Bulletin of the American Physical Society
2005 Joint Spring Meeting Ohio Section of APS and the Southern Ohio Section of AAPT
Friday–Saturday, April 8–9, 2005; Dayton, OH
Session D7: Condensed Matter |
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Chair: Robert Hengehold Room: SC 328 |
Saturday, April 9, 2005 8:00AM - 8:12AM |
D7.00001: Random-phase approximation of core-electron energy-loss spectra in solids Kofi Nuroh The interference between bound-bound transition and bound-free transition in an electron-impact excitation of a core-electron in systems with narrow bands is discussed within the context of diagrammatic perturbation of ladder and ring diagrams in the spirit of random-phase approximation (RPA). [1, 2] The resulting excitation spectrum has been formulated by introducing Fano line shape parameters for the associated autoionization and characteristic decay channels. Along with line widths for these channels, a generalized asymmetric Fano line shape expression is obtained. It is found that while the ring diagrams contribute little numerically to the excitation spectrum in absolute terms, their retention is necessary to provide the asymmetry found in the ratio of experimental electron energy-loss spectrum of metallic cerium to lanthanum. \newline \newline [1] K. Nuroh, Phys. Rev. B 66, 155126 (2002). \newline [2] K. Nuroh, Phys. Rev. B 70, 205115 (2004). [Preview Abstract] |
Saturday, April 9, 2005 8:12AM - 8:24AM |
D7.00002: Josephson vortex state across the phase diagram of La$_{2-x}$Sr$_x$CuO$_4$: a magneto-optics study Sasa Dordevic, D.N. Basov, S. Komiya, Y. Ando, Y.J. Wang We present a detailed doping dependent study of the Josephson vortex state in La$_{2-x}$Sr$_x$CuO$_4$ using infrared spectroscopy. Magnetic field as high as 17 Tesla, applied along the CuO$_2$ planes, is found to suppress the Josephson plasmon in all measured samples. We find the strongest suppression in samples with dopings close to x=1/8 and attribute this effect to the spontaneous formation of in-plane charge inhomogenities (``stripes'') at this doping level. Several theoretical models of the Josephson vortex state are applied to explain the observed effects. [Preview Abstract] |
Saturday, April 9, 2005 8:24AM - 8:36AM |
D7.00003: The Electrical Field Gradient at $^{181}Ta$ in $ZrSiO_{4}$ and $HfSiO_{4}$ Sean McBride, Herbert Jaeger We have used perturbed angular correlation spectroscopy (PAC) to measure the electric field gradient (\textit{EFG}) at the \textit{Zr}-site in zircon (\textit{ZrSiO}$_{4})$ between room temperature and \textit{1100\r{ }C} using $^{181}$\textit{Ta} probe nuclei. The \textit{EFG} is axially symmetric and the quadrupole interaction frequency \textit{$\nu $}$_{Q}$ decreases linearly with increasing temperature. While for some zircon specimens the slope of the \textit{$\nu $}$_{Q}$\textit{ vs. T} increases above \textit{900\r{ }C}, for others this change in slope is not observed. This change in the thermal behavior \textit{$\nu $}$_{Q}$ is consistent with a displacive structural transition reported in the literature.\footnote{Z. Mursic, T. Vogt, and F. Frey, Acta Cryst. \textbf{B48} (1992) 584.} In order to learn more about this structure we have begun performing PAC experiments on isostructural hafnon (\textit{HfSiO}$_{4})$, which was synthesized in our laboratory. PAC spectra of hafnon are very similar to those of zircon but show a small second-site interaction due to residual \textit{HfO}$_{2}$ from the sample preparation. The temperature dependence of the quadrupole interaction frequency will be discussed in context of a displacive phase transition in these materials. [Preview Abstract] |
Saturday, April 9, 2005 8:36AM - 8:48AM |
D7.00004: Effects of spin--orbit interaction on optical properties of narrow-band semiconductor quantum wells Leonid Isaev, Arkady Satanin, Yong Joe We study effects of strong spin--orbit interaction on optical properties of narrow--gap semiconductor quantum films. Electron states in such materials ($e.g. ${\$}Pb{\_}xSn{\_}{\{}1-x{\}}(S,Se,Te){\$}) are well described by the two--band Kane model with the Dirac--type effective Hamiltonian [1]. It may be shown that electron dispersion in a film with identical boundaries still keeps spin degeneracy. In the present work we consider two types of (asymmetric) films with broken mirror symmetry: $i)$ with nonequivalent boundaries, and \textit{ii}) with a linear spatial variation of the forbidden band in the direction of epitaxial growth. It was shown that in both cases there is a noticeable spin--splitting of size--quantized subbands, strongly dependent on parameters in boundary conditions on film's surfaces. Under external illumination this results in an asymmetric distribution of photoexcited carriers in \textbf{k}--space, and therefore, in spin--polarized photocurrents. We also show that measurement of optical absorption coefficient may give direct information about the film surface structure. [1] J. O. Dimmock, G. B. Wright, Phys. Rev. \textbf{135}, A821 (1964). This work is supported by the Indiana 21$^{st}$ Century Research and Technology Fund. [Preview Abstract] |
Saturday, April 9, 2005 8:48AM - 9:00AM |
