Linyou Cao, North Carolina State University
Nader Engheta, University of Pennsylvania
Jeremy Munday, University of Maryland
Shuang Zhang, University of Birmingham
II2: Resonant Optics in Dielectric Structures
Tuesday PM, April 02, 2013
Moscone West, Level 3, Room 3022
2:30 AM - *II2.01
Resonant Metal and Semiconductor Building Blocks for Nanophotonic Devices
Mark L. Brongersma 1
1Stanford University Stanford USAShow Abstract
Nanotechnology has enabled the realization of hybrid devices and circuits constructed from highly-engineered nanoscale metal and semiconductor building blocks. In electronics, it is well known how the distinct material-dependent properties of metals and semiconductors can be combined to realize important functionalities, including transistors, memory, and logic. In this presentation, I will describe several optoelectronic devices for which the geometrical properties of the constituent semiconductor and metallic nanostructures are tuned in conjunction with the materials properties to realize multiple functions in the same physical space. These devices capitalize on the notion that nanostructures possess a limited number of resonant, geometrically-tunable optical modes whose hybridization and intermodal interference interaction can be tailored in a myriad of useful ways.
3:00 AM - *II2.02
Engineering Photonic-plasmonic Coupling in Metal-dielectric Nanostructures for Planar Devices
Luca Dal Negro 1
1Boston University Boston USAShow Abstract
The ability to design and to control nanoscale light-matter interactions using metal-dielectric planar optical chips defines new exciting challenges in the rapidly growing fields of nanoplasmonics and nano-optics. Efficient schemes for nanoscale electromagnetic field enhancement, concentration and control over predefined spatial/spectral bandwidths can be enabled by the manipulation of both propagating and non-propagating electromagnetic fields in resonant scattering nanostructures with multiple length scales. In particular, recent advancements in the design and fabrication of multi-particle arrays of metal-dielectric nanostructures have demonstrated unique opportunities for the engineering of novel functionalities and planar optical devices that leverage photonic-plasmonic coupled resonances, such as broadband optical nano-antennas, near-field concentrators and extractors, laser nanocavities, circular light scatterers and on-chip nonlinear optical elements.
In this talk, I will discuss some of our recent results on the design, nanofabrication and optical characterization of periodic and aperiodic photonic-plasmonic coupled nanostructures for a number of optical engineering device applications. Specifically, I will focus on retardation and multiple scattering effects in nanoplasmonics as a strategy to boost the intensity of optical near-fields at the nanoscale. I will then introduce our work on circular multiple scattering in photonic-plasmonic spiral structures and demonstrate their potential for the engineering of broadband light emission enhancement, solar cell energy harvesting, and the generation and control of Orbital Angular Momentum (OAM) of light using both metallic and dielectric arrays. The generation of well-defined numerical sequences of OAM values by light scattering from engineered particle arrays is relevant to a number of device applications in singular optics, secure communication, classical and quantum cryptography. Finally and time permitting, I will present our recent work on the design and engineering of novel types of Si-compatible light emitting nano-devices, namely the coaxial dielectric slot and the Metal-Insulator-Metal (MIM) coaxial cavity, both supporting nanoscale localized modes for broadband light emission enhancement or Erbium radiation at 1.54µm and the manipulation of spontaneous emission rates at multiple frequencies on planar optical chips.
3:30 AM - II2.03
Novel Resonant Optical Phenomena with Semiconductor Nanostructures
Pengyu Fan 1 Zongfu Yu 2 Shanhui Fan 2 Mark L. Brongersma 1
1Stanford University Stanford USA2Stanford University Stanford USAShow Abstract
Nanoscale semiconductor structures such as nanowires and nanoparticles with high refractive index can support optical resonances that give rise to strong light matter interaction and optical response. These resonances lead to use of semiconductor nanostructures for compact and efficient photonic, optoelectronic and photovoltaic devices. One unique aspect of semiconductor optical resonators, comparing to plasmonic resonant structures made of metals, is that one could gain access to both far-field (scattering) and near-field (absorption) properties of the resonators at the same time, allowing us to comprehensively study and engineer resonant optical phenomena. To show case this interesting notion, we will demonstrate theoretical analysis and experimental observation of optical Fano resonance in a single Si nanostructure, which is often considered challenging comparing to plasmonic structures. Furthermore, due to the advantage of employing semiconductor nanostructure, we can for the first time characterize both scattering and absorption near an optical Fano resonance and identify their very different spectral features. Finally, we would further explore magnetic response from resonant Si nanostructures and its implication for engineering dielectric metamaterials and metasurfaces.
