Bulletin of the American Physical Society
2006 8th Annual APS Northwest Section Meeting
Friday–Saturday, May 19–20, 2006; Tacoma, Washington
Session B1: Condensed Matter I |
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Chair: Janet Tate, Oregon State University and Patricia Mooney, Simon Fraser University Room: Macintyre 103 |
Friday, May 19, 2006 2:00PM - 2:36PM |
B1.00001: Infrared and Raman Spectroscopy of ZnO Nanoparticles Invited Speaker: ZnO is a wide-bandgap semiconductor with emerging optoelectronic applications. In this work, the optical and electrical properties of as-grown and hydrogen-annealed ZnO nanoparticles were investigated. Infrared (IR) reflectance spectra show a dramatic increase in free carrier concentration in the hydrogen- annealed nanoparticles. A difference is observed reststrahlen line shape of the conductive sample compared to that of bulk sample. The effective medium approximation was applied to model the reflectance spectra. The agreement between experimental results and modeling approach suggests that the nanoparticles have inhomogeneous carrier concentrations. In addition, Raman spectroscopy and electrical conductivity measurements were also performed to probe the carrier properties. [Preview Abstract] |
Friday, May 19, 2006 2:36PM - 2:48PM |
B1.00002: Ultraviolet-Photoluminescence and Raman Properties of Mg$_{x}$Zn$_{1-x}$O Nanopowders$^{\ast }$ John Morrison, Xiang-Bai Chen, Jesse Huso, Heather Hoeck, James Mitchell, Leah Bergman, Tsvetanka Zheleva The Mg$_{x}$Zn$_{1-x}$O alloy system may provide a new UV optically tunable family of wide bandgap materials. ZnO has the hexagonal wurtzite structure of bandgap $\sim $ 3.3 eV while MgO has the NaCl cubic structure of bandgap $\sim $ 7.5 eV. Bandgap engineered alloys at the range $\sim $ 3.3 -- 7.0 were achieved. In this communication we present studies on the UV photoluminescence (PL) and Raman properties of wurtzite Mg$_{x}$Zn$_{1-x}$O nanopowders of average size $\sim $ 30 nm that were synthesized via the thermal decomposition method. For the studied composition range of $0\le x\le 0.26$, the room temperature UV-PL was found to be tuned by $\sim $ 0.25 eV towards the UV-spectral range, and the PL emission was established to be due to an excitonic-type recombination mechanism. The first-order LO Raman mode was found to exhibit a blueshift of $\sim$~33 cm$^{-1}$ and the second-order LO a shift of $\sim$~60 cm$^{-1}$. The LO-mode of the nanopowders is discussed in terms of a mixed A$_{1}$-E$_{1}$ symmetry phonon known as a quasi-LO mode. \newline $^{\ast }$L. Bergman, et. al, Appl. Phys. Lett. \textbf{88}, 023103 (2006) [Preview Abstract] |
Friday, May 19, 2006 2:48PM - 3:00PM |
B1.00003: Pressure Response of the UV-Photoluminescence of ZnO and MgZnO Nanocrystallites Jesse Huso, John L. Morrison, Heather Hoeck, Leah Bergman, Slade Jokela, Matthew McCluskey, Tsvetanka Zheleva ZnO and Mg$_{x}$Zn$_{1-x}$O are promising next-generation wide-bandgap semiconductors for high efficiency optical applications. Mg$_{x}$Zn$_{1-x}$O alloys enable the tuning of the photoluminescence\footnote{L. Bergman, et. al, Appl. Phys. Lett. \textbf{88}, 023103 (2006)} [PL] at the range of $\sim $ 3.0 -- 7.0 eV. Additionally, nanomaterial properties under high pressure are of significant importance to the field of devices operating under extreme conditions. Here, we present studies of the pressure response of the UV-PL of ZnO and Mg$_{0.1}$Zn$_{0.9}$O nanocrystallites of size $\sim $ 30 nm. We found that up to 6 GPa the pressure coefficients of ZnO and MgZnO are 23 and 27 meV/GPa, respectively. The pressure coefficient of the ZnO nanocrystallites is similar to that of the bulk ZnO. The higher value found for Mg$_{0.1}$Zn$_{0.9}$O is discussed in terms of the atomic numbers of the cation constituents. L. B. acknowledges NSF-CAREER-DMR-0238845, and DOE--DEFG02-04ER46142. M. M. and L. B. acknowledge the ACS PRF-40749AC10. [Preview Abstract] |
