Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W6: Focus Session: Nanostructures and Metamaterials IV |
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Sponsoring Units: DMP DCMP Chair: Oded Rabin, University of Maryland Room: 006A |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W6.00001: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W6.00002: Electromagnetically assisted synthesis of highly concentrated gold nanoparticle colloids Laura Hernandez, Walter Rosas, Guillermo Naranjo, Xomalin G. Peralta, Watson L. Vargas The synthesis of metallic nanoparticles is currently an extremely active area of research due to the multiple potential applications of nanomaterials to areas ranging from nano-medicine to catalysis. Some of the current challenges of nanoparticle synthesis protocols include synthesizing nanoparticles in high concentrations with a small polydispersity. The present study contrasts and compares the synthesis of highly concentrated colloidal gold using three different sources of electromagnetic radiation to assist the reaction. The first source was a Spectra Physics Mai Tai Ti:Sapphire laser made by Sperian, this laser generates 70 fs FWHM pulses with wavelengths in the range of 690-1040 nm. The second source was sun light; this was measured to have a power of 10W. The third source was a lowelDP lamp with a measured intensity of 25W. Both the solar light and the lamp's rays were concentrated using a 28cm x 28cm Fresnel lens. Results will be presented highlighting differences and similarities in size, shape, crystallinity and time of the reaction. We speculate about the role played by variations in wavelength, temporal profile of the electromagnetic source (pulsed vs. continuous), temperature of the reaction and excitation power in the final structure of the nanoparticles generated. [Preview Abstract] |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W6.00003: Super Resolution Measurements of the Near-Field Coupling of the Polarized Modes of Gold Nanorods to Fluorescent Emitters Benjamin Isaacoff, Jessica Donehue, Julie Biteen The localized surface plasmon resonances of metal nanoparticles result in complex light-matter interactions that depend strongly on the nanoparticle geometry. In this work, we use single-molecule super-resolution imaging and single-particle spectroscopy to study the polarization dependent response of gold nanorods (GNRs), which support two orthogonal plasmon modes. Furthermore, we measure the emission intensity and polarization of single fluorescent molecules coupled to the GNR as a function of excitation polarization and spectral overlap with the GNR modes. Based on such differential excitation, we demonstrate polarization control of plasmon-enhanced fluorescence from single molecules coupled to single nanoparticles. These experiments are compared with broadband finite-difference time domain (FDTD) simulations studying the role of fluorophore position and orientation, revealing the underlying mechanisms of this coupling. These super-resolution measurements and the associated simulations demonstrate how polarization can be used to actively control nanoparticle plasmonics and opens the door to a new framework for controlling and optimizing nanoparticle-fluorophore interactions. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W6.00004: Influence of Surfactant Bilayers and Substrate Immobilization on the Refractive Index Sensitivity of Anisotropic Gold Nanoparticles Mohammad Shahjamali, Nicolas Large, Erik Martinsson, Negin Zaraee, George Schatz, Daniel Aili, Chad Mirkin Shape-controlled synthesis of gold nanoparticles (AuNPs) generally involves the use of surfactants to regulate the nucleation growth process and to obtain colloidally stable AuNPs. The surfactants adsorb on the NP surface making further functionalization difficult and therefore limit their practical use in many applications such as bio- and molecular sensing, surface-enhanced spectrosopies, and NP assembly. Herein, we report on how cetyltrimethylammonium (CTAX, X$=$Cl$^{-}$, Br$^{-})$, a common surfactant used in anisotropic AuNPs synthesis, affectsthe nanoparticle sensitivity to local dielectric environment changes and limitsrefractometric plasmonic sensing. We experimentally and theoretically show that the CTAX bilayer significantly reduces the refractive index (RI) sensitivity of anisotropic AuNPs such as flat and concave nanocubes, nanorods, and nanoprisms. We show that the RI sensitivity can be improvedby up to 40{\%} by removing the CTAXfrom immobilized AuNPs using oxygen plasma treatment. The substrate effect on the RI sensitivity caused by NP immobilization isalso investigated. The strategy presented herein is a simple andeffective method to improvethe RI sensitivity of CTAX-stabilized AuNPs, thus increasing their potential in nanoplasmonic sensingand in biomedical applications. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W6.00005: Surface plasmons excitation and manipulation by low-energy electrons Michael J. Burns, Juan M. Merlo, Yitzi M. Calm, Michael J. Naughton Surface plasmons coupled by optical fields have been widely used to control the propagation of electromagnetic fields in the nanoscale range. We propose numerically the use of low-energy electrons to excite and manipulate surface plasmons in metallic surfaces by using different configurations of tunneling junctions. Modeling the inelastic electron scattering at tunneling junctions as an electric dipole, it is possible to use an electromagnetic model to reproduce experimental results already reported [1]. Following this methodology, we demonstrate that it is possible to mimic novel plasmonic elements that can be excited only by optical fields, i.e. focused beams. Our results open a wide range of applications because it avoids the noise produced by direct light excitation in the detection of surface plasmons. Finally, as an application of our proposed scheme, we study the unidirectional surface plasmon coupler, getting similar results to those recently reported [2]. \\ $[1]$ J .K. Gimzewski, J. K. Sass, R. R. Schlitte and J. Schott, Europhys. Lett, $\bf{8}$, 435 (1989). \\ $[2]$ F. Ye, M. J. Burns and M. J. Naughton, Adv. Optical Mat. $\bf{2}$, 957, (2014). [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W6.00006: Optical Properties of Scalable Nano-Mesh Films Kyle Alvine, Bruce Bernacki, Wendy Bennett, Alan Schemer-Kohrn We describe here the optical properties of a scalable nano-mesh film both experimentally measured and calculated by FDTD numerical modeling. Typically, applications for optically responsive nano-plasmonic or photonic films are limited by virtue of tractable fabrication techniques to several hundred microns or a few millimeters in size. The films described here have been demonstrated over an extent of several inches and could be readily scaled to larger sizes. The films are comprised of a quasi-regular periodic array of nanoscale holes in a metallic film. The nanostructure is fabricated in a scalable fashion in a multi-step fashion via sputtering on a nanoscale template created by nanoparticle self-assembly. Both the numerical modeling and experimentally measured scattering demonstrate that these films are highly resonant with the resonance location in the visible or near infrared and set by the hole size and pattern geometry. Such films can also be readily be made on flexible substrates if desired. Potential applications include new proposed photonic thermal management coatings or plasmoelectric devices. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W6.00007: Dirac-like plasmons in Ag nanopillar honeycomb lattices Siying Peng, Benjamin Brenny, Sondra Hellstrom, Toon Coenen, Albert Polman, Harry Atwater Surface plasmons in honeycomb lattices of Ag nanoparticles exhibit Dirac-like band structures, similar to the electronic band structure of graphene. Full wave simulations for an infinite honeycomb lattice of silver nano-pillars reveal hybridization of localized plasmonic modes between two neighboring pillars and the consequent formation of bonding and anti-bonding modes that are energetically degenerate at Dirac points. Electromagnetic simulations reveal the existence of plasmonic edge states in finite width nanoribbons of the honeycomb nanoparticle lattice. Nanoscale architecture of the honeycomb lattice may provide a new way to control plasmon propagation by selective excitation of directional surface plasmon edge states without backscattering. Experimentally, we have utilized cathodoluminescence (CL) spectroscopy to study angular emission patterns and construct band structures of the silver pillars in honeycomb lattices. In our initial CL measurement, silver pillars in honeycomb lattices, we have observed strong radiation patterns near the Brillouin zone edge, integrated over an interval of wavelength centered on the wavelength of the Dirac points.~ [Preview Abstract] |
Thursday, March 5, 2015 3:54PM - 4:06PM |
W6.00008: MEMS for Tunable Plasmonic Coupling Tom Stark, Matthias Imboden, Sabri Kaya, Alket Mertiri, Shyamsunder Erramilli, David Bishop The localized surface plasmon resonance (LSPR) of sub-wavelength holes in metals depends upon the geometry, composition, refractive index, and near field coupling to neighboring particles. Sub-wavelength holes in metals can exhibit extraordinary optical transmission (EOT) at the resonance frequency and, for certain geometries, polarization-dependent transmission. We present a microelectromechanical system, tunable Fabry-Perot etalon. One interface is a suspended gold metamaterial and the other is a gold reflector. The reflectance, measured with a Fourier transform infrared spectrometer, exhibits the convolution