Bulletin of the American Physical Society
Joint Meeting of the Four Corners and Texas Sections of the American Physical Society
Volume 61, Number 15
Friday–Saturday, October 21–22, 2016; Las Cruces, New Mexico
Session C2: Materials Science I |
Hide Abstracts |
Chair: Anna Zaniewski, Arizona State University Room: Ballroom 2 |
Friday, October 21, 2016 1:00PM - 1:24PM |
C2.00001: Phase transformations in transition metal oxides for electronic device applications Invited Speaker: Alexander Demkov Transition metal oxides (TMO) are currently used in a variety of electronic devices and have been considered for a number of emergent technologies. The unfilled d-shells of transition metals are responsible for many unusual properties of these oxides and in particular, a multitude of phase transitions that range from structural to electronic. The recently developed ability to grow layers of TMOs with the atomic precision by means of physical vapor deposition has led to discovery of many fascinating phenomena that cannot be easily realized in bulk materials and to integration of these oxides on semiconductors. In this talk I will review briefly the ferroic ordering and metal-to-insulator transition in TMOs focusing primarily on the Peierls transition in NbO$_{\mathrm{2}}$. I will discuss the basic properties of NbO$_{\mathrm{2}}$ and our efforts in growing single crystal NbO$_{\mathrm{2}}$ on several oxide substrates. For practical applications relying on the metal-to-insulator transition, the band gap and phase purity of the material are of key importance. I will discuss our present understanding of the electronic structure of the low-temperature insulating phase of NbO$_{\mathrm{2}}$, which is based on photoemission spectroscopy, spectroscopic ellipsometry and density functional theory [1-3]. I will also explain how to distinguish under-oxidized and over-oxidized phases using a combination of first principles modeling with the core-level and valence band spectroscopy [4].\\ \\[1] B. Posadas, A. O'Hara, S. Rangan, R. A. Bartynski, and A. A. Demkov, "Band gap of epitaxial in-plane-dimerized single-phase NbO$_{\mathrm{2}}$ films," Appl. Phys. Lett. \textbf{104}, 092901 (2014). [2] A. O'Hara, T. N. Nunley, A. B. Posadas, S. Zollner, and A. A. Demkov, ``Electronic and optical properties of NbO$_{\mathrm{2}}$,'' J. Appl. Phys. \textbf{116}, 213705 (2014). [3] A. O'Hara and A. A. Demkov, ``The nature of the metal-insulator transition in NbO$_{\mathrm{2}}$,'' Phys. Rev. B \textbf{91}, 094305 (2015). [4] T. Hadamek, A. B. Posadas, A. Dhamdhere, A. J. Smith and A. A. Demkov, ``Spectral identification scheme for epitaxially-grown single-phase niobium dioxide,'' J. Appl. Phys., \textbf{119}, 095308 (2016)\textbf{\textit{.}} [Preview Abstract] |
Friday, October 21, 2016 1:24PM - 1:36PM |
C2.00002: Excitons at interfaces in thin oxide films Nuwanjula Samarasingha, C. Rodriguez, J. Moya, N. Fernando, S. Zollner, P. Ponath, K. Kormondy, A. Demkov, D. Pal, A. Mathur, A. Singh, S. Dutta, J. Singhal, S. Chattopadhyay Using variable angle spectroscopic ellipsometry we explored the behavior of excitons at interfaces of ZnO and SrTiO$_{\mathrm{3}}$ thin films in comparison with bulk GaP which has a much simpler band structure than wurtzite ZnO or perovskite SrTiO$_{\mathrm{3}}$, but shows similar excitonic effects. The influence of excitonic effects on the dielectric function was characterized following Tanguy. We find that the real and imaginary parts of the dielectric function of thin SrTiO$_{\mathrm{3}}$ layers on Si or Ge are much smaller than in the bulk and decrease monotonically with decreasing thickness due to the reduction of the dipole overlap matrix element. A similar effect can be seen for thin ZnO layers on Si as a function of thickness. On the other hand, the dominant absorption peak is larger in SrTiO$_{\mathrm{3}}$ on a LaAlO$_{\mathrm{3}}$ substrate than in bulk SrTiO$_{\mathrm{3}}$ due to the increase of the dipole overlap matrix element. [Preview Abstract] |
Friday, October 21, 2016 1:36PM - 1:48PM |
C2.00003: Band gap engineering of pseudomorphic Ge$_{\mathrm{1-x-y}}$Si$_{\mathrm{x}}$Sn$_{\mathrm{y}}$ alloys on Ge for photonic applications N Fernando, S Zollner, R Hickey, J Hart, R Hazbun, D Zhang, J Kolodzey Band gap engineering of Ge by controlling strain and alloying with Si and Sn has attracted great interest since a Ge$_{\mathrm{1-x-y}}$Si$_{\mathrm{x}}$Sn$_{\mathrm{y}}$ ternary alloy with two compositional degrees of freedom allows decoupling of the lattice constant and electronic structures. We report the effects of alloying and the strain of the direct and indirect band gaps of pseudomorphic Ge$_{\mathrm{1-x-y}}$Si$_{\mathrm{x}}$Sn$_{\mathrm{y}}$ alloys on Ge using deformation potential theory. The predictions for the compositional dependence of the E$_{\mathrm{0}}$, E$_{\mathrm{1}}$ and E$_{\mathrm{1}}+\Delta_{\mathrm{1}}$ band gaps were validated for pseudomorphic Ge$_{\mathrm{1-y}}$Sn$_{\mathrm{y}}$ alloys on Ge using spectroscopic ellipsometry. The complex pseudodielectric functions of pseudomorphic Ge$_{\mathrm{1-y}}$Sn$_{\mathrm{y}}$ alloys grown on Ge by MBE were measured using ellipsometry from 0.1-6.6 eV for Sn contents up to 11{\%}. Critical point energies were obtained by analyzing the second derivative spectra of the dielectric function of the GeSn epilayers. The band gaps of pseudomorphic Ge$_{\mathrm{1-y}}$Sn$_{\mathrm{y}}$ alloys obtained from ellipsometry are in good agreement with the theoretical predictions. [Preview Abstract] |
