Symposium Organizers
Rashid Zia Brown University
Kenneth B. Crozier Harvard University
Nader Engheta University of Pennsylvania
Ganping Ju Seagate Technology
Romain Quidant ICFO - The Institute of Photonic Sciences
M5: Poster Session I
Session Chairs
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
M1: Enhanced Light-Matter Interactions I
Session Chairs
Tuesday PM, November 30, 2010
Room 200 (Hynes)
9:30 AM - **M1.1
Antennas for Light: Interfacing Antennas to Single Photon Emitters.
Niek van Hulst 1 2
1 , ICFO - Institute of Photonic Sciences, Castelldefels - Barcelona Spain, 2 , ICREA – Institució Catalana de Recerca i Estudis Avançats, Barcelona Spain
Show AbstractScaling up antennas to the visible frequency regime, while scaling down to the nanometer scale, opens up the unique opportunity to interface such photonic nano-antennas with single photon emitters: individual molecules, quantum dots, color centers, proteins, etc. The fabrication, losses and dispersion of metals at optical frequencies offer major challenges, yet once surmounted, new avenues in the fields of active photonic circuits, bio-sensing and quantum information technology are opened up.In this presentation the optical analogue of monopole, dipole, multipole and multi element antennas will be presented, focusing on nanoscale field concentration, directionality, femtosecond response, spectral resonances and phase shaped excitation.In receiving mode, single molecules are ideal probes of the local antenna field and here we show optical fields spatially localized within 25 nm in the near field of an optical monopole antenna. In transmitting mode, the single photon emitter locally drives the antenna and the emission pattern is determined by the antenna mode; here we show controlled directed emission of single photons sources by various types of photonic antennas, incl. Yagi-Uda design.Beyond spatial confinement and directivity, the excitation and emission of single photon emitters (molecules, quantum dots), can be controlled also in time on fs scale. Using broad band excitation (~ 120 nm bandwidth) in combination with a pulse shaper we control individual photonic nano-antennas, adapt to the spectral phase development of the antenna and optimize the driving efficiency or generate local spatial hotspots at the antenna.Finally recent advances in our research will be presented.
10:00 AM - **M1.2
Simple Antenna Concepts for Strong Enhancement of Spontaneous Emission.
Vahid Sandoghdar 1
1 , ETH Zurich, Zürich Switzerland
Show AbstractModification of the fluorescence close to metallic nanostructures has been a topic of great interest because the antenna-like behaviour of these structures modifies the radiative decay and the emission pattern of an emitter in its vicinity. Strong local field enhancement and near field confinement make plasmonic antennas also very attractive for increasing imaging resolution. Some years ago, we showed experimentally that a single spherical gold nanoparticle can act as a nanoantenna for enhancing the fluorescence of an emitter by more than an order of magnitude. Here, we present the results of our recent experimental and theoretical studies on enhancements of spontaneous emission up to 10000 times using nanostructures made of various material and geometries. If time permits, we also discuss very high resolution near-field imaging.
10:30 AM - M1.3
Tailoring Light-matter Interaction Using Nanowire Plasmon Resonators.
Nathalie Snapp 1 , Brendan Shields 2 , Chun Yu 1 , Dirk Englund 2 , Frank Koppens 2 , Mikhail Lukin 2 , Hongkun Park 1 2
1 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 Physics, Harvard University, Cambridge, Massachusetts, United States
Show AbstractStrong interactions between light and matter can be engineered by confining light to small volumes. Nanoscale plasmonic structures are capable of confining light well below the diffraction limit; however, building resonant cavities in these devices has proven difficult due to large material losses. We report the design and fabrication of one-dimensional plasmonic crystals utilizing patterned dielectric surrounding low-loss, highly crystalline silver nanowires to make distributed bragg reflectors (DBR). Introduction of a defect in the DBR causes a resonant feature to appear in the stopband. These plasmonic cavities have a Q of up to 100 in a sub-diffraction limit mode volume. Quantum dots coupled to these devices show modified fluorescence spectra, as well as emission enhancement at the cavity resonance.
10:45 AM - M1.4
Enhanced Spontaneous Emission in Plasmonic Ring Cavities.
Ernst Jan Vesseur 1 , Toon Coenen 1 , F. Javier Garcia de Abajo 2 , Albert Polman 1
1 Center for Nanophotonics, FOM Institute AMOLF, Amsterdam Netherlands, 2 , Instituto de Óptica - CSIC, Madrid Netherlands
Show AbstractWe show that plasmonic whispering gallery cavities doped with dye molecules show enhanced spontaneous emission that is resonant with the cavity modes; calculations show Purcell enhancements of over a factor 2000.Circular V-grooves were made by focused ion beam milling into a high-quality crystalline Au surface obtained by template stripping a thick (>2 μm), thermally evaporated Au layer off a mica substrate onto a silicon wafer. Ring diameters of 200-1000 nm were studied, with groove depths in the range 100-500 nm. We excite the plasmonic ring resonances using a 30 keV electron beam in a scanning electron microscope equipped with a parabolic mirror in combination with a CCD imaging detector, that enables – for the first time – the angle-resolved collection of cathodoluminescence radiation from the sample.Resonances in the ring cavities originate from circulating V-groove plasmons for which an integer number of plasmon wavelengths fits the cavity circumference. We measure these resonances and their azimuthal order by spectrally-, spatially- and angle-resolved cathodoluminescence. Resonances with quadrupolar charge distribution (ring with a two-wavelengths circumference) cannot efficiently be excited by free space light; we do however observe their cathodoluminescence emission. The smallest ring cavities (diameter ~200 nm) fit only a single wavelength in their circumference.Boundary-element-method calculations are in excellent agreement with the measurements. The calculations show that the resonant electric field in the ring cavities is confined to a very small volume. We have calculated that ring resonators based on 100-nm deep, 10-nm wide grooves have mode volumes that are smaller than λ0/1000. The ring resonances have a Q factor of 10-50, leading to Purcell factors of over 2000.We studied the interaction of emitters with the resonant cavity modes by embedding ATTO 680 dye molecules in the groove voids. Arrays of rings with different diameters and groove depths were fabricated and a thin polymer layer with dye molecules was applied. The collected fluorescence emission spectrum shows a strong spectral reshaping. The reshaping fits the cavity resonances measured using both cathodoluminescence and white-light scattering measurements. Fluorescence intensity enhancements of over a factor 10 were found at the ring resonance wavelength. Time-correlated single photon counting spectroscopy shows a clear reduction of the fluorescence lifetime concomitant with the emission enhancement.The results show that plasmonic whispering gallery resonators allow for a strong and tunable interaction with optical emitters, paving the way for ultra-small low-threshold plasmonic ring lasers.
11:00 AM - M1: LMI 1
BREAK
M2: Enhanced Light-Matter Interactions II
Session Chairs
Tuesday PM, November 30, 2010
Room 200 (Hynes)
11:30 AM - **M2.1
Control of Radiative Emission in Light Emitting and Absorbing Devices via Cavity-coupled Antennas.
Harry Atwater 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractAt the nanoscale, metallodielectric structures simultaneously embody characteristics of waveguides, antennas and cavities and lead to strong enhancements in the radiative emission rate relative to free space emission, characterized by the Purcell factor. In this talk I will describe nanoscale semiconductor-metal core-shell cavities for dramatic (> 3000x) enhancement of radiative emission rate and also discuss the role of Purcell factor enhancement by metal-dielectric structures on the open circuit voltage and quantum efficiency of thin film solar cells.
12:00 PM - M2.2
Observation of Hot Excitonic Emission in Single CdS Nanowires Integrated with a Plasmon Nanocavity.
Chang-Hee Cho 1 , Carlos Aspetti 1 , Ritesh Agarwal 1
1 Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractSurface plasmons offer great promise for developing subwavelength optical components such as waveguides, photodetectors, and lasers [1-3]. In particular, highly confined surface plasmons inside a metal nanocavity provide an electromagnetic field enhancement, which can be engineered to control the electronic transitions of light emitters [4]. In this work, we report the first observation of nonthermal hot excitonic emission from single CdS nanowires integrated with a nanoscale plasmonic cavity. A clear size-dependence of hot exciton emission is observed below 200 nm lengthscales, which is absent for simple CdS nanowires or for larger plasmonic cavities. The hot excitonic emission is attributed to the large exciton-longitudinal optical phonon coupling and the huge electromagnetic field enhancement by Ag nanocavity plasmons, leading to a nonthermal emission channel of hot excitons by drastically reducing the recombination lifetime. At the resonance condition of thermalized free excitons with the nonthermal hot excitons, the emission rate of free excitons is greatly enhanced and the linewidth is significantly decreased below the thermal energy. This observation indicates that the intrinsic emission properties of semiconductors can be engineered by means of integrating with nanocavity plasmons and is important for understanding and designing nanoscale emitters with novel properties. [1] W. L. Barnes et al., Nature 424, 824 (2003).[2] A. L. Falk et al., Nature Phys. 5, 475 (2009).[3] R. F. Oulton et al., Nature 461, 629 (2009).[4] Z. C. Dong et al., Nature Photon. 4, 50 (2010).
12:15 PM - M2.3
Nonlinear Spectroscopy of a Single Metal Nanoparticle Using a Plasmonic Nanoantenna.
Thorsten Schumacher 1 2 , Kai Kratzer 1 2 , Harald Giessen 2 , Markus Lippitz 1 2
1 , Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , 4th Physics Institute and Research Center SCOPE, Stuttgart Germany
Show AbstractThe dielectric properties of single metal nanoparticles and their surrounding are reflected in the spectral position of the plasmon resonance. In this way, information from the nanoscale can be transmitted into the macroscopic world. Nonlinear pump-probe spectroscopy reveals acoustic oscillations of the metal particles that are triggered by the heating pump pulse, leading to a temporal variation in the electron density and this the plasma frequency. However, the influence of a single nanoparticle on the transmitted light field scales with the third power of the particle's radius. The smaller the particle becomes the more difficult it is to perform nonlinear spectroscopy. We demonstrate how the concepts of optical nano-antennas can be used to couple passive, i.e., not emitting, nanoobjects to the light field to increase the influence a nanoparticle has on the transmitted beam. It will be shown that plasmon hybridization of coupled metallic nanoparticles not only shifts the resonances, but that the variation of one particle's dielectric properties has an increased effect on the total absorption cross section.We prepare by electron beam lithography plasmonic nanoantennas coupled to small metal discs. The acoustic oscillations of individual disc-antenna pairs are investigated by pump-probe spectroscopy and compared with numerical simulations. We find an enhancement of the transient signal of about a factor of 2 that is caused by the optical nanoantenna. This passive use of the antenna - witthout an active quantum emitter - opens the way towards antenna-enhanced sensing and spectroscopy.
12:30 PM - **M2.4
Nonlinear Optical Antennas.
Lukas Novotny 1
1 Institute of Optics, University of Rochester, Rochester, New York, United States
Show AbstractNoble metals exhibit high intrinsic optical nonlinearities, but they are usually not employed for frequency conversion because they are reflective and absorptive. However, these limitations can be overcome with nanostructured metal surfaces or with structures of subwavelength scale. We demonstrate that metalnanostructures can be effectively employed for efficient index modulation, two-photon excited luminescence, harmonic generation, and wave mixing. We discuss and review recent results and applications.
M3: Exciting and Probing Vector Fields at the Nanoscale
Session Chairs
Tuesday PM, November 30, 2010
Room 200 (Hynes)
2:30 PM - **M3.1
Unravelling the Vector Nature of Nanoscale Light.
L. Kobus Kuipers 1
1 , FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractOne of the key features of interest of plasmonic nanostructures is their ability to confine and enhance light fields on a scale that is (much) smaller than the wavelength in the surrounding medium. The strong interplay between the geometry and the light results in highly structured light fields on the nanoscale.In this presentation I will show recent progress in the visualization of such light fields beyond the diffraction limit. Surface plasmons launched from periodic arrays of holes exhibit the Talbot effect. By exploiting a recent advance in the measurement of vector fields with near-field microscopy, we were able to determine the symmetry of MIM modes in plasmonic slot waveguides and of plasmonic nanowire modes. In addition we use dedicated near-field probe geometries to home in on individual vector components of either the electric or the magnetic component of confined light fields.
3:00 PM - M3.2
Magnetic Dipole Transitions Identified by Momentum-space Imaging.
Tim Taminiau 1 2 , Sinan Karaveli 1 , Niek van Hulst 2 3 , Rashid Zia 1
1 Division of Engineering, Brown University, Providence, Rhode Island, United States, 2 , ICFO, Castelldefels, Barcelona, Spain, 3 , ICREA – Institució Catalana de Recerca I Estudis Avançats, Barcelona Spain
Show AbstractOptical antennas improve the interaction of quantum emitters with light by creating strong local electromagnetic fields. Electric dipole transitions in for example fluorescent molecules and quantum dots are enhanced by local electric fields, and have been widely used to characterize local electric fields at antennas and other nanostructures. In a similar way, magnetic transitions in Lanthanide ions are expected to be enhanced by local magnetic fields, and thus have the potential to probe local magnetic fields. However, unlike the linear pure electric dipole transitions of single molecules, the magnetic dipole transitions of lanthanide ions are accessible only in ensemble experiments, are degenerate with electric transitions, and are isotropic. As a result it is challenging to identify and quantify the electric and magnetic contributions, in particular because their ensemble emission is identical in a homogeneous medium. In this talk, we show that within inhomogeneous environments the different symmetries of electric and magnetic dipoles distinguish the electric and magnetic components of transitions. We experimentally study the angular emission of thin layers of lanthanide ions near dielectric interfaces by conoscopy. The obtained frequency-resolved momentum images contain a wealth of information. Electric and magnetic transitions are readily identified, and the components of mixed transitions, which contain both electric and magnetic components, are quantified. The results provide a direct experimental visualization of the different symmetry of electric and magnetic transitions. Finally, we identify transitions that are ideal to simultaneously study both the local electric and magnetic fields at optical antennas and in other nanostructures, such as metamaterials.
3:15 PM - M3.3
Shaping the Optical Response of Nanoantennas.
Giorgio Volpe 1 , Gabriel Molina-Terriza 1 , Romain Quidant 1
1 , ICFO, Castelldefels (BCN) Spain
Show AbstractPlasmonic nanostructures such as antennas, metal-insulator-metal stacks or tapered wires have been designed to confine light in truly sub-wavelength (sub-λ) volumes opening new opportunities to enhance the interaction of light with small quantities of matter down to the molecular level. Beyond confining light at fixed locations, imposed by the structure geometry, there is a need for dynamical spatial control of such hot-spots, for instance to achieve selective optical addressing of different nearby nano-objects. Several strategies borrowed from the field of coherent control have recently been suggested to reach this goal. A first approach relies on temporally shaping the phase and amplitude of an ultrashort laser pulse illuminating the nanostructures [1]. By combining pulse shaping with a learning algorithm, Aeschlimann et al. have recently demonstrated experimentally the feasibility of generating user-specified optical near field response of a star-like silver object [2]. Experimental control of the local optical response of a metal surface was also achieved by adjusting the temporal phase between two unshaped ultrashort pulses [3]. Alternatively, the idea of time reversal has been lately proposed by Li and Stockman [4]. In this approach, a femtosecond optical nano-source is locally coupled to the surface plasmon oscillations of a complex plasmonic system leading to the subsequent radiation of electric field in the far zone. Time-reversing the later and sending it back to the system as an excitation wave thus provides the right illumination conditions for concentrating light at the initial local source location. Here we propose a novel approach based on continuous light flows which aims at achieving a deterministic control of plasmonic fields by using the spatial polarization inhomogeneities of high order beams such as Hermite-Gaussian (HG) [5]. We show both experimentally and numerically that spatial phase shaping of the illumination field provides an additional degree of freedom to drive nano-optical antennas and consequently control their near field response. Furthermore, the potential of this approach to deterministically confine light at specific locations of a more complex metallic nanostructure is also demonstrated [6].References:[1] Stockman, M., Faleev, S. V., Bergman, D. J., Phys. Rev. Lett. 88, (2002) 067402.[2] Aeschlimann, M., et al., Nature 446, 301 (2007)[3] Kubo, A., et al., Nano Lett. 5, 1123 (2005)[4] Li, X., Stockman, M., Phys. Rev. B. 77, 195109 (2008)[5] G. Volpe, et al., submitted (2010) [6] G. Volpe, et al., Nano Lett. 9, 3608-3611 (2009)
3:30 PM - **M3.4
Non-perturbative Visualization of Nanoscale Plasmonic Field Distributions via Photon Localization Microsocopy.
Jim Schuck 1 , Alex McLeod 1 , Alex Weber-Bargioni 1 , Zhaoyu Zhang 2 , Scott Dhuey 1 , Bruce Harteneck 1 , Jeffrey Neaton 1 , Stefano Cabrini 1
1 , Molecular Foundry, LBNL, Berkeley, California, United States, 2 Department of Chemistry, U. C. Berkeley, Berkeley, California, United States
Show AbstractWe demonstrate the non-perturbative use of diffraction-limited nonlinear optics and photon localization microscopy to visualize the nanometer-scale controlled shifts of ultraconfined zeptoliter mode volumes within plasmonic nanostructures. Unlike tip-based or coating-based methods, these measurements do not affect the electromagnetic properties of the nanostructure being investigated. The photon-limited localization accuracy of nanoscale mode distributions is determined for many of the measured devices to be within a 95% confidence interval of +/- 2.5 nm. In addition, because of the accuracy of these photon localization microscopy measurements, we were able to observe and characterize the effects of nm-scale fabrication variations and irregularities on local plasmonic mode distributions.As a proof of concept, we image the local energy-dependent changes in near-field distributions within individual gold asymmetric bowtie nano-colorsorters (ABnCs) [1], a class of plasmonic color sorters, based on the “cross” nanoantenna geometry. These devices are specifically engineered to not only capture and confine optical fields, but also to spectrally filter and steer them while maintaining nanoscale field distributions. Their spectral properties and localized spatial mode distributions can be readily tuned by controlled asymmetry, and each of the zeptoliter mode volumes within an ABnC, separated by only tens of nm, can be individually addressed simply by adjusting the incident wavelength. We imaged relative spatial shifts down to 7 nm of distinct modes within the same device, demonstrating the local field manipulation capabilities of ABnCs, in strong agreement with theoretical calculations.[1] Zhang, Z. et al. Manipulating Nanoscale Light Fields with the Asymmetric Bowtie Nano-Colorsorter. Nano Lett. 9, 4505-4509 (2009).
4:00 PM - M3: VectFld
BREAK
M4: Electron-Beam Characterization
Session Chairs
Tuesday PM, November 30, 2010
Room 200 (Hynes)
4:30 PM - **M4.1
Optical Nanoantennas: Correlative Electron Beam and Optical Spectroscopies and Design of a Broadband Response.
Stefan Maier 1
1 Physics Department, Imperial College, London United Kingdom
Show AbstractThe optical response of a metallic nanoantenna is determined by the interplay between the intrinsic bright and dark plasmon modes supported. A complete characterization hence requires a means to excite dark modes, which do not couple efficiently to far-field optical radiation. We demonstrate that electron energy loss spectroscopy (EELS) is a powerful tool allowing the complete determination of the plasmonic mode spectrum, with nanometre-scale spatial resolution facilitated by the scanning electron beam. Correlations with optical measurements and full-field electrodynamic simulations will be presented for a variety of top-down fabricated nanoantennas supported by ultrathin silicon nitride membranes, as well as for colloidal assemblies based on core/shell structures. A particular focus will lie on different nanofabrication strategies suitable for use with the thin substrates (30-50 nm thickness) required for EELS investigations. Furthermore, we present a comparison of the experimentally acquired data with numerical simulations based on calculations of both optical extinction and electron energy loss. Additionally, the influence of dark modes on the emission properties of nearby single emitters will be discussed.Finally, we will outline a new strategy for the design of optical nanoantennas showing a broadband optical response while maintaining sub-wavelength size, based on the tools of transformation optics.
5:00 PM - M4.2
Surface Plasmon Resonance Effects in Ag Nanoholes Studied by Energy-filtering TEM.
Wilfried Sigle 1 , Burcu Ogut 1 , Christoph Koch 1 , Peter van Aken 1
1 , MPI for Metals Research, Stuttgart Germany
Show AbstractThe visualization of localized plasmon resonances on the nanometer scale in combination with spectral information over the entire visible range is of prime importance in the field of biosensors, surface-enhanced Raman spectroscopy (SERS), apertureless scanning near-field optical microscopy (SNOM), and for the design of metamaterials. With the advent of monochromators and highly dispersive energy filters, energy-filtering TEM has now become available for the study of the optical response of materials well into the infrared range. This technique was applied to the detection of band gaps [1] as well as to the study of surface plasmons on metal particles, like Ag nanoprisms [2–4] or Au nanorods [5]. It offers a spatial resolution in the nanometer range which is well below the resolution of present light-optical techniques.Here, the dielectric response of holes in a Ag film is studied by energy-filtering TEM [6, 7]. Circular holes and rectangular slits were drilled into a 100 nm thick Ag film using a focused ion beam. The arrangement of the circular holes was chosen such that well separated holes, holes that are closely spaced, and interpenetrating holes were present. Slits were cut with different aspect ratios. Taking advantage of the monochromated electron beam (FWHM below 0.1 eV) and the MANDOLINE energy filter of the Zeiss SESAM microscope, energy-filtered images were recorded in the energy range between 0.4 and 4 eV using energy steps of 0.2 eV. Depending on energy loss, we find a number of resonant features that can be ascribed to resonances of single holes, to coupled resonance of several holes, and to Fabry-Pérot-type resonances. Coupling effects are discussed within the hybridization scheme. The experimental results are compared to finite-element calculations. The coupling effects between adjacent holes lead to very strong field enhancements which occur primarily in the infrared range. These results demonstrate the power of the EFTEM technique for the mapping of surface plasmon resonances of complex structures. [8] References[1] L. Gu et al., Phys. Rev. B 75 (2007) 195214.[2] J. Nelayah et al., Proc.14th European Microscopy Congress, Aachen, S. Richter, A. Schwedt (Eds), Springer, Berlin (2008) 243.[3]C.T. Koch et al., Proc. 14th European Microscopy Congress, Aachen, M. Luysberg, K. Tillmann, T. Weirich (Eds.), Springer, Berlin (2008) 447.[4]J. Nelayah et al., Optics Letters 34 (2009) 1003. [5]B. Schaffer et al., Phys. Rev. B 79 (2009) 041401.[6] W. Sigle et al., Optics Letters 34 (2009) 2150.[7]W. Sigle et al., Ultramicroscopy (2010) in press.[8]The authors acknowledge financial support from the European Union under the Framework 6 program under the contract for an Integrated Infrastructure Initiative. Reference 026019 ESTEEM.
5:15 PM - M4.3
Spatially Resolved Directional Emission from Plasmonic Yagi Uda Antennas.
Toon Coenen 1 , Ernst Jan Vesseur 1 , Albert Polman 1
1 Center for Nanophotonics, FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractLinear arrays of metal nanoparticles act as efficient nanoscale receiving antennas for light, as we have demonstrated earlier [1]. These antennas concentrate an incident light beam at a well-defined wavelength-dependent position on the antenna array, similar to Yagi Uda antennas well known for millimeter waves. Vice versa, metal particle arrays can also be used to direct light into a well-defined wavelength-dependent direction. Here, we present angle-resolved emission spectra from Au nanoparticle antenna arrays, and find evidence for strong directional emission, that depends strongly on the emitter position. Angle-resolved emission maps are made using a novel angle-resolved cathodoluminescence (CL) spectroscopy technique with a spatial resolution for the exciting source as small as 10 nm. Linear particle array antennas consisting of five Au nanoparticles with a diameter of 98 nm and 135 nm pitch were fabricated on a silicon substrate using e-beam lithography. Particles are excited using a 30 keV electron beam in an electron microscope. Each incident electron and its image charge in the substrate act effectively as a broadband point dipole that can be accurately positioned at any position in the array by scanning the beam. The emitted radiation is then collected by an Al paraboloid which collects radiation over a large solid angle. The collected radiation is directed onto the imaging plane of a 2D CCD-array: each pixel in the CCD image then corresponds to a zenithal angle θ and azimuthal angle φ of the antenna array emission.The electron beam was focused to a 10 nm spot, and scanned over the antenna array. By selectively exciting each individual particle in the array, we observed different wavelength-dependent emission patterns. For wavelengths below 650 nm strong beaming of light is observed the along the antenna’s major axis if one of the two outer particles is excited. Exciting the center particle, which has two neighboring particles on both sides, leads to a symmetric emission pattern to either side of the array. Above 650 nm the radiation is emitted in a toroidal band along the antenna’s main axis. The emission pattern is independent of excitation position for these wavelengths.The CL-imaging technique also enables imaging spectroscopy of the antenna emission with a spatial resolution of 10 nm. The e-beam was raster-scanned over the antenna in 10 nm steps yielding an excitation map of the CL-intensity for different wavelengths. These measurements, with a spatial resolution >50 times smaller than the wavelength, reveal a detailed picture of the near-field interaction between dipole emitters and the antenna array. For example, we find that the outer particles in the array show significantly brighter radiation, demonstrating that directional emission is coupled to an enhanced emission rate.[1] R. de Waele, A.F. Koenderink, and A. Polman, Nano Lett. 7, 2004 (2007).