Friday, May 19, 2006 3:00PM - 3:12PM |
B1.00004: Quaternary p-type sulfide-fluoride transparent conductor: BaCuSF Robert Kykyneshi, Janet Tate, Cheol-Hee Park, Douglas Keszler Conductive thin films of wide band-gap BaCuSF were prepared by pulsed laser deposition and post-annealing in a H$_{2}$S. High conductivity (up to 500-1800 S/cm), carrier density ($\sim $10$^{21}$ cm$^{-3})$, and mobility (0.7-4 cm$^{2}$/Vs) were measured for the undoped and potassium-doped films, attributed to the textured crystalline structure at low processing temperature (T=235$^{\circ}$C). The positive Seebeck coefficient (+5 $\mu $V/K) identifies holes as majority mobile carriers in this degenerate semiconductor. The conductivity can be significantly reduced ($\sim $10$^{5}$ S/cm) by higher temperature annealing, with observed higher transparency in the visible and near-IR spectrum. The absorption coefficient of the high conductivity BaCuSF films is compared to that of transparent conducting oxides of the delafossite structure. [Preview Abstract] |
Friday, May 19, 2006 3:12PM - 3:24PM |
B1.00005: Thin film growth of the p-type semiconductor BiCuOSe by pulsed laser deposition Paul Newhouse, Peter Hersh, Douglas Keszler, Janet Tate Thin films of p-type semiconductor BiCuOSe were prepared by pulsed laser deposition onto fused SiO$_{2}$ and single crystal MgO and SrTiO$_{3}$ substrates. Their electrical and optical properties were measured. Ca-doped films prepared on MgO or SrTiO$_{3}$ substrates are $c$-axis oriented, and show high electrical conductivity of $\sim $200 S/cm and high reflectivity of 30-50{\%} from $\sim $0.4-4 $\mu$m. Single phase polycrystalline films on fused SiO2 show lower conductivity of $\sim $9 S/cm and reveal a weak transmission turn on near 950 nm (1.3 eV) indicative of the band gap absorption. BiCuOSe is isostructural with the transparent p-type conductor LaCuOSe, but forms at much lower temperatures. Possible applications include use as a solar cell absorber. [Preview Abstract] |
Friday, May 19, 2006 3:24PM - 3:44PM |
B1.00006: BREAK
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Friday, May 19, 2006 3:44PM - 3:56PM |
B1.00007: Barium Hexaferrite Thick Films Made by Liquid Phase Epitaxy Reflow Method Alaaedeen Abuzir In this work, we report on the growing of BaFe$_{12}$O$_{19}$(or BaM) thick films on (0001) sapphire Al$_{2}$O$_{3}$ substrate. Our goal is to fabricate barium ferrite thick films which can be self-biased for circulator application. We have modified the liquid phase epitaxy (LPE) method by conducting the experiment in vacuum. A small chunk piece of the melt weighing about 0.035 g was placed on 1cm x 1cm Al$_{2}$O$_{3}$ substrate and remelted at 1200$^{\circ}$C for one hour. The thickness of our thick films grown by this reflow method range from 300 to 550 $\mu$m. The coercivities of the thick films in the perpendicular direction were about 100Oe. [Preview Abstract] |
Friday, May 19, 2006 3:56PM - 4:08PM |
B1.00008: Gallium Nitride Calcined with Copper Oxide: Structural and Spectroscopic Studies L. Noice, B. Seipel, C. Li, P. Moeck, R. Erni, A. Gupta, N. Browning, K.V. Rao Fabrication of GaN based semiconductor devices often uses transition metals such as titanium and nickel for making ohmic contacts. These metals can diffuse into the semiconductor and, thus, strongly influence the optoelectronic properties of the device. The potential of copper-doped GaN in tuning the optical properties of the semiconductor is largely unexplored. Therefore, several samples of GaN calcined with CuO in either air or nitrogen were analyzed via powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy in order to address the structural characterization of copper-doped GaN. Gallium oxide and multiple copper oxide phases were detected. Significant changes in some GaN lattice parameters and electron structure indicate incorporation of both copper and oxygen into the GaN lattice. [Preview Abstract] |
