9:00 PM - NT1.6.04
Efficient Photo-Reduction of Bi-Carbonate to Formate Catalyzed by TiO2 Nanocatalysts in the Presence of Ag Nanoparticles- A Different Mechanism
Hanqing Pan 1,Alynna Do 1,Alexzander Steiniger 1,Michael Heagy 1,Sanchari Chowdhury 1
1 New Mexico Tech Socorro United States,
Show AbstractIn this study, a new CO2 utilization strategy is developed via the hydrogenation of CO2 derived bicarbonate to produce value-added chemicals such as formate. A high yield of formate (production rate 160 micromol/gm TiO2.hr.), was achieved after reducing sodium bicarbonate in glycerol–water solution at room temperature with the TiO2 nano-catalyst (
9:00 PM - NT1.6.05
Strong Plexcitonic Coupling between Metallic Nanoparticles and Fluorophores for Bio-Sensing Applications
Andrea Rodarte 1,Andrea Tao 1
1 University of California, San Diego La Jolla United States,
Show AbstractMetallic nanostructures can be paired with fluorescent molecules or nanoparticles in order to create a plexcitonic device in which the localized surface plasmon resonance (LSPR) of the metallic nanoparticle couples with the exciton of a fluorescent material. Many applications have been demonstrated in which the LSPR of the metallic nanoparticle is perturbed by the presence of the fluorescent molecule. This interaction is considered weak coupling between the particles. We investigate the strong coupling regime in which the coupling between the exciton and plasmonic cavity result in two hybrid energy states.
A donor/acceptor pair of plasmonic nanoparticle/fluorophore is designed so that the localized surface plasmon resonance (LSPR) band of the plasmonic nanoparticle and the absorption band of the fluorophore overlap. Acceptors are then conjugated to the plasmonic nanoparticles via a chemical linker molecule. When the plasmon and exciton couple we observe a hybrid state where the extinction of the hybrid system is significantly changed, showing two split peaks. We investigate the dependence of donor/acceptor separation distance on coupling as well as the spectral overlap by varying the LSPR of the donor nanoparticles. The versatility of these donor/acceptor pairs make them prime candidates for new solid state optical bio-sensors.
9:00 PM - NT1.6.06
Characterization of InN-In0.25Ga0.75N Quantum Well Laser with In0.4Al0.6N Layers for 1300 nm Band
Md. Mobarak Polash 2,Kamruzzaman Khan 1
2 Electrical and Electronic Engineering (EEE) University of Asia Pacific (UAP) Dhaka Bangladesh,1 Electrical Engineering amp; Computer Science (EECS) University of Toledo Toledo United States
Show AbstractGroup-III nitrides have recently opened the door for devices like lasers and light-emitting diodes (LEDs), power electronics and high frequency electronic devices with exciting performances. Nitride lasers and LEDs have higher lifetimes than previously used II-VI devices. Quite recently nitride quantum wells are studied in the spectral range over 1100nm due to the prospect of their applications in optical communication. For optical communication, 1330nm and 1550nm wavelengths are most important for short distance and long distance communication respectively. At 1330nm, dispersion of a signal is lowest when at 1550nm path loss of a signal is the lowest. As a result, III-nitride semiconductors and their alloys are attracting much interest for optoelectronic devices particularly at around 1300nm band. For designing nitride semiconductor lasers in 1300nm band, generally intersubband optoelectronic devices are studied due to the large conduction band offset of the III-nitride heterostructures. In this range, design of interband structures are hardly proposed in recent works. For attaining these wavelength band, InN has been proposed as well material while In0.25Ga0.75N as barrier material. In0.4Al0.6N has been used as separate confinement heterostructure (SCH) to provide better optical and carrier confinement in the active region. For the analysis, the calculation of the band structures and wave functions has been performed by using a self-consistent model where Schrodinger equation has been solved with Poisson’s equation. For conduction band calculation, Schrodinger equation has been formed with single-band Hamiltonian with effective mass approximation and parabolic band nature consideration. Valence band Hamiltonian has been formed with 6-band k.p formalism with valence band mixing effect, strain effect and polarization effect. Analysis of optical properties including interband momentum matrix elements, spontaneous emission spectrum and optical gain have been carried out after solving the electronic properties of the structure. In previous works, GaN layer has been suggested instead of InAlN layer to attain the communication wavelength. GaN layer introduced a significant strain in well layer which make the structure less suitable for fabrication. Using InAlN layer reduces the strain in well region. Characterization has been performed for 12Å InN QW with 17Å In0.25Ga0.75N barrier. Amount of the compressive strain is 7.33% and the internal electric field is -9.74 MVcm-1 in well layer. C1-HH1, C1-LH1, C2-HH1 and C2-LH1 are the most dominant transitions which made the structure TE polarized. At 3×1019 cm−3 carrier density, the spontaneous emission spectrum gives peak amplitude of 4×1027 s−1cm−3eV−1 at 1308.6nm and the peak optical gain of 251.63 cm−1 occurs at 1336.7nm. At 6×1019 cm−3, the peak amplitude of spontaneous emission spectrum of 9.89×1027 s−1cm−3eV−1 occurs at 1301.7nm and the peak optical gain of 6850.65 cm−1 occurs at 1308.6nm wavelength.
9:00 PM - NT1.6.07
Stable and Highly Loaded CdSe/Cd1-xZnxSe1-ySy Crosslinked Quantum Dot Films with High Gain in the Quasi-Continuous Wave Region
Chun Hao Lin 1,Evan Lafalce 2,Jaehan Jung 1,Marcus Smith 1,Sidney Malak 1,Zhiqun Lin 1,Z. Vardeny 2,Vladimir Tsukruk 1
1 Materials Science and Engineering Georgia Institute of Technology Atlanta United States,2 Physics and Astronomy University of UTAH Salt Lake City United States
Show AbstractThis work demonstrates an effective ligand modification approach that can increase the net gain value of CdSe/Cd1-xZnxSe1-ySy quantum dot (QD) films to 500±100 cm-1, which is many fold higher than values typically reported in literature for cast Cd based QD films, while preserving the photoluminescence stability. Two strategies were implemented to improve the gain performance and achieve high QD loading, including the replacement of the long ligand oleic acid with the short ligand butylamine, and the appropriate selection of a stabilizing bifunctional crosslinker (1,7 diaminoheptane) that has much higher melting and boiling point as well as the lower vapor pressure than those of butylamine. Results indicate that a higher QD loading of the film increases the net gain value significantly while the thermodynamic properties of the ligand are crucial to maintain the gain performance. In addition, we demonstrate free-floating crosslinked QD films on the original solvent used to dissolve the QDs, indicating the crosslinked QD film is much more chemically and mechanically stable than the conventional cast QD film. The high net gain and improved chemical and mechanical stability make these films promising candidates for the fabrication of new photonic systems like parity-time symmetric devices that require stable net gain, an ability to control the ratio between gain and loss, and resilience to the environment.
9:00 PM - NT1.6.08
Dynamic Radiative Thermal Management with Switchable Vanadium Dioxide Based Fabry-Perot Thermal Emitters
Sydney Taylor 1,Yue Yang 1,Liping Wang 1
1 SEMTE Arizona State University Tempe United States,
Show AbstractRadiative cooling and heating are topics of recent interest due to their applications in energy conservation, solar power, and thermal management. Thermal emitters can reduce the surface temperature by selectively radiating thermal energy in the mid-infrared region through the atmospheric window into outer space. Radiative cooling is desired during the daytime when the surface temperature is high but should be minimized during the night when there is no solar heating to prevent the temperature from dropping significantly. Therefore this work seeks to develop a dynamic thermal emitter whose emissivity can respond to temperature changes. A well-performing thermal emitter should be highly reflective in the mid-infrared region when its temperature is lower than the desired temperature, and should exhibit large infrared emissivity when the temperature is higher.
Vanadium dioxide (VO2) is an insulator-to-metal phase transition material, which undergoes a dramatic shift in optical properties during phase transition. This study considers an asymmetric Fabry-Perot cavity with a lossless dielectric spacer sandwiched between a VO2 thin film and an opaque aluminum substrate. Below the phase transition temperature (341 K), the VO2 is insulating and the proposed structure is highly reflective with low emissivity in the mid-infrared region. When the temperature increases beyond 341 K the VO2 top layer becomes metallic and forms a Fabry-Perot resonator to exhibit high emissivity in a broad spectral range around 10 μm. As a result, the surface could cool down due to enhanced radiative cooling with much higher thermal emission loss. The large contrast in the emissivity of the dynamic VO2-based thermal emitter could lead to smaller temperature variations between daytime and nighttime, thus saving energy in cooling and heating.
We have developed a uniaxial transfer matrix method to calculate the radiative properties of VO2 multilayer thin films as a function of temperature. The optical constants of VO2 during phase transition are modelled via Bruggeman effective medium theory. The preliminary results show that the emissive power is increased by a factor of nearly 7 when VO2 changes from insulator to metal between 341 K and 345 K. At a wavelength of 10 μm, the emissivity of the dynamic radiative thermal emitter is about unity with metallic VO2 but as small as 0.1 with insulating VO2. The radiative properties are shown to be insensitive to incidence angle. Fabrication of the designed multilayer structures is in progress, and temperature-dependent spectrometric measurements will be carried out to experimentally verify the dynamic infrared emissivity at different VO2 phases. The ability of the emitter to self-regulate its temperature near the phase transition temperature will also be investigated. The proposed structure could be useful for applications such as building cooling and spacecraft thermal management.
9:00 PM - NT1.6.09
Near-Field Thermal Radiation between Dual Uniaxial Electromagnetic Metamaterials
Jui-Yung Chang 1,Yue Yang 1,Liping Wang 1
1 Arizona State University Tempe United States,
Show AbstractRecently, near-field thermal radiation has attracted much attention since it can exceed the Planck blackbody limit through the coupling of evanescent waves. Numerous studies have been conducted in near-field radiation during the past few years for applications such as thermophotovoltaic and thermal management. Among these researches, the magnetic responses which correspond to s polarized waves are mostly neglected due to the non-magnetic behavior (i.e., permeability μ = 1) of naturally existing materials. However, magnetic resonance has been demonstrated in nanostructured metamaterials to selectively control far-field optical and radiative properties. However, the effect of magnetic response in near-field radiative transfer is little studied and understood.
In this work, the near-field radiative heat transfer between two semi-infinite dual uniaxial electromagnetic metamaterials is theoretically analyzed. The considered metamaterials exhibit both the magnetic and electrical responses with homogeneous uniaxial permeability and permittivity. Hypothesized homogeneous uniaxial properties are chosen over isotropic properties since isotropic magnetic materials do not exist naturally and nanostructured metamaterials can usually be homogenized to uniaxial media via effective medium theory. The near-field radiative heat transfer is calculated by the fluctuational electrodynamics at both s and p polarized waves. Besides the mechanisms such as electrical hyperbolic mode, electrical surface polariton, and epsilon-near-pole which can only occur for p polarized waves, new mechanisms such as magnetic hyperbolic mode, magnetic surface polariton, and mu-near-pole with s polarized waves, will be thoroughly investigated by the contour of transmission coefficient and spectral heat flux. Moreover, the total heat fluxes at different wave polarizations will be studied under different vacuum gap distances as well. The fundamental understandings and insights obtained here could facilitate and enrich the near-field thermal radiation applications through the resonance mechanisms at both s and p polarized waves.
9:00 PM - NT1.6.10
Fe Contacts to GaAs Nanowires
Mingze Yang 1,Ali Darbandi 1,Simon Watkins 1,Karen Kavanagh 1
1 Physics Simon Fraser University Burnaby Canada,
Show AbstractEpitaxial Fe contacts have been selectively fabricated onto the top half of free-standing, Te-doped ((13 ± 7) x 1016 cm-3) (111) GaAs nanowires (NWs) via electrodeposition. The NWs were grown via Au catalyzed metal-organic chemical vapour deposition (MOCVD) using tertiarybutylarsine (TBAs) and trimethylgallium (TMGa) as precursors. The doping concentration was determined using direct probing of the Au/GaAs Schottky interface using a W probe in situ within a scanning electron microscope (SEM). A current density of 0.1 mA/mm2 was used in the electrodeposition, resulting in the growth rate of Fe of 0.8 ± 0.3 nm/s as measured by scanning transmission electron microscopy (STEM). Top views of the Fe films via both SEM and TEM showed them to be hexagonal, even though the shape of the underlying GaAs NWs was found to be triangular. The deposited Fe was shown to be (110) oriented via TEM, epitaxially aligned with the (110) GaAs NW side facets. An insulating polymer (SU-8) was used to fill in between the nanowires preventing deposition directly onto the GaAs substrate, which enabled the measurement of electrical transport through individual wires. Plasma cleaning was used for 2 minutes to remove the residual SU-8 before the electrodeposition, which damaged the nanowire surface. This resulted in a broad variation (4 orders of magnitude) in the current at high bias (> 1 V) indicative in changes in the NW bulk resistivity. But the experimental current-voltage characteristics were highly rectifying with a linear log-current voltage range of 7 orders of magnitude. Combining these results with transport simulations the effective three-dimensional contact area was determined giving an average Fe-GaAs diode barrier height of 0.64 ± 0.02 eV (ideality factor 1.48 ± 0.02).
9:00 PM - NT1.6.11
Electron Beam Induced Current Measurement of Carrier Diffusion Lengths in GaAs Nanowires Studied by the Nanoprobe Method
Ali Darbandi 1,Simon Watkins 1
1 Simon Fraser Univ Burnaby Canada,
Show AbstractIn the last decade there have been numerous attempts to develop nanowire-based semiconductor devices including solar cells, lasers and light emitting diodes. However there are still challenges inherent to NW structures that are not fully understood. This includes the effect and control of the NW sidewall surface states. Due to the large surface-to-volume ratio in NWs the surface states play a major role in limiting the electronic properties of NW devices. The latter translates into the reduction of the minority carrier diffusion length (Ld) in semiconductor NWs since the surface states act as recombination sites.
Here we present the study of electron and hole diffusion lengths in p-type and n-type GaAs NWs using the electron beam induced current (EBIC) method. EBIC measurements were carried out on free standing NWs using a nanoprobe technique implemented inside a scanning electron microscope, without the need for lithographic processing. NWs were grown by the vapor-liquid-solid method using metalorganic precursors at at a growth temperature of 400°C, and using diethyltellurium and diethylzinc as the n- and p-type dopants. Two types of structures were fabricated: (1) single carrier type structures where the depletion region under the Au catalyst particle was used to collect minority carriers, and (2) n-p axial homojunction structures where the EBIC signal was measured separately on either side of the junction. It was observed that for both types of minority carriers Ld reaches a maximum of approximately 170 nm for NWs with radius greater than 400 nm. The obtained results are lower than the reported Ld for GaAs thin films with values larger than 1 µm. Also we observed that the diffusion lengths strongly decrease with NW diameter below 400 nm, indicating the dominant effect of surface states at smaller diameters. In order to improve the electrical properties of GaAs NWs an InGaP shell was grown radially around the GaAs core. The InGaP shell enhances the minority carrier lifetime somewhat, however this process needs further optimization. The key finding of this work is the ability of the nanoprobe technique to provide rapid characterization of an ensemble of NWs without lithographic processing in order to screen potential passivation methods rapidly and accurately.
9:00 PM - NT1.6.12
Enhancement of Sensitivity of the Solution-Phase Localized Surface Plasmon by a Nanostructured Substrate
Shengjie Zhai 1,Hui Zhao 1
1 Dept. of Mechanical Engineering University of Nevada, Las Vegas Las Vegas United States,
Show AbstractThere is a need to design a sensitive and low-cost plasmonic biosensing technique which own biocompatibility and optical stability to detect the low level of analytes in biological samples. In this study, we describe a simple and inexpensive method to enhance the sensitivity or improve the detection limit of solution-phase localized surface plasmon (LSPR) sensors of metallic nanoparticles, which has been entrapped in a thin silicon shells and can be successfully used as versatile plasmonic probe for molecular sensing in solution phase. Furthermore, the substrate surface that supports the LSPR detection contains metallic nanostructures which are replicated from commercial optic disks via the standard soft lithography. As the proof of the concept, by mixing BSA molecules with nanoparticle solution, we demonstrate that the wavelength shift due to the absorption of BSA molecules on nanoparticle surfaces is amplified by more than an order of magnitude in comparison to that over a smooth flat surface. It would be very attractive for investigation of analytes in biological fluids.