5:30 PM - M4.4
Investigations on Plasmonic Modes of Noble Metal Nano-disks Using High-resolution Cathodoluminescence Imaging Spectroscopy.
Anil Kumar 1 , Kin Hung Fung 1 , Nicholas Fang 1
1 Center for Nanoscale Chemical-Electrical-Mechanical Manufacturing Systems, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractSurface plasmon polariton excitation using an electron beam offers several unique advantages. Because the incident electrons have wide range of momenta, this approach allows access to large plasmon wave vectors close to the flat region of dispersion curve. Unlike plane wave excitation, electron excitation can be highly localized allowing imaging of dark modes of optical antennas and cavities. Therefore, probing plasmonic nanostructures using electron beam excitation can provide new insights into their underlying physics, beyond the capability of methods involving optical excitation and imaging, e.g., using Near-field Scanning Optical Microscopy (NSOM). Additionally, investigations using cathodoluminescence (CL) spectroscopy are relatively simpler since no specific sample preparation is required, in contrast to other electron excitation based methodologies, e.g., Electron Energy Loss Spectroscopy (EELS) where the probed nanostructures need to be electron transparent.In this work, we report our recent investigations on plasmonic nano-disks using cathodoluminescence imaging and spectroscopy. These nano-cavities with very small volume find several applications including thresholdless laser operation by combining spontaneous emission with the lasing mode. They are of interest for studying exciton-photon interaction and cavity quantum electrodynamics, and can be potentially used as single photon sources. Noble metal nano-disks of various film thicknesses and diameters were fabricated using electron-beam lithography. CL imaging and spectroscopy were carried out to map the plasmonic—radial and azimuthal—modes of the discs. A direct comparison with analytical solutions of various Bessel modes suggests that the plasmonic modes are red shifted because the zero-field boundary condition at metal edges does not strictly apply. A strong dependence on geometry is observed, resulting into dramatic modification in the radiation pattern from circular to polygonal disks. Additionally, we investigate the possibility to design single mode disk resonators, which are critical for single mode plasmonic lasers. Although silver is the plasmonic material of choice due to low losses, gold disks showed well separated Bessel modes in the visible spectrum.CL simulations were carried out using a newly developed FDTD approach where electron beam was modeled as a series of dipoles with a temporal phase delay based on electron beam velocity. Excellent matching with experimental results was observed. Our investigations on the plasmonic nano-disks allow understanding of light-matter interaction at nanoscale that has important applications in various areas with pressing needs, e.g., chemical and biological sensing, imaging beyond diffraction limit, solar energy harvesting, and disease cure and prevention.
5:45 PM - M4.5
Enhanced Light Emission and Detection with Plasmonic Resonator Antennas.
Edward Barnard 1 , Ragip Pala 1 , Toon Coenen 2 , Ernst Jan Vesseur 2 , Albert Polman 2 , Mark Brongersma 1
1 , Stanford University, Stanford, California, United States, 2 , FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractA combined theoretical and experimental study of detectors and emitters enhanced by wavelength-scale plasmonic resonator antennas is presented. These antennas support standing surface plasmon-polariton (SPP) waves that enable substantial concentration of light at a set of well-defined resonant frequencies. Using full-field electromagnetic simulations and analytical optical antenna models, we are able to derive simple and intuitive design rules to achieve antennas with a desired set of optical properties (field enhancement, scattering cross section, absorption cross section, and resonant frequency) based on their geometric properties. With these design rules, we have constructed resonance maps that allow a designer to choose an antenna structure that provides desired resonant properties for a specific application. We then apply these design rules to create antennas that resonantly enhance absorption on thin silicon detectors as well as enhance emission of cathodoluminescence (CL). Through spatial and spectral mapping of both photocurrent and CL we clearly show the fundamental and higher-order resonant modes of these antennas. In addition to these specific demonstrated applications, the results of this study enable optical engineers to more easily design a myriad of plasmonic devices that employ optical antenna structures, including nanoscale photodetectors, light sources, sensors, and modulators.
M5: Poster Session I
Session Chairs
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
9:00 PM - M5.10
Plasmon-enhanced Emission Rates from III-nitride Quantum Wells Using Tunable Surface Plasmons.
John Henson 1 , Jeff DiMaria 1 , Emmanouil Dimakis 1 , Rui Li 1 , Salvo Minissale 1 , Luca Dal Negro 1 , Theodore Moustakas 1 , Roberto Paiella 1
1 Department of Electrical and Computer Engineering and Photonics Center, Boston University, Boston, Massachusetts, United States
Show AbstractSurface plasmon polaritons at metal surfaces and localized plasmonic resonances of metallic nanoparticles (NPs) can both be used to enhance the decay rate of nearby light emitters, by virtue of their associated large field enhancements and large density of optical modes. If suitably designed, metallic gratings and NPs can also effectively scatter such plasmonic excitations into radiation, thereby leading to an overall enhancement in light emission efficiency. Of particular importance from a technological standpoint is the use of this approach with low-efficiency semiconductor materials, such as InGaN quantum wells (QWs) emitting in the green part of the visible spectrum. In recent years, significant photoluminescence (PL) enhancements have been reported with blue-emitting InGaN QWs coated with Ag films. While simple from a fabrication standpoint, the film geometry offers limited control of plasmonic resonance wavelength and extraction efficiency. These considerations motivate investigating the use of size-controlled metallic NPs in place of continuous films.A key requirement for plasmon-enhanced light emission is the ability to tune the plasmonic resonance to match the emission wavelength, which makes NP arrays fabricated using lithographic techniques such as electron beam lithography (EBL) attractive for this purpose. Typically, gold and silver NP arrays developed with this technique yield plasmonic resonances at wavelengths longer than the green spectral region of interest. In a recent report, we have shown that the plasmonic resonance wavelength of EBL-fabricated arrays can be effectively decreased by increasing the particle height, while at the same time maximizing the scattering efficiency and the field enhancement in the substrate. In the present work, similar arrays were used to demonstrate plasmon-enhanced PL from InGaN QWs emitting near 490 nm.The light emitting material used in this work was grown by rf-plasma-assisted molecular beam epitaxy and consists of three In0.4Ga0.6N QWs with GaN barriers. Guided by FDTD simulations and transmission spectroscopy measurements, several Ag NP arrays with strong plasmonic resonances near the QWs emission wavelength were designed and patterned on the sample top surface. The emission properties of the coated QWs were then studied using both cw PL and ultrafast time-resolved PL (TRPL) measurements. An increase in integrated PL intensity by a factor of up to 2.8 was measured in the NP-coated areas compared to the adjacent regions. This result is consistent with the expected strong resonant coupling between the QW light-emitting excitons and the array plasmonic excitations. At the same time, the total QW recombination lifetime in the regions immediately below the NP arrays was found to be a factor of 1.5 smaller than in the uncoated regions. Using the measured internal quantum efficiency of this material (10%), these results indicate a Purcell enhancement factor of about 6.
9:00 PM - M5.11
Power Flow from a Dipole Emitter Near an Optical Antenna.
Kevin Chih-Yao Huang 1 2 , Min-Kyo Seo 2 4 , Young Chul Jun 2 3 , Mark Brongersma 2
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States, 4 Physics, Korea Advanced Institute of Science and Technology, Yuseong-gu Korea (the Democratic People's Republic of), 3 Applied Physics, Stanford University, Stanford, California, United States
Show AbstractWe present a theoretical methodology to study the time-averaged power flow from a dipole emitter placed in the vicinity of an optical antenna. Moreover, we show that new insights into the emission process can be obtained by separating the total Poynting vector, into contributions from the emitter output and antenna scattering. This separation enables a natural way to visualize the power flow out of an emitter, via an antenna into the far field. It also offers valuable information into key antenna performance parameters, including the emitter-antenna interaction strength, the Purcell effect, the angular emission distribution and the polarization behavior. As such, it unlocks a powerful design strategy for optimizing strongly interacting emitter/ antenna systems used in molecular sensing, on-chip optical interconnects, and single-photon sources.
9:00 PM - M5.12
Plasmonic Nanoresonators for Enhancing Fluorescence Resonant Energy Transfer (FRET).
Valerie Faessler 1 , Calin Hrelescu 1 , Andrey Lutich 1 , Lidiya Osinkina 1 , Sergiy Mayilo 1 2 , Frank Jaeckel 1 , Jochen Feldmann 1
1 Physics, Ludwig-Maximilians-University, Munich Germany, 2 Laboratoire d’Optique Biomedicale, Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractFluorescence resonant energy transfer (FRET) has found wide-spread application ranging from natural and synthetic photosynthesis, organic lighting devices, single-molecule spectroscopy, imaging to sensing. Enhancing and controlling FRET therefore appears desirable. Plasmonic nanostructures are known to enhance optical processes including fluorescence and Raman scattering [1,2]. A particularly interesting plasmonic nanostructure is the so-called plasmonic nanoresonator, i.e., a pair of spherical gold nanoparticles separated by less than the particle radius [3]. Plasmonic nanoresonators exhibit large field enhancements and show a tunable coupled plasmon resonance [4]. Here, we show, for the first time, that plasmonic nanoresonators can be used to accelerate FRET, and that nanoresonators are more efficient than isolated gold nanoparticles. For a FRET-system comprised of R-phycoerythrin (a bacterial light harvesting protein) as donor and Alexa fluors as acceptor, time-resolved fluorescence spectroscopy on the ps-time scale reveals a 33%- acceleration of FRET in the nanoresonator while isolated gold nanoparticles only show 9% acceleration.1.C. Hrelescu, T.K. Sau, A.L. Rogach, F. Jäckel, J. Feldmann Appl. Phys. Lett. 94 (2009) 153113.2.T.K. Sau, A.L. Rogach, F. Jäckel, T.A. Klar, J. Feldmann Advanced Materials 22 (2010) 1805.3.M. Ringler et al. Phys. Rev. Lett. 100 (2008) 203002.4.M. Ringler et al. Nano Lett. 7 (2007) 2753.
9:00 PM - M5.14
Continuous Colloidal Synthesis of Plasmonic Nanostructures in Flowing Microscale Foams.
Saif Khan 1 2 , Suhanya Duraiswamy 1
1 Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore, 2 Chemical and Pharmaceutical Engineering, Singapore-MIT Alliance, Singapore Singapore
Show AbstractThe availability of robust, scalable and automated nanoparticle manufacturing processes is crucial for the viability of emerging nanotechnologies. Metallic nanoparticles of diverse shape and composition are commonly manufactured by solution-phase colloidal chemistry methods, where rapid reaction kinetics and physical processes such as mixing are inextricably coupled, and scale-up often poses insurmountable problems. In this paper we demonstrate extremely robust, scalable and automated nanoparticle processing in self-assembled flowing foams. Flowing microscale foams possess a unique set of structural and functional features that make them attractive for nanoparticle processing. We generate an ordered composite foam lattice in a simple microfluidic device, where the lattice cells are alternately aqueous drops containing reagents or gas bubbles. Microfluidic foam generation enables precise reagent dispensing and mixing, and the ordered foam structure facilitates compartmentalized nanoparticle growth. Aqueous reagents for colloidal synthesis can be controllably dispensed into liquid foam cells of identical size that serve as individual reaction ‘flasks’ and are effectively isolated from other reagent-filled cells and the microchannel walls during their transit through the microchannel. To highlight these salient features, we present the first continuous-flow synthesis of metallodielectric ‘nanoshells’, each comprising a silica nanoparticle core encased within a gold shell of tunable thickness. Further, we also demonstrate the controlled synthesis of silica nanoparticles decorated with gold islands of various sizes, with tunable optical resonances in the visible-NIR range. This method is simple to implement; reagent dispensing and mixing is accomplished in robust, automated fashion with no operator intervention and uniform unaggregated particles are obtained requiring little post-synthesis treatment. We have also used the same method to successfully synthesized gold nanocrystals of controlled size and shape. Our work represents a crucial advance in the area of continuous processes for nanomanufacturing. We are currently working towards scaling of such foam-based reactors for larger volumes of production.
9:00 PM - M5.16
Multiprobe Apertureless Near-field Imaging (MANI) of Optical Plasmonic Distribution.
Boaz Fleishman 1 , Hesham Taha 2 , Aaron Lewis 1
1 Department of Applied Physics Selim and Rachel Benin School of Engineering and Computer Science, The Hebrew University of Jerusalem, Jerusalem Israel, 2 , Nanonics Imaging Ltd., Jerusalem Israel
Show AbstractScattering near-field scanning optical microscopy called ANSOM or sSNOM has been applied to look at plasmonic distribution. Unfortunately, the probes that need to be used in order to effectively scatter the plasmonic signal have significant perturbation on the plasmonic propagation because of the need to use probes with high dielectric constant to obtain effective signal to noise. In this paper, we will demonstrate the application of our development of multiprobe scan probe microscope technology for effective localized illumination of plasmonic structure with an apertured NSOM probe which produces all k-vectors and so it is most efficient for such plasmonic propagation. The propagating plasmons are collected with a second probe which has a very low dielectric constant and minimal perturbation of the plasmonic propagation. In addition, we will describe an active spectral probe that can also be used as a localized detector of plasmonic propagation without significant effect on the distribution of plasmons. The results indicate that localized aperture NSOM illumination and apertureless monitoring of plasmons has significant potential for investigating plasmonic structures.
9:00 PM - M5.17
Three-dimensional Plasmonic Nanofocusing.
Nathan Lindquist 1 , Prashant Nagpal 3 , Antoine Lesuffleur 1 , David Norris 4 2 , Sang-Hyun Oh 1
1 Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 3 , Los Alamos National Lab, Los Alamos, New Mexico, United States, 4 , ETH Zurich, Zurich Switzerland, 2 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe concentration of light into nanoscale “hot spots” requires manipulation of optical energy well below its wavelength, λ. While dielectric structures cannot achieve this due to diffraction, patterned metals that support surface plasmons provide a solution. Due to their evanescent nature, if plasmons are allowed to propagate towards and focus at a sharp tip or apex, excitation of highly local and extremely intense optical fields is possible. While all nanoscale metallic tips exhibit some local-field enhancement (i.e., due to an optical lightning rod effect), plasmonic nanofocusing schemes use gratings, prisms, slits, or butt-end couplers to launch plasmons into metallic structures that then deliver those plasmons into nanoscale volumes. Indeed, various metallic films, trenches, tapers, gaps, and tips, have shown promise for unprecedented control and delivery of optical energy into subwavelength hot spots. However, the ability to focus photogenerated plasmons from multiple directions toward a specific location on a nonplanar device has proven challenging. Here, we demonstrate such three-dimensional plasmonic nanofocusing of light with patterned ultrasharp gold and silver pyramids obtained via template stripping. Gratings placed on all four faces of these pyramids convert normally-incident, linearly-polarized light into plasmons that propagate towards and converge at their ~10 nm apex, producing a 5x10-5 λ3 spot. Finite-difference time-domain simulations confirm the nanofocusing effect, and show that only gratings placed asymmetrically on opposing faces of the pyramids will generate plasmons that interfere constructively at the tip. Additionally, because the template-stripped surfaces are extremely smooth, plasmons are allowed to propagate towards the tip with minimal scattering. Identical devices produced with additional nanometer-scale roughness did not show a nanofocusing effect. Because these structures produce an optical hot spot at the end of a sharp tip and are easily and reproducibly produced, these results have implications for many applications, including imaging, sensing, optical trapping, or high-density data storage.
9:00 PM - M5.18
Selective Thermal Emission from Micro-patterned Steel Surfaces.
Joshua Mason 1 , David Adams 1 , Zachariah Johnson 1 , Shaun Smith 1 , Andrew Davis 2 , Daniel Wasserman 1
1 Physics, University of Massachusetts, Lowell, Lowell, Massachusetts, United States, 2 , Alloy Surfaces Inc., Boothwynn, Pennsylvania, United States
Show AbstractAbstract: Periodically patterned metal films have been shown to possess unique optical properties resulting from the excitation of electromagnetic waves bound to the metal surfaces. The periodicity of the patterned surface can be designed to enhance the out-coupling of these waves into unbounded radiation. Selective thermal emission at a wavelength of 10 μm has been realized from rolled steel substrates exploiting a subwavelength patterning method. Inexpensive and quick processes have been developed to prepare and pattern the steel to provide wavelength-selective thermal emission with intensity 2.6 times greater than the unselected wavelengths. Changes in the selective thermal emission due to alterations in the geometry of the patterned grooves have been noted and studied and the temperature dependence of the effect has been measured. Angular analyses of the selective emission and thermal imaging have been utilized to illuminate the nature of the thermal selectivity of these devices.
9:00 PM - M5.2
Nanoantenna Effect of Small Gold Nanoparticles on Photoluminescence from Self-assembled Quantum Dot Arrays.
Jaydeep Basu 1 , Haridas Mundoor 1 , Laxminarayan Tripathi 1
1 Physics, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractUsing a block copolymer template of vertically aligned cylindrical domains loaded with CdSe quantum dots (QDs) we demonstrate how small gold nanoparticles can be used to effectively modify the emission properties of the QDs using the nanoantennae effect. The block copolymer template essentially consisted of cylindrical domains aligned perpendicular to the substrate with inter-cylinder spacing of ~ 100-150 nm and cylinder sizes of ~ 50 nm. The capping of the CdSe QDs (~4-6 nm) and the gold nanoparticles (4-5 nm) were controlled [1] to ensure that they occupy the respective blocks of the copolymer template. We have used confocal and near field optical measurements on such self-assembled structures to study the role of nanoantenna effect of small gold nanoparticles on luminescence properties of the assemblies. Samples were studied in transmission mode and illuminated with 488 nm line of Ar laser. The time resolved photoluminescence (PL)measurements were performed using a custom built single photon counting device with the samples being illuminated with Ti:Sapphire laser of wavelength 481 nm with a pulse rate of 76.7 MHz. We have observed that both the intensity and decay rate of emission from such arrays can be precisely controlled by tuning the separation of gold nanoparticles from the CdSe QD loaded cylindrical domains, through the nanoantenna effect of the gold nanoparticles mediated through the plasmons in gold nanoparticles interacting with the excitons in the CdSe QDs. This opens the possibility of using such self-assembled structures for use in wide ranging applications from plasmonic solar cells to SERS and single molecule spectroscopy as well as in smart photonic devices and sensors.Reference: 1. Tripathi, L.N., Haridas, M., and Basu, J.K., AIP Conf. Proc. 1147, 415 (2009).2. "Controlled photoluminescence from self - assembledsemiconductor-metal quantum dot hybrid array films",M. Haridas and J.K. Basu (Submitted, 2010).3. "Photoluminescence spectroscopy and lifetime measurements from novel self-assembledsemiconductor-metal nanoparticle hybrid arrays"M. Haridas and J.K. Basu,D. J. Gosztola and G. Wiederrecht (Under Preparation).Acknowledgment: We acknowledge DST, India for financial support and CNM, Argonne National Laboratory for assistance with the time resolved PL measurements.
9:00 PM - M5.20
Measurements of RF Photonic Bandgap Structure Localized Electromagnetic Fields for Application in NonLinear Material Measurements.
Ricky Moore 1 , Eric Kuster 1 , Stephen Blalock 1 , Brian Cieszynski 1
1 GTRI/STL, Georgia Tech, Atlanta, Georgia, United States
Show AbstractMeasuring nonlinear AC dielectric or magnetic properties of ferro and ferri magnetic materials have required large, extremely high power and bulky equipment configurations for production of the required intense electric and/or magnetic fields. RF cavities, striplines or waveguide test fixtures may require 10s of cubic millimeter too centimeter material volumes. PBG structures exhibit negative phase-frequency transmission slopes that are correlated with negative index behavior and the onset of highly localized electromagnetic fields, with increased power density, within small volumes of the PBG. Field localization is recognized and has been applied in biological diagnostics and treatment [Phys. Rev. V. 109, 1492; Phys. Rev. B, V 55 and 62, nos. 19 and 16, pp 13234 and 11230 and Chem.Soc.News, 1998, V. 27,241]. In the 2008 MRS Proceedings, the current authors presented an initial experimental design for a ultra wideband microwave photonic bandgap (PBG) based free space based measurement concept with purpose to measure nonlinear electric or magnetic properties of small material volumes such as nano and micro particulates or particulate composites. The 2008 design applied wideband radiators at modest powers to pump localized electromagnetic modes in various thicknesses of a two dimensional Alumina photonic PBG structure. The current paper reports measured verifications of the previous paper’s predictions. Ultra wideband free space reflection and transmission amplitude and phase measurements are augmented with electrically small, probe measurements of internal PBG field intensities. The probe samples locations, between Alumina strips, where electromagnetic codes predict large field enhancements. Agreement between electromagnetic code predictions and measurement are shown for reflection, transmission and internal local field enhancements for multiple thicknesses of the Alumina PBG structure. Experiments show that onset of localization is correlated with a negative phase-frequency slope in the transmission coefficient and thus onset of an effective negative index behavior. Free field space measurements are in agreement within in 10% in amplitude and 5 degrees in phase over a 3:1 bandwidth. Overall power density enhancements exceeded 10 4 over their free space values within the PBG. Discrepancies between model and measurement are attributed to an increase in Alumina electrical loss factor and small imperfections in the PBG assembly geometry. By fitting model and measurement it was determined that electrical Alumina permittivity agrees to 2% with nominal design values. Actual PBG dimensions are within 1 % of design values.
9:00 PM - M5.21
Metal-Enhanced Multiphoton Absorption Polymerization (MEMAP) is Driven by Multiphoton-Absorption-Induced Luminescence (MAIL) in Gold Nanowires.
Sanghee Nah 1 , John Fourkas 1
1 Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States
Show AbstractTo better understand the connections among different field-enhanced phenomena in metal nanostructures, we have studied metal-enhanced multiphoton absorption polymerization (MEMAP) and multiphoton-absorption-induced luminescence (MAIL) using gold nanowires. It is well established that gold nanowires can strongly enhance optical field enhancement at their ends due to the “lightning rod” antenna effect. When the gold nanowires absorb two or more near-infrared photons simultaneously, they can emit visible luminescence strongly at their ends due to this field enhancement. This MAIL emission from gold nanowires can range from the visible into the near ultraviolet region of the spectrum. In the presence of photoresist near a gold nanowire, MEMAP is observed at the ends of the nanowire. The connections between MEMAP and MAIL were explored by using a set of three different photoresists that induce either radical or cationic polymerization processes under UV excitation. We found that MAIL and MEMAP are strongly correlated. By tuning the wavelength to 890 nm, where two-photon absorption polymerization cannot occur for these photoresists, we were able to demonstrate that MEMAP is a direct result of the broadband MAIL emission, which induces single-photon excitation of the photoinitiator.
9:00 PM - M5.22
Ag Nanoparticle Antennas on Ultrathin Oxides for Nanorectennas.
Richard Osgood 1 , Mark Kinnan 1 , Peter Stenhouse 1 , Megan Hoey 1 , Caitlin Quigley 1 , Joel Carlson 1 , Stephen Giardini 1
1 , US Army NSRDEC, Natick, Massachusetts, United States
Show AbstractResonant optical antennas concentrate and manipulate electromagnetic energy on the scale of nanometers or tens of nanometers. Optical antennas have been successfully demonstrated for use with data storage, light emission, spectroscopy, and enhanced photodetectors, and are currently actively researched for on-chip communication and energy harvesting, where they must be connected to a nanodiode (usually a metal-insulator-metal diode). The nanodiode rectifies the very high frequencies, generated by incident visible/near-infrared light, in the nanoantenna. The nanodiode must be thin enough to allow electron transport in less than the period of the optical wave, and must also have sufficiently small capacitance to ensure a fast electrical response. NSRDEC scientists have recently developed a NiO-based diode with such an ultrathin (~ 7 nm) barrier layer [1]. If perfect periodicity is not essential, nanoparticle-based optical antennas can be fabricated by relatively straightforward chemical methods, instead of more expensive, lithography-based approaches. For example, arrays of single crystal Ag nanoparticles, with no functionalizations or chemical additives that might reduce the field enhancement needed for a nanoantenna, have been fabricated via chemical methods [2]. We report on the use of these and other (Al, Cu) nanoparticles as optical antennas, and the use of several different ultrathin insulating films (NiO, Al2O3, etc.) as barrier layers for nanodiodes. We present experimental (spectroscopy, scanning near-field optical microscopy (SNOM), two-photon luminescence (TPL), etc.) and modeling results from the optical antennas, discuss experimental results from nanodiode candidate materials, and report on integrating the optical antenna and nanodiode into a nanorectenna.[1] “RF Plasma Oxidation of Sputter-Deposited Ni Thin Films to Generate Thin Nickel Oxide Layers”, Hoey, M. L., Carlson, J. B., Osgood III, R. M., Kimball, B. R., submitted (2010).[2] “Plasmon Coupling in Two-Dimensional Arrays of Silver Nanoparticles: I. Effect of the Dielectric Medium”, Kinnan, M. K., Kachan, S., Simmons, C. K., and Chumanov, G., (2009) J. Phys. Chem. C 113, 7079-84.