3:45 AM - II2.04
General Properties of Optical Resonance in Dielectric Structures
Lujun Huang 1 Yiling Yu 1 Linyou Cao 1
1North Carolina State University Raleigh USAShow Abstract
Dielectric structures can provide strong, tunable optical resonances that are similar to those in plasmonic structures. However, much less has been known about the dielectric resonance. Here we demonstrate the general correlation between the optical resonance with the leaky optical mode in dielectric objects. This correlation is evidenced by a linear dependence of the resonance on the physical features of the structure, and can be excellently interpreted with a simple Fabry-Perot model. Similar correlation can be generally found in dielectric structures with different dimensionality (1D nanowires and 0D nanoparticles) or different morphology (rectangular or triangular cross sections). This fundamental understanding can serve as a powerful predictive tool to guide the engineering of optical resonances.
4:30 AM - *II2.05
Enhancing Optoelectronics with Metallo-dielectric Optical Nano-antenna
Hooman Mohseni 1
1Northwestern University Evanston USAShow Abstract
Recent progress on optical antenna has led to many exciting new devices. However, one of the key issues of optical antenna is the increasing metal loss at shorter wavelength. While this is not a significant limitation for some applications, reducing the optical antenna loss is a major priority for many important applications such solar energy harvesting.
I will present some of our new findings based on metallo-dielectric optical nano-antenna that show excellent properties over a wide spectral range. Most importantly, they can simultaneously produce a high antenna gain and directivity.
5:00 AM - *II2.06
Beyond the Electric Dipole Approximation: Higher Order Transitions for Nanophotonics
Rashid Zia 1
1Brown University Providence USAShow Abstract
Although it is often assumed that all light-matter interactions at optical frequencies are mediated by electric dipole transitions, we regularly observe higher-order transitions. For example, we see magnetic dipole emission every day from the many lanthanide ions (such as trivalent europium and erbium) that help to illuminate everything from fluorescent lighting to telecom fiber amplifiers. Magnetic dipole and electric quadrupole transitions also play an important part in the light emission from transition metal ions and semiconductor quantum dots. In this presentation, we will experimentally characterize the "forbidden" transitions in a range of solid-state emitters, and we will illustrate how these higher-order processes can provide new tools for active electronic and photonic devices.
5:30 AM - II2.07
Low-loss, Localized Surface Phonon Polariton Modes in Silicon Carbide Nanopillars: Beyond Plasmonics
Joshua D Caldwell 1 Nicholas Sharac 2 Francisco Bezares 3 James P Long 1 Jeffrey C Owrutsky 1 Joseph Tischler 1 Orest J Glembocki 1 Igor Vurgaftman 1 Ronald W Rendell 1 Eugene Imhoff 1 Loretta Shirey 1 Nabil Bassim 1 Richard Kasica 4
1Naval Research Laboratory Washington USA2University of California - Irvine Irvine USA3ASEE Postdoctoral Fellows (residing at NRL) Washington USA4National Institutes of Standards and Technology Gaithersburg USAShow Abstract
Over the past decade, significant effort has been focused on the field of plasmonics and its applications in enhanced spectroscopy, light emitters, waveguides, and absorbers for photodetectors. The enhanced capabilities are made possible by exciting plasmons at the interfaces of metals, and within metallic nanostructures. While plasmonic nanopillars have attracted attention for their ability to achieve extreme sub-wavelength photon confinement, large concentrations of optical energy, and enhancements to various optical processes, they are severely limited by the inherent and detrimental losses due to the high carrier densities within metals. Therefore, it is highly desirable to identify new materials capable of supporting such sub-diffraction limited electromagnetic modes without the disadvantages that arise from such excessive losses.