9:00 PM - NT1.6.13
Oxidative Photocatalysis at TiO2 Aerogels Driven by Surface Plasmon Resonance of Non–Precious Metal Nanoparticles
Jeremy Pietron 1,Paul DeSario 1,Todd Brintlinger 2,Rhonda Stroud 2,Debra Rolison 1
1 Chemistry Division Naval Research Laboratory Washington United States,2 Material Science amp; Technology Division Naval Research Laboratory Washington United States
Show AbstractIn the present study, we describe the incorporation of surface plasmon resonance (SPR)-active, non–precious metal nanoparticles into TiO2 aerogels. Titanium dioxide (TiO2) aerogels feature inherent design flexibilty that make them superior design platforms for composite photocatalysts. The sol–gel-derived nanoscale titania networks of the aerogel act as an interconnected system of covalently bonded nanowires with readily modifiable structure, enabling efficient transfer of electrons to reactive catalytic sites.1 Additionally, plasmonic metal nanoparticulate guests can be readily incorporated into the mesoporous host, sensitizing the metal-modified aerogels to visible light and enabling visible light–driven photocatalytic oxidation of water and alcohols.2,3 The composite aerogels feature clear optical SPR signatures, and drive the photoelectrochemical oxidation of methanol in aqeuous base. We will also describe some of the specific advantages inherent to TiO2 aerogels for supporting plasmonic nanoparticles derived from non-precious metals.
This work was supported by the Office of Naval Research.
References:
1. P. A. Desario, J. J. Pietron et al., J. Phys. Chem. C 119 (2015) 17529
2. P. A. Desario, J. J. Pietron et al., Nanoscale 5 (2013) 8073.
3. D. A. Panayotov, P. A. DeSario et al., J. Phys. Chem. C 117 (2013) 15035.
9:00 PM - NT1.6.14
Probing Radiative Heat Transfer in the Extreme Near-Field
Bai Song 1
1 University of Michigan, Ann Arbor Ann Arbor United States,
Show AbstractBai Song1, Kyeongtae Kim1, Víctor Fernández-Hurtado2, Woochul Lee1, Wonho Jeong1, Longji Cui1,
Dakotah Thompson1, Johannes Feist2, M. T. Homer Reid3, Francisco J. Garcia Vidal2, 4,
Juan Carlos Cuevas2, Edgar Meyhofer1 and Pramod Reddy1, 5
1Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
2Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, 28049, Spain
3Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
4Donostia International Physics Center (DIPC), Donostia/San Sebastián, 20018, Spain
5Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
Fluctuational electrodynamics computations have long predicted dramatic enhancements of radiative energy flow across nanometer gaps. Such phenomenon is expected to be of great importance to diverse novel technologies including near-field thermophotovoltaics and lithography. While experimental advances have enabled exploration of near-field radiative heat transfer in gaps as small as 20 to 30 nm, quantitative analysis in the extreme near-field (<10 nm) has been greatly limited by a range of challenges. Further, pioneering measurements reported results that differ from theoretical predictions by orders of magnitude. In our study1, we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with novel suspended microdevices capable of periodic temperature modulation, to systematically measure radiative heat transfer in gaps as small as 2 nm. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica–silica, silicon nitride–silicon nitride and gold–gold surfaces to reveal dramatic, gap size-dependent enhancements of radiative heat transfer. Furthermore, our boundary-element-method calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results providing unambiguous evidence that confirms the validity of this theory for modeling radiative heat transfer in the extreme near-field. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale thermal radiative heat transfer.
[1] K. Kim*, B. Song*, V. Fernández-Hurtado*, W. Lee, W. Jeong, L. Cui, D. Thompson, J. Feist, M.T.H. Reid, F. J. García-Vidal, J. C. Cuevas, E. Meyhofer and P. Reddy, Radiative heat transfer in the extreme near-field, Nature, In Press.
9:00 PM - NT1.6.15
Decoding Supercrystal Structure by "Supercrystallography"
Ruipeng Li 1,Zhongwu Wang 1
1 Cornell Univ Ithaca United States,
Show AbstractNanocrystals (NCs) behave like atoms, functionalize with surface-coating molecules, and self-assemble into periodically ordered superlattice (SL). Recent advances on synthesis and assembly of NCs have been witnessed by fast growth of NC-assembled superlattices, made up of single, binary or ternary components over control of NC size, shape and composition. However, programmable design of supercrystals with expected structure for desirable applications is still constrained by limited understanding NC−ligand interactions in solvent-mediated NC assembly processes. Meanwhile, low penetration of electron beam used for structural characterization in electron microscopy provides information of only very thin layers, which differs significantly from large assembled samples.
We have grown large single supercrystals and developed ‘supercrystallography’ as a synchrotron-based Small/Wide Angle X-ray Scattering (SAXS/WAXS) approach for single supercrystal to overcome the low in-depth penetrating ability and resolve the structure of nanocrystal assembly from atomic to mesoscale. We collected a series of SAXS/WAXS images of supercrystal, which allow us to accurately reconstruct the shape orientations of NCs at various crystallographic sites and explore the inter-particle packing configurations. In situ SAXS measurements under high pressure offer additional insights into surface ligand density and nature of ligand–NC interactions, as well as the correlations between strain and lattice distortion, which present a primary image of various superlattice polymorphs to elucidate the superlattice transformations and associated developing pathways. These results provide detailed structural information towards controlled design and efficient materials-processing for fabrication of nano-based functional materials with tailored structures and desired properties
9:00 PM - NT1.6.16
Effect of Nanostructure Embedding on the Light Matter Interactions at Metal/Polymer Interface
Binxing Yu 3,Martin Vacha 2,Deirdre O'Carroll 3
3 Department of Chemistry and Chemical Biology Rutgers Univ. Piscataway United States,2 Tokyo Institute of Technology Tokyo Japan1 Department of Materials Science amp; Engineering Rutgers Univ Piscataway United States,3 Department of Chemistry and Chemical Biology Rutgers Univ. Piscataway United States
Show AbstractIt is well known that exciton quenching can be significant at metal-semiconductor spacings of a few nanometers due to very efficient dipole-dipole energy transfer between the conjugated polymer materials and the metal. However, certain nanoantenna designs can mitigate the effects of dipole-dipole interactions by having high radiative nanoantenna efficiency and a large local density of optical states in the nanoantenna near field. Optical response in a structure with ultra-thin conjugated polymer film sandwiched between metal nanostructure and metal thin film was identified and manipulated. Single-particle dark-field scattering spectra showed distinct resonance features assigned to four different modes: a horizontal image dipole coupling mode, a vertical image dipole coupling mode and horizontal and vertical coupling modes between localized surface plasmon resonances (LSPRs) and surface plasmon polariton (SPPs). We found that Au nanostructure with sufficient size can result in partial embedding when positioned on top of conjugated thin films such as P3HT and MEHPPV. Simultaneous dark-field and photoluminescence measurements was conducted to investigate whether the significantly enhanced electric fields in this “sphere on plane” system can outpace the metal quenching and result in the enhancement of emission efficiency in the embedded system. Through multi-beam defocused imaging, a full 3D orientation of the scattering dipole moment can be extracted. Compared with polymers that exhibit no embedding, we found that not only does embedding situation show a more complex electromagnetic interaction, but also proved that the strong field enhancement in the gap region not only compensates the quenching of emission brought by the metallic ground plane, but also increases the emission efficiency.
9:00 PM - NT1.6.17
A Kinetic Investigation of Charge Transfer Characteristics of Hyperbolic Metamaterials
Olivia Penrose 1,Carl Bonner 1
1 Center for Materials Research Norfolk State University Norfolk United States,
Show AbstractThe motivation of the research is to understand the quantum phenomena of charge transfer characteristics of hyperbolic metamaterials, specifically materials in which the dielectric constant is different in different directions and negative in one direction. The metamaterials are alternating layers of Au and MgF2 with a metal-like negative dielectric constant perpendicular to the stack and a positive dielectric constant in the plane of the stack. The research will observe the enhancement kinetic rate of electron transfer, which cannot be fully explained by the distance dependence of Marcus theory.
We have used Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) to study the rate of electron transfer (ET) at the surface of the electrode in our electrochemical cell. Our system consists of a SCE reference electrode, a Pt counter electrode, and Au on In-doped SnO2 (ITO) working electrode with a range of materials between the ITO and exterior Au surface. The redox couple is K3Fe(CN)6 , a stable, reversible, well characterized one-electron redox couple. The interior materials in the working electrode included, thick (~200 nm) and thin (25 nm) Au layers, thick and thin MgF2 layers, a 20 nm Au - 20 nm alkanethiol self-assembled monolayer (SAM) as well as multilayer stacks of alternating Au-MgF2, which formed our metamaterial.
As expected, the electron transfer rates of our redox couple on bare Au, Au layers coated with self-assembled monolayers (SAM) followed the usual distance dependence. Further, the ET rate for layer of MgF2 were slower than our SAM in accordance with the difference in the dielectric constants of MgF2 and the SAM. The observed ET rate for our electrode with the metamaterial was competitive with the thin and thick Au layers. We compare our rates to the variable directional dielectric constants. CV data and EIS measurements are used to understand the mechanism of reduction of the redox couple and to extrapolate ET kinetic and carrier diffusion coefficients.
9:00 PM - NT1.6.18
Photothermal Response of Gold Nanorods Prepared in the Presence of Salicylic Acid Derivatives
Iris Guo 1,Michael Wang 1,Idah Pekcevik 1,Byron Gates 1
1 Simon Fraser University Burnaby Canada,
Show AbstractAnisotropic metal plasmonic nanomaterials, such as gold nanorods, are attractive for a variety of applications that utilize localized heating effects that result from photothermal processes. Through photothermal processes, the gold nanorods can be used as a platform to trigger small molecule release and/or localized cell death. These nanomaterials have an advantage that their localized surface plasmon resonance properties are coupled to both their shape and aspect ratio; tuning the physical features of gold nanorods during their synthesis is a simple means to control their optical properties and, thus, photothermal efficiencies over a variety of electromagnetic energies. The second component of utilizing gold nanorods as vehicles for photothermal triggered events is to understand (and control) the evolution of their size and shape under photothermal conditions. High photon fluxes during photothermal processes are known to induce structural and morphological changes to gold nanorods, but these changes are dependent on a number of factors that include the surface chemistry of these materials. Understanding the potential instability of gold nanorods is vital to retain their plasmonic properties for prolonged or repeated use in photothermally triggered processes. The study discussed here introduces the photothermal response of gold nanorods prepared by a modified seed mediated synthesis that uses a mixture of surfactants to control and direct the growth of the nanorods. One class of surfactants, salicylic acid derivatives, have been recently introduced for high yield, controlled synthesis of gold nanorods, and their photothermal response will be discussed based on the results of a combined analysis from extinction spectroscopy, dynamic light scattering, and electron microscopy techniques (e.g., STEM, EDS, and HR-TEM).
9:00 PM - NT1.6.19
Highly Uniform Self-Assembled Metasurfaces for Enhanced Emission
Matthew Rozin 1,Eric Brown 1,Andrea Tao 1
1 NanoEngineering Univ of California-San Diego San Diego United States,
Show AbstractTowards realization of nanoscale opto-electronic devices, nanocube-on-metal metasurfaces show particular promise in large spontaneous emission rate and fluorescence enhancement. Previously reported emission enhancement using film-coupled nanocubes varies widely based on the degree of spatial control of the emitter in the nanocube cavity. Here, we demonstrate an optimized structure where a dense-packed layer of CdSe/ZnS quantum dots is precisely positioned in the cavity formed by the film-coupled Ag nanocubes. The quantum dot layer—electromagnetically isolated from the metal film and nanocubes—provides a uniform spacer layer for maintaining a precise nanocube-film gap. We observe uniform fluorescent and radiative rate enhancement of the quantum dots as a function of the plasmon gap-mode resonance.
9:00 PM - NT1.6.20
Solar Steam Generation by Concentrating Heat
Fatih Canbazoglu 1,Prabhakar Bandaru 1
1 UCSD La Jolla United States,
Show AbstractRecent solar steam generation technologies require high solar concentration to be able to heat the bulk liquid to high temperatures which has drawbacks such as high optical loss, surface heat loss and high system cost. We are working on a one layer porous structure which stays on top of the water and enhance the evaporation rate and solar-thermal efficiencies rapidly. The main characteristic of the structure is localizing heat in the top region of the water while wicking the water through the porous structure. Four main characteristic of the structure helps to have the heat localization and high efficiencies which are high solar absorption, insulating behaviour of the porous structure to keep the heat on the top hot region, hydrophilic surfaces to promote wicking and interconnected porosity for fluid flow movement through the structure. We achieved almost four times more steam generation with carbon structure (1.56 kg/m2) than pure water case ( 0.392 kg/m2) under 1 Sun ( 1000W/m2) situation. Right now, we are working on new materials to improve the efficiencies of the system. This new way of comparatively cheap steam generation will have many applications.
9:00 PM - NT1.6.21
High-Density 2D Homo- and Hetero- Plasmonic Dimers with Universal sub-10-nm Gaps
Mingliang Zhang 3,Nicolas Large 4,Ai Leen Koh 3,Yang Cao 4,Alejandro Manjavacas 4,Robert Sinclair 3,Peter Nordlander 4,Shan Wang 3
1 University of Pennsylvania Philadelphia United States,3 Stanford University Stanford United States,2 Northwestern University Evanston United States,4 Rice University Houston United States3 Stanford University Stanford United States4 Rice University Houston United States
Show AbstractFabrication of high-density plasmonic dimers on a large (wafer) scale is crucial for applications in surface-enhanced spectroscopy, bio- and molecular sensing, and optoelectronics. Here, we present an experimental approach based on nanoimprint lithography and shadow evaporation that allows for the fabrication of high-density, large-scale homo- (Au�Au and Ag�Ag) and hetero- (Au�Ag) dimer substrates with precise and consistent sub-10-nm gaps. We performed scanning electron, scanning transmission electron, and atomic force microscopy studies along with a complete electron energy-loss spectroscopy (EELS) characterization. We observed distinct plasmonic modes on these dimers, which are well interpreted by finitedifference time-domain (FDTD) and plasmon hybridization calculations.
9:00 PM - NT1.6.22
Azopolymer-Based Nanofabrication Method for Fluorescence-Enhancing Plasmonic Nanostructures
Ville Pale 1,Jorma Selin 1,Christoffer Kauppinen 1,Markku Sopanen 1,Ilkka Tittonen 1
1 Department of Micro and Nanosciences Aalto University Espoo Finland,
Show AbstractFluorescence-based measurement techniques are fundamentally limited in terms of performance by the intrinsic quantum yield of a fluorophore. The fluorescence emission of a fluorophore can be significantly improved with radiative decay engineering enabled by metallic nanostructures. Especially, periodic arrays of metallic nanostructures have the advantage of exhibiting a strong and prescribed optical response, which is beneficial for improving sensitivity in surface enhanced spectroscopic techniques
Usually, these arrays are fabricated using electron beam lithography (EBL), in which the size of the array typically lies in the order of 100 x 100 µm2. Due to its serial nature, EBL is not particularly suitable for high-throughput, large-scale fabrication. In this work we present a variant of interfencence lithographic method to create periodic plasmonic nanoparticle arrays for fluorescence enhancement that utilizes azobenzene-containing polymers (azopolymers) as the resist material. This approach allows us to circumvent the generation of a standing wave pattern within the resist when performing the exposure on a reflective surface and substantially mitigates the processing requirements. Hence, this enables a cost-effective and large-scale fabrication scheme for plasmonic arrays with tunable response.