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Dipolar Emitters Coupled to Optical Nano-rod Antennas.
Tim Taminiau 1 , Fernando Stefani 2 , Niek van Hulst 1 3
1 , ICFO, Castelldefels, Barcelona, Spain, 2 Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires Argentina, 3 , ICREA – Institució Catalana de Recerca I Estudis Avançats, Barcelona Spain
Show AbstractOptical antennas improve the interaction of a nano-scale object with light by a near field coupling. The object absorbs and emits radiation through the resonant antenna modes. The positions of these resonances for nano-rod antennas have been successfully described by treating the antenna as a (Fabry-Perot) cavity. However, the properties of a nano-rod working as an optical antenna are determined by how its modes interact with a local object and with radiation. We derived a novel analytical model to describe the interaction of dipolar emitters, such as molecules, ions and quantum dots, with light through nano-rod modes [T. H. Taminiau et al., arXiv:0912.2024v1 (2009)]. In this contribution we will present our analytical approach, and validate it with comparisons to experimental and numerical results for electric dipole transitions coupled to metal nanorods.The key idea of the model is that a local source launches surface charge waves along the nano-rod, which are reflected at the rod ends with a reflection coefficient that depends on the radiative decay of the formed antenna modes. The analytical model accurately describes the complete emission process: the radiative rate, quantum efficiency, and the angular emission. By reciprocity, it also describes the absorption of light by a local receiver. We use the model to quantitatively reveal the continuous evolution of the antenna modes from perfectly-conducting antenna theory to quasistatic plasmonics, and to derive a straightforward phase-matching equation that governs the angular emission. Our results provide a general description for the interaction of nanorods with light, and are thus widely applicable.
9:00 PM - M5.24
Mapping Surface Plasmons in Silver Nanoantennas with a Sub Nanometer Electron Probe.
David Rossouw 1 , Martin Couillard 1 , Jemma Vickery 2 , Eugenia Kumacheva 2 , Gianluigi Botton 1
1 Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada, 2 Chemistry, University of Toronto, Toronto, Ontario, Canada
Show AbstractThe localization of electromagnetic energy into nanometer dimensions is feasible through the interaction of light with metallic nanostructures. Metallic nanowires support surface plasmons which confine electromagnetic energy into nanometer dimensions, producing large local field enhancement. Surface plasmon supporting nanostructures have attracted recent attention due to their potential applications in nanodevices, including their use in sub-wavelength photonic circuits, data storage, solar cells and bio-sensors [1]. For a greater understanding of field localization, optical modes in individual nanostructures need to be probed with nanoscale precision, below the light diffraction limit. Traditional optical techniques are thus rendered inadequate for such analysis. Near-field scanning optical microscopy can exceed the diffraction limit, however the spatial resolution is rapidly limited by the loss of signal with the reduction in the probe size. We report the detection of multiple optical mode harmonics from a single, silver nanoantenna with a sub-nanometer electron probe.The optical modes setup in a nanostructures may be studied in a transmission electron microscope through the acquisition of a spectrum image (SI). This method involves recording an electron energy loss spectrum at each pixel in a two dimensional, focussed electron probe scan. Thus, a three dimensional data cube (x,y,E) is recorded in a SI. Plasmon maps may be extracted from selected energy loss windows in a SI to create an energy filtered image. Selected energy loss windows centered on energy loss peaks in the spectrum reveal the striking spatial variation of optical modes in the nanoantenna. Furthermore, maps of several optical modes ranging from the near-infrared to ultraviolet may be extracted from a single SI. Experimental data were recorded on a monochromated FEI 80-300keV Titan electron microscope at 0.1eV energy resolution (FWHM). Strong features in the collected raw data are present below 0.5eV in the energy loss spectrum. The rich details in the low loss region of the energy loss spectrum are accessible for the first time owing to the highly monochromatic electron source and resulting narrow zero loss peak. The quality of raw data demonstrates the validity of the technique for future work on related studies. Such investigations will lead to a greater understanding of the relationship between the size, shape and optical properties of nanoparticles.[1] W. L. Barnes, A. Dereux, T. W. Ebbesen, Nature, 424, 824, 2003.
9:00 PM - M5.25
Transparent Conductive Oxide Antennas.
Alok Vasudev 1 , Kevin C.Y. Huang 1 , Mark Brongersma 1
1 The Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States
Show AbstractThe interaction between light and nanometer-scale structures has been of great interest for both fundamental studies and technological applications. Metallic nanostructures and their ability to concentrate light into deep-subwavelength volumes has launched the field of plasmonics, while semiconductor nanostructures have also been shown to support optical resonances that facilitate enhanced photodetection, improved solar absorption efficiency and more. Recently transparent conductive oxides (TCO) have been suggested as candidates for alternative plasmonic materials. Here we theoretically investigate the light scattering properties of Indium Tin Oxide (ITO) nanowires. Using the Lorenz-Mie solution to Maxwell’s equations we calculate extinction, scattering and absorption cross-sections for a single ITO nanowire whose optical constants were ellipsometrically measured from a commercially acquired thin-film. We report that a single ITO nanowire supports both surface plasmon resonances and dielectric resonances. A strong plasmonic resonance is found near the optical communication wavelengths. In addition to these distinct regimes we find a spectral transition region in which the real part of ITO’s dielectric constant is near zero, leading to minimal extinction. These unique optical properties of TCO nanostructures demonstrate potential for enabling a new class of nanophotonic devices.
9:00 PM - M5.26
Assembly and Analysis of Semiconductor Nanocrystal/J-aggregate Constructs and Applications to Light Harvesting and Energy Transfer.
Brian Walker 1 , Valdimir Bulovic 2 , Moungi Bawendi 1
1 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe report the preparation and self-assembly of semiconductor nanocrystals with cyanine J-aggregates, making use of the size tunable emission and favorable transport properties of nanocrystals and the narrow, intense absorption of J-aggregates. These hybrid materials have been analyzed in solution, in large-area solid-state thin films, and in devices, exhibiting >90% energy transfer efficiency and making the nanocrystal/J-aggregate system the most efficient configuration yet reported for energy transfer from organic fluorophores to semiconductor nanocrystals. Because the presence of the J-aggregates enhances the excitation density on the nanocrystals by up to 4-fold, and because we can readily transfer these materials to the solid state via solution phase processing, these nanocrystal/J-aggregate constructs may be useful in downconversion applications, in luminescent solar concentrators, or in fundamental investigations of light harvesting.
9:00 PM - M5.27
Plasmonic and Molecular Resonance Coupling on Gold Nanorods.
Jianfang Wang 1
1 Physics, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong
Show AbstractLocalized plamsons have been widely used to enhance optical signals, such as Raman scattering, fluorescence, light absorption, two-photon fluorescence and photopolymerization, and second-harmonic generation. These plasmon-enhanced spectroscopies require the placement of optically active species in the region very close to the metal surface. On the other hand, the adsorption of optically active species can also affect localized plasmon resonances. Understanding the effects of adsorbed species on localized plasmons is of importance not only for various plasmon-enhanced spectroscopies, but also for developing plasmon shift-based ultrasensitive sensing devices. We have studied the resonance coupling between the localized plasmons of Au nanocrystals and adsorbed dyes both on the ensemble level (JACS 2008, 130, 6692; 2010, 132, 4806) and on the single-particle level (NL 2010, 10, 77) by constructing freestanding hybrid nanostructures between organic dyes and colloidal gold nanocrystals. The coupling strength is tuned by using Au nanorods with varying longitudinal plasmon wavelengths. The maximum coupling-induced plasmon shift is observed to reach above 120 nm, which is about one order of magnitude larger than that caused by the local refractive index increase. The plasmon shift is found to decay rapidly with increasing spacing between the dye and nanorod. In addition, the coupling strength is found to approximately increase as the molecular volume-normalized absorptivity is increased. It is mainly determined by the plasmon resonance energy of Au nanocrystals instead of their shapes and sizes. Moreover, the resonance coupling can be switched on and off by adjusting the pH of the solution, using photodecomposition, or adding metal ions. It is difficult to extract all of the resonance coupling features from the ensemble measurements due to the extinction peak broadening arising from inhomogeneous size distributions. We have therefore further measured the resonance coupling on single Au nanorods by utilizing the dark-field scattering technique. The nanorods are embedded in hydrogel to facilitate uniform dye adsorption. The adsorbed dye molecules exhibit both monomer and H-aggregate absorption bands. The same gold nanorods are measured before and after the dye adsorption. Both strong and weak coupling are investigated by tuning the longitudinal plasmon band of the nanorods. Excellent agreement between the experiments and an analytic theory has been obtained. The resonance coupling reveals a unique three-band structure. The tunability of the coupling on the individual nanorods has also been demonstrated by photodecomposing the adsorbed dye molecules and modeled theoretically. These unprecedented single-particle resonance coupling studies will greatly help in understanding the fundamental aspects of the plasmon-molecular resonance hybridization and designing various plasmon-enhanced spectroscopies with improved signal enhancements.
9:00 PM - M5.28
A White-light Apertureless Scanning Near-field Optical Microscopy Method for Gold Nanoantennas.
Matthias Wissert 1 , Gabor Varga 1 , Carola Geiger 1 , Konstantin Ilin 2 , Michael Siegel 2 , Uli Lemmer 3 , Hans-Juergen Eisler 1
1 Light Technology Institute (LTI), DFG Heisenberg Group 'Nanoscale Science', Karlsruhe Institute of Technology (KIT), Karlsruhe Germany, 2 Institute for Micro- and Nanoelectronic Systems (IMS), Karlsruhe Institute of Technology (KIT), Karlsruhe Germany, 3 Light Technology Institute (LTI), Karlsruhe Institute of Technology (KIT), Karlsruhe Germany
Show AbstractWe present an apertureless scanning near-field optical microscopy (a-SNOM) technique for nanostructures such as optical antennas, which is based on movement of an AFM (atomic force microcopy) cantilever over the nanostructure while the latter is kept in a fixed position. An antenna white-light response is generated by application of two-photon absorption with a Ti:Sa-laser operated at a wavelength of 810 nm. The emission intensity is observed using a single-photon-counting avalanche photodiode, the response spectrum is investigated with an electron multiplying CCD camera. With the movement of the cantilever over the excited antenna, we observe a white-light near-field response of the gold nanostructures, superimposed on a constant far-field white-light offset, with very high spatial optical resolution. Thus both an AFM image and an optical intensity image are recorded simultaneously. The power of the method is demonstrated on gold optical antennas comprised of two arms of length 100-120 nm each, width 20 nm, and height 30 nm separated by a 20 nm gap. Results are presented for intermittent contact and contact mode operation of the AFM cantilever.
9:00 PM - M5.3
Polarization Control and Engineering with Plasmonic Antenna Structures.
Paolo Biagioni 1 , Jer-Shing Huang 2 , Matteo Savoini 1 , Lamberto Duo 1 , Marco Finazzi 1 , Bert Hecht 2 , Jord Prangsma 2
1 Physics, Politecnico di Milano, Milano Italy, 2 Experimentelle Physik 5, Physikalisches Institut, Wilhelm-Conrad-Roentgen-Center for Complex Material Systems, Universitaet Wuerzburg, Wuerzburg Germany
Show AbstractThe analysis and control of polarized fields on the nanometer scale is a crucial issue for many developments in nanoplasmonics, as the scaling down of widely used optical techniques relies upon the availability of polarized near fields. The possibility to shape the polarization properties of local fields, moreover, would open the road towards controlled interaction between polarized light and matter at the nanoscale.Resonant optical antennas, which have been recognized as one of the most promising way to enhance the interaction between light and nano-objects, have been realized mainly as linear antennas so far. Coupling to nanomatter is therefore restricted to transitions with dipole moment projections oriented along the antenna axis. Moreover, linear antennas completely rule out applications involving circularly-polarized fields.We present extended simulations for a cross antenna structure, constituted by two perpendicular dipole antennas with a common feed gap, and show how this novel configuration allows for a complete control of light with an arbitrary polarization state in the plane of the antenna [1,2].The structure, simulated by finite-difference time-domain methods, consists of two perpendicular gold dipole antennas on a glass substrate, while excitation is provided either by a focused Gaussian beam (to study localization of propagating waves) or by a point dipole in the antenna feed-gap (to study the emission properties of the antenna). We focus the simulation analysis on three different case studies. We first show that the antenna is capable of resonantly confining and enhancing propagating fields inside the small modal volume of its feed-gap, while maintaining their polarization state with high fidelity. In particular, we analyze the performances of the antenna as a local source of circularly polarized photons.In a second part, we study the far-field emission pattern of a dipole placed in the antenna feed-gap. We show that the radiated fields follow the dipole orientation, in striking contrast with linear antennas, where the polarization of emitted waves is dictated by the antenna axis.Finally, we exploit the phase response of plasmonic antennas of different lengths and propose an asymmetric cross structure acting as a nano quarter-wave plate: upon illumination with linearly polarized light, the asymmetric arms provide a controlled phase shift between different field components, which effectively builds up circularly-polarized near fields in the feed-gap. We also show examples obtained by structuring cross antennas starting from single-crystal Au microplates grown by electrochemical methods and present preliminary experimental results. Finally, we envisage possible strategies to experimentally characterize the degree of circular polarization in the feed-gap of a cross antenna.
9:00 PM - M5.30
Two-photon Photoluminescence Image from Single Gold Nanospheres above a Gold Substrate.
Tatsuya Yamaguchi 1 , Kotaro Kajikawa 1
1 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama Japan
Show AbstractWe show two-photon photoluminescence (TPPL) image of isolated single gold nanospheres immobilized above a gold surface (SIGN) in order to reveal the plasmonic structure of SIGNs. The gap between the gold nanosphere and the gold surface is supported by a self-assembled monolayer (SAM) of aminoundecanthiol (AUT). TPPL images were taken, using optical microscope equipped with a cooled CCD camera. A mode-locked Ti:sapphire laser (τ=120 fs, f =80 MHz, λ=830 nm) was used for excitation. The laser light was incident on the sample surface at oblique incidence. The observed TPPL images excited by p-polarized incident light were obviously brighter than excited by s-polarized incident light in the SIGN. This remarkable difference in TPPL signal is due to the polarization dependence of LSPR in the SIGN. In addition, strong TPPL signals were observed at the edge of gold surface, caused by the propagation of surface plasmons along the edge. TPPL imaging can be powerful probe for investigating the local electric-field distribution associated with LSPR in metal surface.
9:00 PM - M5.31
Towards Reduction of Optical Losses in Transition Metal Based Nanomaterials.
Alexander Gavrilenko 1 , Doyle Baker 1 , Casey Gonder 1 , Carla McKinney 1 , Vladimir Gavrilenko 1
1 Center for Materials Research, Norfolk State University, Norfolk, Virginia, United States
Show AbstractReduction of optical losses in meta-materials containing transition metals is a hot area of modern materials science with variety of applications in nano-photonics and nano-plasmonics. This work demonstrates that fabrication of new material composites and alloys based on transition metals and molecular adsorption on metallic surfaces are powerful tools for the band structure engineering and reduction of optical losses. It is shown that these approaches are increasingly important with reduction of characteristic materials sizes.The first principles density functional theory is applied to study effects of molecular adsorption on silver (111) oriented nano-films and the alloying effects of Ag1-xCdx, and Ag1-xInx based nanostructures on their optical losses. Ground state of the systems including methanol, ethanol, and water molecules adsorbed on Ag(111) surface was obtained by the total energy minimization method within the local density approximation. Optical functions are calculated within the Random Phase Approximation approach. The light excitations of plasmons are described by the Drude model. Changes of the optical absorption spectra caused by the variations of the alloy contents are studied in the range of x-values varying up to 9 percent. Contribution of the surface states to optical losses is studied by calculations of the dielectric function of bare Ag(111) surface. Substantial modifications of the real and imaginary parts of the dielectric functions spectra in near infrared and visible spectral regions, caused by surface states and molecular adsorption, are obtained. Strong increase of optical losses in infrared and visible range is predicted. In contrast, the molecular adsorption reduces optical losses in ultraviolet (above 4.0 eV). Optical absorption spectra corresponding to the plasmon and band-to-band transitions of alloys show opposite trends in spectral shifts caused by a variation of the content, x. With increase of x, the electronic energies of band-to-band transitions associated with optical excitations of d-electrons indicate well pronounced red shifts. On the other hand, optical absorption peaks located in the near infrared spectral region and associated with excitations of the d-p hybrid electronic states show clear blue shifts with increase of x. The predicted variations of optical absorption spectra of transition metals alloys agree with experimental data measured on Ag-In and Ag-Cd alloys. The results obtained contribute to better understanding of the mechanisms of optical properties engineering in transition metal based materials. They also highlight the ways for variety of applications in materials science by developing the efficient optoelectronics and nano-photonics devices.
9:00 PM - M5.4
Photonic-plasmonic ``Fano-Molecules".
Svetlana Boriskina 1 , Luca Dal Negro 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractWe demonstrate dramatic broadband field enhancement in nanoscale volumes and strong resonant modification of radiative rates of emitters in hybrid photonic-plasmonic structures termed "Fano-molecules". These structures are composed of photonic atoms (optical microcavities) and plasmonic atoms (metal nanoantennas), and their improved performance is a result of a perfect marriage of the strong resonant modification of the local density of optical states in microcavities and nanoscale light localization on nanoantennas. We theoretically predict formation of ultra-narrow Fano lineshapes in the optical spectra of photonic-plasmonic molecules as a result of coupling of high-Q microcavity modes (an equivalent of a discrete energy state) and low-Q localized surface plasmon (LSP) resonances on nanoantennas (an equivalent of the continuum). We observe three orders of magnitude resonant enhancement of the field intensity in photonic-plasmonic Fano-molecules over isolated plasmonic antennas, which is a result of the constructive interference of optical modes and LSP resonances. Furthermore, as the resonant light confinement in microcavities dramatically enhances the effect of refractive index change on their spectral characteristics, we predict the potential of the Fano-molecules to dynamically tune the hot spot spectra and to manipulate the optical energy flow and optical forces on the nanoscale via either optical or electrical tuning of microcavities. A possibility to dynamically re-configure the near-field intensity distribution on the microcavity-coupled complex nanoantenna configurations is also explored.
9:00 PM - M5.5
Resonant Optical Properties of a Periodic System of Quantum Well Excitons at the Second Quantum State.
Vladimir Chaldyshev 1 , Alexander Poddubny 1 , Alexey Vasil ev 1 , Y. Chen 2 , Zhiheng Liu 2
1 , Ioffe Institute, St.Petersburg Russian Federation, 2 Physics, Brooklyn College, Brooklyn, New York, United States
Show AbstractOptical properties of the media with periodic modulation of the dielectric response have attracted growing attention since the seminal paper by Yablonovich. The diffraction of electromagnetic waves in such system leads to formation of a super-radiant optical mode, which develops into a photonic band structure with increasing number of periods. A special kind of such media proposed by Ivchenko is based on a periodic system of the quantum-well (QW) excitons. Such system exhibits resonance properties due to the enhanced coupling between light and the QW excitonic states when the spatial periodicity of the QWs meets the Bragg diffraction condition at the frequency of the exciton-polariton state. Several research efforts on such systems have always focused on the lowest energy state of the exciton-polaritons in the QWs. The resonant reflection, however, does not require any population of the excitonic or electronic state and can be realized for higher quantum confinement levels.In this paper such the resonant conditions were realized for the first time by tuning of the Bragg diffraction resonance to the frequency of the exciton-polaritons associated with the second quantum state of electrons and heavy holes (e2-hh2) in GaAs QWs separated by AlGaAs barriers. The samples with up to 60 quantum wells were grown by molecular-beam epitaxy on 2-inch GaAs (001) substrates. For the sample containing a single QW, the excitonic state associated with the second quantum level of the electrons and heavy holes is hardly detectable optically, whereas the excitons at the ground quantum state e1-hh1 give rise to sharp features in optical reflection, electro-reflection and photoluminescence spectra. For the sample with a large number of QWs, our experiments show a substantial enhancement of the exciton-photon interaction when the Bragg wavelength is tuned to the energy of the e2-hh2 excitons by varying the angle of the light incidence, or when the exciton energy is tuned to the Bragg wavelength by varying the sample temperature. Parameters of the optical features in reflection and electro-reflection spectra are evaluated in- and out of the resonance conditions. A comparison has been done for the experimental optical spectra and calculated ones, which allow us to evaluate the parameters of the super-radiant optical mode and extract the radiative and nonradiative broadening for the e2-hh2 exciton-polariton state in the QW.
9:00 PM - M5.6
Three-dimensional Periodic Resonant Nanocrescent Array.
H. Chen 1 2 , Lin Pang 1 , Yeshaiahu Fainman 1
1 Department of Electrical Engineering, University of California, San Diego, La Jolla, California, United States, 2 , Naval Air Warfare Center, China Lake, California, United States
Show Abstract Gold nanoparticles exhibit localized surface plasmon resonance (LSPR) near its surface that is extremely sensitive to biomolecule binding where its resonant wavelength is dependent not only on the material and the geometry but also on the refractive index of its surrounding. For an array of nanostructures having a periodicity that is similar to the wavelength of the scattered light, there is the possibility of coherent interaction arising from multiple scattering off of these nanoparticles. It has been shown that when the wavelength falls in the same spectral range as the LSPR, a drastic modification of the optical extinction is observed: when these spherical nanoparticles are arranged in a periodic array with interparticle spacing close to the single particle resonance and with the wave vector and the polarization perpendicular to the array axis, extremely narrow linewidth is possible due to coherent coupling. More importantly, the electric field is increased in the near-field. Experimentally, we have shown that it is possible to control and arrange spherical nanoparticles into a periodic array to take advance of this phenomenon. With this new fabrication method, periodic array of more complex structures are possible, such as the nanocrescent cavity antenna. At the conference, we will show simulation results using both finite difference time domain (FDTD) and finite element method (FEM) methods of these nanocrescent structures forming a periodic array and giving at least a factor of two improvements in the near-field compare to its corresponding individual structure. The geometric properties of the nanocrescent are varied to tune its resonant wavelength. As expected, local field enhancement can be increased by increasing the sharpness of the tips; however, to model realistic structure and to avoid computational anomaly, our structures have at least a fillet of 1nm radius at the rim. A parametric study on the periodicity, polarization, and angle of incidence will be presented. Furthermore, the electrical field can be further enhanced by incorporating a gain medium inside the cavity of the nanocrescent array structure. Initial results show approximately a factor of two improvement for a typical gain medium. More detailed simulation results will be presented at the conference.
9:00 PM - M5.7
Optical Properties of Emitters in Close Proximity to Gold Nanorods.
Jinsong Duan 1 4 , Dhriti Nepal 2 4 , Kyoungweon Park 3 4 , Richard Vaia 4 , Ruth Pachter 4
1 , General Dynamics Information Technology, Dayton, Ohio, United States, 4 , Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio, United States, 2 , Universal Technology Corp, Dayton, Ohio, United States, 3 , UES, Inc., Dayton, Ohio, United States
Show AbstractGaining insight into fluorescence enhancement or quenching by an emitter close to a metal nanoparticle surface has been difficult, primarily because of the large number of parameters that determine the radiative and nonradiative decay in such systems. In particular, because we are interested in quantitative prediction of optical properties for enhanced emission, as well as the parameters that cause quenching, for example, for loss mitigation in gold nanorods (AuNRs), finite-difference time-domain (FDTD) calculations were carried out. An emitter (described by a dipole oscillating at the fluorescence frequency, representing its transition dipole moment) was included in the FDTD simulations, placed at varying positions from the AuNR. Effects of distance, orientation, enhanced local field, AuNR size and aspect ratio, will be explained in detail, for single and self-assembled AuNRs, also in comparison with experiment in some cases.
9:00 PM - M5.8
Optical Properties of Asymmetric and Layered Caps Fabricated via Colloidal Lithography.
Maj Frederiksen 1 , Abbas Maaroof 1 , Duncan Sutherland 1
1 iNANO, Aarhus University, Aarhus Denmark
Show AbstractNanoscale noble-metal structures and their optical properties have received considerable research interest in recent years. The interesting optical properties of noble-metal nanostructures, which rely on the Localized Surface Plasmon Resonances (LSPR), have made these structures attractive in several applications such as surface-enhanced spectroscopy and refractive index sensing platforms. Here, we report on two experimental systems of metallic nanostructures with plasmonic properties that have been fabricated and studied. The fabrication in both systems builds on colloidal lithography. The first system consists of layered (Au-SiO2-Au) cap and hole structures. In the second system we have explored the fabrication of asymmetric nanostructures through colloidal lithography in combination with glancing angle deposition (GLAD). Colloidal particles were deposited on a glass substrate and silica deposited from a low angle to grow the particles in a controlled direction and introducing asymmetry. A gold layer was subsequently evaporated on top creating gold caps on the asymmetric particles and a thinfilm with asymmetric holes directly on the substrate. Elliptical holes in gold films were investigated in the same study. The structures have been characterized with optical spectroscopy where both scattering and absorption measurements were performed. Distinct LSPRs for caps and for holes were observed in both systems. For the layered structures a blue shift of the cap and holes LSPRs were observed for scattering and absorption as the thickness of the upper gold cap was increased. In the case of the asymmetric structures an asymmetric line shape was found to be associated with the holes. The asymmetry of the line shape increases with increasing asymmetry of the structures. In conclusion, we have been able to produce structures with a systematic change in shape and introduce asymmetry and direction which in turn shifts the position and changes the line shape of the LSPRs. Furthermore the effect on the plasmonic response of the thickness of the upper layer in layered Au-SiO2-Au caps and holes has been investigated and evaluated in terms of plasmon hybridization.
