Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session W30: Nanowires and Nanotubes: Optical Properties and Spectroscopy |
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Sponsoring Units: DCMP Chair: Alec Talin, National Institute of Standards and Technology Room: C147/154 |
Thursday, March 24, 2011 11:15AM - 11:27AM |
W30.00001: ABSTRACT WITHDRAWN |
Thursday, March 24, 2011 11:27AM - 11:39AM |
W30.00002: Low temperature electron transport spectroscopy of mechanically templated carbon nanotube quantum dots Saiful Khondaker, Paul Stokes We report on the low temperature electronic transport measurements of mechanically templated carbon nanotube quantum dots (QDs). The devices were fabricated by precise dielectrophoretic placement of single walled carbon nanotubes (SWNTs) between 1 $\mu $m spaced Pd electrodes and over a local Al/Al$_{2}$O$_{3}$ bottom gate. The local gate defines the quantum dot due to the bending of SWNT at the edges of the gate, as well as controls its operation [1]. We performed detailed transport spectroscopy measurements of the templated SWNT QDs to determine how the tunnel barriers evolve with both the global back gate and local gate voltage. We will present models to explain the evolution of these devices as a function of local gate and back gate voltage. This study may allow for future size tunabiliy of SWNT QDs by further control over the tunnel barrier transparency and source, drain, and gate capacitance to fabricate room temperature single electron transistors. \\[4pt] [1] Paul Stokes and Saiful I. Khondaker, Appl. Phys. Lett. \textbf{92}, 262107 (2008). [Preview Abstract] |
Thursday, March 24, 2011 11:39AM - 11:51AM |
W30.00003: Tunneling spectroscopy using carbon nanotubes quantum dots Yanjing Li, Nadya Mason Tunneling spectroscopy is an important measurement technique, encompassing, for example, planar tunneling, scanning tunneling microscopy and superconducting tunnel probes. Here, we demonstrate that carbon nanotube quantum dots (QDs) can be used as tunneling probes. The sharp features in the density of states of the QDs in the Coulomb blockade regime can map out the density of states and the energy distribution function of the system to be studied. We present preliminary data showing tunneling from a carbon nanotube quantum dot into mesoscopic metal wires that have been driven out of equilibrium by a bias voltage. Previous measurements of these systems using superconducting probes [1-2] showed that the electron energy distribution functions and electron interactions can be determined. With the present measurements, the use of a QD instead of a superconductor allows us to probe at significantly higher temperatures and biases. \\[4pt] [1] H. Pothier, S. Gueron, Norman O. Birge, D. Esteve, and M. H. Devoret, Phys Rev Lett 79, 3490 (1997) \\[0pt] [2] Yung-fu Chen, Travis Dirks, Gassem Al-Zoubi, Norman O. Birge, and Nadya Mason, Phys Rev Lett 102, 036804 (2009) [Preview Abstract] |
Thursday, March 24, 2011 11:51AM - 12:03PM |
W30.00004: Photoconductivity Spectroscopy of Colloidal Lead Selenide Nanowires Rion Graham, Ka Leung, Dong Yu PbSe, with a large Bohr exciton radius of 46 nm, is ideally suited to study strong quantum confinement effects. Photoconductivity spectroscopy of single PbSe nanowire devices can remove the inhomogeneous broadening of ensemble measurements and allows for extraction of fine electronic structures in two dimensionally confined semiconductors. We have grown PbSe nanowires via a colloidal, oriented attachment mechanism, with diameters down to 6nm. Using a tunable wavelength laser, we have measured photoconductivity of single nanowire field effect transistors (FETs) as a function of excitation energy, temperature, and nanowire diameters. [Preview Abstract] |
Thursday, March 24, 2011 12:03PM - 12:15PM |
W30.00005: The optical properties of SnO$_{2}$ nano-wires by THz time-domain spectroscopy Dongwook Lee, Xingquan Zou, Chuanwei Cheng, Saritha K. Nair, Hongjin Fan, Elbert E.M. Chia As feature seizes of devices are reduced below a hundred nanometers and chip frequencies reaches high GHz, a convenient method of characterizing thin films in the GHz to THz frequency range has been required. THz time-domain spectroscopy provides a non-destructive, non-contact, and high-sensitive tool to characterize thin films as well as nano-materials. The optical properties of SnO$_{2}$ nano-wires, which were grown on z-cut quartz, have been investigated by THz time-domain spectroscopy. The real and imaginary parts of the complex refractive index and optical conductivity are measured at THz frequency. [Preview Abstract] |
Thursday, March 24, 2011 12:15PM - 12:27PM |
W30.00006: Direct mapping of the exciton-polariton dispersion in tree-like ZnO micro-structures Xiangshun Lu, Huajun Zhou, Z. Ryan Tian, Min Xiao We report a direct observation of branches of the exciton polaritons in tree-like ZnO micro-structures using second-harmonic generation (SHG) spectroscopy. Within the tunable range of a mode-locked Ti:Sapphire laser with pulse width of 100 femto-second, we are able to tune the second harmonic energy of the incident laser across the A, B and C excitons of ZnO. Under the resonant enhancement of the strong coupling between photons and excitons, we obtain for the first time the direct mapping of the branches of exciton-polariton dispersion at the room as well as liquid nitrogen temperatures. We also observed strong modulation of the polariton spectra by the whispering-gallery modes (WGMs) formed inside the tree-like micro-structure. The disappearance of the SHG in tree-like ZnO near/above the energy of the excitonic band gap indicates the much higher efficiency of energy conversion, comparing to the simple ZnO rod, and reveal the practical and important applications of the tree-like micro-structures in solar cell. [Preview Abstract] |