We demonstrate the creation of periodic arrays of symmetrical metallic nanostructures that exhibit a good long-range order. Furthermore, the dimensions of the array and the structures can be tuned by changing the exposure or process parameters. The optical properties of the fabricated structures was studied both experimentally and theoretically. The fluorescence enhancement performance was verified by using Rhodamine 6G and Cascade Blue as the fluorophores for blue and green wavelength regions. We expect that this fabrication approach could be advantageous for other application areas of plasmonics, such as SERS or sensing.
9:00 PM - NT1.6.23
pH Imaging of Multiphase Systems in Microfluidic Channels Using an Embedded Silica-Shell Nanoparticle with Plasmonic Enhancement
Mazeyar Gashti 1,Jeremie Asselin 1,Denis Boudreau 1,Jesse Greener 1
1 Chemistry Laval University Québec Canada,
Show AbstractWe demonstrate a nanoparticle-based pH sensing surface embedded in a microfluidic device for in situ chemical mapping of heterogeneous systems relevant to chemical biology and environmental science. A planar glass substrate is covalently grafted with core-shell nanoparticles, comprised of a spherical silver core covered by a pH-sensitive fluorescent indicator encased in a uniform silica shell. By allowing the conducting electrons in the metal core to couple to the fluorophores, this nanoarchitecture provides improved brightness and robustness with regards to photobleaching. In addition, the immobilized fluorophores within the silica shell are protected from shear-force driven detachment and diffusion into the surrounding media. The resulting sensing system was used for quantitative, spatially-resolved pH measurements in multiphase systems at high frame rates with standard epifluorescence microscopes. A variety of validation and proof-of-concept measurements were conducted. These included spatially resolved pH mapping of co-flowing streams, monitoring proton diffusion across flowing liquid-liquid interfaces, monitoring the acidification of an aqueous environment by CO2 gas bubbles and observing time- and spatially-dependent extracellular acidification by oral biofilms.
9:00 PM - NT1.6.24
Strong Chiroptical Response of Biomolecule-Coupled Plasmonic Nanostructure: Ultrasensitive Detection of Chiral Molecules
Hyo-Yong Ahn 1,Hye-Eun Lee 1,Ki Tae Nam 1
1 Material Science and Engineering Seoul National University Seoul Korea (the Republic of),
Show AbstractThe chirality of organic and biomolecules is exhibited by molecular structures, which is one of the crucial determinants for many biological reactions. Though diverse methods are used to probe the chirality of molecules, chiroptical spectroscopic methods such as optical rotation dispersion(ORD), circular dichroism(CD) and Raman optical activity(ROA) are mainly used to analyze the chirality and conformational information of molecules. However, the optical transitions of molecules are generally in ultraviolet(UV) region, and the intensity of their chiroptical signal is very weak. To detect the chiroptical signal in practice, the amount of molecules is limited to microgram level. Meanwhile, noble metal nanostructure has strong absorption band in visible region, corresponding to localized surface plasmon resonance(LSPR) phenomenon, and plasmon resonance effect can be utilized to amplify molecular signals such as surface enhanced Raman scattering(SERS) and enhanced fluorescence. Recently it was theoretically and experimentally demonstrated that the coupling of plasmonic structure and chiral molecule can generate new plasmon induced chiroptical signal in visible range, which has enhanced intensity in comparison with weak molecular signal in UV region. Here we demonstrate strong chiroptical responses in plasmon resonance using various plasmonic nanostructures coupled with chiral molecules. Using nanofabrication techniques such as colloidal synthesis, nanosphere lithography and e-beam lithography, we fabricated novel plasmonic nanostructures including chiral and achiral geometries. Those nanostructures are coupled with various biomolecules such as amino acid, peptide assembly, protein and DNA, so we constructed combinations of achiral structure-chiral biomolecule and chiral structure-chiral biomolecules with different scale and directionality. Using those biomolecule-coupled plasmonic nanostructures, we observed strong chiroptical responses originated from interaction of biomolecule and plasmon at nanogram level. We expect that this research will provide ultrasensitive probing of chiral molecules and further understanding of plasmon induced chiroptical phenomenon.
9:00 PM - NT1.6.25
Brookite TiO2 Nanorods as Ideal Building Blocks for Photoelectrochemical Water Oxidation: Bulk versus Surface Plasmonic Decoration
Alberto Naldoni 1,Francesco Malara 1,Marta Mroz 2,Alessandro Beltram 3,Tersilla Virgili 2,Marcello Marelli 1,Tiziano Montini 3,Vladimiro Dal Santo 1,Paolo Fornasiero 3
1 CNR-Istituto di Scienze e Tecnologie Molecolari Milan Italy,2 Dipartimento di Fisica CNR - Istituto di Fotonica e Nanotecnologie (IFN) and Politecnico di Milano Milan Italy3 Dipartimento di Scienze Chimiche e Farmaceutiche e Unità di Ricerca ICCOM-CNR Università degli Studi di Trieste Trieste Italy
Show AbstractA promising strategy to extend the harvested solar light by TiO2 to the visible/NIR wavelength range consists in its sensitization with plasmonic metal nanostructures (e.g., Au). [1] By acting as an antenna that localizes the optical energy by localized surface plasmon resonance (LSPR), Au sensitizes TiO2 to light with energy below the bandgap generating additional charge carriers for water oxidation. [2,3] Moreover, plasmonic metallic centers can generate increased light absorption through radiative scattering. In order to build efficient plasmonic PEC devices, one of the key design issues to be still clearly defined is the effect of the location of plasmonic component with respect to both the semiconductor and the electrolyte. [4-6] In this contribution we show that brookite TiO2 nanorods are the ideal building blocks for addressing these unanswered questions on plasmonic geometry. [7] Through a precise control of Au nanoparticles deposition, we show that the bulk (TiO2/Au-bulk) versus preferential surface (TiO2/Au-surface) Au decoration generates profound difference in PEC activity and photoinduced charge separation processes occurring in the photoelectrodes.
Brookite nanorods photoanodes showed a maximum photocurrent of 0.14 mA/cm2 and a record onset potential of -0.2 V (RHE). Au-decorated samples showed no change in onset potential. However, the photocurrent of TiO2/Au-surface was almost doubled if compared to reference TiO2 and TiO2/Au-bulk. Electrochemical impedance measurements showed that TiO2/Au-surface had lower charge transfer resistance and higher donor density than both pure TiO2 and TiO2/Au-bulk. Femtosecond ultrafast pump-probe spectroscopy revealed that in both samples containing Au nanoparticles, plasmonic hot electrons injection occurred in ~150 fs. Most importantly, in TiO2/Au-bulk all excited carriers recombine on the same timescale of plasmonic injection, whereas in TiO2/Au-surface we detected two and four orders magnitude longer charge decay times (ps and ns). These results are in agreement with the photocurrent trend. When Au nanoparticles are homogeneously dispersed in the film of brookite nanocrystals (TiO2/Au-bulk), they act as recombination centres. Differently, if Au is preferentially deposited close to the electrode/electrolyte interface (TiO2/Au-surface) the plasmonic sensitization is effective providing extra charges for water oxidation.
[1] M .L. Brongersma et al. Nat Photonics 2015, 10, 25–34. [2] Y. C. et al. Nano Lett 2013, 13, 3817–23. [3] L. Amidani et al. Angew Chemie Int Ed 2015, 54, 5413–6. [4] E. Thimsen et al. Nano Lett 2011, 11, 35–43. [5] I. Thomann et al. Nano Lett 2011, 11, 3440–6. [6] Z. Zhan ACS Appl. Mater. Interfaces 2014, 6, 1139−44. [7] A. Beltram et al. Appl. Catal. A 2015, doi:10.1016/j.apcata.2015.09.022.
9:00 PM - NT1.6.26
Revealing Self-Induced InAlN Core-Shell Nanorod Formation Mechanism and Their Unique Optical Properties
Justinas Palisaitis 1,Ching-Lien Hsiao 1,Lars Hultman 1,Jens Birch 1,Per Persson 1
1 Linkoping University Linkoping Sweden,
Show AbstractSemiconductor materials fabricated in the form of nanorods (NRs) offer fascinating physical properties and engineering capabilities in future nanoscale functional units [1]. In particular, group-III nitride semiconductor NRs based on AlN, GaN, InN and their ternary alloys are attractive due to the widely tunable direct bandgap (0.64-6.2 eV), high crystal quality and improved light extraction efficiency. The implementation of heterostructures inside ternary NRs (e.g., core-shell InAlN) drastically extends their optical performance together with advantages of the 1D geometry. Recently, self-induced ternary nitride core-shell NRs have been demonstrated [2-4]. However, the understanding of the formation mechanism and optical properties remains debated.
We have examined the magnetron sputter expitaxy grown self-induced InAlN core-shell NR formation processs by means of transmission electron microscopy methods. The results show that the grown structure phase separates during the initial moments of deposition into AlN-rich (majority) and InN-rich islands. The islands possess polygonal shapes and are mainly c-axis oriented. The growth proceeds with densification and coalescences of the InN-rich islands, resulting in a base for the InN-rich NR cores with shape transformation to hexagonal. The AlN-rich shell formation around such early cores is observed at this stage. The matured core-shell structure grows axially and radially, eventually reaching a steady growth state which is dominated by the axial NR growth. To account for the present observations we consider a number of factors affecting the NRs evolution, including: adatom (In, Al, and N) surface kinetics (adsorption, desorption and surface diffusion), chemical potential of islands, surface energy, thermal stability, and incoming flux (shadowing effect). Herein we provide direct atomic scale experimental observations of core-shell NRs nucleation, coalescence and growth, through which we present a growth model.
In parallel, we explored the optical properties of self-induced InAlN core-shell NR. We will demonstrate how implementation of curved-lattice epitaxial growth (CLEG) [5] could be used for synthesizing chiral InAlN core-shell NRs and tailor their optical properties. CLEG growth induces curved lattice and composition grading along the lateral direction of NRs. The reflected lights exhibit very high degree of circular polarization of around 80%, indicating nearly circular polarization with opposite right- and left-handed polarization, respectively, from the two opposite chirality NR samples.
References:
[1] C. R. Eddy Jr., et al., J. Vac. Sci. Technol. A 31, 058501 (2013).
[2] C.-L. Hsiao, et al., Appl. Phys. Exp. 4, 115002 (2011).
[3] M. Gómez-Gómez, et al., Nanotechnology. 25, 075705 (2014).
[4] R. F. Webster, et al., Phys. Status Solidi C 11, 417–420 (2014).
[5] G. Z. Radnóczi et al., Phys. Stat. Sol. (a) 202, R76 (2005).
9:00 PM - NT1.6.27
Nickel Electrodeposition on Anodized Aluminum Oxide Films as Selective Absorbing Coating Made by AC Voltage with Variable Frequency
Samuel Santiago 2,Arturo Fernandez Madrigal 2,Julio Rodriguez Gonzalez 1,Eduardo Mercado Aguilar 1,Ogilver Teniza Garcia 1
1 Universidad Tecnologica de Huejotzingo Huejotzingo Mexico,2 Solar Materials UNAM Temixco Mexico,2 Solar Materials UNAM Temixco Mexico1 Universidad Tecnologica de Huejotzingo Huejotzingo Mexico
Show AbstractAnodized aluminum oxide films (Al2O3) on aluminum substrates 1050 (99.5% w Al) was impregnated with nickel (Al2O3-Ni) by electrodeposition technique with alternating current (AC) voltage with variable frequency. In this paper, we report the synthesis of Ni using the galvanostat mode, as well as some experimental variations in the frequency and intensity of AC voltage in order to optimize the amount of nickel in the oxide aluminum substrates. EDS, XRD, SEM and UV-VIS spectrophotometry techniques was used to analyses the atomic composition, structural morphology and optical properties of the samples. Additionally, an emissometer was used to measure the hemispherical thermal emissivity. Data values of the total reflectance for the visible solar spectrum (VIS) and near infrared (NIR) as a function of voltage and frequency for fixed times nickel impregnation were analyzed, several experiments were performed with in order to correlate these parameters with the nickel content in the bottom of the pores of the films and their optical properties. Absorptance values between 0.09 to 0,15 and emittance values of 0.09 to 0.15 were obtained, the pores of the films developed to 11 Vrms and 60 Hz are filled with nickel 30% by volume pore and optical properties αs= 0.83, ET(80oC) = 0.11 that make them good prospects for application in solar collectors.
9:00 PM - NT1.6.28
Aligned Epitaxial Titanium Nitride (TiN) and Titanium Oxynitirde (TiNO) Nanowires for Solar Energy and Optical Applications
Chandra Shekar Reddy Nannuri 1,Mayur Singh 1,Rahul Goud Ponnam 1,Svitlana Fialkova 1,Sergey Yarmolenko 1,Zhigang Xu 1
1 North Carolina Aamp;T State Univ Greensboro United States,
Show AbstractThis paper reports a first-hand fabrication of single crystalline titanium nitride (TiN) nanowires using a bottom-up method on sapphire (single crystal Al2O3) by catalyst-assisted pulsed laser deposition. The growth strategy involves depositing ultra-thin gold films and subjecting them to in-situ annealing in high vacuum for 10 min at 800 °C to form gold nanodots. This is followed by TiN nanowire deposition by ablating TiN target in 200 mtorr of nitrogen ambient. After deposition the samples were cooled down to room temperature in same ambient pressure. By this simple growth strategy we fabricated highly oriented and epitaxial TiN nanowires. The influence of the deposition pressure, seed-particle, temperature, and annealing time on the composition, structure and internal stress was studied systematically. As the deposition pressure is increased from (100 mtorr-350 mtorr), the nanowires evolves from mixture of α-TiN0.30 (002) and pure TiN (200) to stoichiometric pure TiN (200), and finally to overstoichiometric TiN. At a critical pressure of 200 mtorr, vertically aligned, highly oriented, and epitaxial TiN1+x (x≥0) (200) nanowires possess a cubic structure with diameter of (20-30) nm, length (500-550) nm. We found that in-situ gold annealing time plays a major role in TiN phase formation, crystal growth direction and morphology. In addition we investigated how growth parameters mainly substrate temperatures (600- 800 °C), laser fluence (2-5 J/cm2), growth time (5-60 min), particle size (20-60nm) and nanowires length (500-600nm) affect typical growth characteristics such as morphology, crystal growth direction, nucleation, crystal structure, and growth rate. The study of electrical resistance as a function of temperature shows that these nanowires have semiconducting behavior. Mainly the effect of deposition pressure, temperature and catalyst on structural and electrical properties of nanowires has been studied by transport measurements for tuning electrical properties. Further the metallic TiN nanowires were converted to TiN1-xOx (TNO) oxinitride nanowires that have potential application in water splitting and hydrogen generation using visible solar light. The band gap of TNO was tailored to be in the visible range (λ > 415 nm) by controlling the oxygen content in TNO. In brief we demonstrate the growth phenomenon of high crystalline quality of the TiN nanowires on single crystal Al2O3. The epitaxial growth of semiconductor nanowires with high structural quality has major importance in device applications in electronics, photonics, optical, and solar cells.
9:00 PM - NT1.6.29
Fabrication of Defect-Rich TiO2, and ZrO2 and SnO2 Nanostructured Devices for Enhanced Solar Energy Conversion
Md Anisur Rahman 1
1 WATLab, Dept of Chemistry Univ of Waterloo Waterloo Canada,
Show AbstractEngineering the defects in wide-band gap transparent conductive oxide semiconductors are crucial in governing the physical and chemical properties of these oxides. Enormous efforts have been made to narrow the band gap and to extend the working spectrum to the visible light region. Unfortunately, all of these efforts provides two to three orders less photoactivity when ultraviolet light (<430 nm) is filtered out from the AM 1.5 G spectrum. Compared to other type of defects (such as those introduced by doping, hydrogen treatment), oxygen vacancy defects are desirable for wide band gap semiconductors because the oxygen vacancies act as electron donors and could therefore significantly enhance light absorption and electrical conductivity. The dependence of photoelectrochemical activity on the surface morphology of and the amount of oxygen vacancy defects in the 1D nanostructures are also not well understood.
