Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session S44: Focus Session: Optical Properties of Plasmonic Nanostructures |
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Sponsoring Units: DMP Chair: Emily Townsend, National Institute of Standards and Technology Room: Colorado Convention Center 507 |
Wednesday, March 7, 2007 2:30PM - 2:42PM |
S44.00001: Au Bowtie Nanostructures for Surface-enhanced Raman Spectroscopy Daniel Ward, Nathaniel Grady, Carly Levin, Naomi Halas, Douglas Natelson Designing nanostructures for surface-enhanced Raman spectroscopy (SERS) is an active area of research because of the potential for chemical sensing with single-molecule sensitivity. We report preliminary SERS measurements on Au bowtie structures with nanometer size interelectrode gaps fabricated by electromigration. Initial data suggest that the bowtie structure provides a large electromagnetic enhancement for SERS over a small volume, enabling few or single molecule spectroscopy. The local plasmon resonance of the bowtie structure is tunable by varying the width of the gap between the two halves using electromigration. Additionally we report on a multiple bowtie structure that combines several bowtie devices in parallel allowing for the simultaneous electromigration of several devices at once to similar gap sizes. [Preview Abstract] |
Wednesday, March 7, 2007 2:42PM - 2:54PM |
S44.00002: Optical Response of Metal Nanoantennas to Femtosecond Pulses Sushmita Biswas, Albert Heberle Nanoscale metal antennas are promising devices for focusing light down to dimensions much smaller than the wavelength of light. This focusing can lead to strong optical enhancement of the response of single molecules or quantum dots placed in the antenna gap, as well as strong nonlinearities. The optical response of such antenna, however, is not well understood yet. Here, we will present results of our investigations of the linear and nonlinear optical response of silver nanoscale bowtie antennas to excitation with near-infrared pulses from a femtosecond Ti:sapphire laser. The antennas were fabricated with electron beam lithography and a lift-of process on glass substrates and semiconductor materials. They have lengths of a few hundred nanometers and gaps between 10 and 100 nanometers. We will discuss polarization dependence of the excitation sensitivity, second harmonic generation and other nonlinear effects. \newline References: \newline [1] P. Muhlschlegel et al., Science ,1607(2005). \newline [2] J.N. Farahani et al., Phys. Rev. Lett. 95,017402(2005). [Preview Abstract] |
Wednesday, March 7, 2007 2:54PM - 3:06PM |
S44.00003: Two-Photon Vibrational Spectroscopy using local optical fields of gold and silver nanostructures Katrin Kneipp, Janina Kneipp, Harald Kneipp Spectroscopic effects can be strongly affected when they take place in the immediate vicinity of metal nanostructures due to coupling to surface plasmons. We introduce a new approach that suggests highly efficient two-photon labels as well as two-photon vibrational spectroscopy for non-destructive chemical probing. The underlying spectroscopic effect is the incoherent inelastic scattering of two photons on the vibrational quantum states performed in the enhanced local optical fields of gold nanoparticles, surface enhanced hyper Raman scattering (SEHRS). We infer effective two-photon cross sections for SEHRS on the order of 10$^{5}$ GM, similar or higher than the best known cross sections for two-photon fluorescence. SEHRS combines the advantages of two-photon spectroscopy with the structural information of vibrational spectroscopy, and the high sensitivity and nanometer-scale local confinement of plasmonics-based spectroscopy. [Preview Abstract] |
Wednesday, March 7, 2007 3:06PM - 3:18PM |
