Prineha Narang, Harvard University
Emiliano Cortes, Imperial College London
Suljo Linic, University of Michigan–Ann Arbor
Marin Soljacic, Massachusetts Institute of Technology
NG Next, Northrop Grumman
ED13.1: Excited-State Plasmonics and Nanophotonics
Tuesday AM, April 18, 2017
PCC North, 100 Level, Room 132 B
11:30 AM - *ED13.1.01
Excited States Phenomena in Organic Solids and Hybrid Interfaces with AB Initio Many-Body Perturbation Theory
Jeffrey Neaton 1 2 Show Abstract
1 Department of Physics, University of California, Berkeley, Berkeley, California, United States, 2 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Organic crystals and hybrid interfaces are a highly tunable, diverse class of cheap-to-process materials promising for next-generation optoelectronics. Further development of new materials requires new intuition that links atomic- and molecular-scale morphology to underlying excited-state properties and phenomena. Here, I will cover the use of first-principles density functional theory – including tuned hybrid functionals – and many-body perturbation theory – within the GW approximation and the Bethe-Salpeter equation approach – for computing and understanding spectroscopic properties of selected organic crystals, including acenes from benzene to hexacene; and, as time permits, I will additionally cover low-dimensional materials, such as 2d chalcogenides and halide perovskites. We elucidate the nature of low-lying solid-state singlet and triplet neutral excitations, which have significant charge-transfer character in these systems. For organic systems, implications for singlet fission rates are discussed. I will also discuss our studies of level alignment at metal-molecule interfaces, where we generalize optimally-tuned range-separated hybrid functionals to treat the electronic structure of several metal-organic interfaces, in agreement with experiment and with accuracy comparable to many-body perturbation theory.
12:00 PM - *ED13.1.02
Catalytic Reactions on Plasmonic Metal Nanoparticles—Known Knows and Known Unknowns about Hot Carrier Distribution
Suljo Linic 1 Show Abstract
1 Department of Chemical Engineering, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States
In has been recognized for some time that strong interaction of electromagnetic fields with plasmonic nanomaterials offers opportunities in various technologies that take advantage of photo-physical processes amplified by this light-matter interaction. More recently, we demonstrated that in addition to photo-physical processes, optically excited plasmonic nanoparticles can also activate chemical transformations directly on their surfaces. We proposed that these transformations are driven by energetic charge carriers that are transferred from plasmonic nanoparticles to the reacting adsorbates.
I will discuss underlying mechanisms associated with these phenomena; including the mechanism of charge-carrier driven chemical transformations on metals as well as the mechanisms behind the plasmon-induced charge injection processes. We propose that this new family of photo-catalysts could prove useful for in the field of selective chemical synthesis. I will show an example of such a process.
1. C Boerigter, R Campana, M Morabito, S Linic, Nature communications, 7, 2016
2. C. Boerigter, U Aslam, S Linic, ACS Nano 10 (6), 6108-6115, 2016
3. S. Linic, U Aslam, C Boerigter, M Morabito, Nature Materials 14 (6), 567-576
4. Andiappan, S. Linic Science, 339, 1590, 2013
5. D. B. Ingram, S. Linic, JACS, 133, 5202, 2011
6. Suljo Linic, Phillip Christopher and David B., Nature Materials, 10, 911, 2011.
7. P. Christopher, H. Xin, S. Linic, Nature Chemistry, 3, 467, 2011.
8. P. Christopher, H. Xin, M. Andiappan, S. Linic, Nature Materials, 11, 1044, 2012.
12:30 PM - *ED13.1.03
Photonic Design as a Probe of Nanoscale Energy Conversion Mechanisms
Harry Atwater 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States
Nanophotonic design represents a powerful tool to investigate energy conversion mechanisms at the nanoscale. In this talk I will discuss i) photonic design of ultrathin transition metal dichalcogenide solar cells that reveals aspects of resonant absorption and carrier collection that can enable very high external quantum efficiency; ii) resonant ultrathin metallic structures that serve as probes of hot carrier photocurrent generation at metal/wide bandgap semiconductor interfaces and thin resonant absorbers for studying photocatalysis; and iii) thermoelectric-junction nanantenna arrays coupled to guided mode resonant waveguides that give rise to narrowband absorption at a wavelength defined by the array geometrical parameters; when these antennas are defined as thermoelectric junctions on a low thermal conductivity membrane substrate, the temperature rise associated with resonant optical absorption induces a measurable thermoelectric potential, with potential to serve as component elements of resonant photodetectors with sensitivity over a very broad spectral range.
ED13.2: Atomic-Scale Nanophotonics and Plasmonics I
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 132 B
2:30 PM - *ED13.2.01
Salient Features of Extreme Photonics
Inigo Liberal 1 , Nasim Mohammadi Estakhri 1 , Brian Edwards 1 , Nader Engheta 1 Show Abstract
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
The ability to design and construct composite materials at the subwavelength scales has provided novel platforms and exciting paradigms for unprecedented control of light-matter interaction. The notion of metamaterials has opened new venues for engineering and manipulating waves at will. This has led scientists and engineers to conceive scenarios beyond what natural materials exhibit. One such scenario is the extreme-parameter metastructures, in which sculpting and controlling of waves can possess certain extreme characteristics.
In our group, we have been investigating some of the wave physics and the quantum features of these extreme wave-based platforms such as near-zero relative permittivity, near-zero relative permeability, very high phase velocity, low group velocity, photonic doping in epsilon-near-zero (ENZ) structures, quantum ENZ photonics, zero-index-based control of vacuum fluctuations, nonreciprocal metastructures, giant anisotropy and nonlinearity, wave-based informatic devices for mathematical computation, metasurfaces with unprecedented functionalities, and optical metatronics, to name a few. Such “extreme photonics” offers unconventional platforms with exotic quantum and classical features and characteristics in wave-based and diffusion-based systems.
In this talk, we will give an overview of some of our ongoing research in these areas.
3:00 PM - ED13.2.02
Enabling and Controlling "Forbidden" Light-Matter Interactions in Polaritonic Media
Nicholas Rivera 1 , Ido Kaminer 1 , Francisco Machado 3 , Bo Zhen 1 , Hrvoje Buljan 2 , John Joannopoulos 1 , Marin Soljacic 1 Show Abstract
1 Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Physics, University of California, Berkeley, Berkeley, California, United States, 2 Physics, University of Zagreb, Zagreb Croatia
The diversity of light-matter interactions accessible to a system is limited by the small size of an atom relative to the wavelength of the light it emits, as well as by the small value of the fine-structure constant.
In the first part of this work, we developed a general theory of light-matter interactions with two-dimensional systems supporting plasmons. These plasmons effectively make the fine-structure constant larger and bridge the size gap between atom and light. This theory reveals that conventionally forbidden light-matter interactions—such as extremely high-order multipolar transitions, two-plasmon spontaneous emission, and singlet-triplet phosphorescence processes—can occur on very short time scales comparable to those of conventionally fast transitions. In fact we find that the rates of these transitions can all consistently fall in the microsecond to picosecond range for infrared transitions. These results extend to other polariton-sustaining systems where the confinement factor of the polaritons is very large (typically greater than 200).
Showing a means to access these transitions at very fast rates with polaritons, we move on in the second part of this work to show two schemes by which forbidden transitions can be made dominant over allowed transitions. In the first scheme, we imbue polariton wavepackets with angular momentum, changing the selection rules for both multipolar single polariton and multipolariton interaction processes. In the second scheme, we take advantage of the narrow Reststrahlen bands of polar dielectrics to selectively enhance slow transitions like two-photon spontaneous emission processes to the point where they are not only fast but dominate over all other decay mechanisms.
3:15 PM - *ED13.2.03
Quantum and Nonlocal Electrodynamics in Plasmonic Nanoparticles
N. Asger Mortensen 1 Show Abstract
1 , Technical University of Denmark, Kongens Lyngby Denmark
Plasmonics is commonly explored and interpreted within the framework of classical electrodynamics. On the other hand, with the increasing ability to explore plasmonics in nanostructures with yet smaller characteristic dimensions, intrinsic length scales of the electron gas are anticipated to manifest in a nonlocal plasmonic response and other quantum corrections to the light-matter interactions. Efforts to make semi-classical hydrodynamic extensions [1,2] will be addressed, as well as developments beyond these simplified models [3,4]. In nanoparticles, nonlocal response promotes frequency blueshifts and nonlocal damping of high-order modes, as has been observed in single-particle EELS . The nonlocal damping has implications for single-particle spectroscopy versus far-field measurements of ensemble-averaged spectral properties, where Landau-related homogenous broadening dominates size-dependent inhomogeneous broadening . As to the quantum mechanical origin of these effects, one can quantify the degree of nonclassical effects from an energy perspective . This provides a direct link between the experimentally observed resonance blueshift and the fraction of electromagnetic energy attributed to quantum degrees of freedom.
 N.A. Mortensen, S. Raza, M. Wubs, T. Sondergaard, and S.I. Bozhevolnyi, "A generalized non-local optical response theory for plasmonic nanostructures", Nature Communications 5, 3809 (2014)
 S. Raza, S.I. Bozhevolnyi, M. Wubs, and N.A. Mortensen, "Nonlocal optical response in metallic nanostructures",
J. Phys. Cond. Matter. 27, 183204 (2015)
 G. Toscano, J. Straubel, A. Kwiatkowski, C. Rockstuhl, F. Evers, H. Xu, N. A. Mortensen, and M. Wubs, "Resonance shifts and spill-out effects in self-consistent hydrodynamic nanoplasmonics," Nature Communications 6, 7132, (2015)
 W. Yan, M. Wubs, and N. A. Mortensen, "Projected Dipole Model for Quantum Plasmonics", Phys. Rev. Lett. 115, 137403 (2015)
 S. Raza, S. Kadkhodazadeh, T. Christensen, M. Di Vece, M. Wubs, N.A. Mortensen, and N. Stenger, "Multipole plasmons and their disappearance in few-nanometer silver nanoparticles", Nature Communications 6, 8788 (2015)
 C. Tserkezis, J.R. Maack, Z. Liu, M. Wubs, and N.A. Mortensen, "Robustness of the far-field response of nonlocal plasmonic ensembles", Sci. Rep. 6, 28441 (2016)
 W. Yan and N.A. Mortensen, "Nonclassical effects in plasmonics: An energy perspective to quantify nonclassical effects", Phys. Rev. B 93, 115439 (2006)
4:15 PM - *ED13.2.04
Scalable, Ultra-Resistant Structural Colors Based on Network Metamaterials
Federico Capasso 1 , Henning Galinski 1 2 , Andrea Fratalocchi 3 Show Abstract
1 John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Laboratory for Nanometallurgy, ETH Zurich, Zurich Switzerland, 3 PRIMALIGHT, King Abdullah University of Science and Technology (KAUST), Thuwal Saudi Arabia
Structural colors have drawn wide attention for their potential as a future printing technology for various applications, ranging from biomimetic tissues to adaptive camouflage materials. However, an efficient approach to realise robust colors with a scalable fabrication technique is still lacking, hampering the realisation of practical applications with this platform. Here we develop a new approach based on large scale network metamaterials, which combine de-alloyed subwavelength structures at the nanoscale with loss-less, ultra-thin dielectrics coatings.1 By using theory and experiments, we show how sub-wavelength dielectric coatings control a mechanism of resonant light coupling with epsilon-near-zero (ENZ) regions generated in the metallic network, manifesting the formation of saturated structural colors that cover a wide portion of the spectrum. Ellipsometry measurements demonstrate the efficient observation of these colors even at angles of 70 degrees. The network-like architecture of these nanomaterials allows for high mechanical resistance, which is quantified in a series of nano-scratch tests. With such remarkable properties, these metastructures represent a robust design technology for real-world, large scale commercial applications.
Collaborations with Gael Favraud, Hao Dong, Juan S. Totero Gongora, Grégory Favaro, Max Döbeli, Ralph Spolenak are gratefully acknowledged. This work was supported by AFOSR contract FA9550-12-1-0289
H. Galinski, et al. Light: Science & Applications (2017) 6, e16233; doi: 10.1038/lsa.2016.233.
4:45 PM - *ED13.2.05
Optoelectronics of Graphene-Based Van der Waals Heterostructures
Qiong Ma 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
The photoresponse of materials is governed by energy relaxation pathways of photo-excited electron-hole pairs. In graphene, due to frequent electron-electron collision and weak electron-lattice coupling, a novel transport regime is reached in which the photo-generated carrier population can remain hot while the lattice stays cool. In this talk, I will show that light is converted to electrical currents through a hot-carrier assisted thermoelectric effect in intrinsic graphene. The thermal energy slowly leaks to the lattice via two distinct processes of electron-phonon coupling that can be tuned by temperature and charge density. We also implemented a scheme to control the initial stage of photo-excited carriers before they collide with ambient carriers (less than ten femtoseconds) to form a hot Fermi-Dirac distribution, which is realized in a graphene-boron nitride-graphene heterostructure.
The weak electron-phonon coupling and frequent electron-electron scattering revealed above strongly alter the nature of particle and energy transport, leading to a collision dominant fluid behavior for electrons. In the last part of the talk, I will discuss our observation of highly-ordered photocurrent patterns at the charge neutral point of graphene, which is likely related to the ballistic thermal transport of hot electron-hole plasma in the hydrodynamic regime.
5:15 PM - ED13.2.06
Bianisotropy—A New Route towards Non-Reciprocal Optical Metasurfaces
Mark Lawrence 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Directional light flow is fundamental to the development of photonic information processors. To observe such nonreciprocal transport, time reversal symmetry must be broken. Unfortunately, mechanisms which violate time reversal symmetry, such as magneto-optic effects, are incredibly weak which generally leads to very bulky optical isolators. Recently, on-chip one way transmission was observed with asymmetrically arranged Si micro cavities due to the nonlinear Kerr effect in which the refractive index depends on the local electric field intensity . However, such demonstrations still involve optical paths that are tens to hundreds of microns in length.
Here, we show that Kerr based nonreciprocal devices can be miniaturized to the nanoscale by working with Si nanoantenna-based metasurfaces. Our chosen structure consists of a rectangular Si grating patterned with periodic notches on either side. Individual nanoantennas possess a high quality factor, Q~1950, trapped mode . This mode radiates via a weak (sub-radiant) electric dipole moment in the direction perpendicular to the gratings, originating from the difference in amplitude of anti-phase displacement currents at the unit cell centre and edge. Its linewidth and corresponding field enhancement can thus be engineered by controlling the overall volume occupied by the notches.
In the subwavelength regime structural asymmetry alone isn’t enough to generate directionally-dependent field amplification. We overcome this limitation by overlapping the sub-radiant electric dipolar mode with a super-radiant magnetic dipole directed parallel to the gratings. In this case, breaking out-of-plane inversion symmetry leads to nearfield coupling between the two excitations. Interference between nearfield and far field magneto-electric coupling then causes the electric dipole to be suppressed only for an incident wave propagating in the positive z direction (‘backward’) and not incident excitation in the negative z direction (‘forward’). Finally, when the metasurface is illuminated with power densities of a few 100kW/cm2, the electric field strength within the Si becomes sufficient to change its refractive index, red-shifting the narrow transmission dip. For forward excitation the electric dipole mode is shifted by a significant portion of the FWHM, making the metasurface transparent. For backward excitation the much smaller shift renders the transmission very low.
We show, for the first time, that bianisotropy provides a means to achieve optical nonreciprocity at the nanoscale. Relying simply on collocated dipolar excitations, the scheme presented here has, in principle, no lower size limitation and could be miniaturised further by making use of gain assisted plasmonics.
 L. Fan, et al, "An all-Silicon passive optical diode", Science 335, 447–450 (2012).
 J. Zhang, et al, "Near-infrared trapped mode magnetic resonance in an all-dielectric metamaterial", Optics express, 21, 26721 (2013).
5:30 PM - ED13.2.07
Coherent Control of the Optical Absorption and Fluorescence Enhancement in a Plasmonic Lattice Coupled to a Luminescent Layer
Giuseppe Pirruccio 1 2 , Mohammad Ramezani 2 4 5 , Said Rahimzadeh-Kalaleh Rodriguez 2 3 , Jaime Gomez Rivas 2 4 5 Show Abstract
1 , UNAM, Mexico City Mexico, 2 , FOM Institute AMOLF, Amsterdam Netherlands, 4 , Dutch Institute for Fundamental Energy Research, Eindhoven Netherlands, 5 , Eindhoven University of Technology, Eindhoven Netherlands, 3 , Laboratoire de Photonique et de Nanostructures, Paris France
Optical loss and absorption associated with metallic structures have been one of the long-lasting drawbacks of plasmonic materials and is considered as a major obstacle for various applications spanning from solid state lighting to solar cells.
In this work, we have used an array of aluminium nanoparticles covered with 200 nm layer of polymer (polystyrene) doped with fluorescent organic molecules. Our array supports localized surface plasmon resonances (LSPRs) as well as a collective surface lattice resonance (SLR) that are weakly coupled to the molecules. We experimentally demonstrate the coherent control, of the optical losses and the modulation of the emission from the ensemble of molecules through phase-dependent enhancement and suppression of the electromagnetic field intensity .
For the coherent control experiment, we have used a Mach-Zender interferometer comprising two coherent, collinear and counter-propagating laser beams illuminating the sample at normal incidence with equal intensities. The relative phase is controlled by changing the optical path length of one beam with respect to the other. In order to probe the response of the system with respect to the relative phase of the incident beams, we have measured the modulation of the photoluminescence intensity emitted by the sample at fixed angle, which reaches a value as high as 50%.
This result is explained in terms of the coherent control of the symmetry of the excitation field at the position of the dye layer. This leads to efficient control of the resonant excitation based on the match between the symmetry of the incident field in the dye layer and the symmetry of the field scattered off the nanoparticles. Spatial redistribution of the electric field intensity in the near-field for different phases implies a change in the relative absorption in the polymer layer and the metallic particles.
We have calculated the ratio of the absorption in the dye layer to the total absorption (dye+metallic particles) for different relative phases. This ratio is increased to 90% for coherently controlled excitation while, in the case of single wave excitation, it is 63%. The significantly higher absorption ratio for the two-waves illumination is the result of reduced pump enhancement by the nanostructure.
Creating a condition where the absorption in the plasmonic particles can be controlled and efficiently suppressed solves one of the major barriers in the field of plasmonics and opens up a new degree of freedom to control the unwanted dissipations in the metals.
 G. Pirruccio, M. Ramezani, S. R. K. Rodriguez and J. Gomez Rivas “Coherent control of the optical absorption in a plasmonic lattice coupled to a luminescent layer”, Phys. Rev. Lett. 116, 103002 (2016).
ED13.3: Poster Session I: Novel Photonic, Electronic and Plasmonic Effects in Materials I
Tuesday PM, April 18, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED13.3.01
High Damage Threshold Ga2O3 Dielectric Laser Accelerator
Huiyang Deng 1 , Kenneth Leedle 2 , Karel Urbanek 2 , Yu Miao 1 , Si Tan 2 , Jiaqi Jiang 3 , Andrew Ceballos 1 , Akito Kuramata 5 , Olav Solgaard 1 , Robert Byer 2 , James Harris 1 2 4 Show Abstract
1 Department of Electrical Engineering, Stanford University, Stanford, California, United States, 2 Department of Applied Physics, Stanford University, Stanford, California, United States, 3 Department of Physics, Tsinghua University, Beijing China, 5 , Tamura Corporation, Saitama Japan, 4 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States
The widespread use of high-energy particle beams in scientific research and medical applications currently requires enormous and expensive radio frequency (RF) accelerator facilities, thus spawning a strong need for alternatives. Dielectric laser accelerators (DLAs)– laser-driven dielectric nano-structures whose near fields can synchronously accelerate charged particles – recently demonstrated high-gradient acceleration [1,2].
The electron acceleration gradient scales linearly with incident laser electric field, thus limited by the laser-induced damage threshold (LIDT) of the constituent materials. So far, silicon dioxide (SiO2) has been used to fabricate relativistic DLAs because of its high LIDT . At sub-relativistic electron speeds, silicon (Si) with moderate conductivity is used instead to prevent severe beam steering due to charge accumulation. However, the LIDT of Si is much lower compared with SiO2 [3,4]. A material with high LIDT as well as moderate conductivity will be an ideal replacement for Si in the sub-relativistic regime for DLAs.
