Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session X31: Synthesis of Nanotubes and Nanowires |
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Sponsoring Units: DCMP Chair: Paola Barbara, Georgetown University Room: Colorado Convention Center 401 |
Friday, March 9, 2007 8:00AM - 8:12AM |
X31.00001: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 8:12AM - 8:24AM |
X31.00002: Bismuth Nanowires: Synthesis, Microscopy and Transport Properties Jason Reppert, Jian He, Malcolm Skove, Brad Edwards, Terry Tritt, Apparao Rao Thermoelectric materials approaching the atomic level possess unique quantum confinement properties that have generated much interest in recent history. Theoretical investigations have suggested that nanowires with diameters $<$10 nm will possess a ZT $>$2. Previously, bismuth nanowires have been successfully synthesized by means of electrochemical deposition, liquid-phase pressure injection, and vapor-phase deposition. Here, we report the synthesis of bismuth nanowires via the pulsed laser deposition method (PLD). Using this approach, we have been successful in producing nanowires ranging in diameters of 10 - 20 nm, with the majority ranging 10 -- 12 nm, and lengths 200 - 300 nm. The structure of the as-prepared nanowires was characterized using scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy, x-ray diffraction and electron diffraction. The HRTEM images of the bismuth nanowires show a crystalline Bi core that is wrapped in an amorphous oxide layer. The lattice spacing of planes parallel to the length of the Bi core was found to be 0.328 nm, corresponding to the (012) planes of Bi. Temperature dependent thermopower measurements obtained from our narrow diameter Bi nanowires will be presented. [Preview Abstract] |
Friday, March 9, 2007 8:24AM - 8:36AM |
X31.00003: Growth of Carbon Nanotubes on Metallic Superalloys Saikat Talapatra, Swastik Kar, Sunil Pal, Pethuraja Gopal, Lijie Ci, Robert Vajtai, Pulickel Ajayan There are several advantages of growing carbon nanotubes (CNT) directly on bulk metallic substrates, for example in the formation of robust CNT-metal contacts during growth. Recently, we have shown that multi-wall carbon nanotubes can be grown on Inconel 600, a super alloy, using vapor phase catalyst delivery. The single-step growth of high-quality aligned nanotubes (comparable to those grown on SiO$_{2}$ substrates) show encouraging electrical and mechanical properties. The in situ growth opens up a large number of possibilities for nanotube-based devices. Here, we present detailed investigations on the kinetics of the growth under various experimental conditions, and analyze the nanotube growth mechanism on the generic super alloy systems in the framework of our investigations. [Preview Abstract] |
Friday, March 9, 2007 8:36AM - 8:48AM |
X31.00004: VLS growth of $<$111$>$ oriented Silicon nanowires on Si (111) and Si (100); Growth rate dependence of growth defects Joonho Bae, Shawn Coffee, John Ekerdt, Chih Kang Shih Recently, models have been developed to explain the relation between the growth direction and the diameter of VLS grown silicon nanowires. In this study, we present experimental evidences showing growth rate dependence of growth defects such as bending and kink formation of silicon nanowires grown by SiCl$_{4}$ as a precursor and H$_{2}$ as a carrier gas. We find that the high growth rate tends to result in nanowires with less growth defects permitting well oriented nanowires. By applying this finding and controlling growth conditions, large area silicon nanowires along $<$111$>$ direction were successfully demonstrated on Si (111) and Si (100) substrates. On Si (111) substrates, we achieve large area vertically aligned [111] oriented nanowires. On Si (100) substates, nanowires with four different $<$111$>$ orientations form a large area of inter-lacing network pattern. The underlying growth mechanism and pattern formation are discussed. [Preview Abstract] |
Friday, March 9, 2007 8:48AM - 9:00AM |
