Bulletin of the American Physical Society
2014 Annual Spring Meeting of the APS Ohio-Region Section
Volume 59, Number 3
Friday–Saturday, April 4–5, 2014; Youngstown, Ohio
Session E3: Condensed Matter Physics: Oxide Materials |
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Chair: Tom Oder, Youngstown State University Room: Williamson Hall 3422 |
Saturday, April 5, 2014 8:00AM - 8:12AM |
E3.00001: Hydrogen in Insulating Oxides David Winarski, F.A. Selim Hydrogen is known to strongly affect the structural and electrical properties of many materials. Its effects have been extensively investigated in semiconductors, theoretically and experimentally. However, no attention has been paid to the role of hydrogen in insulators. In this work we show that hydrogen has profound effects on the optical properties of Y$_{3}$Al$_{5}$O$_{12}$ insulating oxide, an important photonic material with wide range of applications in laser, scintillation and illumination. Thermo-luminescence measurements were carried out from 77 K-675 K on undoped Y$_{3}$Al$_{5}$O$_{12}$ single crystals. The measurements showed that hydrogen eliminates most of the deep and shallow traps in Y$_{3}$Al$_{5}$O$_{12}$ single crystals and dramatically affect the luminescence and scintillation properties of the crystals. These effects are explained due to the recently discovered phenomena, passivation of cation vacancies by hydrogen [Phys. Rev. B 88, 174102, 2013]. [Preview Abstract] |
Saturday, April 5, 2014 8:12AM - 8:24AM |
E3.00002: Comparison of uniform and delta doped p-type ZnO thin films Ravichandra Gade, Tom Oder The properties of uniform and delta doped p-type ZnO thin films deposited by RF magnetron sputtering from ZnO and Li$_{3}$PO$_{4}$ solid targets on c-plane sapphire substrates have been characterized. Uniform doping was achieved by simultaneous deposition of the films from the ZnO and Li$_{3}$PO$_{4}$ targets at 300 $^{\circ}$C to a thickness of about 1 $\mu $m. For delta doping, the deposition from the Li$_{3}$PO$_{4}$ target was blocked every two minutes. Post-deposition annealing was carried using a rapid thermal processor in O$_{2}$ at 500 - 900 $^{\circ}$ C for 3 min. Analyses performed using photoluminescence spectroscopy measurements revealed luminescence peaks at 3.35 and 3.30 eV at 12 K for the uniform doped and delta-doped films, respectively. Hall effect measurements revealed $p$-type conductivities with average Hall concentrations of 2.71 x 10$^{14}$ and 2.17 x 10$^{15}$ cm$^{-3}$ for the uniform and delta doped films, respectively. These p-type conductivities however were unstable and sometimes yielded $n$-type conductivities with repeated measurements. The fluctuation in the carrier type could be due to small Hall voltages in the measurements, which can be significantly impacted by small spikes in signal noise inherent in the measurements. [Preview Abstract] |
Saturday, April 5, 2014 8:24AM - 8:36AM |
E3.00003: ZnO Doped by Neutron Transmutation Bryan Smith, Farida Selim Neutron transmutation doping has been shown to be an effective method to produce Cu dopants on Zn sites in ZnO single crystals (F. A. Selim et al., Applied Physics Letters 99, 202109, 2011). These Cu dopants lie 160 meV below the conduction band minimum acting as deep acceptors and dramatically modify the electrical properties of the samples. In this work we investigate the change in optical properties due to Cu doping and neutron irradiation. Measurements are performed before and after annealing to distinguish between the effect of radiation damage and Cu doping. Finding was provided by the National Science Foundation (DMR1359). [Preview Abstract] |
Saturday, April 5, 2014 8:36AM - 8:48AM |