We proposed gallium oxide (Ga2O3), a semiconductor with resistivity between 10Ω-cm and 1mΩ-cm depending on doping level to be the best candidate material. We also present the first measurements of LIDT of Ga2O3. We measured LIDT of unintentionally-doped single-crystalline β-Ga2O3 (-201) wafer at 800nm using a Ti:sapphire laser with 766fs pulse length at a vacuum level of 1E-6 Torr, which are the same conditions as current DLA experiments. The measured LIDT of Ga2O3 is 3.4J/cm2, while Si is only 0.21J/cm2. This suggests that Ga2O3 can replace Si in sub-relativistic DLAs. Furthermore, compared to SiO2 with LIDT 2.2J/cm2, Ga2O3 is also an excellent candidate for relativistic DLAs. In addition, Ga2O3 has a refractive index of 1.9 at 800nm compared to 1.45 for SiO2, and hence serves as a better phase mask to more efficiently utilize the laser field to accelerate electrons. Along with high DC breakdown voltage and recent breakthroughs in fabrication , Ga2O3 could provide all the components: electron source, sub-relativistic DLA and relativistic DLA monolithically-integrated on a single-crystalline Ga2O3 substrate to realize a complete “accelerator on a chip.”
 Peralta, E. A., et al. "Demonstration of electron acceleration in a laser-driven dielectric microstructure." Nature 503.7474 (2013): 91-94.
 Breuer, John, and Peter Hommelhoff. "Laser-based acceleration of nonrelativistic electrons at a dielectric structure." Physical review letters111.13 (2013): 134803.
 Leedle, Kenneth J., et al. "Dielectric laser acceleration of sub-100 keV electrons with silicon dual-pillar grating structures." Optics letters 40.18 (2015): 4344-4347.
 McNeur, Joshua, et al. "Elements of a dielectric laser accelerator." arXiv preprint arXiv:1604.07684 (2016).
 Higashiwaki, Masataka, et al. "Recent progress in Ga2O3 power devices."Semiconductor Science and Technology 31.3 (2016): 034001.
9:00 PM - ED13.3.02
Design and Optimization of Hybrid Structure for Fast and deep SPP Electric Modulation
Chenlei Pang 1 , Hangwen Lu 2 , Minghua Zhuge 1 , Xiaowei Liu 1 , Pengfei Xu 1 , Zhechao Wang 3 , Qing Yang 1 4 Show Abstract
1 College of Optical Engineering, Zhejiang University, Zhejiang China, 2 Department of Electrical Engineering, California Institute of Technology, Pasadena, California, United States, 3 INTEC-department, Ghent University, Gent Belgium, 4 Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan China
Surface Plasmon Polariton (SPP) is the coupling effect of photons and electrons along the interface of materials, typically, between a metal and a dielectric. Because SPP’s unique properties, such as strong filed localization and manipulating light below diffraction limit, SPP is a promising candidate in the field of modern optoelectronic devices demanding higher speed and smaller size.
In our previous study, SPP’s electrical modulation based on graphene-nanowire hybrid structure has been demonstrated . However, modulation speed can only go to tens of kHz limited by the device’s huge electrical capacitance. On the other hand, low coupling efficiency between graphene and optical field makes modulation depth relatively small. In this work, we theoretically analyzed and compared the optical and electrical properties of different SPP modulation structures. After a series of optimization, a novel vertical hybrid metal-graphene-semiconductor structure with estimated modulation figure of merit (FoM) of more than 70% and response speed of hundreds of GHz is achieved , which is a great improvement compared to previous optical modulators. Our devices provide a way of fabricating ultra-compact nano photonic devices and may find its applications in optical computing, optical communications, nanoscaled SPP sources, etc.
 Qian, H. L.; Ma, Y. G.; Yang, Q.; Chen,B. G. Liu, Y.; Guo, X.; Lin, S. S.; Ruan, J. L.; Liu, X.; Tong, L. M.; Wang. Z. L. ACS Nano 2014, 8, 2584-2589.
 Pang, C. L.; Lu, H W.; Xu, P. F.; Qian, H. L.; Liu, X. W.; Liu X.; Li, H. F.; Yang, Q. Opt. Express 2016, 25, 17069-17079.
9:00 PM - ED13.3.03
Theoretical Study on the Effects of Atomic Size Defects on Hot Electron Generation of Noble Metal Nanoparticle for Photocatalytic Reaction
Tae Kyung Lee 1 , Sang Kyu Kwak 1 Show Abstract
1 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Hot electron (HE) produced by the localized surface plasmon resonance (LSPR) of metal nanoparticle has been receiving significant attention in the photocatalyst community. Although there have been many attempts to improve the performance of heterogeneous catalysis by utilizing the HE phenomenon, one fundamental issue, which is the influence of surface defect on the HE generation, remains unexplored. In this study, we investigate the effects of surface defects of atomic size on the generation of HE of gold nanocube through discrete dipole approximation (DDA) calculation. The cubic-shaped structure is considered to investigate the sole influences of defects on HE generation, where the plasmon resonance direction is a key factor. More interestingly, when the edge site is doped with silver, generation and lifetime of HEs are enhanced. For a 12 nm length gold nanocube doped with only a single-atomic-layer of silver (50 % doping concentration), absorption intensity at peak wavelength and total dephasing time are enhanced by 6.5 % and 11.2 %, respectively. This is a promising result for improving the performance of plasmon-mediated photocatalyst using HEs compared to conventional methods, which are tunable LSPR intensity and wavelength through size, structure shape, plasmon coupling and ambient medium.
KEYWORDS: hot electron, localized surface plasmon resonance, atomic size defect, doping effect, discrete dipole approximation calculation
9:00 PM - ED13.3.04
New Organic Fluorescent Small Molecules for Detection of Sensitive Radioactive Nuclear Materials
Henok Yemam 1 , Adam Mahl 1 , Uwe Greife 1 , Alan Sellinger 1 Show Abstract
1 , Colorado School of Mines, Golden, Colorado, United States
Plastic scintillators are commonly used as first-line detectors for special nuclear materials. Current state-of-the-art plastic scintillators based on polyvinyltoluene (PVT) matrices containing high loadings (>15.0wt%) of fluorescent dopant 2,5-diphenyloxazole (PPO) offer neutron signal discrimination in gamma radiation background, however they suffer from poor mechanical properties. We have developed a series of PPO, fluorene and p-terphenyl derivatives to mitigate this problem. The new series of organic fluorescent molecules have high quantum yield, are thermally stable and offer similar detection to special nuclear materials as commericial plastic scintillators but with superior hardness.
9:00 PM - ED13.3.05
Second Harmonic Generation Assisted Nonlinear Response of Double Metal Plasmonic Interfaces for Photovoltaic Applications
Mona Zolfaghari Borra 1 , Hisham Nasser 1 , Rasit Turan 1 , Alpan Bek 1 Show Abstract
1 , Middle East Technical University, Ankara Turkey
A limitation in silicon based solar cells is poor absorption near its band gap. Around 20% of solar radiation in the near infrared region is not utilized by c-Si solar cell because of its 1.12 eV indirect bandgap. In the field of optics, Nonlinear optics explain the behavior of light in media that its dielectric polarization responds nonlinearly to the electric field of the incident light. These nonlinearity properties are observed at high incidence intensities, such as pulsed lasers, due to the small cross-section of the strong coupled oscillations of conduction and valance electrons. Plasmonic effects result increase in effectiveness of nonlinear optical response. When two plasmon supporting metal nanoparticles (MNPs) are brought in close vicinity of each other, they overlap in localized surface plasmon fields of the two particles. When the plasmon oscillation frequencies and their lifetimes fulfill certain requirements, such as asymmetry of the fields, an effective second harmonic generation (SHG) can emerge from the interaction in the presence of an incident field. In the current study, we investigate the nonlinear response of SHG of double plasmonic interfaces consisting of plasmonic nanoparticles. One of the studied structure consist of MNPs of the same material (either silver or gold) with different average particle diameters. Another structure consists of MNPs of different material with the same average particle diameters. In this structure, the Si3N4 dielectric spacer layer is formed between two different plasmonic metal interfaces. Furthermore, the plasmonic metal interfaces are fabricated directly a top one each other without dielectric spacer layer. We propose double plasmonic interfaces as potential effective frequency up-converters which would change the wavelength of the solar flux above the Si absorption edge to about its half by SHG so that this lost part of the solar spectrum can be absorbed by Si based solar cells.
9:00 PM - ED13.3.06
Hydrogen-Plasma Induced Insulator-to-Metal Transition in Ba0.5Sr0.5Tio3 Thin Films
John Connell 1 , Allen Reed 2 , Jared Johnson 3 , Namal Wanninayake 2 , Maryam Souri 1 , Justin Thompson 1 , John Gruenewald 1 , Jinwoo Hwang 3 , Joseph Brill 1 , Doo Young Kim 2 , Ambrose Seo 1 Show Abstract
1 Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky, United States, 2 Department of Chemistry, University of Kentucky, Lexington, Kentucky, United States, 3 Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States
High carrier mobilites near room temperature represent a major step toward complex oxide device applications. Ba0.5Sr0.5TiO3 (BST), an oxide that has a large increase in dielectric permittivity at the transition between the paraelectric and ferroelectric phases near room temperature, appears to be a good candidate for the realization of high mobility devices. However, BST single crystals and thin-films do not become conducting upon conventional chemical doping or the addition of oxygen vacancies. Here we demonstrate a clear defect-driven insulator–to-metal transition of hydrogen-plasma exposed BST thin-films on (110)-oriented GdScO3 substrates. Five minutes of hydrogenation introduces a large amount of defects and carriers to the BST thin-films generating a low-mobility metallic state, which is indicated by structural and transport properties. Low temperature magnetoresistance measurements of the films demonstrate that strong electron correlations play an important role in their conductivity. This low-mobility metallic state demonstrates that BST thin-films become conducting when defects and strong electron correlations are present, limiting the application of BST as a high mobility device.
9:00 PM - ED13.3.07
Altering the Optical Properties of Graphene by B (N) or B/N Co-Doping
Pooja Rani 1 , Sarita Mann 2 Show Abstract
1 , Modi College, Patiala India, 2 Department of Physics, Panjab University, Chandigarh, Chandigarh, India
We performed ab-initio calculations based on density functional theory (DFT) to analyse the optical properties of pure graphene as compared BN co-doped graphene sheet. The effect of doping has been investigated by varying the concentrations of dopants of B (N) from 3.125 %(one atom of the dopant in 32 host atoms) to 37.5 % and 6.25 % to 75 % for BN co-doping also varying the doping sites for a particular concentration of doping. The dielectric function has been calculated within the random phase approximation (RPA) using VASP (Vienna ab-initio Simulation Package) code. The dielectric function, absorption spectrum and energy loss-function of single layer graphene sheet have been calculated for light polarization parallel and perpendicular to the plane of graphene sheet and compared with doping graphene. The calculated dielectric functions and energy-loss spectra are in reasonable agreement with the available theoretical and experimental results. It has been found that while there is no shift in the peak of absorption spectra of graphene is found with individual B (N) doping with only affecting the intensity of the peak, significant red shift in absorption towards visible range of the radiation at high doping concentration. The results suggest further investigations in this direction for application of graphene in photonics in visible region of light.
9:00 PM - ED13.3.08
Metamaterial for Enhanced Light Absorption in CZTS Solar Cells
Omar Abdelraouf 1 , Nageh Allam 1 Show Abstract
1 Energy Materials Laboratory (EML), Department of Physics, School of Sciences and Engineering, The American University in Cairo, Cairo Egypt
The efficiency of Cu2ZnSnS4 (CZTS)-based solar cells increased from 2% in 2001 to over 9% in 2016. CZTS is a non-toxic, earth-abundant, and low cost material, which make it a good competitor for current bulk photovoltaic materials. However, most of the current CZTS-based solar cells are made of planar structures, which limits their charge carriers collection. Therefore, including artificial, two-dimensional metamaterial nanostructured absorbers should confine more sunlight inside the active layer and enhance the overall efficiency.
Our target in this paper is designing metamaterial surface with maximum light absorption at visible range. Thus, we studied the effect of depositing different two-dimensional molybdenum metamaterial cross grating structures over active layer of CZTS solar cell. Changing the dimensions of metamaterial structures led to a shift in the absorption peak into visible region, thus increasing the overall efficiency of the solar cell. Then, we replace molybdenum and use refractory plasmonics such as titanium nitride (TIN) and compare differences between results. TiN is a promising plasmonics material and has similar properties of gold at visible spectrum. All optical models here built in three dimensional using finite element method simulator, refractive index of used materials came from literature.
9:00 PM - ED13.3.09
Directional and Frequency-Selective Thermal Emission in Midinfrared
Ahmad Khayyat Jafari 1 , Ayrton Bernussi 1 Show Abstract
1 , Texas Tech University (TTU), Lubbock, Texas, United States
Recently, spectral and directional control of thermal emission has increasingly become important due to its applications. In this research, thermal radiation from a metasuraface is simulated and measured in order to demonstrate its ability to emit directionally and at narrow-bad frequency in mid-infrared range. These properties are attributed to the thermal excitation of surface polaritons. We analyze the influence of the nanostructure parameters and temperature on the emission properties by modeling reflection of electromagnetic wave from this surface. From numerical part, it is possible to find the optimum design parameters for final fabrication of sample. In order to compare with this theoretical study, emission and reflection of this metasurface is measured in the range of 8 to 12 μm. The experimental measurement is based on interference effect carried out by our home-made optical design.
9:00 PM - ED13.3.10
SERS Molecular Sensing Using Regular Arrays of Plasmonic Nanostructures Fabricated by Nanosphere Lithography
Erika Rodriguez-Sevilla 1 , Cecilia Salinas 1 , Tannia Sandoval 1 , Erick Flores-Romero 1 2 , Ulises Morales 3 , Juan-Carlos Cheang-Wong 1 Show Abstract
1 , Instituto de Física, Universidad Nacional Autónoma de México, México Mexico, 2 , Catedrático CONACYT, México Mexico, 3 Departamento de Química, Universidad de Guanajuato, Guanajuato, Gto., Mexico
When linked to a rough metal surface or to noble metal nanostructures, Raman active molecules interact with the localized electromagnetic field and take advantage of the plasmonic effects to achieve surface-enhanced Raman scattering (SERS), whose intensity may be many orders of magnitude larger than that of the incident light. In this work we combine a low-cost technique, nanosphere lithography (NSL), and thin film thermal evaporation to fabricate large arrays of metallic nanoparticles that can be used as efficient substrates for Raman-SERS molecular sensing. Spherical submicrometer-sized silica particles were prepared by sol-gel and deposited onto silica glass plates by means of a spin coater system. This silica monolayer is then used as a mask to create regular arrays of nanoscale features in the surface sample by a combination of nanosphere lithography and thin film thermal evaporation. In this case, an ordered array of metallic nanostructures is obtained on the substrate surface after the deposit of a 50 nm thick Ag or Au film and the removal of the silica mask. The size, size distribution and shape of both the colloidal silica mask and the array of Ag and Au nanoparticles were determined by scanning electron microscopy. The long range order of both the self-assembled monolayer of silica particles and the metallic nanoparticle arrays were characterized by a Fast Fourier Transform study. The plasmonic properties of the embedded metallic nanoestructures were characterized by optical absorption measurements. Finally, the use of the Au and Ag arrays as Surface-Enhanced Raman Spectroscopy substrates was evaluated while detecting rhodamine 6G molecules.
9:00 PM - ED13.3.11
Vacancy-Induced Phase Transitions in Non-Stoichiometric Nickel and Tungsten Oxides
Vidhya Chakrapani 1 , Qi Wang 1 , Ajinkya Puntambekar 1 Show Abstract
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Metal-insulator transitions (MIT) have attracted significant research in the last decade in a number of strongly-correlated, undoped and doped transition metal oxides such as nickelates, manganites and vanadates. The transitions between the insulating and metallic phases can be induced by different types of external stimuli, such as temperature, strain, pressure, electron doping, chemical doping, magnetic field, disorder, and light. In addition, electrochemical charging (or gating) has been used to suppress and induce phase transitions, which has been attributed to both electrostatic charge injection and to the formation of vacancy defects during gating. However, the role of native defects in affecting these transitions is not clear. Here, we report a new type of phase transition in p-type, non-stoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition (SIMT) along with the complete reversal of conductivity from p- to n-type at room temperature induced by electrochemical charging in a Li+-containing electrolyte.1 Direct observation of vacancy-ion interactions using in-situ near-infrared photoluminescence spectroscopy show that the transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li+ insertion into the lattice. Changes in the oxidation states of nickel due to defect interactions probed by X-ray photoemission spectroscopy support the above conclusions. In contrast, n-type, non-stoichiometric tungsten oxide shows only insulator-to-metal transition, which is a result of oxygen vacancy formation. The defect-property correlations shown in these model systems can be extended to other oxides.
1. Wang, Q.; Puntambekar, A.; Chakrapani, V., Vacancy-induced Semiconductor-Insulator-Metal Transitions in Non-Stoichiometric Nickel and Tungsten Oxides. Nano Lett. 2016, Article ASAP, Wed Pub. Oct 3 2016.
Prineha Narang, Harvard University
Emiliano Cortes, Imperial College London
Suljo Linic, University of Michigan–Ann Arbor
Marin Soljacic, Massachusetts Institute of Technology
NG Next, Northrop Grumman
ED13.4: Quantum Plasmonics and Nanophotonics
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 132 B
9:00 AM - *ED13.4.01
Peter Nordlander 1 Show Abstract
1 , Rice University, Houston, Texas, United States
Recently it has been demonstrated that quantum mechanical effects can have a pronounced influence on the physical properties of plasmons. Examples include the charge transfer plasmon enabled by conductive coupling (tunneling) between two nearby nanoparticles and nonlocal screening of the plasmonic response of small nanoparticles and narrow nanoscale junctions. I will discuss a multitude of recent hot quantum plasmonics topics such as: how to fundamentally distinguish plasmons from excitons in small systems; molecular plasmons in polycyclic aromatic hydrocarbons; plasmon-phonon coupling; plasmons in doped semiconductor nanocrystals; plasmons in two-component hole liquids; plasmon-induced luminescence; and plasmon-induced hot carrier generation.
9:30 AM - ED13.4.02
Electronic Factors Governing the Electron-Phonon Coupling in Metal-Adsorbate Systems—An Ab Initio Study
Priyank Kumar 1 , David Norris 1 Show Abstract
1 Optical Materials Engineering Laboratory, ETH Zurich, Zurich Switzerland
Plasmon-induced chemical reactions on metallic nanoparticles are gaining significant attention since they provide a platform to utilize sunlight as a renewable source of energy. In order to design such efficient catalytic systems, it is important to understand and control (1) the coupling of plasmons (or photons) to hot carriers, and (2) the coupling of generated hot carriers to the adsorbates. We present an ab initio study of the latter process based on density functional theory calculations. Our analysis, based on several adsorbates and metallic substrates, reveals different parameters that could be controlled to efficiently transfer energy from hot carriers to adsorbate molecules. Specifically, we show how the interatomic matrix elements and the degree of hybridization between the metal and adsorbate states govern the electron-phonon interactions and can be utlized to tune the energy transfer. Thus, our computations provide theoretical guidelines and outline material parameters in order to design more efficient photocatalytic systems.
9:45 AM - ED13.4.03
Power Conversion via Unidirectional Tunneling of Plasmonic Hot Electrons
Matthew Sheldon 1 Show Abstract
1 Chemistry, Texas A&M University, College Station, Texas, United States
Optically excited plasmonic nanostructures display remarkable electron dynamics in the form of coherent electron displacement motion, as well as efficient generation of non-thermal ‘hot electrons’ with large kinetic energy. Here, we provide a theoretical and experimental overview of our studies of photo-induced charge transport across plasmonic tunneling junctions composed of nanoscale metallic gaps, as a strategy for taking advantage of such electron motion for optoelectronic energy conversion.