X31.00005: Self-assembled Silicon Nanotubes: new 1D semiconductors Ming Xie, Jiesheng Wang, Yoke Khin Yap Silicon nanotubes (SiNTs) have recently attracted attention because of the peculiar properties. SiNTs is also compatible to the present Si microelectronic technology. Theoretically, many research groups have investigated the possible existence of SiNTs. Experimentally, amorphous SiNTs have been synthesized by using template methods. Nevertheless, these SiNTs cannot form good crystal structure due to disordered aggregation of silicon atoms in the inner wall of the templates. Recently, self- assembled silicon nanotubes were reported, which have good crystal structure under supercritically hydrothermal conditions. Here we report self-assembled SiNTs via dual RF-plasma treatments. This technique is compatible to the present integrated circuit technology without involving excessive synthesis pressures and temperatures. Furthermore, our SiNTs are vertically aligned on substrates, which can be easily extracted for devices fabrication. Tunneling spectroscopy was used to characterize the local density of states of these SiNTs. Results indicate that these SiNTs are p-type semiconductors, a new 1D semiconductor for future nanoelectronic devices. [Preview Abstract] |
Friday, March 9, 2007 9:00AM - 9:12AM |
X31.00006: Controlled In-Situ Microscopy Studies of the Effect of Heterogeneous Catalysis on the Growth, Structure and Composition of GaN Nanowires M. Taheri, T. Lagrange, B. Simpkins, N. Browning Controlled growth of GaN nanowires is vital to the efficient production of blue light emitting diodes and other nanoscale optoelectronic devices. The VLS (vapor-liquid-solid) method, which often uses foreign metal catalysts, is a mechanism by which nanowires grow using chemical vapor deposition. Defects, grain boundaries and impurity incorporation that arise during heterogeneous catalysis of nanowires can negatively impact a wire's electronic properties. These properties are directly related to the microstructure and composition of a wire. To understand the specific effects of these metal catalysts on a nanowire's electrical characteristics, a clear understanding of the structural evolution as a function of catalyst (Ni) must be obtained. This is achieved by using in-situ microscopy-based growth methods. In-situ TEM annealing is coupled with high resolution TEM/STEM and Energy Dispersive Spectroscopy (EDS) to study the structure and chemistry of the growing Ni-catalyzed GaN nanowires. Concurrently, laser controlled methods using a Dynamic Transmission Electron Microscope (DTEM) are used to monitor the various stages of the VLS method during microstructural evolution. Each step of wire nucleation and growth during VLS is triggered by a pulsed laser while being monitored in-situ in the TEM. Trends in impurity incorporation with morphology and defect concentration are compared for nanowires grown by both methods of in-situ TEM growth, and to those grown the conventional CVD-based VLS methods. [Preview Abstract] |
Friday, March 9, 2007 9:12AM - 9:24AM |
X31.00007: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 9:24AM - 9:36AM |
X31.00008: Optimum growth of vertically-aligned boron nitride nanotubes at low temperatures Jiesheng Wang, Ming Xie, Yoke Khin Yap Boron nitride nanotubes (BNNTs) are well recognized as the candidate that will complement the uses of carbon nanotubes in nanotechnology. However, high growth temperatures ($>$1100 ${^\circ}$C), low production yield, and impurities have hindered research and applications of BNNTs. We have recently reported the first success of growing pure BNNTs by RF-plasma enhanced pulsed-laser deposition at 600 ${^\circ}$C. These BNNTs can be grown vertically aligned into arrays of regular patterns, and can be used for applications without purification. In this work, we have compared the growth of these BNNTs by a series of catalysts. Electron microscopy images indicate the growth of pure BNNTs with high structural order. UV Raman Spectroscopy demonstrates a peak at 1372 cm$^{-1}$, which corresponds to a E2g mode of h-BN networks of these BNNTs. The effect of catalyst, growth temperatures, ambient gas pressures, substrate bias voltages and the growth mechanism will be described in detail in the meeting. [Preview Abstract] |
Friday, March 9, 2007 9:36AM - 9:48AM |