We have succeeded in synthesizing several defect-rich 1D nanostructures of TiO2, SnO, and ZrO2 for the first time by by an efficient vapour deposition approach, with the goal to reduce cost, to simplify the process and to greatly improve the performance and stability. Photoelectrochemical measurement of TiO2 nanowires under simulated sunlight shows that the observed photocurrent densities in AM 1.5G light were found to reduce by nearly 50% when ultraviolet light was filtered out (>430 nm), we observe only a 13% reduction with just the visible light component in the present work.1 Similarly, the defect-rich p-type hierarchical ZrO2 nanowires also showed high photoelectrochemical activity in the longer wavelength visible light. A remarkable improvement in the solar cell performance, including open circuit voltage, short circuit current density, fill factor, and photoconversion efficiency is observed for the hierarchical SnO2 nanostructured photoanode.2 More importantly, precisely controlled deposition of size-selected TiO2 NCs produced by gas-phase aggregation in a special magnetron sputtering system exhibit remarkable photoelectrochemical water splitting performance in spite of a small amount of material loading.3
We expect these results (and precisely defect-rich decorated 1D nanostructured materials) to have a significant impact in the design of efficient and low-cost photoanodes working in visible light for green energy applications.
References
1. Md Anisur Rahman et al.,, “Defect-rich decorated TiO2 nanowires for super-efficient photoelectrochemical water splitting driven by visible light.” 2015, Energy & Environmental Science (DOI: 10.1039/C5EE01615K).
2. M. Abd-Ellah, Md Anisur Rahman, et al., “Hierarchical Tin Oxide Nanostructures for Dye-Sensitized Solar Cell Application.” 2015, Advanced Electronic Materials, 1, 9.
3. S. Srivastava, Md. Anisur Rahman, et al., “Size-Selected TiO2 Nanocluster Catalysts for Efficient Photoelectrochemical Water Splitting.” 2014, ACS Nano, 8(11), 11891-11898.
Symposium Organizers
Alexander Govorov, Ohio University
Renaud Bachelot, University of Technolology of Troyes, Charles Delaunay Institute, CNRS
Din Ping Tsai, Academia Sinica
Gary Wiederrecht, Argonne National Laboratory
NT1.7: Photovoltaics with Advanced Nanomaterials
Session Chairs
Phillip Christopher
Alexander Eychmueller
Thursday AM, March 31, 2016
PCC North, 100 Level, Room 129 A
9:30 AM - *NT1.7.01
Multiple Exciton Generation in Semiconductor Quantum Dots and Rods, Arrays, Buried Junctions, and Novel Molecules: Applications to Future Generation Solar Photon Conversion to Photovoltaics and Solar Fuels
Arthur Nozik 2
1 Department of Chemistry University of Colorado Boulder United States,2 NREL Golden United States,
Show AbstractIn order to utilize solar power for the production of solar electricity and solar fuels on a global scale, it will be necessary to develop solar photon conversion systems that have an appropriate combination of high efficiency (delivered watts/m2) and low capital cost ($/m2). One potential, long-term approach to attain high conversion efficiencies above the well-known Shockley-Queisser thermodynamic limit of 32% is to utilize the unique properties of quantum dot/rod (QD/QR) nanostructures to control the relaxation dynamics of photogenerated carriers to produce either enhanced photocurrent through efficient photogenerated electron-hole pair multiplication or enhanced photopotential through hot electron transport and transfer processes. To achieve these desirable effects it is necessary to understand and control the dynamics of hot electron and hole relaxation, cooling, charge transport, and interfacial charge transfer of the photogenerated carriers. These fundamental dynamics in various bulk and nanoscale semiconductors have been studied for many years using transient absorption, photoluminescence, photocurrent, and THz spectroscopy with fs to ns time resolution The prediction that the generation of more than one electron-hole pair (which exist as excitons in size-quantized nanostructures) per absorbed photon would be an efficient process in QDs and QRs has been confirmed over the past several years in different classes of materials and their architectures. Very efficient and ultrafast multiple exciton generation (MEG), also called Carrier Multiplication (CM), from absorbed single high energy photons has been reported in Group IV-VI and Group IV semiconductors and associated solar photon conversion devices for solar electricity and solar fuels (e.g. H2) production. Selected aspects of this work will be summarized and recent advances will be discussed. Finally, the analogous MEG effect in molecules (called singlet fission) and its use in molecular-based solar cells will also be discussed
10:00 AM - NT1.7.02
Electrocatalysis in Photovoltaics:#xD;
Research on Counter Electrode in Dye-Sensitized Solar Cells
Yantao Shi 1,Suxia Liang 1,Jiahao Guo 1,Huawei Zhou 1,Chunyu Zhao 1,Tingli Ma 1
1 State Key laboratory of Fine Chemicals, School of Chemistry, Dalian University of Technology Dalian China,
Show AbstractAmong various photovoltaics, some require electrolyte to serves as “shuttles” for charge transmission, e.g. dye-sensitized solar cells (DSCs). As one key component in DSCs, counter electrode is responsible for collection of electrons from external circuit and reduction of the redox couple, e. g. triiodide (I3–) and iodide (I–). Generally, CE can be prepared by sputtering of platinum (Pt) on conductive glass. However, there are many limitations in terms of using Pt as CEs, like resource scarcity. Consequently, minimizing the use of Pt or replacing Pt with inexpensive but efficient catalyst is meaningful and has become one of the priorities in this field. Recent years, we have developed dozens of inorganic materials that proved very efficient and nearly approached Pt when fabricated into CE for DSCs. These non-Pt materials include oxides, sulfides, selenides, and tellurides. In our work, the structure-effect relationships at multiscale were revealed systematically, for example, the dependence of catalytic activity and selectivity on crystallinity, microscopic morphology, surface structure, and so on.
Single-atom catalysts (SACs) currently is a new frontier in the fields of catalytic science. SACs can be regarded as one extreme case because the particle size reaches the limit. In our work, we for the first time demonstrated the use of SAC of FeOx-supported Pt single atoms (Pt/FeOx-SAC) as counter electrode (CE) in dye-sensitized solar cells (DSCs). The electrocatalytic and photovoltaic behaviors of such SACs in mesoporous photovoltaic device, and the remarkable atom utility were well illustrated. Compared with conventional Pt CE, the SAC-based CE exhibited a much better activity and reversibility for catalytic reduction of triiodide into iodide. Pt/FeOx-SAC with an extremely Pt loading (only 0.08%) exhibited the most effective atom utilitzation and doubled the power conversion efficiency (PCE) of the DSCs based on bare FeOx. Using such Pt/FeOx-SACs, high PCEs were achieved while the consumption of Pt in DSCs would be reduced significantly. We ascribed the superior catalytic performance of Pt/FeOx-SAC to the unsaturated coordination environment of Pt single atom. Besides, the Pt/FeOx-SAC also exhibited good stability in the electrolyte solution because Pt single atoms were chemically and tightly bonded on the support. Finally, we proposed some effective strategies to further improve the performance of SAC in DSCs.
10:15 AM - NT1.7.03
The Grass is Always Greener: Lawn-Like TiO2 Nanofiber-Carbon Nanotube-Composite Dye-Sensitized Solar Cells
Thomas Macdonald 1,Ivan Parkin 1,Joseph Shapter 2,Thomas Nann 3
1 Department of Chemistry University College London London United Kingdom,2 Centre for Nanoscale Science and Technology Flinders University Bedford Park Australia3 MacDiarmid Institute for Advanced Materials and Nanotechnology Victoria University of Wellington Wellington New Zealand
Show AbstractElectrospun titanium dioxide nanofibers (TiO2-NFs) and single-walled carbon nanotubes (SWCNTs) were combined to form a nanocomposite light-scattering layer for dye-sensitized solar cells (DSSCs). No nanoparticulates were present in the light-scattering layer and the combination of TiO2-NFs and SWCNTs and formed a fibrous lawn-like nanoarchitecture. The integration of SWCNTs to the TiO2-NFs DSSCs increased the power conversion efficiency (PCE) from 2.90 % to 4.83 % under 1 sun illumination. Furthermore, TiO2-NF and TiO2- NF/SWCNT-based DSSCs reached PCE values of up to 3.7 % and 6.6 % under reduced light intensities (0.25 sun). We hypothesize that the addition of SWCNTs provides additional charge-transport channels, which contributes to an increase in the diffusion coefficient and significant improvement in device performance.1
References
(1) Macdonald, T. J.; Tune, D. D.; Dewi, M. R.; Gibson, C. T.; Shapter, J. G.; Nann, T. ChemSusChem 2015, n/a – n/a
10:30 AM - NT1.7.04
Multiple Plasmonic Effect on Organic Thin Film Solar Cells
Akira Baba 1,Supeera Nootchanat 2,Apichat Pangdam 2,Sanong Ekgasit 2,Chutiparn Lertvachirapaiboon 1,Kazunari Shinbo 1,Keizo Kato 1,Futao Kaneko 1
1 Niigata Univ Niigata Japan,1 Niigata Univ Niigata Japan,2 Chulalongkorn University Bangkok Thailand2 Chulalongkorn University Bangkok Thailand
Show AbstractThe use of plasmonic structures have been a great deal of interest in fabricating electric-field enhanced organic device applications such as biosensors and photovoltaic devices. Especially, the plasmonic solar cell is a promissing approach to create additional light traping layer facilitating the improvement light absorption capability and efficiency of the solar cells without increase of the active layer thickness. In this work, we studied the effect of grating-coupling surface plasmon excitation on organic thin film solar cells. The solar cell Al/P3HT:PCBM/PEDOT:PSS/ITO/glass was fabricated. The subwavelength diffraction grating pattern was transferred form a master template to the active layer of the solar cell using PDMS mold. The formation of the grating structure in the surface of the blended polymer was studied. The effect of two different diffraction gratings, in particular periodic (BD-R) and non-periodic (BD) were studied. The use of used-BD-R and BD can be an alternative way to reduce electronic wastes yet benefit the energy industrial. The SPR reflectivity results reveal the increase of trapped light as a broad band absorption from 400 nm to 650 nm in the device with grating structure which is originated from the effect of light scattering. The increase of the absorption at the wavelength long than 650 nm can be observed and assigned to the GCSPR of Al grating as the present of red-shifted dip when increase the incident angle. Introducing BD and BDR diffraction grating patterns as the additional light trapping layer could increase the short-circuit photocurrent and the efficiency of the solar cells. Furthermore, gold nanoparticles were added in the devices to study the mutiple plasmonic effext, i.e. both garting-coupled propagating plasmon and gold nanoparticles localized surface plasmon., on the perfoemance of organic thin film solar cells.
10:45 AM - NT1.7.05
Enhanced Absorption and Charge Photogeneration in Polymer: Fullerene Thin-Films with MoS2-Metasurface Heterostructures for Photovoltaics
Christopher Petoukhoff 2,M. Bala Murali Krishna 2,Damien Voiry 1,Ibrahim Bozkurt 1,Skylar Deckoff-Jones 2,Manish Chhowalla 1,Deirdre O'Carroll 3,Keshav Dani 2
1 Materials Science and Engineering Rutgers University Piscataway United States,2 Femtosecond Spectroscopy Unit Okinawa Institute of Science and Technology Onna Japan,2 Femtosecond Spectroscopy Unit Okinawa Institute of Science and Technology Onna Japan1 Materials Science and Engineering Rutgers University Piscataway United States1 Materials Science and Engineering Rutgers University Piscataway United States,3 Chemistry and Chemical Biology Rutgers University Piscataway United States
Show AbstractPolymer:fullerene-based photovoltaics have shown great promise as third-generation solar cells due to their solution-processability, low toxicity, earth-abundant elemental constituents, and short energy payback times. Although polymer:fullerene-based photovoltaic efficiency has recently exceeded 10 %, the efficiency is still limited for two primary reasons: 1) the competing constraints on the thickness of the polymer:fullerene active layer, in that it must be kept thin enough to minimize charge recombination while simultaneously being thick enough to absorb all of the incident light; and 2) conjugated polymers typically have narrow absorption bandwidths, preventing absorption of the full solar spectrum. Here, we simultaneously offer solutions to both efficiency limitations by employing plasmonic metasurfaces modified by MoS2 thin-film coatings. We demonstrate through integrating sphere reflectance measurements that the plasmonic metasurface improves absorption within thin-films of P3HT:PCBM, one of the most widely-studied polymer:fullerene active layers. Using electromagnetic simulations, we show that the absorption enhancement arises from excitation of both localized and propagating surface plasmon modes, in addition to electromagnetic coupling between surface plasmons from the metasurface and the optical transitions of the P3HT:PCBM. To address the narrow absorption bandwidth of typical polymer:fullerene active layers, we employed MoS2-metasurface heterostructures, and we show that the MoS2 plays an active role in the charge carrier photogeneration in P3HT:PCBM, resulting in a 6-fold increase in the P3HT polaron population. Using microscope-coupled reflectance measurements and electromagnetic simulations, we show that active layer absorption is broadened by 170 nm for P3HT:PCBM using MoS2-metasurface heterostructures as substrates. We show that the broadened and enhanced absorption spectrum and enhanced polaron population can only be achieved through the combined synergistic effect of the MoS2 and the plasmonic metasurface. Future work includes employing MoS2-metasurface heterostructures as electrodes in polymer:fullerene photovoltaics.
11:30 AM - *NT1.7.06
Coherent Light-Trapping in Nanostructured Solar Cells: New Limits, New Challenges
Stephane Collin 1,Andrea Cattoni 1,Nicolas Vandamme 1,Julie Goffard 1,Alexandre Gaucher 1,Jean-Francois Guillemoles 3
1 LPN-CNRS Marcoussis France,2 LIA NEXT-PV, RCAST Tokyo Japan,3 IRDEP-CNRS Chatou France
Show AbstractConventional light trapping in solar cells is based on incoherent light scattering achieved with rough interfaces. However, this approach is not suitable for thin-film solar cells with thicknesses below 1µm.
We propose a new paradigm for light trapping. It is based on multi-resonant absorption in periodically nanostructured absorbers. Broadband absorption is achieved with a series of overlapping resonant modes in the critical coupling regime. We have developed a simple theoretical model and derived a closed-form expression for the absorption limit. We demonstrate that this multi-resonant critical coupling limit exceeds the conventional lambertian limit (4n2) for any absorber thickness (Jsc).
These results could allow a drastic reduction of the absorber thickness in thin-film photovoltaics. We provide numerical and experimental examples of multi-resonant absorption in ultra-thin semiconductor layers. We also present our latest experimental results of ultra-thin solar cells made of various semiconductor materials (GaAs, CIGS, c-Si). We will discuss the record short-circuit currents achieved in ultra-thin photovoltaic devices, and the technological challenges that should be addressed to reach the theoretical limits.
12:00 PM - NT1.7.07
Downscaling Diameter of Self-Organized TiO2 Nanotube towards Higher Efficiency of Hybrid Photochemical Solar Cells
Milos Krbal 1,Hanna Sopha 1,Jan Macak 1
1 Center of Materials and Nanotechnologies (CEMNAT) University of Pardubice Pardubice Czech Republic,
Show AbstractToday, there is a clear worldwide consensus regarding the need for the long-term replacement of fossil fuels by low-cost, high-efficient, renewable and environmentally friendly sources of energy. The solar cell technology becomes tremendously developing field of research which can meet the target. While the single crystal silicon solar cells possess high efficiency ~25 % [1], the initial cost and their fragility motivated researchers to focus on the new type thin film-based devices, such as amorphous silicon [2], CdTe [3] or CuGa1-xInxSe2 (CIGS) [4], dye-sensitized cells (DSSC) [5], organic cells [6] and perovskites [7] which can be deposited on any substrates. Still, there is a reason why thin film solar panels have not replaced older types yet. They are just not as efficient. Additionally, some thin film materials have shown degradation of performance over time and can be toxic (CdTe). However, the hybrid photocells employing TiO2 oxide/chromophore interface have potential to improve the functionality of the new solar cells [8].
For instance, tailoring the TiO2 anode chromophore interface can increase the efficiency of the cells, such as DSSC and perovskite-based solar cells. The enhancement can be achieved by increasing the interfacial surface area between the chromophore and the TiO2 oxide in order to facilitate charge separation. Unlike randomly ordered mesoporous TiO2 support, ordered nanostructures, such as self-organized TiO2 nanotubes with high aspect ratio or TiO2 nanowires, offer the advantage of directed charge transport and controlled phase separation between donor and acceptor materials and thus they seem to be one of the most promising nanoscale solar hybrid technologies [9].