D7.00005: Electrical properties of Al$_{x}$Ga$_{1-x}$N implanted with Si at low doses Elizabeth Moore, Timothy Zens, Mee-Yi Ryu, Yung Kee Yeo, James Fellows, Robert Hengehold The investigation of ion implanted Al$_{x}$Ga$_{1-x}$N is still an immature subject compared to the research that explores the properties of GaN. A systematic electrical activation study of Si implanted Al$_{x}$Ga$_{1-x}$N grown on sapphire substrates by molecular beam epitaxy has been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with does ranging from 1x10$^{13}$ to 1x10$^{14}$ cm$^{-2}$ at room temperature. The samples were proximity cap annealed from 1100 to 1350 $^{o}$C with a 500 {\AA} AlN cap in a nitrogen environment. Hall Effect measurements show that an electrical activation efficiency of almost 100{\%} can be obtained for the Al$_{0.2}$Ga$_{0.8}$N implanted with doses of 5x10$^{13}$ and 1x10$^{14}$ cm$^{-2}$ and annealed at 1350 and 1300 $^{o}$C, respectively, for 20 min. An electrical activation efficiency of 87{\%} was achieved for the Al$_{0.1}$Ga$_{0.9}$N implanted with a dose of 1x10$^{14}$ cm$^{-2}$ after annealing at 1250 $^{o}$C for 20 min. These samples also exhibited a large mobility of 89 cm$^{2}$/V\textbullet s. [Preview Abstract] |
Saturday, April 9, 2005 9:00AM - 9:12AM |
D7.00006: LabVIEW for Admittance Spectroscopy Automation Robert J. Brodrick, Mo Ahoujja, Rex L. Berney Admittance spectroscopy (AS) and capacitance-voltage (C-V) measurements have long been characterization tools used to study properties of deep level defects in semiconductor devices. Measurements of conductance and capacitance of semiconductor devices are made typically as a function of temperature, voltage, and voltage signal frequency. To fully automate the system for data acquisition, LabVIEW, a virtual graphical programming language developed by National Instruments, is used to interface a computer with the measurement instruments. In this paper, the LabVIEW modules used and highlights of data from wide bandgap semiconductor devices will be presented. [Preview Abstract] |
Saturday, April 9, 2005 9:12AM - 9:24AM |
D7.00007: \textit{$\mu $}-Raman studies of residual stress in SiC MEMS Chris Zingarelli, Michael Marciniak, Jason Foley \textit{$\mu $}-Raman spectroscopy is used to measure residual stress in single-crystal, 6H-SiC used in MEMS devices. These structures are bulk micro-machined by back etching a 250-$\mu $m-thick, single-crystal 6H-SiC wafer to form a 50-$\mu $m thick diaphragm. A Wheatstone bridge, patterned of piezoresistive elements, is formed across the membrane from a 5-$\mu $m, 6H-SiC epilayer; the output of the bridge is proportional to the flexure of the MEMS diaphragm. \textit{$\mu $}-Raman spectroscopy was performed with an Ar$^{+}$ laser ($\lambda $ = 514.5 nm). By employing an incorporated piezoelectric stage with submicron positioning capabilities along with the Raman spectral acquisition, spatial scans revealed areas in the MEMS structures that contain residual stress. Shifts in the transverse optical (TO) Stokes peaks of up to 2 cm$^{-1}$ along the edge of the diaphragm and through the piezoresistors indicate significant material strain induced by the MEMS fabrication process. The phonon deformation potential was measured to quantify the material stress as a function of the shift in the Raman peak position. [Preview Abstract] |
Saturday, April 9, 2005 9:24AM - 9:36AM |
D7.00008: Effect of Interfaces on the Band Gaps of InAs/GaSb Superlattices Beyond the Standard Envelope-function Approximation Frank Szmulowicz, Heather Haugan, Gail Brown We have grown several series of InAs/GaSb superlattices by molecular beam epitaxy with precisely calibrated growth rates. The superlattice parameters such as the InAs and GaSb layer widths were varied in order to produce a device with an optimum mid-infrared photoresponse and a sharpest photoresponse cut-off. The effect of design parameters on the photoresponse cut-off are explained by a nonperturbative, modified envelope function approximation (EFA) calculation that includes the interface coupling of heavy, light, and spin-orbit holes resulting from the in-plane asymmetry at InAs/GaSb interfaces. Interface effects on the EFA-calculated band structure are manifested by large band splittings and avoided crossings. The physics of these effects has been modeled analytically in several important limits. Very good agreement was found between experimental results and theory on several sets of SLs (both MWIR and LWIR) with symmetric InSb-like interfaces and mixed GaAs- and InSb-like interface. We explain the band gaps as a function of GaSb and InAs widths in terms of variations of the heavy-hole and conduction band bandwidths. Therefore, a consistent application of the EFA method with the inclusion of well established IF effects provides useful physical insights and possesses good predictive capacity in the design of NCA SLs. [Preview Abstract] |
Saturday, April 9, 2005 9:36AM - 9:48AM |
D7.00009: Magnetic properties of ZnO nanotips ion-implanted with Fe or Mn Jeremy Raley, Yung Kee Yeo, Mee-Yi Ryu, Robert Hengehold, Todd Steiner, Pan Wu, Yicheng Lu ZnO nanotips grown on quartz, sapphire, and glass were implanted with Fe or Mn to a dose of 5 $\times $ 10$^{16}$ ions/cm$^{2}$ and subsequently annealed at temperatures from 575 to 800$^{\circ}$C in O$_{2}$ flowing at 25 sccm. This experiment was undertaken in an attempt to create dilute magnetic semiconductors with ferromagnetic properties persisting to room temperature. After implantation and annealing, the samples were characterized by field and temperature dependent magnetization measurements in a SQUID magnetometer and photoluminescence. All of the samples demonstrated signatures of ferromagnetism (coercive and remanent fields in hysteresis measurements), but not all manifest an optimal annealing temperature. PL measurements are used to detect implant damage recovery and the incorporation of the implanted transition metal into the ZnO nanotips. [Preview Abstract] |
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