We report on sharp surface-phonon resonances in 1um tall nanopillars fabricated from semi-insulating silicon carbide, with diameters ranging from 100-250 nm, as exemplifying one potential system for meeting these goals in the mid-wave IR, SiC in particular should prove useful militarily and commercially important 8-12 um atmospheric window. In a polar semiconductor, surface electromagnetic modes can be supported by optical phonons, where the charge separation between the atoms is akin to charge carriers in the plasma. The coupling of electromagnetic waves to optical phonon modes in polar semiconductors such as SiC, AlN or GaAs drives the real part of the dielectric constant εr negative at infrared frequencies, as is necessary for confined subwavelength optical modes, in perfect analogy to conventional plasmons. These “bound-charge” surface phonon polaritons are the electromagnetic equivalent of the free-electron surface plasmons. While electronic plasmas are damped by scattering on a time scale of tens to hundreds of fs, optical phonon modes decay via much weaker anharmonic phonon-phonon interactions on a time scale of a few ps. For nanoscale surface modes, this improves the attainable Q factors by an order of magnitude (from several tens to several hundreds). We report on Q-factors from these initial structures in excess of 40 with calculations showing that values up to 500 being possible. Furthermore, the Q factor was found to be only weakly dependent upon the size of the nanostructure. These large quality factors were achieved with field confinements of the incident mid-IR wavelengths on the order of lambda;/40-lambda;/75. We observe two peaks that can be tentatively assigned as transverse and longitudinal modes, however electromagnetic simulations indicate that these surface modes demonstrate a much more complex field profile than would be anticipated from an spherical subwavelength particle. We also observe surface-enhanced IR absorption from a deposition of anthracene, illustrating the promise of these systems for applications such as molecular spectroscopy.
5:45 AM - II2.08
Nanowire Antenna Emission
Grzegorz Grzela 1 Ramon Paniagua-Dominguez 2 Tommy Barten 1 Yannik Fontana 1 4 Jose A. Sanchez-Gil 2 Jaime Gomez Rivas 1 3
1FOM Institute AMOLF Eindhoven Netherlands2Consejo Superior de Investigaciones Cientamp;#237;ficas Madrid Spain3Eindhoven University of Technology Eindhoven Netherlands4Ecole Polytechnique Famp;#233;damp;#233;rale de Lausanne Lausanne SwitzerlandShow Abstract
We experimentally demonstrate the directional emission of polarized light from single semiconductor nanowires. The directionality of this emission has been directly determined with Fourier micro-photoluminescence measurements of vertically oriented InP nanowires. Nanowires behave as efficient optical nanoantennas, with emission characteristics that are not only given by the material but also by their geometry and dimensions. By means of finite element simulations, we show that the radiated power can be enhanced for frequencies and diameters at which leaky modes in the structure are present. These leaky modes can be associated to Mie resonances in the cylindrical structure. The radiated power can be also inhibited at other frequencies or when the coupling of the emission to the resonances is not favored. We anticipate the relevance of these results for the development of nanowire photon sources with optimized efficiency and controlled emission by the geometry.
 G.Grzela, R. Paniagua-Domínguez, T. Barten, Y. Fontana, J. A. Sánchez-Gil, J. Goacute;mez Rivas, Article ASAP, Nano Letters (2012), DOI: 10.1021/nl301907f
II1: Optical Metamaterials
Luca Dal Negro
Tuesday AM, April 02, 2013
Moscone West, Level 3, Room 3022
9:00 AM - *II1.01
Photonic Metamaterials: Recent Progress
Johannes Kaschke 1 2 Martin Wegener 1 2
1Karlsruhe Institute of Technology Karlsruhe Germany2Karlsruhe Institute of Technology Karlsruhe GermanyShow Abstract
One winding of a metal helix can be seen as a planar split-ring resonator, one end of which is pulled into the third dimension. For several windings, the interplay of the helix resonance together with the Bragg resonance gives rise to a one-octave broad circular-polarization stop band (Science 325, 1513 (2009)). Arrays of such helices can be used as a compact broadband circular polarizer. To further improve the performance of the device in terms of bandwidth and extinction, we have previously explored tapered-helix metamaterials (Appl. Phys. Lett. 100, 101109 (2012)), which do increase the bandwidth but still suffer from some finite circular-polarization conversion, which limits the extinction and the purity of the emerging polarization.
In this contribution, we focus on metamaterials composed of metallic quadruple-helices arranged into a square array. By recovering a four-fold rotational axis, circular polarization conversion can strictly be eliminated. However, metamaterial circular polarizers based on quadrupel helices, unlike single helices, inherently require absorption of the constituent metal. Otherwise, the combination of a four-fold rotational axis and time-inversion symmetry strictly forbids circular-polarizer action. Our symmetry analysis is confirmed by extensive numerical calculations comparing results for perfect electric conductors with those for a free-electron Drude metal with finite damping (Opt. Express, in press (2012)).
We also present our experimental status regarding fabricating such complex structures. We combine three-dimensional (3D) stimulated-emission-depletion (STED) direct-laser-writing (DLW) optical laser lithography using negative-tone photoresists and gold electroplating.
