Instituto de Optica, CSIC, Madrid Spain
Show AbstractResearchers have devoted considerable effort to controlling light emission from semiconductors and molecules using geometries that exhibit high Purcell factors. To effectively enhance the rate of spontaneous emission, one must maximize the quantity Q/V. This is traditionally achieved by designing dielectric resonators with ultra-high quality factors, Q. Although plasmonic nanocavities generally support resonant modes with low quality factors (Q<50), these modes are highly confined to subwavelength (sub-λ) mode volumes (V<<λ3) and hence can be used to achieve very large Purcell enhancements. Here, we explore plasmonic nanocavities and nanoantennas theoretically and experimentally, and demonstrate that high Q/V and ultrafast spontaneous emission rates are achievable in sub-λ devices.
We investigate a single, deeply sub-λ nanohole resonator in Ag filled with Si analytically using the boundary element method. This geometry allows precise control of the local density of optical states (LDOS), and thus the radiative emission rate, by changing the dimensions of the Si core. For each resonant mode, we determine the LDOS, quality factor Q, and effective mode volume Veff, as well as the enhancement in the radiative and total decay rates normalized to vacuum. Results are summarized in the table below. For all dimensions, we find modes strongly confined within the Si core. Moreover, ultra-small resonators still sustain reasonable Q, resulting in Q/V~105(λ/n)3, radiative rate enhancements >3000, and quantum efficiency ~25%.
Additional geometries for enhancing spontaneous emission will also be presented. We investigate a plasmonic nanoantenna, coupling a light-emitting polymer segment, poly(3-hexylthiophene) (P3HT), to an Au nanowire. Longitudinal plasmon resonances in the Au nanowire modify the spontaneous emission spectrum, polarization, and emission lifetime of the P3HT segment. We calculate a 7-fold increase in the radiative rate of the P3HT upon coupling to the Au nanowire, which agrees well with experimental observations. Finally, devices consisting of novel combinations of waveguides, antennas, and cavities (deemed “wantecas”) and their applications to enhancing spontaneous emission will also be discussed. This work demonstrates the promise of sub-λ plasmonic structures for enhancing the emission rate of active semiconductor materials.
O21: Plasmons in Nanostructures IV
Session Chairs
Friday PM, December 04, 2009
Back Bay B (Sheraton)
2:30 PM - O21.1
Electronic Tuning of the Surface Plasmon Resonances of Single Gold Nanorods.
Carolina Novo 1 , Alison Funston 1 , Paul Mulvaney 1
1 The School of Chemistry, The University of Melbourne, The University of Melbourne, Victoria, Australia
Show AbstractThe spatial confinement of conduction electrons in sub-wavelength structures such as metal nanocrystals leads to surface plasmon resonances. The energy of the plasmon resonance for a given particle is extremely sensitive to the structural details of the crystals, including size, shape and surface roughness at the atomic level. For very small particles, the surface plasmons excited by light are primarily dipolar in character and SPR peaks occur whenε(ω) = -((1 – L)/L) εmWhere εm is the dielectric constant of the surrounding medium, ε(ω) is the dielectric function of gold and L is the shape factor of the particle, which may be calculated numerically. The dielectric function of gold is well described in the visible region using the Drude model and is a function of the electron density in the particle. If the electron density changes, the bulk plasma frequency alters correspondingly and therefore the dielectric properties of the gold [1].We demonstrate here that the surface plasmon resonance of a single gold nanocrystal can be both passively and actively modulated directly by altering the electron density of the metal. The changes in the plasmon resonance of single particles are detected in situ using dark field microscopy to study the scattered light (Rayleigh Spectra) from single gold nanocrystals. Using this technique we are able to observe chemical reactions of single gold nanocrystals, including a catalytic cycle [2]. Electrochemical charging of the nanoparticles allows the reversible, active modulation of the surface plasmon resonance. The scattering spectra of single gold rods have been measured as a function of the applied potential in an electrochemical cell using dark field microscopy. It is demonstrated that the surface plasmon resonance can be reversible and rapidly tuned by tens of nanometres. The dependence of the particle shape on the magnitude of the shift is discussed. The SEM image of the particles investigated were collected before and after electrochemical charging using the Focussed Ion Beam Registration Method [3] to assess morphological changes occurring as a result of charging as well as to determine the exact particle morphology and therefore avoid the effects of polydispersity.This modulation of the scattering spectra provides a basis for information storage in single gold rods and a method for transmitting signals through coupled plasmonic superstructures.1) Mulvaney, P., Perez-Juste, J., Giersig, M., Liz-Marz an, L., and Pecharroman, C., Plasmonics, 2006, 1(1), 61-66.2) Novo, C., Funston, A. M., Mulvaney, P., Nature Nanotech., 2008, 3(10), 598-602.3) Novo, C., Funston, A. M., Pastoriza-Santos, I., Liz-Marzán, L. M., Mulvaney, P., Angew. Chemie. Int. Ed., 2007, 46, 3517-3520.
2:45 PM - O21.2
Obtaining Circularly Polarized Optical Spots beyond the Diffraction Limit using Plasmonic Nano-Antennas.