In a symmetric plasmonic tunneling gap the energetic distribution of electrons due to photo-induced thermalization and hot electron generation is not sufficient to provide significant electrical currents, either through conventional excitation over the interface potential barrier, or via tunneling currents that exhibit a net preference for the direction of charge transfer. However, asymmetric resonant structures can provide optical absorption and photo-excitation that induce significant temperature gradients and local variations in the hot electron population. Such asymmetry can be used to promote unidirectional tunneling transport currents with significant enhancement compared with conventional photoelectron and thermionic emission (~ 10^15 current density enhancement), and thus comprises an intriguing mechanism for providing electrical work. This presentation will introduce the theoretical framework of tunneling phenomena associated with photon-induced hot electrons in plasmonic structures, including principles of electron distribution under photon excitation, strategies for amplifying hot electron generation currents (e.g. manipulating hot spots in nano-antennas) and provide a mechanistic quantum model of power conversion devices based on unidirectional electron tunneling across nanoscale plasmonic junctions.
10:00 AM - *ED13.4.04
Surface-Enhanced Raman Spectroscopy and Imaging with Molecularly Functionalized Noble Metal Nanoparticles—From Experimental Precision Plasmonics to iSERS Microscopy and Chemical Energy Conversion
Sebastian Schluecker 1 , Jun Hee Yoon 1 , Wei Xie 1 , Xinping Wang 1 , Bernd Walkenfort 1 Show Abstract
1 , University Duisburg-Essen, Essen Germany
Surface-enhanced Raman scattering (SERS) is nowadays widely used in the chemical, life and material sciences. In this contribution, our recent results on experimental precision plasmonics for applications in biomedical imaging and chemical energy conversion, using molecularly functionalized noble metal colloids in conjunction with SERS, will be discussed.[2-3] Firstly, a highly efficient synthesis of SERS labels/nanotags is presented, which generates extremely bright dimer particles in very high yield with precise distance control at the level of single chemical bonds. Correlative microscopic and microspectroscopic experiments at the single-particle level demonstrate their unprecedented optical properties. Secondly, applications of immuno-SERS microscopy (iSERS) for tissue-based cancer diagnostics using SERS-labeled antibodies are presented. Thirdly, our most recent efforts on using hot electrons in conjunction with photorecyling employing plasmonic nanostructures  for performing reduction chemistry, involving multiple electron and proton transfer steps, are highlighted.
 S. Schlücker, “Surface-Enhanced Raman Spectroscopy: Concepts and Chemical Applications”, Angew. Chem. Int. Ed. 53, 4756 (2014).
 W. Xie, S. Schlücker, “Hot electron-induced reduction of small molecules on photo-recycling metal surfaces”, Nature Comm. 7, 7570 (2015).
 W. Xie, R. Grzeschik, S. Schlücker, “Metal Nanoparticle-Catalyzed Reduction Using Borohydride in Aqueous Media: A Kinetic Analysis of the Surface Reaction by Microfluidic SERS”, Angew. Chem. Int. Ed. (2016), doi: anie.201605776.
ED13.5: Topological Photonics and Symmetry
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 132 B
10:45 AM - *ED13.5.01
Topological Photonics and Phononics in Non-Reciprocal Metasurfaces
Andrea Alu 1 Show Abstract
1 , The University of Texas at Austin, Austin, Texas, United States
We discuss our recent efforts in the context of topologically protected signal transport for photons and phonons in metasurfaces. After introducing non-reciprocal metamolecules biased by angular momentum or self-biased through nonlinear effects, we discuss our recent efforts in inducing topologically protected bandgaps that support one-way edge signal transport. We discuss the fundamental physics behind these phenomena and their impact on devices and technology, from radio-waves to nanophotonics and acoustics.
11:15 AM - *ED13.5.02
Topological One-Way Fiber of Second Chern Number
Ling Lu 1 , Zhong Wang 2 Show Abstract
1 , Institute of Physics, Beijing China, 2 Tsinghua University, Institute for Advanced Study, Beijing China
We propose topological one-way fibers enabled by the recently discovered Weyl points in a double-gyroid (DG) photonic crystal. By annihilating two Weyl points by supercell modulation in a magnetic DG, we obtain the photonic analogue of the 3D quantum Hall phase with a non-zero first Chern number (C1). When the modulation becomes helixes, one-way fiber modes develop along the winding axis, with the number of modes determined by the spatial frequency of the helix. These single-polarization single-mode and multi-mode one-way fibers, having nearly identical group and phase velocities, are topologically-protected by the second Chern number (C2) in the 4D parameter space of the 3D wavevectors plus the winding angle of the helixes. They are readily realizable at microwave frequencies with magnetic materials. This work suggests a unique way to utilize higher-dimensional topological physics without resorting to artificial dimensions.
11:45 AM - ED13.5.03
Double Gyroid Photonic Crystal—Synthesis and Mid-Infrared Photonic Characterization
Siying Peng 1 , Runyu Zhang 2 , Emil Khabiboulline 1 , Vitoria Barim 1 , Hongjie Chen 1 , Philip Hon 3 , Juan Garcia 3 , Luke Sweatlock 3 , Paul Braun 2 , Harry Atwater 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States, 2 , University of Illinois at Urbana-Champaign, Urbana-Champaign, Illinois, United States, 3 , Northrop Grumman, Redondo beach, California, United States
Gyroid crystals are triply symmetric and have surfaces containing no straight lines. Single gyroid photonic crystals have a large band gap, while double gyroid photonic crystals bring quadratic point degeneracy into the band gap. Breaking the parity of double gyroids can be accomplished by introducing an air sphere, the quadratic point lifts its degeneracy and form a pair of Weyl points. Weyl points are the degenerate energy states resulting from band crossings of linear dispersion features in three dimensional momentum space. Unlike Dirac points in two-dimensional systems, Weyl points have been shown to be stable and the associated surface states are predicted to be topological with non-trivial Chern number . These topologically protected surface states give rise to various interesting phenomena such as backscattering immune unidirectional transport.
We have synthesized and characterized the first mid-infrared (Mid-IR) gyroid photonic crystals , including both single and double gyroid crystals with Weyl points present, in the Mid-IR regime. Simulations reveal that gyroids must be composed of high refractive index materials such as a-Si in order for gyroids to possess interesting properties such as band gaps and Weyl points. Two-photon lithography was utilized to write polymer gyroid scaffold with unit cell sizes of 4-6 µm composed of 40x40x5 unit cells, on intrinsic Si substrates. We inverse the structure by atomic layer deposition of Al2O3 until the surface of the gyroid is closed. We then perform reactive ion etching of Al2O3 with Cl2 to facilitate polymer removal, yielding a hollow inversed Al2O3 structure. The inversed structure was then conformally coated and in-filled with a-Si. Lastly, we remove the Al2O3 structure with phosphoric acid. The resulting double gyroids have unit cell sizes of 4.68 µm oriented along  direction, with Weyl points at 8 µm and k between 0.3π/a and 0.5π/a. Characterization of single and double gyroid photonic crystals has been performed by angle resolved spectroscopy with a quantum cascade laser. The photonic crystal bandstructure is constructed from angle resolved reflectance and transmittance spectra, all the way close to the light line. Constructed bandstructures from single gyroids clearly exhibit a photonic bandgap. Characterization from double gyroids reveals defect photonic states emerging inside the bandgap. Measured bandstructures of single and double gyroids are compared with simulated bandstructures projected based on crystal orientation.
1. L. Lu, L. Fu, J.D. Joannopoulos, M. Soljačić, “Weyl points and line nodes in gyroid photonic crystals”, Nature Photonics 7, 294–299 (2013)
2. S. Peng, R. Zhang, V. H. Chen, E. T. Khabiboulline, P. Braun, H. A. Atwater, “Three-Dimensional Single Gyroid Photonic Crystals with a Mid-Infrared Bandgap”, ACS Photonics 3, 1131 (2016)
12:00 PM - ED13.5.04
Topologically Enabled Optical Nano Motors
Ognjen Ilic 1 2 , Ido Kaminer 2 , Bo Zhen 2 , Owen Miller 3 , Hrvoje Buljan 4 , Marin Soljacic 2 Show Abstract
1 Applied Physics and Materials Science, California Institute of Technology, Pasadena, California, United States, 2 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Applied Physics, Yale University, New Haven, Connecticut, United States, 4 Department of Physics, University of Zagreb, Zagreb Croatia
Shaping the topology of light, by way of spin or orbital angular momentum engineering, is a powerful tool to manipulate matter on the nanoscale, facilitating applications such as optical transport and trapping. Conventionally, however, this involves shaping of the light beam alone, and not the full interaction between the light and the object to be manipulated. Here we show that tailoring the topology of the phase space of the light-particle interaction is a fundamentally more versatile approach: it enables new dynamics that cannot be achieved by shaping of the light alone, as it is applicable to many particles at once.
This allows us to explore an intriguing question: when a beam of light illuminates a particle and rotates it into a steady orientation, it is commonly expected that no additional angular momentum transfer would occur, unless the light itself carries some form of angular momentum. On the contrary, here we show that the dynamical process governing the rotation of particles in optical fields contains rich physics: specifically, even linearly polarized light that carries zero angular momentum can give rise to a steady-state in which a particle is spinning indefinitely around its stable orientation.
To achieve this, instead of tailoring the light beam, we turn to particle asymmetry as a degree of freedom. In this work, we show that a spherical asymmetric (Janus) particle illuminated with light in the appropriate spectral range can become a stable nanoscale motor. When illuminated by a plane wave, such a Janus particle—consisting of a 1μm dielectric (silica) core and a thin (60nm) gold half-shell—exhibits the existence of precessing steady states in a light field that carries no angular momentum. We find that the dynamics is characterized by a set of optical torque field vortices that evolve according to basic topological rules. While it is unexpected that a spherical particle should rotate in a light field of zero angular momentum, we show that such precessing steady states are possible in the effective phase space of the light-particle interaction and result from topologically-protected anti-crossing behavior.
Furthermore, we characterize the complete phase space for the interaction of the Janus nanoparticle and identify all attractors for rotational dynamics. We show that the wavelength of the incident light is closely coupled to the asymmetry and the size of the particle. Accordingly, the wavelength of light (in the 532-1600nm range) allows for external control of the number and the location of these attractors, enabling the control of steady state positions regardless of the initial orientation.
These observations imply that the combination of phase-space topology and asymmetry, though somewhat underutilized in optical control of nanoparticles so far, can be a powerful degree of freedom in designing nanoparticles for optimal external control in applications that include molecular winding, nanoparticle sorting, and in vivo manipulation.
12:15 PM - ED13.5.05
Searching for Topological Materials
Su-Yang Xu 1 , Qiong Ma 1 , Cheng-Long Zhang 3 , Shuang Jia 3 , Ching-Kit Chan 1 , Patrick Lee 1 , Guoqing Chang 2 , Hsin Lin 2 , Pablo Jarillo-Herrero 1 , Nuh Gedik 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , Peking University, Beijing China, 2 , National University of Singapore, Singapore Singapore
A topological phase is a crystalline solid characterized by a nontrivial topological invariant, which is a global quantity of the electronic wavefunctions. Owing to the nontrivial topology, topological materials exhibit a kaleidoscope of new physics that is not possible in conventional materials: They show protected transport or spectroscopic properties that are strongly robust against local imperfections of the crystals; Low-energy properties of these crystals may have deep connections to important topics in high-energy physics such as Weyl fermions, Majorana fermions, the chiral anomaly, and supersymmetry.
Despite these predicted fascinating properties, a crucial question is what materials can realize the topological states in real experiments. In this talk, I will present our methodology of searching for materials candidates for novel topological phases including topological insulators, Weyl semimetals and topological superconductors. I will then describe how we use photoemission spectroscopy to experimentally demonstrate the nontrivial topology in these new materials.
12:30 PM - ED13.5.06
Tuning the Transition from Spontaneous Emission to Lasing by Gate Control of the Local Density of Optical States
Yu-Jung Lu 1 , Ruzan Sokhoyan 1 , Harry Atwater 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States
Plasmonic nanolasers have attracted great attention due to their ultrasmall mode volumes and subwavelength feature sizes, which can enable truly nanoscale ultralow power light sources for future interesting potential applications in optical computation and communication . We report a new approach to modulating laser emission in which, at constant optical pumping rate, a gated field effect structure is used to control the local density of density for InP quantum dots coupled to TiN plasmonic cavity heterostructures that tuning the quantum from spontaneous emission to lasing. In the measurements, we apply a bias voltage between the TiN film and silver back reflector to electronically modify the local density of optical states (LDOS) at the position of the InP quantum dots. The plasmonic heterostructure forms a metal-oxide-semiconductor (MOS) capacitor, and applying a bias voltage give rise to electron accumulation in the doped TiN at the TiN/ SiO2(or HfO2) interface, thus modifying LDOS in the vicinity of the InP quantum dots. We observed lasing spectra from the InP QDs coupled with the plasmonic heterostructure and performed light-in and light-out measurements of the lasing signature, which indicated a zero-bias lasing threshold of 4.5 kW/cm2 at room temperature. A 40% change of the lasing intensity was seen under applied electrical bias from -1 V to 1 V, which we interpret as a field-effect induced change in the LDOS. By adjusting the excitation power density to around lasing threshold, we further observed the transition from spontaneous emission to lasing by gate tuning of the LDOS. The temporal signatures of lasing and spontaneous emission were determined by second-order correlation function measurements. We will report a detailed analysis of the relation between the lasing threshold and LDOS, and discuss applications of this novel pumping configuration to electrical modulation of optically pumped on-chip coherent light sources using this LDOS modulation effect. Fabrication details: we used DC magnetron sputtering to fabricate TiN layers at room temperature on Ag back reflectors. By changing sputtering parameters, such as the nitrogen flow rate for TiN, and growth temperature, we controlled the carrier concentration, and the complex refractive index in TiN films; for TiN, the experimentally accessible carrier concentration ranges from 2.3 x1020 cm-3 to 1.8 x1022 cm-3. We fabricated plasmonic cavity heterostructures consisting of silver (or Au) back reflectors, SiO2 or high-k dielectric (HfO2 or Al2O3) spacers, and TiN films. The InP quantum dots were embedded in this plasmonic metal-oxide-semiconductor heterostructure and we performed pump power-dependent photoluminescence (PL) intensity and lifetime measurements to observe the non-linear lasing signature of InP quantum dots coupled to plasmonic heterostructures.
12:45 PM - ED13.5.07
Hidden Anisotropy of Gold Nanorods
Ji-Young Kim 1 , Miao-Bin Lien 1 , Myung-Geun Han 2 , John Schotland 1 , Sergei Magonov 3 , Yimei Zhu 2 , Heather Ferguson 1 , You-Chia Chang 1 , Theodore Norris 1 , Nicholas Kotov 1 Show Abstract
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States, 3 , NT-MDT Development Inc., Tempe, Arizona, United States
Understanding symmetry of nanoscale object is fundamental in many areas of nanotechnology associated with optics, diagnostics, chemistry, and materials science. Assigning correct symmetry to dispersed nanocolloids is, however, problematic due to structural complexity and dynamics of nanomaterials. Gold nanorods (Au NRs) have been considered as centrosymmetric structure based on their electron microscopic images that usually visualize only the metal cores but not the surrounding organic shells. Direct observations of electrostatic properties of Au NRs via off-axis electron holography and Kelvin force microscopy show that Au NRs have distinct anisotropy of surface charge density and therefore, may behave as non-centrosymmetric structures even with nearly perfect cylindrical core. Importantly, this anisotropic potential in Au NR is associated with uneven distribution of cetyltrimethylammonium (CTA) moieties capping two ends of NRs. Removal of excess CTA on one of the ends leads to disappearance of anisotropy often found in plasmon mapping of NRs with electron energy-loss spectroscopy. The retardation-corrected nonlinear optical (NLO) emission studies of Au NR composite films clearly indicated that both second harmonic generation (SHG) and nonlinear photoluminescence (NPL) are significantly suppressed if individual Au NRs lose their electrostatic anisotropy. More interestingly, we observe that inter-particle coupling in large AuNR ensembles enhanced SHG but not NPL. These findings explain previously puzzling discrepancies in NLO effects in metallic nanostructures and will aid in interpretation of fundamental properties of various nanostructures.
ED13.6: Quantum Photonics and Plasmonics
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 132 B
2:30 PM - *ED13.6.01
Jelena Vuckovic 1 , Kevin Fischer 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Nanophotonic structures that localize photons in sub-wavelength volumes are possible today thanks to modern nanofabrication and optical design techniques. Such structures enable studies of new regimes of light-matter interaction, quantum and nonlinear optics, and new applications in computing, communications, and sensing. The traditional quantum nanophotonics platform is based on InAs quantum dots inside GaAs photonic crystal cavities. Recently, alternative material systems have emerged, such as color centers in diamond and silicon carbide, that could potentially bring the described experiments to room temperature and facilitate scaling to large networks of resonators and emitters. Finally, the use of inverse design nanophotonic methods, that can efficiently perform physics-guided search through the full parameter space, leads to optical devices with properties superior to state of the art, including smaller footprints, better field localization, and novel functionalities.
3:00 PM - *ED13.6.02
Quantum Plasmonics, Polaritons and Strong Light-Matter Interactions with 2D Material Heterostructures
Frank Koppens 1 2 Show Abstract
1 ICFO-Institute de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels Spain, 2 , ICREA – Institució Catalana de Recerça i Estudis Avancats, Barcelona Spain
The control of polaritons are at the heart of nano-photonics and opto-electronics. Two-dimensional materials have emerged as a toolbox for in-situ control of a wide range of polaritons: plasmons, excitons and phonons. By stacking these materials on top of each other, heterostructures of these materials can be controlled at atomic scale, with extremely high quality and clean interfaces.
In this talk, we will show several examples of 2d material heterostructure devices with novel ways of exciting, controlling and detecting polaritons [1,2,3]. We challenge the limits of quantum light-matter interactions [5,6] as well as extremes in propagating plasmon confinement, down to the scale of a few nanometers.
The advances on ultra-high quality materials allow for plasmon propagation at extremely small electron densities, with de Broglie wavelength above 50 nm. This is an excellent platform for testing quantum theories of the dynamic response of the electron system, including spatial dispersion and electron-electron correlation effects.
Finally, we present novel results on Super-Planckian energy transfer between hot electrons and hyperbolic phonon polaritons . Future directions on new directions in quantum materials will be addressed.
 Near-field photocurrent nanoscopy on bare and encapsulated graphene. A. Woessner et al., Nature Communications (2016)  Thermoelectric detection and imaging of propagating graphene plasmons. Lundeberg et al., Nature Materials (2016)  Ultra-confined acoustic THz graphene plasmons revealed by photocurrent nanoscopy. Alonso-Gonzalez et al., Nature Nanotechnology (2016)  Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators. Nikitin et al., Nature Photonics (2016)  Electro-mechanical control of optical emitters using graphene. Reserbat-Plantey et al.,Nature Communications (2016)  Electrical Control of Optical Emitter Relaxation Pathways enabled by Graphene. K.J. Tielrooij et al., Nature Physics (2015)  Super-Planckian electron cooling in a van der Waals stack. Principi et al., Arxiv 1608.01516 (2016)
ED13.7: Atomic-Scale Nanophotonics and Plasmonics II
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 132 B
4:30 PM - *ED13.7.01
Atomic Color Centers in Wide-Bandgap Semiconductors—Applications as Quantum Memories, Sensors and Single Photon Sources
Dirk Englund 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
A central goal in semiconductor quantum optics is to develop efficient and well-behaved atom-like solid-state systems for applications including single photon sources, quantum memories, and sensors. In recent years, there has been tremendous progress in realizing such atom-like systems in a range of crystallographic defects in wide-bandgap semiconductors. Nitrogen vacancy (NV) color centers in diamond have well-defined optical transitions, and their electronic spin states can be controlled precisely through microwave or optical transitions. The NV-diamond color center has enabled a number of break-through quantum technologies, including long-lived quantum memories with error correction, entanglement between two NV spins separated by more than a kilometer, and precision sensing of magnetic and electric fields. Here, we will discuss recent progress towards constructing modular quantum computers based on NV centers, including the integration of multiple NV centers in photonic integrated circuits1 that contain many of the necessary processing elements for scaling such systems to quantum repeater networks or modular quantum computing2.
In recent years, it has become clear that NV-diamond sensors are not the only promising solid-state color centers for quantum information processing. Silicon-vacancy centers have particularly narrow and stable optical transitions, and as we will discuss, they can be implanted into diamond with nanoscale precision using focused ion beam irradiation. In addition, several non-diamond materials have emerged as promising host materials for atom-like quantum systems, including silicon carbide (SiC)3,4, III-nitride semiconductors such as gallium nitride (GaN)5,6, and layered materials such as hexagonal boron nitride (hBN)7,8. We will discuss recent photophysics experiments of several such emitter systems and consider applications as quantum light sources and memories.