II3: Poster Session
Tuesday PM, April 02, 2013
Marriott Marquis, Yerba Buena Level, Salons 7-8-9
9:00 AM - II3.01
Plasmoelectric Potentials Modify the Optical Absorption of Plasmonic Nanoparticles
Ana M. Brown 1 Matthew T. Sheldon 1 Harry A. Atwater 1
1Caltech Pasadena USAShow Abstract
We report here results of experiments that indicate modified optical absorption in plasmonic nanoparticles excited by narrowband radiation relative to white light excitation. The plasmonic resonance frequency and spectral shape for metallic nanoparticles is dependent on the charge density of the particle . We have recently proposed theoretical models for the ‘plasmoelectric effect&’ in which optical excitation of metallic nanostructures can result in changes of charge density, producing electrochemical potentials (i.e. plasmoelectric potentials) . When a plasmonic nanostructure is illuminated at frequencies higher than the plasmon frequency, a plasmoelectric response will increase charge density and blue-shift the plasmon resonance to produce increased absorption. Increased heat from absorption thermodynamically drives this response. At frequencies lower than the plasmon frequency, a plasmoelectric potential will red-shift the plasmon resonance by decreasing charge density.
We have performed optical experiments to excite and probe plasmoelectric potentials. Optical absorption experiments can manifest a plasmoelectric response because the induced change in charge density is indicated by a change of the resonance frequency. Monochromatic radiation at frequencies on either side of the neutral particle plasmonic resonance will induce a plasmoelectric potential, altering charge density in the structure and increasing absorption at that frequency. However, radiation at the resonance frequency will not induce a plasmoelectric response because no change in charge density will produce increased absorption at this frequency. Thus, in a plasmoelectric system, extinction spectra measured by scanning monochromatic illumination will show apparent broadening of the resonance compared with spectra measured under white light illumination.
To monitor the plasmoelectrically induced change in the optical spectrum we use a lock-in amplifier technique to measure the extinction of monodisperse (8% coeff. of variation) 60nm diameter Ag and Au colloids in solution (OD=1.2). For white light illumination extinction measurements, the sample was placed in the beam path of a white light source before a monochromator, while for monochromatic illumination extinction measurements, the sample was placed in the beam path after a monochromator. Strikingly, we found spectra collected with monochromatic illumination at a power density of 0.2W/cm^2 showed up to a 3% increase in extinction on either side of the extinction peak when compared to spectra collected under white light illumination. Further, increases in extinction to either side of the resonance scale with incident intensity and are of similar magnitude to theoretical predictions. These results are strong evidence for an optically induced plasmoelectric potential in noble metal nanoparticles.
 S. K. Dondapa, et al., Nano Letters 2012, 12 (3)
 M.T. Sheldon, et al., 2012 in submission, arXiv:1202.0301
9:00 AM - II3.02
Towards Low-cost Miniature Sensing Platforms: A Detection Principle Based on Tunable 1D Photonic Crystals
Ida Pavlichenko 1 2 Armin T. Exner 3 Paolo Lugli 3 Giuseppe Scarpa 3 Bettina V. Lotsch 1 2
1Max Planck Institute for Solid State Research Stuttgart Germany2Ludwig Maximilian University of Munich Munich Germany3Technical University of Munich Munich GermanyShow Abstract
One-dimensional photonic crystals (1D PCs), also known as Bragg stacks (BSs), represent a promising class of “smart” environmentally responsive nanostructures featuring optically encoded stimuli detection. Aptly, these periodic nanostructures are functional systems with an inherent response to physical stimuli such as temperature and humidity changes, and are capable of translating the chemical fingerprint of chemical and biological analytes into a visibly perceptible optical read-out. A variety of fabrication methods and numerous combinations of organic and inorganic materials together with surface functionalization and morphology tuning opens up new avenues to the design of simple, yet versatile sensing devices. Optical sensing is realized via tracking the behavior of the photonic stop band - a characteristic spectral region allowing for the modulation of the transmission/reflection properties of PCs. By virtue of the tunability of the stop band position, the intensity of light propagating through the Bragg stack is modulated upon varying the environmental conditions. Herein, we present a detection principle based on utilizing 1D PCs as responsive optical filters for intensity tuning of narrow-band light sources. The tunable range for the stop band modulation lies in the visible region and can thus be detected in a straightforward and inexpensive fashion by a visible-light photodetector. We demonstrate a route towards the bottom-up assembly of a fully functional, integrated miniature sensing platform and show temperature, humidity and chemical analyte detection as a proof of the proposed sensing concept.