9:00 PM - M5.9
Plasmonic Circular Dichroism of Chiral Metal Nanoparticle Assemblies.
Alexander Govorov 1 , Zhiyuan Fan 1
1 , Ohio University, Athens, Ohio, United States
Show AbstractWe describe from the theoretical point of view a plasmonic mechanism of optical activity in chiral complexes composed of metal nanoparticles (NPs). In our model, the circular dichroism (CD) signal comes from the Coulomb interaction between NPs. We show that the CD spectrum is very sensitive to the geometry and composition of a chiral complex and also has typically both positive and negative bands [1]. In our calculations, the strongest CD signals were found for the helix geometry resembling helical structures of many biomolecules. For chiral tetramers and pyramids, the symmetry of a frame of a complex is very important for the formation of a strong CD response. Chiral natural molecules (peptides, DNA, etc.) often have strong CD signals in the UV range and typically show weak CD responses in the visible range of photon energies [1]. In contrast to the natural molecules, the described mechanism of plasmonic CD is able to create strong CD signals in the visible wavelength range. We also note that another mechanism leading to strong CD signals in the visible range is due to plasmon enhancement of chiral biomolecules coupled with metal nanocrystals [2]. The plasmonic mechanisms offer a unique possibility to design colloidal and other nanostructures with strong optical chirality. Potential applications of chiral plasmonic systems include sensors and photonics materials.[1] Z. Fan, A.O. Govorov, Nano Letters, DOI: 10.1021/nl101231b (2010). [2] A.O. Govorov, Z. Fan, P. Hernandez, J.M. Slocik, R.R. Naik, Nano Letters 10, 1374 (2010).
Symposium Organizers
Rashid Zia Brown University
Kenneth B. Crozier Harvard University
Nader Engheta University of Pennsylvania
Ganping Ju Seagate Technology
Romain Quidant ICFO - The Institute of Photonic Sciences
M6: Coupled Resonances
Session Chairs
Wednesday AM, December 01, 2010
Room 200 (Hynes)
9:30 AM - **M6.1
Plasmon Nanocavities: Controlled Gaps as Optical Antennas.
Hideki Miyazaki 1 , Yoichi Kurokawa 1
1 , National Institute for Materials Science, Tsukuba Japan
Show AbstractSilver and gold nanoparticle dimers are known to be efficient plasmon resonators that exhibit gigantic Raman scattering enhancement [1]. Artificial nanostructures with similar functions are indispensable for realization of controlled enhanced spectroscopy or creation of novel optical materials. In a resonant nanoparticle dimer, the electric field is localized at the nanometric gap between metal walls. This resonance can be viewed as a Fabry-Perot resonance in a narrow metal-insulator-metal (MIM) waveguide with a finite length, as well as a coupled Mie resonance. The lowest-order propagation mode of a MIM waveguide has a larger wave vector for a narrower gap and is reflected at open and closed ends due to impedance mismatch. In consequence, a MIM waveguide with a finite length works as a nanocavity [2]. The most fundamental cavity structure is a rectangular nanotrench supporting a quarter-wave resonance [3], which is one of the primitive forms of optical antennas. In this talk, we first give a basic idea on how to design a nanogap cavity resonant at a specific wavelength. Then, we will visually demonstrate why a nanogap can be regarded as "an antenna". Gigantic field enhancement in a resonant nanogap arises because the gap collects incident light from an area much wider than its geometrical width and then store the energy for a certain time duration [4]. This is a function equivalent to a radio-wave-harvesting antenna made of a thin wire. Finally, by experimentally demonstrating the enhancement of Raman scattering and thermal emission [5], it will be shown that such nanogap cavities are manufacturable and useful. References: [1] H. Xu et al., Phys. Rev. Lett. 83, 4357 (1999). [2] H. T. Miyazaki and Y. Kurokawa, Phys. Rev. Lett. 96, 097401 (2006). [3] H. T. Miyazaki and Y. Kurokawa, Appl. Phys. Lett. 89, 211126 (2006). [4] H. T. Miyazaki and Y. Kurokawa, IEEE J. Sel. Top. Quantum Electron. 14, 1565 (2008). [5] K. Ikeda, H. T. Miyazaki et al., Appl. Phys. Lett. 92, 021117 (2008).
10:00 AM - M6.2
Vertically Oriented Plasmonic Nanogap Arrays.
Hyungsoon Im 1 , Kyle Bantz 2 , Nathan Lindquist 1 , Christy Haynes 2 , Sang-Hyun Oh 1
1 Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2 Chemistry, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractNanometric gaps in noble metals can harness surface plasmons, collective excitations of the conduction electrons, for extreme subwavelength localization of electromagnetic energy. Positioning molecules within such metallic nanogaps dramatically enhances surface-plasmon-mediated light-matter interactions, increasing absorption, emission, and most notably, surface-enhanced Raman scattering (SERS). SERS is a powerful analytical signal transduction mechanism for the detection of analytes in aqueous environments, largely free from interfering water signals and capable of obtaining unique molecular signatures. Literature work suggests that large SERS enhancements are achieved when the analyte of interest is placed near a noble metal gap or crevice feature. However, the lack of reproducible high-throughput fabrication techniques with nanometric control over the gap size has limited practical applications. Here we show sub-10 nm metallic nanogap arrays with precise control of the gap’s size, position, shape, and orientation. The vertically oriented plasmonic nanogaps are formed between two metal structures by a sacrificial layer of ultrathin alumina grown using atomic layer deposition (ALD). A metal film is first pre-patterned with optical lithography or focused ion beam milling. An ALD layer is then deposited, conformally covering the top and sidewalls of the pre-patterned metal. With subsequent metal deposition and anisotropic physical ion milling, a nanogap is formed between the two metal layers whose geometry is defined by the pre-patterned metal sidewalls and the thickness of the ALD layer. We show increasing local SERS enhancements of up to 109 as the nanogap size decreases to 5 nm. Additionally, by assembling a nanogap over a tunable nanosphere scaffold makes it easy to achieve the desired optical properties and/or feature size for sensing applications. Because these sub-10 nm gaps can be simply fabricated at high densities using conventional optical lithography over an entire wafer with large and tunable enhancement factors, these results will have significant implications for spectroscopy and nanophotonics.
10:15 AM - M6.3
Far-field Imaging and Selection of the Bonding and Antibonding Modes in Au Dipole Antennas.
Jer-Shing Huang 2 , Johannes Kern 2 , Peter Geisler 2 , Pia Weinmann 3 , Martin Kamp 3 , Alfred Forchel 3 , Paolo Biagioni 1 , Bert Hecht 2 , Jord Prangsma 2
2 Expererimentelle Physik 5, Physikalisches Institut, Wilhelm-Conrad-Roengten-Center for Complex Material Systems, Universitaet Wuerzburg, Wuerzburg Germany, 3 Technische Physik, Physikalisches Institut, Wilhelm-Conrad-Roengten-Center for Complex Material Systems, Universitaet Wuerzburg, Wuerzburg Germany, 1 Physics, Politecnico di Milano, Milano Italy
Show AbstractIn the last few years large efforts have been devoted in the field of optical antennas and noble-metal nanoparticles to implement and address spectral features with large quality factors, i.e. resonances with low associated losses that are best suited for strong coupling in light-matter interaction and high sensitivity in plasmonic sensors. Deep subwavelength integration of high-definition plasmonic nanostructures is also of key importance for the development of future optical nanocircuitry [1] for high-speed communication, quantum computation, and lab-on-a-chip applications. So far the realization of extended plasmonic networks consisting of multiple functional elements remains challenging, mainly due to the multi-crystallinity of commonly used Au layers. Resulting structural imperfections in individual circuit elements will drastically reduce the yield of functional integrated nanocircuits. Here we demonstrate the use of very large (side >10 µm) but thin (thickness <80 nm) chemically grown single-crystalline Au flakes, which serve as an ideal basis for focused-ion beam milling and other top-down nanofabrication techniques. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features [2]. As an example, we study a set of dipole Au antennas with varying length and well-controlled dimensions [3]. The strong coupling across the small (16 nm) gap results in large energy splitting between the low-quality radiative bonding mode and the high-quality dark antibonding mode of the system. However, far-field excitation of the antibonding mode is forbidden for plane-wave illumination by the symmetric character of the associated currents. Here we study the antenna array by means of confocal two-photon photoluminescence (TPPL) at fixed excitation wavelength. As the length of the antenna is increased, such resonances spectrally shift to lower frequencies, so that our excitation wavelength is first resonant with the bonding mode and then with the antibonding one. While confocal TPPL imaging of the bonding mode results in a single rounded spot originated from the large field enhancement at the antenna feed-gap, for the antibonding mode a two-lobe pattern appears as a result of the symmetry requirements in the excitation process. We are therefore able to selectively excite the antibonding resonance of a dipole nano-antenna. This is made possible by the small gap achieved starting from single-crystalline Au plates, which results in strong coupling and therefore large separation between the hybridized modes. The high quality factor, different resonance frequency, and different field distribution of the antibonding mode make it interesting for sensors applications, near-field engineering, and coherent control schemes.[1] J.-S. Huang et al., NanoLetters 9, 1897 (2009).[2] J.-S. Huang et al., arXiv:1004.1961 (2010).[3] J.-S. Huang et al., Nano Letters 10, 2105 (2010).
10:30 AM - **M6.4
Fano Resonances in Plasmonic Nanostructures.
Peter Nordlander 1
1 Physics and Astronomy, Rice University, Houston, Texas, United States
Show AbstractPlasmonic nanostructures such as narrow plasmonic cavities, strongly interacting nanoparticle aggregates, and hybrid plasmonic/excitonic systems offer highly tunable platforms for the study of radiative interference and coherence effects such as subradiance, superradiance, and electromagnetically induced transparency (EIT). In structures with reduced symmetry, narrow Fano resonances can appear in their extinction spectra resulting from the interference between superradiant and subradiant modes. Apart from their fundamental importance, such phenomena are also of practical interest in metamaterial and chemical and sensing applications because of the extraordinarily narrow linewidths and strong sensitivities to the dielectric properties of the environment. In this talk, I will present a general framework for the description of radiative interference effects in plasmonic systems and illustrate the concepts with examples from recent applications to symmetry broken nanoshells, Fanoshells [1], small nanoparticle clusters of D6h symmetry (Heptamers) [2], planar ring-disk systems (Fanocavities) [3], and plasmonic heterodimers.[4] References[1] S. Mukherjee et al., Nano Lett. 10(2010)10.1021/nl1016392[2] J.A. Fan et al., Science 328(2010)1135[3] Y. Sonnefraud et al., ACS Nano 4(2010)1664.[4] L. Brown et al., ACS Nano 4(2010)819
11:00 AM - M6: Coupled
BREAK
M7: Antenna Arrays
Session Chairs
Wednesday PM, December 01, 2010
Room 200 (Hynes)
11:30 AM - **M7.1
Surface-coupled Metal Nanoparticle Arrays – Science and Applications.
Pieter Kik 1 , Amitabh Ghoshal 1
1 CREOL, The College of Optics and Photonics, UCF-CREOL, Orlando, Florida, United States
Show AbstractControl over resonantly enhanced localized electric fields has led to a variety of new photonic devices, including high sensitivity biosensors, surface enhanced Raman spectroscopy substrates, nanoscale optical waveguides, and low power optical switches. An important device element is the optical coupler, which converts far-field radiation into guided surface plasmon modes and vice-versa. Manipulation of far-field to near-field coupling efficiency in periodic structures can be used to develop efficient normal-incidence optical interconnects to nanoplasmonic circuits, beam collimation elements for nanoscale emitters, improved thin-film solar cells, and plasmon-based biosensors with improved sensitivity. Here we present recent experimental and theoretical work on plasmon enhanced grating couplers utilizing geometrically tuned surface coupled nanoparticle arrays. The first part of the presentation covers a numerical study of the excitation of propagating surface plasmons (SPs) on a silver-SiO2 interface through an array of ellipsoidal silver nanoparticles. By varying both the particle aspect ratio and the particle volume in these structures, the key characteristics of the coupling process are revealed. It is found that while the excited SP amplitude depends sensitively on the particle volume for each selected aspect ratio, the maximum SP amplitude obtained for the different particle shapes is remarkably similar. These observations are explained in terms of particle-mediated SP excitation, counteracted by a size dependent particle-induced damping. An analytical model is presented that quantitatively describes the observed trends in SP damping. In the second part of the presentation experimental studies of nanoparticle based coupling devices are discussed. The devices consist of arrays of gold nanoparticles fabricated by e-beam lithography near a 65nm thick gold film on an SiO2 spacer layer, with a varying number of nanoparticle rows. The structures are excited by convergent white light, which results in the particle-mediated excitation of propagating surface plasmons on the underlying gold film. Through a combination of reflection spectroscopy and leakage radiation microscopy as well as spectroscopy, the nature of the various plasmon excitation resonances is revealed. Clear evidence for strong coupling between localized and propagating plasmons is presented, and the dependence of an observed mode splitting on the array size is discussed in terms of plasmon excitation and plasmon scattering cross-sections. In addition, measurements of the absolute frequency dependent SP excitation efficiency are presented. Implications for device design will be discussed.
12:00 PM - M7.2
Planar Multi-band Optical Nanoantennas with Nanoscale Spatial Resolution.
Svetlana Boriskina 1 , Jacob Trevino 1 , Bo Yan 1 , Linglu Yang 1 , Bjoern Reinhard 1 , Luca Dal Negro 1
1 , Boston University, Boston, Massachusetts, United States
Show AbstractWe propose, design and characterize novel multi-band plasmonic nanoantennas, which are formed by enclosing conventional nanodimer or nanocluster antennas into multiple-periodic gratings of metal nanoparticles, and meet the requirements of (i) high near-field enhancement, (ii) broadband frequency operation, (iii) reproducibility and (iv) compatibility with standard lithographic techniques. We exploit light scattering at multiple length scales within the structures to expand the device bandwidth and to overcome the limitations on the near-field intensity imposed by the minimum interparticle separation achievable in lithographically-fabricated arrays. Multi-peak near-field intensity spectra of the grating-assisted antennas are theoretically predicted and explained by the complex interplay between diffractive and near-field coupling of localized surface plasmon modes on metal nanoparticles resulting in the formation of Fano-type resonances. The spectral positions of the resonant peaks in the nanoantenna spectrum can be tuned across the visible and IR bands and used for multi-spectral near-field imaging or can be aligned with absorption bands and/or vibrational modes of several molecules for detection and recognition of multiple target molecules. We fabricate grating-assisted nanoantennas composed of Au nanoparticles on quartz substrates by using standard electron beam lithography and confirm their multi-peak scattering response by using the dark-field microscopy measurements. Multi-band nanoantennas can be used as versatile nano-tools for background-free sensing of trapped molecules, selective enhancement/suppression of specific fluorescent tags, broadband near-field imaging, and multiplexed single-molecule sensing.
12:15 PM - M7.3
Multi-wavelength Mid-infrared Antennas.
Romain Blanchard 1 , Jean-Philippe Tetienne 1 , Svetlana Boriskina 2 , Mikhail Kats 1 , Luca Dal Negro 2 , Federico Capasso 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Electrical and Computer Engineering & Photonics Center, Boston University, Boston, Massachusetts, United States
Show AbstractWe demonstrate a novel photonic-plasmonic antenna capable of confining light at several mid-infrared (mid-IR) wavelengths to a single sub-wavelength spot. The structure relies on the coupling between the localized surface plasmon (LSP) resonance of a bow-tie nano-antenna with the photonic modes of surrounding multi-periodic array antennas. While the bowtie antenna provides large field enhancement over a wide frequency range, the array antennas further enhance selected wavelengths according to the arrays periodicities. The flexibility of the design enables to obtain a high (10^3) enhancement at widely spaced wavelengths (e.g. 5, 8 and 10 μm).We use finite-difference time-domain (FDTD) simulations to design the structures and understand the dephasing effects induced by the index mismatch between the substrate and air. In order to minimize these effects and obtain sharper spectral features, we use barium fluoride (BaF2) substrates for the relatively low index (~1.4) and good mid-IR transmittance of this material. The fabrication of the antenna on this unusual substrate is achieved by decal transfer of the metallic structures defined by standard electron beam lithography on silicon wafers. Experimental enhancement factors are measured using a mid-IR aperture-less near-field scanning optical microscope (NSOM). The samples are illuminated using several quantum cascade lasers emitting at different wavelengths. At each resonant wavelength, an intensity map is obtained which enables to study the corresponding photonic-plasmonic modes. The development of such multi-wavelength antennas could be significant for mid-IR sub-wavelength chemical and biological imaging and spectroscopy. The antennas could be integrated on the facet of optical fibers to create high-resolution high-brightness scanning probes for a mid-IR NSOM.
12:30 PM - M7.4
Temporal Coupled-mode Theory for Resonant Apertures.
Lieven Verslegers 1 , Zongfu Yu 1 , Peter B. Catrysse 1 , Shanhui Fan 1
1 Electrical Engineering, Stanford University, Stanford, California, United States
Show AbstractAbsorption, scattering and extinction cross sections are concepts that are fundamentally important for characterizing electromagnetic properties of individual objects. These concepts are now being applied in nanophotonics to individual nanoparticles and optical antennas. The transmission cross section of an individual aperture, to an extent the dual of the extinction cross section of a nanoparticle, has also been calculated and experimentally measured for specific geometries. Here, we aim to illustrate some of the general aspects of the transmission and absorption cross sections of resonant apertures with the use of temporal coupled-mode theory (CMT). In contrast to the existing detailed numerical and experimental work on individual apertures, temporal CMT provides a general framework for the study of many optical devices. In optics, temporal CMT is mostly used to describe coupling between resonant cavities and discrete propagating waveguide modes. Due to its generality, it reduces the understanding of a complex system to a few parameters. We extend the use of temporal CMT for calculations of cross sections of objects without rotational symmetry in free space. To illustrate our theory, we focus on the simplest of apertures: the slit. The theory we set forth, however, applies equally well to the general case of a resonant aperture. We treat the aperture as a resonance (or multiple resonances at different frequencies). The approach is analytical and, depending on the application, can account for directivity, surface plasmon excitation and material absorption. We compare our theory with direct numerical simulations and obtain excellent agreement. The theory demonstrates that the maximum transmission cross section is only related to the wavelength of the incident light and directivity of the aperture’s radiation pattern. We prove a general relation between the transmission cross section and the directivity. Such an understanding should be beneficial for the design and optimization of new components. We also apply our theory towards the absorption cross section of aperture-enhanced photo-detectors, and provide a critical coupling condition that maximizes the performance of such a detector.For the case of the slit, part of our theory constitutes a reformulation of antenna theory and the concept of an effective area. We believe our formalism is more general – it only relies upon the existence of a resonance in the system, and therefore is applicable to cases where the description of the slit as a transmission line is not immediately apparent, such as many optical antenna structures.
12:45 PM - M7.5
Array of Plasmonic Antennas: The Concept and Novel Applications.
Akram Ahmadi 1 , Hossein Mosallaei 1
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractAntenna is a key element in microwave spectrum to enable wireless data communication. In this work, the idea will be transformed into the optics to engineer optical characteristics and wireless optics. Noble metals in optics offer negative permittivity parameters where one can combine them with dielectric materials to achieve desired properties and required resonant characteristics. A unique array of core-shell dielectric and plasmonic materials are designed to control both the amplitude and phase of an incoming wave and create a desired field pattern in near-zone establishing a directive emission in far-field. Arraying plasmonic nanoparticles in novel fashions can enhance the directivity of a single source from 1.5 dB to about 15 dB. This means narrowing the beamwidth of the source radiation by a factor of about 5. Further improvement can be achieved by proper tailoring the nanoantennas. Other configurations, such as plasmonic loops or patches, arranged in unique patterns are also designed to successfully engineer both the near- and far-fields photonic radiations.The concept, mathematical theory, and numerical analysis of array of plasmonic nanoantennas are fully described in this talk. The physics and novel applications, such as wireless optical interconnect, QCL with narrow beam, molecular communication, and nanometer near-field engineering are highlighted.
M8: Sensing, Spectroscopy, and Optical Forces
Session Chairs
Wednesday PM, December 01, 2010
Room 200 (Hynes)
2:30 PM - **M8.1
Plasmonics Nanoantennas for Ultrasensitive Biomolecular Identification.
Hatice Altug 1 2 , Ronen Adato 1 , Ahmet Yanik 1 , Serap Aksu 2 , Alp Artar 1 , Min Huang 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States, 2 Material Science and Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractPlasmonics, by localizing light to the sub-wavelength volumes and dramatically enhancing local fields, is enabling myriad of new exciting possibilities in bio-detection field. In this talk, we will present novel plasmonic systems for ultrasensitive infrared vibrational nanospectroscopy and biomolecular identification.Infrared absorption spectroscopy is an important tool for functional studies of bio-molecules. The method enables direct access to the vibrational fingerprints of the biomolecular structure at the mid-infrared spectral region (~3-20μm). Sensitivity limitations, however, hinders the applicability of the technique to single molecule/monolayer studies. By engineering diffractive couplings among nano-antenna arrays, we will show demonstration of an ultra-sensitive plasmonic vibrational spectroscopy technique with zepto-mole level sensitivities. Engineered arrays support collective plasmonic resonances leading to stronger near-field intensities than what is achievable with individual antennas. Using this approach, we achieve up to 100,000 fold enhancements of the amide-I and II backbone signatures of proteins and obtain direct detection of absorption signals from 145 proteins per antenna. In addition, we will demonstrate high-throughput fabrication of these tailored infrared plasmonic nanorod antenna arrays using nanostencil lithography (NSL). NSL, a shadow-mask patterning technique, relies on direct deposition of materials through a pre-patterned stencil mask. We show that optical responses of the engineered antenna arrays fabricated by NSL are comparable to that of the arrays fabricated by electron beam lithography. More importantly, we show that nanostencil masks can be reused multiple times to create series of nanoantenna arrays leading to identical optical responses. This fabrication approach, by enabling the reusability of the stencil and also offering flexibility on the substrate choice and nanopattern design, could facilitate wide-spread use of plasmonics.Finally, we will also show merging of plasmonics and nanofluidics on nanohole array platform to overcome mass transport limitation. Performances of surface biosensors are often limited by the analyte delivery rate to the sensing surface instead of sensors intrinsic detection capabilities. In a microfluidic channel, diffusive analyte transport to the biosensor surface severely limits the sensor performance. At low concentrations, this limitation causes impractically long detection times. Using our novel platform, we demonstrate how nanoholes can be harnessed both to manipulate light and to transport liquid for targeted analyte delivery. We will present our results on 14-fold increase in mass transport rate constant.
3:00 PM - M8.2
Tight Integration of Plasmonic Resonant Nanoantennas with On-chip Silicon Nitride Photonic Waveguides and Microresonators for Sensing and Spectroscopy.
Maysamreza Chamanzar 1 , Ehsan Shah Hosseini 1 , Siva Yegnanarayanan 1 , Ali Adibi 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractPlasmonic resonant nanoantennas exhibit large localized field enhancements and have been widely used for sensing and spectroscopy and are conventionally prepared either in a solution or on a substrate and are usually excited using free space light. Since the extinction cross section of these plasmonic nanoantennas is very small, coupling of light to the localized surface plasmon resonance (LSPR) modes is not efficient. In this paper, we demonstrate a hybrid material platform in which plasmonic nanoantennas (nanorods) are lithographically fabricated and integrated onto silicon nitride (SiN) photonic waveguides and travelling wave microresonators on a SiO2 substrate. SiN material is transparent over the visible-NIR range, which covers the operation range of the plasmonic resonant nanoantennas. We have demonstrated earlier that this high-index SiN material platform permits realization of ultra-high Q microresonators and low-loss optical waveguides.In our hybrid platform, the LSPR mode of each individual plasmonic nanoantenna is efficiently excited through the evanescent tail of the optical guided mode in the core of the SiN waveguide or microresonator. Nanorods integrated on top of SiN waveguides can be excited in a wide range of frequencies and therefore, many of them can be interrogated using a single waveguide. On the other hand, the integration of nanorods on microresonators benefits from the optical feedback mechanism in the microresonator for more efficient excitation of the LSPR mode. Specifically, the nanoantenna is excited each round trip and hence coupling efficiency to the nanoantenna is significantly enhanced compared to the conventional free-space excitation. We have shown more than 50% coupling efficiency improvement to each individual gold nanorod by using a SiN ring resonator of 10μm radius. The hybrid structure is designed using finite difference time domain (FDTD) method and is fabricated in a two-step electron beam lithography (EBL). In the first EBL step, SiN waveguides and microresonators are defined and etched using inductively coupled plasma (ICP) and then in the second step of EBL, nanorods are defined and then electron beam evaporation is used to deposit the gold layer followed by a lift-off process. Accurate alignment between the two steps of lithography is crucial for accurate positioning of the nanorods. We have achieved registration accuracy of better than 20nm in our fabrication. We will show that in practice, single nanorods (110nm×56nm×20nm) can be efficiently excited by using SiN waveguides with 200nm×700nm cross section and ring microresonators of 10μm radius with the same cross section. The operation wavelength range is around780nm. Efficient excitation of individual nanoantennas enables sensing of a very small amount of target analyte. The tight coupling of plasmonic nanoantennas with the SiN high-index contrast photonic platform promises significant potential for on-chip sensing and spectroscopy applications.
