Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W22: Transparent Conductors, Titania, and Other Oxides |
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Sponsoring Units: FIAP Chair: Kartik Ghosh, Missouri State University Room: 324 |
Thursday, March 21, 2013 2:30PM - 2:42PM |
W22.00001: The doping effect of Mn and Co ions in PbPdO$_{2}$ Kyujoon Lee, Seong-Min Choo, Jihoon Hwang, Jeongsoo Kang, Myung-Hwa Jung Spintronics is a promising field in which the spin of electrons along with the charge is used for data storage and data manipulation. For spintronics application a long mean free path with high spin polarization is required. In this sense, the magnetic gapless semiconductor is a promising material since it satisfies both conditions. Here we have studied PbPdO$_{2}$, which is predicted to be a gapless semiconductor, and its Co and Mn doping to be a spin gapless semiconductor. We have tried to tune its electrical and magnetic properties with magnetic ions such as Co and Mn, in order to achieve the magnetic gapless semiconductors for spintronics application. A drastic change in the magnetic properties has been observed when doped with magnetic ions. The Co doping induces a weak ferromagnetic exchange, while the Mn doping induces an antiferromagnetic exchange. To investigate the electronic structures of PbPdO$_{2}$ we have measured the valence band photoemission spectroscopy and X-ray absorption spectroscopy. The results show Mn$^{4+}$ and Co$^{3+}$ states for the Mn and Co doped PbPdO$_{2}$, respectively. This implies that the magnetic and electrical properties of PbPdO2 can be easily tuned by chemical doping, and it leads to possible applications for spintronics. [Preview Abstract] |
Thursday, March 21, 2013 2:42PM - 2:54PM |
W22.00002: P-type K-doping of BaSnO$_3$ and its pn junctions Hoonmin Kim, Chulkwon Park, Useong Kim, Kookrin Char We have recently reported high mobility in La-doped BaSnO3 (BSO), whose transparency and chemical stability promises large potential for scientific and technical applications. The doping possibility with p-type carrier will further enhance its utility in scientific and technical endeavors. For such purpose, we will present our work in p-type doping BSO by epitaxially growing K-doped BSO by pulsed laser ablation on SrTiO3 substrates. We have found that K replaces Ba from EPMA. Although K-doped BSO exhibited rather high resistivity at room temperature, its conductivity increased dramatically at high temperature and the conductivity decreased when small amount of oxygen was removed from the thin films, consistent with the behavior of p-type doped oxides. The carrier type of K-doped BSO will be further confirmed by direct high-temperature Hall measurement. We will report on the mobility of the K-doped BSO and the performance of pn junctions fabricated by using K- and La-doped BSO. [Preview Abstract] |
Thursday, March 21, 2013 2:54PM - 3:06PM |
W22.00003: Role of annealing temperature on microstructural and electro-optical properties of ITO films produced by sputtering Abdulkadir Senol, Mahir Gulen, Gurcan Yildirim, Ozgur Ozturk, Ahmet Varilci, Cabir Terzioglu, Ibrahim Belenli In this study, we investigate the effect of annealing temperature on electrical, optical and microstructural properties of indium tin oxide (ITO) films deposited onto Soda lime glass substrates by conventional direct current (DC) magnetron reactive sputtering technique at 100 watt using an ITO ceramic target (In$_{2}$O$_{3}$:SnO$_{2}$, 90:10 wt. {\%}) in argon atmosphere at room temperature. The films obtained are exposed to the calcination process at different temperature up to 700 $^{\circ}$ C. Resistivity, Hall Effect, X--ray diffractometer (XRD), ultra violet-visible spectrometer (UV--vis) and atomic force microscopy (AFM) measurements are performed to characterize the samples. Moreover, phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. Furthermore, mobility, carrier density and conductivity characteristics of the samples prepared are carried out as function of temperature in the range of 80-300 K at the magnetic field of 0.550 T. The results obtained show that all the properties depend strongly on the annealing temperature and in fact the film annealed at 400 $^{\circ}$ C obtains the better optical properties due to the high refractive index while the film produced at 100 $^{\circ}$C exhibits much better photoactivity than the other films as a result of the large optical energy band gap. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W22.00004: Transparent oxide semiconductors (Ba,La)SnO$_{3}$ with high mobility at room temperature Hyung Joon Kim, Useong Kim, Tai Hoon Kim, Jiyeon Kim, Hoon Min Kim, Byung-Gu Jeon, Woong-Jhae Lee, Hyo Sik Mun, Kwang Taek Hong, Jaejun Yu, Kookrin Char, Kee Hoon Kim We present our discovery of (Ba,La)SnO$_{3}$ system exhibiting electrical mobility at 300 K of 200-320 cm$^{2}$V$^{-1}$s$^{-1}$ in a doping range from 1.0x10$^{19}$ to 4.0x10$^{20}$ cm$^{-3}$. Moreover, their conductivity values were as large as around 10$^{4}$ S/cm, being comparable to those of indium tin oxides. The system yet shows the optical gap around 3.33 eV and only slight increase of the in-gap states, maintaining visual transparency. Several unique physical properties of (Ba,La)SnO$_{3}$ are also discussed: a superior oxygen stability evidenced by persistent transport properties under high temperature environments, a small effective mass coming from the ideal Sn-O-Sn bonding in a cubic perovskite, small disorder effects due to doping away from the main conduction channels (SnO$_{6}$ octahedra network) and reduced carrier scattering due to the high dielectric constant. (Ba,La)SnO$_{3}$ thus holds great potential for realizing transparent, high power, high temperature functional devices. [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W22.00005: Small polarons and their interaction with donor centers in Titania Anderson Janotti, Cesare Franchini, Joel Varley, Georg Kresse, Chris Van de Walle The use of TiO$_{2}$ in photocatalysis, photosensitized solar cells, and memristors strongly depends on the behavior of conduction-band electrons, prompting a more profound understanding of conduction mechanisms. The reported results for the behavior of excess electrons in TiO$_{2}$ are contradictory. High carrier mobilities, characteristic of delocalized electrons, have been observed in Hall measurements, whereas optical spectra indicate the presence of localized, small polarons. Using first-principles calculations based on a hybrid functional we study the formation of small polarons, comparing it to delocalized electrons in the conduction band of TiO$_{2}$. From the calculated configuration coordinate diagram and migration energy barriers, we discuss the coexistence of small polarons with delocalized electrons, and address how the observed behavior depends on the type of experiment being conducted. The interaction of small polarons with intrinsic defects such as the oxygen vacancy and donor impurities will also be discussed. [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W22.00006: Preparation of perpendicular oriented TiO2 films via hydrothermal method: phase selection and growth control Yun Gao, Meilan Guo, Xiaohong Xia, GuoSheng Shao Either rutile or anatase vertical orientated TiO$_2$ array films were synthesized successfully on FTO (F: SnO$_2)$ substrate via hydrothermal method through controlling the concentration of Cl$^-$ and SO$_4^{2-}$. The density of nanorods can be adjusted by varying the volume ratio of ethanol/water, and the degree of orientation and crystallinity of TiO$_2$ nanofilms were enhanced with increasing dosage of ethanol. Meanwhile, completely dense anatase films with [004] oriented growth appear within a very narrow concentration window when adding sulfuric acid into precursor. Besides, other alcohols such as methanol, n-propanol and n-butyl were also used as solvent to examine the role of alcohol type during hydrothermal process for both two phase films. The growth rate and degree of perpendicular orientation declined as the alkyl length of solvents increases. Hydrogen sensing characteristics of dense films of both rutile and anatase phases showed that there was a remarkable improvement of sensitivity response over reported data. It was found that rutile films have higher sensitivity while anatase films have faster response. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W22.00007: Visible Light Sensitization of TiO$_{2}$ Films by co-doping with Nitrogen and Carbon Inci Ruzybayev, Emre Yassitepe, Awais Ali, Arshad S. Bhatti, Syed Ismat Shah Anatase phase of TiO$_{2}$ has a band gap of 3.20 eV. Therefore, only UV light can be absorbed from the solar spectrum. Introducing defect states narrows the band gap of TiO$_{2}$ semiconductor and enhances the visible light activity. In this study, the defect states in the band gap are created by nitrogen and carbon dopants. Reactive pulsed laser deposition technique is used to prepare nitrogen and carbon co-doped TiO$_{2}$ films. Total pressures of nitrogen and methane gases are kept at 100 mTorr. Two types of co-doped samples are investigated with partial pressures of 80 mTorr nitrogen with 20 mTorr methane and 20 mTorr nitrogen with 80 mTorr methane. Undoped, control, sample is also prepared under 100 mTorr oxygen gas. All films show polycrystalline anatase structure. Nitrogen dopant is calculated from XPS high resolution scans while carbon incorporation into TiO$_{2}$ lattice is supported by XRD and FESEM analyses. Also, direct relation between oxygen vacancies and nitrogen doping concentration is observed from XPS high resolution scans of N 1s and Ti 2p regions. Band gap is calculated using absorption coefficient obtained from UV-Vis diffuse reflection spectroscopy measurements. 