Here, we will present initial photo-electrochemical results for anodic TiO2 nanotubes grown with different diameter sizes utilized as highly ordered n-type conductive scaffold for inorganic chromophores [10, 11]. Downscaling the nanotube diameter significantly increases the number of nanotubes per square unit and thus the active surface area increases as well. The photo-chemical cells were fabricated using the solvent solution method, when TiO2 nanotubes were infilled with inorganic chromophores dissolved in appropriate solvents by soaking or spin-coating. The possible improvement of such hybrid solar cells will be discussed.
[1] M. A. Green et al. Progress in Photovoltaics: Research and Applications 23 (2015) 1.
[2] D. E. Carlson and C. R. Wronski, Apllied Phis. Lett. 28 (1976) 671.
[3] J. Britt and C. Ferekides Apllied Phisi. Lett. 62 (1993) 2851.
[4] P. Jackson et al. Photovoltaics: Research and Applications 19 (2011) 894.
[5] B. ORegan and M. Grätzel, Nature 353 (1991) 737.
[6] D. Wohrle and D. Meissner Advanced Materials 3 (1991) 129.
[7] M. Liu et al. Nature 501 (2013) 395.
[8] J. M. Macak et al., Curr. Opin. Solid State Mater. Sci. 1-2 (2007) 3.
[9] E. C. Garnet et al. Annual Review of Materials Research 43 (2011) 269.
[10] MS in preparation
[11] MS in preparation.
12:15 PM - *NT1.7.08
Plasmon-Induced Resonance Energy Transfer and Hot Electron Injection for Solar Energy Conversion
Nianqiang Wu 1
1 West Virginia Univ Morgantown United States,
Show AbstractFor plasmonic metal-semiconductor heterojunctions, plasmon can induce the charge carries in semiconductors via two near-field mechanisms, that is, the plasmon-induced resonance energy transfer (PIRET) and the hot electron injection. This presentation will discuss the difference between the two mechanisms. PIRET proceeds via the dipole-dipole interaction between the metal and the semiconductor. It depends on the gap and the spectra overlap between the metal and the semiconductor. The hot electron injection from the metal to the semiconductor depends on the Schottky barrier at the metal-semiconductor interface. The occurrence of two mechanisms in a metal-semiconductor heterojunction is controlled by some factors such as the physical contact and the spectral overlap.
12:45 PM - NT1.7.09
Ultrafast Dynamics of Electron-Hole Pairs in Two-Dimensional InSe Layers
Jannika Lauth 1,Frank Spoor 1,Aditya Kulkarni 1,Arjan Houtepen 1,Juleon Schins 1,Sachin Kinge 2,Laurens Siebbeles 1
1 Delft University of Technology Delft Netherlands,2 Toyota Motor Europe Materials Research amp; Development Zaventem Belgium
Show AbstractGraphene-like two-dimensional (2D) crystals with non-zero band gaps exhibit highly interesting anisotropic dimensionality-dependent properties and bear high potential for ultrathin electronics. Amongst the most investigated 2D semiconductors, one material recently moved into focus: Exfoliated InSe, a van-der-Waals layered III-VI metal chalcogenide with an atomically smooth surface. It has proven its highly promising (opto-)electronic properties as high mobility field-effect transistor [1] and even outperformed other 2D crystal-based compounds like MoS2 and GaSe as high responsivity (visible to NIR) photodetector [2, 3].
We have synthesized ultrathin 2D InSe layers (<6 nm with organic ligands) by a ligand templated colloidal method and have fully characterized the 2D structures with electron and atomic force microscopy, X-ray photoelectron spectroscopy and scattering methods [4]. By applying ultrafast transient absorption spectroscopy, we evaluate the charge carrier and recombination dynamics in atomically thin InSe and extract (intrinsic) mobilities of ~30 cm2/Vs by using time-resolved terahertz spectroscopy. The combination of colloidal synthesis and pump-probe spectroscopy allows us to assess the potential of solution-processed atomic InSe layers for next generation electronics.
[1] Sucharitakul, S.; Goble, N. J.; Kumar, U. R.; Sankar, R.; Bogorad, Z. A.; Chou, F.-C.; Chen, Y.-T.; Gao, X. P. A., Nano Lett. 2015, DOI:10.1021/acs.nanolett.5b00493.
[2] Tamalampudi, S. R.; Lu, Y.-Y.; Kumar, R. U.; Sankar, R.; Liao, C.-D.; Moorthy, K. B., Karukanara; Cheng, C.-H.; Chou, F. C.; Chen, Y.-T., Nano Lett. 2014, 14, 2800-2806.
[3] Lei, S.; Ge, L.; Najmaei, S.; George, A.; Kappera, R.; and Lou, J.; Chhowalla, M.; Yamaguchi, H.; Gupta, G.; Vajtai, R.; Mohite, A. D.; Ajayan, P. M.; ACS Nano 2014, 8, 1263-1272.
[4] ] Lauth, J.; Gorris, F. E. S.; Samadi Khoshkhoo, M.; Chassé, T.; Wiebke Friedrich, W.; Lebedeva, V.; Meyer, A.; Klinke, C.; Kornowski, A.; Scheele, M.; Weller, H., submitted.
NT1.8/EE3.8: Joint Session: Recent Developments in Optoelectronics and Photovoltaics
Session Chairs
Thursday PM, March 31, 2016
PCC North, 100 Level, Room 129 A
2:45 PM - *NT1.8.01/EE3.8.01
Optoelectronics: Is There Anything It Cannot Do; Can Opto-Electronics Provide the Motive Power for Future Vehicles
Vidya Ganapati 1,T. Xiao 1,Eli Yablonovitch 1
1 Electrical Engineering and Computer Sciences Dept. University of California, Berkeley Berkeley United States,
Show AbstractA new scientific principle[i] has produced record-breaking solar cells. This is exemplified by the mantra: “A great solar cell also needs to be a great LED”. It is essential to remove the original semiconductor substrate, which absorbs luminescence, and to replace it with a high reflectivity mirror.
In thermo-photovoltaics, high energy photons from a thermal source are converted to electricity. The question is what to do about the majority of low energy infrared photons? It was recognized that the semiconductor band-edge itself can provide excellent spectral filtering for thermophotovoltaics, efficiently reflecting the unused infrared radiation back to the heat source. Exactly those low energy photons that fail to produce an electron-hole pair, are the photons that need to be recycled.
Thus the effort to reflect band-edge luminescence in solar cells has serendipitously created the technology to reflect all infrared wavelengths, which can revolutionize thermo-photovoltaics. We have never before had such high rear reflectivity for sub-bandgap radiation, permitting step-function spectral control of the unused infrared photons for the first time. This enables conversion from heat[ii] to electricity with >50% efficiency. Such a lightweight “engine” can provide power to electric cars, aerial vehicles, spacecraft, homes, and stationary power plants.
[i] O. D. Miller, Eli Yablonovitch, and S. R. Kurtz, “Strong Internal and External Luminescence as Solar Cells Approach the Shockley–Queisser Limit”, IEEE J. Photovoltaics, vol. 2, pp. 303-311 (2012). DOI: 10.1109/JPHOTOV.2012.2198434
[ii] The heat source can be combustion, radio-activity, or solar thermal.
3:15 PM - *NT1.8.02/EE3.8.02
Controlling both Solar and Thermal Spectra for Solar Cell Applications
Shanhui Fan 1
1 Stanford Univ Stanford United States,
Show AbstractWe show that the use of photonic structures, which allows control of both solar and thermal radiation spectra, has important implications for various aspects of solar energy conversion, including voltage, current and cooling considerations.
3:45 PM - NT1.8.03/EE3.8.03
Highly Conductive Ag Nanowire Meta-Electrodes Improve Silicon Heterojunction Solar Cells
Mark Knight 1,Jorik Van De Groep 1,Paula Bronsveld 2,Wim Sinke 1,Albert Polman 1
1 FOM Institute AMOLF Amsterdam Netherlands,2 Energy research Centre of the Netherlands Petten Netherlands2 Energy research Centre of the Netherlands Petten Netherlands,1 FOM Institute AMOLF Amsterdam Netherlands
Show AbstractSilicon heterojunction (SHJ) solar cells, where the crystalline Si is passivated by thin layers of a-Si:H, have attracted significant interest due to their record voltages. However, reflection from macroscopic metallic ‘fingers’ has constrained current generation – and efficiency – in front contacted cells. These fingers are essential for harvesting electrons due to poor lateral transport in indium tin oxide (ITO), which is both the most common transparent conductive electrode (TCE) and limited by a fundamental tradeoff between transmission and conductance. Since the optimal finger spacing depends on TCE conductivity, the efficiency of SHJ cells is married to the quality of the TCE layer.
In this presentation we introduce a hybrid TCE which decouples the optical and electrical functionalities, and enables the independent optimization of each function. The geometry consists of Ag nanowires (80 nm wide, 120 nm tall) arranged in a sparse square grid, fabricated on top of an ultrathin ITO layer to transport charge in the interstitial regions. The nanowires are conformally coated with Si3N4, providing both environmental stability and an antireflection coating free from the interband and free carrier losses in ITO. For cells with fingers spaced by the standard 2 mm, replacing ITO with Si3N4 reduces optical loss by 1.1 mA cm-2.
We apply this nanostructured hybrid electrode to large-area (4 cm2) untextured SHJ solar cells using substrate-conformal imprint lithography (SCIL), a fabrication method that enables rapid, wafer-scale fabrication of nanowire (NW) arrays with full geometric control. The SCIL fabrication process does not damage the passivating a-Si:H layer, with consistent values for Voc measured on cells with and without nanowire modification. Optically, the nanowire networks exhibit broadband anomalous transmission due to detuning of the plasmonic nanowire resonances from the solar spectrum, shading 30% less light than the NW area coverage. Electrically, the square grids of nanowires have measured sheet resistances of 4.0, 7.2, and 15.0 Ω/sq. for pitches of 1, 2, and 4 µm, respectively. This is a significant (10x) improvement relative to an industrially processed ITO electrode with a measured 150 Ω/sq. sheet resistance. Due to the improved transmission and conductivity, the hybrid electrode enables an increase in finger pitch from 2 to 5 mm, reducing shading. For the champion hybrid electrode SHJ cell we measure a Jsc enhancement of 1.4 mA cm-2 (32.7 to 34.1 mA cm-2) with a simultaneous increase in FF (0.622 to 0.670), yielding an absolute efficiency enhancement of 2.2% (13.8% to 16.0%).
This demonstration of an engineered ‘meta-electrode’ within the electrical and optical environment of high performance SHJ solar cells shows that large-area nanostructuring provides practical pathway to increased performance and a reduced dependence on rare metals, especially indium.
4:00 PM - NT1.8/EE3.8
BREAK
NT1.9: Hybrid Nanomaterials for Energy and Optics
Session Chairs
Thursday PM, March 31, 2016
PCC North, 100 Level, Room 129 A
4:30 PM - *NT1.9.01
Functional Nanostructures and Their Applications in Catalysis, Sensing and Color Conversion
Alexander Eychmueller 1
1 Physical Chemistry TU Dresden Dresden Germany,
Show AbstractGels and aerogels manufactured from a variety of nanoparticles available in colloidal solutions have recently proven to provide an opportunity to marry the nanoscale world with that of materials of macro dimensions which can be easily manipulated and processed, whilst maintaining most of the nanoscale properties [1]. The materials carry an enormous potential for applications. This is largely related to their extremely low density and high porosity providing access to the capacious inner surface of the interconnected nanoobjects they consist of. The aerogel materials may be further processed in order to achieve improvements in their properties relevant to applications in optical sensing and catalysis.
The commercialization of polymer electrolyte fuel cells (PEFC) is still hindered by the cathode electrocatalyst for the oxygen reduction reaction (ORR) not fulfilling the criteria of low cost, high performance, and high durability. We recently developed a facile strategy for the controllable synthesis of nanoparticle-based bimetallic PtxPdy aerogels with high surface area and large porosity, which act as highly active and stable catalysts for the ORR in PEFC cathodes. In addition to excellent durability the PtxPdy aerogels show superior electrocatalytic activity towards the ORR with the Pt80Pd20 aerogel exhibiting a five times mass activity enhancement compared to commercial Pt/C catalysts [2].
The reminder of the presentation will be devoted to a) sensors derived from aerogels [3], and b) nanocrystals incorporated into macrocrystals of varying compositions [4]. In the latter superstructures the nanocrystals exhibit remarkable photostabilities, enhanced emission quantum yields and may act as color conversion materials.
References
[1] a) Mohanan JL, Arachchige IU, Brock SL (2005). Science 307, 397-400, b) Herrmann AK, Formanek P, Borchardt L, Klose M, Giebeler L, Eckert J, Kaskel S, Gaponik N, Eychmüller A (2014). Chem. Mater.Acc. Chem. Res. 48, 154-162.
[2] Liu W, Rodriguez P, Borchardt L, Foelske A, Yuan J, Herrmann AK, Geiger D, Zheng Z, Kaskel S, Gaponik N, Kötz R, Schmidt TJ, Eychmüller A (2013). Angew. Chem. Int. Ed. 52, 9849-9852.
[3] Yuan J, Gaponik N, Eychmüller A (2012). Anal. Chem. 84, 5047-5052, (2013) Angew. Chemie Int. Ed. 52, 976-979.
[4] a) Otto T, Müller M, Mundra P, Lesnyak V, Demir HV, Gaponik N, Eychmüller A (2012). Nano Lett. 12, 5348-5354, b) Müller M, Kaiser M, Stachowski GM, Resch-Genger U, Gaponik N, Eychmüller A (2014). Chem. Mater. 26, 3231-3237, c) Adam M, Tietze R, Gaponik N, Eychmüller A (2015). Z. Phys. Chem. 229, 109-118. d) Adam M, Wang Z, Dubavik A, Stachowski GM, Meerbach C, Soran-Erdem Z, Rengers C, Demir HV, Gaponik N, Eychmüller A (2015). Adv. Funct. Mat. 25, 2638-2645.
5:00 PM - *NT1.9.02
The Role of Hot Electrons, Hot Spots and Interfacial Electronic Transitions in Photocatalysis on Metal Nanoparticles
Phillip Christopher 1
1 University of California, Riverside Riverside United States,
Show AbstractPhoton driven chemical reactions at metal surfaces have been studied for over forty years with a majority of research focused on non-thermal, electron driven chemical processes in the context of controlling reaction selectivity and understanding fundamentals of non-adiabatic surface reactivity. A majority of these studies have been executed on metal single crystals, where surface electric fields have relatively small magnitudes and chemistry is typically driven through substrate-mediated excitation of adsorbate-metal bonds that competes with hot charge carrier diffusion into the bulk. These characteristics of photon driven reactions on metal single crystals result in processes with characteristically low yields and minimal, if any, ability to control the outcome of probed chemistry as the processes of photon absorption and induced chemical reactions are delocalized from each other.
Metal nanoparticles offer opportunities to overcome these limitations through the enhanced electric fields created in response to excitation of localized surface plasmon resonance and exploiting huge surface area to volume ratios that allows chemistry by direct photoexcitation of adsorbate-metal bonds. In this talk I will discuss recent results where we show that decaying plasmonic excitations at junctions of Ag nanocrystals can be efficiently funneled into catalyzing O2 dissociation on the Ag surface. Associated with plasmon driven chemical reactivity are unique wavelength, intensity and isotope dependencies, which shed light on fundamental mechanistic insights. The critical role of “hot spots” at nanoparticle clusters will be addressed. In a second example, I will describe how the large surface area to volume ratio characteristic of sub 5 nanometer diameter metal crystals can be exploited to control outcome of catalytic processes through direct photoexcitation of targeted adsorbate metal-bonds. The implications of these results and unresolved questions will be discussed.