3:15 PM - M8.3
Comparison of the Linear and Nonlinear Optical Hot Spots of Rough Silver Films Used for Surface-enhanced Raman Scattering.
Nicholas Borys 1 , John Lupton 1
1 Physics and Astronomy, University of Utah, Salt Lake City, Utah, United States
Show AbstractRough silver films grown following the Tollens silver mirror reaction are uniquely suited for high resolution single molecule surface-enhanced Raman (SERS) spectroscopy [1]. In addition to SERS, these rough silver films show intrinsic linear luminescence and a nonlinear optical response consisting of second-harmonic generation (SHG) that blinks [2] and continuum emission (CE) that can be used for simple, but high resolution transmission microscopy [3].We use an ensemble of spectroscopic tools on both the linear and nonlinear emission to further study these rough silver films. Using wide-field microscopy we show that both the linear and nonlinear emission from these films originates from discrete diffraction-limited hot spots. Further, by changing the amount of silver coverage, we relate the density and brightness of these hot spots to the film morphology as measured under scanning electron microscopy (SEM). The temporal fluctuations on the second timescale of these hot spots reveal a drastic amount of blinking from the linear hot spot emission while the nonlinear hot spot emission, which is dominated by CE, is essentially stable. Furthermore, time resolved spectroscopy on the picosecond timescale shows that the nonlinear emission is ultrafast within instrument resolution while the linear emission consists of both an ultrafast component and a slower decay component which is indicative of luminescence with a finite lifetime, perhaps arising from a small silver cluster. The above observations indicate that there is an intrinsic difference between emission processes of the linear and nonlinear hot spots. On the other hand, additional studies including excitation spectroscopy and polarization anisotropy measurements indicate that the linear and nonlinear hot spots behave in a similar manner. Such correlated behavior is an indication that although the emission process may be different, the excitation process of the hot spots appears to be the same.A complete understanding and characterization of these rough metal films is crucial for a further understanding and utilization in regards to SERS. For example, we recently showed that a striking anti-correlation exists between the SERS hot spots and the nonlinear emission hot spots in these films thus potentially providing a method that can be used to assess the quality of a SERS substrate [4]. Accordingly, these additional studies provide a wealth of information that can be used to further understand the optical enhancement effects responsible for SERS. [1] Walter et al. Phys. Rev. Lett. 98, 137401 (2007).[2] Borys et al. Phys. Rev. B 80 161407 (2009).[3] Chaudhuri et al. Nano Lett. 9, 952 (2009).[4] Walter et al. J. Am. Chem. Soc. 130, 16830 (2008).
3:30 PM - M8.4
Modification of Raman Spectra on Nanoengineered Plasmonic Substrates.
Semion Saikin 1 , Yizhuo Chu 2 , Dmitrij Rappoport 1 , Kenneth Crozier 2 , Alan Aspuru-Guzik 1
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractSurface enhanced Raman spectroscopy provides a highly sensitive molecular detection method with a great potential for chemical sensor applications. The signal enhancement effects are attributed to a strong amplification of the electromagnetic fields near the resonances of plasmonic substrates and to spatially-local effects, which are commonly referred to as chemical enhancement effects. Additionally, the enhanced spectra are modified compared to the spectra of neat substances: many vibrational frequencies are shifted and relative intensities undergo significant changes upon attachment to the metal. These modifications of Raman spectra complicate molecular identification, especially in mixtures, where responses from different analytes may interfere with each other.We explore the origin of the Raman spectra modification of benzenethiol adsorbed on nanostructured gold surfaces with engineered plasmonic resonances. Two major contributions are identified: the variation in electromagnetic enhancement with frequency and the chemical effect. We show that access to the extinction spectra of substrates in combination with first-principle computation of small cluster models of metal-molecular complexes provides a readily accessible tool for the semi-quantitative characterization of the Raman spectra modification effect. We introduce a theoretical approach which accounts for both plasmonic and chemical effects in the molecular response within a unified approximation scheme.
3:45 PM - M8.5
Optimization of Optical Antenna Trapping.
Kai Wang 1 , Kenneth Crozier 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractStandard ways of numerical calculation of the potential depth, a key parameter of optical trapping by nanostructures such as optical antennas, are usually very computationally extensive. The dipole approximation can simplify this problem greatly, but suffers from inaccuracy, especially when the size of the particle to be trapped is comparable to the decay length of the field around the plasmon resonance structure. We propose a new way, comprising a first order correction to the dipole approximation, to calculate the optical trapping potential depth. This method gives reasonably accurate results, differing by <10% from the exact results found using the Maxwell stress tensor (MST) method. It requires much less numerical calculation than MST, however. Using this method, the optical trapping potential depth for polystrene particles with a range of diameters by various types of optical antennas are calculated. Interestingly, the results show that antennas with the strongest surface field enhancement do not necessarily exhibit the deepest optical trapping potential depth. For a fixed illumination intensity, and for trapping a given particle size, a set of optimized optical antenna designs can be found. If there is a limitation on the maximum heating power from ohmic loss in the optical antenna that can be tolerated, a different set of optimized optical antenna designs can be found. To estimate thermal effects fully, finite element method (FEM) calculations are made of the thermal convection velocity and temperature distributions. This work could be very useful in future experimental studies of resonance enhanced optical forces from optical antennas.
4:00 PM - M8: Sensing
BREAK
M9: Metamaterials
Session Chairs
Wednesday PM, December 01, 2010
Room 200 (Hynes)
4:30 PM - **M9.1
Recent Progresses in Optical Metamaterials.
Xiang Zhang 1
1 Mechanical Engineering, University of California at Berkeley, Berkeley, California, United States
Show AbstractMetamaterials are artificially designed subwavelength composites that possess extraordinary properties not existing in naturally occurring materials. In particular, they can alter the propagation of electromagnetic waves resulting in negative refraction, subwavelength focusing and even in cloaking of macroscopic objects. Such unusual properties can be obtained by a careful design of dielectric or metal-dielectric composites on a deep sub-wavelength scale. The metamaterials may have profound impact in wide range of applications such as nano-scale imaging, nanolithography, and integrated nano photonics. I will discuss a few recent experiments demonstrating intriguing phenomena associated with Metamaterials. These include subdiffraction limit imaging and focusing, low-loss and broad-band negative-refraction of visible light, negative-index metamaterials and the first cloak operating at optical frequencies; an all-dielectric “carpet cloak” with broad-band and low-loss performance. I will also present our recent demonstration of a deep sub-wavelength plasmonic laser.
5:00 PM - M9.2
Metamaterials Design Using Numerical Optimization Methods.
Kenneth Diest 1 , Luke Sweatlock 1 , Daniel Marthaler 1
1 Aerospace Research Labs, Northrop Grumman, Redondo Beach, California, United States
Show AbstractElectromagnetic resonances in sub-wavelength metallic structures can be used to design composites with optical properties not found in naturally occurring materials. Such optical metamaterials have recently received a large amount of attention for their use in many exotic physical effects including slow light, optical chirality, and nanoscale focusing of light, and these materials hold great promise for applications in many areas of optical engineering. Technological applications of engineered materials will require increasingly sophisticated design of the metamaterials' broadband spectral response. As the complexity of the specified requirements increases, so too does the number of geometrical parameters required to supply sufficient design degrees of freedom. In this work, we characterize optical metamaterials with full-field electromagnetic (FDTD) simulations, and convert the output to a scalar valued objective functions. Evolution of the device design is then cast as a minimization problem in parameter space, which we address using gradient descent and a derivative-free, nonlinear mesh adaptive search technique. We apply these numerical optimization methods, in combination with full-field electromagnetic simulations, to tailor the broadband spectral response of metamaterials to have predetermined resonances. A test case is presented in which oblate spheroids are modeled using both an analytic, quasistatic scattering model and FDTD simulations. The results of both models and search techniques are compared and the derivative-free technique is shown to be a more robust and efficient search algorithm. This technique is then used to optimize the design of gold and silver split-ring resonators to pre-specified broadband resonances at 1500 and 2500 nm with pre-determined reflection intensities at those wavelengths. Finally, this technique is used to design split-ring resonator “notch filters”, with narrow pass bands at 1310, 1550, and 1800 nm which have a 45% change in reflectivity at the pass band and a corresponding linewidth of 185 ± 40 nm.
5:15 PM - M9.3
Compliant Optical Metamaterials with Large Frequency Tunability.
Koray Aydin 1 , Imogen Pryce 1 , Yousif Kelaita 1 , Ryan Briggs 1 , Harry Atwater 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractResonant optical elements such as optical antennas, coupled nanoparticles and split ring resonators (SRRs) have recently garnered a burgeoning amount of interest because of their ability to control the flow of light at the nanoscale. Light-matter interactions can be enhanced by the high electric fields attainable in the nanoscale gap regions of such resonant structures. Accessing and exploiting the high electric fields using resonator elements may find applications in surface enhanced sensing, light trapping in solar cells and improving the efficiency of light emitting devices. Resonant elements are prepared using either top-down or bottom-up fabrication techniques after which the devices are passive and not tunable. Controlling the size of the gap regions and the ability to tune the resonance frequency via application of an external stimulus remain a challenge.
Here, we present the novel use of an elastomeric substrate as a compliant platform for tuning the response of metamaterials based on coupled SRR. Dynamic control of metamaterial resonance frequencies has been demonstrated using semiconductors, liquid crystals, and phase-transition materials; however, due to the limited material responses, linewidth tunability has yet to be achieved. Particularly at optical frequencies, the fabrication limitations make it much more difficult to obtain the drastic optical and electrical changes required to significantly tune the metamaterial resonance frequency. We demonstrate the first mechanically tunable metamaterial in the near infrared, where modifying the distance between coupled resonator elements drastically changes the resonance frequency by a line-width (~400 nm).
Coupled resonator elements are first fabricated on Si using e-beam lithography and the structures are then transferred to PDMS, an elastomeric polymer. Fourier Transform Infrared (FTIR) spectrometry is used to characterize the optical properties of the compliant infrared metamaterials. We examine uncoupled and coupled split-ring resonator designs with resonance wavelengths spanning the 2 – 6 μm range. We show that by introducing coupled resonator elements, the planar metamaterial arrays can be designed to yield greater than linewidth tunability (~400 nm) upon uniaxially stretching the substrate to 50% strain. We show that the gap size between coupled resonator elements can be controlled by stretching the polymer. Moreover, we investigated a tunable Fano resonance using coupled plasmonic elements and showed that by changing the coupling strength between two individual resonators, the Fano resonance can be modulated. We will also discuss the application of compliant optical metamaterials to surface enhanced infrared spectroscopy, in which the resonance wavelength of the metamaterial-based sensor can be tuned to overlap with the vibrational mode of the C-H stretch bond. Preliminary results suggest that absorption signal can be enhanced by a factor of almost 180.
5:30 PM - M9.4
Design, Fabrication and Characterization of Wide-angle Polarization-insensitive Optical Metamaterial Absorbers.
Zhi Hao Jiang 1 , Seokho Yun 1 , Fatima Toor 2 , Douglas Werner 1 , Theresa Mayer 1
1 Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractMetamaterial research has been an area of substantial interest over the last decade due to the existence of exotic electromagnetic properties not readily found in natural materials. Various novel metamaterial devices have been realized in the microwave, terahertz, infrared, and even visible wavelength bands. These previously reported metamaterial designs, including sub-diffraction-limited negative index super-lenses and electromagnetic invisibility cloaks, have primarily attempted to exploit the real parts of the permittivity and permeability (or refractive index) and minimize the absorption loss. However, the recently proposed concept of a perfect metamaterial absorber has attracted the attention of both the scientific and engineering communities, which exploits control over the oft-overlooked loss component (extinction coefficient) of the optical constants. The basic idea is to match the structure's input impedance to free space while simultaneously maximizing the loss component of the effective refractive index, thus allowing the implementation of thin metamaterial absorbers with high absorption efficiency. To date, most work on metamaterial absorbers has been performed only in the microwave and terahertz bands; the absorption performance of these existing designs has also been limited by strong sensitivity to polarization and angle-of-incidence. In this talk, we introduce a feed-forward design methodology, which employs a robust genetic algorithm optimization technique coupled with an efficient full-wave electromagnetic solver, for the synthesis of metamaterial absorbers in the optical range. Several optimized designs possessing multiple absorption bands that are independent of both the polarization and the angle-of-incidence will be presented. Particularly, a dual-band design for the mid-IR was fabricated by electron beam lithography followed by metal lift-off. The fabricated structure consists of a patterned top Au screen separated from an Au backplane by a thin polyimide spacer. The measurement of the absorber sample was found to be in strong agreement with the numerical simulation, therefore validating the predicted device performance. Moreover, the performance of the resulting flexible highly efficient metamaterial absorber is independent of the mounting structure or device it is intended to shield.
5:45 PM - M9.5
Rotated Fishnet Metamaterial Design for Compact and High Speed Optical Modulator.
Hyungjin Ma 1 , Jun Xu 2 , Nicholas Fang 2
1 Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show Abstract We investigate a novel design of metamaterial for compact and high speed optical modulator. A LC-circuit-based modeling for fishnet metamaterial modulator reveals two operation modes: one due to absorption and the other due to impedance matching. To improve the coupling of gain media with external optical excitation, the fishnet metamaterial is rotated and further optimized based on the model. Numerical studies indicate a strong modulation of optical signal, when the resonance frequency of the metamaterial is detuned with optical excitation. Experimentally, the rotated fishnet structure is fabricated using a sequence of e-beam evaporation, focused ion beam milling, sputtering and electrochemical etching. A pump-probe technique is employed to measure the modulation characteristics. Our results show the modulation depth of 34% and very fast operation time of 2ps with relatively low pump fluence. This device can be a potential candidate for the compact on-fiber modulator with high speed, small footprint and low power consumption.
M10: Poster Session II
Session Chairs
Thursday AM, December 02, 2010
Exhibition Hall D (Hynes)
9:00 PM - M10.1
Engineering Infrared Nanoantenna Arrays with Nanostencil Lithography for Spectroscopic Sensing.
Serap Aksu 1 2 , Ahmet A. Yanik 2 3 , Ronen Adato 2 3 , Alp Artar 2 3 , Min Huang 2 3 , Hatice Altug 1 2 3
1 Materials Science and Eng., Boston University, Allston, Massachusetts, United States, 2 Photonics Center, Boston University, Boston, Massachusetts, United States, 3 Electrical and Computer Eng., Boston University, Boston, Massachusetts, United States
Show AbstractIn this talk, we will demonstrate a novel fabrication approach for high-throughput fabrication of engineered infrared plasmonic nanorod antenna arrays with nanostencil lithography (NSL). NSL technique, relying on deposition of materials through a shadow mask, offers the flexibility and the resolution to radiatively engineer nanoantenna arrays for excitation of collective plasmonic resonances. As stencil, we use suspended silicon nitride membrane patterned with nanoapertures and fabricate nanorod antenna arrays. Our spectral measurements and electron microscopy images faithfully confirm the feasibility of NSL technique for large area patterning of nanorod antenna arrays with optical qualities achievable by electron-beam lithography. Furthermore, we show nanostencils can be reused multiple times to fabricate selfsame structures with identical optical responses repeatedly and reliably. This capability is particularly useful when high-throughput replication of the optimized nanoparticle arrays is desired. In addition to its high-throughput capability, NSL permits fabrication of plasmonic devices on surfaces that are difficult to work with electron/ion beam techniques. Nanostencil lithography is a resist free process thus allows the transfer of the nanopatterns to any planar substrate whether it is conductive, insulating or magnetic. As proof of the versatility of the NSL technique, by simply changing the aperture pattern on the silicon nitride membrane, we show fabrication of plasmonic structures in variety of geometries and on different substrates. Nanostencil Lithography enables plasmonic substrates supporting spectrally narrow far-field resonances with enhanced near-field intensities. Overlapping these collective plasmonic resonances with molecular specific absorption bands can enable ultrasensitive vibrational spectroscopy. We will also present our recent results on spectroscopic identification of proteins with antenna arrays fabricated by nanostencil lithography.
9:00 PM - M10.10
Fabrication of Bowtie Slot Nanoantennas and Nanodisc Dimer Structures using ``Salting Out-quenching" Technique and Colloidal Lithography.
Bala Krishna Juluri 1 , Neetu Chaturvedi 2 , Qingzhen Hao 1 4 , Lasse Jensen 3 , Darrell Velegol 2 , Tony Jun Huang 1
1 Department of Engineering Science and Mechanics, Pennsylvania State University, University park, Pennsylvania, United States, 2 Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 4 Department of Physics, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractNanoparticle dimers consisting of nanoparticles at close proximity and bowtie slot antennas consisting of bowtie aperture in metal film have attracted immense attention due to their characteristic large enhancements in electric field. This has opened up unprecedented opportunities in surface enhancement Raman spectroscopy, fluorescence enhancement, second harmonic light generation, lasing, broadband light harvesting etc. Traditionally, top-down fabrication methods (e-beam and focused ion beam) are used to fabricate these structures. However both these methods are expensive and not scalable. On the other side, some progress has been made in bottom-up fabrication methods (random self-assembly and DNA hybridization) to make nanoparticle dimer structures. However these methods rely on capillary forces which result in random formation of dimers or complicated DNA functionalization and separation to enable dimer fabrication. Here, we report a combination of bottom-up and top-down methods to fabricate bowtie slot nanoantennas and nanodisc dimer structures over a large area with easily achievable geometric tunability. We use “Salting Out-Quenching” (SQ), a novel bottom-up technique to fabricate colloidal doublets from polystyrene (PS) singlets and use them as templates for top-down fabrication of bowtie slot nanoantennas and nanodisk dimer structures. The formation of colloidal doublets of otherwise stable suspension is stimulated by increasing the ionic strength and quenching the reaction approximately after the rapid flocculation time. These results in the formation of PS doublets with a yield (defined as ratio of twice the number of doublets to singlets before SQ technique) to approximately 40%, which can be further improved by separation of singlets. Bowtie slot antennas are fabricated by settling PS doublets synthesized by SQ technique on glass substrates, depositing metal film and later removing the doublets. Nanodisc dimers are obtained by settling colloidal doublets on gold film, performing Ar milling with colloidal doublets acting as etch masks and finally removing beads. Optical properties of these structures can be further tuned by controlling the gap in bowtie apertures and nanodisc dimers. Oxygen reactive ion etching of PS beads was used to reduce the diameter and hence the gap in dimers and apertures after subsequent processes. Using the above process, we achieved repeatable control over gaps in dimers and bowtie aperture structures anywhere between 50 nm and 10 nm. Further geometric tunability is achieved by changing the thickness of metal film and changing the diameter of PS singlets. Plasmonic properties of these structures are currently being characterized by dark field microscopy and validated against electrodynamic calculations.
9:00 PM - M10.11
The Design and Fabricated GaxIn1-xAs Bowtie Photomixer for Terahertz Continuous-wave Power Enhancement.
Dongsuk Jun 1
1 , ETRI, Deajeon Korea (the Republic of)
Show AbstractThe Recent Trend of photomixer compensates the defect of compact, low-cost and high-power, high bandwidth and high repetition rate terahertz sources that has limited the widespread scientific and commercial adoption of terahertz technology. Narrow band gap semiconductors are strong candidates for compact and lightweight time-domain THz spectroscopy and imaging systems powered by femtosecond fiber lasers with emission wavelengths at λ=1550 nm (E=0.8eV). Therefore, qualitative and quantitative understanding of THz emission from narrow direct band gap semiconductors has attracted great interest recently. Terahertz PCA (Photoconductor antenna) based on GaxIn1-xAs are not well established. The primary reason for this is the lack GaxIn1-xAs with simultaneously high resistivity (>106 Ωcm), high mobility (>103 cm2 /Vs), and subpicosecond carrier lifetimes (<1 ps).PCA design is a bowtie and fold dipole combined with the advantages of bowtie antenna. Power enhancement to bowtie antenna input resistance of high designed. The finger was fabricated in the shape of interdigitated capacitor having 4 fingers with 0.3 um finger width and 1.7 um finger gap, and located at the feed point of a resonant antenna. The fabricated GaxIn1-xAs thin film is grown by metal organic chemical vapor deposition (MOCVD). For the fabrication of the GaxIn1-xAs bowtie photomixer, 1.3 MeV Fe+ ions were irradiated onto a 0.7-μm-thick undoped GaxIn1-xAs layer on a 2-inch InP wafer with the dose of 6x1014 cm2. And then, the wafer was annealed in a rapid thermal anneal (RTA) system at 500°C in a hydrogen environment. Finally, the antenna and the interdigitated finger patterns were defined by using a stepper system and formed by the evaporation of Ti/Au metals. A cryogenic bolometer operating at 4.2 K was used to measure the power of THz wave emitted from the photomixers. In order to enhance the detection sensitivity, we used a lock-in amplifier with a square-wave pulse generator which modulated the photomixer bias. The high carrier mobility along with high resistivity and subpicosecond carrier lifetimes make GaxIn1-xAs:Fe an excellent candidate for PCA based terahertz emitters. The band gap of GaxIn1-xAs:Fe is low enough.
9:00 PM - M10.12
SERS Measurement on Shape-controlled Au Nanodot Array Prepared by Using Anodic Porous Alumina Mask.
Toshiaki Kondo 2 , Kazuyuki Nishio 1 2 , Hideki Masuda 1 2
2 , Kanagawa Academy of Science and Technology, Sagamihara Japan, 1 , Tokyo Metropolitan University, Hachioji Japan
Show AbstractThe functional optical devices based on the localized surface plasmon (LSP) in small metal particles have attracted increasing attention due to its applicability in various fields, such as chemical or biological sensing. We have reported the fabrication of ordered metal nanodot arrays on the substrate using anodic porous alumina masks, and its application to surface-enhanced Raman scattering (SERS) measurements [1]. SERS on the metal fine structures is a typical phenomenon originating from the enhancement of the electric field of incident light. There have been numerous reports on the preparation of an ordered nanostructure of metals for optimizing the efficiency of SERS. However, processes for precise control of the shape of metal nanostructures have not been established. The advantage of the use of vacuum deposition using an anodic porous alumina mask for the preparation of the metal nanostructure for SERS is the controllability of the dimension of the dots in addition to the ease of preparation. In this presentation, we describe the dependence of the SERS efficiency of pyridine on the shape-controlled Au nanodot arrays on a substrate. The shape of nanodot was controlled by changing the hole shape of the porous alumina mask. The hole shape of the mask was controlled by texturing process before anodization of Al [2]. By using these mask for thermal deposition of Au, the circular, rectangular, triangular, and rod shaped Au nanodots were obtained. The height of the dots was controlled by changing the nominal thickness of the evaporated Au. Raman scattering spectra of pyridine were obtained using a Raman scattering spectrometer equipped with a He-Ne laser (633 nm) as a light source. The substrate with the nanodot array was dipped into pyridine solution and dried in air before measurements. Two characteristic peaks from the adsorbed pyridine molecules were observed at 1014 cm-1 and 1040 cm-1. The SERS intensity was dependent on the shape of nanodots. The obtained SERS substrates will be used for the Raman spectra measurement with high sensitivity.[1] T. Kondo, F. Matsumoto, K. Nishio, and H. Masuda, Chem. Lett., 37, 466 (2008).[2] H. Masuda, H. Asoh, M. Watanabe, K. Nishio, M. Nakao, and T. Tamamura, Adv. Mater., 13, 189 (2001).
9:00 PM - M10.13
Probe and Instrument Development for Tip Enhanced Raman Scattering and Shadow Near-field Scanning Optical Microscopy.
Hesham Taha 2 , Rimma Dichter 2 , Aaron Lewis 1
2 , Nanonics Imaging Ltd., Jerusalem Israel, 1 Department of Applied Physics Selim and Rachel Benin School of Engineering and Computer Science., The Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractResearch will be described that has focused on optimizing the essential components of instrumentation and probes for tip enhanced Raman scattering (TERS) and associated techniques based on full integration of scanned probe microscopy with microRaman spectroscopy. The results of this research effort have allowed for a general TERS solution that can be applied for both opaque and transparent samples. It also permits for integration with all upright, inverted and dual 4 Pi microscope solutions. The probes that have worked best have been those that are based on single gold nanoparticles at the exposed tip of a low dielectric glass probe. These probes were originally designed for use in tip enhanced non-linear optical microscopy. Such probes will be compared to other solutions in the literature especially those based on etched wires of gold or silver or coated silicon probes. The data indicate that single gold nanoparticle probes provide artifact free TERS results.