of the EOT through the holes and Fabry-Perot resonances. Using MEMS, we modulate the etalon length from 1 to 20 $\mu$m, thereby tuning the free spectral range from about 5000 to 250 cm$^{-1}$ and shifting the reflection minima and maxima across the infrared. When the separation between the metamaterial and gold reflector approaches the decay length of the LSP electric fields, interactions with image currents generated in the gold reflector become significant. By tuning the separation in this regime, we will tune the near field coupling between the LSPR and image currents and tune the LSPR of the system, effectively creating a sensing substrate with a tunable LSPR frequency. [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W6.00009: Digitally Programmable Micro Evaporation Source for Nanofabrication Han Han, Matthias Imboden, Pablo Del Corro, Thomas Stark, Richard Lally, Flavio Pardo, Cris Bolle, David Bishop There is a significant world-wide effort to develop nano-manufacturing methods that can extend into the deep nanoscale region, below 20 nm. Techniques include photolithography, nano-imprint and direct write methods such as dip-pen lithography and atomic calligraphy. A central component of any fabrication setup is the deposition control of the materials to be used. Here we present a MEMS based, multi-material evaporation source array with each source element consisting of a polysilicon plate suspended by two electrical constriction leads. When resistively heating the plate, the pre-loaded material is thermally evaporated off of the plate. By arranging many of these devices into an array, one has a multi-material, digitally programmable evaporation source. Pulsing the source with precisely controlled peak voltage and timing can emit atom fluxes with an unprecedented level of control in terms of what, when and how many atoms get deposited. By varying their dimensions and arrangement, the source array can provide controllable atom fluxes ranging over ten orders of magnitude. Such a material source can provide precise control and flexibility when conducting nanopatterning and nanolithography. [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W6.00010: Soft Nanoimprint Lithography for Direct Printing of Crystalline Metal Oxide Nanostructures Rohit Kothari, Michael Beaulieu, James Watkins We demonstrate a solution-based soft nanoimprint lithography technique to directly print dimensionally-stable crystalline metal oxide nanostructures. A patterned PDMS stamp is used in combination with a UV/thermal cure step to imprint a resist containing high concentrations of crystalline nanoparticles in an inorganic/organic binder phase. The as-imprinted nanostructures are highly crystalline and therefore undergo little shrinkage (less than 5{\%} in some cases) upon thermal annealing. High aspect ratio nanostructures and sub-100 nm features are easily realized. Residual layer free direct imprinting (no etching) was achieved by choosing the resist with the appropriate surface energy to ensure dewetting at stamp-substrate interface. The technique was further extended to stack the nanostructures by deploying a layer-by-layer imprint strategy. The method is scalable and can produce large area device quality nanostructures in a rapid fashion at a low cost. CeO$_{2}$, ITO and TiO$_{2}$ nanopatterns are illustrated for their potential use in fuel cell electrodes, solar cell electrodes and photonic devices, respectively. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W6.00011: Resolving the two-dimensional self-assembly of iron oxide nanoparticles on a liquid surface Jiayang Hu, Datong Zhang, Chenguang Lu, Seung Whan Lee, Fan Ye, Irving P. Herman In situ small-angle X-ray scattering (SAXS) is used to monitor the self-assembly of iron oxide nanoparticles (NPs) dispersed in alkanes that are drop-cast on a diethylene glycol liquid surface. We found that the surface separations of NP cores in 2D superlattices (SLs) are generally farther apart than in 3D SLs with corresponding NPs. At these separations, the van der Waals (vdW) energy is smaller than the Brownian motion energy and so the previous 3D vdW force driven self-assembly models fail to explain the stable closed-packed structure. Strong ligand-ligand interactions likely bind the structure after the upper solvent dries. Entropy effects are found not to be the likely driving force for the observed close packing structures. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W6.00012: Imaging of Bottom-up Graphene Nanoribbons Synthesized Using Combined Solution and Surface Reactions Danny Haberer, Chen Chen, Zahra Pedramrazi, Ryan Cloke, Tomas Marangoni, Won-Woo Choi, Felix Fischer, Crommie Michael Bottom-up graphene nanoribbons (GNRs) are a new class of material that has promising applications in next-generation electronic, spintronic, and optical devices. Bottom-up synthesis using molecular precursors provides precise control over GNR width and edge geometry, which determine GNR electronic structure. However, previously used on-surface polymerization techniques can be hindered by molecular diffusion barriers and by undesired side products. Alternative in-solution polymerization techniques potentially have better yield and higher selectivity. Using combined in-solution polymerization and on-surface cyclodehydrogenation reactions, we have successfully synthesized N$=$9 armchair GNRs. Scanning tunneling microscopy was used to reveal the precise width and edges of the resulting nanoribbons. This method may be generalized to synthesize graphene nanoribbons that are difficult to fabricate through exclusive on-surface reactions. [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W6.00013: Dynamically tunable graphene/dielectric photonic crystal transmission lines Ian Williamson, S. Hossein Mousavi, Zheng Wang It is well known that graphene supports plasmonic modes with high field confinement and lower losses when compared to conventional metals. Additionally, graphene features a highly tunable conductivity through which the plasmon dispersion can be modulated. Over the years these qualities have inspired a wide range of applications for graphene in the THz and infrared regimes. In this presentation we theoretically demonstrate a graphene parallel plate waveguide (PPWG) that sandwiches a 2D photonic crystal slab. The marriage of these two geometries offers a large two dimensional band gap that can be dynamically tuned over a very broad bandwidth. Our device operates in the low-THz band where the graphene PPWG supports a quasi-TEM mode with a relatively flat attenuation. Unlike conventional photonic crystal slabs, the quasi-TEM nature of the graphene PPWG mode allows the slab thickness to be less than 1/10 of the photonic crystal lattice constant. These features offer up a wealth of opportunities, including tunable metamaterials with a possible platform for large band gaps in 3D structures through tiling and stacking. Additionally, the geometry provides a platform for tunable defect cavities without needing three dimensional periodicity. [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W6.00014: Toward Controlled In-Solution Stacking of Solvent Exfoliatied 2-Dimensional Nanoflakes and Heterostructures Dale Brown, A. Nicole Chang, Richard Livingston, David Estrada As a result of quantum confinement, materials with one dimension confined to a few atomic diameters, including single- and few-layer graphene and transition metal dichalcogenides (TMDs), often have properties unique from those of their bulk counterparts. Included in these emergent properties is photoluminescence in thin flakes of some semiconducting TMDs. Additionally, the creation of heterostructures via the stacking of 2D materials allows for the synthesis of new materials with properties unique from those of the starting materials. While much of the research published to date in this area relies on labor intensive methods, including stacking each subsequent layer by hand to synthesize these heterostructures, some researchers have demonstrated random stacking of suspended 2D flakes in solution, with limited control over the thickness of the resulting heterostructures. By modifying the surface energy mismatch between a solvent and the suspended, exfoliated 2D materials therein, we aim to demonstrate the ability to actively control the propensity for and duration of stacking in liquid suspensions of 2D materials. [Preview Abstract] |
Thursday, March 5, 2015 5:18PM - 5:30PM |
W6.00015: Bottom-up synthesis of N$=$11 armchair graphene nanoribbons via new sp3 to sp2 cyclization route Zahra Pedramrazi, Chen Chen, Danny Haberer, Wade Perkins, Felix Ficsher, Michael Crommie Bottom-up synthesis is a powerful fabrication tool for controlling the atomic scale structures of graphene nanoribbons (GNRs). The electronic properties of GNRs, 1D strips of graphene that exhibit energy gaps in their electronic structure due to quantum confinement, is highly dependent on precise width and atomic edge structure. The molecular precursors used to date for bottom-up synthesis are based on conjugated systems of sp2-bonded carbon atoms. Here we demonstrate a new molecular precursor for synthesis of bottom-up N$=$11 armchair GNRs that exhibits cyclodehydrogenation of ``out-of-plane'' sp3-bonded elements. Scanning tunneling microscopy imaging was used to characterize the GNR growth reaction at different annealing temperatures, allowing observation of the sp3 to sp2 cyclization process. This demonstrates a new chemical route for achieving armchair GNRs, as well as new insight into surface-based covalent self-assembly of organic molecules. [Preview Abstract] |
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