Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session G35: Nanoparticles, Nanotubes and Nanocrystals: Optical and Structural Properties |
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Sponsoring Units: DCMP Chair: Alexander Efros, Naval Research Laboratory Room: Baltimore Convention Center 338 |
Tuesday, March 14, 2006 8:00AM - 8:12AM |
G35.00001: Simulations of the Optical Properties of Silicon Nanoparticles Embedded in Silicon Nitride Sebastien Hamel, Andrew Williamson, Giulia Galli, Luca Dal Negro, Jae Hyung Yi, Victor Nguyen, Yasha Yi, Jurgen Michel, Lionel C. Kimerling There is currently a strong interest in the material science community in the optical properties of silicon nanoparticles embedded in silicon nitride. These nanostructures are CMOS-compatible materials which exhibit efficient and fast light emission. The optical properties of these embedded silicon nanoparticles are studied using first-principles Density Functional Theory simulations. We present simulations of the structural, electronic and optical properties of nitrogen-doped silicon nanoparticles both in the gas phase and embedded in a silicon nitride environment. These simulations point to the crucial role played by nitrogen atoms bonded to the surface of small ($\sim$ 1nm) silicon nanoparticles in the light emission mechanism of SiN$_x$ films. We compare the calculated optical gaps and radiative lifetimes of the nanoparticles with recent experimental measurements of light-emitting silicon-rich silicon nitride films obtained by PE-CVD deposition followed by low temperature (500-900 $^\circ$C) thermal annealing. This work was performed under the auspices of the U.S. Dept. of Energy at the University of California/Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48. [Preview Abstract] |
Tuesday, March 14, 2006 8:12AM - 8:24AM |
G35.00002: Multi-valued analog information storage using self-assembled nanoparticle films. Al-Amin Dhirani, Yoshinori Suganuma Digital computers use binary states, typically represented by 0 and 5 V, to store and process information at all stages of a calculation. If more states (ideally a continuum) were available in between, density of information could be dramatically increased. Here we show that self-assembled nanoparticle films can feature such continuous state or analog information storage. Nanoparticle films were prepared on gate oxides by alternate immersion in solutions of gold nanoparticle and dithiol linker molecules. These films afford microlithography-free fabrication bridging nanometer to micrometer length scales as well as a layer-by-layer assembly yielding three-dimensional functional structures. Information provided by an arbitrary gate voltage was 'written' by trapping charges in local, gate-modified potentials when films were cooled below 175 K. The information was 'read' using the film's built-in ability to sense charge via Coulomb blockade. Application of a time-dependent, multi-step writing gate voltage generates conductance maps corresponding to multi-valued analog information. As a proof of concept, we exploited this technique to store 'UT' in Morse code. [Preview Abstract] |
Tuesday, March 14, 2006 8:24AM - 8:36AM |
G35.00003: Using Accumulated Charge to Monitor Nanoparticle Deposition Rates Via Electrospray Ionization Joel Therrien, Amir Dindar, David Smith Electro-Spray Ionization (ESI) is a handy technique for depositing nanoparticles onto a substrate directly from a liquid suspension. ESI atomizes the suspension via high electric fields. The solvent in which the particles were suspended rapidly evaporates resulting in a stream of charged particles. This technique can be used to deposit a sub-monolayer dispersion of particles on any conducting substrate. AFM studies have been performed on ESI deposited samples to determine the correlation between the net charge deposited on the substrate via the deposition and the surface density of particles. This correlation may be used as a means of rate monitoring to assure higher reliability in achieving desired particle densities. [Preview Abstract] |
Tuesday, March 14, 2006 8:36AM - 8:48AM |
G35.00004: Enhanced optical luminescence in ZnO nanostructures following O 1s to p$_{z}$ excitation R.A. Rosenberg, G.K. Shenoy, X.-T. Zhou, T.K. Sham Room temperature ultraviolet ($\sim $385 nm) lasing in ZnO nanostructures has recently been demonstrated.$^{1}$ This phenomenon is thought to arise from the natural cavity formed by the wurtzite nanostructure and its faceted ends. X-ray excited optical luminescence (XEOL) provides the capability to determine the nature of the sites responsible for producing low energy (1-6 eV) fluorescence. We will present XEOL excitation curves taken at the Zn L and O K edge obtained using both the defect ($\sim $510 nm) and bandgap ($\sim $370 nm) transitions as signals. Results obtained at the Zn L edge resemble the x-ray absorption curve of the nanostructure. However, striking differences are observed at the O K edge. Excitation to states of p$_{z}$ symmetry (along the c axis) leads to enhanced luminescence while excitation to p$_{x,y}$ states (lying in the basal plane) decreases the yield. We interpret this phenomenon as resulting from the lower probability of quenching by near surface defects for states excited along the c-axis as opposed to those excited perpendicular to it. 1. M.H. Huang, \textit{et al}., Science \textbf{292}, 1897 (2001). [Preview Abstract] |