Friday, May 19, 2006 4:08PM - 4:44PM |
B1.00009: Brownian Motors from Biology to Quantum Electronics Invited Speaker: Molecular motors in living cells have solved a problem that nanotechnology still chews on: how to generate directed motion with a machine that is so small that thermal fluctuations are of substantial magnitude. From a physics point of view, a possible way of dealing with thermal fluctuations is to use them instead of fighting them -- that is, to incorporate thermal fluctuations as an integral part of the operational principle of nanoscale machines. Motors based on this idea are called Brownian motors or thermal ratchets. To function, they require (i) thermal fluctuations, (ii) broken symmetry (a ``ratchet''), and (iii) thermal non-equilibrium (a source of free energy). I will introduce the basic concepts of ratchets and Brownian motors in the context of biomolecular motors, and will present three different experimental systems: liquid droplets coaxed by a ratchet to move uphill, a concept for a DNA-based single-molecular motor, and new insights on thermoelectric power generation that are a direct spin-off from research into quantum ratchets. [Preview Abstract] |
Friday, May 19, 2006 4:44PM - 4:56PM |
B1.00010: The Heat Pulse Porpagations in Multiwall Carbon Nanotubes Taejin Kim, Mohamed Osman, Cecilia Richards, Robert Richards, David Bahr The microscopic mechanism of heat transport in armchair and zigzag double wall carbon nanotube (DWCNT) was studied by using Molecular Dynamics (MD) simulations. In order to generate heat waves in different phonon modes, strong heat pulse was applied to DWCNT. It was observed that leading heat wave packets in both DWCNTs and those in corresponding single wall carbon nanotubes (SWCNTs) move at the speed of longitudinal acoustic (LA) phonon modes. The kinetic temperatures of leading heat wave packets in inner and outer shell of DWCNT were greater than those of corresponding SWCNT. Within the leading heat wave packets, inner shell was longitudinally compressed while outer shell was expanded. However, it was observed the smaller longitudinal compression or expansion in SWCNT. The compression and expansion mechanism in both DWCNTs was found to depend on chirality. The local deformation of atomic structure in DWCNT is believed to increase the potential energy at corresponding regions and it is responsible for strong leading heat wave packets in each shell. [Preview Abstract] |
Friday, May 19, 2006 4:56PM - 5:08PM |
B1.00011: Radial Heat Transfer Dynamics in Multiwall Carbon Nanotubes Mohamed Osman, Taejin Kim The dynamics of radial heat transfer in zigzag and armchair double wall carbon nanotubes (DWCNT) have been examined using molecular dynamic (MD) simulations with the goal of understanding the role of radial phonon modes in heat transfer. The MD model uses Tersof-Brenner potential for bonded C-C interactions within each shell and non-bended van der Wall interaction between inner and outer shells. The simulation procedure involves, (1) quenching the DWNT to 0 K, (2) minimization of the potential energy and (3) raising the temperature of the outer shell to the desired steady state temperature while maintaining the inner tube at 0.1 K. The heat baths are removed from the outer and inner shell and their energies are examined. The energies of inner and outer exhibit an out of phase oscillatory behavior due the exchange of the energies between the two shells. The energy of the inner tube shows a weak gradual increase due to the temperature gradient. The beat frequencies determined from the Fourier transform of the energy oscillations of the inner and outer nanotubes were found to be in the tera Herz range. We will also discuss the temperature and length dependence of oscillatory energy exchange between the nanotube shells. [Preview Abstract] |
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