 A. T. Exner, I. Pavlichenko, B. V. Lotsch, G. Scarpa, P. Lugli, Towards Low-Cost Thermo-Optic Imaging Sensors: A Detection Principle Based on Tunable 1D Photonic Crystals, 2012, submitted.
9:00 AM - II3.03
Enhancing Photothermal Imaging of Metallic Nanoparticles to Study Nanoscopic Liquid Crystalline Phase Transitions
A. Nicholas G. Parra-Vasquez 1 2 3 Laura Oudjedi 3 Stephen K. Doorn 2 Juan G. Duque 1 Laurent Cognet 3 Brahim Lounis 3
1Los Alamos National Laboratory Los Alamos USA2Los Alamos National Laboratory Los Alamos USA3CNRS amp; Institut d'Optique, Bordeaux Talence FranceShow Abstract
As new techniques are employed to obtain smaller and smaller nanoparticles, difficulties rise in characterizing and utilizing these nanoparticles for applications, such as biological sensing. Non-Fluorescent nanoparticles are especially difficult, however, in some cases, resonant absorption introduces an avenue for optical imagining. In this study, we implore the photothermal heterodyne imaging (PHI) technique, which enables studies of individual weakly absorbing nano-objects in various environments. Briefly, PHI microscopy uses a tightly focused time-modulated, resonant heating beam superimposed with a nonresonant probe beam. The heating beam is absorbed by the nanoparticle and a photoinduced change in the refractive index of the environment produces a measurable signal. Taking advantage of the dramatic index of refraction change occurring around a thermotropic liquid-crystalline phase transition, we demonstrate a 40-fold signal-to-noise ratio enhancement for gold nanoparticles imaged in 4-cyano-4prime;-pentylbiphenyl (5CB) liquid crystals over those in a water environment. We studied the photothermal signal as a function of probe laser polarization, heating power, and sample temperature quantifying the optimal enhancement. This study established photothermal microscopy as a valuable technique for inducing and/or detecting local phase transitions at the nanometer scales, which allows studies of phase change dynamics and confinement effects.
9:00 AM - II3.04
Organized Plasmonic Clusters with High Coordination Number and Extraordinary SERS Enhancement
Nicolas Pazos Perez 1 Claudia Simone Wagner 2 Luis Mauel Liz Marzan 3 Javier Garcia de abajo 4 Alexander Wittemann 2 Ramon Alvarez Puebla 5 Andreas Fery 1 Moritz Tebbe 1
1University of Bayreuth Bayreuth Germany2University of Konstanz Konstanz Germany3University of Vigo Vigo Spain4Instituto de Quimica-Fisica Rocasolano-CSIC Madrid Spain5Universitat Rovira i Virgili Tarragona SpainShow Abstract
Noble metal nanoparticles exhibit optical excitations known as surface plasmons. Plasmonic nanoparticles are in the focus of attention because of their interesting electric and optical properties. These types of materials produce a large enhancement of the local light intensity under external illumination. Plasmons are highly related to the specific particle size and shape. There are various synthetic procedures which allow us to fine tune these parameters in order to adjust their plasmonic response. However, the enhancement of the local light increases particularly when particles are arranged in closely spaced configurations. This is due to the formation of hotspots with high electromagnetic fields. Thus, a critical role in the hot spot generation is the inter-particle gap distance.
Controlled assembly using colloidal chemistry is an emerging and promising field for high yield production of metal nanoparticle clusters with small inter-particle gaps. However, most of the reported methods rely on the use of nucleic acids or other organic molecules as linking elements, which yield long separation distances and thus small plasmon coupling. Additionally, only simple clusters such as dimmers and trimmers have been efficiently synthesized. In this work, we report the controlled assembly of gold nanospheres into well-defined nanoparticle clusters with large coordination numbers (up to 7) and high symmetry. We further demonstrate ultrasensitive direct and indirect surface-enhanced Raman scattering (SERS) sensing, thus corroborating the outstanding optical performance of these clusters with robust enhancement factors over 3 orders of magnitude higher than those of single particles.
N. Pazos-Perez et al., Angew. Chem. Int. Ed., (2012-DOI: 10.1002/anie.20120701)
9:00 AM - II3.05
Metallic Rugate Structures for Near-perfect Absorbers in Visible and Near-infrared Regions
Shiwei Shu 1 Yang Yang Li 1
1City University of Hong Kong Hong Kong Hong KongShow Abstract
Metallic rugate structures are theoretically investigated for achieving near-perfect absorption in the visible and near-infrared regions. Our model builds on nanoporous metal films whose porosity (volume fraction of voids) follows a sine-wave along the film thickness. By setting the initial phase of porosity at the top surface as 0, near-perfect absorption is obtained. The impacts of various structural parameters on the characteristic absorption behaviors are studied. Furthermore, multiple peaks or bands with high-absorption can be achieved by integrating several periodicities in one structure. The rugate absorbers show near-perfect absorption for TE and TM polarizations and large incident angles.