Thursday, March 24, 2011 12:27PM - 12:39PM |
W30.00007: Optical anisotropy of transparent multiwalled carbon nanotube sheets Julia Bykova, Yakov Lesnichii, Aleksey Arsenin, Dmitry Fedyanin, Jonathon Smith, William Holmes, Anvar Zakhidov Replace this text with your abstract body. The oriented carbon nanotube (CNT) sheets absorb polarized light anizotropically depending on its relative orientation to the incident light. Oriented aerogel of multi-walled carbon nanotubes (MWNT) created by dry-drawing of spinnable CNT forests has been shown to be a relatively good polarizer [1] even at high temperatures [2]. In this presentation it is shown how the qualitative factor of polarization (QFP) depends on the CVD synthesis conditions and CNT sheets process. The optimized QFP of MWNT sheet is found to be 2-3 times higher than reported before for CNT-based polarizers. Systematic characterization by UV-Vis spectroscopy, elipsometry combined with SEM showed how the polarization properties can be improved by annealing, stretching and electrical field, which enhance the anisotropy of MWCNT sheets. This work is supported by AFOSR grant FA 9550-09-10384 and AFRL/Rice grant via CONTACT consortium of Texas. [1] M. Zhang et al., Science, 309 (2005) 1215 [2] A. Aliev at al. Phys Let A, 372 (2008) 4938 [Preview Abstract] |
Thursday, March 24, 2011 12:39PM - 12:51PM |
W30.00008: Synthesis and Optical Properties of Free Standing Titania Nanotubes Arrays for Photovoltaic and Photocatalytic Applications Dalmau Reig-i-Plessis, Mohamed Abd Elmoula, Eugen Panaitescu, Donald Heiman, Latika Menon Titanium oxide nanostructures, nanotubes arrays in particular, are key components for several emerging technologies, notably dye sensitized solar cells and supported gold nanoparticle catalysts. Free standing nanotube ordered arrays were produced by anodization of titanium foil in non-aqueous solutions. For optical measurement purposes the arrays were flaked off the titanium substrate. Flakes as large as several square centimeters, with a thickness of 30-50 $\mu $m were obtained, and coated either with N719 dye, or with gold nanoparticles (2-7nm). Both annealed (crystalline) and non-annealed (amorphous) samples were characterized by means of SEM and TEM imaging coupled with EDS and XRD spectroscopy. Subsequent optical measurements on gold decorated nanotubes offered insight on the gold-titania interaction, while measurements on both naked and dye coated tubes provided information on diffraction and thin film effects. These effects caused a significant wavelength dependent difference in the reflection spectrum depending on whether illumination was incident on the open or closed side of the tubes. [Preview Abstract] |
Thursday, March 24, 2011 12:51PM - 1:03PM |
W30.00009: Electro-Optic Effects in Colloidal Dispersion of Metal Nano-Rods with Nematic Ordering Oleg D. Lavrentovich, Andrii B. Golovin, Jie Xiang, Heung-Shik Park, Luana Tortora, Yuriy A. Nastishin, Sergij V. Shiyanovskii In modern transformation optics, one explores metamaterials with properties that vary from point to point in space and time, suitable for applications in devices such as an ``optical cloak'' [1] and an ``optical black hole'' [2]. We propose an approach to construct spatially varying and switchable metamaterials that are based on colloidal dispersions of gold (Au) nano-rods (NRs) in dielectric fluids [3], in which dielectrophoretic forces, originating in the electric field gradients, create spatially varying configurations of aligned NRs. We quantify the electric field induced orientational order and concentration distribution of Au NRs and the describe the ensuing optical effects. We demonstrate that the gradient electric-field induces a nematic birefringent phase in the toluene dispersions of AuNR and determine how the refractive indices change in space. [1] W. Cai, U.K. Chettiar, A.V. Kildishev, V.M. Shalaev, Nature Phot. \textbf{1}, 224 (2007); [2] E.E. Narimanov, A.V. Kildishev, Appl. Phys. Lett. \textbf{94}, 041106 (2009); [3] A.B. Golovin, O.D. Lavrentovich, Appl. Phys. Lett. \textbf{95}, 254104 (2009). [Preview Abstract] |
Thursday, March 24, 2011 1:03PM - 1:15PM |
W30.00010: Measurement of carrier lifetimes in silicon vapor-liquid-solid wires Brian Bryce, Mark Reuter, Brent Wacaser , Sandip Tiwari Minority carrier lifetimes are critically important to many semiconductor devices. For example, optimal photovoltaic design is almost completely dependent on knowledge of carrier lifetimes. We have extended traditional microwave photoconductance methods for use on aggregated films of nanowires. Using these methods we have measured the carrier lifetimes of both gold and aluminum catalyzed silicon vapor-liquid-solid wires in the 100-800 nm range. This approach allows for rapid characterization of wire quality prior to device design and fabrication. [Preview Abstract] |