5:30 PM - *NT1.9.03
Efficiently Wave-Front Manipulations by Gradient Metasurfaces
Shulin Sun 1
1 Department of Optical Science and Engineering Fudan University Shanghai China,
Show AbstractManipulating light in a controllable manner is always highly desired in photonics research. In a long time, the phase control plays the vital role. Recently, electromagnetic meta-surfaces, made by carefully designed inhomogeneous microstructures to supply abrupt phase changes for impinging light, were found to exhibit strong abilities to control light propagations, leading to extraordinary physical effects such as generalized Snell’s law [1-4], a new bridge to link propagating-wave and surface-plasmon-polariton (SPP) [3,5], flat-lens focusing [6], meta-hologram [7].
In this talk, I will introduce our recent works on gradient metasurfaces. The first one is about the experimental realization of photonic spin Hall effect (PSHE) with nearly 100% efficiency [8], where a general criterion to achieve this goal is theoretically derived based on the Jones Matrix analysis. The second one is about a newly proposed concept to design the high efficiency surface plasmon coupler. The new coupler can solve the inherent problems in conventional ones (i.e., the reflection and the decoupling effect) and therefore exhibits the high-efficiency performance [9].
1. N. Yu, P. Genevet, M. A. Kats, et al.. Science 334, 333 (2011).
2. X. Ni, N. K. Emani, A. Kildishev, et al. Science 335, 427 (2012).
3. S. L. Sun, Q. He, S. Y. Xiao, et al. Nature Materials 11, 426 (2012).
4. S. L. Sun, K.-Y. Yang, C.-M. Wang, et al. Nano Letters 12, 6223 (2012).
5. C. Qu, S. Y. Xiao, S. L. Sun, EPL 101, 54302 (2013).
6. X. Li, S. Y. Xiao, B. Cai, et al. Optics Letters 37, 4940 (2012).
7. W. T. Chen, K.-Y. Yang, C.-M. Wang, et al. Nano Letters 14,225-230 (2014).
8. W. Luo, S. Xiao, Q. He, et al. Advanced Optical Materials 3, 1102 (2015).
9. W. Sun, Q. He, S. L. Sun, et al. Light: Science & Applications 5, e16003 (2016).
NT1.10: Poster Session III: Photovoltaics
Session Chairs
Friday AM, April 01, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NT1.10.01
Bottom-Up Approaches for Precisely Nanostructuring Hybrid Organic/Inorganic Multi-Component Composites for Organic Photovoltaics
Yang Qin 1
1 Univ of New Mexico Albuquerque United States,
Show AbstractNanostructuring organic polymers and organic/inorganic hybrid materials and control of blend morphologies at the molecular level have become the prerequisites for organic photovoltaics (OPVs) that are widely perceived as low-cost alternative energy sources. To achieve all-around high performance, multiple organic and inorganic entities, each designed for specific functions, are commonly incorporated into a single device. Current state-of-the-art approaches to morphology control in these multi-component systems typically involve physical blending and optimization via thermal/solvent annealing. Such trial-and-error approaches are however highly system dependent, lack controllability on the molecular level and generally lead to morphologies at only thermodynamically meta-stable states. We present our efforts in developing a versatile toolbox employing supramolecular chemistry that is capable of precisely nanostructuring multi-component organic/inorganic hybrid materials through self-assembly processes. Specifically, we show that well-defined core-shell composite nanofibers (NFs) containing precisely placed conjugated polymers, inorganic quantum dots and fullerene derivatives, can be obtained through cooperation of orthogonal non-covalent interactions including conjugated polymer crystallization, fullerene aggregation, hydrogen bonding interactions and metal-ligand coordination.1-4 OPV devices applying these NFs display much improved efficiencies and stability over their conventional bulk heterojunction (BHJ) counterparts.
1. Li, F.; Yager, K. G.; Dawson, N. M.; Yang, J.; Malloy, K. J.; Qin, Y.* Macromolecules 2013, 46, 9021.
2. Li, F.; Yager, K. G.; Dawson, N. M.; Jiang, Y.-B.; Malloy, K. J.; Qin, Y.* Chem. Mater. 2014, 26, 3747.
3. Li, F.; Yager, K. G.; Dawson, N. M.; Jiang, Y.-B.; Malloy, K. J.; Qin, Y.* Polym. Chem. 2015, 6, 721.
4. Li, F.; Dawson, N.; Jiang, Y.-B.; Malloy, K. and Qin Y.* Polymer 2015, 76, 220.
9:00 PM - NT1.10.02
Fullerene-Modified Zinc Oxide Thin Films Grown by Electrochemical Deposition for Hybrid Solar Cell Applications
Jennifer Damasco Ty 1,Hisao Yanagi 1
1 Graduate School of Materials Science Nara Institute of Science and Technology Ikoma Japan,
Show AbstractAs interfacial layers play a crucial role in determining device efficiency and lifetime, the introduction of appropriate interfacial layers has become a significant approach in improving the performance of hybrid solar cells. Recently, the addition of fullerenes as modifiers of cathode buffer layers (CBLs) such as zinc oxide has shown promising results. Aside from improving the interfacial contact between the inorganic CBL and the organic active layer, fullerenes as interfacial layers have also been reported to induce better crystallinity in the active layer. For ZnO CBLs, modification with fullerenes exhibited the passivation of surface defect states and increase in work function. The solubility of fullerenes and its derivatives, however, is challenging, thus limiting their application in solution processes. Herein, using a water-soluble fullerene derivative, C60 pyrrolidine tris-acid (CPTA), we demonstrate the growth of fullerene-modified ZnO thin films by electrochemical deposition. These films were used as CBLs for inverted hybrid solar cells with the structure Au/MoO3/P3HT:PCBM/ZnO-CPTA/ITO. Our films had a nanorod array morphology and exhibited high optical transmittance. The devices showed improved charge current density compared with devices using unmodified ZnO.
9:00 PM - NT1.10.03
Optically Enhanced Semi-Transparent Organic Solar Cells through Hybrid Metal/Nanoparticle/Dielectric Nanostructure
Xingang Ren 1,Xinchen Li 1,Wallace Choy 1
1 Univ of Hong Kong Hong Kong China,
Show Abstract
Semi-transparent organic solar cells (st-OSCs) not only inherit the unique properties of organic solar cells (OSCs), but also bring innovation to both anode and cathode to preserve high transparency. The high recovered efficiency of st-OSCs with sunlight illumination from both electrodes is of great interest in different applications. However, the performance of st-OSCs is still low compared to opaque OSCs (o-OSCs) due to single pass of the light through devices and thus reduction of light absorption. In addition, the severe imbalance of device efficiency can exist between top- and bottom-illumination cases. Here, we propose a hybrid light incoupling design with structure of metal/nanoparticle/dielectric (M/NP/D) to optically improve the recovered efficiency of st-OSCs and achieve a more balance recovered efficiency between top- and bottom-illumination cases.[1] The M/NP/D nanostructure consists of high index and low-loss nanoparticles (NPs) (here we use Si NPs scatter instead of metal NPs) and index matching material (here we use Tris(8-hydroxyquinolinato) aluminium-Alq3) on ultra-thin Ag film, i.e. Ag/Si NPs/Alq3 as the top hybrid electrode of st-OSCs. It should be noted that the usage of Alq3 and Si NP in the proposed hybrid M/NP/D nanostructure has less intrinsic loss as compared the previous reported metal nanomaterials.
With the excitation of magnetic resonance of Si NP, wave destructive interference from Alq3, and total internal reflection existed in the hybrid structure, the transmission of the electrode is improved complementary in long (due to Si NPs) as well as short wavelength regions (due to Alq3 layer) with additional synergetic improvement (due to the hybrid M/NP/D nanostructure), resulting in a broadband enhancement that almost cover the whole visible spectrum. After the fabrication of the st-OSC with the hybrid M/NP/D structure as top electrode, the overall transparency of the st-OSCs is improved by 61%. Simultaneously, st-OSCs with hybrid electrode achieved PCE enhancement of about 34% compared to the optimized st-OSCs without light incoupling structure. The high recovered efficiency up to 68% and 87% are demonstrated in top and bottom illuminated devices, respectively. Notably, besides the large enhancement of light incoupling from hybrid Ag/Si NPs/Alq3 nanostructure, the theoretical and experimental results show that the utilization of Si NPs can not only promote active layer absorption at long wavelength region but also favor an alleviated angular dependence of device performance (Jsc and PCE) in top-illumination.
Consequently, the hybrid transparent electrode with M/NP/D nanostructure can be beneficial to the future transparent photovoltaic applications.
[1] X. G. Ren, X. C. Li, W. C. H. Choy, Optically enhanced semi-transparent organic solar cells through hybrid metal/nanoparticle/dielectric nanostructure, Nano Energy, 2015. 17, 187.
9:00 PM - NT1.10.04
Aligned Silver Nanowire Transparent Electrodes for High Performance Solar Cells and Light Emitting Diodes
Saewon Kang 1,Taehyo Kim 1,Seungse Cho 1,Youngoh Lee 1,Ayoung Choe 1,Jin Young Kim 1,Hyunhyub Ko 1
1 UNIST Ulsan Korea (the Republic of),
Show AbstractSilver nanowires (AgNWs) are promising materials for use in flexible, transparent electrodes for optoelectronic devices. However, random networks of AgNWs in traditional solution process have a large surface roughness and junction contact resistances, limiting the optoelectronic device performances. Controlling the NW alignment can significantly affect the performance of transparent electrodes. Here, we introduce a capillary printing technique to fabricate uniformly aligned AgNW networks, which greatly lower the percolation threshold and surface roughness of AgNW networks, resulting in a sheet resistance of 19.5 Ω sq-1 and an optical transmittance of 96.7%, which can be favorably compared to random AgNWs (92.9%, 20 Ω sq-1). Polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs) using aligned AgNW electrodes show superior optoelectronic performances, including luminance and power efficiencies of 14.25 cd A-1 and 10.62 lm W-1, respectively, in PLEDs, and power conversion efficiencies of 8.57% in PSCs, which is the highest value reported so far using AgNW-based transparent electrodes for fluorescent PLEDs and PSCs.
9:00 PM - NT1.10.05
Cost-Effective Fabrication of Transparent Electrode with Embedded Metal Mesh for Flexible Organic Solar Cells
Arshad Khan 1,Yu-Ting Huang 1,Peng Zhai 1,Shien Ping Feng 1,Wen-Di Li 2
1 Department of Mechanical Engineering, The University of Hong Kong Hong Kong China,1 Department of Mechanical Engineering, The University of Hong Kong Hong Kong China,2 HKU-Shenzhen Institute of Research and Innovation (HKU-SIRI) Shenzhen China
Show AbstractTransparent electrode as a front contact of flexible organic thin film solar cells requires three properties simultaneously, which are high electrical conductivity, high optical transparency, and high mechanical flexibility. To achieve these characteristics, new-generation transparent electrodes based on metal nanowire networks, graphene, carbon nanotube, and metal mesh are recently investigated. In particular, transparent electrodes based on regular metal mesh show promising performance. However, widespread adoption of metal-mesh based transparent electrodes has been hindered by several challenges. First, fabricating metal-mesh transparent electrodes often involves the physical deposition of metal materials from the vapor phase, which requires expensive and time-consuming vacuum-based processing. Second, a thick layer of metal mesh on the substrate, as required to achieve sufficiently high conductivity in many applications, may easily cause electrical short circuiting. Third, the weak adhesion between the metal mesh and substrate surface results in poor flexibility. The aforementioned limitations call for new metal-mesh electrode structures as well as improved fabrication methods for its production and applications.
In this study, we propose a new structure for flexible transparent electrodes with fully embedded metal mesh, develop a vacuum-free solution-processed fabrication for the metal-mesh electrode, and present its applications in dye sensitized solar cells (DSSCs) and perovskite solar cells. The fabrication process consists of simple solution-processed steps involving lithography, electroplating and imprint transfer. The embedded metal-mesh electrodes exhibited an optical transmittance higher than 90 % (over a wide spectrum of wavelength from 300 nm to 1200 nm), sheet resistance lower than 1 Ω/sq, and a ratio of electrical conductivity to optical conductivity (σdc/σopt) of more than 104, among the highest of all reported transparent electrodes. Furthermore, it can be bent to 3 mm radius of curvature with negligible degradation of conductance. Based on the proposed electrodes, prototype DSSC and perovskite solar cells are fabricated. In the preliminary experiments, using it as a cathode in the DSSCs, the prototype samples demonstrated power conversion efficiency of 6.3 % for front-side illumination and 4.6 % (higher than FTO glass and ITO-PEN based DSSCs) for back-side illumination. The improvement in the back-side illumination configuration is attributed to higher short-circuit current density (Jsc = 9.04 mA/cm2, 40% higher as compared to standard ITO-PEN based DSSCs). The promising optical and electrical properties of our transparent electrode offer the potential use in other type of flexible solar cells such as perovskite solar cells and other flexible optoelectronic devices that we are currently investigating.
9:00 PM - NT1.10.06
Dopant-Free All-Back-Contact Si Nanohole Solar Cells Using MoOx and LiF Films
Han-Don Um 1,Namwoo Kim 1,Kangmin Lee 1,Inchan Hwang 1,Ji Hoon Seo 1,Kwanyong Seo 1
1 Ulsan National Institute of Science and Technology Ulsan Korea (the Republic of),
Show AbstractWe demonstrate novel all-back-contact Si nanohole solar cells via the simple direct deposition of molybdenum oxide (MoOx) and lithium fluoride (LiF) thin films as dopant-free and selective carrier contacts (SCCs). This is in contrast to conventionally used high-temperature thermal doping processes, which require multistep patterning processes to produce diffusion masks. Both MoOx and LiF thin films are inserted between the Si absorber and Al electrodes interdigitatedly at the rear cell surfaces, facilitating effective carrier collection at the MoOx/Si interface and suppressed recombination at the Si and LiF/Al electrode interface. With optimized MoOx and LiF film thickness as well as the all-back-contact design, our 1-cm2 Si nanohole solar cells exhibit a conversion efficiency of up to 15.4 %, with an open-circuit voltage of 561 mV and a fill factor of 74.6 %. In particular, because of the significant reduction in Auger/surface recombination as well as the excellent Si-nanohole light absorption, our solar cells exhibit an external quantum efficiency of 83.4 % for short-wavelength light (~400 nm), resulting in a dramatic improvement (54.6%) in the short-circuit current density (36.8 mA/cm2) compared to that of a planar cell (23.8 mA/cm2). Hence, our all-back-contact design using MoOx and LiF films formed by a simple deposition process presents a unique opportunity to develop highly efficient and low-cost Si nanostructured solar cells.
9:00 PM - NT1.10.07
The Implementation of CuI Hole-Transport Layers in Organic-Based Solar Cells
Sayantan Das 1,Zhao Zhao 1,Terry Alford 1
1 Arizona State Univ Tempe United States,
Show AbstractOur investigation demonstrates that a solution-processed CuI hole-transport layer is a viable and promising alternative to the acidic and more expensive PEDOT:PSS material. This approach incorporates a p-type CuI hole-transport layer that replaces the conventional accepted standard, PEDOT:PSS layer, during the fabrication of high-efficiency poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester solar cells. By optimizing the concentration (0.8 M) of CuI in the precursor solution, the performance of the solar cell is comparable to that of the solar cell using PEDOT. Given the advantageously low processing temperature of CuI, this novel approach leads itself available for the enabling the next generation of flexible solar cells.