9:00 AM - II3.06
Investigations of Double Quantum Light Emission from Gold Nanomaterials
Mourad Abid 1 Sophie Brasselet 2
1King Abdullah Institute for Nanotechnology Riyadh Saudi Arabia2Institut Fresnel, Universite d'Aix en Provence Marseille FranceShow Abstract
Over the last two decades, metallic nanomaterials such as gold, silver and copper have attracted much more attention due to their unique electronic and optical properties compared to the "bulk" system . These properties are strongly dependent on the characteristics of the metallic nanomaterials like the size, shape, environment and nature of the materials . Noble metal nanomaterials present a strong absorption in the visible region coined as the collective oscillation of the conduction electrons and named surface plasmon polariton. Such resonance occurs when the incident photon frequency matches with the collective oscillations of the conduction electrons of the metallic nanoparticles. Due to the discrete size of the materials, the possibility to confine the charge density oscillations (Surface plasmons) and thus, the local electric field at the vicinity of the nanomaterials opens new avenues in biology, photonics and catalysis . While the linear optical processes in small metallic nanomaterials are well understood, few investigations have been carried out to understand the nonlinear optical processes involved in metallic nanomaterials . In nonlinear optics, two photons of frequency omega; are converted into one photon of frequency 2omega; and arises from the quadratic susceptibility of the material. This process is consequently forbidden, under the dielectric dipole approximation in media with inversion symmetry and makes the nonlinear optical techniques, good candidates for probing interfaces and surfaces where the centrosymmetry is broken .
In this study, we investigated the second harmonic emission of gold nanomaterials with different size, shape and state of aggregation using a second harmonic generation microscope. Angular resolved measurements were carried out to quantify and qualify the second harmonic emission modes in spherical nanomaterials, aggregates of nanomaterials and in gold nanowires. The study led to the identification of nonlocal dipole and local quadrupole emission in spherical nanomaterials depending on the size, the shape of the nanomaterial. By changing the polarization orientation in anisotropic metallic nanomaterials like nanowires or aggregates, it has been possible to select and control the mode of emission (dipole or quadrupole modes). Finally, we demonstrate the possibility to fashion the cartography of the local electric fields by selecting the excitation wavelength and the polarization state of the excitation source.
 P. C. Ray, Chem.Rev, 110(9), 5332-5365, 2010.
 U. Kreibig, M. Vollmer, Optical Properties of Metal Clusters(1995), Springer, Berlin.
 RW Murray, Chem. Rev, 108, 2688, 2008.
 J. Nappa, I. Russier-Antoine, G. Benichou, B.C Jonin, P.F Brevet, J. chem.Phys, 125,184712,2006.
 J.P Abid, P-F. Brevet, H.H Girault, J.Phys.Chem C. 111(25), 8849, 2007.
9:00 AM - II3.07
Localized Surface Plasmon Resonance of Metal Nanoparticles Modified by Different Dielectric Surroundings
Pin Ann Lin 1 2 Jonathan Winterstein 3 Henri Lezec 1 Renu Sharma 1
1National Institute of Standards and Technology Gaithersburg USA2University of Maryland College Park USA3FEI Co. Hillsboro USAShow Abstract
Metal nanoparticles are being used in nanosensing and optical devices due to their surface plasmon resonances (SPR). The SPR peak positions and intensities are critical parameters for their applications and they have been shown to depend on the particle size and shape [ 1,2 ]. There are reports that SPR can also be modified by the dielectric surroundings, such as substrates; but no systematic experimental study with high spatial resolution is available. Electron energy-loss spectroscopy (EELS) data collected by scanning transmission electron microscope (STEM) with a monochromator significantly facilitates the ability to detect dark modes and weak dipoles for localized SPRs with high accuracy, and high spatial and energy resolution . We have utilized this technique to measure the effect of the nature of substrates with different refractive index (n) values on the localized SPRs of gold nanoparticles. The STEM-EELS data were obtained with a beam size on the order of 1 nm and 0.14 eV energy resolution from individual gold nanoparticles on various substrates (i.e., carbon, SiO2, TiO2, and HfO2) with n values ranging from 1 to 2.6. A comparative study including nanoparticles in vacuum and gaseous atmosphere will also be presented.