80 mTorr nitrogen and 20 mTorr methane co-doped TiO$_{2}$ film has the lowest band gap among all with 2.17 eV which lies near the most intense peak in the visible part of the solar spectrum. Therefore, co-doping TiO$_{2}$ with nitrogen and carbon is a possible method for visible light sensitization. [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W22.00008: the effect of electron doping in TiO2 assessed by ARPES Luca Moreschini, Simon Moser, Jacim Jacimovic, Osor Barisic, Helmut Berger, Arnaud Magrez, Young Jun Chang, Keun Su Kim, Aaron Bostwick, Laszlo Forro, Eli Rotenberg, Marco Grioni The titanium oxide TiO2 has been object of extensive studies because of its suitability in many practical fields, ranging from photovoltaic applications, to catalysis, memristors, and others. As for many other transition metal oxides, great attention has been devoted to the impact on the electronic structure of different doping mechanisms, either extrinsic or due to the creation of oxygen vacancies. Here we report an angle-resolved photoemission (ARPES) work on TiO$_2$ single crystals and epitaxial films grown wIth the \textit{in situ} pulsed-laser-deposition (PLD) system available on beamline 7.0.1 at the Advanced Light Source. We show the evolution of the electronic structure as a function of the amount of oxygen vacancies induced by the photon beam. [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W22.00009: Thermodynamic Effects on Phase Stabilities and Structural Properties of TiO2 from the First-principles Yuta Aoki, Susumu Saito Titanium dioxide (TiO2) is one of the most representative photocatalytic materials and much attention is focused on understanding and improvement of its photocatalytic activity. At the same time, TiO2 is known to be a highly polymorphic material and as many as eleven crystal phases have been identified so far. It is expected that TiO2 show various photocatalytic properties depending on crystal phases. However, relative stabilities of these identified phases are still controversial. In order to clarify the thermodynamic phase stabilities of TiO2, we obtain the free energies of its several representative phases, rutile, anatase, brookite, and TiO2-II within the framework of the density-functional theory using the pseudopotential method. We calculate both the static energy and the contribution of phonons to the free energy through the quasiharmonic approximation for each phase. It is found that treatment of semicore electrons in constructing the pseudopotential of the Ti atom significantly affects the relative phase stabilities. From the phase diagram obtained, we find that the anatase phase is the most stable at lower temperature and pressure. We also discuss the thermodynamic effects on structural properties such as thermal expansion. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W22.00010: Properties of p-type ZnO Films co-doped with Lithium and Phosphorus Tom Oder, Michael McMaster, Andrew Smith Thin films of ZnO co-doped with lithium and phosphorus were deposited on sapphire substrates by RF magnetron sputtering. The films were sequentially deposited from ZnO and Li$_{3}$PO$_{4}$ solid targets on the substrates maintained at 500 $^{\circ}$C. An undoped ZnO buffer layer was first deposited at a substrate temperature of 900 $^{\circ}$C for 2 hours. Post deposition annealing was carried using a rapid thermal processor in N$_{2}$ and O$_{2}$ at temperatures ranging from 400 $^{\circ}$C to 900 $^{\circ}$C for 3 min. Analyses performed using low temperature photoluminescence spectroscopy measurements reveal several luminescence peaks at 3.36, 3.353, 3.317, 3.11and 2.33 eV whose relative intensities vary with annealing environments and temperatures. We will discuss the origins of these luminescence peaks and their relevance to p-type doping of ZnO films. The x-ray diffraction 2$\theta $-scans for all the films showed a single peak at about 34.4$^{\circ}$ with FWHM of about 0.17$^{\circ}$. Hall Effect measurements revealed conductivities that change from p-type (with concentration up to about 1.3 x 10$^{17}$ cm$^{-3})$ to n-type (with concentration up to about 1.5 x 10$^{19}$ cm$^{-3})$ as the annealing temperature is increased to 900 $^{\circ}$C. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W22.00011: Magnetic and Optical Properties of Co-doped ZnO Nanorods N. Das, R. Delong, A. Wanekaya, K. Ghosh Transition-metal doped ZnO is considered as an ideal system for carrying out research in the field of spintronics as well as optoelectronics as they can successfully combine magnetism and electronics in a single substance. ZnO is a wurtzite-type wide-bandgap semiconductor of the II-VI semiconductor group with band gap energy of 3.37 eV. Synthesis of undoped and Co-doped ZnO nanorods is carried out using aqueous solutions of Zn(NO$_{3})_{2}$.6H$_{2}$O, and Co(C$_{2}$H$_{3}$OO)$_{2}$.4 H$_{2}$O, using NH$_{4}$OH as hydrolytic catalyst by hydrothermal process. For optimizing the nanorod growth condition, parameters such as concentration, pH, synthesis time and temperature are varied. Optimum condition for the growth of pure zinc oxide nanorods is found 0.15 M pH 9, 6 hrs and 130$^{\circ}$C respectively. Structural, morphological, optical and magnetic properties are studied using XRD, Raman spectroscopy, SEM, UV-vis spectroscopy, PL spectroscopy and SQUID magnetometer.Detailed structural, optical, and magnetic properties will be discussed in this presentation. This work is supported by National Science Foundation (Award Number DMR-0907037). [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W22.00012: Effective Lifetimes of Atomic Layer Deposited Diffusion Barrier Films for Silver Artifacts Amy Marquardt, Eric Breitung, Glenn Gates, Terry Weisser, Gary Rubloff, Ray Phaneuf We investigated using atomic layer deposition (ALD) to create dense, transparent oxide diffusion barrier coatings to reduce the tarnishing rate for silver art objects. An elevated H$_{\mathrm{2}}$S aging chamber was used for accelerated aging to directly compare the effectiveness of 5-100nm Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ ALD thin films and nitrocellulose coatings, the current technique for silver preservation, at reducing the tarnishing rate of silver while minimally affecting the visual appearance of the silver. Reflectance spectroscopy and an integrated sphere spectrophotometer were used to measure the thickness of the tarnish layer and indicate the lifetimes of the ALD and nitrocellulose coatings. Electrochemical impedance spectroscopy (EIS) was used to determine the porosity and average pore size of ALD films. Failure mechanisms for the two types of films were observed, the ALD films failing in defects or pinholes in the films and the nitrocellulose failing due to non-uniform in coating thickness. Thin Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ ALD films were found to be more porous than thick ALD films, sufficient in protecting silver five times longer and effected the overall color change of the object less than micron thick nitrocellulose films. [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W22.00013: Impact of carbon and nitrogen on gate dielectrics in metal-oxide-semiconductor devices Minseok Choi, John L. Lyons, Anderson Janotti, Chris G. Van de Walle Al$_2$O$_3$ and HfO$_2$ are used as alternative gate oxides in CMOS technology. Promising results have been achieved with Al$_2$O$_3$/III-V and HfO$_2$/Si MOS structures, which exhibit relatively low densities of interface states. However, the presence of charge traps and fixed-charge centers near the oxide/semiconductor interface still poses serious limitations in device performance. Native point defects are usually proposed as an explanation; unintentional incorporation of impurities in the gate dielectric during the deposition process has so far received less attention. Using first-principles calculations based on hybrid functionals we investigate the effects of carbon and nitrogen impurities in Al$_2$O$_3$ and HfO$_2$. By analyzing the position of the impurity levels with respect to the III-V and Si band edges, we determine if these impurities can act as charge traps or sources of fixed charge. Our results show that carbon can act as a charge trap and lead to leakage current through the gate dielectric. Nitrogen can act as a source of negative fixed charge, but may be effective in alleviating the problem of charge traps and fixed charges associated with Al, Hf, and O vacancies. [Preview Abstract] |
Thursday, March 21, 2013 5:06PM - 5:18PM |
W22.00014: Characterization of Er$^{+3}$:Y$_2$O$_3$ films made via Atomic Layer Deposition Nicholas Becker, Thomas Proslier, Jeffrey Klug, John Zasadzinski, Jeffrey Elam, Carlo Segrey, Tigran Sanamyan, Mark Dubinskiy, Michael Pellin Er$^{+3}$:Y$_2$O$_3$ thin films with spatially-controlled Er$^{+3}$ ion incorporation, were deposited on various substrates using Atomic Layer Deposition. By systematically varying the Erbium precursors used in the deposition of the films, a method to spatially control the Erbium has been realized. All films were polycrystalline as deposited and no appreciable change was detected after post-deposition annealing. Emission spectra for all precursors used show crystalline emission lines, similar to those grown via a melt process. Photoluminescent lifetimes up to 6.5ms have been recorded from these films, the largest to date in films deposited with Atomic Layer Deposition. Films have been characterized using XRD/GIXRD, UV-Vis spectroscopy, XAFS, RBS, HFS, SEM, TEM, and AFM. The results of these various measurements, and the influence on photoluminescent lifetime will be discussed. [Preview Abstract] |
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