1. Mouradian, S. L. et al. Scalable Integration of Long-Lived Quantum Memories into a Photonic Circuit. Phys. Rev. X 5, 031009 (2015).
2. Najafi, F. et al. On-chip detection of non-classical light by scalable integration of single-photon detectors. Nat. Commun. 6, (2015).
3. Christle, D. J. et al. Isolated electron spins in silicon carbide with millisecond coherence times. Nat. Mater. 14, 160–163 (2015).
4. Lienhard, B. et al. Bright and photostable single-photon emitter in silicon carbide. Optica, OPTICA 3, 768–774 (2016).
5. Berhane, A. M. et al. Bright Room-Temperature Single Photon Emission from Defects in Gallium Nitride. arXiv [cond-mat.mtrl-sci] (2016).
6. Koehl, W. F. et al. Resonant optical spectroscopy and coherent control of Cr4+ spin ensembles in SiC and GaN. arXiv [cond-mat.mes-hall] (2016).
7. Grosso, G. et al. Tunable and high purity room-temperature single photon emission from atomic defects in hexagonal boron nitride. arXiv [cond-mat.mes-hall] (2016).
8. Tran, T. T., Bray, K., Ford, M. J., Toth, M. & Aharonovich, I. Nat. Nanotechnol. 11, 37–41 (2016).
5:00 PM - ED13.7.02
Super-Planckian Energy Transfer via Hyperbolic Phonons in a van der Waals Stack
Niels Hesp 1 , Klaas-Jan Tielrooij 1 , Alessandro Principi 2 , Mark Lundeberg 1 , Marco Polini 3 , Frank Koppens 1 4 Show Abstract
1 , ICFO—Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels (Barcelona) Spain, 2 , Radboud University, Institute for Molecules and Materials, Nijmegen Netherlands, 3 , Istituto Italiano di Tecnologia, Graphene Labs, Genova Italy, 4 , ICREA–Institució Catalana de Recerça i Estudis Avancats, Barcelona Spain
After graphene, the rise of van der Waals heterostructures has led to a second wave of discoveries of physical phenomena and new device functionalities [1,2]. In particular, hexagonal boron nitride (hBN) has become the standard substrate and encapsulation material for high-quality devices due to its superior properties . At the same time, hBN is a fascinating infrared optical material, as its intrinsic hyperbolic nature allows for low-loss phonon modes propagating as optical rays but at deep sub-wavelength scale.
Due to their high-quality resonances at very high momenta, they can also facilitate an efficient energy transfer pathway for hot carriers in the vicinity of the hBN. Due to the nearfield coupling, the efficiency of this process can exceed the blackbody limit, and is therefore denoted as “super-Planckian” thermal emission.
In this work [4,5] we study experimentally for the first time the energy transfer between graphene and hBN hyperbolic phonons. We find that hot-electron cooling in hBN-encapsulated graphene occurs via efficient super-Planckian processes, mediated by the hyperbolic phonons in the hBN. We employ time-resolved photocurrent measurements  and find that with two local gates, we can quantify and control the efficiency of this heat transfer process.
We explain our results via a theoretical model that describes radiative heat transfer from hot electrons to hyperbolic hBN phonons . We approach this cooling model either via microscopic kinetics or fluctuation electrodynamics, and find a strong agreement with the experimental results without using any fit parameters. This work constitutes a crucial step in the understanding of the electron dynamics in van der Waals heterostructures, and is vital in finding the limits of photodetection efficiency and speed.
 Geim, A.K. et al. Nature 499, 419–425 (2013)
 Koppens, F.H.L. et al. Nature Nanotech. 9, 780–793 (2014)
 Dean, C.R. et al. Nature Nanotech. 5, 722–726 (2010)
 Tielrooij, K.J., Hesp, N.C.H. et al. Manuscript submitted for publication (2016)
 Principi, A., Lundeberg, M., Hesp, N.C.H., Tielrooij, K.J., et al. Manuscript submitted for publication (2016) (arXiv:1608.01516)
 Tielrooij, K.J. et al. Nature Nanotech. 10, 437–443 (2015)
5:15 PM - *ED13.7.04
Driving Photonics to the Atomic Scale
Javier Aizpurua 1 Show Abstract
1 , CSIC-UPV/EHU, San Sebastian Spain
Plasmonic nanocavities are known to provide localization and enhancement of light at the nanoscale resulting in very efficient platforms for field-enhanced spectroscopy and sensing of molecular species. Quantum calculations within the Time-Dependent Density Functional Theory (TDDFT) reveal that the fine atomistic details of the metallic surfaces forming such nanocavities can further concentrate light into localization volumes of a few cubic Ångstroms, so-called 'pico-cavities', thus bringing photonics to the realm of the atomic scale . The electric field concentration induced in vertices, edges and tips formed by a few atoms can be understood as an atomic-scale lightning rod effect produced by the atomic wavefunctions landscape on top of the standard plasmonic background.
This extreme localization of light provided by atomic features can be exploited to probe vibrations in molecular spectroscopy, as in Tip-Enhanced Raman Spectroscopy (TERS), where intramolecular features can be now resolved when conveniently scanned by such 'pico-cavities' . Furthermore, these tiny volumes can be used as convenient platforms for quantum nanooptics where the photons in these special cavities can be coupled to excitons of a nearby emitter, or to the vibrations of nearby molecules. Indeed, it is possible to interpret plasmon-enhanced Raman spectroscopy as an optomechanical process which is particularly boosted when the photons of a plasmonic 'pico-cavity' properly interact with the vibrations of a single molecule leading to novel non-linear quantum effects in molecular spectroscopy [3,4]. Finally, the dependence of the optical spectrum of a nanocavity on tiny atomic rearrangements across the cavity junction  can be also exploited in active control strategies of optoelectronics, where electromigration of groups of atoms can produce fast and low-energy optical switch effects.
The atomic scale, previously forbidden to photonics, is now opened for exploration of new forms of interactions between light and matter. This extreme regime requires theoretical approaches that allow to understand and develop novel emerging effects in single molecular sensing, quantum nanooptics, and optopelectronics.
 M. Barbry et al., "Atomistic Near-Field Nanoplasmonics: Reaching Atomic-Scale Resolution in Nanooptics," Nano Lett. 15, 3410 (2015).
 R. Zhang et al., "Chemical mapping of a single molecule by plasmon-enhanced Raman scattering," Nature 498, 82 (2013).
 M. K. Schmidt et al., "Quantum Mechanical Description of Raman Scattering from Molecules in Plasmonic Cavities," ACS Nano 10, 6291 (2016).
 F. Benz et al., "Single molecule optomechanics in 'pico-cavities'," Science (2016).
 F. Marchesin et al., "Plasmonic Response of Metallic Nanojunctions Driven by Single Atom Motion: Quantum Transport Revealed in Optics," ACS Phot. 3, 269 (2016).
ED13.8: Poster Session II: Novel Photonic, Electronic and Plasmonic Effects in Materials
Wednesday PM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED13.8.01
Nanoporous Silver Double-Layers by Convenient Electrochemical Method for SERS Applications
Yawen Zhan 1 , Yang Yang Li 1 Show Abstract
1 , City University of Hong Kong, Hong Kong Hong Kong
Double-layered nanoporous silver is fabricated by dealloying an electrodeposited AgCu double-layer with different composition in each layer. The pore/ligament size and porosity of each layer can be conveniently tailored by controlling the electrodeposition voltage profile used for fabricating the AgCu double-layer precursors. Therefore, nanoporous Ag double-layers with tailor-made porous profile along the film thickness can be easily fabricated. The Ag structures thus obtained prove to be particularly attractive for surface enhanced Raman spectroscopy (SERS) applications by serving as novel multi-functional SERS substrates. When a higher porosity is created in the top layer, the double layer can trap more light due to the anti-reflection effect, enabling stronger SERS enhancement. On the other hand, with smaller pores formed in the top layer, the double layer readily works as a size-screening SERS substrate that can help distinguish SERS signals from a mixture of reagents of different sizes. Theoretical simulation has been carried out showing good agreement with the experimental observations.
9:00 PM - ED13.8.02
Deep Ultraviolet Photodetector Based on Wide Bandgap Semiconductor Gallium Oxides
Zhenping Wu 1 , Weihua Tang 1 Show Abstract
1 , Beijing University of Posts & Telecomm, Beijing China
Deep ultraviolet (DUV) photodetectors have attracted intensive interests for the development of civil surveillance applications, such as chemical/biological analysis, ozone holes monitoring, and so on. One of the notable features of a DUV photodetector is the detection accuracy of very weak signals because of the “black background” on earth, where wavelengths shorter than 280 nm are absent in solar radiation and artificial light. During the past decade, several materials such as AlGaN, ZnMgO, diamond and β-Ga2O3 with a wide bandgap (> 4.4 eV) have been employed to fabricate DUV photodetectors. Among them, as a transparent semiconductor with a band gap of ~ 4.9 eV, monoclinic β-Ga2O3 (space group: C2/m) with the lattice parameters of a = 12.23 Å, b = 3.04 Å, c = 5.80 Å, and β = 103.7O has been considered as one of ideal candidates for DUV photodetector. Our studies indicate that β-Ga2O3 based metal-semiconductor-metal (MSM) and p-n junction structure photodetectors show both easy growth and high responsivity characteristics. Moreover, by in situ annealing in the chamber to reduce the oxygen vacancy, we could change the metal-semiconductor contact from Ohmic contact to Schottky contact. In compare with the Ohmic-type photodetector, the Schottky-type photodetector takes on lower dark current, higher photoresponse and shorter switching time, which benefit from Schottky barrier controlling electron transport and the quantity of photogenerated carriers trapped by oxygen vacancy significant decreasing.
9:00 PM - ED13.8.03
Electrohydrodynamic Jet-Printed ZTO TFT and Its Electrical Properties
Young-Jin Kwack 1 , Kyung-Hyung Lee 1 , Namhoon Baek 1 , Woon-Seop Choi 1 Show Abstract
1 , Hoseo University, Asan Korea (the Republic of)
EHD-jet printing is used as a drop-on-demand printing process for non-contact printing without a complex photolithography process. EHD-jet printing can provide simple patterning and complex patterning with better resolution. The process can use an electric field to create jetting droplets for the delivery of a liquid portion to a designated substrate. Although inkjet printing is greatly influenced by the ink viscosity, EHD-jet printing can produce any pattern with a charged ink formulation with less viscosity dependence. In this study, ZTO TFTs were fabricated by an EHD-jet printing process. A uniform active layer was obtained using a steel needle with an inner diameter of 100 μm without any treatments, a robust and simple process, to obtain a reasonable channel width and better mobility. An EHD-jet printed zinc-tin oxide (ZTO) active layer was patterned with a 60 μm width using a 100 μm inner diameter metal nozzle. The electrical properties of an EHD-jet printed ZTO thin-film transistors (TFTs) showed a mobility of 9.82 cm2/Vs, an on-off current ratio of 3.7x106, a threshold voltage of 2.36 V, and a subthreshold slope of 0.73 V/dec at 500oC. Significantly improved properties were obtained compared to the spin-coated and inkjet-printed ones. Better hysteresis behavior and positive bias stability of the ZTO TFTs were also achieved using EHD-jet printing technology.
9:00 PM - ED13.8.04
Enhancement of Properties of Perovskite Solar Cell and LED by Surface Plasmon Resonance of Graphene Quantum Dots/Ag Nanowires
Sungwon Hwang 1 Show Abstract
1 , Konkuk University, Chungju-si Korea (the Republic of)
The Graphene optoelectronic devices such as displays, touch screens, light-emitting diodes and solar cells require materials with low sheet resistance and high transparency. The graphene quantum dots/Ag nanowires provide superior charge collection in the nanocomposites. For the application of graphene quantum dots (GQDs) to optoelectronic nano-devices, it is of critical importance to understand the mechanisms which result in novel phenomena of their light absorption/emission. We demonstrate bright, efficient, and graphene quantum dots/Ag nanowires nanocomposites perovskite nano-devices through the direct charge carrier collection into GQDs and the efficient radiative exciton recombination within QDs. Here, we present size-dependent shape/edge-state variations of GQDs and visible photoluminescence (PL) showing anomalous size dependences. With varying the average size of GQDs from 5 to 35 nm, the peak energy of the absorption spectra monotonically decreases. Graphene quantum dots (GQDs) have received much attention due to their novel phenomena of charge transport and light absorption/emission. Thus, the demonstration of photovoltaic efficiency with GQDs would be the basis for a plenty of applications not only as a flexible device in perovskite nano-devices but also a key component in the optoelectronic integrated circuits. The enhancements of short-circuit current density and photoelectric conversion efficiency are attributed to the increase of light coupling and thus the light absorption of the dye due to the localized surface plasmon resonance and the possible enhanced light scattering of graphene quantum dots/Ag nanowires. We believe that such a comprehensive scheme in designing device architecture and the structural formulation of GQDs provides a device for practical realization of environmentally benign, high performance flexible devices in the future.
This material is based upon work supported by the Ministry of Trade, Industry & Energy(MOTIE, Korea) under Industrial Technology Innovation Program. No.10067533 , 'Development of transfer printing equipment for micro LED chip for smart watch application and array transferring'
9:00 PM - ED13.8.06
Electrodeposited, Transverse Nanowire Electroluminescent Junctions
Shaopeng Qiao 1 , Qiang Xu 1 , Rajen Dutta 1 , Mya Le 1 , Xiaowei Li 1 , Reginald Penner 1 Show Abstract
1 , University of California, Irvine, Irvine, California, United States
The preparation by electrodeposition of transverse nanowire electroluminescent junctions (tn-ELJs) is described, and the electroluminescence (EL) properties of these devices are characterized. The lithographically patterned nanowire electrodeposition process is first used to prepare long (millimeters), linear, nanocrystalline CdSe nanowires on glass. The thickness of these nanowires along the emission axis is 60 nm, and the width, wCdSe, along the electrical axis is adjustable from 100 to 450 nm. Ten pairs of nickel–gold electrical contacts are then positioned along the axis of this nanowire using lithographically directed electrodeposition. The resulting linear array of nickel–CdSe–gold junctions produces EL with an external quantum efficiency, EQE, and threshold voltage, Vth, that depend sensitively on wCdSe. EQE increases with increasing electric field and also with increasing wCdSe, and Vth also increases with wCdSe and, therefore, the electrical resistance of the tn-ELJs. Vth down to 1.8(±0.2) V (for wCdSe ≈ 100 nm) and EQE of 5.5(±0.5) × 10–5 (for wCdSe ≈ 450 nm) are obtained. tn-ELJs produce a broad EL emission envelope, spanning the wavelength range from 600 to 960 nm.
9:00 PM - ED13.8.07
Electronic Structure and Optical Response of Atomically-Thin Sheets of Plasmonic Metals
Tuan Nguyen 3 , Marin Soljacic 2 , Prineha Narang 1 , Ravishankar Sundararaman 4 Show Abstract
3 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Physics Department, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 1 Faculty of Arts and Sciences, Harvard University, Cambridge, Massachusetts, United States, 4 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Conventional plasmonic metals are useful for exploiting surface plasmon resonances in visible and ultraviolet frequencies, while two-dimensional plasmonic materials like graphene exhibit higher mode confinement and lower losses, albeit at lower frequencies. Two-dimensional layers of conventional plasmonic metals could bring together the best features of these two classes of materials. The higher electron density should result in higher frequency plasmon resonances, while the two-dimensional geometry should provide higher mode confinement and reduce losses. However, such two-dimensional layers have not yet been characterized experimentally, and their theoretical properties have only been studied at a free-electron gas level that does not account for electronic structure effects, phonons and environmental effects such as the substrate.
Here, we present first-principles calculations of the structure, electronic states, phonon modes and optical response of atomically-thin two-dimensional sheets of silver and aluminum, which are the two conventional plasmonic metals which exhibit lowest losses at high frequencies. We find stable hexagonal close-packed structures with bond lengths approximately five percent shorter than the bulk material. The electronic states near the Fermi level resemble that of a two-dimensional free electron gas, while the d bands of the silver sheet are narrower and deeper than the corresponding bands in the bulk metal. We identify z-polarized phonons as the dominant intraband loss mechanism for the atomically-thin sheets, and explore avenues for minimizing these losses by tuning substrate-sheet interactions.
9:00 PM - ED13.8.08
Plasmon-Induced Hot Electron Generation in Nanoparticle Dimers
Francisco Ramirez 1 , Alan McGaughey 1 Show Abstract
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Surface plasmon decay into hot electrons in plasmonic nanoparticles has the potential to improve photovoltaic energy conversion and photocatalytic devices. Although experimentally demonstrated, the physics underlying this phenomenon is not well understood, especially regarding light absorption in nanoparticle clusters. In this work, we study the influence of surface plasmon hybridization in silver nanoparticles dimers on the generation of hot electrons. Using numerical simulations based on the boundary element method, we characterize the electromagnetic energy distribution as a function of the separation, size, and shape of the nanoparticles. These results are then used to predict the distribution of hot electrons using the free-electron model and density functional theory.
9:00 PM - ED13.8.09
Nanometer-Scale Metal Meshes across Device-Relevant Areas for Transparent Electrodes and Optical Metamaterials
Anna Hiszpanski 1 , Carla Watson 1 , Timothy Yee 1 , Juan J. Diaz Leon 1 , Eyal Feigenbaum 1 , Yong-jin Han 1 Show Abstract
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Metal meshes with nanometer-scale lattice spacings are promising for a number of electronic and optical applications, including as transparent electrodes and meta-surfaces. However, fabricating such structures across application-relevant areas requires bridging length scales separated by six orders of magnitude – a formidable fabrication challenge. The top-down lithographic techniques typically required to achieve nanometer-scale resolution are not scalable to such large areas or to more complex 3D geometries. We have demonstrated and will describe a new fabrication approach to meet this need. Our approach has enabled us to fabricate meta-surfaces consisting of platinum and gold nanowire meshes with tunable dimensions and geometry over device-relevant areas. The optical properties of these surfaces will be presented, as well as their electronic properties from conductive AFM studies. Given the tunability afforded by our experimental approach, we have also performed simulations of the optical and electronic properties of the various accessible structure geometries, which will help to guide design towards the targeted applications of transparent electrodes and optical metamaterials.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
9:00 PM - ED13.8.10
Magnetotransport Properties of Mechanically Stable Graphene Foam
Rizwan Ur Rehman Sagar 1 2 , Florian Stadler 1 Show Abstract
1 College of Materials Science and Engineering, Shenzhen Key Laboratory of Polymer Science and Technology, Guangdong Research Center for Interfacial Engineering of Functional Materials, Nanshan District Key Lab for Biopolymers and Safety Evaluation, Shenzhen University, Shenzhen 518060, Shenzhen, China, 2 Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, Shenzhen, China
Detection of magnetotransport properties of three-dimensional graphene foam (GF) is a challenge due to porous morphology. Herein, we present the first observation of magnetotransport properties of GF composed of few layers in a wide temperature range of 2 − 300 K. Large room temperature linear positive magnetoresistance (LPMR ~ 171 % at B ~ 9 T) has been detected. The largest LPMR ~ 213 % has been obtained at 2 K under a magnetic field of 9 T, which can be tuned by the addition of poly (methyl methacrylate) to the porous structure of the foam. The origin of this remarkable is explained on the basis of quadratic magnetoresistance. The excellent magnetotransport properties of GF open a way towards three-dimensional graphene-based magnetoelectronics.
9:00 PM - ED13.8.11
Photoresponsivityenhancementin Multilayer MoS2phototransistor with Local Bottom Gate Structure
Seongin Hong 1 , Healin Im 1 , Young Ki Hong 1 , Gyuchull Han 2 , Youngki Yoon 2 , Sunkook Kim 1 Show Abstract
1 School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon Korea (the Republic of), 2 Department of Electrical and Computer Engineering and Waterloo Institute for Nanotechnology (WIN), University of Waterloo, Waterloo, Ontario, Canada
2D layered transition metal dichalcogenides (TMDs), such as Molybdenum disulfide (MoS2), have attracted a lot of attention for next-generation electronics and optoelectronics. MoS2 thin-film transistors (TFTs) have shown excellent electrical and optical properties such as high on/off current ratio, low subthreshold swing, high field effect mobility and interesting photoresponsivity. Unlike photoresponsivity (from 7.5 mA W-1 to 880 A W-1) of single layer MoS2 phototransistor due to its direct band-gap property, responsivity of indirect-multilayer MoS2 phototransistor limit its utility in a highly sensitive photodetector.