Tuesday, March 14, 2006 8:48AM - 9:00AM |
G35.00005: Silicon nanoporous pillar array: template for fabricating silicon-based nanocomposites with enhanced physical properties Xin Jian Li, Xiao Nan Fu, Hai Jun Xu, Wei Feng Jiang A triple hierarchical structure, silicon nanoporous pillar array (Si-NPA), was formed on silicon wafers by a hydrothermal method. The structure of Si-NPA is characterized by the regular array of micron-sized silicon pillars, quasi-identical nanopores densely distributing over each pillar, and silicon nanocrystalllites composing the walls of the nanopores. Utilizing the excellent structural regularity and high chemical reactivity of Si-NPA, patterned nanocomposites of CdS, carbon nanotubes (CNTs), Au, and Fe3O4/Si-NPA were fabricated. Their element compositions, morphologies and microstructures were characterized. Ideal physical properties of I-V curve in CdS/Si-NPA heterojunction, field emission in Si-NPA, CNTs/Si- NPA, Au/Si-NPA, and humidity/gas sensitivity in Fe3O4/Si-NPA were observed and the corresponding mechanisms were analyzed. These results indicate that Si-NPA could be employed as an ideal template to assembly silicon-based functional nanosystems, and might find multiple applications in fabricating novel electronic devices. [Preview Abstract] |
Tuesday, March 14, 2006 9:00AM - 9:12AM |
G35.00006: Excitons in Negative Band Gap Nanocrystals James Sims, Garnett W. Bryant, Howard Hung Exploiting quantum confinement in nanocrystals made from materials with negative bulk band-gap will be critical for nanosensor applications in the far infrared. However, understanding quantum confinement, excitonic states and optical response in negative band-gap nanocrystals provides challenges not posed for usual nanocrystals with positive bulk band-gaps. We show that intrinsic surface states occur in nanocrystals made from negative gap semiconductors such as HgS. We use atomistic tight-binding theory that accounts for band mixing critical in negative-gap semiconductors but unimportant in positive-gap systems. Such band mixing makes effective mass theory inadequate for negative-gap nanocrystals. In small HgS dots, the lowest conduction band states are cation-derived and the band-edge valence states are anion-derived, as for finite-gap dots. However, in bigger HgS dots, the lowest conduction band state has a high density at the surface that slowly decays into the dot. As the dot size increases, this conduction state crosses the valence band edge, reaching a limit inside the bulk negative gap for very large dots. In this limit, the state is localized to the surface. The excitonic states and optical response of HgS dots are discussed to identify signatures for intrinsic surface states and to assess nanosensor applications with these systems. [Preview Abstract] |
Tuesday, March 14, 2006 9:12AM - 9:24AM |
G35.00007: Freely-Suspended Monolayers of Gold Nanocrystals: Fabrication and Elastic Properties Klara Elteto, Xiao-Min Lin, Sang-Kee Eah, Heinrich M. Jaeger We present a method to produce freely-suspended monolayers of 5.5nm-diameter gold nanocrystals, ligated with dodecanethiol, over holes with widths up to 2microns (about 250 particles). The holes are etched through a 120nm thick silicon nitride membrane. A water droplet initially covers the substrate. When nanocrystals suspended in toluene are added, they spread over the water-air interface, forming an extended, compact monolayer. As the water dries, the monolayer settles over the substrate and drapes itself over the holes. The resulting freely-suspended monolayers are stable in air and vacuum, as observed with optical, atomic force and transmission electron microscopy. No additional polymer or crosslinking of the ligands is required. Possible mechanisms for the stability of the monolayer include ligand interdigitation and van der Waals interaction between the gold cores. We report on measurements of the elastic properties of such monolayers, obtained by applying point forces to the suspended areas with an atomic force microscope and measuring the vertical elastic deformation. [Preview Abstract] |
Tuesday, March 14, 2006 9:24AM - 9:36AM |