E3.00004: Exploration of Ti-doped CuGaO$_{2}$ delafossite M. Kylee Rice, James P. Lewis In their most simple form, delafossite materials are of the form ABO$_{2}$ where A is a $+$1 metal cation and B is a $+$3 metal cation. Since O is in the -2 ionization state in the crystal, this results in a charge balanced and stable crystal. Delafossite materials have been studied for their p-type and n-type conductivity, however. This means that studied material samples have extra holes or electrons due to defects resulting in a net charge and thus allow for conductivity within the sample. Since types of defects inherent in a sample are due to the structure of the sample, they can then be doped with other elements to increase the p- or n-type conductivity. For example, CuCrO$_{2}$ is found to be of p-type defect chemistry, and when doped with Mg ($+$2), has a conductivity of 220 S cm$^{-1}$. In this research we computationally explore electronic properties of a new material, p-type CuGaO$_{2}$ doped with Ti ($+$2), and the resulting defects. This delafossite is a wide band gap semiconductor and has shown promise as a p-type material and a photocatalyst with the ability to reduce CO$_{2}$ to CO. An understanding of the doping of Ti in CuGaO$_{2}$ could lead to a material with a smaller band gap, better photocatalytic abilities, and enhanced conduction. [Preview Abstract] |
Saturday, April 5, 2014 8:48AM - 9:00AM |
E3.00005: Microstructural Investigation of ZnO Thin Films Using Transmission Electron Microscopy (TEM) Techniques Matthew Kelly, Tom Oder, C. Virgil Solomon ZnO thin films were synthesized by RF magnetron sputtering of high purity ZnO solid targets on c-plane sapphire substrates. Post-deposition annealing was performed at various temperatures ranging from room temperature (RT) to 900$^{\circ}$C for 3 min. Cross-sectioned samples for TEM investigations were prepared from three different materials: non-annealed (RT), 200$^{\circ}$C and 700$^{\circ}$C annealed ZnO thin films. Electron transparent sample were prepared by lift-out technique in a Focused Ion Beam instrument. The investigated materials show remarkable uniformity of the ZnO thin film thickness (about 1 $\mu$m), as determined by dark-field scanning transmission electron microscopy imaging. Irrespective of the annealing time the ZnO thin films are polycrystalline. Individual grains have a columnar morphology with the long axis oriented perpendicular to the ZnO/sapphire interface. The grain size is temperature dependent, the largest grains being observed in the 700$^{\circ}$C annealed material. Edge dislocations have been observed by atomic resolution TEM of the investigated materials. On-going work using analytical TEM techniques aims to clarify into the relationship between microstructure and photoluminescence in ZnO thin films. [Preview Abstract] |
Saturday, April 5, 2014 9:00AM - 9:12AM |
E3.00006: ZnO/metal layered 3D Photonic crystals Michael McMaster, Donald Priour, Tom Oder Three-dimensional (3D) photonic crystals are deposited by sputtering multilayer mesoscopic pillars of zinc oxide and a metal, either chromium or aluminum, in a triangular lattice. As a preliminary step, ZnO/metal one-dimensional photonic crystals are deposited with varying layer thicknesses. The layer thicknesses corresponding to the most prominent band gap are chosen for the layered pillars of the 3D crystal structure. The photonic crystals are tailored to ensure that the optical band gap lies within the spectrum of visible light for near normal incidence. The band gap of the 3D photonic crystal is measured by collecting the absorption spectrum. [Preview Abstract] |
Saturday, April 5, 2014 9:12AM - 9:24AM |
E3.00007: First-principles investigation of the structural, mechanical and electronic properties of the NbO-structured 3d, 4d and 5d transition metal nitrides Zhi Liu, Xiuquan Zhou, Daniel Gall, Sanjay Khare We performed ab initio calculations on 29 transition metal nitrides from the 3d, 4d and 5d rows, in NbO structure. We calculated cohesive energy, lattice constant and elastic constants C$_{\mathrm{11}}$, C$_{\mathrm{12}}$ and C$_{\mathrm{44}}$, and derived mechanical moduli, related ratios and hardness. For five of the ten 3d transition metal nitrides, cohesive energy in this new structure is similar to that of the same composition in the rocksalt structure. The lattice constant and bulk modulus were found to be anti-correlated. We observed the correlation between the shear modulus (G), Pugh's ratio (k) and derived Vickers hardness (H$_{\mathrm{V}})$. The nitrides, CrN, MoN and WN in NbO structure show values of H$_{\mathrm{V}}$ larger than 20 GPa. We showed systematically that C$_{\mathrm{44}}$, G, k and H$_{\mathrm{V}}$ are anti-correlated with the number of electronic states around E$_{\mathrm{F}}$. The local density of states demonstrating systematic evolution of the electronic structure was studied. Bader charge transfer analysis was performed. This work has been published as Liu et al., Comput. Mater. Sci. 84, 365 (2014). [Preview Abstract] |