In order to increase photoresponsivity of multilayer MoS2 phototransistor, we suggest local bottom gate structure, where the gate length is shorter than the channel length in comparison with the conventional gate structure. The photoresponsivity of multilayer MoS2 phototransistor with local bottom gate structure exhibits the giant photoreponsivity of 342.6AW-1 (λ: 532 nm and power: 2 mW cm −1), which is 3 orders of magnitude larger than typical multilayer MoS2 TFTs from previous study. These results of our experiment and simulation demonstrate that multilayer MoS2 phototransistor with local bottom gate can be used as a variety of optoelectronics applications.
Prineha Narang, Harvard University
Emiliano Cortes, Imperial College London
Suljo Linic, University of Michigan–Ann Arbor
Marin Soljacic, Massachusetts Institute of Technology
NG Next, Northrop Grumman
ED13.9: Phonon-Polaritons and MIR-THz Photonics
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 132 B
9:00 AM - *ED13.9.01
Mid-IR to THz Polaritonics—Realizing Alternative Materials
Joshua Caldwell 1 , Alexander Giles 1 , Igor Vurgaftman 1 , Chase Ellis 1 , Joseph Tischler 1 , Pratibha Dev 1 , Orest Glembocki 1 , Jeffrey Owrutsky 1 , Thomas Reinecke 1 Show Abstract
1 , U.S. Naval Research Laboratory, Washington, District of Columbia, United States
The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. Up until recently, research in this field has been primarily focused on the use of plasmonic metals. However, the high optical losses inherent in such metal-based surface plasmon materials has led to an ever-expanding effort to identify, low-loss alternative materials capable of supporting sub-diffractional confinement. Beyond this, the limited availability of high efficiency optical sources, refractive and compact optics in the mid-infrared to THz spectral regions make nanophotonic advancements imperative. One highly promising alternative are polar dielectric crystals whereby sub-diffraction confinement of light can be achieved through the stimulation of surface phonon polaritons within an all-dielectric, and thus low loss material system. Due to the wide array of high quality crystalline species and varied crystal structures, a wealth of unanticipated optical properties have recently been reported. This talk will discuss recent advancements from our group including the realization of localized phonon polariton modes, the observation and exploitation of the natural hyperbolic response of hexagonal boron nitride. Beyond this, methods to improve the material lifetime and to induce additional functionality through isotopic enrichment and hybridization of optical modes will also be presented.
9:30 AM - ED13.9.02
Hyperbolic Phonon Polaritons in Hexagonal Boron Nitride
Siyuan Dai 1 Show Abstract
1 , University of California, San Diego, La Jolla, California, United States
Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. While hyperbolic responses are normally achieved with metamaterials, hexagonal boron nitride (hBN) naturally possesses this property due to the anisotropic phonons in the mid-infrared. Using scattering-type scanning near-field optical microscopy, we studied polaritonic phenomena in hBN. We performed infrared nano-imaging of highly confined and low-loss hyperbolic phonon polaritons in hBN. The polariton wavelength was shown to be governed by the hBN thickness according to a linear law persisting down to few atomic layers . Additionally, we carried out the modification of hyperbolic response in meta-structures comprised of a mononlayer graphene deposited on hBN . Electrostatic gating of the top graphene layer allows for the modification of wavelength and intensity of hyperbolic phonon polaritons in bulk hBN. The physics of the modification originates from the plasmon-phonon coupling in the hyperbolic medium. Furthermore, we demonstrated the “hyperlens” for subdiffractional focusing and imaging using a slab of hBN .
 S. Dai et al., Science, 343, 1125 (2014).
 S. Dai et al., Nature Nanotechnology, 10, 682 (2015).
 S. Dai et al., Nature Communications, 6, 6963 (2015).
9:45 AM - ED13.9.03
Controlling Localized Surface Phonon Polariton Resonances in Indium Phosphide Antennas via Carrier Injection
Chase Ellis 1 , Joseph Tischler 1 , Chul Soo Kim 1 , Mijin Kim 2 , Igor Vurgaftman 1 , Joshua Caldwell 1 Show Abstract
1 , US Naval Research Laboratory, Washington, District of Columbia, United States, 2 , Sotera Defense Solutions, Inc, Columbia, Maryland, United States
The high optical losses of metal-based plasmonic materials have driven an extensive search for alternative lower-loss materials that can support plasmonic-like effects, such as sub-diffraction confinement of optical fields. One such alternative employs phonon-mediated collective-charge oscillations (surface phonon polaritons, SPhPs) that can be optically excited in nanostructured polar dielectrics. In this study, we investigate localized SPhP resonances supported by cylindrical indium phosphide nanopillars with a fixed height of 1500 nm and diameters that range from 150 to 20000 nm. Infrared reflectance measurements reveal localized SPhP resonances that span the far-infrared spectral range bounded by the bulk LO and TO phonons of InP, ωLO = 344 cm-1 and ωTO=303 cm-1, respectively. In addition to demonstrating the ability to tune resonances by altering the pillar design, we also show that localized SPhPs can be actively tuned by photoinjecting carriers. The optical injection introduces a reversible, free-carrier perturbation to the dielectric permittivity that results in a spectral shift of resonances. The results described in this work may open the door to tunable, narrow-band thermal sources in the far-infrared.
10:00 AM - ED13.9.04
Field Effect Optoelectronic Modulation of Quantum-Confined Carriers in Black Phosphorus
Michelle Sherrott 1 , William Whitney 1 , Deep Jariwala 1 , Wei-Hsiang Lin 1 , Hans Bechtel 2 , George Rossman 1 , Harry Atwater 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States, 2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
The isolation of atomically thin black phosphorus (BP) in recent years has attracted a great deal of attention in the scientific community, as it bridges the technology gap between graphene and transition metal dichalcogenides with an infrared energy gap and typical carrier mobilities intermediate between the two. This has opened the potential for many novel devices, including optical modulators and photodetectors for the mid-infrared. Theoretical predictions have suggested novel infrared optical phenomena, such as anisotropic plasmons, field-effect tunable exciton stark shifts, and strong Burstein-Moss and quantum-confined Franz-Keldysh effects that promise to open new directions for both fundamental nanophotonics research and applications. However, while a number of experimental works exist on the interesting visible-frequency optical properties of BP, much less experimental data exists in the IR. This is a result, in part, of the limited lateral size of BP flakes that can be mechanically exfoliated; we address this experimental challenge by doing measurements using the diffraction limited, high-brightness IR beam at the LBNL Advanced Light Source.
We report here the infrared optical response of thin black phosphorus under field-effect modulation. In a thin flake (6.5nm), we observe tunable, oscillatory spectral features which we attribute as arising from a combination of a Burstein-Moss (BM) optical bandgap shift due to band-filling and Pauli-blocking under gate control, together with a quantum confined Franz-Keldysh (QCFK) effect. These effects have been proposed theoretically to occur for BP flakes under electric field modulation. The QCFK effect arises from the high field strength and vertical confinement of charge in the thin van der Waals material. This is in good agreement with electronic transport characterization. In a thicker flake (25nm), we observe large modulation amplitudes consistent with a BM band-filling effect, suggesting the potential for use of black phosphorus as an active material in mid-infrared optoelectronic modulator applications. In addition, the observed modulation depends on both the polarity and strength of the gate voltage, indicating an ambipolar BM effect due to the filling of the valence or conduction bands, consistent with the measurement of ambipolar transport characteristics.
 Whitney, W. S.*; Sherrott, M.C.;*Jariwala, D; Lin, W-H; Bechtel, H.A.;Rossman, G.R.; Atwater, H. A. . arXiv:1608.02561 2016.
10:15 AM - ED13.9.05
Electrical Properties of Gated Bismuth Telluride Selenide
Brandon Clark 1 , Lia Krusin-Elbaum 2 , Zhiyi Chen 2 Show Abstract
1 , Worcester Polytechnic Institute, Worcester, Massachusetts, United States, 2 Physics, City College of New York, New York City, New York, United States
Three-dimensional topological insulator crystals (TIs) are narrow-band-gap semiconductors with metallic surface states. These 2D states have Dirac-type (relativistic) linear energy-momentum dispersion and spin-momentum locking and are protected by time reversal symmetry, which makes them potentially useful for spintronics and fault-tolerant quantum computing. However, ubiquitous charged defects can cause surface transport to be intermixed with detrimental bulk conductivity. Prof. Krusin’s lab recently proved that irradiating TIs with high energy electron beams can compensate bulk defects, bring the bulk to a charge neutrality point (CNP), and increase bulk resistivity, enabling access to the Dirac bands and increasing surface conductivity. Electrostatic gating, where a charge is added to one surface of the TI to force charged bulk defects to the surface, has recently generated interest because, unlike irradiation, it is a reversible and tunable method to increase surface conductivity in TIs.
Bi2Te2Se (BTS) is a ternary TI with high natural bulk resistivity in which giant surface carrier lifetime was observed in angle-resolved photoemission spectroscopy, which we hypothesized may be a result of the formation of impurity bands 30 meV above the valence band and bending of the bulk bands at the TI’s subsurface. Thus, we predicted that, after tuning the Fermi level of BTS across CNP using gating, the signatures of the impurity bands and an increase in surface conductivity would appear. The signatures would show as abnormal features in resistivity vs. gate voltage that are distinct from ambipolar conduction.
In this study, we applied gating to probe the electronic properties of BTS. The bulk resistivity of gated 200 nm thick BTS samples increases by an average of 3.5% under a gate voltage of 100 V, failing to reach a resistivity peak that would indicate CNP. Furthermore, the resistance-temperature trend of thinner samples around 30 nm seems metallic, while that of samples around 200 nm resembles an insulator. This suggests the dominance of surface states as thickness decreases and highlights the possible importance of thickness on gating to CNP. Charge mobility was found to be five times lower (0.002 – 0.005 m2/V-s) than Bi2Te3, indicating that the bulk contribution to charge transfer in BTS is lower than in other TIs. Finally, we found that our BTS does not experience a shift from n-type to p-type as temperature increases above 80K. This suggests that our samples might not have the previously reported impurity band in thick samples (~20 micron) that accepts thermally-activated valence electrons at 80K.
BTS (200 nm) exhibits little change in resistivity during gating. 30 nm thick BTS needs to be gated to understand thickness dependence further. Since impurity bands might be responsible as well, one might verify the existence of them in thin BTS is by tuning the Fermi level to the putative impurity band level and studying charge transport.
10:30 AM - ED13.9.06
Ultrasensitive Surface Enhanced Infrared Absorption Spectroscopy on Patternless, Uniform Field Enhancement Surfaces
Gokhan Bakan 1 , Sencer Ayas 1 , Erol Ozgur 1 , Kemal Celebi 1 , Aykutlu Dana 1 Show Abstract
1 , Bilkent University, Ankara Turkey
Infrared absorption spectroscopy is a crucial tool for label-free molecular detection. However, the interaction between infrared light and molecules is weak. Therefore, in order to improve the signal from small number of molecules, the use of plasmonic enhancement has gained significant interest over the last few decades, resulting in a field of study generally referred to as Surface Enhanced Infrared Absorption (SEIRA). There have been numerous papers on SEIRA that report extremely high field enhancements at the edges of nanoscale metallic features, albeit localizing only to the nanoscale volumes at such edges. This localization of the high field enhancement is a fundamental drawback in SEIRA.
In the present work, we demonstrate that a simple, pattern-less thin film surface that generates a modest (~4) but spatially-uniform field enhancement can outperform the plasmonic platforms in terms of IR absorption performance. We have both numerically and experimentally scrutinized the difference between such thin film surfaces and plasmonic surfaces. For comparison, we have used a specifically-designed CaF2/Al thin film platform and an Ag nanoantenna surface that was optimized for plasmonic IR enhancement. Thin film platform greatly outperforms plasmonic surfaces, providing much higher signal intensities, a much improved bandwidth that spans almost the whole active IR spectrum and a depth of field that is one order of magnitude larger, compared to the optimized Ag nanoantennas.(1)
(1) Ayas, S.; Bakan, G.; Ozgur, E.; Celebi, K.; Dana, A. ACS Photonics 2016, 3 (3), 337–342.
ED13.10: Tunable Plasmonic, Photonic and Electronic Effects I
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 132 B
11:15 AM - *ED13.10.01
After the Plasmon—Designing Materials to Exploit Non-Equilibrium Carriers
Ravishankar Sundararaman 1 , Prineha Narang 2 , Zachary Hall 3 , Tuan Nguyen 4 , Marin Soljacic 4 , Steven Claybrook 5 , Litao Zhao 1 Show Abstract
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Faculty of Arts and Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Physics Department, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 5 Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States
Surface plasmon resonances of metallic nanostructures enable efficient light absorption at sub-wavelength length scales. Non-radiative decay of plasmon modes produce energetic electrons and holes in the material, which can potentially be utilized for photovoltaic or photochemical energy conversion with high efficiency, or for photodetection with high sensitivity. However, a fundamental challenge in utilizing plasmon-generated hot carriers remains that these carriers scatter against each other and phonons, losing energy rapidly prior to extraction.
We present a framework for first-principles calculations of hot carrier excitation, transport and relaxation, critically accounting for the role of electronic structure and phonons. We demonstrate that in conventional plasmonic materials, the electronic structure characteristics that enable light absorption at small length scales also facilitate rapid thermalization of energetic carriers. We investigate whether this undesirable link can be severed in new classes of materials, by exploiting change of dimensionality and distinct electronic properties in heterostructures in order to retain efficient light absorption while minimizing carrier thermalization.
11:45 AM - ED13.10.02
Multi-Refractive-Index Metamaterials Using Subwavelength Waveguide Arrays
Zhaoning Yu 1 , Chenghao Wan 2 , Bradley Gundlach 3 , Jad Salman 3 , Yuzhe Xiao 3 , Zongfu Yu 3 2 , Mikhail Kats 3 2 1 Show Abstract
1 Physics, University of Wisconsin–Madison, Madison, Wisconsin, United States, 2 Materials Science & Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Electrical & Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
A refractive index can typically be assigned to both conventional materials and metamaterials if the constituent elements are much closer together than the wavelength of light, as described by effective medium theory. For dispersive and birefringent materials, the refractive index (as well as the impedance) acquires a dependence on the wavelength and polarization of light, respectively. However, for a given wavelength and a polarization along some symmetry axis, a natural material or a typical metamaterial has only one well-defined value of the refractive index. Here, we demonstrate a type of metamaterial that cannot be described by a single set of refractive index and impedance values, even though the unit cell is much smaller than the wavelength of light. This metamaterial comprises multiple subwavelength waveguides with different mode indices, resulting in a structure that appears to be an effective medium, yet must be described with multiple simultaneous values of refractive index.
Using the finite-difference time-domain (FDTD) method, we simulate a prism cut out of such a multi-index metamaterial, which yields multiple distinct refracted beams given a linearly polarized single-wavelength input beam. As an initial demonstration, we used alternating metal-insulator-metal waveguides with thickness smaller than ~λ/20 and different fundamental mode indices, determined by the refractive index of the insulator layer. With light propagating simultaneously in different waveguides of subwavelength spatial extent, the structure must be defined by multiple refractive indices at the same time, even for a particular polarization and wavelength. By tuning the thickness ratio and refractive indices of the insulator layers, we are able to control the power distribution between the different refracted beams, as well as the effective refractive indices of the whole structure.
Our results can be generalized to metamaterials comprising a variety of subwavelength waveguides, as long as the modes are well confined and have no cutoff frequency. The ability to engineer materials with multiple simultaneous refractive index values may enable new optical devices and components, including refractive lenses with multiple focal spots and Fabry-Perot etalons with an enhanced density of resonant modes.
12:00 PM - ED13.10.03
Dynamic Plasmonic Tuning of Infrared Metasurface Mie Resonators
Jon Schuller 1 , Prasad Iyer 1 , Mihir Pendharkar 1 , Chris Palmstrom 1 Show Abstract
1 , University of California, Santa Barbara, Santa Barbara, California, United States
The possibility of engineering electromagnetic phase at subwavelength dimensions has led to metasurfaces that provide unprecedented control of electromagnetic waves. The ability to dynamically tune this phase would unlock the potential of metasurfaces and establish disruptive new paradigms in reconfigurable optics. The central challenge of making 2π-reconfigurable metasurfaces is the need for very large refractive index modulation (Δn≥1) due to the subwavelength scale of the underlying resonators. Here, we demonstrate dynamic, large magnitude tuning of InSb metasurface Mie resonators through two distinct plasmonic effects: modulation of the 1) density and 2) effective mass of electrons.
We fabricate high refractive index MBE-grown undoped InSb Mie resonators on highly doped InSb ENZ substrates. We experimentally demonstrate two distinct resonances with weak and strong coupling to the ENZ substrate. These different coupling strengths lead to drastic differences in both static (i.e. size-dependent) and dynamic (temperature-based) dispersion. Weakly-coupled resonators exhibit large blue-shifts upon heating due to an increase in free carriers within undoped regions and associated reduction in refractive index. Strongly-coupled resonators exhibit large red-shifts upon heating due to changes of the effective mass in the ENZ substrate and associated increase in its refractive index. We conclude by showing how these effects can be exploited to make electrically reconfigurable metasurfaces capable of arbitrary electromagnetic mappings.
12:15 PM - *ED13.10.04
Transgressing Effective Medium Theories with Epsilon-Near-Zero Media
Inigo Liberal 1 , Nader Engheta 1 Show Abstract
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
We theoretically investigate the electromagnetic scattering properties of epsilon-near-zero (ENZ) bodies of arbitrary cross-section polluted with dielectric particles. We analytically demonstrate that the external fields excited by such bodies are identical to those of an ENZ body with engineered effective permeability. In stark contrast with conventional effective medium and metamaterial theories, our effect holds independently of the size and number of particles. In other words, the description via effective parameters applies even if there is a single and electrically large pollutant. The effective permittivity is also independent of the position of the pollutants and the shape of the ENZ host, thus establishing a link between electromagnetic theory and doping mechanisms in semiconductor physics. The theory is numerically validated with full-wave simulations of a silicon carbide host polluted with germanium particles.
Our results provide additional degrees of freedom in engineering the magnetic response of nonmagnetic matter at optical frequencies, and, in general, the properties of media with near-zero parameters. As particular examples, we analytically and numerically demonstrate the realization of epsilon-and-mu-near-zero (EMNZ) and perfect magnetic conducting (PMC) bodies of arbitrary geometry. These results might find applications in flexible and reconfigurable photonics, nonlinear optics, as well as in tailoring thermal and quantum emission of light.
12:45 PM - ED13.10.05
Nanowire Light Emitting Devices and their Applications in Wide-Field Far-Field Sub-Diffraction Imaging
Qing Yang 1 , Xiaowei Liu 1 , Pengfei Xu 1 , Chenlei Pang 1 , Minghua Zhuge 1 , Xu Liu 1 Show Abstract
1 , Zhejiang University, Hangzhou China
Owing to their strong light localization, large length-to-diameter ratio, and large fractional evanescent field, 1D nanomaterials could allow wide-field far-field sub-diffraction imaging at multiple wavelengths, which has not been achieved yet in nanoscopy.
Here, we present our work on fabrication and controlling NW light emitters as well as their applications in wide-field far-field sub-diffraction imaging. At the beginning, various nanowire light sources was fabricated1-4. Then, tuning/modulating/enhancing of the afore-mentioned NW light sources were achieved.5,6. Finally, we demonstrate an active method enabling wide-field far-field sub-diffraction imaging, where a fluorescent nanowire ring acts as a localized source and is combined with a film waveguide to produce omnidirectional illuminating evanescent waves. A structure featuring 70 nm wide slots spaced 70 nm apart has been resolved at a wavelength of 520 nm with a 0.85 numerical aperture (NA) standard objective. The versatility of this approach has been demonstrated by imaging integrated chips, Blu-ray DVDs, biological cells, and various subwavelength 2D patterns. This new resolving technique could become an important tool in cellular biology, the on-chip industry, and other fields requiring wide-field nanoscale visualization.