9:00 PM - NT1.10.08
Misfit-Strain Relaxation and Its Suppression in InAs Quantum Dots for Intermediate Band Solar Cells
Hongen Xie 2,Fernando Ponce 2,R. Jakomin 4,M. Pires 5,Rodrigo Menezes 6,P. Souza 6
1 School for Engineering of Matter, Transport, and Energy Arizona State University Tempe United States,2 Department of Physics Arizona State University Tempe United States,2 Department of Physics Arizona State University Tempe United States3 Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores PUC-Rio Brazil,4 Campus de Xerem UFRJ Duque de Caxias Brazil3 Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores PUC-Rio Brazil,5 Instituto de Física UFRJ Rio de Janeiro Brazil3 Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores PUC-Rio Brazil,6 Pontificia Universidade Católica do Rio de Janeiro Rio de Janeiro Brazil
Show AbstractAn intermediate band in a semiconductor opens new paths for light absorption and increases the conversion efficiency of light into electricity. Closely positioned quantum dots are being considered as an approach to realize efficient and tunable intermediate bands.[1] We have studied the structural and electronic properties of InAs quantum dots (QDs) embedded in Al0.3Ga0.7As, (bandgap of 1.99 eV) designed for optimized intermediate band solar cells.[2]
The InAs/AlGaAs QD structures were grown by metalorganic chemical vapor deposition. InAs dots formed as a result of Stranski-Krastanov growth. Each layer of QDs was capped by a 20 nm and 5 nm GaAs layer in samples A and B, respectively. The temperature was then raised during deposition of the capping layer. Once the capping layer was completed, not necessarily fully covering the dots, growth was halted and the temperature was raised to 630 oC which is known as indium flushing.[3] The structure consisted of ten layers of InAs dots separated by 90-nm-thick Al0.3Ga0.7As barriers. Two-beam diffraction contrast images of the QDs in each sample were recorded in a Philips CM200-FEG electron microscope. The InAs dots were also studied from high-angle annular dark field images which were taken in a JEOL ARM200F electron microscope.
The large lattice mismatch between the QDs and the matrix results in misfit dislocations. Fully-capped QDs (in sample A) exhibit moiré fringes in transmission electron microscope images, indicating significant misfit strain relaxation. Partially-capped QDs (in sample B) are found to be fully strained. The critical thickness for misfit strain relaxation has been determined by experiments. A model based on the equilibrium of the lattice misfit force and the dislocation line tension acting on misfit dislocation loops, is used to understand the experimental observations.
Strong photoluminescence peaks were observed at around 1.3 eV for the strained QDs (Sample B), a value that is close to optimum for intermediate band solar cells. No such luminescence is observed from relaxed QDs. The suppression of plastic strain relaxation improves the photoluminescence of the system indicating that the intermediate band solar cells are promising devices to overcome the standard solar cell efficiency limit leading to better harvesting of light and energy conversion.
References:
[1] A. Martí et al, in Conference Record of the 28th IEEE Photovoltaics Specialists Conference, (IEEE, New York, USA, 2000), pp.940–943.
[2] R. Jakomin et al, J. Appl. Phys. 116, 093511 (2014).
[3] Z. Wasilewski et al, Cryst. Growth 202, 1131(1999).
9:00 PM - NT1.10.10
From Wurtzite to Cubic Structures: Large Tunability in Composition of ZnMgO Nanostructures Fabricated by Vapor Transport Technique for UV Applications
Jignesh Vanjaria 1,Ebraheem Azhar 1,Hongbin Yu 1
1 Arizona State University Tempe United States,
Show AbstractSemiconductor nanostructures are the most attractive class of materials for current and future functional nanodevices in many applications. Zinc oxide (ZnO) is one such promising semiconductor, which has recently attracted significant attention due to its wide direct band gap, high exciton binding energy and its ability to form a variety of nanostructured configurations. One interesting feature of ZnO is the possibility of tuning its band gap by incorporating magnesium in the structure via alloying. The ZnMgO alloy system raises the possibility of a new optically tunable family of wide band gap materials, which can be used for UV optoelectronic devices. Previous attempts have been made to grown ZnMgO nanostructures with a high Mg content using a variety of techniques, but have not been very fruitful, with results being mainly restricted to a low Mg content and thus a wurtzite structure. Here we report a large tuning in the Mg content of ZnMgO nanostructures grown via vapor transport method, with varying Mg content under different growth conditions. The grown nanostructures, accordingly, varied from wurtzite structure with a low Mg content, to cubic structure with a large Mg content. The vapor transport method was used as it is a simple and cost effective technique for the growth of nanostructures and allows for readily varying the composition of the nanostructures by varying the input content of source materials and the operating conditions.
ZnMgO nanostructures were synthesized using ZnO and magnesium boride (MgB2) powders as source materials on ZnO coated Si substrates. Two different types of nanostructures were grown with two different growth conditions. The structural, compositional and optical properties of the grown nanostructures were investigated by field emission scanning electron microscopy, energy dispersive x-ray spectroscopy and Raman scattering. In the first type, cubic nanostructures were observed while in the second type, branched nanowires along with wurtzite nanoclusters were observed. EDX analysis of the grown nanostructures revealed a non-uniform concentration of Mg in both types. The cubic nature of the first type points to a Mg concentration of above 67% while the wurtzite nature of the nanoclusters in the second type points to a Mg concentration below 36%, as per literature. The Raman spectra of both types exhibited peaks corresponding to the host phonons of ZnO and peaks in the 600-650 cm-1 region corresponding to ZnMgO alloy system. The peaks in 600-650 cm-1 region are indicative of a blue shift brought about by Mg substitution. The first type exhibited a single peak in the 600-650 cm-1 region while the second type exhibited two peaks in the region possibly indicating the occurrence of phase separation in the second type.
The fabrication of the above mentioned nanostructures along with the results of the various characterization techniques performed, including optical properties in UV range, will be presented in detail.
9:00 PM - NT1.10.11
Conformal Core-Shell Nanostructured Photodetectors with Enhanced Photoresponsivity by High Pressure Sputter Deposition
Filiz Keles 1,Hilal Cansizoglu 1,Matthew Brozak 1,Tansel Karabacak 1
1 Univ of Arkansas-Little Rock Little Rock United States,
Show Abstract
Working gas pressure during sputter deposition can significantly affect the conformality of a thin film when it is grown on a nanostructured surface. In this study, we fabricated core-shell nanostructured photodetectors, where n-type In2S3 nanorod arrays (core) were coated with p-type CuInS2 (CIS) films (shell) at relatively low and high Ar gas pressures. In2S3 nanorods were prepared by glancing angle deposition (GLAD) technique using a thermal evaporator unit. CIS films were deposited by RF sputtering at Ar pressures of 2.75x10-2 mbar (high pressure) and 7.5x10-3 mbar (low pressure). The morphological characterization was carried out by means of the SEM. The photocurrent measurement was conducted under AM 1.5 irradiance. Nanostructured photodetectors of high pressure CIS films were shown to demonstrate enhanced photoresponse with 0.099 mA photocurrent value about ~2.4 times higher than low pressure CIS thin film devices. The enhancement originates from the improved core-shell structure achieved by more conformal coating of the CIS shell. In addition, the results were compared to their counterpart thin-film devices for both high and low pressure growth conditions. Nanorod devices with high and low pressure CIS films showed photocurrent values ~20-fold and
~18-fold increase compared to those of high and low pressure film devices, respectively. This finding can be explained by the higher light absorption property of nanorods, and the reduced inter-electrode distance as a result of core-shell structure, which allows the effective capture of the photogenerated carriers. Therefore, the results of this work can pave way to the development of high photoresponce core-shell semiconductor devices fabricated by physical vapor deposition.
9:00 PM - NT1.10.12
Omnidirectional Broadband Antireflection Coating for Silicon Solar Cell Using ITO Nanostructures
Sang Hyuk Won 1,Min Joo Park 1,Sungbum Kang 1,MinJi Im 1,Kyoung Jin Choi 1,Chan Ul Kim 1
1 UNIST Ulsan Korea (the Republic of),
Show AbstractAnti-reflection coatings (ARCs) in typical solar cells (SCs) adopt single- or multi-layered thin films with intermediate refractive indices between air and SC materials with a thickness corresponding to quarter wavelength. But they are effective only for a limited range of wavelength and incident angle. In this work, we fabricated a variety of ITO nanostructures such as thin films, nanorods, nanotrees etc. through an oblique angle deposition technique using electron-beam evaporator and applied these nanostructures into ARCs for planar p-Si SCs. From SEM and TEM analyses, the ITO nanotree was found to be grown via a self-catalytic mechanism above ~ 200 °C and the branches have an epitaxial relationship with the trunks. We prepared four Si solar cells with different ARCs; a thin film of TiO2 with quarter-wavelength thickness (thin film ARC), dense ITO nanorods (dense ARC), dense ITO nanorods/porous ITO nanotrees (hybrid ARC) along with a reference solar cell without any ARC (no ARC). The reflectance is significantly decreased from 35% (no ARC) to 12% (thin film ARC), 9% (dense ARC) and finally 7% (hybrid ARC), which is responsible for the enhancement of solar cell efficiency to 25% (thin film ARC), 38% (dense ARC), and 47% (hybrid ARC) compared with the reference cell. Also in the angular reflectance measurements from 20° to 70°, the hybrid ARC has a very low reflectance of 7% and excellent omni-directionally reflectance, which is significantly low compared with 11% (dense ARC), 18% (thin film ARC), and 45% (no ARC). By considering the angular dependence of solar cells, the annual power density was calculated based on the meridian transitaltitude of Seoul, Republic of Korea. The power enhancement by omnidirectional light absorption is as high as 33.5% in the hybrid ARC solar cell, compared with 16.3% (dense ARC) and 1.4% (thin film ARC). Our results suggest that onmi-directional ARC can be a breakthough technology for the solar power generation.
9:00 PM - NT1.10.13
Heavy-Metal-Free Copper-Indium-Selenide Quantum Dot Solar Cells Exceeding 8% Photoconversion Efficiency
Jiwoong Yang 2,Taeghwan Hyeon 2
1 Center for Nanoparticle Research Institute for Basic Science Seoul Korea (the Republic of),2 School of Chemical and Biological Engineering Seoul National University Seoul Korea (the Republic of),
Show AbstractCopper-indium-selenide (CISe) quantum dots (QDs) are promising candidates which can replace the toxic cadmium- and lead-chalcogenide QDs typically employed in QD solar cell (QDSC) applications. However, there is still a huge gap between the performance of CISe QDSCs and that of conventional toxic QD based devices. Here, we present highly efficient heavy-metal-free CISe QD sensitized solar cells exceeding 8% photoconversion efficiency.1 By changing the size of QDs, electronic band alignment of QDs can be tuned to optimize the energetics for the effective light absorption and injection of electrons into the TiO2.2 In addition, we find that much thicker ZnS protecting layers compared to the conventional one are required to suppress the recombination losses. Both interfacial electron recombination with the electrolyte and nonradiative recombination associated with QDs are graetly reduced, while energetic characteristics of the photoanode are maintained. Finally, our best cell yields a photoconversion efficiency of 8.10% under AM 1.5 G one sun illumination, a record high value for heavy-metal-free QDSCs.
Reference
1) ACS Nano, 2015, 9, 11286–11295.
2) Phys. Chem. Chem. Phys. 2013, 15, 20517-20525.
Symposium Organizers
Alexander Govorov, Ohio University
Renaud Bachelot, University of Technolology of Troyes, Charles Delaunay Institute, CNRS
Din Ping Tsai, Academia Sinica
Gary Wiederrecht, Argonne National Laboratory
NT1.11: Metamaterials and Nanostructures for Various Applications
Session Chairs
Jerome Plain
Joel Yuen-Zhou
Friday AM, April 01, 2016
PCC West, 100 Level, Room 105 C
9:30 AM - *NT1.11.01
Metafilms and Metasurfaces for Solar Energy Harvesting
Mark Brongersma 1
1 Stanford Univ Stanford United States,
Show AbstractMost devices used for solar energy harvesting consist of thin, stacked films of metals and semiconductors. In this presentation, I will demonstrate how one can improve the performance of such devices by nano-structuring the constituent layers at length scales below the wavelength of light. The resulting metafilms and metasurfaces offer opportunities to dramatically modify the optical absorption and reflection properties of device layers. This is accomplished by encoding the optical response of nanoscale resonant building blocks into the effective properties of the films and surfaces. To illustrate these points, I will show how nanopatterned metal and semiconductor layers may be used to enhance the performance of solar energy harvesting devices.
10:00 AM - *NT1.11.02
Motion Detectors Based on Graphene-Integrated Plasmonic Metasurfaces
Gennady Shvets 1
1 Department of Physics and Center for Nano and Molecular Science and Technology The University of Texas at Austin Austin United States,
Show AbstractPlasmonic metasurfaces enhance light-matter interaction by focusing light into extremely subwavelength dimensions. These carefully designed structures have been used in extremely thin optical component which can mold the wavefront, with exciting applications in optical lenses, beam steering, and biosensing applications. Adding dynamic tunability to these devices opens up the possibility for new application in single pixel detection and 3D imaging as well as optical modulators and switches. However the existing approaches for designing active optical devices in infrared, are either slow or have small refractive index change. Integrating plasmonic metasurfaces with single-layer graphene (SLG) opens exciting opportunities for developing active plasmonic devices because the amplitude and phase of the transmitted and reflected light can be rapidly modulated by injecting charge carriers into graphene [1]. I will describe our recent experimental results demonstrating strong phase modulation in reflection. The phase change due to electric gating of the SLG in the mid-infrared frequency band was measured using a Michelson interferometer. It is shown that the phase of the reflected light can be modulated while keeping its amplitude constant. The phase change is used to demonstrate an electrically controlled (i.e. no moving parts) interferometry capable of measuring distances with sub-micron accuracy. Because of the potentially nanosecond-scale measurement time, active metasurfaces represent a promising platform for ultra-fast standoff detection. [1] Nima Dabidian, Iskandar Kholmanov, Alexander B. Khanikaev, Kaya Tatar, Simeon Trendafilov, S. Hossein Mousavi, Carl Magnuson, Rodney S. Ruoff, and Gennady Shvets, “Electrical Switching of Infrared Light Using Graphene Integration with Plasmonic Fano Resonant Metasurfaces”, ACS Nano 2, 216 (2015).
10:30 AM - NT1.11.03
Growth of Multisegment ZnxCd1-xSySe1-y Nanosheets for Photonic Applications in Full Visible Spectrum
Sunay Turkdogan 2,Fan Fan 1,Seyed Ebrahim Hashemi Amiri 1,Cun-Zheng Ning 1
1 School of Electrical, Computer and Energy Engineering Arizona State University Tempe United States,2 Electronic and Communication Engineering University of Yalova Yalova Turkey,1 School of Electrical, Computer and Energy Engineering Arizona State University Tempe United States
Show AbstractWe report the growth of compositionally graded ZnCdSSe nanosheet heterostructures realized by a novel growth method using a simple CVD route. The resulting products show great promise for lasers and LEDs emitting the white light or any color in the CIE chromatic coordinates. The nanosheets have thicknesses in the range of 60-350 nm and lateral dimensions of up to 60 μm by 40 μm. Compositionally graded heterostructures have attracted a great deal of attentions and various applications were demonstrated using such structures [1-3]. It was shown that nanosheets are the preferred morphology for photonic applications especially for lasers [2]. However, the realization of such nanosheets with high ZnS (Se)-contents for blue emission represent a significant challenge due to the low vapor pressure of ZnS (Se). To overcome such low pressure restriction and to realize multisegment ZnxCd1-xSySe1-y quaternary alloy nanosheets in a side-by-side cavity to emit in the full visible spectrum, we developed a two-step strategy [1]. The novel growth method takes full advantage of the interplay between VLS and VS growth mechanisms, followed by a dual-ion (simultaneous anion and cation) exchange process. The latter one is the most important aspect of our growth method and the evidence of this process was studied in detail through EDS, XRD and PL analyses.Specifically, ZnS and CdSe powders were used as precursors and temperature-dependent composition control was utilized in the growth. As the growth temperature decreases composition of ZnCdSSe structures shifts from ZnS-rich to CdSe-rich side and the morphology changes from nanowire to nanosheet, respectively. First, Cd- and Se-rich ZnCdSSe nanosheet structures are grown at 640°C. The substrate was then moved to 780°C region using a magnet driven rod to further promote diffusion processes. This causes the structures to transform uniformly into a Zn- and Se-rich ZnCdSSe alloy without changing morphology or crystal structure, allowing blue emission. The growth process was then followed by growth at 740°C and the second segment was synthesized by incorporating more Cd and Se ions for green emission. The final growth step at 640°C, added the CdSe-rich segment for red emission, resulting finally in multisegment heterostructure capable of simultaneous RGB (white) light emission. The lower substrate temperatures during third and fourth steps of the growth favor the VS mechanism for 2D nanosheet growth unlike the second case where the exchange process is dominant over the ion transport. By manipulating the position of the substrate and the growth sequence we can grow multiple parallel segments consisting of desired alloy compositions in an ordered or any desired manner for a specific sequence of segments with different bandgaps. [1] F. Fan et al. Nature nanotechnology 10, 796-803 (2015) [2] F. Fan et al. Semicond. Sci. Technol. 28, 065005 (2013)[3] Z. Liu et al. Nano letters 13.10 4945-4950 (2013)
10:45 AM - NT1.11.04
Turning Windows into Daytime Power Supplies: Luminescent Solar Concentrators Enabled by CuInSeS Quantum Dots
Hunter McDaniel 2,Francesco Meinardi 3,Victor Klimov 2,Sergio Brovelli 3
1 UbiQD, LLC Los Alamos United States,2 Los Alamos National Laboratory Los Alamos United States,3 University of Milan-Bicocca Milan Italy2 Los Alamos National Laboratory Los Alamos United States
Show AbstractBuilding-integrated sunlight harvesting could revolutionize urban architecture by enabling buildings to generate their own electricity. Luminescent solar concentrators (LSCs) are one promising approach wherein windows are turned into daytime power supplies. LSCs work by tinting windows with a fluorophore that down converts direct or diffuse light into a wave guided luminescence for collection by an edge-coupled photovoltaic. The fluorophores typically investigated are highly emissive dyes or quantum dots that are then embedded in or coated upon a glass or plastic waveguide. The luminescence propagates to the waveguide edges by total internal reflection and is converted into electricity by high-efficiency solar cells installed along the slab perimeter. Since the surface of the slab exposed to sunlight can be much larger than the surface of its edges, the LSC effectively increases the photon density incident onto the solar cell, which boosts both the photocurrent and the photovoltage. Moreover, by matching the emission wavelength of active chromophores to the spectral peak of the external quantum efficiency, one can achieve a further increase in the power output of the devices. It is also noteworthy that the color and the degree of transparency of an LSC, that are defined by the type and the concentration of the fluorophore, can be chosen according to specific building requirements and/or aesthetic criteria.
