Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X26: Nanowire & Nanotube Synthesis and Properties |
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Sponsoring Units: DCMP Chair: Michael Mehl, Naval Research Laboratory Room: 328 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X26.00001: Aligned Gallium Nitride Nanowire Growth by Chemical Beam Epitaxy Method Ryan Munden, Aleksandar Vacic, Erik Castiglione, Weihua Guan, Christine Broadbridge, Mark Reed Gallium Nitride (GaN) Nanowires (NWs) have successfully been grown via a chemical beam epitaxy method. Source gases of Trimethylgallium (TMGa) and Ammonia (NH3) are impinged directly onto a hot growth substrate ($\sim $800 \r{ }C) in high vacuum ($\sim $1x10$^{-8}$ torr, base; $\sim $1x10$^{-5}$ torr, growth). A thin metal film acts as catalyst, but NWs were also grown without catalyst. By this method NWs have been grown on silicon, alumina, sapphire, and GaN-film substrates. NWs grown on GaN films grow aligned to the growth substrate, perpendicular to the c-plane GaN film surface. Wires aligned to the GaN a-planes can also be observed. NWs have been studied by SEM, TEM, and electrical characterization. NW lengths are $\sim $2.5 micron with diameters of $\sim $25 nm. NWs are uniform, straight, and aligned with the substrate over large areas. However closer inspection of the NWs by TEM shows that the NWs are often polycrystalline in nature. There are distinct segments ``stacked'' into a nanowire leading to noticeable diameter variations on the nanoscale. Diameter modulation can be enhanced through choice of growth substrate, temperature, and pulsing of the TMGa source. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X26.00002: Temperature Evolution of Gallium Nitride Nanowire Vapor-solid Growth Matrix K. McElroy, B.W. Jacobs, T.R. Bieler, M.A. Crimp, V.M. Ayres Recent results indicate that vapor-solid growth mechanisms can yield semiconductor nanowires with high crystallinity. In the present experiments, gallium nitride nanowire growth is initiated following formation of a microcrystalline growth matrix. A change in nanowire orientation from wurtzite $<$2-1-10$>$/zinc-blende $<$011$>$ directions at 850\r{ }C and 950\r{ }C to the wurtzite [0001] direction at 1000\r{ }C is observed. The change in nanowire orientation is correlated with changes in the growth matrix. Investigations of the evolution of the growth matrix as a function of temperature using x-ray diffraction with orientation analysis, atomic fore microscopy, high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) are presented. [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X26.00003: Interaction between the boron nitride nanotube and biological molecules Chih-Kai Yang By calculating the interaction between boron nitride nanotubes (BNNT) and a variety of biological molecules, including amino acids and nitrogenous bases that are part of a nucleotide, using density functional theory, we conclude that there is no bonding or chemical adsorption between the wide band-gap BNNT and the biological molecules considered. This weak interaction suggests that BNNTs may be used as a safe nanoscale channel for transporting biological molecules. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X26.00004: Formation of Silicon Carbide Y Junctions by the Coalescence of Catalysts Zhenyu Liu, Judith C. Yang, V. Srot, Peter A. van Aken, M. R\"uhle We previously reported the formation of crystalline SiC nanocones by the released iron catalytic procedure, where the initially carbon- encapsulated iron nanoparticles escape from their carbon shells and agglomerate while catalyzing 1D SiC growth. Here we show that the coalescence of the iron nanoparticles can lead to Y junctions. Y junctions where the SiC branches are either parallel or inclined with respect to each other have been observed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The microstructure of the resulting products is analyzed by various techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) as well as electron energy loss spectroscopy (EELS). The Y junction with two parallel branches of various diameters suggests that the Y junction can be induced by the growth kinetics attributed to the diameter dependence, such as by the Gibbs-Thomson or surface tension effect. The proposed formation mechanism of Y junctions by the coalescence of catalyst droplets is a promising method to the construction of heterostructure nanowire devices. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X26.00005: Quantum Confinement in PbS nanowire Subhasish Mandal, Ranjit Pati One dimensional nanowires have become leading candidates in building nano sensor, nano transistor, optoelectronic devices and logic circuit. In last several years, PbS nanowire has drawn considerable interest for their potential applications in optical switch and solar cell. Controlled synthesis of PbS nanowire with diameter ranging from 1.2 nm to 20 nm have been reported with the photo luminescence study revealing wide band gap behavior for the nanowire. This offers exciting opportunities to study theoretically quantum confinement effect in PbS Nanowire. Here we report first principles density functional calculations of the electronic properties of PbS nanowire as a function of diameter. Our calculation shows, by varying the diameter of the nanowire from $\sim$ 1.17 nm to $\sim$ 3.64 nm, the energy band gap is found to change from 1.55 eV to 0.93 eV, substantially higher than the band gap observed for the PbS bulk - confirming the role of quantum confinement. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X26.00006: Toward complex nanostructures: lead chalcogenide nanoparticles, nanowires, and more Weon-kyu Koh, David K. Kim, Cherie R. Kagan, Christopher B. Murray Lead chalcogenides have been shown to be interesting semiconductor materials due to their small bandgaps and large Bohr radii. Based on lead chalcogenide nanoparticles as building blocks, we studied anisotropic growth of their nanowires and other structures. Growth mechanism of those structures is believed to oriented attachment which is mainly driven by dipole moment; in addition the role of surfactant is also important due to their dynamic binding on the nanoparticle surface. As-synthesized nanoparticles and nanowires were characterized using electron microscopy, X-ray diffraction, optical and electrical measurement. Our initial results open up new opportunities for photovoltaic device, sensor, and other application using those unique structures. [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X26.00007: Optimal Annealing Conditions, Mechanism, and Applications for the Crystallization of Titania Nanotubes Powders Obtained by Anodization Eugen Panaitescu, Latika Menon Titanium oxide nanotubes have drawn recent interest due to their possible application in photocatalysis, water splitting and photovoltaics, as they combine the wide gap semiconductor properties of the material with the high surface per unit volume of the nanostructures. Amorphous ordered titania nanotubes arrays can be obtained by anodization of titanium foils, and our group developed a method of ultrafast synthesis of powders containing such nanotubes bundles. Crystallization can be achieved by annealing, and we investigated the influence of annealing parameters using differential scanning calorimetry coupled with spectroscopy and imaging techniques such as SEM, TEM and XRD. Our extensive study revealed the optimal parameters for crystallization without structural damage at the nanoscale, which can occur for temperatures as low as 270 degrees Celsius. Mechanistic explanations and numerical studies offered us a theoretical insight on the phase transition process. Further employing of our crystalline powders in dye sensitized solar cells revealed efficiency results superior to those previously reported for crystallization at higher temperatures and annealing rates. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X26.00008: Controlled Attachment of Gold Nanoparticles on Ordered Titania Nanotube Arrays Mohamed AbdElmoula, Eugen Panaitescu, Christiaan Richter, Laura Lewis, Latika Menon Gold nanoparticles have been deposited on electrochemically synthesized high-aspect ratio Titania nanotubes. Titania nanotubes with very long aspect ratio as long as 50microns are synthesized by means of electrochemical anodization of titanium foils in chlorine containing electrolytes. The tube dimensions (diameter, wall thickness and length) of the tubes can be controlled in our fabrication approach. The gold particles are deposited on the tubes by means of a modified deposition-precipitation method in HAuCl4 solution under controlled concentration of the solution. We show that by adjusting the fabrication conditions, we can obtain a high deposition density of the gold particles over the nanotube surface (over 90{\%} coverage percentage ) and also have good control over the size of the gold nanoparticles ($<$5 nm). We show that there is an increase in particle size upon increasing the deposition period. The samples have been characterized by means of scanning and transmission electron microscopy. The optical and preliminary catalytic properties of such gold-supported Titania nanotubes will also be reported. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X26.00009: Novel Fabrication and Enhanced Photosensitivity of Selenium Filament Arrays by Optical-Fiber Thermal Drawing Daosheng Deng, N. Orf, A. Abouraddy, Y. Fink Structures with high aspect ratio and nanometer cross-sectional dimensions have been the subject of recent studies. These nanometer-scale wire structures are typically processed through a bottom-up approach that yields limited wire lengths lacking global orientation and presenting challenges to handling and electrical contacting. Here, we report a novel physical phenomenon in which a cylindrical shell undergoing a scaling process evolves into an ordered array of filaments upon reaching a characteristic thickness. We propose a fluid front instability mechanism to account for the observed phenomena. The fleeting evolution of fluid breakup from a thin film to a filament array is captured in the frozen state by a thermal drawing process which results in extended lengths of solid sub-100nm filaments encapsulated within a polymer fiber. Furthermore, we demonstrate that the electrical connectivity of centimeter-long filament arrays to external circuitry is readily achieved by contacting the fiber ends, allowing one to study their electrical and optoelectronic properties. Enhanced photosensitivity of filaments is observed compared to a selenium film. This approach offers unique opportunities for fabrication of nanometer scale devices of unprecedented lengths allowing simplified access and connectivity. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X26.00010: Self-assembled Au nanorods - polymer composites Heung-Shik Park, Oleg Lavrentovich, Ashish Agarwal, Nicholas Kotov The unique optoelectronic properties of the anisotropic metallic nanorods (NRs) are of great interest because of their potential applications in biological sensing, solar energy conversion, cloaking devices, etc. In order to utilize NRs, tuning their properties and immobilizing NRs into polymer matrix are essential. We present a simple and universal process for formation of self-assembled nanorods polymer composite. This approach is based on the anisotropic electrostatic interaction between aggregates of chromonic molecules and NRs that lead to either end-to-end or side-by-side assembly of NRs. We discuss encapsulation of these structures with polymer matrices. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X26.00011: Focused Ion Beam Treatment of ZnO Nanowires Gagik Shmavonyan We investigated vapour-liquid-solid-grown ZnO nanowires (NWs) on a Si substrate by SEM. SEM investigations show that there are single NWs and ensembles of NWs, among which we found straight and bend, perfect and non-perfect NWs, as well as NWs with clean surfaces and surfaces with the dark spots and features. After focused ion beam polishing we found that every NW has a clean homogeneous surface, which allow us to conclude that all those dark spots and surface features of the NWs really are just surface features. The focused ion beam milling gives information of the deeper interior of the NWs, i.e. buried structures within the NWs and whether those structures are propagating within the NWs. But also here we found that there are no buried structures inside the NWs and the dark spots and features are not propagating within the NWs, which leads to the result that the NWs are totally homogeneous. The sizes of the NWs were determined: the length is about 2-24 $\mu$m, and the width and height are about 200-500 nm. [Preview Abstract] |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X26.00012: Controlled Growth of Zinc Oxide Nanostructures for Applications Abhishek Prasad, Archana Pandey, Yoke Khin Yap Zinc Oxide (ZnO) has proven to be a versatile functional material with promising properties. Here we discuss about the controlled growth and applications of various ZnO nanostructures including novel ZnO nanotubes (NTs) and nanosquids (NSqs). We use a conventional thermal CVD technique for the synthesis of ZnO nanostructures. We found that ZnO nanowires, nanobelts and nanocombs can be readily obtained by applying appropriate gas flow rates and growth temperatures.