S44.00004: Interparticle and Interfacial Effects on Second Harmonic Generation from Gold Nanoparticles Matthew McMahon, Davon Ferrara, Richard Haglund We have studied the angular dependence of second-harmonic generation (SHG) from symmetric gold nanoparticles arranged in lithographically fabricated gratings. For example, we have measured the effects of electric-field enhancement on second-harmonic generation by controlling the separation between closely spaced nanoparticles; changing the separation should change the strength of the interaction. Near-field interparticle interactions are observed to have characteristic effects on both the extinction spectra and the second-harmonic signals. Moreover, the substrate plays an important role in the way dipoles and higher-order multipoles contribute to the harmonic radiation. We have computed the dipole and quadrupole contributions in order to fit the measured SHG angular distributions. Theoretically, however, most of the harmonic light should be radiated into the substrate rather than into free space, making waveguiding applications particularly intriguing. [Preview Abstract] |
Wednesday, March 7, 2007 3:18PM - 3:30PM |
S44.00005: Strong Field Enhancement in a Scanning Nanogap for Infrared Imaging of Single Nanoparticles (lambda/1000) Javier Aizpurua, Antonija Cvitkovic, Nenad Ocelic, Reinhard Guckenberger, Rainer Hillenbrand Far-field infrared analysis of individual nanoparticles has not been possible so far due to the extremely weak scattering cross section of nanosize objects at infrared wavelengths, which is 5 orders of magnitude smaller than at visible wavelengths. Scattering type near-field optical microscopy (s-SNOM) offers nanoscale spatial resolution at IR wavelengths and background- free imaging [1,2]. We investigate theoretically and experimentally the use of strong optical field enhancement in the nanogap formed between the s-SNOM tip and the substrate supporting the particles. We show the key role of the substrate response to obtain strong field enhancement at the scanning gap, and therefore spatially resolve the nanoparticles. We provide clear experimental evidence that for highly reflective substrates, single particles as small as 8 nm can be detected with a mid-IR s-SNOM operating at 10 micrometer wavelength. [1] F Keilmann and R. Hillenbrand, Phil. Trans. Roy. Soc. A 362, 787 (2004). [2] A. Cvitkovic et al., Phys. Rev. Lett. 97, 060801 (2006). [Preview Abstract] |
Wednesday, March 7, 2007 3:30PM - 3:42PM |
S44.00006: Enhanced thermal emission from individual antenna-like nanoheaters Snorri Ingvarsson, James A. Lacey, Hendrik F. Hamann We report polarization-sensitive, thermal radiation measurements of individual, antenna-like, thin film Platinum nanoheaters. These heaters confine the lateral extent of the heated area to dimensions smaller or comparable to the emission wavelengths. We investigate the polarization patterns of the far-field radiation from individual nanoheaters as a function of length and width. For very long and narrow heater structures, we measure dipolar-like polarization patterns of the thermal radiation with high extinction ratios. Associated with these high extinction ratios for narrow and long heater structures, a significant enhancement of the thermal emission is observed. Our findings suggest the possibility of a strong infra-red near-field in the close vicinity of the nanoheaters with potential applications e.g. in microscopy. [Preview Abstract] |
Wednesday, March 7, 2007 3:42PM - 3:54PM |
S44.00007: Plasmon Assisted Heating of Metal Nanoparticles Adam Bushmaker, David Boyd, Rajay Kumar, David Goodwin, Stephen Cronin Optical heating of Au nanoparticles by light at the plasmonically resonant frequency is studied. Block copolymer lithography is used to create highly uniform monodisperse arrays of Au nanoparticles. Extremely high temperatures and electric fields are produced locally with relatively low intensities of laser light. The heating is quantified using three approaches: melting of glass, dissociation of carbon monoxide, and Stokes/anti-Stokes Raman spectroscopy. Temperatures in excess of 375$^{o}$C are observed in the nanoparticles for incident light intensities of less than 7x10$^{3}$ W/cm$^{2}$. Anti-Stokes:Stokes Raman spectra of PbO deposited by plasmon assisted chemical vapor deposition (PACVD) [1] on top of the nanoparticles show a heating factor 1570 times larger than a bulk reference sample. We show that temperature rises of this magnitude are consistent with our model of reduced heating at the nanoscale. [1] D. A. Boyd et al, Nano Lett., \textbf{6}, 2592 (2006). [Preview Abstract] |
Wednesday, March 7, 2007 3:54PM - 4:06PM |