1. Q. Yang*, X. Jiang, X. Guo, Y. Chen, L. Tong, Appl. Phys. Lett. 94 101108 (2009).
2. Q. Yang, W. Wang, S. Xu, Z. L. Wang, Nano Lett. 11 4012-4017 (2011).
3. Q. Yang, Y. Liu, C. Pan, J. Chen, X.Wen, Z. Lin Wang, Nano Lett. 13, 607-613 (2013).
4. Y. Wu, T. Hasan, X. Li, P. Xu, Y. Wang, X. Shen, X. Liu, and Q. Yang*, Appl. Phys. Lett. 106, 051108 (2015).
5. J. Li , C. Meng , Y. Liu , X. Wu , Y. Lu , Y. Ye , L. Dai , L. Tong, X. Liu , Q. Yang* Adv. Mater. 25, 833-837 (2013).
6. Z. Yang, D. Wang, C. Meng, Z. Wu, Y. Wang, Y. Ma, L. Dai, X. Liu, T. Hasan, X. Liu, and Q. Yang*, Nano Lett. 14, 3153-3159 (2014).
ED13.11: Tunable Plasmonic, Photonic and Electronic Effects II
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 132 B
2:30 PM - ED13.11.02
Electron Energy-Loss Spectroscopy Calculation in Finite-Difference Time-Domain: EELS-FDTD
Nicolas Large 1 , Alejandro Manjavacas 2 , Emilie Ringe 3 , George Schatz 4 , Shan Wang 5 , Peter Nordlander 3 Show Abstract
1 Department of Physics & Astronomy, The University of Texas at San Antonio, San Antonio, Texas, United States, 2 Department of Physics & Astronomy, University of New Mexico, Albuquerque, New Mexico, United States, 3 Department of Materials Science and NanoEngineering, Rice University, Houston, Texas, United States, 4 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 5 Department of Materials Science & Engineering, Stanford University, Stanford, California, United States
Electron energy-loss spectroscopy (EELS) is a unique tool that is extensively used to investigate the plasmonic response of metallic nanostructures since the early works in the '50s. To be able to interpret and theoretically investigate EELS results, a myriad of different numerical techniques have been developed for EELS simulations: boundary element method (BEM), discrete dipole approximation (DDA), finite-element method (FEM), Galerkin discontinuous time-domain (GDTD) method. Although these techniques are able to predict and reasonably reproduce experimental results, they possess significant drawbacks and are often limited to highly symmetrical geometries, non-penetrating trajectories, free-standing nanostructures, small nanostructures, and may present some complexity in their implementation and use.
Here, we present a novel approach for EELS calculations using the finite-difference time-domain (FDTD) method that goes beyond these limitations. We benchmark our EELS-FDTD implementation by direct comparison with results from the well-established BEM and published experimental results. In particular, we compute EELS spectra for spherical nanoparticles, nanoparticle dimers, nanodisks supported by various substrates, and supported gold bowtie antennas.[1,2] The flexibility our EELS-FDTD method allows for easily extending to more complex geometries and configurations. To illustrate this we investigate the plasmonic properties of (i) high density sub-10-nm-gap homo- and hetero-dimers, (ii) encapsulated gold nanoparticle chains, and (iii) hollow gold nanorods.[2,3] This implementation can also be directly exported beyond the FDTD framework and implemented within other numerical methods.
 Y. Cao, A. Manjavacas, N. Large, and P. Nordlander, ACS Photonics 2 , 369 (2015)
 M. Zhang, N. Large, A.-L. Koh, Y. Cao, A. Manjavacas, P. Nordlander, R. Sinclair, and S. X. Wang, ACS Nano 9, 9331 (2015)
 S. Yazdi, J.R. Daniel, N. Large, G.C. Schatz, D. Boudreau, E. Ringe, Nano Letters, DOI:10.1021/acs.nanolett.6b02946
ED13.12: Magnetic and Chiral Light-Matter Interactions
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 132 B
2:45 PM - *ED13.12.01
Enhancing Chiral Light-Matter Interactions with Achiral Nanostructures
Jennifer Dionne 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Light can exert differential forces on left- and right-handed enantiomers, promising an all-optical route towards chiral resolution and controlled assembly of chiral nanostructures. However, enantioselective optical forces on nano-specimens are challenging to both control and quantify, since their magnitudes are predicted to be sub-piconewton-scale with nanometer-scale spatial variation. Here we demonstrate new methods to both strengthen and visualize these forces using achiral nanostructures. First, we show how plasmonic optical tweezers can enable selective optical trapping of enantiomers. Our technique combines plasmonic optical tweezers with a chiral atomic force microscope (AFM) probe. Illumination of the plasmonic tweezers with left- and right- circularly polarized light (CPL) results in distinct forces on the chiral AFM tip: the total optical forces exerted on a left-handed chiral tip are 10 pN stronger when illuminated with left-CPL than with right-CPL. Additionally, the transverse optical forces on this chiral tip are attractive with left-CPL, but repulsive with right-CPL. We use the AFM tip to map such chiral optical forces over the plasmonic tweezers with 2 nm lateral spatial resolution, showing distinct force distributions in all three dimensions for each handedness. Then, we show how high-index dielectric nanostructures and metasurfaces can increase enantiomer separation yields more than 50 times beyond CPL in free space. Mie theory and a local optimization algorithm indicate that magnetic multipolar Mie resonances supported by sub-micron silicon spheres increase both the circular dichroism signal and Kuhn's dissymmetry factor compared to CPL in free space. Importantly, these enhancements maintain the total molecular absorption rate, enabling efficient selective photoexcitation. Combined, our results suggest that achiral photonic nanostructures can significantly enhance chiral light-matter interactions, potentially enabling controlled enantiopure chemical syntheses, single molecule chiral spectroscopy, and dynamic monitoring of structural changes of chiral molecules with sub-nanometer resolution.
3:15 PM - *ED13.12.02
Synthetic Magnetic Fields and Synthetic Dimensions in Photonic Lattices
Tena Dubcek 1 , Karlo Lelas 2 , Dario Jukic 3 , Robert Pezer 4 , Marin Soljacic 5 , Hrvoje Buljan 1 Show Abstract
1 , University of Zagreb Faculty of Science, Zagreb Croatia, 2 , University of Zagreb, Faculty of Textile Technology, Zagreb Croatia, 3 , University of Zagreb, Faculty of Civil Engineering, Zagreb Croatia, 4 , University of Zagreb, Faculty of Metallurgy, Zagreb Croatia, 5 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
We present a grating assisted tunneling scheme for creating tunable synthetic magnetic fields in optically induced one- and two-dimensional (dielectric) photonic lattices . As a signature of the synthetic magnetic fields, we present conical diffraction patterns in lattices with Dirac points in k-space. We compare the light propagation in these realistic (continuous) systems with the evolution in discrete models representing the Harper-Hofstadter Hamiltonian, and obtain excellent agreement.
Synthetic magnetism for photons is a unique tool for the manipulation and control of light, and for the design of novel topological phases and states in photonics (e.g., see  and references therein). Topological photonics is a rapidly growing field, advancing in parallel to analogous efforts in ultracold atomic gases, inspired by the development of topological insulators in condensed matter physics .
The topic is closely related to the possibility of creating synthetic dimensions in photonic lattices. We present recent developments in the context of our previous work , in which we studied discrete photonic lattices in more than three dimensions. In Ref.  we pointed out that such systems can exist in continuous three-dimensional space. We studied discrete diffraction in the linear regime and demonstrated the existence of four-dimensional (4D) tesseract solitons in nonlinear 4D periodic photonic lattices. Finally, we proposed a design towards a potential realization of such periodic 4D lattices in experiments.
 T. Dubček, K. Lelas, D. Jukić, R. Pezer, M. Soljačić, H. Buljan, The Harper–Hofstadter Hamiltonian and conical diffraction in photonic lattices with grating assisted tunneling, New J. Phys. 17, 125002 (2015).
 L. Lu, L. Fu, J.D. Joannopoulos, and M. Soljačić, Topological photonics, Nature Photon. 7, 294 (2013).
 D. Jukić and H. Buljan, Four-dimensional photonic lattices and discrete tesseract solitons, Phys. Rev. A 87, 013814 (2013).
3:45 PM - ED13.12.03
Ab Initio Insights into Novel Magnetic Behavior in the Mn1-xFexRu2Sn Pseudo-Binary Heusler
Elizabeth Decolvenaere 1 , Michael Gordon 1 , Anton Van der Ven 1 , Ram Seshadri 1 Show Abstract
1 , University of California, Santa Barbara, Santa Barbara, California, United States
Heusler compounds often have unique magnetic properties, resulting in interest for their potential applications as spintronic materials. The pseudo-binary Mn0.5Fe0.5Ru2Sn, formed as a solid solution of the full Heuslers (Mn, Fe)Ru2Sn, has been recently shown to exhibit exchange-bias-like magnetic hardening implicative of two magnetic phases, despite the presence of only one chemical phase. We have performed ab-initio studies of over one hundred chemical and magnetic orderings of the Mn1-xFexRu2Sn pseudo-binary to better understand the unique magnetic behavior developing in this system. We find a transition from ferromagnetic (FM) to antiferromagnetic (AFM) behavior dependent on composition, with (111) AFM ordering on the Mn species at equiatomic composition, in agreement with the experimental study. By exploring and examining the lowest-energy magnetic and chemical configuration at multiple compositions, we can identify the mechanism behind the apparent magnetic hardening, driven by alternating planes of FM and AFM-ordered spins along the (111) direction. Additionally, examination of the ab-initio electronic density of states lets us probe the metallic behavior of these compounds.
 J. E. Douglas, E. E. Levin, T. M. Pollock. J. C. Castillo, P. Adler, C. Felser, S. Krämer, K. L. Page, R. Seshadri. Phys. Rev. B 94, 094412 (2016)
4:30 PM - ED13.12.04
Exciton Bose-Einstein Condensation in Double Walled Carbon Nanotubes
Igor Bondarev 1 , Adrian Popescu 1 Show Abstract
1 , North Carolina Central University, Durham, North Carolina, United States
Exciton Bose-Einstein condensates (BECs), coherent many-particle states of excitons with zero translational momentum, have received a considerable attention since their first theoretical prediction in the 1960’s[1-6]. This has been motivated by fundamental as well as practical interest. Fundamental interest comes from the aspiration to understand the physical nature of coherent collective electron-hole excitations in low-dimensional semiconductors. Practical interest is prompted by the need to develop sustainable and efficient coherent light emission sources using the photoluminescence of the exciton Bose-Einstein condensate. Here we demonstrate theoretically the possibility for exciton BEC in a novel quasi-one-dimensional (quasi-1D) system -- a double walled semiconducting carbon nanotube (CN). Because of the peculiar quasi-1D character of small-diameter CNs, both excitons and interband plasmons can coexist in the same energy range of the order of 1 eV in these structures[6-8]. The proposed condensation mechanism is enabled by the near-field coupling of excitons residing on one tubule with the interband plasmon mode of the same energy on the other coaxial tubule, to form new bosonic excitations -- exciton-plasmons. Possibilities for achieving BEC in 1D and 2D systems are theoretically demonstrated in the presence of an extra confinement potential[9,10]. We show that the strongly correlated exciton-plasmon system in an appropriately chosen double walled CN combination presents such a special case. We derive the analytic solutions for the coupled exciton-plasmon quasiparticle dispersion relation and give the selection rules for forming the double walled CN system to exhibit the robust exciton-plasmon BEC phenomenon. We further present the calculated exciton participation fraction in the exciton-plasmon condensate and discuss the possibility for experimental observation of the exciton BEC phenomenon. The effect we predict offers a testing ground for fundamentals of condensed matter physics in one dimension and opens up perspectives to develop a coherent polarized light source with double walled semiconducting carbon nanotubes.
I.V.B. is supported by DOE (DE-SC0007117). A.P. is supported by NSF (ECCS-1306871).
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4:45 PM - ED13.12.05
Magnetic Assembly of Nanocubes into Responsive Photonic Crystals
Zhiwei Li 1 , Yadong Yin 1 Show Abstract
1 Chemistry, University of California, Riverside, Riverside, California, United States
Nanoscale assembly coupled with competing anisotropic effects can result in the formation of complex structures, and further provide additional degrees of freedom for tailoring their collective properties. In this presentation, we report the synthesis of superparamagnetic nanocubes with shape and magnetocrystalline anisotropy and their assembly into magnetically responsive photonic crystals. Simulations reveal that  mode (corner by corner), favored by magnetocrystalline anisotropy, has strongest Zeeman coupling whereas  mode (face by face), favored by shape anisotropy, has strongest interparticle coupling when exposed to uniform magnetic field. Under experiment conditions, however, they tend to assemble along  direction (edge by edge) as determined by the interplay of the two anisotropic effects. Under a magnetic field, the assembled 1D structures exhibit unique optical properties. Light with higher frequency will be reflected along a large angle, showing viewing angle-dependent features. Interestingly, the structural colors can be tuned across the visible range by controlling the orientation of nanochains through external magnetic field, which is significantly different from 1D photonic crystal with nanospheres as building block whose optical properties are mainly controlled by interparticle separation. Another important feature is the in-plane orientation of the nanochains, which makes it possible to produce vivid structural colors in thin films with thickness as small as 10 µm.
5:00 PM - ED13.12.06
Light-Driven Self-Organization of Mesoscale Optical Matter
Zijie Yan 1 Show Abstract
1 , Clarkson University, Potsdam, New York, United States
Optical matter is a unique class of materials, especially when the meta-atoms are plasmonic nanoparticles. Mesoscale photonic interactions among the plasmonic nanoparticles can create resonant photonic lattices strongly coupled to light, leading to coupled plasmonic-photonic properties and new types of functional materials. Here we report our recent work on optical self-assembly of plasmonic nanoparticles into mesoscale clusters and arrays via optical binding interactions. We use advanced laser beam shaping techniques and the significant electrodynamic interactions among strongly scattering Ag nanoparticles to induce self-organization in optical fields. By controlling the intensity, phase and polarization of light, we can design and tailor the assembled optical matter, and even create unusual structures, such as quasicrystalline clusters with five-fold symmetry.
ED13.13: Imaging—A Nanophotonics and Plasmonics Approach I
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 132 B
5:15 PM - *ED13.13.01
Tailoring, Visualizing and Exploiting Field Confinement in Plasmonic and Phononic Nanoantennas
Stefan Maier 1 Show Abstract
1 , Imperial College London, London United Kingdom
In this talk we will study the field-confinement propoerties of two different nanoantenna systems: plasmonic and polar dielecric. For plasmonic nanoantennas, the link between electromagnetic field hot spots and hot spots for chemical reactivity will be studied, using the example of a silver bow tie covered with a molecular monolayer. Plasmon-induced hot electron emission enables nanoscale surface chemistry, and we map the reacitiviy sites directly via the attachment of reporter particles. Mapping of the electromagnetic hot spot in the far field is enabled via a super-resolution microscopy scheme based on single-molecule localization microscopy.
The second part of the talk will focus on localized phonon polaritons in silicon carbide. Here, excitation of plasmonic modes in nanopillars enables high field confinement in the mid-infrared part of the spectrum. First results for applications in surface-enhanced sensing and second harmonic generation will be reported.
5:45 PM - ED13.13.02
Quantum Plasmonic Theory of Small Metallic Chains
Vincenzo Giannini 1 , Jamie Fitzgerald 1 Show Abstract
1 , Imperial College London, London United Kingdom
Quantum Plasmonics is an exciting sub-branch of nanoplasmonics where quantum theory is used to describe light-matter interactions on the nanoscale. Plasmonic materials allow extreme sub-diffraction confinement of light to regions so small that the quantization of both light and matter may be necessary for an accurate description.
State of the art experiments now allow us to probe these regimes and push existing theories to the limits which opens up the possibilities of exploring the nature of many body collective oscillations as well developing new plasmonic devices, that use the particle quality of light and the wave quality of matter, and have a wealth of potential applications in sensing, lasing and quantum computing.
We are using time-dependent density-functional theory (TDDFT) to explore how single electron transitions, induced by a classical light field, can form a collective plasma oscillation. In particular, we focus on the collectivity of the electron eigenmodes and how the geometry and size of atomic chains modifies this. TDDFT includes essential behavior such as size quantization, electron-electron interaction and electron spill out and allows one to see the quantum origin of localized plasma resonances as well predict where quantum effects are important to include and how we can manipulate them in future plasmonic devices.
Prineha Narang, Harvard University
Emiliano Cortes, Imperial College London
Suljo Linic, University of Michigan–Ann Arbor
Marin Soljacic, Massachusetts Institute of Technology
NG Next, Northrop Grumman
ED13.14: Nonlinear and MIR-THz Photonics
Friday AM, April 21, 2017
PCC North, 100 Level, Room 132 B
9:00 AM - *ED13.14.01
Enhancing Nonlinear Effects in Plasmonic Nanostructures
Sylvain Gennaro 1 , Michael Nielsen 1 , Mohsen Rahmani 1 , Miguel Navarro-Cia 1 , Stefan Maier 1 , Rupert Oulton 1 Show Abstract
1 , Imperial College London, London United Kingdom
Nonlinear phenomena are central to modern photonics but, being inherently weak, typically require gradual accumulation over macroscopic length scales. Recently, metamaterials imbued with artificial nonlinearity from their constituent nanoantennas have generated excitement by opening the possibility of wavelength-scale nonlinear optics. In this talk, I will discuss recent works on enhancing second harmonic generation (SHG) in metallic nano antennas and four wave mixing (FWM) in plasmonic waveguides. In the case of SHG, we explore the use of both nanoantenna symmetry and multiple harmonics to control the strength, polarization and radiation pattern of SHG from a variety of antenna configurations incorporating simple resonant elements. We find that strong linearly polarized dipolar SHG is only possible for noncentro-symmetric antennas that also minimize interference between their dipolar and quadrupolar responses. In the case of FWM we explore frequency conversion in plasmonic waveguides at telecoms frequencies. When strong optical confinement and efficient coupling can be achieved, we observe strong FWM despite the limited propagation length of the plasmonic modes involved. These studies highlight the exciting potential of nonlinear optics at the wavelength scale.
9:30 AM - ED13.14.02
Independent Infrared and Visible Electrochromism in Plasmonic Nb-Doped TiO2 Nanocrystals
Clayton Dahlman 1 , Jacob Adair 1 , Delia Milliron 1 Show Abstract
1 , University of Texas at Austin, Austin, Texas, United States
Degenerately doped metal oxide nanocrystals have emerged as tunable plasmonic materials that can be integrated into a variety of optoelectronic applications. Metal oxide composition, defect equilibrium, nanocrystal geometry and induced charge can shift the material’s localized surface plasmon resonance (LSPR) across the visible and infrared (IR) spectrum. A recent addition to the library of plasmonic metal oxides is anatase TiO2, a wide bandgap semiconductor often used with other functional light-absorbing metals, semiconductors or organic materials as a scaffold, sensitizer or charge separating medium. Through colloidal synthesis methods, degenerate Nb-doped TiO2 nanocrystals have been found to show LSPR in the IR, indicating metallic transport through the metal oxide lattice. LSPR energy and coloration is controllable by changing the free electron concentration with different substitutional Nb dopant concentrations (de Trizio et al, Chem. Mater., 2013). A similar LSPR modulation is induced in a mesoporous film of colloidal Nb-doped TiO2 nanocrystals upon charging in an electrochemical cell (Dahlman et al, J. Am. Chem. Soc., 2015). Depending on applied potential and doping level, a reversible electrochromic coloration can be modulated between the near- and mid-IR, similar to other plasmonic electrochromic materials such as doped indium oxide and zinc oxide nanocrystals.
Interestingly, if an intercalating cation electrolyte such as a Li+ salt is used in the electrochemical cell, the TiO2 nanocrystal film can be independently colored in the IR and visible regions depending on applied electrochemical potential. At sufficient reducing potentials, Li+ is incorporated into the Nb-doped TiO2 lattice through a phase transition to a distorted LixTiO2 structure (x ~ 0.5), causing electron localization and a visible spectrum absorption feature, as observed by X-ray absorption and X-ray scattering measurements. Intercalated lithium ions are in effect a secondary dopant within the nanocrystal, and the interaction between the inserted lithium and donor defect sites in the lattice generate novel optical functionality. This independent dual-spectrum behavior is promising for energy-saving “smart” windows, and can be exploited to dynamically control radiation transfer in interior spaces. To probe this phenomenon, IR transmittance of Nb-doped TiO2 nanocrystal films is measured in situ during charging, revealing that substitutional Nb5+ and interstitial Li+ show subtle effects on plasmon resonance by altering defect equilibrium and inducing charge localization in the lattice. By deconvoluting optical modulations occurring in well-defined regimes of Li+ intercalation and capacitive charging, the distinct effects of substitutional and intercalative point defects on dynamic plasmonic behavior in metal oxides can be studied at a fundamental level.