9:00 PM - M10.14
Dimers of Silver Nanospheres: Facile Synthesis and Application in Surface-enhanced Raman Scattering.
Weiyang Li 1 , Younan Xia 1
1 Biomedical Engineering, Washington University, Saint Louis, Missouri, United States
Show AbstractThere has been a renewed interest in surface-enhanced Raman scattering (SERS) due to its application in ultrasensitive trace analysis and single-molecule detection. It has been shown that the hot spot, or the gap region of a pair of strongly coupled Ag (or Au) nanoparticles, can provide an SERS enhancement factor several orders in magnitude greater than those of individual nanoparticles. We have successfully demonstrated a simple and versatile method that generates dimers of Ag nanospheres by etching Ag nanocubes with Fe(NO3)3 in ethanol with the assistance of poly(vinyl pyrrolidone) (PVP). By starting with Ag nanocubes of different sizes, we obtained well-defined dimers of Ag spheres 40, 63, and 80 nm in diameter with percentages of dimerization >60%. Since this approach can be extended to fabricate dimers of Ag nanospheres with a range of different sizes, it allows for a systematic study of the hot-spot phenomenon in SERS. By correlating with SEM imaging, we have measured the SERS enhancement factors for individual dimers consisting of Ag spheres 40, 63, and 80 nm in diameter, and a value as high as 1.7e+8 was obtained for the dimer made of 80-nm spheres. These new dimers consisting of Ag nanospheres hold great promise in ultrasensitive and single-molecule detection by SERS and are expected to find a range of applications in fields such as surface plasmonics, chemical and biological sensing, and imaging contrast enhancement.
9:00 PM - M10.15
Beam Steering Devices with Nanohole Antennas.
Takayuki Matsui 1 , Atsushi Miura 1 , Tsuyoshi Nomura 1 , Hisayoshi Fujikawa 1 , Kazuo Sato 1 , Naoki Ikeda 2 , Daiju Tsuya 2 , Yoshimasa Sugimoto 2 , Hideki Miyazaki 2 , Kiyoshi Asakawa 2 , Masanori Ozaki 3 , Masanori Hangyo 3
1 , Toyota Central R&D Labs., Inc., Aichi Japan, 2 , National Institute for Materials Science, Tsukuba Japan, 3 , Osaka University, Osaka Japan
Show AbstractWe have been developing a planar prism with metal-dielectric composite structures for beam steering applications, especially for laser radar. Conventional laser radar consists of, mainly, three components including a laser, a photo diode and a polygon mirror. While conventional one limits the size and costs, a planar prism has a potential to realize on-chip laser radar. That's our motivation. To realize a planar prism, a metal-dielectric composite structure, known as a metamaterial, is a key issue. This artificial material allows us to control wave propagation. We have focused on an alternating stack of metal and dielectric film with sub-wavelength holes. With changing a hole shape, we can control an effective refractive index. Therefore continuous change of the hole shape result in a in-plane graded index material. When a light goes through a perpendicular to this plane, this metal-dielectric composite structures act as a planar prism.We have designed the structure which has 5 Al layers embedded in SiO2. Each layer of the stack is 100nm thick, composed of 20nm thick Al film on 80nm thick SiO2 layer. The hole array is composed by square holes whose lattice constant is 1000nm. In order to build graded index distribution, the curvatures of corners of the square holes, R, are controlled. The R's are gradually changed from 0nm (square) to 250nm (circle). This prism is designed for telecom wavelength range (approx. 1500nm). From a computational simulation, we have found that this prism has 12.5 degree of beam steering capability.To verify our designed prism, we have fabricated two basic structures which has 5 Al/SiO2 layer stacks with sub-wavelength hole array. One has circular holes, and the other has square holes. These two are fabricated by electron-beam lithography and a reactive ion etching. In addition, we fabricated a special microscope system which contains three optical systems. The first is a basic microscope to magnify the real space images. The image forms on a CCD through objective lens and imaging lens. The next is a microscope to observe an angular distribution of the light from the sample. In this system, we can observe a Fourier plane image which is formed at the back focal point of above mentioned objective lens. And the last is a micro spectroscope system. We can obtain a spectrum of confined regions. Until now, we have measured transmission spectra of above mentioned two basic structures with circular or square sub-wavelength holes. The spectra of those two are in good agreement with the simulation. Now, we have fabricated an in-plane graded index structures with sub-wavelength holes, whose hole shape is changing continuously from square to circle in one plane.This work was partly supported from NEDO program.
9:00 PM - M10.17
A Negative Index Metamaterial for UV / Visible Light: Theory and Experiment.
James Parsons 1 , Ewold Verhagen 1 , Rene de Waele 1 , Laurens Kuipers 1 , Albert Polman 1
1 , FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractWhilst there are no examples of naturally occurring negative-index materials at microwave and optical frequencies, a number of artificial metamaterials have been experimentally realised in recent years using periodic arrays of sub-wavelength resonators. In addition to resonator-based metamaterials, left-handed behaviour has also been observed in planar metal-insulator-metal (MIM) waveguides, due to the dispersion of the coupled surface plasmon-polariton (SPP) modes in these structures. Despite these advances, an isotropic left-handed medium at ultraviolet and visible frequencies has not been demonstrated so far. At these frequencies, resonator-based metamaterials are unsuitable candidate structures, since the electric and magnetic polarisabilities are isotropic only for resonators which possess cylindrical or spherical symmetry and absorption losses are extreme.Here, we demonstrate a three-dimensional negative index metamaterial formed from a periodic arrangement of MIM waveguides. The SPP modes of individual MIM waveguides facilitate the two-dimensional negative refraction of waves which propagate in the plane of the waveguides. In addition, negative refraction occurs along the third dimension (perpendicular to the metal-insulator interfaces) which arises from coupling between adjacent waveguides. We use both coupled mode theory and finite difference time domain simulations to demonstrate that refraction of light into the coupled MIM geometries can be engineered to be negative, and optimise the design for an isotropic negative index. When plotting the modal dispersion of the periodic structure, the isotropic response is verified by a spherical isofrequency surface in a wave vector diagram. Losses are characterised by a figure of merit (defined as Re(n)/Im(n)) which is of the order of 10, which is large considering the operating wavelength of 350 - 600 nm.Experimental samples based upon our optimised design are fabricated by using a focused ion beam to mill one-dimensional gratings with a double-periodicity of 65 nm / 45 nm / 30 nm / 45 nm into a 100 nm thick Silicon Nitride membrane. A silver layer with thickness 100 nm is evaporated into the grating using resistive heating, forming a periodic metal-insulator structure which is shaped into a prism geometry by further ion beam milling. The prism surface is milled at an angle of 1.1 degrees with respect to the surface of the membrane. We fabricate prisms with gradients running parallel to both the xy and yz planes, allowing the refraction along polar and azimuthal angles to be characterised independently. Fourier plane imaging allows measurement of the refraction angle of a beam of light in the material and for wavelengths below 400 nm negative refraction is observed experimentally for the first time.
9:00 PM - M10.18
Towards Optimized Geometries of Plasmon Resonant Nanostructures.
Prathamesh Pavaskar 1 , Jesse Theiss 1 , Stephen Cronin 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractWe perform finite difference time domain (FDTD) simulations to find the electric field intensity at the center of a cluster of plasmonic nanoparticles irradiated by a planewave source. Using an iterative optimization algorithm, the electric field intensity is maximized. The optimized geometries found are non-symmetric and non-intuitive, and cannot be obtained by analytical calculation methods. There is a monotonic increase in the optimized electric field intensity with the number of nanoparticles in the cluster. This produces a 6 million-fold enhancement in the surface enhanced Raman spectroscopy (SERS) intensity with respect the incident electromagnetic field, and a 25-fold enhancement with respect to a linear chain of nanoparticles. Experimentally, we investigate a novel method that uses angle evaporation to produce 1-2 nm gaps in plasmonic nanostructures. The plasmonic activity of these nanostructures is measured and evaluated both experimentally and theoretically using SERS measurements and FDTD simulations, respectively. We also evaluate the performance of thin plasmonic films as efficient SERS substrates by FDTD simulations. These simulations of the plasmonic films are based on their high resolution transmission electron microscope images, and yield extremely large SERS enhancement factors.
9:00 PM - M10.19
Polynorbornene as a Low Loss Matrix Material for IR Metamaterial Applications.
Roger Rasberry 1 , Yun-Ju Lee 2 , James Ginn 3 , Paul Hines 4 , Christian Arrington 5 , Michael Sinclair 2 , Paul Clem 6 , Andrea Sanchez 1 , Shawn Dirk 1
1 Organic Materials, Sandia National Laboratories, NM, Albuquerque, New Mexico, United States, 2 Electronic Materials and Nanostructures, Sandia National Laboratories, NM, Albuquerque, New Mexico, United States, 3 Applied Photonic Microsystems, Sandia National Laboratories, NM, Albuquerque, New Mexico, United States, 4 Integrated Microdevice Systems, Sandia National Laboratories, NM, Albuquerque, New Mexico, United States, 5 Photonic Microsystems Technologies, Sandia National Laboratories, NM, Albuquerque, New Mexico, United States, 6 Direct Write Technology Group, Sandia National Laboratories, NM, Albuquerque, New Mexico, United States
Show AbstractNovel low loss photopatternable matrix materials for IR metamaterial applications were synthesized using the ring opening metathesis polymerization reaction (ROMP) of norbornene followed by a partial hydrogenation to remove most of the IR absorbing olefin groups which absorb in the 8-12 μm range. Photopatterning was achieved via crosslinking of the remaining olefin groups with alpha, omega-dithiols via the thiol-ene coupling reaction. Since ROMP is a living polymerization the molecular weight of the polymer can be controlled simply by varying the ratio of catalyst to monomer. In order to determine the optimum photopattenable IR matrix material we varied the amount of olefin remaining after the partial hydrogenation. Hydrogenation was accomplished using tosyl hydrazide. The degree of hydrogenation can be controlled by altering the reaction time or reaction stoichiometry and the by-products can be easily removed during workup by precipitation into ethanol. Several polymers have been prepared using this reduction scheme including two polymers which had 54% and 68% olefin remaining. Free standing films (approx. 12 μm) were prepared from the 68% olefin material using draw-down technique and subsequently irradiated with a UV lamp (365 nm) for thirty minutes to induce crosslinking via thiol-ene reaction. After crosslinking, the olefin IR-absorption band disappeared and the Tg of the matrix material increased; both desirable properties for IR metamaterial applications. The polymer system has inherent photopatternable behavior primarily because of solubility differences between the pre-polymer and cross-linked matrix. Photopatterned structures using the 54% as well as the 68% olefin material were easily obtained. The synthesis, processing, and IR absorption data and the ramifications to dielectric metatmaterials will be discussed.
9:00 PM - M10.2
Broadband Polarization-independent Light Absorption over the Whole Visible Spectrum via Ultra-thin Plasmonic Absorbers.
Koray Aydin 1 , Vivian Ferry 1 , Ryan Briggs 1 , Harry Atwater 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractMetallic nanostructures have been shown to absorb light resonantly around their plasmonic resonance wavelengths, however such resonant absorption is limited to a narrow band of wavelengths and generally depends on the incident electromagnetic field polarization. Harvesting unpolarized light over broadband wavelength ranges is required for many applications including solar energy conversion and black-body thermal emission. To overcome the limited optical response from conventional plasmonic nanostructures such as nanoparticles, nanoslits and metallic gratings, novel and unconventional designs are needed. Here, we propose a three-layer metal-insulator-metal (MIM) layer absorber device, in which the top layer consists of an array of crossed trapezoids, which allows us to tune plasmonic resonances over the whole visible spectrum yielding resonant absorption at relatively broad range of energies.
Our absorber devices are formed as a three-layer /SiO2/Ag with a total thickness of 260 nm which is clearly a subwavelength device. 60-nm SiO2 middle layer is sandwiched between 100-nm Ag layers. The top Ag layer is structured as an array of crossed trapezoid shaped resonators, with an in-plane periodicity of 300 nm. Full-field electromagnetic simulations indicate that the trapezoid nanostructure arrays yield localized surface plasmon resonances over a broader wavelength regime. Crossed trapezoid array structure provides an in-plane symmetry assuring that the absorber is resonant both for transverse-electric (TE) and transverse-magnetic (TM) polarizations of the incident light.
We fabricated the absorber structures using electron beam lithography followed by a metal deposition and lift-off process. An inverted optical microscope is used to measure the total transmission and reflection and absorption where absorbance is derived from the relation A=1-T-R. We observed broadband resonant light absorption between 400-750 nm with an average absorption value of 0.67. Absorption in the metallic sections is calculated using the divergence of Poynting vector and results are extremely good agreement with the experimental data.
We will also discuss the tunability of broadband absorption peak with different parameters including the thicknesses of top and bottom metal layer and SiO2 thickness, as well as the refractive index of the insulating spacer layer. We will also present initial simulation results for using broadband resonant absorbers in thin film solar cells.
9:00 PM - M10.22
Surface-enhanced Infrared Absorption and Raman Scattering of Adsorbate Molecules on Self-assembled Au Nanorods.
Li-Lin Tay 1 , John Hulse 1 , Nelson Rowell 1
1 , National Research Council, Ottawa, Ontario, Canada
Show AbstractWe have investigated the surface enhanced infrared absorption spectroscopy (SEIRAS) of cetyltrimethylammonium bromide (CTAB) functionalized Au nanorods that are 60 nm long and 20 nm in diameter. The ambiphilic nature of the CTAB molecule directed the assembly of the Au nanorods on the surface of Si substrates. The coupling of the Au nanorods resulted in a shift and broadening of their surface plasmon resonance (SPR), such that the resonance extended into the near-IR and mid-IR spectral ranges, thus enabling the study of surface adsorbed species with SEIRAS and SERS. The large and localized optical fields present in the interparticle gaps where some of the CTAB molecules reside made them readily detectable with these vibrational spectroscopies. For the SEIRAS study, we used an infrared imaging microscope containing a focal plane array (FPA) detector coupled to a scanning FTIR spectrometer. The hyperspectral chemical images comprising 128x128 elements had a spatial resolution of 5 um. Separate reflectance spectra ranging from 900 to 4000 cm-1 were acquired simultaneously for each element. The spatial distribution of Au nanorods on the Si substrate was non-uniform. The C-H stretches (~ 2900 cm-1) of the CTAB molecules colocalized with the location of Au nanorods and their spectral signature varied widely across the image both in absorption strength and spectral line shape. Due to conduction electron effects in the adjacent metal, the reflectance resonances for the CTAB molecules were intense with Fano-type lineshapes, which were asymmetrically increased on the high wavenumber sides of the lines and had reflectance minima 9 cm-1 lower than the actual vibrational frequencies. When the asymmetric reflectance lines were simulated with an effective medium model for a layered thin film system comprised of an organic layer, with a dielectric constant incorporating harmonic oscillator C-H vibrations, and a 1 nm thick gold layer, with a Lorentz-Drude dielectric function, on a Si substrate, good qualitative agreement was obtained with the measured Au nanorod-CTAB reflectance spectrum. For the metal, such a small model thickness – representative of the averaged Au nanorod coverage – was needed to obtain the asymmetric SEIRA lineshape, which arose from coupling of the CTAB vibrational modes and the metal’s conduction electrons (i.e., SPR) and from interference in the metal. We will compare the results obtained on SEIRAs and SERS and comment on the applications of self-assembled nanostructures as chemical sensors.
9:00 PM - M10.23
Integrated Photomixer/Resonant-antenna on Nitrogen-ion-implanted GaAs for Terahertz Continuous-wave Power Enhancement.
Han-Cheol Ryu 1 2 , Sungil Kim 1 , Se-Young Jeong 1 , Min-Hwan Kwak 1 , Seung-Beom Kang 1 , Dong-Suk Jun 1 , Mun-Cheol Paek 1 , Kwang-Yong Kang 1 , Seong-Ook Park 2
1 , Electronics and Telecommunications Research Institute, Daejeon Korea (the Republic of), 2 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractWe fabricated and characterized the photoconductive integrated photomixer/resonant-antenna on nitrogen-ion-implanted GaAs. Nitrogen ions with energy of 400 keV and doses ranging from 1x10^13 to 1x10^16 cm^-2 were implanted into GaAs substrates. The post-implantation annealing dynamics were investigated to control the carrier lifetime of the N+-implanted GaAs and increase the terahertz continuous-wave output power at antenna resonant frequency. The annealing was performed at various temperatures from 300 to 700 °C for 10 min in nitrogen atmosphere by using rapid thermal annealing furnace. The carrier lifetime of the annealed N+-implanted GaAs was characterized by time-resolved reflectance measurements using a femtosecond self-mode-locked Ti:sapphire laser tuned to λ=790 nm. As the annealing temperature of the N+-implanted GaAs with dose 1x10^14 and 1x10^15 cm^-2 is increased up to 550 °C, the carrier lifetime remains about 100 fs. Above 550 °C, the lifetime increases rapidly from 100 fs to around 1.1 ps. Photoconductive photomixer was fabricated in the shape of interdigitated capacitor having 4 fingers with 0.3 um gap and 1.7 um width, and located at the feed point of a resonant antenna. The photocurrent is generated in the voltage-biased photomixers at the difference frequency of two near 855 nm distributed feedback diode lasers. The lasers is stabilized by electronic feedback from precise interferometer to control the difference frequency in the 1 MHz level. The generated photocurrent in the photomixer is coupled to an antenna according to the impedance matching condition between a photomixer output impedance and an antenna input impedance. The output impedance of a photomixer is very high, typically 10~100 kΩ, and the input impedance of a conventional broadband THz antenna is below 100 Ω. Consequently, the terahertz output power is proportional to the input impedance of the antenna. Resonant antennas are suitable for a terahertz continuous-wave at the system operation frequency. For the optimum terahertz continuous-wave antenna design, the input impedance of a resonant antennas was numerically calculated by electromagnetic simulation. The designed antennas were fabricated on the annealed N+-implanted GaAs substrates having various carrier lifetime. The fabricated antennas were measured by two methods, silicon bolometer operating over 300 GHz and all-optoelectronic terahertz continuous-wave photomixing system operating in the range of 10 ~ 1000 GHz. These results show that the optimized resonant antenna and the carrier lifetime of the annealed N+-implanted GaAs could increase the terahertz continuous-wave output power at the system operation frequency.
9:00 PM - M10.24
Fabrication of Tunable Plasmonic Materials with Extremely High Optical Efficiencies.
David Sebba 1 , Andrew Siekkinen 1 , Charles Holz 1 , Thomas Darlington 1 , Steven Oldenburg 1
1 , nanoComposix, Inc., San Diego, California, United States
Show AbstractNoble metal nanoparticles that support surface plasmons have very large scattering and absorption cross sections at visible and near-infrared wavelengths, making these materials promising for numerous optical applications including surface enhanced Raman scattering (SERS), plasmon-enhanced solar cells, and metamaterials. The wavelengths of light at which plasmonic materials absorb and scatter strongly can be tuned to any wavelength in the visible and near-infrared spectral regions by changing particle size, shape, and material. Nonconducting shells can be added to the surface of metal nanoparticles to further tune the spectral properties as well as aid in device integration. Given the sensitivity of plasmonic nanoparticle optical properties to size and shape, applications are limited by the difficulties associated with fabricating the monodisperse and unagglomerated nanoparticles required to obtain the optical cross sections predicted by theory. Numerous plasmonic nanoparticles including gold and silver spheres, rods, and triangular and disclike platelets were fabricated at scale and extensively characterized using transmission electron microscopy, extinction spectroscopy, dark field microscopy, and dynamic light scattering. Measured extinction cross sections are compared to predicted cross sections calculated using validated numerical modeling routines. Measured and predicted cross sections are within a few percent, demonstrating that spherical and anisotropic plasmonic particles with cross sections approaching the theoretically predicted maxima can be fabricated at scale.
9:00 PM - M10.25
Enhanced Transmission Through a Sub-wavelength Aperture Using Epsilon-near-zero Material.
David Slocum 1 , Daniel Wasserman 1 , Viktor Podolskiy 1
1 Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractThere has been recent interest in the phenomenon of wave propagation through materials with relative permittivity near zero [1]. These materials so called epsilon-near-zero (ENZ) materials have unique properties that could potentially be exploited for applications such as all-optical computing or wave-guiding light in sub-wavelength geometries. Intrinsic resonances in many materials result in not only frequency-dependent dielectric constants, but, at certain frequencies, can also result in negative permittivities. At the transition between negative and positive permittivity, such a material will have a naturally-occurring ENZ frequency range. Artificial ENZ metamaterials can also be engineered to operate at desired frequencies. These ENZ materials have previously been shown to improve the transmission of light through sub-wavelength waveguides as well as through waveguides with sharp bends and turns [2,3]. It has also been suggested that index-near-zero materials could be used to improve transmission through a sub-wavelength aperture in a perfectly electrically conducting medium. Here we present the transmission through a sub-wavelength aperture in a gold film modeled using Comsol Multiphysics. It was found that a 23 times enhancement of power through the aperture is achieved by the introduction of an ENZ material between the substrate and the aperture when compared with the same structure without the ENZ layer. In the geometry studied, the ENZ material funnels the light into the sub-wavelength aperture producing the enhanced transmission. The optimal dimensions of the ENZ material are examined as well as the relationship between the ENZ permittivity and incident light frequency which achieves the largest enhancement. The study also compares TE versus TM propagation modes through the structure. The modeled ENZ material is a highly doped n-InSb layer. The ENZ material was achieved by modeling transmission near the Plasma frequency of the doped InSb. The dielectric function of the ENZ material at the operating frequency was calculated using the Drude Model. Preliminary transmission results on doped InSb epilayers will be presented.[1]M. Silveirinha and N. Engheta, Phys. Rev. Lett. 97, 157403 (2006).[2]B. Edwards, A. Alù, M. E. Young, M. Silveirinha, and N. Engheta, Phys. Rev. Lett. 100, 033903 (2008)[3]B. Edwards, A. Alù, M. Silveirinha, and N. Engheta, J. Appl. Phys. 105, 044905 (2009).
9:00 PM - M10.26
Label-free Bio-sensing with Planar Terahertz Metamaterials Fabricated on Ultra-thin Substrates.
Hu Tao 1 , Andrew Strikwerda 2 , Xin Zhang 3 , Richard Averitt 2 , Fiorenzo Omenetto 1
1 Biomedical Engineering, Tufts University, Medford, Massachusetts, United States, 2 Department of Physics, Boston University, Boston, Massachusetts, United States, 3 Mechanical Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractWe design, fabricate and characterize split-ring resonator (SRR) based planar terahertz metamaterials (THz-MMs) on ultra-thin silicon nitride substrates for bio-sensing applications. Biologically compatible and degradable silk fibroin thin films with various thicknesses and fluorescent dopants have been used for proof of principle demonstrations. SRR-MMs fabricated on thin film substrates show significantly better performance with an order of magnitude improvement in terms of sensitivity, characterized using THz Time-domain Spectroscopy, than SRR-MMs fabricated on bulk silicon substrates, which shows a good agreement with simulation results.
9:00 PM - M10.27
Coupling Solar Concentrators to Plasmonic Solar Cell.
Shu-Yi Wang 1 , Deborah Kaminski 1 , Diana-Andra Borca-Tasciuc 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractCoupling photoluminescent solar concentrators with plasmonic solar cells is a potential method to increase conversion efficiencies, while reducing cost. The main idea is to match the emission wavelength of photoluminescent dye with the absorption peak of the solar cell, which can be tuned via surface plasmons. In this work we investigate this approach employing copper phthalocyanine (CuPc) organic solar cells and polymethylmethacrylate (PMMA) based solar concentrators. The absorption enhancement of a CuPc medium with nanoparticles embedded inside is carried out employing Mie theory, taking into considerations size effects on nanoparticles properties. An optimal particle size and particle material emerges from the analysis for specific fluorescent dye used in the concentrator.
9:00 PM - M10.28
Reproducible Fabrication of Optical Antennae on Scanning Probe Tips for High Resolution Spectral Raman Mapping of Carbon Nano Tubes.
Alexander Weber-Bargioni 1 , Schwarzberg Adam 1 , Matteo Cornaglia 1 , Jeff Urban 1 , David Frank Ogletree 1 , Stefano Cabrini 1 , P. Jim Schuck 1
1 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe goal of this work is the reproducible implementation of well-defined coupled optical antennae with Scanning Probe Tips to perform Near Field Optical Spectroscopy with unprecedented resolution and near field enhancement. Here we demonstrate the fabrication and the successful near field imaging/mapping of Carbon Nano Tubes with these next generation Near Field Probes. Research and Development of plasmonic/optical antennae is a topic of high interest since these antennae allow the manipulation of light in the visible spectrum on the nm scale, enabling an optical resolution down to 10nm and therewith well below the diffraction limit. Specifically coupled plasmonic antennae combine high optical resolution with enormous near field enhancements, that allow even single molecule detection. Hence, there is a huge interest to implement these optical antennae reproducibly and well defined (since their resonance is sensitively dependent on their geometry and material) into actual devices such as Scanning Probe Tips to fabricate the next generation Near Field Probes. These will allow optical spectroscopy of matter with unprecedented resolution and access a new parameter space in matter to investigate. Here we show the successful implementation of two promising antenna geometries on AFM tips. We employed Induced Deposition Mask Lithography (IDML) as well as Focused Ion Beam Machining to fabricate bowtie like as well as coaxial optical antennae. We implemented these tips in our Near Field Optical Microscope to prove their performance by measuring Tip Enhanced Raman Spectroscopy Mapping of Carbon Nano Tubes. The bowtie antennae showed a Raman signal enhancement of 500 times, the coaxial tips enhanced the Raman signal 30 times. Latter allowed topography AFM images of Carbon Nano Tubes and optical spectroscopy mapping (Tip Enhanced Raman Spectroscopy) of the CNTs with 10nm optical resolution.This work represents a substantial contribution towards the goal of reliable high resolution/near field enhancing NSOM probes that will enable unprecedented insights into optical, optoelectronic and chemical properties of matter.