[1.] J. A. Scholl et al. Nature 2012 483, 421-428
[2.] V. Myroshnychenko et al. Nano Letters 2012 12 (8), 4172-4180
9:00 AM - II3.08
Coherent Absorption in Nanometric Light Emitting Layers
Giuseppe Pirruccio 2 Shunsuke Murai 2 Gabriel Lozano 2 Said Rodriguez 2 Raquel Gomes 1 Zeger Hens 1 Jaime Gomez-Rivas 2 3
1Physics and Chemistry of Nanostructures, Center for Nano and Biophotonics, Ghent University Ghent Belgium2Center for Nanophotonics, FOM Institute AMOLF Amsterdam Netherlands3COBRA Research Institute, Eindhoven University of Technology Eindhoven NetherlandsShow Abstract
The recently introduced concept of coherent perfect absorption and its interpretation in terms of time reversed lasing has attracted significant attention as a mean to achieve perfect absorption in weakly absorbing media . In this framework, we demonstrate that the weak optical absorption in nanometric layers of CdSe/CdS quantum dot-in-rods  or of Ce doped yttrium aluminum garnet  can be overcome by exploiting coherent absorption, i.e., by the interference and dissipation of the light scattered at the different interfaces of the sample. The excitation of eigenmodes of the structure is intrinsically related to the interference pattern that traps the incident radiation in the absorbing layer. We make use of this enhanced coherent absorption to increase the fluorescence emission from nanometric layers of light emitting materials.
 W. Wan et al., Science, 331, 889 (2011).
 G. Pirruccio et al., Phys. Rev. B 85, 165455 (2012).
 S. Murai et al., Opt. Mat. Expr. 2, 1111 (2012).
9:00 AM - II3.09
Nanopillar Array on a Fiber Facet by Interference Lithography for Highly Sensitive SERS Detection
Xuan Yang 1 2 Nazar Ileri 1 Cindy C. Larson 1 Thomas C. Carlson 1 Jerald A. Britten 1 Allan S. P. Chang 1 Claire Gu 2 Tiziana C. Bond 1
1Lawrence Livermore National Laboratory Livermore USA2University of California at Santa Cruz Santa Cruz USAShow Abstract
In this study, we develop a highly-sensitive optical fiber surface-enhanced Raman scattering (SERS) sensor by using interference lithography. While one facet of the optical fiber is patterned with silver-coated nanopillar array as a SERS-active substrate, the other end of the probe is used, in a remote end detection, to couple the excitation laser into the optical fiber and send the SERS signal back to the Raman spectrometer. SERS performance of the probe is characterized using trans-1,2-bis(4-pyridyl)-ethylene (BPE) monolayer and an enhancement factor of 1.2×10^7 can be obtained by focusing the laser light directly onto the nanopillar array substrate (front end detection). Furthermore, we demonstrate that this probe can be used for the in-situ remote sensing of toluene and 2,4-dinitrotoluene vapor by the remote end detection. Such a fiber SERS probe is very promising for molecular detection in various sensing applications.
9:00 AM - II3.10
A Colloidal Metafluid Exhibiting Strong Optical Magnetism
Sassan Nathan Sheikholeslami 1 Hadiseh Alaeian 1 Ai Leen Koh 1 Jennifer Dionne 1
1Stanford University Stanford USAShow Abstract
Advances in the field of metamaterials have enabled unprecedented control of light-matter interactions. Metamaterial constituents support high-frequency electric and magnetic dipoles, which can used a building blocks for new materials capable of negative refraction, electromagnetic cloaking, and enhancing magnetic or chiral transitions in ions and molecules. While all metamaterials to date have existed in the solid-state, considerable interest has emerged in designing a colloidal metamaterial or ‘metafluid&’. Such metafluids would combine the advantages of solution-based processing with facile integration into conventional optical components.
Here we demonstrate the colloidal synthesis of an isotropic metafluid that exhibits a strong magnetic response at visible frequencies. Protein-antibody interactions are used to direct the solution-phase self-assembly of discrete metamolecules comprised of silver nanoparticles (36 nm diameter) tightly packed around a single dielectric core (90 nm diameter). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to characterize the structure of the assembled metamolecules. TEM tomography is also used to confirm the three-dimensional structure.