G35.00008: Mapping Elastic Strain in Electrophoretically-Deposited CdSe Nanocrystal Films Irving Herman, Sarbajit Banerjee, Shengguo Jia, Dae-In Kim, Richard Robinson, Jeffrey Kysar, Joze Bevk The mechanical stability of nanocomponent films is critical for applications and yet is a largely unexplored area of research. Raman microprobe analysis has been used to probe elastic strain in the cores of thick, fractured electrophoretically-deposited CdSe nanocrystal films. Strain in these films arises from solvent evaporation and can be as much as 2.5{\%} in the cores of CdSe nanocrystals for 3.2 $\mu $m thick films. The overall strain in these films, as determined by optical microscopy, is $\sim $11.7{\%}. The in-plane stress developed in these films is $\sim $1.6 GPa. The biaxial modulus of the films is determined to be $\sim $13.8 GPa. Using micromechanics models, a value of $\sim $5.1 GPa is inferred for the biaxial modulus of the trioctylphosphine oxide ligand matrix. Since, solvent loss leads to strain in most ensembles of colloidal nanocrystals, this method has the potential for being broadly generalizable to other films made of nanocrystalline components. Support for this work was provided by the Materials Research Science and Engineering Center of the NSF under Grant No. DMR-0213574 and by NYSTAR. [Preview Abstract] |
Tuesday, March 14, 2006 9:36AM - 9:48AM |
G35.00009: White-Light Emission from Magic-Sized Cadmium Selenide Nanocrystals Michael Bowers , James McBride, Sandra Rosenthal Magic-sized cadmium selenide (CdSe) nanocrystals have been pyrolytically synthesized. These ultra-small nanocrystals exhibit broadband emission (420 -710 nm) that covers most of the visible spectrum while not suffering from self absorption. This behavior is a direct result of the extremely narrow size distribution and unusually large Stokes shift (40-50 nm). The intrinsic properties of these ultra-small nanocrystals make them an ideal material for applications in solid state lighting$^{ }$and also the perfect platform to study the molecule-to-nanocrystal transition. [Preview Abstract] |
Tuesday, March 14, 2006 9:48AM - 10:00AM |
G35.00010: Antenna Effects in Arrays of Aligned Carbon Nanotubes K. Kempa, J. Rybczynski, Y. Wang, Z. Ren, Z. P. Huang, D. Cai, J. B. Kimball, J. Carlson, G. Benham We have demonstrated earlier [1], that carbon nanotubes respond to light as radio antennas. Specifically, we have demonstrated the polarization and length antenna effects. Here we show yet another, a more subtle antenna effect: the multi-lobe reflection pattern with the specular enhancement. We demonstrate this effect in a random array of aligned, widely spaced carbon nanotubes. We show via calculation and computer simulations that these effects are results of the conventional antenna theory. \newline \newline [1] Y. Wang, K. Kempa, B. Kimball, J. B. Carlson, G. Benham, W. Z. Li, T. Kempa, J. Rybczynski, A. Herczynski, and Z. F. Ren, Applied Physics Letters \textbf{85}, 2607 (2004). [Preview Abstract] |
Tuesday, March 14, 2006 10:00AM - 10:12AM |
G35.00011: Aligned carbon nanotubes as nanocoax cables for subwavelenght light transmission Jakub Rybczynski, Krzysztof Kempa, Yang Wang, Zhongping Huang, Dong Cai, David Carnahan, Renata Jarzebinska, Michael Giersig, Zhifeng Ren We are presenting for the first time that vertically aligned carbon nanotubes can be used for fabrication of large-scale arrays of nanocoax cables. Multicoating with insulating and metallic layers results in a coaxial structure where light can be transmitted along the nanotube axis in the visible frequency range. We have shown that unlike simple optical waveguides, coaxial nanocables exhibit subwavelength transmission of light. Results obtained with near-field optical microscope confirm our predictions. Some aspects of nanocoax cables farbication and optical properties studies will be presented. [Preview Abstract] |
Tuesday, March 14, 2006 10:12AM - 10:24AM |
G35.00012: Theory of plasmon excitations in coaxial cylindrical geometries: finite magnetic field Manvir Kushwaha, Bahram Djafari-Rouhani We report on a theoretical investigation of the plasmon propagation in the coaxial cylindrical geometries using Green's function (or response function) theory in the presence of an applied axial magnetic field ($\vec{B}\parallel \hat{z}$). Green's function theory generalized to be applicable to such quasi-one dimensional (1D) systems enables us to derive explicit expressions for the corresponding response functions (associated with EM fields), which can in turn be used to compute numerous physical properties of the system under consideration. As an application, we present several illustrative examples on the dispersion characteristics of the confined and extended magnetoplasmons in the single- and double-interface structures. These dispersive modes are also substantiated through the computation of local as well as total density of states (DOS). It is found that, unlike the zero-field case, the magnetoplasma propagation is nonreciprocal with respect to the sign of the index $m$ of the Bessel functions involved. We also briefly clarify some delusive traces of the edge magnetoplasmpons for a plasma shell embedded between two identical or unidentical dielectrics. Our theoretical framework can also serve as a powerful technique for studying the intrasubband plasmons and magnetoplasmons in the emerging multiwall carbon nanotubes. [Preview Abstract] |
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