9:45 AM - ED13.14.03
Mid-Infrared Optics Using Low-Loss Materials with Refractive Index below Unity
Alireza Shahsafi 1 , Yuzhe Xiao 1 , Jad Salman 1 , Bradley Gundlach 1 , Chenghao Wan 2 , Patrick Roney 1 , Mikhail Kats 1 2 Show Abstract
1 Electrical Engineering, University of Wisconsin–Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Research in designing and utilizing nontrivial effective refractive index values of synthetic materials has opened up exciting opportunities in optics. For example, recently, materials and metamaterials with near-zero refractive index values (i.e. “epsilon-near-zero” or “mu-near-zero”) have attracted attention due to a variety of predicted properties including the decoupling of wavelength and frequency, a divergence of the density of states, and other remarkable effects. However, material systems with refractive indices near zero are often rather lossy, limiting their utility.
In this work, we explored new optical phenomena enabled by refractive indices slightly below unity, rather than very close to zero. We found that in certain polar materials close to their intrinsic phonon resonances, refractive indices less than one can be achieved with relatively low losses. These materials include silicon dioxide (SiO2), aluminum oxide, aluminum nitride, and many others. For example, in SiO2, the real part of refractive index (n) is below one in the wavelength range of 7.37 micron to 7.67 micron, where the extinction coefficient (k) remains below 0.03. Here, we present experimental demonstrations of two new optical phenomena using SiO2 in this wavelength region: frustration of external reflection, and direct coupling to surface plasmon polaritons (SPPs) from free space.
When light is incident on a low-loss medium with a refractive index less than one beyond a critical angle, it is reflected with high efficiency, similar to the case of total internal reflection. While this phenomenon of external reflection (ER) is widely used in x-ray optics, it is rarely observed at optical frequencies. We demonstrate that, using SiO2 at infrared frequencies, we can observe both ER and the related phenomenon of frustrated external reflection (FER). We utilized SiO2 films with thicknesses in the range of a few micron, on the order of the evanescent decay length in the SiO2 when light is incident on the film at an oblique angle of incidence beyond the critical angle. Decreasing the film thickness is shown to increase the amount of light transmitted through the film, providing evidence of the frustration mechanism.
In parallel, we demonstrated direct excitation of SPPs from free space without the need of typical momentum matching structures such as prisms and gratings. Conventionally, direct coupling of free space light to SPPs is impossible because the wave vector of the SPP is always greater than the free-space wave vector. We showed that SPPs can be excited from free space at the interface between a metal and SiO2, enabled by a reduction of the SPP wave vector in the region where the refractive index of the SiO2 is less than one and the losses are not too large.
10:00 AM -
10:15 AM - ED13.14.05
Ultra-Low Loss Polaritons in Hexagonal Boron Nitride—A New Approach
Alexander Giles 1 , Siyuan Dai 2 , Igor Vurgaftman 1 , Chase Ellis 1 , Joseph Tischler 1 , Thomas Reinecke 1 , Nathaniel Assefa 3 , Takashi Taniguchi 6 , Kenji Watanabe 6 , Michael Fogler 2 , James Edgar 4 , Dmitri Basov 5 2 , Joshua Caldwell 1 Show Abstract
1 , US Naval Research Laboratory, Washington, District of Columbia, United States, 2 , University of California, San Diego, San Diego, California, United States, 3 , Rice University, Houston, Texas, United States, 6 , National Institute for Materials Science, Ibaraki Japan, 4 , Kansas State University, Manhattan, Kansas, United States, 5 , Columbia University, New York, New York, United States
We use scattering-type scanning near-field optical microscopy (s-SNOM) to study the response of hexagonal boron nitride nanocones at infrared frequencies, where this material behaves as a hyperbolic medium. The obtained images are dominated by a series of “hot” rings that occur on the sloped sidewalls of the nanocones. The ring positions depend on the incident laser frequency and the nanocone shape. Both dependences are consistent with directional propagation of hyperbolic phonon-polariton (HPhP) rays that are launched at the edges and zigzag through the interior of the nanocones, sustaining multiple internal reflections off the sidewalls. Additionally, we observe a strong overall enhancement of the near-field signal at discrete resonance frequencies. These resonances attest to low dielectric losses that permit coherent standing waves of the subdiffractional polaritons to form. We also discuss potential applications of such shape-dependent resonances and the field concentration at the hot rings. Further, in another experiment, we demonstrate significant improvements in HPhP lifetimes by using isotopically enriched hexagonal boron nitride, whereby 3-4x increases in the phonon lifetimes are observed, with theory predicting the potential for a 14-fold increase if other point defects can be mitigated. Using s-SNOM we further demonstrate a commensurate increase in the HPhP propagation length and, due to the drastic reduction in losses, were able for the first time to quantify the corresponding losses for the higher order optical modes, which exhibit significantly higher optical confinement. Our results provide the foundation for a materials-growth-directed approach to further mitigating losses in polaritonic systems and towards the realization of extended propagation lengths required for many nanophotonic optical designs.
10:30 AM - ED13.14.06
Active Tuning of Surface-Phonon Polariton Resonances in Silicon Carbide
Adam Dunkelberger 1 2 , Daniel Ratchford 2 , Alexander Giles 3 , Joshua Caldwell 3 , Jeffrey Owrutsky 2 Show Abstract
1 , NRC Research Associateship Fellow, Washington, District of Columbia, United States, 2 Chemistry Division, U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 3 Electronics Division, U.S. Naval Research Laboratory, Washington, District of Columbia, United States
The infrared spectrum of SiC is dominated by the highly reflective reststhralen band that occurs between the transverse and longitudinal optical phonons. Through the LOPC effect, free carriers shift the reststrahlen band to higher frequencies. We have previously shown that photoinjected carriers transiently and reversibly modify the infrared reflectivity of bulk SiC. Within the reststrahlen band, SiC nanostructures can exhibit surface-phonon polariton resonances. Here we report, for the first time, active tuning of SiC surface-phonon polariton resonances via carrier photoinjection, achieving better modulation depths than active tuning in plasmonic systems. Ultraviolet excitation induces >10 cm-1 shifts in the transverse dipole resonance (Γ = 7 cm-1). Time-resolved infrared reflection spectroscopy reveals that the photoinduced shifts decay in tens of ps, depending on the initial carrier density. Our results suggest that spatial redistribution of photoexcited carriers dominates the time dependence of the active tuning. This work lays the foundation for further studies of the physics of active tuning and optimization of the tuning for infrared nanophotonics applications.
ED13.15: Tailoring Light-Matter Interactions
Friday AM, April 21, 2017
PCC North, 100 Level, Room 132 B
11:15 AM - ED13.15.01
Shape and Crystalline Anisotropy Convoluted Effect on Localized Surface Plasmon Resonance of Semiconductor Nanocrystals
Ankit Agrawal 1 , Jongwook Kim 1 , Franziska Krieg 2 , Amy Bergerud 1 , Delia Milliron 1 Show Abstract
1 , The University of Texas at Austin, Austin, Texas, United States, 2 Institute of Inorganic Chemistry, ETH Zurich, Zurich Switzerland
Doped semiconductor nanocrystals have been shown to host a tunable localized surface plasmon resonance (LSPR) over a wide optical range depending upon controlled dopant and carrier concentration. Metal nanoparticles such as gold and silver, have high free electron densities (~1023/cm3) creating resonances with ωlsp in the visible region whereas, in doped semiconductor nanocrystals, a highly variable carrier density, (1018~1022/cm3) enables ωlsp over the entire infrared region. Employing anisotropic particle shapes in metal nanoparticles and nanostructures have given an additional control over ωlsp. For instance, in metal nanostructures, it has allowed LSPR band spitting and realization of resonance in near-infrared for high aspect ratio nanorods. In semiconductor nanocrystals, studies so far have focused on tuning LSPR frequency (ωlsp) and the influence of anisotropic nanocrystal shape and intrinsic crystal structure remain poorly explored.
Unlike typical plasmonic metals like Ag or Au, doped semiconductors can have anisotropic crystal structures for example, Cu2-xS (layered) or Cs:WO3 (hexagonal), which is the focus of our current study1. Here in this study, we have shown that colloidally synthesized hexagonal phase Cs:WO3 nanocrystals exhibit strong aspect ratio-dependent LSPR absorption peaks that can only be explained via a cooperative influence of crystalline and shape anisotropies. We demonstrate the dominant influence of crystalline anisotropy, which uniquely causes strong LSPR band-splitting into two distinct peaks with comparable intensities. This finding highlights the limitations of conventional treatments of LSPR that assume isotropic dielectric constants and attribute multimodal peaks uniquely to shape anisotropy effects. This understanding extends our ability to rationally tune LSPR lineshape and near-field enhancement via synthetic control of shape and crystalline anisotropies of semiconductor nanocrystals. Furthermore, in this work we explore the how this crystalline anisotropy effects the plasmon coupling between NC in dimer, chain of NC and NC packed in hexagonal lattice. In particular, the demonstrated multimodal LSPR with near-equal intensities of h-Cs:WO3 nanocrystals covers the near-infrared (NIR) region of great importance in photonic, solar, and clinical applications while maintaining high visible transparency due to its wide band gap.
(1) Kim, J.; Agrawal, A.; Krieg, F.; Bergerud, A.; Milliron, D. J. The Interplay of Shape and Crystalline Anisotropies in Plasmonic Semiconductor Nanocrystals. Nano Lett. 2016, 16 (6), 3879–3884.
11:30 AM - *ED13.15.02
Nanophotonic Design of Semiconductor Nanopillar Arrays—Fundamentals and Applications
Katherine Fountaine 1 2 Show Abstract
1 , Northrop Grumman Aerospace Systems, Redondo Beach, California, United States, 2 Applied Physics, California Institute of Technology, Pasadena, California, United States
We present fundamental nanophotonics principles and potential applications of semiconductor nanopillar arrays, supported by analytic theory, full-wave simulations and experimental results, ranging spectrally from the visible to the mid-infrared. In the semiconductor nanopillar array design space, a wide range of optical responses are achievable. The optical response, as well as the underlying optical principles, depends strongly on both array geometry and material selection, and can range from unselective ‘perfect’ absorption via lossy waveguide modes to narrow band reflection via guided mode resonances, to name a few. The fundamental optical principles at work in various regions of the semiconductor nanopillar array design space and related applications will be discussed.
Results to be presented in this talk include design, fabrication and characterization of semiconductor nanopillar arrays for various energy and sensing applications. A number of devices will be discussed including, (1) sparse III-V nanowire and nanocone arrays as unselective ‘perfect’ absorbers and emitters in the UV to mid-IR for photovoltaic, photodetection and thermal management applications; (2) a-Si nanopillar arrays as polarization- and angle-insensitive subtractive color filters for compact, high resolution imaging in the visible; and (3) c-Si nanopillar array metasurfaces as polarization-independent narrow band reflectors for hyperspectral imaging applications in the infrared.
12:00 PM - ED13.15.03
Photonically Enhanced Strain Sensors Based on a Hybrid Structure of Crumpled Graphene and Colloidal Photonic Crystals
Peter Knapp 1 , Pilgyu Kang 1 , Juyoung Leem 1 , SungWoo Nam 1 Show Abstract
1 Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Compact, integratable strain gauges have numerous applications ranging from structural health monitoring, to human body motion sensing. An interesting concept is that of a photonic strain sensor. Photonic strain sensors have existed for some time in the literature and are typically based on materials or structures that experience changes in their peak transmitted or reflected wavelengths. The most interesting of these systems are colloidal photonic crystals (CPCs). CPCs are composed of nanoscale polystyrene beads, self-assembled into a hexagonal close pack structure embedded in a polydimethylsiloxane (PDMS) matrix. The periodic change in the refractive index of this structure results in what is essentially a photonic bandgap, leading to peak reflection at a particular wavelength. Furthermore as the system is stretched its periodicity is changed resulting in a change in peak reflected wavelength which can be measured and correlated to strain. The major limitation on integrating CPCs into compact strain sensors is the difficulty of quantifying their response to strains which is typically done with expensive and bulky spectrometers. Here we report photonically-enhanced strain sensors based on a hybrid structure of CPC and crumpled graphene. Crumpled graphene devices are integrated to CPC to be used as a compact stretching and bending tolerant photo-signal transducer. Crumpled graphene is two dimensional graphene that has been deformed, usually by contracting the substrate onto which it has been adhered, to adopt a crumpled or undulating surface, if the substrate remains flexible it is possible to partially or fully reverse crumpling by re-stretching the system. Crumpling adds increased flexibility and stretchability and has already been used to create super-elastic flexible strain sensors. As the system is stretched the peak reflected wavelength from the CPC layer shifts changing the amount of light reaching the crumpled graphene substrate modulating the photocurrent in an easy to measure manner. Using this system we have produced a conformable and stretchable strain sensor (capable of standing at least 30% strain) which demonstrates a near order of magnitude increase in sensitivity over an unilluminated crumpled graphene strain sensor. Our sensor shows potential applications in structural health monitoring and human body motion detection where systems need to discrete and highly flexible/conformable.
12:15 PM - ED13.15.04
Light Scattered by 'Hedgehog' Particles
Joong Hwan Bahng 1 2 , Douglas Montjoy 1 2 , Wei-Shun Chang 3 , Stephan Link 3 , Alexander Govorov 4 , Nicholas Kotov 1 2 Show Abstract
1 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan, United States, 3 Chemistry, Rice University, Houston, Texas, United States, 4 Physics and Astronomy, Ohio University, Athens, Ohio, United States
Sensitive to even a small perturbation in its construct, particles provide versatile and compact platforms with which to design electromagnetic responses. With great advances in the nanofabrication, diverse particle types exhibiting unique and useful scattered radiation patterns have been realized or theoretically predicted. In particular, particles exhibiting broadband scattering with flexibility to suppress backscattering and enhance forward scattering hold promises in a diverse array of photonics devices servicing photodetectors, antennas and photovoltaics. Recently, we have reported the ‘hedgehog’ particles whose high aspect-ratio surface roughness, composed of ZnO nanospikes, on a polymeric microsphere elicits anomalous dispersion behavior that breaks the well-known “similarity rule”. The ‘hedgehog’ particles represent a novel class of “rough” particles comprised of all dielectric components that lies within the Mie scattering regime due to wavelength comparable dimensions. It should be noted that such types of particles are barren in previous endeavors, both experimentally and theoretically. In this research, in addition to deviation in the interaction potential as reported previously, we will show that high aspect ratio nano-topography also modifies electromagnetic responses from what is predicted by Mie theory for smooth dielectric particles. In detail, the high aspect-ratio interfacial nano-corrugation 1) educes broadband scattering at the visible spectrum, 2) suppresses resonant modes within the ‘hedgehog’ particles despite its sizes and constitutive properties and 3) creates near-field profiles that elicits broadband suppression of backscattering and enhancement of forward scattering at two spectral regions inclusive to telecommunication range and mid-infrared. Addition to a library of electromagnetic responses of diverse particle types is expected further enrich scientific foundation and engineering of photonic devices.
12:30 PM - ED13.15.05
Probing the Surface Plasmon Resonance Behavior of Refractory Nanomaterials using Electron Energy Loss Spectroscopy
Andrew Herzing 1 , Urcan Guler 2 , Xiuli Zhou 3 , Vladimir Shalaev 2 , Andreas Trugler 4 , Alexandra Boltasseva 2 , Theodore Norris 3 Show Abstract
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , Purdue University, West Lafayette, Indiana, United States, 3 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 4 , TU Graz, Graz Austria
The surface plasmon resonances resulting from the interaction of light with nanostructures offer a promising route to controlling the properties and propagation of light at length scales which are far below the diffraction limit. Additional applications in sensing and photocatalysis are also being intensively studied. Most studies in this area have focused on noble metals, which often exhibit strong, well-defined resonances. However, the practical application of these materials has been limited due to chemical and/or thermal instability, barriers to integration with existing microelectronic fabrication methods, and the heavy losses they often exhibit in the optical range.
Recently, refractory transition metal nitrides have been proposed as a promising class of alternative materials for plasmonic applications. In particular, TiN exhibits similar optical properties to those of Au, but is much more thermally stable, less expensive, and is compatible with traditional semiconductor fabrication technology. Its plasmon response has been studied by optical techniques, however, these are not sensitive to changes in the plasmon resonances arising from local variations in chemistry and structure. Herein, we have employed monochromated electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) to study the local plasmonic response of TiN thin-films and nanocubes produced via chemical methods. While EELS can reveal the local plasmon resonance behavior of such nanostructures, it is only by careful comparison with simulated spectra and the results of density functional theory calculations that the origin of experimental resonances can be properly understood.
12:45 PM - ED13.15.06
Detecting Surface Energy Correlation with Crystal Orientation in Native Oxides Grown on Si(100) and Si(111) Using Three Liquid Contact Angle Analysis (3LCAA)
Ryan Van Haren 2 , Edgar Ocampo Landeros 2 , Matthew Bade 2 , Alvaro Martinez 2 , Yash Pershad 2 , Sabrina Suhartono 2 , Ryan Francis 2 , Nicole Herbots 2 1 , Shawn Whaley 2 , Robert Culbertson 2 , Harshini Thinakaran 4 , Abijith Krishnan 3 Show Abstract
2 Department of Physics, Arizona State University, Tempe, Arizona, United States, 1 , SiO2 Innovates, Tempe, Arizona, United States, 4 , BASIS HS Scottsdale, Scottsdale, Arizona, United States, 3 Department of Physics, Harvard University, Cambridge, Massachusetts, United States
The goal of this work is to establish whether a difference in the surface energy of native oxides on Si(100) and Si(111) can be detected using Three Liquid Contact Angle Analysis (3LCAA) metrology. Si(100) and Si(111) differ in their areal surface density by 12%, with Si(100) exhibiting 6.8 × 1014atoms/cm2 density while Si(111) exhibits a higher density of 7.8 × 1014 atoms/cm2. The motivation of this research is to establish quantitative analysis of the total surface energy density γT of semiconductor and oxide surfaces, including probing the contribution of Lifshitz-Van der Waals molecular interactions and electron acceptor and donor interactions. Such a metrology can then correlate surface structure and density to the reliability and lifespan of integrated electronic sensors hermetically sealed via NanoBondingTM . Highly polished hydrophobic surfaces with low roughness RMS yield low total surface energies because these surfaces exhibit few dangling bonds, surface defects, and impurities. These three characteristics negatively impact hermetic bonding in integrated electronic sensors exposed to saline environments by permitting fluid percolation and mobile ion diffusion. Measuring surface energy via 3LCAA makes it possible to estimate the number of dangling bonds, surface defects, and impurities on the surface of a material; and determine the optimal materials for hermetically sealed electronic sensors. 3LCAA with 18 MegaOhms Deionized water, glycerine, and alpha-bromonaphthalene is used to measure the total surface energy density γT. Based on the Van Oss theory, γT can be computed by combining the contributions to the surface energy due to three distinct interactions characteristic of insulators and semiconductors: (1) surface interaction of the surface with molecular dipoles, known as the Lifshitz-Van der Waals energy, γLW, (2) surface interaction with electron donors, γ+, and (3) electron acceptors, γ-. 3LCAA is performed in a class 100 hood using the Sessile Drop method to extract the contact angle by fitting an ellipse to the full drop, using multiple droplets for each liquid. Each droplet is only a few µl in volume in order to avoid gravitational effects; measurements are taken quickly after the droplets are placed to avoid the effects of evaporation. Native SiO2/Si(100) yields a total surface energy γT of 51 ± 3 mJ/m2. This energy is lower than γT for Si(111), 57 ± 2 mJ/m2 by 11% ± 6%. Measurements of the Lifshitz-Van der Waals surface energy component γLW for Si(100) yield 37 ± 1 mJ/m2 which is lower than γLW for Si(111), 39 ± 1 mJ/m2 by 5% ± 3%. Therefore, 3LCAA can detect, with an accuracy of a few percent, changes in the surface energy of native oxides. In this work, 3LCAA can accurately demonstrate that the surface energy γT of native oxides on the two different crystal orientations studied, Si(100) and Si(111), scales linearly with the difference in surface areal density.