S44.00008: Modifying the visual appearance of metal nanoparticle composites by infrared laser annealing Andrej Halabica, J. C. Indrobo, R. H. Magruder III, R. F. Haglund Jr., J. M. Epp, S. Rashkeev, L. A. Boatner, S. J. Pennycook, S. T. Pantelides It has long been known that noble-metal nanoparticles in insulators can alter their visual appearance. Many metal nanoparticle composites can be created by ion implantation and subsequent annealing to initiate phase separation, nucleation and growth of nanoparticles. The size and size distribution of the nanoparticles - and therefore the color of the composite - are determined by the chemistry and thermodynamics of the annealing process. In this paper we report that we can also alter the color of gold- and silver-implanted silica and alumina by tunable infrared laser irradiation. Essentially a variant of rapid thermal annealing, this laser treatment can shift the plasmon band of the nanoparticles by tens of nm, resulting in significantly altered visual appearance. The amount of energy delivered to the implanted layer, and the subsequent color variation, can be adjusted by changing the wavelength and fluence of the laser. This makes it possible, as we will show, to write or pattern the composite material with 200~$\mu $m linewidths. This work is partially supported by DOE (DE-AC05-00OR22725), NSF (DMR-0513048), and by Alcoa Inc. [Preview Abstract] |
Wednesday, March 7, 2007 4:06PM - 4:18PM |
S44.00009: First Principles Absorption Spectra of Si$_n$ ($n=20-28$) Clusters: TDLDA versus Predictions from Mie Theory Koblar Jackson, Juan C. Idrobo, Serdar Ogut, Mingli Yang First-principles absorption spectra calculated within the time- dependent local-density approximation for Si$_n$ ($n=20-28$) clusters reveal that prolate and compact clusters have distinct shape signatures, but no clear size dependence for a given shape.\footnote{Idrobo, Jackson, Yang, and Ogut, Phys. Rev. B {\bf 74}, 153410 (2006)} The shape dependence and size independence of the spectra and most of the peak positions and intensities can be explained remarkably well within the {\em classical} Mie theory, developed for light absorption by {\em metallic} particles using the {\em bulk} dielectric function of Si. Moreover, the experimental spectrum of Si$_{21}$ is in very good agreement with the theoretical spectrum of the prolate cluster, which is lower in energy than the compact one at this size. [Preview Abstract] |
Wednesday, March 7, 2007 4:18PM - 4:30PM |
S44.00010: Optical Properties of Cage Versus Space-Filling Gold Clusters: A TDLDA Study Weronika Walkosz, Juan C. Idrobo, Serdar Ogut, Jinlan Wang, Julius Jellinek Recent DFT computations\footnote{J. Wang {\em et al.}, J. Chem. Phys. A {\bf 109}, 9265 (2005).} have revealed that medium size Au$_n$ clusters form hollow cage and space-filling structures that are energetically competitive. In fact, for $n=32$ and 50 the cage structures are more stable than their space-filling counterparts. Here we report results of large-scale computations on the optical absorption spectra of the most stable cage and space-filling forms of Au$_n$, $n=32,38,44,50$. The computations are performed using the time-dependant linear-response density functional formalism within the local- density approximation (TDLDA). We examine the trends in the low-energy ($<$ 6 eV) parts of the spectra as a function of the cluster size and structure and compare them with the predictions of the classical Mie theory. [Preview Abstract] |
Wednesday, March 7, 2007 4:30PM - 4:42PM |
S44.00011: Isomeric Forms, Polarizabilities, and Optical Absorption Spectra of Ag$_{11}$ Serdar Ogut, Juan C. Idrobo, Karoly Nemeth, Julius Jellinek First principles based computational results on the atomic structures, static polarizabilities, and optical absorption spectra of eight low-energy isomers of Ag$_{11}$ are presented and discussed. The computations were performed using the static and time-dependent formalisms of the density functional theory. Comparison of the computed spectra with those measured for Ag$_{11}$ embedded in Ar and Ne matrices\footnote{F. Conus, V. Rodrigues, S. Lecoultre, A. Rydio, and C. Felix, J. Chem. Phys. {\bf 125}, 024511 (2006).} shows that it is the spectrum of the lowest energy isomer that exhibits the best overall agreement with the experiment. The theoretical analysis indicates that the $d$ electrons play a more important role in optical transitions in Ag$_{11}$ than in smaller Ag$_n$,$n\le 8$, clusters.\footnote{J. C. Idrobo, S. Ogut, and J. Jellinek, Phys. Rev. B {\bf 72}, 085445 (2005).} [Preview Abstract] |