X31.00009: Controlling the dielectrophoretic assembly of single-walled carbon nanotubes Sarbajit Banerjee, Brian White, Blake Rego, Stephen O'Brien, Nicholas Turro, Irving Herman The AC dielectrophoretic assembly of single-walled carbon nanotubes (SWNTs) represents an attractive approach for the fabrication of SWNT devices. The dielectrophoresis approach relies on the deposition of water-soluble surfactant-wrapped individualized SWNTs in electrode gaps. We have tested a variety of different anionic, non-ionic, and cationic surfactants for their ability to dissolve SWNTs. The zeta potential of the dissolved nanotubes, which is a measure of their surface charge, can be adjusted by varying the surfactant, the pH, and the surfactant concentration. The resulting modulation in surface conductance has implications for the chiral selectivity of the dielectrophoretic process. The surfactant-wrapped SWNTs have been precisely positioned in device geometries by designing appropriate electrode structures based on electric-field simulations. The influence of the surfactant on the transport properties of these devices will also be discussed. This work is primarily supported by the Nanoscale Science and Engineering Center at Columbia University, which is supported under NSF Award Number CHE-0641523. It is also partially supported by the MRSEC program of the NSF under Award Number DMR-0213574 and by NYSTAR. [Preview Abstract] |
Friday, March 9, 2007 9:48AM - 10:00AM |
X31.00010: Au-Induced Assembly of Protective Carbon Shells on Ge Nanowires Eli Sutter, Peter Sutter Semiconductor nanowires (NWs) are promising materials for novel devices. Among them group IV semiconductors offer compatibility and facile integration with conventional electronic circuitry. Given the large surface-to-volume ratio of NWs, it is especially important that the NW surface be protected against oxidation to avoid uncontrolled property changes. For Ge NWs such oxidation protection is not provided by a stable native oxide (as is the case for Si). Hence, any Ge NW-based devices will require the development of passivation or encapsulation techniques. Here we discuss real-time observations by high-resolution transmission electron microscopy during annealing of individual carbon-supported Ge NWs [1]. At moderate temperatures ($\sim $300C) even thick oxide layers on the Ge NWs are reduced rapidly. This is followed by the assembly of crystalline carbon shells that depends critically on traces of Au on the NW surface originating from the Au/Ge catalyst nanoparticles used for the NW synthesis. We demonstrate that the C-shells provide efficient protection of the Ge NW surface against oxidation in ambient air. More generally, our results point at using metal surface decoration to trigger the encapsulation of a wide variety of NW materials in protective C-shells. \newline [1] E. Sutter, P. Sutter, Adv. Mater. 18, 2583 (2006). [Preview Abstract] |
Friday, March 9, 2007 10:00AM - 10:12AM |
X31.00011: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 10:12AM - 10:24AM |
X31.00012: High Yield Fabrication of Single-Walled Carbon Nanotube Devices via Self-Assembly George S. Tulevski, James B. Hannon, Ali Afzali Single-walled carbon nanotubes (SWCNTs) are attractive materials for many technological applications. Success in the large-scale integration of SWCNTs will depend upon progress in processing to address challenges such as separation, chemical doping and selective placement. This work will highlight recent progress in the selective placement of SWCNTs into predefined positions on gate oxide surfaces, allowing for the fabrication of large arrays of SWCNT devices. SWCNTs are first functionalized with organic compounds that selectively bind to metal oxide surfaces. Electron beam lithography is then employed to pattern hafnium oxide trenches into which the functionalized SWCNTs selectively bind. The surface functionalization is shown to be fully reversible. Once the nanotubes are assembled into the trenches, the molecules are then removed leaving the unfunctionalized SWCNTs behind. This technique allows for hundreds of working devices to be fabricated with high yield. The electrical properties of the subsequent devices are excellent, showing no performance deterioration as a result of the placement process. [Preview Abstract] |
Friday, March 9, 2007 10:24AM - 10:36AM |
