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
Tuesday PM, November 30, 2010
Exhibition Hall D (Hynes)
1:00 AM -
M5.15 Transferred to M10.32
M1: Enhanced Light-Matter Interactions I
Session Chairs
Tuesday AM, November 30, 2010
Room 200 (Hynes)
9:15 AM -
Opening Remarks
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.
M2: Enhanced Light-Matter Interactions II
Session Chairs
Tuesday AM, 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).
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
Tuesday PM, November 30, 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.
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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.
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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.
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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.
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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.
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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.
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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 r