Wide use of LSCs has so far been hindered by the lack of suitable emitters. Typically used conjugated organic fluorophores provide a limited coverage of the solar spectrum and suffer from significant optical losses associated with re-absorption of guided luminescence. These deficiencies reduce the light harvesting efficiency of LSCs and also lead to strong coloring of devices, which imposes certain constrains on their usage in architecture. Colloidal quantum dots can help overcome these limitations. They can feature near unity photoluminescence quantum yields (QY) and narrow, widely tunable emission spectra that can be readily matched to various low-cost, high-efficiency solar cells.
An interesting class of low-toxic materials that provide a large, hundreds of meV Stokes shift are QDs of ternary I-III-VI2 semiconductors such as CuInS2, CuInSe2, and their alloys (CuInSeS). An attractive feature of these QDs is that they do not contain toxic heavy metals and can be fabricated in large quantities via high-throughput, non-injection techniques using inexpensive precursors. Furthermore, their large absorption cross-sections and a spectrally tunable, near-IR absorption onset are well suited for harvesting solar radiation. In this presentation, McDaniel will discuss recent colorless LSC results published in Nature Nanotechnology (2015, 10, 878–885) demonstrating a power conversion efficiency of 3.2% at 80% transmittance using CuInSeS quantum dots.
11:30 AM - *NT1.11.05
Metamaterial Infrared Absorber and Its Application for Attomole Detection of Organic Molecules
Takuo Tanaka 2,Atsushi Ishikawa 3
1 Metamaterials Laboratory RIKEN Wako Japan,2 Tokyo Institute of Technology Yokohama Japan,1 Metamaterials Laboratory RIKEN Wako Japan,3 Okayama University Okayama Japan
Show AbstractMetamaterial infrared absorber was applied for a background-suppressed surface-enhanced molecular detection technique. By utilizing the resonant coupling of plasmonic modes of a metamaterial absorber and infrared (IR) vibrational modes of a self-assembled monolayer (SAM), attomole level sensitivity was experimentally demonstrated. IR absorption spectroscopy of molecular vibrations is of importance in chemical, material, medical science and so on, since it provides essential information of the molecular structure, composition, and orientation. In the vibrational spectroscopic techniques, in addition to the weak signals from the molecules, strong background degrades the signal-to-noise ratio, and suppression of the background is crucial for the further improvement of the sensitivity. Here, we demonstrate low-background resonant Surface Enhanced IR Absorption (SEIRA) by using the metamaterial IR absorber that offers significant background suppression as well as plasmonic enhancement. The fabricated metamaterial consisted of 1D array of Au micro-ribbons on a thick Au film separated by a transparent gap layer made of MgF2. The surface structures were designed to exhibit an anomalous IR absorption at ~ 3000 cm-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick SAM with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes were clearly observed as reflection peaks within a broad plasmonic absorption of the metamaterial. Our metamaterial approach may open up new doors for further lowering the detection limit of far-field IR vibrational spectroscopy.
[1] A. Ishikawa and T. Tanaka, Scientific Reports 5, 12570 (2015).
12:00 PM - NT1.11.07
Circularly Polarized Light Detection with Hot Electrons in Chiral Plasmonic Metamaterials
Wei Li 1,Zachary Coppens 1,Lucas Besteiro 2,Wenyi Wang 1,Alexander Govorov 1,Jason Valentine 1
1 Vanderbilt University Nashville United States,2 Ohio University Athens United States
Show AbstractCircularly polarized light is utilized in various optical techniques and devices. However, using conventional optical systems to generate, analyse and detect circularly polarized light involves multiple optical elements, making it challenging to realize miniature and integrated devices. While a number of ultracompact optical elements for manipulating circularly polarized light have recently been demonstrated, the development of an efficient and highly selective circularly polarized light photodetector remains challenging. Here we report on an ultracompact circularly polarized light detector that combines large engineered chirality, realized using chiral plasmonic metamaterials, with hot electron injection. We demonstrate the detector’s ability to distinguish between left and right hand circularly polarized light without the use of additional optical elements. Implementation of this photodetector could lead to enhanced security in fibre and free-space communication, as well as emission, imaging and sensing applications for circularly polarized light using a highly integrated photonic platform.
12:15 PM - NT1.11.08
Metamaterial Sensor Based on Vertical Split-Ring Resonator
Wei-Yi Tsai 1,Yi-Hao Chen 1,Pin Chieh Wu 1,Wei Ting Chen 1,Yao-Wei Huang 1,Wei-Lun Hsu 1,Greg Sun 2,Din Ping Tsai 3
1 Physics National Taiwan University Taipei Taiwan,2 Engineering University of Massachusetts Boston Boston United States1 Physics National Taiwan University Taipei Taiwan,3 Research Center for Applied Sciences Academia Sinica Taipei Taiwan
Show AbstractSplit-ring resonators (SRRs) is a promising reserach theme that have been attracted a lot of interest in the field of plasmonics sensor. SRRs be implament by sensing plasmon resonance shift (∂λ) when exposed to a medium with a refractive index change ∂n. In general, the plasmon field of planar SRRs leak into the substrates, which decrease volume of response and performance. These limitations can be solved by utilizing vertical SRRs. The plasmon fields localized in vertical SRR gaps keep away the substrate, allowing for significantly enhanced sensitivity. Here, we demonstrated the highest sensitivity among reported SRR-based sensors in optical region.
NT1.12: Novel Nanomaterials for Optics
Session Chairs
Friday PM, April 01, 2016
PCC West, 100 Level, Room 105 C
2:30 PM - NT1.12.01
Chiroptical Polymer Film Exhibiting Tunable Chirality and Circularly Polarized Luminescence
Hirotaka Ihara 2,Taisei Goto 1,Yutaka Okazaki 1,Masahiro Ueki 1,Yutaka Kuwahara 1,Makoto Takafuji 1,Reiko Oda 4
1 Kumamoto Univ Kumamoto Japan,2 Phoenics Kumamoto Japan,1 Kumamoto Univ Kumamoto Japan3 CBMN Bordeaux France,4 University of Bordeaux Bordeaux France
Show AbstractWe demonstrate a new strategy for fabricating next-generation light management film using molecular assembling-based chirality. This is based on nano-fibrillar aggregation of the fluorescent glutamide derivatives in polymer and induction of enhanced circular dichroism (CD) and circularly polarized luminescence (CPL) through highly ordered chiral arrangement. Glutamide is a generic term to indicate a glutamic acid derivative, which is characterized by the fact that a functional head group such as a fluorescent group and double alkyl chains are combined into a glutamic acid through amide bonds.
When the glutamides functionalized with fluorophores such as pyrene and anthracene were dissolved in proper organic solvents and then kept at 20 C, not only high Stokes shifts were observed in their fluorescent spectra, but also strong CD signals were detected around their absorption bands. These phenomena can be explained by their excimer emissions through chirally ordered stacking among the fluorophores due to self-assembling driven with the glutamide units. TEM observations indicated that nanofibillar aggregates were mainly produced in their cast films.
The polymer film was prepared from a mixture of the fluorophoric glutamide (1 wt%) with polymer (99 wt%) such as polystyrene and poly(methyl methacrylate) by a usual casting method. The resultant films were transparent and colorless, but exhibited excimer emission with large CD signals similarly to those in the solution states. In addition, the TEM observation indicated nanofibrillar aggregates in the polymer film. These results indicate that the chirally ordered stacking states of the fluorophores can be reproduced even in polymer. We detected circularly polarized luminescence (CPL) signals around their emission bands in both a solution and a polymer film. In this paper, we also describe that the intensity and emission bands can be tuned by adjusting the secondary chirality based on the glutamide aggregates as chiral templates.
2:45 PM - NT1.12.02
Plasmonic Copper Chalcogenide Nanostructures: Controllable Synthesis, Properties and Applications
Feifan Wang 1,Qi Li 1,Li Lin 1,Hailin Peng 1,Zhongfan Liu 1,Dongsheng Xu 1
1 Peking University Beijing China,
Show AbstractRecently, localized surface plasmon resonances (LSPRs) arising in copper chalcogenide nanocrystals (NCs), also called “self-doped” semiconductor NCs, are under intense investigation and expected to facilitate the light harvesting, nonlinear optics, and quantum information processing. However, systematic studies of the influence factors on the plasmonic properties are rarely achieved due to the poorly-controlled synthesis or the mutable light-mater interactions. Therefore, controllable synthesis of copper chalcogenide NCs, including desired geometry, composition and surrounding environment, is of high significance for the modulation of their optoelectronic response and the corresponding applications.
In this study, highly monodisperse copper chalcogenide (Cu2-xS) NCs are synthesized through a one-pot strategy by using copper nitride as “uncontaminated” copper precursors. Following this method, the size of Cu2-xS NCs and composition of Cu2-xSySe1-y NCs can be readily controlled by varying the ratio of the precursors. The plasmonic properties of the copper chalcogenide NCs are investigated under a steady state by tuning the plasmonic resonance absorption band to a limiting condition (denoted “pinning” phenomena). It is observed that the pinning frequency increases (from 1.09 to 1.23 eV) with the increment of the NC size (from 5.4 to 11.0 nm) and blue-shifts (from 0.90 to 1.00 eV) with the increase of selenium content (from 11% to 66%), which can be attributed to the influence of surface scattering and effective mass of free carriers, respectively. Additionally, the plasmonic absorption bands of Cu2-xS NCs encapsulated by two single-layer graphene pin at 1525−1550 nm during the oxidation process, which is influenced by both the dielectric constant and redox potential of the surrounding environment. This study demonstrates the controllable synthesis and precise fundamental plasmonic properties of the copper chalcogenide NCs, ensuring the potential plasmonic-related techniques (photothermal therapy, photoacoustic tomography, photothermal catalysis, etc.) with high efficiency, accuracy and excellent spatial resolution.
3:00 PM - NT1.12.03
Plexcitons: Energy Transfer, Dirac Cones and Topological Modes
Joel Yuen-Zhou 1
1 University of California San Diego San Diego United States,
Show AbstractPlexcitons are hybrid plasmon-exciton states with properties that interpolate between photonic and material excitations. They serve as an interesting laboratory to explore the interplay between coherent and incoherent excitation energy transfer pathways between molecular assemblies. Here, I present a theoretical study of a model system composed of two weakly coupled plexciton films and the rich phase diagram that ensues as a function of angle of excitation of the donor plexciton, the orientation of the acceptor plexciton, and the distance separating these moieties. Coherence is imprinted into the system by default due to the inherent spatial coherence of the plasmons. An exquisite experimental control of the different channels of energy transfer can be obtained. This work is in collaboration with experimentalist Prof. Vinod Menon at CCNY. Our studies suggest interesting opportunities in molecular polaritonics, from the design of exotic states of matter (topological phases, analogues of topological insulators) to a more refined control of energy transfer in the nanoscale. This model system serves as a platform to understand the opportunities that plexcitons offer for solar light-harvesting.
3:15 PM - NT1.12.04
Responsive Gold Nanorod (AuNR) Nanocomposites: Colorimetric and Polarization Sensing via In Situ Reshaping of Nanorods with Light
Kyoungweon Park 2,Richard Vaia 1
1 Air Force Research Laboratory Wright Patterson AFB United States,2 UES Dayton United States,1 Air Force Research Laboratory Wright Patterson AFB United States
Show AbstractThe stability of AuNRs is critical for various optoelectronic and sensing systems since their optical properties depend on their shape and volume. How reshaping depends on the structure, diffusivity and chemistry of the local environment though, has not been systematically studied. To address this challenge, we discuss the reshaping of AuNRs embedded in poly(vinyl alcohol) (PVA) upon exposure to UV-Vis light. The optical stability depends significantly on the initial aspect ratio and volume of the AuNR, as well as the chemistry and composition of the surface stabilizers. Fundamentally, optical reshaping is accelerated by increasing hexadecyltrimethylammonium bromide(CTAB) concentration at high convex curvature. These parameters can be rationally introduced to fabricate colorimetric sensing nanocomposites which reflect the history of UV-Vis light exposure. Furthermore, combining patterned intensity with deformation induced rod alignment creates a mechanically compliant nanocomposite with polarization and spectral responsivity for the fabrication of optoelectronic devices, sensors, and optical filters.
3:30 PM - NT1.12.05
Hybrid Thermodynamics for Hydrogen in Palladium Nanocubes and Nanoparticles for Active Plasmonics
Nikolai Strohfeldt 1,Ronald Griessen 2,Harald Giessen 1
1 4th Physics Institute, University of Stuttgart Stuttgart Germany,2 Faculty of Sciences, Division of Physics and Astronomy VU University Amsterdam Netherlands
Show AbstractPalladium-hydrogen is a prototypical metal-hydrogen system, which is well suited for active plasmonics. Upon hydrogenation of Pd to PdHx, it is possible to change the dielectric function and hence the plasmonic resonance1–3. Recently, also materials such as Yttrium and Magnesium have shown such properties4,5. It is therefore not at all surprising that a lot of attention has been devoted to the ab- and desorption of hydrogen in nanosized plasmonic palladium particles. Here, we show that the large body of data on the thermodynamics of palladium nanostructures available so far in literature6–10 exhibits general patterns that lead to unambiguous conclusions about the detailed microscopic processes involved in H absorption and desorption in Pd nanoparticles that can be used as prototypes for active plasmonic elements. On the basis of a remarkably robust scaling law for the hysteresis in absorption-desorption isotherms, we show that hydrogen absorption in palladium nanoparticles is consistent with a coherent interface model and is thus clearly different from bulk Pd behavior. However, H desorption occurs fully coherently only for small nanoparticles (typically smaller than 50 nm) at temperatures sufficiently close to the critical temperature. For larger particles it is partially incoherent as in bulk, where dilute α-PdHx and high concentration β-PdHx phases coexist. In support of these conclusions, we also developed a semi-analytical model that is able to reproduce all the essential features of the thermodynamics of H in Pd nanoparticles over a wide range of sizes (from a few nm up to hundreds of nm) as long as no dislocations are generated in the core of the particles.
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