9:00 PM - M10.29
Longitudinal and Transversal Coupled Nanoantenna Plasmon Resonance Spectra from Two-photon Laser Excitation.
Matthias Wissert 1 , Konstantin Ilin 2 , Michael Siegel 2 , Uli Lemmer 3 , Hans-Juergen Eisler 1
1 Light Technology Institute (LTI), DFG Heisenberg Group 'Nanoscale Science', Karlsruhe Institute of Technology (KIT), Karlsruhe Germany, 2 Institute for Micro- and Nanoelectronic Systems (IMS), Karlsruhe Institute of Technology (KIT), Karlsruhe Germany, 3 Light Technology Institute (LTI), Karlsruhe Institute of Technology (KIT), Karlsruhe Germany
Show AbstractWe report on the two-photon laser excitation and subsequent plasmonic mode relaxation of coupled optical gold nanoantennas, two arms separated by a small gap. We observe plasmon mode relaxation spectra for such antennas of width 20 nm, height 30 nm and variable arm length of 25 to 65 nm, with a 20 nm gap between the arms, fabricated on an ITO covered glass substrate using electron beam lithography and gold evaporation. The excitation laser wavelength for all characterization experiments is 810 nm. Single two-arm structures are observed by the use of a raster scanning piezo stage and exact placement in the laser focus. An oil immersion objective lens (100 x, NA 1.46) is used both for the excitation and detection channel. A single-photon-counting avalanche photodiode detects the plasmon emission intensity, the response spectrum is observed with an electron multiplying CCD camera.We demonstrate that the integrated far-field emission intensity from the plasmon is enhanced by up to a factor of 65 compared to the mode emission of single gold rods of the same dimensions. We also show that the plasmon spectra are very similar to the well known scattering resonances [1] for such structures, albeit now obtained from single frequency excitation. It is thus possible to obtain resonance spectrum information for coupled or single nanostructures without the need for a broadband, high-power white-light continuum light source.Finally, we show that not only the longitudinal, but also the transversal plasmon mode can be excited, using excitation light polarized exclusively along the long axis of the dipole antenna. We thus provide evidence for a loss in polarization information from the excitation channel to the luminescence response due to the nature of the energy and momentum transfer. The observation of the emission intensity of the transversal mode allows for an accurate intensity mapping for different arm lengths under fixed excitation power and thus the determination of the resonant antenna arm length for a given excitation laser wavelength.[1] M.D. Wissert, A.W. Schell, K. Ilin, M. Siegel, and H.-J. Eisler. Nanoengineering and characterization of gold dipole nanoantennas with enhanced integrated scattering properties, Nanotechnology 20, 425203 (2009)
9:00 PM - M10.3
Vertical Nanowire Arrays for Tunable Plasmon Resonant Nanocavities.
Mihail Bora 1 , Benjamin Fasenfest 1 , Elaine Behymer 1 , James Chan 1 , Allan Chang 1 , Tiziana Bond 1
1 Engineering Technologies Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractWe investigate tunable plasmon resonant cavity arrays in paired nanowire waveguides. Resonances are observed when the waveguide length is an odd multiple of quarter plasmon wavelengths, consistent with boundary conditions of node and antinode at the ends. Two nanowire waveguides satisfy the dispersion relation of a planar metal-dielectric-metal waveguide of equivalent width equal to the square field average weighted gap. Confinement factors over 1000 are possible due to plasmon focusing in the inter-wire space. Tuning of the plasmon resonance in the 500-800 nm range is demonstrated by controlling the geometrical dimensions of the cavity: nanowire height and inter-wire separation. The gap plasmons propagating in the inter-wire space have a strong dependence on the dielectric properties of the insulator. Immersion in solvents of refractive index from 1.31 to 1.45 demonstrates resonance tuning of 180 nm per refractive index unit, consistent with analytical calculations of the dispersion relations. Future applications for the nano-cavities are envisioned in enhanced fluorescence, Raman spectroscopy and subwavelength plasmonic lasers that require high local electromagnetic fields and alignment between the plasmon resonance and excited and emitted light. Since the device structure relies on vertical free standing nano-wires the plasmonic cavity region can be filled with any material of choice. In addition to the high confinement factors shown, the cavity plasmon resonance can be adjusted for better overlap with the absorbance and emission of the active material.
9:00 PM - M10.30
Near Infrared Metallo-dielectric ZIMs with Matched Impedance.
Seokho Yun 1 , Zhi Hao Jiang 1 , Qian Xu 1 , Douglas Werner 1 , Zhiwen Liu 1 , Theresa Mayer 1
1 Electrical Eng., Penn State Univ., University Park, Pennsylvania, United States
Show AbstractThere has been increasing interest in optical metamaterials for new properties and applications such as negative index of refraction and super-resolution optical imaging. Compared with negative index metamaterials (NIM), zero/low index metamaterials (ZIM/LIMs) have received limited attention despite many practical applications that would benefit from their unique optical properties. For example, ZIMs can be used for far-field focusing lenses, cylindrical-to-plane wave transformers, sub-wavelength waveguides, and compact zero-phase delay lines. We previously demonstrated a ZIM that was composed of a single metallodielectric layer with an effective zero index and high transmission in the long-wave infrared. However, the single layer structure does not allow control over the effective permeability because it lacks a strong magnetic resonance; this also prevents designs that are impedance matched to the surrounding medium.In this talk, we will present the design, fabrication, and characterization of a ZIM that overcomes these drawbacks and achieves an impedance-matched near zero effective refractive index at a near-infrared wavelength of 1.55μm. The metamaterial structure is composed of a freestanding Au-polyimide-Au thin film stack that is patterned with nm-scale air holes. A Genetic algorithm coupled with a full-wave periodic finite element boundary integral simulation was used to synthesize a structure to optimize the ZIM-band figures-of-merit and to achieve an impedance match to free space. The optimized ZIM design was fabricated by first depositing the Au-polyimide-Au stack and then defining the air holes by electron-beam lithography and reactive ion etching. The measured transmission and reflection spectra of the freestanding ZIM structure that were collected using a supercontinuum laser source were found to be in strong agreement with those predicted theoretically.
9:00 PM - M10.31
Understanding Plasmon-enhanced Fluorescence through Both Excitation and Emission Polarization Studies on Single Gold Nanorods.
Tian Ming 1 , Lei Zhao 1 , Jianfang Wang 1
1 Department of Physics, The Chinese University of Hong Kong, Hong Kong China
Show AbstractNoble metal nanostructures exhibit extraordinary plasmonic properties, owing to their localized surface plasmon resonances (LSPRs). They can largely enhance the fluorescence of adjacent fluorophores, which is often called plasmon-enhanced fluorescence (PEF). Previous experiments on PEF have been performed mostly on ensemble metal nanocrystal samples or on spherical metal nanoparticles, where the plasmonic properties cannot be precisely controlled. In addition, the fluorescence enhancement factors have been difficult to be determined accurately, because in most experiments, the spatial arrangement and concentration of fluorophores cannot be controlled to be identical in the presence and absence of metal nanostructures. Furthermore, the effects of the excitation and emission on the fluorescence enhancement have so far been mixed together in nearly all of previous PEF experiments. All of the above difficulties have severely precluded a thorough understanding of PEF.In our work, we have fabricated hybrid nanostructures composed of gold nanorod cores and mesostructured silica shells that contain fluorophore molecules. Gold nanorods are used because of their inherent geometrical symmetry breaking-induced splitting of LSPRs into the transverse and longitudinal plasmon modes. By using the excitation light that is resonant with the longitudinal plasmon mode of the nanorods, strong excitation polarization-dependent plasmon-enhanced fluorescence is observed (NL 2009, 9, 3896). This result is ascribed to the dependence of the average electric field intensity enhancement within the silica shell on the excitation polarization. The polarization dependence enables us to turn on and off the PEF readily by controlling the polarization of the excitation light.We have further observed strongly polarized emission from the individual hybrid nanostructures. The emission polarization is found to be along the nanorod length axis. This result indicates that the emission from the fluorophores is first coupled to the longitudinal plasmon mode of the nanorod through the near-field interaction. The light is subsequently emitted out from the longitudinal plasmon mode, and therefore carries the polarization character of the longitudinal plasmon mode of the nanorod. As a result, the emitted light cannot be thought of as coming from the fluorophore molecules any more. It instead comes from the entire hybrid nanostructure. Each hybrid nanostructure is a "plasmophore", as proposed by Lakowicz J. R. et al. (Analyst 2008, 133, 1308). We believe that our results provide the first direct experimental evidence of "plasmophores" in the PEF involving metal nanocrystals.
9:00 PM - M10.32
Stimulated Emission of Surface Plasmon Polaritons with Resonant Feedback.
John Kitur 1 , M. Noginov 1 , V. Podolskiy 2
1 CMR, Norfolk State University, Norfolk, Virginia, United States, 2 Physics, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractOptical gain can compensate metallic loss and enable a variety of dream applications of metamaterials predicted over the last decade. If the total gain in plasmonic systems exceeds total loss, the stimulated emission can occur, as it has been predicted theoretically and demonstrated experimentally. In this work, we have observed stimulated emission of surface plasmon polaritons (SPPs) in dye-doped polymeric microring cavities deposited onto gold and silver wires. The stimulated emission spectra featured characteristic series of laser modes, which spacing corresponded to SPPs propagating at the interface between metal and dielectric. We have also studied stimulated emission of SPPs on corrugated metallic surfaces. The character of the stimulated emission spectra is indicative of a coherent SPP feedback provided by scatterers – plasmonic random laser.
9:00 PM - M10.4
A Systematic Study for the Plasmonic Thin-film Solar Cell with Periodic Structure.
Wallace C.H. Choy 1 , Sha E.I. Wei 1 , Weng Cho Chew 1
1 Department of Electrical & Electronic Engineering, The University of Hong Kong, Hong Kong, ----------------, China
Show AbstractA Systematic Study for the Plasmonic Thin-Film Solar Cell with Periodic StructureWallace C.H. Choy*, Wei E.I. Sha, and Weng Cho ChewDepartment of Electrical and Electronic Engineering, the University of Hong Kong, Pokfulam Road, Hong Kong.*Email:
[email protected] systematic study of the plasmonic thin-film solar cell with the periodic strip structure is presented in this paper. The finite-difference frequency-domain method is employed to discretize the inhomogeneous wave function for modeling the solar cell. In particular, the hybrid absorbing boundary condition and the one-sided difference scheme are adopted. The parameter extraction methods for the zero-order reflectance and the absorbed power density are also discussed: they are important for testing and optimizing the solar cell design. Furthermore, we study the semi-infinite metal-dielectric structure, and propose the phase and attenuation constants conditions of the surface plasmon polariton for lossy materials. For the numerical results, the physics of the absorption peaks of the amorphous silicon thin-film solar cell is explained by electromagnetic theory and correspond to the waveguide mode, Floquet mode, surface Plasmon resonance, and the constructively interference between adjacent metal strips. The work is therefore important for the theoretical study and optimized design of the plasmonic thin-film solar cell.
9:00 PM - M10.5
Switchable Plasmonic Nano-antennas Based on the Shape Memory Effect?
Michael Cortie 1 , Vijay Bhatia 1 , Annette Dowd 1
1 Institute for Nanoscale Technology, University of Technology Sydney, Broadway, New South Wales, Australia
Show AbstractNanoscale shapes of materials such as gold and silver can act as nano-antennas, capturing the electric field of incident light and concentrating it to sub-wavelength volumes. The phenomenon exploits the plasmon resonance between light of a suitable wavelength and a nanoscale object of appropriate shape and composition. A variety of passive nano-antennas have been previously investigated in the field, including nano-rods, crossed rods, nano-shells and semi-shells, nano-crescents and others. Here, we examine a new idea: modulating the plasmon resonance of a nano-antenna by forcing a geometry change using either the shape memory effect peculiar to certain coinage metal alloys, or by simple bimetallic thermal actuation. We use computational simulations to investigate how the optical extinction efficiency of nano-scale coils, cantilevers and springs made from a gold-based shape memory alloy, or from composites of suitable elements, might change with temperature. Although the dielectric properties of the alloy and/or composite bimetallic structures are more lossy than those of pure gold or silver, we predict that suitably designed nano-actuators will manifest a switchable plasmon resonance of significant amplitude. Furthermore, plasmonic heating in the nanostructure can be used to drive the shape change, thereby providing a far-field control of the plasmonic actuator. Simulations of various designs of actuator are considered and their predicted performance compared. Switching appears to be achievable from the lower visible right through to the near infra-red by careful choice of materials and geometry.
9:00 PM - M10.6
A Hot-carrier Solar Cell with Optical Energy Selective Contacts.
Daniel Farrell 1 , Ned Ekins-Daukes 1 , Yasuhiko Takeda 2 , Kazutaka Nishikawa 2 , Tomoyoshi Motohiro 2
1 Blackett Laboratory, Imperial College London, Prince Consort Road, SW7 2BZ, London United Kingdom, 2 , Toyota Central Research and Development Laboratories, Inc., 41-1 Yokomichi, Nagakute, Aichi, 480-1192 Japan
Show AbstractPhotovoltaic conversion of solar energy to electrical work is a processes thermodynamically limited to 41% for a single bandgap material. By contrast, the conversion of solar energy by a thermal system is much higher, being limited to 85%. However, the high physical temperature required to reach this efficiency (2478K) forces solar thermal systems to operate at much more modest temperatures and efficiency ranges. In principle, a hot-carrier solar cell allows extremely high temperatures to be attained by decoupling the temperature of the electronic carrier population from that of the lattice. This decoupling of the carrier and lattice temperature occurs in semiconductors only over very short time scales (ps), before the onset of phonon emission. Phonons allow the hot-carrier population to equilibrate with lattice and resulting in carrier cooling Critically for a hot carrier solar cell, the rate of equilibration between the carrier and lattice population must proceed more slowly than rate of carrier extraction. To achieve this without further cooling during the extraction process mono-energetic, ballistic transport of hot-carriers, over length scales of the optical depth of the absorber is required. We show that this mono-energetic, ballistic transport could be achieved optically by fabricating resonant structures that accelerate the rate of radiative recombination to a point that it proceeds faster than carrier-lattice equilibration.
9:00 PM - M10.7
Enhanced Optical Angular Momentum Transfer in Metal Nanopolygons Due to Broken Rotational Symmetry.
Kin Hung Fung 1 , Nicholas X. Fang 1
1 Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractRecently, there has been a significant progress in understanding the angular momentum of light in the classical-wave picture. Many theoretical works focused on the separation of spin angular momentum of free-space electromagnetic field from its orbital angular momentum and the coupling between the two. There were some experiments showing that the spin and orbital angular momentum of light can be transferred to microscopic particles and anisotropic structures. However, studies on the effects of particle symmetry and plasmon resonance are rare in the literature. We numerically study the transfer of optical spin and orbital angular momentum to metal nanopolygons, such as triangles, stars, and hexagons. The effects of broken rotational symmetry and plasmon resonance on the angular momentum transfer are discussed.We use the Maxwell’s stress tensor to calculate the angular momentum transfer from a circularly polarized light to thin nanopolygons. While a circular disk possesses continuous rotational symmetry, polygons can break the continuous rotational symmetry while keeping some discrete rotational symmetries. While the translational symmetry is related to the conservation and change of linear momentum, the rotational symmetry is related to the angular momentum. The broken rotational symmetry lead to the ability of transferring low angular momentum to high angular momentum. With the help of high-order plasmon resonances, the spin angular momentum transfer can be significantly enhanced. We also study the lattice effect in arrays of nanopolygons. For the structures we have studied, the angular momentum transfers more efficiently for high-order resonances than dipole resonances.
9:00 PM - M10.8
Semiconductor Quantum Dot – Gold Nanoparticle Array Interaction Modeling for Nano-photovoltaic Applications.
Richard Grote 1 , Jusitin Abramson 2 , Matteo Palma 3 , Manolis Antonoyiannakis 4 3 , Nicolae Panoiu 5 , James Hone 2 , Richard Osgood 3 1
1 Electrical Engineering, Columbia University, New York, New York, United States, 2 Mechanical Engineering, Columbia University, New York, New York, United States, 3 Applied Physics and Applied Mathematics, Columbia University, New York, New York, United States, 4 Physical Review Letters, The American Physical Society, Ridge, New York, United States, 5 Electronic & Electrical Engineering, University College London, London United Kingdom
Show AbstractPairs of Semiconductor quantum dots (SQD) attached to Metallic nanoparticles (MNP) can be fabricated in large arrays, which have the potential for integration into high quantum efficiency photovoltaic solar cells. We present a method for modeling carrier generation in the SQD while taking into account Localized Surface Plasmon (LSP) effects from the MNP array, and aim to maximize the quantum efficiency of the SQD array. The spacing between the SQD and the MNP is the key parameter in this optimization: it determines the trade-off between LSP electromagnetic field enhancement and LSP energy loss. It has been shown that placing a SQD in the vicinity of a MNP can increase the absorption in the SQD due to near-field enhancement from LSP resonances in the MNP. However, if the SQD is too close to the MNP, energy transfer between excitons in the SQD and LSPs in the MNP provides a non-radiative recombination loss channel. Thus any SQD/MNP array must incorporate the optimal particle spacing such that field enhancement is maximized, while simultaneously attempting to minimize non-radiative exciton recombination due to LSPs. Simulation results for predicting the optimal dot spacing while taking into account the size, shape and array periodicity of the MNPs are presented. Rigorous-Coupled Wave-Analysis (RCWA) is used to determine the field profile inside the SQD and a dipole approximation is used to calculate the non-radiative recombination due to the presence of the MNP. The quantum efficiency of the SQD array is determined for a number of different MNP shapes as a function of particle spacing and frequency.Our model is validated by comparison with experimental measurements, confirming that the MNP array significantly improves the performance of the SQD array due to strong local field enhancement. Such arrays have potential solar cell applications.
9:00 PM - M10.9
Enhancing the Optical Properties and Chemical Stability of Plasmonic Nanoholes Using Atomic Layer Deposition of Dielectric Overlayers.
Hyungsoon Im 1 , Nathan Lindquist 1 , Antoine Lesuffleur 1 , Sang-Hyun Oh 1
1 Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractNanohole arrays in a metallic film present enhanced transmission at certain wavelengths mediated by the excitation of surface plasmons (SP) which are electromagnetic surface waves propagating along a metallic surface. This effect, commonly called extraordinary optical transmission (EOT), has been used for biosensing in and around the nanoholes due to the strong confinement (within ~100 nm) of the optical field. In this work, conformal atomic layer deposition (ALD) of thin alumina overlayers is used to precisely tune the EOT properties of periodic nanohole arrays made in gold and silver films. Experiments and 3-D finite-difference time-domain (FDTD) simulations confirm that as the resonance wavelength is red-shifted by the deposition of alumina overlayers, the transmission intensity increases up a factor of about 5 until the alumina layer reaches a certain thickness. The transmission increases because of the lower SP damping losses at longer wavelengths, increased cut-off wavelength through the nanoholes by conformally filling with higher index alumina, and an effective refractive index matching effect between both sides of the metal film. Also, it was experimentally shown that alumina overlayers up to 50 nm thick did not degrade the detection sensitivity of the nanohole sensors. Thus gold or silver periodic nanohole arrays coated with a sub-50 nm alumina overlayer can function as a biochemical sensor. These results can be useful for encapsulating silver nanohole arrays with a thin alumina overlayer, protecting the patterned surfaces from unwanted oxidation and chemical instability, which would limit the use of silver for biosensing. The ALD encapsulation technique using thin alumina, silica or hafnium oxide overlayers can also be easily applied to metallic nanostructures made from Au, Ag, Cu or Al, precisely tuning their plasmonic resonances while protecting their surfaces. This may benefit a broad range of patterned plasmonic nanostructures with improved optical properties and stable functional surfaces for many applications, including biosensing and fluorescence imaging.
Symposium Organizers
Rashid Zia Brown University
Kenneth B. Crozier Harvard University
Nader Engheta University of Pennsylvania
Ganping Ju Seagate Technology
Romain Quidant ICFO - The Institute of Photonic Sciences
M11: Applications in HIgh Density Data Storage
Session Chairs
Thursday AM, December 02, 2010
Room 200 (Hynes)
9:30 AM - **M11.1
The E-antenna and Its Use for Data Storage at up to 1 Tb/in2.
Barry Stipe 1
1 , Hitachi Global Storage Technologies, San Jose, California, United States
Show AbstractPlasmonic antennas and apertures can focus optical fields down to the nanometer-scale while simultaneously enhancing the field amplitude by many orders of magnitude. These abilities make them well-suited for use in thermally-assisted magnetic recording (TAR), where one must create a heat spot less than 40 nm across in a magnetic recording medium at the sub-nanosecond timescale. TAR is one of the most promising technologies for surpassing the fundamental limitations of conventional magnetic recording used in today’s hard drives because it allows one to use extremely high anisotropy media (such as L10 FePt) for reduced grain size while maintaining the requirements of thermal stability and writability. In this talk, I will describe a new plasmonic antenna design called the "E-antenna", it's properties, relationship to other types of antennas, and how it can be integrated into a magnetic recording head. Recently, a fully integrated E-antenna was used for recording on both granular and patterned media [1]. In the case of patterned media, we found that TAR allows for dramatic reductions in track pitch (down to 24nm) and optical power requirements (factor of five) while recording at up to 1Tb/in2. Storing the world’s information may turn out to be the most important application of plasmonic devices. 1) B. C. Stipe et al., "Magnetic recording at 1.5 Pb m-2 using an integrated plasmonic antenna," Nature Photon., in press.
10:00 AM - **M11.2
Heat-assisted Magnetic Recording using a Recording Head Integrated with a Plasmonic Near Field Transducer.
A. Itagi 1 , W. Challener 1 , Chubing Peng 1 , Darren Karns 1 , Yingguo Peng 2 , Nils Gokemeijer 1 , James Kiely 1 , Ganping Ju 2 , Michael Seigler 1 , E. Gage 1
1 , Seagate, Bloomington, Minnesota, United States, 2 , Seagate, Freemont, California, United States
Show AbstractWe demonstrate magnetic recording on a spinning magnetic disk using heat assist from a plasmonic near field transducer (NFT) flying over an air bearing. The NFT is used to efficiently heat a sub-diffraction-limit region on a rotating magnetic disk to above the Curie point. The NFT is integrated with a magnetic writer and reader. The track width and the areal density achieved are of the same order of magnitude as conventional perpendicular recording. Heat assisted magnetic recording will pave the way for the extension of conventional magnetic storage technology.
10:30 AM - M11.3
Birefringent and Dichroic Plasmonic Nano-antennas and Subwavelength Apertures.
Erdem Ogut 1 , Kursat Sendur 1
1 , Sabanci University, Istanbul Turkey
Show AbstractPolarized electromagnetic radiation has led to interesting technical applications and significant advancements at both optical and microwave frequencies. With advances in nanotechnology, electromagnetic radiation beyond the diffraction limit with a particular polarization is an emerging need for plasmonic nano-applications. Among these, all-optical magnetic recording requires circularly polarized optical spots. It has been demonstrated that the magnetization can be reversed in a reproducible manner using a circularly polarized optical beam without an externally applied magnetic field. To advance the areal density of hard disk drives, a sub-100 nm circularly polarized optical spot beyond the diffraction limit is required.Recently, there has been growing interest in obtaining optical spots with various polarizations using plasmonic nano-antennas and subwavelength apertures. Although, plasmonic nano-antennas and subwavelength apertures have been investigated for potential utilization as nano-optical polarization elements, two crucial polarization related properties, birefringence and dichroism, have not been investigated. In this study, we examine the birefringence and dichroism of plasmonic nanoantennas and subwavelength apertures. The underlying reasons of birefringent and dichroic behaviour in nano-antennas are provided.
10:45 AM - M11: Data
BREAK
M12: Devices and Electrical Integration
Session Chairs
Thursday PM, December 02, 2010
Room 200 (Hynes)
11:15 AM - **M12.1
Resonant Generation of Macroscopic Currents Mediated by Surface Plasmon Polaritons.
