Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session H4: Materials Physics IV |
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Chair: Mark Siemens, University of Denver Room: Macey Center Silver |
Saturday, October 27, 2012 10:12AM - 10:24AM |
H4.00001: Absorption measurements of very low quantities of graphite microfibers and nanofibers Michael Boergert In order to determine the absorption coefficients of graphite microfibers, a He-Ne laser incorporating a 2-D photoacoustic system was used. In this system particles were deposited through fluid suspension onto polycarbonate filters. One objective was to determine if the absorption coefficient of vapor-grown microfibers as well as of three size distributions of nanofibers could be measured in areal densities as low as a single fiber in a focused beam. Although measuring single vapor-grown microfibers was deemed not possible with this equipment, the mass density limit was approximately 20 ng/cm$^2$ for a beam of approximately 2100 microns in diameter, giving about 690 pg or several thousand fibers in the beam spot. However, if the beam were fully focused, it would have a diameter of approximately 310 microns, which would correspond to about 15 pg or approximately 100 particles in the beam. The absorption coefficient analysis was then extended to three size distributions of graphite nanotubes. The mass normalized absorption cross sections were determined from measurements of absorption vs. areal mass density on filters. Calibration was done by using the published value for soot. [Preview Abstract] |
Saturday, October 27, 2012 10:24AM - 10:36AM |
H4.00002: Carbon Nanotube Microfabrication Steven Noyce, Robert Davis, Richard Vanfleet An overview of several unique and powerful methods of microfabrication using Carbon Nanotubes as the basic framework for fabricating a myriad of incredible devices will be presented. Countless astounding properties and useful material properties can be obtained with one of the world's most extraordinary nanomaterials combined in creative combinations. A summary of several years of research will be presented along with recent developments and continuing areas of focus. [Preview Abstract] |
Saturday, October 27, 2012 10:36AM - 11:00AM |
H4.00003: Accelerating Nanoscale Research with Neutron Total Scattering: Linking Structure and Function in Finite Materials Invited Speaker: Katharine Page h $-abstract-$\backslash $pard In contrast to bulk materials, nanomaterials and nanoparticles, comprised of a few hundred to tens of thousands of atoms, require every atom's position to be located in order to understand their structure-property relationships. New behavior can arise with a constricted, expanded, or distorted lattice, variation in surface termination structure, ligand capping or stabilization, or with the increasingly diverse set of shapes and architectures appearing in nanoscience literature today: tubes, pyramids, stars, core-shell and matrix-confined particles, multilayer films, etc. Pair distribution function (PDF) analysis, based on spallation neutron or synchrotron x-ray total scattering data, has emerged as a very promising characterization method for nanomaterials in recent years. Total scattering methods provide information about every pair of atoms probed in a diffraction experiment and thus contain an unexploited wealth of information for finite systems. In this contribution we will present our work establishing the influence of particle size and shape on the nature and correlation of local atomic dipoles in finite ferroelectric systems. We also review current data-driven modeling capabilities and outline the need for evolution of robust computational tools to follow other complex nanoscale phenomena with scattering data. $\backslash $pard-/abstract-$\backslash $\tex [Preview Abstract] |
Saturday, October 27, 2012 11:00AM - 11:12AM |
H4.00004: Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain Andrew Copple, Nathaniel Ralston, Xihong Peng One dimensional semiconductor nanowires have been extensively researched in the past years because of their unique characteristics. Group III-V semiconductors show special promise in a wide range of applications, such as field-effect transistors, light-emitting diodes, and optical sensors. The fundamental properties of these materials are essential to their applications, particularly the electronic properties. In this presentation, we report first principles density-functional theory study on the electronic properties of wurtzite GaAs nanowires along the (0001) direction, with the diameter of the wires up to 3.0 nm [1]. It was found that the band gap of GaAs nanowires experience a direct-to-indirect transition when the diameter of the nanowires is smaller than $\sim $2.8 nm. For those thin GaAs nanowires with an indirect band gap, it was found that the gap can be tuned to be direct if a moderate external uniaxial strain is applied. Both tensile and compressive strain can trigger the indirect-to-direct gap transition. The critical strains for the gap-transition are determined by the energy crossover of two states in conduction bands. \\[4pt] [1] A. Copple, N. Ralston, X.-H. Peng, Appl. Phys. Lett.100, 193108 (2012). [Preview Abstract] |
Saturday, October 27, 2012 11:12AM - 11:24AM |
H4.00005: Resistivity of Endotaxial Silicide Nanowires Measured with STM Nanoprobe Peter Bennett, Samuel Tobler We present in situ UHV measurements of the resistivity of self-assembled endotaxial FeSi$_{2}$ nanowires (NWs) on Si(110) using a variable-spacing two-point method with an STM tip and a fixed contact pad. Boundary scattering causes the resistivity to vary with NW width as: $\rho _{NW}$ = 200 uohmcm at 12 nm and 300 uohmcm at 2 nm. The relative weakness of boundary scattering is attributed to a high concentration of point defects in the bulk FeSi$_{2}$ structure. It is remarkable that the defect concentration persists in very small structures, and is not changed by surface oxidation. [Preview Abstract] |
Saturday, October 27, 2012 11:24AM - 11:36AM |
H4.00006: Nickel Infiltration of Vertically Aligned Carbon Nanotube Forests via Pulsed Electro Deposition Lawrence Barrett, Steven Noyce, Robert Davis Carbon nanotube forests have been used as a template for building micro-scale high aspect ratio devices. Vertically aligned carbon nanotube forests are grown on a patterned catalyst, but these structures are extremely fragile. So we then infiltrate them with another material. For some devices, such as micro-filters for liquid and gas and micro-scale antennas the forest must be infiltrated with a metal, and we have developed a process using pulsed electro deposition of nickel to infiltrate these forests. We will present on mechanical and electrical characterization of the composite material and show device structures. [Preview Abstract] |
Saturday, October 27, 2012 11:36AM - 11:48AM |
H4.00007: Ultrasonic Spraying of Carbon Nanotubes using Organic Solvents Anthony Willey, Robert Davis, Richard Vanfleet Because of their unique electrical and mechanical properties, thin films of carbon nanotubes have several potential applications, especially in the fields of organic electronics and photovoltaics. We present a method for spraying thin films of nanotubes that have been suspended in organic solvents N-methyl Pyrollidone (NMP) and N-Cyclohexyl-2-pyrrolidone (CHP). The sprayed nanotubes are randomly oriented, and films are transparent, conductive, and mechanically stable. [Preview Abstract] |
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