The electromagnetic properties of the metamolecules are simulated with a generalized multi-particle Mie theory, a semi-analytical solution of Maxwell&’s equations for a system of spheres. Near and far field calculations are performed to elucidate the nature and spectral position of the electric and magnetic modes. The magnetic dipole mode, spectrally in the 600 nm to 700 nm range, is confirmed in the simulations through its strongly enhanced magnetic field and circulating displacement currents.
The electric and magnetic modes of individual metamolecules and the bulk metamaterial solution are directly probed with optical scattering and spectroscopy. Single metamolecules are characterized by polarization filtered darkfield scattering spectroscopy in an optical microscope. Using crossed polarizers to filter out the electric dipole scattering, we directly observe a strong magnetic mode in single metamolecule measurements. A home-built angle and polarization resolved ensemble light scattering system was used to directly measure the strong magnetic dipole scattering from the bulk metafluid solution. Using a 633 nm HeNe excitation source, we observe magnetic dipole scattering from the metafluid that is approximately 12% of the strength of the electric dipole scattering and more than 10 times greater than the control sample of unassembled silver and dielectric nanoparticles. This colloidal metamaterial can be synthesized in large-quantity and high-quality, and may accelerate development of advanced nanophotonic and metamaterial devices.
9:00 AM - II3.12
Metal-semiconductor Core-shell Nanowire Photovoltaics
Sander Mann 1 Erik Garnett 1
1AMOLF Amsterdam NetherlandsShow Abstract
The major hurdles to implementing solar energy on a large scale are cost, manufacturing throughput and elemental abundance. A 50% cost reduction would make solar energy competitive without subsidies in most world markets. Thin-film solar cells (such as CdTe) cost about 50% as much to manufacture as crystalline silicon, but have roughly the same cost per watt of output power due to their lower efficiency (typically 12%). Doubling their efficiency to bring them in-line with crystalline silicon while maintaining low manufacturing cost would cut the cost per watt in half and could have a large impact on the world energy market.
This talk will discuss a novel geometry for low-cost and high performance thin-film solar cells: metal-semiconductor core-shell nanowires. Solid semiconductor nanowires (as have been used for photovoltaic applications) have particularly strong absorption in the TM polarization (electric field parallel to the length of the nanowire) but less in the TE polarization (electric field perpendicular to the length of the nanowire). Because metal nanowires have a strong localized surface plasmon resonance in the TE polarization, the core-shell geometry may therefore provide the best response for unpolarized light (like solar irradiation). In fact, our analytical Mie calculations show that such radially symmetric structures outperform their semiconductor nanowire counterparts by absorbing over 25% more photons. We will discuss the fundamental mechanisms for these extreme absorption enhancements, including plasmonic/photonic mode coupling and splitting, based on Mie theory and FDTD simulations.
Optimized structures absorb more than 95% of above band gap photons with 15-40 times lower film thickness than needed in a thin-film geometry. These optimized structures have large metal core diameters (~100 nm) and thin semiconductor shells (46 nm for CdTe, 20 nm for a-Si), which would also allow for improved fill factors via lower series resistance and shorter diffusion lengths, and ultimately for high efficiencies with low-cost and abundant semiconductors.
9:00 AM - II3.13
Super-absorption in Sparse Arrays of GaAs Nanowire Optical Waveguides
Katherine Fountaine 1 3 Shu Hu 1 3 Nathan S. Lewis 1 3 Harry A. Atwater 2 3
1California Institute of Technology Pasadena USA2California Institute of Technology Pasadena USA3California Institute of Technology Pasadena USAShow Abstract
GaAs nanowire (NW) arrays represent an approach to enable high-quality, lattice-mismatched growth via radial strain relaxation, and also to reduce material usage and cost of photovoltaic and photoelectrochemical devices. Even at very low areal fill fractions, GaAs NW arrays exhibit strong absorption due to light trapping effects. In NW arrays, light can potentially couple into several types of modes: i) photonic crystal modes, ii) longitudinal modes (Fabry-Perot resonances), and iii) optical waveguide (radial) modes. We report here the very strong light absorption and current collection properties of sparse (<5% fill fraction) GaAs NW arrays grown on both GaAs and Si substrates, supported by experiments, simulations and analytical theory. These results reveal that GaAs NW arrays with 4% fill fraction absorb between 60 and 100% of the incident light, and that the absorption fraction depends strongly on wavelength and incidence angle. These absorption characteristics indicate a 15-25x enhancement in the effective cross section of the NWs.
We assess the mechanism for the observed strong absorption enhancement and find that mechanism iii) coupling to radial waveguide modes makes the dominant contribution.
Optical absorption and e