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).