X31.00013: New High Aspect-Ratio Titania Nanotubes Eugen Panaitescu, Christiaan Richter, Latika Menon Titanium oxide nanotubes show great promise in photocatalytic, gas sensing, biological, and other applications. Techniques for the fabrication of titania nanotubes include electrodeposition in polymer molds starting from alumina templates, anodization of titanium in fluoride containing solutions, and hydrothermal treatment of nano- and micropowders. We have developed a new synthesis route for the production of new ultra-high aspect-ratio (over 1000:1) titania nanotubes by anodization in chloride containing acid solutions. The fabrication process occurs rapidly, in a fraction of the time when compared with other methods such as anodization in the highly toxic fluoride-containing electrolytes. We have demonstrated nanotubes with diameters as small as 25 nm, and lengths of up to 50 $\mu $m, and we have produced them with varying carbon content through the addition of organic acids in the electrolyte. This opens up new possibilities for many advanced applications of such nanotubes. Various synthesis conditions (pH, chloride content, electrolyte nature), and their influence on morphology, composition, and crystalline structure will be presented. Preliminary results on photocatalytic and transmission properties will also be discussed. [Preview Abstract] |
Friday, March 9, 2007 10:36AM - 10:48AM |
X31.00014: Template-Grown TiO2 Single-Nanowires for Gas Sensing Yaping Dan, Stephane Evoy, A. T. Charlie Johnson A number of contemporary research efforts are directed towards realization of an ``electronic nose'' system where a sensor array is coupled to signal-conditioning electronics and sensor responses fed to odor recognition algorithms to perform detection and classification of vapors. Metal oxides thin films and nanowires are candidates for use in such systems, with the latter having performance advantages associated with their small footprint and enhanced quasi one-dimensional carrier confinement. Here we report experiments exploring the use of template-grown TiO$_{2}$ single-nanowires for gas sensing. TiO$_{2}$ nanowires were prepared by electroplating Ti(OH)$_{x}$ sol-gel into anodic aluminum oxide membranes and then annealing at 450\r{ }C for 12 h. These nanowires are typically 10$\pm $1$\mu $m long and 100$\pm $20nm in diameter. When the temperature is elevated from 20\r{ }C to 200\r{ }C, the conductance of a single nanowire increases from 30pS to 330pS, from which an activation energy of 0.51 $\pm $ 0.02 eV is extracted. When exposed to 20{\%} O$_{2 }$at a working temperature of 200\r{ }C, the conductance of the wires increases by 100{\%} within a few seconds. We will report on sensing experiments for O$_{2}$, H$_{2}$ and CO with different concentrations as well as the effects of sample annealing and working temperature. This work was supported by the National Science Foundation NIRT Grant {\#}0303981. [Preview Abstract] |
Friday, March 9, 2007 10:48AM - 11:00AM |
X31.00015: Self assembly of organic nanostructures and dielectrophoretic assembly of inorganic nanowires. Geetha Dholakia, Steven Kuo, E. L. Allen Self assembly techniques enable the organization of organic molecules into nanostructures. Currently engineering strategies for efficient assembly and routine integration of inorganic nanoscale objects into functional devices is very limited. AC Dielectrophoresis is an efficient technique to manipulate inorganic nanomaterials into higher dimensional structures. We used an alumina template based sol-gel synthesis method for the growth of various metal oxide nanowires with typical diameters of 100-150 nm, ranging in length from 3-10 $\mu $m. Here we report the dielectrophoretic assembly of TiO$_{2}$ nanowires, an important material for photocatalysis and photovoltaics, onto interdigitated devices. Self assembly in organic nanostructures and its dependence on structure and stereochemistry of the molecule and dielectrophoretic field dependence in the assembly of inorganic nanowires will be compared and contrasted. Tunneling spectroscopy and DOS of these nanoscale systems will also be discussed. [Preview Abstract] |
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