Erdem Ogut 1 , Gullu Kiziltas 1 , Kursat Sendur 1
1 , Sabanci University, Istanbul Turkey
Show AbstractDiffraction-limited circularly-polarized electromagnetic radiation has been widely used in the literature for various applications at both optical and microwave frequencies. With advances in nanotechnology, circularly-polarized electromagnetic radiation beyond the diffraction limit is desired in emerging plasmonic nano-applications, such as all-optical magnetic recording. In the literature, it has been demonstrated that the magnetization can be reversed in a reproducible manner by using a circularly polarized optical beam without any externally applied magnetic field. To advance the areal density of hard disk drives beyond 1 Tbit/in.2, magnetization reversal areas much smaller than 100 nm are required. To achieve sub-100 nm bits, circularly polarized optical spots beyond the diffraction limit are necessary.In this study, a cross-dipole nano-antenna is investigated to achieve circularly polarized near-field radiation beyond the diffraction limit. The cross-dipole nano-antenna is composed of four gold metallic nano-rods placed at a vertical orientation with respect to each other. In addition to providing an intense optical spot in the vicinity of its gap, two conditions that are required for circular polarization are met: (1) the phase difference between the electric field components is 90° and (2) the ratio of the magnitudes of the electric field components is equal to 1 in the vicinity of the gap. The near-field radiation characteristics of a plasmonic cross-dipole nano-antenna are investigated when illuminated with linearly-polarized and circularly-polarized incident radiation. It is found that a plasmonic cross-dipole nano-antenna can achieve an intense and circularly-polarized optical spot sized smaller than the diffraction-limit of incident light. Amplitude-ratio and phase-difference between field components are compared for linearly and circularly polarized optical spots beyond the diffraction limit. In addition, various antenna configurations are investigated to achieve light localization, circular polarization, and intensity enhancement.
3:00 PM - O21.3
Near-field Characterization of a Metallic UV Nanoantenna.
Liangcheng Zhou 1 , Qiaoqiang Gan 2 , Filbert Bartoli 2 , Volkmar Dierolf 1
1 Physics, Lehigh University, Bethlehem, Pennsylvania, United States, 2 ECE, Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractStudy of Ultraviolet Surface Plasmon Polariton (UV-SPP) is of special interest because of UV light’s wide applications in both civil and military industries. It has previously been shown that a UV-NSOM is capable of imaging UV-SPP modes with a sub-diffraction-limit resolution. In this work, we report a direct near-field imaging of metallic optical nanoantennas designed for enhancing and localizing UV light. A strong UV hot spot was observed at the antenna gap because of the surface plasmon resonance. The relationship of optical field enhancement and antenna size is discussed using both numerical simulations and NSOM experiments. FDTD calculations predicted that in UV domain there exists a resonance behavior as a function of antenna size. We experimentally proved such effect and it shows a good agreement with our simulations results. Direct reading of optical field is crucial to design a UV nanoantenna with maximum performance. A sub-diffraction-limit UV hot spot has profound impact on the research for novel photonic applications in the UV domain.
3:15 PM - O21.4
Photo-Electron Emission Microscopy of Gold-Black IR-Absorbing Films.
Robert Peale 1 , Justin Cleary 1 , Kenneth Beck 2 , Alan Joly 2 , Wayne Hess 2 , Christopher Fredricksen 3 , Oliver Edwards 3
1 Physics, University of Central Florida, Orlando, Florida, United States, 2 EMSL, Pacific Northwest Nat Lab, Richland, Washington, United States, 3 , Zyberwear, Inc., Ocoee, Florida, United States
Show AbstractNano-structured metals have significantly different optical response than do bulk metals, with plasmon absorption resonances appearing when the wavelength significantly exceeds characteristic particle dimensions. Metal-blacks are nano-structured conducting films that have been widely investigated as broad band absorbers of infrared radiation for bolometric applications. These films feature a broad range of characteristic length scales, so that one expects plasmon excitation over a broad range of wavelengths. Systematic study of plasmons in such films has been difficult in the absence of sharp absorption resonances for light which interrogates all surface length scales simultaneously. This paper reports a study of plasmons in gold-black films by Photo-Electron Emission Microscopy (PEEM), which maps the two-dimensional distribution of photoelectrons emitted from a surface. Excitation wavelengths of 400 or 800 nm rule out the possibility of single-photon photoemission. Electrons are emitted where excited plasmon modes relax non-radiatively, especially at positions with strong resonances. A range of gold- black samples were prepared in a thermal evaporator on silicon substrates during a two-level full factorial optimization program to maximize IR absorption and adhesion. Variables included sample temperature, inert gas pressure, boat current, and saturation by polymer vapors, giving a range of samples that were characterized for absorbance at 10 and 100 micron wavelengths by Fourier spectroscopy and for morphology by Scanning Electron Microscopy. Near-field mapping using photoemission electron microscopy (PEEM) reveals plasmon standing-wave patterns or “hot spots” centers, the distributions of which are correlated with IR absorbance and morphology.