Saturday, April 5, 2014 9:24AM - 9:36AM |
E3.00008: Photo-catalytic reduction of CO$_{2}$ using Au--ZnO heterostructured nano-pyramids Oshadha Ranasingha, Congjun Wang, Christopher Matranga, James Lewis Au-ZnO heterostructures were synthesized to create Au nanoparticles ($\sim$ 5 nm) attached to the basal surface of pyramid-shaped ZnO nanocrystals ($\sim$ 20 nm). The Au-ZnO heterostructures showed a large absorption peak around 521 nm which is assigned to the surface plasmon resonance of the Au nanoparticles. The photocatalytic activity of the Au-ZnO sample was evaluated inside a reaction cell purged with a 50 {\%} CO$_{2}$ and 50 {\%} H$_{2}$ gas mixture. The sample was then exposed to a 532 nm pulsed laser source to excite the plasmon resonance of Au and generate heat to drive the catalytic reaction of CO$_{2}$ and H$_{2}$ on the ZnO substrate. The primary products detected with gas chromatography were CO, CH$_{4}$ and C$_{2}$H$_{6}$. A maximum CO$_{2}$ conversion rate of 43.15 $\mu$ mol g$^{-1}$h$^{-1}$ was observed at the available highest laser power. [Preview Abstract] |
Saturday, April 5, 2014 9:36AM - 9:48AM |
E3.00009: On the optical properties of strontium titanate Rebekah Thomas, Farida Selim Complex oxide SrTiO3 exhibits a range of novel physical phenomena and unusual electronic transport behavior. Recently we have discovered two orders of magnitude persistent photoconductivity in bulk single crystals after heating the samples with strontium oxide powder at 1200 C. In the present work SrTiO3 single crystals are annealed in various atmospheres to populate different types of defects. The formation of color centers and luminescence defects in the samples are investigated through optical absorption and luminescence measurements. UV-VIS-NIR absorption spectra are recorded at room temperature and luminescence emission spectra are recorded as a function of temperature from 77 k to 775 K. The study reveals the great influence of point defects on the optical properties of SrTiO3 bulk single crystals. Funding was provided by the National Science Foundation (DMR1359523 grant). [Preview Abstract] |
Saturday, April 5, 2014 9:48AM - 10:00AM |
E3.00010: Band Gap Transition Studies of U:ThO2 Using Cathodoluminescence Joshua Reding, David Turner, Robert Hengehold The Department of Defense has an interest in thorium dioxide (ThO$_2$) and uranium dioxide (UO$_2$) as possible candidates for use in designing neutron detectors. Three U$_x$:Th$_{1-x}$O$_2$ (x= 0.00, 0.01, 0.22) hydrothermally grown single crystals were examined using cathodoluminescence to interrogate the changing electronic properties of ThO$_2$ as it became an alloy. Both depth-resolved and temperature-dependent cathodoluminescence studies were performed to examine the crystal structure and the defects present. An ultra-high vacuum system operating at 10$^{-8}$ Torr was used with electron beam energies ranging from 2 to 14 keV. Spectra were taken on all three samples before and after a proprietary chemical cleaning process involving a crown ether/picric acid solution was applied to the crystals to remove surface contaminants. Spectral deconvolution of the spectra showed evidence of both direct and indirect gap photon transitions from the O~2p to Th~6d at 4.2 eV and 4.8 eV respectively. Uranium-doped spectra showed evidence of the midgap O 2p to U 5f quadrupole transition and O~2p to U~6d transition at 5 eV. [Preview Abstract] |
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