Thursday, March 24, 2011 1:15PM - 1:27PM |
W30.00011: Exciton dynamics for single walled carbon nanotubes in the presence of a single ion Benjamin Tayo, Slava Rotkin We study the dynamics of excitons in single walled carbon nanotubes in the presence of a single ion placed on the surface of the tube. The scattering process is described in three main stages. First, we solve the Schr\"{o}dinger equation in the tight binding approximation to calculate the quasiparticle wave functions and energies. Second, we use quasiparticle wave functions and energies in the Bethe-Salpeter equation to calculate exciton binding energies and wave functions. Finally, we use the exciton energies and wave functions to investigate the process of exciton-ion scattering. We model the potential of the single ion by that of a point charge. Our studies show exciton trapping in the presence of the ion. [Preview Abstract] |
Thursday, March 24, 2011 1:27PM - 1:39PM |
W30.00012: The emissivity of an incandescent carbon nanotube B.C. Regan, Scott Singer, Matthew Mecklenburg, Edward White A classical thermal emitter has physical dimensions large compared to the wavelength $\lambda$ of the emitted light, and radiates power in proportion to its surface area. To explore the non-classical limit, we build tiny incandescent lamps with individual multi-walled carbon nanotubes as their filaments. We image a filament with atomic resolution in a transmission electron microscope, determining its length $L$ and radius $r$. Separately we apply Joule heating to reach temperatures $\sim 2000$~K, where the nanotube radiates in the visible ($L \sim \lambda \gg r$), and collect the light with an optical microscope. Comparing the filament's brightness with its tiny physical dimensions, we find that a single carbon nanotube is surprisingly black. [Preview Abstract] |
Thursday, March 24, 2011 1:39PM - 1:51PM |
W30.00013: Polarized Light Emission from a Single Hot Carbon Nanotube S.B. Singer, Matthew Mecklenburg, Edward White, B.C. Regan We fabricate nanoscale lamps, incandescent in the visible, which have a filament consisting of a single multiwall carbon nanotube. The radius $r$ of the nanotube is much smaller than the wavelength $\lambda$ of the emitted light, making it a very unusual thermal emitter. Transmission electron microscopy is used to determine the nanotube's axis as well as the parameters of the tube's geometry. We image both light polarizations on a CCD camera simultaneously and observe a degree of polarization between 70\% and 85\% along the tube's axis at visible wavelengths--highly polarized, yet less so than is expected for a conducting antenna. Furthermore, the polarization's variation with wavelength trends opposite to that predicted by classical models and analogy with graphene. [Preview Abstract] |
Thursday, March 24, 2011 1:51PM - 2:03PM |
W30.00014: Photoconductivity of complexes of chrysotile with tetra(4-sulfonatophenyl) porphyrins created via ionic self-assembly Wesley Chu, Walter Smith, Ye Lu, A.T. Johnson, Giovanna De Luca, Luigi Scolaro Tetrakis(4-sulfonatophenyl) porphine (TPPS4) molecules form complexes with chrysotile nanotubes in a chloroform-methanol solvent; the self-assembly is driven by Coulombic attractions. The UV/vis absorption spectrum indicates J-aggregation. In AFM, the complexes appear as straight, long tubes when deposited onto oxidized silicon substrates. Preliminary experiments conducted in a dry nitrogen atmosphere (0.2{\%} oxygen concentration) show that the aggregates are photoconductive. When illuminated for long periods at 428 nm, the photoconductivity grows slowly, and there is also a growth of persistent photoconductivity. These observations are similar to those for nanorods self-assembled from TPPS4 (without chrysotile),\footnote{C. K. Riley et al., \textit{J. Phys. Chem. C }\textbf{2010}, 114, 19227--19233.} though the current levels are much lower in the chrysotile complexes. [Preview Abstract] |
Thursday, March 24, 2011 2:03PM - 2:15PM |
W30.00015: A confinement phase in carbon nanotubes as captured by the extended massive Schwinger model Takashi Oka, Hideo Aoki We propose that the strong-coupling excitons in carbon nanotubes with electric fluxes confined in one dimension can be a condensed-matter candidate for a confinement phenomenon. Namely, we show that the system, with the Coulomb interaction proportional to $\vert x\vert $, is in a confinement phase with many properties similar to QCD in 4D. Low-energy physics is described by the massive Schwinger model with multi-species fermions labelled by the band and valley indices. We propose two means to detect this. One is an optical measurement of the exciton spectrum, where the confinement phase should be hallmarked by an absence of continuous component in the exciton spectrum. The spectrum is actually calculated with the 't Hooft-Berknoff equation utilizing the light-front field theory, where the Gell-Mann-Oakes-Renner relation is shown to be satisfied by dark excitons. The second way is through the nonlinear transport, which is shown to be related to Coleman's ``half-asymptotic" state. (arXiv:1007.5393) [Preview Abstract] |
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