 US Patent 9,018,077, (2015) Herbots et al.
ED13.16: Imaging—A Nanophotonics and Plasmonics Approach II
Friday PM, April 21, 2017
PCC North, 100 Level, Room 132 B
2:30 PM - *ED13.16.01
Tip-Enhanced Raman Spectroscopy for Nanoscale Reaction and Characterization
Bin Ren 1 , Jin-Hui Zhong 1 , Shengchao Huang 1 , Kaiqiang Lin 1 , Zhicong Zeng 1 Show Abstract
1 Department of Chemistry, Xiamen University, Xiamen China
Tip-enhanced Raman spectroscopy (TERS) can not only obtain the topological but also vibrational information of a sample at the nanometer resolution. It is a very promising nanospectroscopy. In this talk, we used TERS to spatially resolve the site-specific electronic and catalytic properties of an atomically well-defined Pd/Au(111) bimetallic model catalyst at 3 nm resolution with molecular fingerprints. Benefiting from this high spatial resolution, we can directly visualize the distinct chemical (electronic) and physical (plasmonic) properties of the Pd island edges compared with the Pd terrace sites on a Au(111) surface.
Up to now most of previous TERS studies were performed in air or in the ultrahigh vacuum. If TERS study can be performed in the electrochemical environment, the electronic properties of the surface can be well controlled so that the interaction of the molecules with the substrate and the configuration of the molecules on the surface can also be well controlled. We designed a special spectroelectrochemical cell to eliminate largely the distortion of the liquid layer to the optical path and have been able to obtain TER spectra of reasonably good signal to noise ratio for surface adsorbed molecules under electrochemical potential control. Furthermore, we are able to synergistically control the reaction by both electrode potential and laser power, and characterize the reaction with nanometer spatial resolution. We further address the relative intensity issue in TERS by using single nanorod as a model and reveal that it is important to correct plasmon shaping effect for the experimentally obtained Raman spectra of molecular species.
3:00 PM - ED13.16.02
Plasmonic Enhancement in Surface-Enhanced Raman Scattering is much Stronger than Commonly Accepted
Niclas Mueller 1 , Sebastian Heeg 3 2 , Uwe Huebner 4 , Patryk Kusch 1 , Etienne Gaufres 5 , Nathalie Tang 5 , Richard Martel 5 , Aravind Vijayaraghavan 3 , Stephanie Reich 1 Show Abstract
1 , Freie Universität Berlin - Department of Physics, Berlin Germany, 3 School of Materials and National Graphene Institute, The University of Manchester, Manchester United Kingdom, 2 Photonics Laboratory, ETH Zürich, Zürich Switzerland, 4 , Leibniz Institute of Photonic Technology, Jena Germany, 5 Regroupement québécois sur les matériaux de pointe and Département de chimie, Université de Montréal, Montréal, Quebec, Canada
Surface-enhanced Raman scattering (SERS) is the giant increase of the Raman cross section of a molecule close to a metallic nanostructure. The major underlying mechanism is the interaction of the molecule with a localized surface plasmon in the metal. Additionally, chemical interactions with the metal can change the Raman cross section. The different enhancement mechanisms act simultaneously which hampers a meaningful comparison to theory. Measurements on well-defined plasmonic hotspots resulted in an enhancement that was two to three orders of magnitude stronger than predicted by the widely used theory of electromagnetic enhancement [1-3]. The discrepancy was attributed to a possible chemical enhancement.
I will present a SERS experiment in which we succeeded in isolating the plasmonic enhancement and compare it to the predictions from a recently proposed treatment of SERS as a higher-order Raman process. We used carbon nanotubes (CNTs) to carry encapsulated rod-like molecules into the plasmonic hotspot of a lithographic gold nanodimer. The CNTs thereby determined the position and orientation of the molecules. We measured a thousand-fold integrated enhancement of the Raman cross section which originated only from plasmonic interactions, because the nanotube walls shielded the molecules from chemical interactions with the metal. The measured plasmonic enhancement was two orders of magnitude stronger than the electromagnetic enhancement obtained from finite-difference time-domain simulations.
We propose a treatment of SERS as higher-order Raman scattering, in which the plasmonic excitation is an integral part of the Raman process . I will present model calculations with which we estimated the plasmonic enhancement in our experiments. Our treatment of SERS lead to an intrinsically stronger plasmonic enhancement that excellently matched the measured enhancement factors. I will discuss the implications of our experimental findings for optimizing and tailoring rational SERS substrates.
 W. Zhu and K. B. Crozier, Nature Communications 5, 5228 (2014).
 D.-K. Lim, K.-S. Jeon, J.-H. Hwang, H. Kim, S. Kwon, Y. D. Suh and J.-M. Nam, Nat Nano 6, 452-460 (2011).
 K. L. Wustholz, A.-I. Henry, J. M. McMahon, R. G. Freeman, N. Valley, M. E. Piotti, M. J. Natan, G. C. Schatz and R. P. V. Duyne, J. Am. Chem. Soc. 132, 10903-10910 (2010).
 N. S. Mueller, S. Heeg and S. Reich, Phys. Rev. A 94, 023813 (2016).
3:15 PM - ED13.16.03
Near-Field Detection and Application of Optical Orbital Angular Momentum Modes in an Electron Microscope
Jordan Hachtel 2 , Sang Yeon Cho 3 , Roderick Davidson 1 , Matthew Chisholm 2 , Richard Haglund 1 , Sokrates Pantelides 1 , Juan-Carlos Idrobo 2 , Benjamin Lawrie 2 Show Abstract
2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , New Mexico State University, Las Cruces, New Mexico, United States, 1 , Vanderbilt University, Nashville, Tennessee, United States
We examine near-field optical orbital angular momentum (OAM) modes directly at the near-field using cathodoluminescence (CL) within a scanning transmission electron microscope (STEM). STEM-CL allows for the spatial precision and broad range of excitation available in electron microscopy to be combined with the spectral resolution of photonics. Spiral holes in silver films are an ideal structure in which to study OAM, as the chiral geometry facilitates coherent interference between surface plasmon polaritons (SPPs). In an OAM mode, the SPP field profile is described by an nth order Bessel function, where the topological charge, n, is determined by the charge of the structure as well as the exciting source. Since the electron beam can be treated as an n=0 Bessel-like beam, we can use STEM-CL to spatially and spectrally map the formation of the SPP Bessel modes, and hence OAM, at the nanoscale.
Subsequently, a second set of spirals is made with smaller chiral substructures fabricated at the origin of the larger OAM spiral: one with the same chirality as the outer structure, and one with the opposite chirality. The luminescence of the same-chirality structure is enhanced two-fold above the Ag background with respect to the opposite-chirality structure. The results unveil a wide range of opportunities for chirality detection in nanoscale materials with CL spectroscopy.
This work was supported by DE-FG02-09ER4655, DE-FG02-01ER45916, the ORNL Historically Black Colleges and Universities and Minority Education Institutions Summer Faculty Research Program, the Laboratory Directed Research and Development program. Additional support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division and the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, and the Center for Nanophase Materials Sciences (CNMS), which is sponsored at ORNL by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
ED13.17: Light-Scattering and Imaging
Friday PM, April 21, 2017
PCC North, 100 Level, Room 132 B
3:30 PM - *ED13.17.01
Light Generation and Scattering in a Photonic Network of Sub-Wavelength Nanofibres
Riccardo Sapienza 1 Show Abstract
1 Department of Physics, King’s College London, London United Kingdom
Nanoscale generation of individual photons in confined geometries is an exciting new research field aiming at exploiting localised electromagnetic fields for light manipulation. One of the outstanding challenges of photonic systems combining emitters with nanostructured media is the selective channelling of photons emitted by embedded sources into specific optical modes and their transport at distant locations in integrated systems. Here we discuss coupling experiments in plasmonic networks and electrospun nanofibres networks. While the former achieve large Purcell factors , the latter combine subwavelength field localisation and large broadband near-field coupling with low propagation losses . By momentum spectroscopy, as in Figure, we quantify the modal coupling efficiency identifying the regime of single-mode coupling . Moreover we identify an hybrid dielectric-plasmonic geometry as the most convenient for long-range energy transfer . The hybrid dielectric networks do not rely on resonant interactions making them ideal for room-temperature operation, and offer a scalable platform for future quantum information technology.
 M. Gaio, M. Castro-Lopez, J. Renger, N. van Hulst, and R. Sapienza, Percolating Plasmonic Networks for Light Emission Control, Faraday Discussions, 178, 237-252 (2015).
 M. Gaio, M. Moffa, M. Castro-Lopez, D. Pisignano, A. Camposeo, and R. Sapienza “Modal coupling of single photon emitters within nanofibre waveguides” ACS Nano 10 (6), pp 6125–6130 (2016).
 P. M. de Roque, N. F. van Hulst and R. Sapienza, Nanophotonic boost of intermolecular energy transfer, New Journal of Physics 17, 113052 (2015).
4:30 PM - ED13.17.02
Highly Effective Light Trapping in 2D Absorbers
Sidan Fu 1 , Xiaobai Yu 1 , Yi Song 2 , Haozhe Wang 2 , Jing Kong 2 , Jifeng Liu 1 Show Abstract
1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States, 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
2D materials, such as graphene, transition metal dichalcoginides (e.g. MoS2), and hexagonal boron nitride (h-BN), have very little optical absorption due to the atomically thin layers. For example, only 2.3% of incident light can be absorbed in single layer graphene (SLG), which significantly limits their efficiencies as photonic and optoelectronic devices. A novel technology is introduced here to use low-temperature fabricated and self-assembled SnOx (x<1) transparent conductive oxide (TCO) with Sn/SnO core/shell nano-needle structure, instead of plasmonic or dielectric optical coatings1,2, to enhance the absolute light absorption of 2D absorbers by 2% - 15% across a broad wavelength range from 500 nm to 2500 nm. The nano-needle structured SnOx TCO is fabricated by co-sputteing Sn and SnO2 followed by N2 annealing at 225 °C, with a high electrical conductivity of ~2000 S/cm. These nano-needle structures can strongly scatter the incident light into lateral directions and greatly increase the infrared (IR) light absorption of Ge thin film by up to 30x, as demonstrated in our previous works3,4. When applied to 2D materials, however, electro-magnetic interactions at the interface of SnOx/2D materials is a more favored mechanism, analogous to meta-surface effect. This achieves a significantly enhanced light absorption in 2D absorbers in visible and near IR (NIR) spectral range. Up to 15% enhancement in absolute optical absorption is found in SLG with 80 nm nano-needle structured SnOx; and up to 14% enhancement is found in MoS2 with 100 nm SnOx. These nano-needled SnOx coatings even make SLG and single layer MoS2 clearly visible to naked eyes under white light, thanks to the strong light trapping effect. We analyzed the 2D material optical absorption enhancement as a function of the SnOx thicknesses and composition as well as the number of layers of 2D absorbers. Techniques to avoid introducing defects to 2D absorbers during the sputtering process are developed, too. We discovered that adding nanometer-thick optically transparent layers between SnOx and 2D materials would reduce the light trapping effect, confirming that the optical response at the interface of SnOx/2D material is indeed critical to the light trapping. The highly effective light trapping provided by the SnOx could greatly benefit the future development of efficient 2D photonics devices and broaden the applications of TCO.
 H. A. Atwater and A. Polman, Nature Mateirals 9, 205-213 (2010)
 X. Sheng, J. Liu, I. Kozinsky, et al., Advanced Materials 23, 843-847 (2011)
 X. Wang, A. Wong, S. Malek, et al., Optics Letter 40, 2603-2606 (2015)
 A. Wong, X. Wang, and J. Liu, Journal of Applied Physics 117, 103109 (2015)
4:45 PM - *ED13.17.03
Angle-Selective Filters for Position-Sensitive Illumination and Shadowing
Enas Sakr 1 , Peter Bermel 1 Show Abstract
1 Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States
Selective filtering of spectral and angular optical transmission holds great promise for applications such as solar and thermal energy harvesting and sensitive optical detectors. While optical passband and stopband spectral filters are already widely used, angular selective transmission and reflection filtering represents a less-explored alternative. The latter could be uniquely promising for several applications, including stray radiation minimization, directionally selective thermal absorption, thermal emission exclusion, and position-sensitive illumination and shadowing. Thus, a simple implementation of angle-selective reflection filters using guided mode resonance structures is proposed. Although guided mode resonance structures are already used as spectral reflection filters, here we investigate their use as angle-selective reflection filters. Combining these filters with thermal emitters can exclude selected emission angles for spatially selective thermal emissivity reduction toward sensitive targets, as well as directionally selective emissivity exclusion for suppression of solar heating. We show a very large selective reduction of heat exchange of 99.77% between an engineered emitter and a distant receiver, using just a single groove grating and an emitting substrate in the emitter’s side. Also, we demonstrate a selective reduction of heat exchange by approximately 77% between an emitter covered by angle-selective reflection filters and a nearby sensitive target. The suggested angle-selective structure may have applications in excluding background optical radiation without losses: in particular, these include thermal absorption reduction for daytime radiative cooling, sensitive IR telescope detectors, high-fidelity thermoluminescent spectroscopy, and position-sensitive illumination and shadowing of nearby objects.
5:15 PM - ED13.17.04
Electron Dynamics and Charge Injection in Au Nanoparticle - TiO2 Thin Films
Daniel Ratchford 1 , Adam Dunkelberger 2 , Jeffrey Owrutsky 1 , Igor Vurgaftman 1 , Pehr Pehrsson 1 Show Abstract
1 , U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 2 , Research Associateship Program, National Research Council, Washington, District of Columbia, United States
We used transient absorption spectroscopy to probe electron dynamics in TiO2 thin films embedded with Au nanoparticles (NPs) after excitation of the plasmon band. Samples were made of multi-layered stacks of Au nanoparticles sandwiched between TiO2 atomic layer deposited (ALD) thin films. For control samples, similar structures were fabricated with ALD Al2O3. Sub-percolation thin films of Au resulted in <20 nm islands with plasmon resonances at ~650 nm (~560 nm) in the TiO2 (Al2O3) samples. The electron dynamics were monitored by independently probing in both the visible (550 nm – 750 nm) and infrared (~5 μm) spectral regions. The transients in the visible appear to be dominated by changes in the plasmon band and reflect electron-phonon coupling. The visible probe decay times were measured as a function of pump power for each sample. The TiO2-Au consistently showed faster decays than Al2O3-Au. Differences in the decay times were used to estimate the charge injection efficiencies in the TiO2-Au samples. The samples were probed in the mid-IR to measure free carrier absorption. When pumped around the plasmon resonance, the Al2O3-Au sample generated no mid-IR transient signal, however, the TiO2-Au sample exhibited a decay similar to direct excitation of TiO2 films. This provides direct evidence of charge injection into the TiO2. Using the amplitude of the mid-IR signal to determine charge injection efficiencies yields similar estimates to those derived from the visible probe measurements.
5:30 PM - ED13.17.05
All-Electrical Detection and Imaging of Propagating Graphene Plasmons
Achim Woessner 1 , Mark Lundeberg 1 , Pablo Alonso-Gonzalez 2 , Yuanda Gao 3 , Alexey Niktin 4 , Alessandro Principi 5 , Kenji Watanabe 6 , Takashi Taniguchi 6 , Marco Polini 7 , James Hone 3 , Rainer Hillenbrand 4 , Frank Koppens 1 Show Abstract
1 , ICFO - The Institute of Photonic Sciences, Castelldefels, Barcelona, Spain, 2 Departamento de Física, Universidad de Oviedo, Oviedo Spain, 3 Department of Mechanical Engineering, Columbia University, New York, New York, United States, 4 , CIC nanoGUNE, San Sebastian Spain, 5 Institute for Molecules and Materials, Radboud University, Nijmegen Netherlands, 6 , National Institute for Materials Science, Tsukuba Japan, 7 , Istituto Italiano di Tecnologia, Genova Italy
Controlling, detecting and generating propagating plasmons by all-electrical means is crucial for on-chip nano-optical circuits. Graphene can carry long-lived plasmons that are highly confined and controllable in-situ.[1,2,3] However, electrical detection of propagating graphene plasmons has thus far been elusive.
Here, we show how high-resolution photocurrent nanoscopy can be not only applied to directly measure the charge neutrality point as well as the carrier density profile of encapsulated graphene devices in real space but also to detect and image propagating graphene plasmons. Instead of achieving detection via added optoelectronic materials, as is typically done in other plasmonic systems, our device harvests the natural decay product of the plasmon - hot carriers - and converts them directly into a voltage through the thermoelectric effect.[6,7]
We use high quality graphene encapsulated between two layers of hexagonal boron nitride and employ two local metal gates to fully tune the thermoelectric and plasmonic behavior. We investigate the plasmon propagation, frequency dispersion, and thermoelectric generation. We electrically measure propagating graphene plasmons both for mid-infrared and THz frequencies. In the case of the THz frequency range we find that the graphene plasmon couples with the underlying metal gate. This so called graphene-insulator-metal plasmons exhibit a linear, acoustic, dispersion instead of the common square root dispersion and are strongly confined.
This work paves the way for efficient ultra-compact detectors in both the mid-infrared and THz frequency range based on graphene plasmons as well as fully integrated graphene plasmonic circuits and THz sensors.
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 P. Alonso-González, A.Y. Nikitin, Y. Gao, A. Woessner et al., Nature Nanotechnology (2016) doi:10.1038/nnano.2016.185
5:45 PM - ED13.17.06
Polarized Light Emission from Isotropic Colloidal Quantum Dots Coupled to a Plasmonic Cavity
Kivanc Gungor 1 , Burak Guzelturk 1 , Onur Erdem 1 , Shinae Jun 3 , Eunjoo Jang 3 , Hilmi Demir 1 2 Show Abstract
1 Electrical and Electronics Engineering, Bilkent University, Ankara Turkey, 3 Inorganic Material Lab, Samsung Electronics, Suwon Korea (the Republic of), 2 Luminous! Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore Singapore
Colloidal semiconductor quantum dots (QD) recently have attracted great interest from the display industry owing to their superior color purity. The QD-based backlights in the liquid crystal displays (LCD) can favorably enhance the color gamut as compared to commonly used phosphor based white light-emitting diodes and enable unprecedented level of color enrichment. However, these QD-backlights provide randomly polarized light and thus lead to a major power penalty in the optical backplane of LCDs, which is a typical problem for any of the backlight source reported to date. This problem for the QD-based color conversion is caused by using of isotropic QDs that emit randomly polarized light. Colloidal synthesis of anisotropic-shaped semiconductor nanocrystals including nanorods [1,2] and nanoplatelets  has been shown to generate polarized light in the colloidal semiconductor QDs. However, this requires such anisotropic emitters to be properly arranged in a specific orientation in the ensemble film, which is prohibitively challenging. Magnetically aligned metallic nanowire composites integrating the QDs realizes polarized light emission. However, metallic losses and inhomogeneity observed in the resulting films make it difficult to use them in display applications . The use of metal nanoparticle – QD composites enables plasmonically coupled anisotropic enhancement in radiative decay rates of the QDs and polarized QD emission in the planar composite architectures. However, this method requires oblique illumination at large angles, which is not suitable as display backlight .
In this study, we proposed and demonstrated novel plasmonic-QD composites on flexible patterned surfaces to achieve highly polarized light generation under normal incidence at the front plane. For this purpose, we harnessed the inherent polarization dependence of the plasmonic structures on nanopatterned surfaces. Additionally, we utilized plasmon–exciton coupling to enhance the QD emission. Our structure plasmonically enhances TM polarization and suppresses TE polarization without absorbing it. This leads to overcompensation of the losses observed in conventional polarizing architectures. Using numerical simulations, under normal incidence illumination, we computed a TM/TE ratio of 270 corresponding to a degree of polarization as high as 0.993. In the experiments, we achieved a polarization degree up to 0.78 and a TM/TE ratio of ~8. The observed anisotropic emission from the fabricated plasmonic-QD composites using isotropic nanoemitters under normal incidence illumination with impressive polarization ratio is very promising for the development of the next-generation high-quality high-efficiency flexible displays in the near future.
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