Friday, October 21, 2016 1:48PM - 2:00PM |
C2.00004: Infrared and Visible Dielectric Properties of LSAT J.A. Cooke, T.N. Nunley, T. Willett-Gies, S. Zollner LSAT stands for the chemical formula (LaAlO$_{3})_{0.3\, }$(Sr$_{2}$AlTaO$_{6})_{0.35}$ and is a common substrate for epitaxial growth of complex metal oxides. Precise knowledge of the optical constants is useful to investigate the properties of epitaxial films grown on LSAT. We investigate the band gap and the infrared-active phonons as well as determine the dielectric function of LSAT, from the mid-IR to the deep UV (0.03 to 6.5 eV). Between 0.8 and 6.5 eV, we measured the normal-incidence transmission and the ellipsometric angles from 60 to 80 degree incidence in 2 degree steps on a J.A. Woollam variable angle of incidence ellipsometer. We also measured in the mid-IR on a rotating compensator FTIR ellipsometer. Transmission measurements show a steep rise of the absorption coefficient ($\alpha )$ between 4.6 and 4.8 eV where LSAT becomes opaque. Plotting $\alpha^{2}$ versus photon energy yields a direct band gap of 5.8 eV. An Urbach tail extends towards lower energies. The resulting dielectric function is in agreement with previous ellipsometry and minimum-deviation prism measurements. The mid-IR dielectric function shows four $\varepsilon $ peaks due to TO phonon absorption. The loss function shows four LO peaks. A fifth TO phonon was seen at 155 cm$^{-1}$ in far-IR ellipsometry. The presence of FCC ordering was also confirmed with x-ray diffraction. We will also discuss temperature dependent ellipsometry and transmission measurements. [Preview Abstract] |
Friday, October 21, 2016 2:00PM - 2:12PM |
C2.00005: Raman Microscopic Analysis of Internal Stress in Boron-Doped Diamond Emma Sundin, Kevin Bennet, Kendall Lee, Jonathan Tomshine, William Durrer, Felicia Manciu Boron-doped diamond (BDD) thin films are of interest in neurosurgical applications due to the superior stability of BDD-coated electrodes compared to that of carbon-fiber electrodes. BDD film stability is therefore relevant, as delamination and dislocation of films, which can occur during surgical electrode implantation, negatively impact biosensing by fast-scan cyclic voltammetry. This study investigated induced stress in both undoped and BDD-doped diamond thin films using confocal Raman mapping. In addition to dopant quantity, sample chemical composition and substrate effects were also compared. Electrodes were fabricated by chemical vapor deposition in a custom-built reactor, on cylindrical tungsten substrates. Results of the spectroscopic mapping and stress-analysis revealed a correlation between regions of pure diamond and enhanced stress, while greater boron incorporation coincided with stress release throughout the film. Preferential boron incorporation into the diamond lattice was also observed. Sp2-type carbon impurities may also have contributed to high values of compressive stress. [Preview Abstract] |
Friday, October 21, 2016 2:12PM - 2:24PM |
C2.00006: Friction Stir Welded Electrical Splice Joint Joshua Kellams, Peter McIntyre Electrical power is distributed from power plants primarily using 3-phase overhead lines. Each overhead head line is typically a bare aluminum cable or a cable of cables. The cable has a maximum continuous length of \textasciitilde 3.6 km that can be supplied on spools, so that long distance transmission lines require splicing. Currently crimp splices using a sleeve around the butt jointed cables are used. This crimp provides strength against pull out and conduction from wire-to-wire and wire-to-sleeve, but all current must flow through the layers of oxide that are present on all aluminum surfaces prior to crimping. The degradation of aluminum cable is dependent upon temperature, causing the more resistive splice to become the most likely point of cable failure. The use of friction stir welding (FSW) on the splice joint can provide a metallurgical bond between the wires and the wires and sleeve so that current will never be forced to flow through an oxide layer, therefore reducing the resistance of the splice. Progress on the development of using FSW for electrical splice joints will be presented. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700