N. Noginova 1 , A. Yakim 1 , M. Noginov 1
1 Center for Materials Research, Norfolk State University, Norfolk, Virginia, United States
Show AbstractPlasmonic metamaterials have promise to revolutionize information technology by merging advantages of compact modern electronics and fast photonics. Coupling electric and optical effects in plasmonic circuit elements is of imminent importance for photonic nanocircuitry applications as it provides an opportunity to include plasmonic elements into electronic circuits and/or control surface plasmon effects electrically. In this work, we have studied photo-excitation of macroscopic electric currents in silver films both under the condition of SPP excitation (in Kretchman geometry) and in the configurations where SPPs were not excited. We have also shown that SPP can be controlled externally by propagating electric current in metallic films. Experimentally, silver films (35-60 nm) were deposited on high-index glass prisms and glass slides. When films were excited with the laser light from the side of the prism, a characteristic dip was observed in the angular dependence of reflectance manifesting excitation of SPP. Laser light illumination induced electric signal, which temporal profile approximately corresponded to that of the laser pulse. Remarkably, the sign of the drag effect at the resonance angle corresponding to excitation of SPP was different from that at off-resonance angles, at which SPPs were not excited. Thus, electrons dragged by SPPs propagated along the projection of the incident light k vector onto the film surface, while at off-resonance incidence angles, electrons were dragged in the direction opposite to the light k vector. The magnitude of the electric signal at resonant excitation exceeded that of the off-resonant signal fivefold to tenfold. Both resonant and off-resonant electric signals were nearly linearly proportional to the laser light intensity at small excitation energies and showed some saturation at stronger pumping values.In another set of experiments, silver film on the prism was illuminated with a cw He-Ne laser (632.8 nm) while rectangular voltage pulses were applied to the film by a pulse generator (~1V, 1ms). The driving voltage caused the change of the reflectance, which temporal profile followed the shape of the voltage pulse. The dependence of the reflectance change on the excitation angle closely followed the angular reflectance profile of the SPP, although with an opposite sign. The modeling of the SPP reflectance angular profile has shown that the experimentally measured dependence cannot be explained by the change of the real or imaginary parts of the dielectric constant of silver or the change of the film thickness caused by thermal expansion.
11:45 AM - M12.2
Electrically Integrated Plasmonic Nanocavities.
Robb Walters 1 , Albert Polman 1 , Ihor Brunets 2 , Jurriaan Schmitz 2
1 Center for Nanophotonics, AMOLF, Amsterdam Netherlands, 2 MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractCurrent state-of-the-art microphotonic resonator designs, such as waveguide ring and disc resonators and defect cavities in photonic crystals, are unlikely to scale to single device footprints below ~100 μm2. Proposed integration schemes typically assume that many passive microcavity devices will be driven via fiber-coupled external sources and measured by external detectors. By applying plasmonic design concepts, it is possible to create nanophotonic resonators that are more compact and more suitable for dense integration in active device arrays. These plasmonic nanocavities can be combined with recently reported electrical sources of surface plasmon polaritons (SPPs) to create an active CMOS-compatible plasmonic backplane platform. Hybrid electronic/plasmonic integrated circuits using this platform can include both driving and detection circuits, in addition to signal processing and logic functionality in underlying device layers. Such chips are promising for future low cost chemical and biological sensors.We have designed and fabricated devices incorporating silicon-based electrically integrated plasmonic nanocavities with geometrically tunable resonances. The nanocavities are driven by locally generated SPPs in an asymmetric metal-insulator-metal (MIM) waveguide geometry having optically thick aluminum and gold cladding layers that surround a semi-insulating layer of alumina containing silicon nanocrystals. The nanocrystals are excited through an impact ionization process when a current flows through the insulator layer. For sufficiently thin insulator layer thicknesses, the only radiative decay pathway available to excited nanocrystals is via the symmetric TM0 SPP mode of the MIM waveguide, resulting in efficient coupling and SPP emission in the near-infrared. The coupling efficiency of these SPPs to a particular nanocavity depends on the impedance match between the waveguide and the nanocavity, which varies with geometry and the local material composition. This provides a mechanism for an electrically integrated nanoscale sensor. An electrical readout of the power coupled to the nanocavity is provided by an underlying photodiode, forming a complete plasmonic sensing pixel. Our prototype devices simulate an active plasmonic backplane fabricated using back-end compatible processes on a polished aluminum metallization layer in a CMOS device stack.
12:00 PM - M12.3
Dipole Antenna Couplers for Deep Subwavelength Plasmonic Interconnects.
Mehmet Cengiz Onbasli 1 , Ali K. Okyay 2 3
1 Department of Materials Science and Engineering, MIT, Boston, Massachusetts, United States, 2 Department of Electrical and Electronics Engineering, Bilkent University, Ankara Turkey, 3 UNAM, Institute of Materials Science and Nanotechnology, Ankara Turkey
Show AbstractDue to increasing spatial power dissipation arising from chip downscaling and RC delays that limit operation bandwidth; interconnect solutions that alleviate these issues must be introduced in addition to the state-of-the-art copper interconnects (CIs). Performance of CIs degrades at higher operational frequencies. Optical waveguides are suggested as an alternative interconnnect solution, however, waveguide cross-sections are on the wavelength-scale. For achieving higher bandwidth-density interconnects, plasmonic waveguiding through the metal-insulator-metal (MIM) topology has been proposed by a number of researchers. Deep sub-wavelength confinement combined with wide bandwidth capability make MIMs attractive for high sensitivity spectroscopy, biosensing, waveguiding, nonlinear optics, in addition to on-chip signal processing and interconnections.Ohmic loss of the metal claddings in the optical wavelengths causes high attenuation in MIM waveguides. For increasing the propagation distance, research efforts focused on the analysis of the MIM architecture and the supported electromagnetic modes. There are a limited number of reports on the coupling of external electromagnetic radiation into the MIM, where many focus on the use of a tapered architecture. These structures must be longer than about 4λ for adiabatic tapering, which does not serve the purpose of high-density integration of interconnects. Therefore, it is necessary to introduce effective and compact coupling methods from micron-size fibers to the waveguides of less than a few hundred nanometers wide. In this study, we propose dipole antenna-MIM system to show that dipole antennas can be integrated with MIM for enhancing coupling into the MIM plasmon modes and tuning the mode field intensity profile inside the dielectric core by changing the antenna length, width and the antenna-waveguide separation. 2D finite difference time domain simulations of combined antenna-waveguide structures were done using Lumerical FDTD SolutionsTM. The same baseline waveguide was used for all different antenna cases throughout the analysis. The MIM structure consists of 100-nm-wide silver claddings and 100-nm-wide SiO2 core. TE and TM incident plane waves were simulated for λ = 1300 to 1600 nm. We systematically varied the dipole antenna coupler structure in front of the MIM baseline.When the antenna is disconnected from the MIM, a strong field confinement is obtained at the MIM-antenna gap region. A limited amount of energy is coupled into the waveguide since the near-field radiation pattern cannot initiate MIM plasmon modes. It enhances Fabry-Perot like resonances between the antenna and MIM. The overlap integral of the plasmon modes and the emission pattern is smaller than that in the connected antenna case. When the antenna structure is connected to the MIM, much stronger coupling is observed. The E-field intensity inside the core is enhanced more than 5 times, varying with the antenna dimensions.
12:15 PM - M12.4
Semiconductor Nanowire in a Metallic Slit: a Photodetector Enhanced by Two Optical Antenna Effects.
Pengyu Fan 1 , Linyou Cao 1 , Ragip Pala 1 , Mark Brongersma 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractRecently, optical antennas based on metallic nanostructures, such as metallic slit antenna, attracted great attention due to their unique ability to concentrate light into a deep subwavelength volume. At the same time, semiconductor nanowires are also found to be optical antennas which can absorb light much more efficiently than bulk structures due to leaky mode resonances (LMRs) that can be supported inside the nanowires. Here we hope to combine these two antenna effects in one device by having a germanium nanowire sitting beneath a metallic slit. Thus when the device is illuminated, electromagnetic fields will be greatly enhanced both through metallic slit antenna and by semiconductor nanowire antenna at the same time, letting to highly efficient optical absorption in the nanowire with extremely small active device volume. Using full-field electromagnetic simulations, we can develop simple design rules for maximized optical absorption inside the nanowire at desired wavelength by exploring geometric properties of the system (e.g. slit width, metal thickness, nanowire size and etc.) We also experimentally demonstrate such antenna enhanced optical absorption effect by measuring photocurrent generated in the nanowire when illuminated, comparing to that of a bare nanowire without metallic slits. Moreover, spectral and spatial photocurrent measurements also suggest by having a metallic slit antenna, polarization dependent absorption properties of nanowires can also be modified. This work provides new approach of incorporating multiple optical antenna effects to build up on-chip nanoscale high-speed photodetectors and other novel optoelectronic devices.
12:30 PM - M12.5
Plasmonic Nanowire Antennas for Next-generation Semiconductor Light-emitting Devices.
Deirdre O'Carroll 1 , Dennis Callahan 2 , Martin Schierhorn 3 , Harry Atwater 2
1 , ISIS, University of Strasbourg and CNRS, Strasbourg France, 2 , California Institute of Technology, Pasadena, California, United States, 3 , University of California, Santa Barbara, Pasadena, California, United States
Show AbstractNanoscale light-emitting devices stand to benefit substantially from the integration of optical frequency antennas with semiconducting materials. In particular, plasmonic nanoantennas have been widely studied in recent years to improve the emission quantum efficiency (QE), directionality and rate of light emission from semiconductors. In this work, we present the design and experimental realization of split dipole gold nanowire antennas incorporating a light-emitting semiconductor, polythiophene, P3HT, in the slot region at the centre of each antenna. When designed to resonate at the wavelength of the semiconductor (650 to 700 nm for P3HT) full-field electromagnetic simulations predict enhancements in radiative emission rate by factors of up to 60 and QE enhancements of 30 (intrinsic P3HT QE ≈ 1%) for nanowire antenna dimensions of 200 nm in length, 60 nm in diameter and a semiconductor active region of 20 nm. The antennas were fabricated using a template-directed sequential electrodeposition process in nanoporous alumina templates [1]. Transient photoluminescence (PL) measurements of the fabricated nanostructures show reductions in total lifetime by a factor of 10 (to 75 ps) compared to the neat semiconductor. Given a PL intensity enhancement of 3, the radiative decay rate of P3HT was estimated to increase from 14 MHz to 440 MHz using the nanowire antenna geometry. Theoretical simulations predict that optimum radiative decay rate and QE enhancements of up to 550 and 40, respectively, could be achieved by further reducing the nanowire antenna dimensions. Such substantial gains in semiconductor emission rate and QE suggest that split dipole optical antennas could enable a wide variety of semiconductor materials that do not exhibit high intrinsic emission QE (but which may exhibit other advantageous properties such as high charge carrier mobilities or non-linear optical properties) to be used as on-chip optical light sources.In addition to yielding substantial improvements in the light emitting properties of P3HT, the split dipole nanowire antenna geometry lends itself to electrical excitation of the semiconductor. Since the antennas are fabricated in vertically-oriented arrays in alumina on an indium-tin oxide working electrode, which can act as the anode, electrical excitation is facilitated by means of directly probing the top gold segments of an array of antennas. Initial characterization of electrically driven gold nanowire antenna devices incorporating P3HT and optimized device formats will be presented. Integrated arrays of electrically driven optical frequency antenna/semiconductor heterostructures can find applications in large area opto-electronic devices and provide a pathway for the realization of single electrically driven optical nanoantenna-mediated light-emitting devices. [1] D. M. O’Carroll, C. E. Hofmann, H. A. Atwater, “Conjugated Polymer/Metal Nanowire Heterostructure Plasmonic Antennas,” Adv. Mater. 22, 1223-1227 (2010).
12:45 PM - M12.6
Mid-Infrared Plasmonic Beam Steering.
David Adams 1 , Sukosin Thongrattanasiri 2 , Troy Ribaudo 1 , Viktor Podolskiy 1 2 , Daniel Wasserman 1
1 Physics, University of Massachusetts at Lowell, Lowell, Massachusetts, United States, 2 Physics, Oregon State University, Corvallis, Oregon, United States
Show AbstractA plasmonic device comprised of a sub-wavelength slit patterned in a gold film on a GaAs substrate and flanked on either side by a series of grooves is presented for mid-infrared beam steering applications. Light incident upon such a device reemerges on the back side of the structures in the form of high quality beams, whose beaming angles, as measured from normal, depend primarily on the periodicity of the flanking grooves and the permittivity of the GaAs near the metal-GaAs interface. Here we demonstrate how the dispersion of the device may be exploited to achieve steering of the transmitted beams for a fixed device geometry. We show that by shifting the frequency of the incident radiation we are able to control the angular distribution of the transmitted beams. In addition we will present results from an investigation of the transmitted beam profile as a function of incident wavelength, with a focus on the beam profile near the normal beaming wavelength. Finally, we demonstrate that a similar steering effect can be achieved when the incident radiation frequency is fixed and the permittivity of the GaAs substrate is tuned. We demonstrate that minor tuning of the permittivity of the GaAs below the plasmonic surface (corresponding to a refractive index shift of less than 1%) results in a 3° angular shift in the transmitted beams. These results, as well as progress towards voltage controlled steering devices will be presented.
M13: Advanced and Improved Antenna Designs
Session Chairs
Thursday PM, December 02, 2010
Room 200 (Hynes)
2:30 PM - **M13.1
A Comparison of Plasmonic and Semiconductor Optical Antennas.
Mark Brongersma 1
1 , Stanford, Stanford, California, United States
Show AbstractMetamaterials and nanophotonic devices are most commonly constructed from metallic (i.e. plasmonic) nanostructures. However, recent research has begun to also exploit the optical resonances of high-permittivity semiconductor and dielectric nanostructures to realize similar optical functionalities. In this talk, I will illustrate the use of plasmonic, semiconductor, and dielectric nanostructures in a variety of applications (sources, modulators, detectors, sensors) and discuss their relative strengths and weaknesses.
3:00 PM - **M13.2
Parabolic Nanoantennas: Properties, Manipulation, and Applications.
Nicholas King 2 4 , Yu Zhang 2 4 , Travis Brannan 2 4 , Shaunak Mukherjee 3 4 , J. Lassiter 2 4 , Naomi Halas 1 3 4
2 Physics and Astronomy, Rice University, Houston, Texas, United States, 4 Laboratory for Nanophotonics, Rice University, Houston, Texas, United States, 3 Chemistry, Rice University, Houston, Texas, United States, 1 Electrical and Computer Engineering, Rice University, Houston, Texas, United States
Show AbstractHemispherical metallic nanoparticles, also known as “nanocups” or “semishells”, have both axial and transverse plasmon modes. The transverse plasmon mode scatters light in the direction of nanoparticle orientation, a characteristic unique to this nanoparticle geometry, allowing it to function as a nanoscale parabolic transmitter. These nanostructures are prepared straightforwardly, by deposition of a metallic layer onto a substrate upon which spherical dielectric nanoparticles have been deposited, followed by removal from the metalized growth substrate. Angular scattering measurements, comparing the axial and transverse mode scattering characteristics of this nanostructure, will be described. The use of parabolic nanoantennas in applications requires that the transfer of these nanostructures from their growth substrate and placement on a structure or device of interest in such a manner that their three-dimensional orientation is precisely preserved. We have developed a transfer lamination process to facilitate the orientation-preserving transfer of these three-dimensional nanoantennas. Control of the orientation of these structures also allows us to investigate their nonlinear frequency generation and scattering characteristics, where reduced symmetry and controlled orientation facilitates second-order nonlinear optical processes.
3:30 PM - **M13.3
Improving Plasmonic Nanoantennas.
Vladimir Shalaev 1 , Kuo-Ping Chen 1 , Vladimir Drachev 1 , Joshua Borneman 1 , Alexander Kildishev 1
1 Birck nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractImprovements in energy damage threshold and quality factor of plasmonic nanoantennas were studied usingstabilizing dielectric films and annealing.
4:00 PM - M13: Designs
BREAK
M14: Applications in Solar Energy Conversion
Session Chairs
Thursday PM, December 02, 2010
Room 200 (Hynes)
4:30 PM - M14.1
Beating Traditional Photovoltaic Designs through Optical Concentration via Plasmonic Grating and Antenna Structures.
Jeremy Munday 1 , Harry Atwater 1
1 Applied Physics, Caltech, Pasadena, California, United States
Show AbstractWe explore the maximum photocurrent enhancement due to plasmonic grating and antenna structures for ultrathin (50-300 nm) crystalline silicon solar cells and compare the results to traditional light trapping structures and dielectric antireflection coatings. The frequency dependent absorption is found to strongly correlate with the occupation of optical modes of the thin film structure, as determined by comparison to calculated dispersion relations. Spatially resolved electron generation rates are used to determine the total integrated cell photocurrent under AM 1.5 solar illumination. We find that plasmonic gratings and antireflection coatings can produce comparable enhancements; however, by conformally coating a grating structure with a dielectric antireflection coating, the integrated current enhancement over the solar spectrum can reach above 180%, significantly greater than the enhancement due to either an antireflection coating or a grating individually. Improved absorption is mainly attributed to improved coupling to guided modes rather than coupling to localized resonances when an antireflection coating is added. Three-dimensional full field electromagnetic simulations of periodic antenna structures reveal even larger integrated absorption enhancements, reaching values of ~200%.
4:45 PM - M14.2
Light Trapping in Thin Si Solar Cells Using Coupled Plasmonic Antenna Arrays.
Pierpaolo Spinelli 1 , Maarten Hebbink 1 , Lachlan Black 2 , Claire van Lare 1 , Rene de Waele 1 , Frank Lenzmann 2 , Albert Polman 1
1 Center for Nanophotonics, FOM-Institute AMOLF, Amsterdam Netherlands, 2 , Energy research Centre of the Netherlands, Petten Netherlands
Show AbstractWe demonstrate how the incoupling and trapping of light in thin Si solar cells can be improved by using an array of metallic nanoscatterers placed at the surface of the solar cell. The silver antennas act as efficient receivers for a broad spectral band within the solar spectrum and reradiate the incident light over a wide angular range and (for very thin cells) into waveguide modes of the solar cell. In this way the effective optical path length is increased and the photocurrent of the solar cells enhanced. This work enables the design of (ultra-)thin solar cells while maintaining efficient spectral conversion of the sunlight.Our work is comprised of finite-difference time domain (FDTD) modelling, fabrication of antenna arrays on single-crystal solar cells, optical measurements and photocurrent spectroscopy. First, FDTD simulations were carried out to study the incoupling of light into a Si substrate using a single Ag nanoparticle (diameter 100-300 nm). We find that the scattering and incoupling spectra depend strongly on particle shape and dielectric environment, in particular in the near-field region close to the substrate. Due to the coupling to the high-index substrate, the resonant scattering spectra from these Ag antennas are quite complex. By carrying out a systematic study in which we gradually increase the refractive index of the substrate we identify all scattering peaks and relate them to the (strongly anisotropic) field distribution in the contact area between antenna and substrate. In some geometries we find strong Fano resonance effects that reduce the light incoupling for short wavelengths. Placing the antennas on a thin transparent spacer layer provides further control over the scattering and coupling spectra. We carried out a systematic analysis of all antenna coupling parameters, finding an optimized geometry for 130 nm tall, 200 nm diameter Ag antennas at a 450 nm pitch, placed on a 50 nm Si3N4 layer on Si. Most interestingly, we find that this geometry is more efficient for light incoupling than the standard Si3N4 anti-reflection coating.These simulation results are confirmed by optical reflection spectroscopy carried out on 200 micron thick Si solar cells covered with different Si3N4 spacer layers (thickness 20-90 nm). By using electron-beam lithography, we fabricate 80x80 μm arrays of Ag antennas, each array with different antenna diameter and pitch. The optical measurements are in full agreement with the trends found with FDTD simulations regarding particle size, array pitch and Si3N4 layer thickness. Most importantly, the optimal antenna array has a reflection coefficient (averaged over the solar spectrum) of only 2%, much better than the standard AR coating. Ag nanoparticle antenna arrays thus provide full impedance matching between sunlight and the semiconductor. The physical insights from this work are applicable to any type of solar cell, including polycrystalline Si, amorphous Si and CdTe thin film solar cells.
5:00 PM - M14.3
An Efficient Broadband Thin Film Infrared Absorber/Emitter Based on Optical Antennas.
Yanxia Cui 1 2 , Jun Xu 1 , Kin Hung Fung 1 , Anil Kumar 3 , Sailing He 2 , Nicholas Fang 1
1 Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Centre for Optical and Electromagnetic Research, Zhejiang University, Hangzhou China, 3 Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractOptical antennas, based on metallic nanostructure design, have been found great applications in the design of thin film absorbers, which are viable solutions for new-generation solar cells, optical detectors and biosensors. By using the resonant condition of optical antennas to excite localized surface plasmon (LSP), incident light shining from a wide angle could be completely trapped and dissipated due to ohmic losses. According to the Kirchhoff’s law, the emissivity is equal to the absorptivity, so the optical antennas are also quite applicable for novel thermal emitters. Here, we propose a new design of an efficient thin film infrared absorber/emitter with very broad band by combining different sized optical antennas. Our device is a metal-insulator-metal multilayer structure on silicon substrate with gold as the metal and germanium as the dielectric at the working band from 8 to 12 μm. By carefully decorating the width of top gold strips, the optical antennas with mixed sizes are formed to respond to different incident wavelengths. The normal incident absorption spectra was simulated, that shows a very broad band with FWHM around 30% at the center wavelength of 10 μm. Attributed to the principle of LSP modes, the absorption spectrum are almost angle-independent, that is also verified by simulation results. In addition, we studied the influence of the antenna size as well, which shows that the spectrum will split to multiple strong bands as we keep increasing the difference between the size of neighboring antennas. It is noticed that our design of absorbing/emitting layer is as thin as about 500 nm in total, which corresponds to only 1/20 of the incident center wavelength. We anticipate that by scaling down the structural parameters, our proposal might act on improving the performance of thin film solar cell devices a lot in the future.
5:15 PM - M14.4
Resonant Light Absorption in Thin Film Photovoltaics via Whispering Gallery Nano- and Microspheres.
Jonathan Grandidier 1 , Dennis Callahan 1 , Jeremy Munday 1 , Harry Atwater 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractWavelength-scale dielectric spheres are interesting photonic elements because they can support confined resonant modes. Moreover, the periodic arrangement of nanospheres can lead to coupling between the spheres resulting in mode splitting and rich bandstructure. The coupling originates from whispering gallery modes inside the spheres. When resonant dielectric spheres are in proximity to a high index photovoltaic absorber layer, incident light can be coupled into the high index material and increase light absorption. We investigate several photovoltaic absorber configurations based on resonant silica nanospheres either embedded in or atop an amorphous silicon layer. Here we demonstrate that strong whispering gallery modes can significantly increase light absorption in amorphous silicon thin film absorbers. Another important aspect of nanosphere-based photovoltaics is the relative insensitivity of absorption to angle of incidence. The size and spherical geometry of the incoupling elements allows light to be efficiently coupled into the solar cell over a large range of incident angles. We investigated the coupling from whispering gallery modes into thin film photonic or plasmonic modes within the absorber layer. We optimize the silicon layer thickness for the best absorption enhancement for a given sphere geometry. The results presented here are performed using three-dimensional full field electromagnetic simulations to determine the expected absorption enhancement compared to amorphous Si absorbers without a layer of dielectric spheres. We also compare these results to analytical models.
5:30 PM - M14.5
General Properties of Dielectric Optical Antennas.
Jon Schuller 1 , Mark Brongersma 2
1 , Columbia University, New York, New York, United States, 2 , Stanford University, Stanford, California, United States
Show AbstractUsing Mie theory we derive a number of general results concerning the resonances of spherical and cylindrical antennas. Specifically, we prove that the peak scattering cross-section of radiation- limited antennas depends only on the resonance frequency and thus is independent of refractive index and size, a result which is valid even when the resonator is atomic-scale. Furthermore, we derive scaling limits for the bandwidth of dielectric antennas and describe a cylindrical mode which is unique in its ability to support extremely large bandwidths even when the particle size is deeply subwavelength. Finally, we show that higher Q antennas may couple more efficiently to an external load, but the optimal absorption cross-section depends only on the resonance frequency.
5:45 PM - M14.6
Absorption Enhancement in Thin-Film P3HT:PCBM Solar Cells Via Plasmonic Concentrators.
Aminy Ostfeld 1 , Domenico Pacifici 1
1 School of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractThe requirements for active layer thickness and quality in photovoltaic cells can be greatly relaxed by the addition of nanoscale metal patterns that support surface plasmons. The use of these plasmonic concentrators is especially well suited to organic photovoltaics, which offer the potential for easy and inexpensive fabrication but are fundamentally limited in charge carrier mobility. Here we demonstrate surface plasmon enhanced absorption in ultrathin film organic photovoltaic cells using periodic and quasiperiodic subwavelength hole arrays. Cells were fabricated using an active layer of poly(3-hexylthiophene) (P3HT) and phenyl C61-butyric acid methyl ester (PCBM) on silver substrates patterned with focused ion beam lithography. Reflectance measurements were performed on the arrays with and without the active layer, and absorption enhancement was studied as a function of array type and dimensions. We also performed FDTD simulations for the patterns and simulated reflectance in unpatterned films using a multiple reflection model. Experimental and simulated data as well as design strategies to improve the overall external quantum efficiency will be discussed.