\footnote{S. L. Mensah et al, J. Phys. Chem. C (Letter) 111, 16092 (2007).} ZnO NTs and NSqs can be formed on the substrates when appropriate cooling rate was applied.\footnote{S. L. Mensah et al, Appl. Phys. Letts. 90, 113108 (2007).} These nanostructures were characterized using XRD, HRTEM, FESEM, Raman spectroscopy, and photoluminescence. Results show that ZnO nanostructures were single crystals in wurtzite structure. Among these ZnO NWs were found to be excellent electron field emitters and field effect transistors. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X26.00013: CO Gas Sensing with ZnO Nanowire Mat Sirisha Chava, Christine Berven, Daquing Zhang We report the electrical properties of a gas sensor constructed from mats of ZnO nanowires grown on sapphire substrate that shows a reversible response which is unique to CO exposure. The sensor is a two terminal design, where the terminals consist of two 25 \textit{$\mu $}m diameter gold wires laid parallel on the nanowire mat. The individual nanowires have an average diameter of 50 nm with lengths of about 10 \textit{$\mu $}m. The nanowire mat is about 20 \textit{$\mu $}m thick and extends over an area of about 1 cm2. When exposed to Ar, CO2 or H2 no significant changes in the current-voltage behavior of the mat are observed. CO exposure results in approximately a three-fold increase in current. The response is reversible after evacuation. Typical currents when exposed to pure CO under room temperature without prior introduction to any other gas are in the range of 40 nA compared to non-exposed 15 nA. Growth technique of nanowires and comparative work will be discussed. [Preview Abstract] |
Thursday, March 19, 2009 5:06PM - 5:18PM |
X26.00014: Transparent Thin Film Transistors based on Pristine and Doped Indium Oxide Nanowires Po-Chiang Chen, Guozhen Shen, Saowalak Sukcharoenchoke, Chongwu Zhou The key to the realization of transparent electronics is the development of transparent thin film transistors (TTFT) with good device performance, in terms of high device mobility, low temperature fabrication, and optical transparency. We present our work on the fabrication of high performance TTFTs using both pristine In$_{2}$O$_{3}$ nanowires and doped In$_{2}$O$_{3}$ nanowires. In$_{2}$O$_{3}$ nanowire TTFTs were made on glass and PET substrates with Al$_{2}$O$_{3}$ as gate insulator and ITO source/drain electrodes. These devices showed a transparency of about 80{\%} and n-type transistor performance. The device characteristics exhibit a subthreshold slope of 0.2 V/dec, a current on/off ratio of 10$^{6}$, and a field-effect mobility of 514 cm$^{2}$V$^{-1}$S$^{-1}$. We also fabricated TTFTs wbuilt on Arsenic-doped In$_{2}$O$_{3}$ nanowires with a field-effect mobility of 1,183.8 cm$^{2}$V$^{-1}$S$^{-1}$ without any post-treatments. In addition, we integrated TTFTs with organic light emitting diode (OLED) to make an active matrix organic light emitting diode (AMOLED) display, and thus made an animation by controlling the OLED light output. [Preview Abstract] |
Thursday, March 19, 2009 5:18PM - 5:30PM |
X26.00015: Studies of Surface Exciton Polaritons in Nano-Materials by Electron Energy-Loss Spectroscopy. C.H. Chen, C.T. Wu, M.W. Chu, L.C. Chen, C.W. Chen, K.H. Chen Surface plasmon polaritons (SPPs), which normally occur in the optically \textit{metallic} spectral regime, are collective charge density oscillations of conduction electrons at the surface of metals. In sharp contrast to SPPs, the excitations of surface exciton polaritons (SEPs), which are collective oscillations of delocalized excitons at the surface of semiconductors or insulators, have been shown to be correlated with distinct excitonic onsets (interband transitions) in these materials. Using electron energy-loss spectroscopy (EELS) with a 2-{\AA} electron probe in the near-field geometry and energy-filtered spectral imaging in real space, we have unambiguously demonstrated the existence of the SEP excitations on the surfaces of GaN and ZnO nanorods at energies near the interband transitions. [Preview Abstract] |
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