Wednesday, March 7, 2007 4:42PM - 4:54PM |
S44.00012: Preparation and control of optical properties of plasmonic crystals using colloidal crystals as templates. Zhen-Lin Wang, Peng Zhan, Nai-Ben Ming Plasmonic crystals show promise for applications from optical, electronic devices, nanolithography, metamaterials to enhanced Raman scattering sensors. For such applications it is important to develop simple routes to prepare such metallic films with two-dimensional (2D) regular nanostructure ordering. We will show that templating against 2D colloidal crystal is a convenient route to prepare such crystals that are composed of rigid array of metal nanoparticles. We also discuss how to excise rational methods which allow control over the morphology of the crystal unit, thus tuning optical properties of the prepared plasmonic crystals. By implementation of physical, chemical, or electrochemical deposition of metal in combination with micromolding, a variety of morphologies of the metallic nanoparticles can be created. The nanoscale morphology and optical transmission properties of the prepared 2D metallic membranes have been characterized. [Preview Abstract] |
Wednesday, March 7, 2007 4:54PM - 5:06PM |
S44.00013: Optical Metamaterials at Near IR Range Fabricated by Nanoimprint Lithography E. Kim, W. Wu, E. Ponizovskaya, Y.R. Shen, A. Bratkovsky, S.Y. Wang Metamaterials operating at near-IR frequencies have been designed, fabricated by nanoimprint lithography (NIL), and characterized by laser spectroscopic ellipsometry. The structure was a metal/dielectric/metal stack ``fishnet'' structure that demonstrated negative permittivity and permeability in the same frequency region and hence exhibited a negative refractive index at a wavelength near 1.7 micron. The results of the transmittance and the reflectance measurements of the ``fishnet'' structure show a strong resonance appears in the vicinity of 1.67 micron. This resonance comes from the negative permittivity combined with the magnetic resonance. The position of the resonance agrees with predictions from FDTD simulation. This work demonstrates the feasibility of designing various optical negative-index metamaterials and fabricating them using the NIL as a low-cost, high-throughput fabrication approach. [Preview Abstract] |
Wednesday, March 7, 2007 5:06PM - 5:18PM |
S44.00014: Nanoparticles in alumina: Microscopy and Theory Juan C. Idrobo, Andrej Halabica, Sergey Rashkeev, Michael V. Glazoff, Lynn A. Boatner, Richard F. Haglund, Stephen. J. Pennycook, Sokrates T. Pantelides Transition-metal nanoparticles formed by ion implantation in alumina can be used to modify the optical properties of naturally oxidized and anodized aluminum. Here, we report atomic-resolution Z-contrast images using a scanning transmission electron microscope (STEM) of CoFe and other metal nanoparticles in alumina. We also report electron energy loss spectra (EELS) and relate them to visual appearance and optical properties. Finally, we report first-principles density- functional calculations of nucleation mechanisms for these nanoparticles. This research was sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy, under contract DE-AC05- 00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, by NSF grant No. DMR-0513048, and by Alcoa Inc. [Preview Abstract] |
Wednesday, March 7, 2007 5:18PM - 5:30PM |
S44.00015: Probing the Surface Guided Modes from Infrared to Ultraviolet by Fast Electrons Aycan Yurtsever, Martin Couillard, David A. Muller We use monochromated, 200 kV electrons with high spatial resolution to study guided modes and surface plasmons in thin silicon slabs. We observe, both theoretically and experimentally, the presence of multiple plasmonic modes in a range from infrared to ultraviolet. We observe one mode at a thickness of $\sim $20 nm and up to five modes at a slab thickness of $\sim $250 nm, which agrees remarkably well with the relativistic dielectric theory. Finally, we use our technique to examine effective dielectric medium theories by studying silicon nanoparticles embedded in silicon oxide, a materials system with potential technological applications. [Preview Abstract] |
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