Electronic Structure of Molybdenum Oxide Oxidized at Different Pressures
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XVIII INTERNATIONAL SYMPOSIUM “NANOSTRUCTURES: PHYSICS AND TECHNOLOGY”, MINSK, REPUBLIC OF BELARUS, SEPTEMBER, 2020. NANOSTRUCTURE CHARACTERIZATION
Electronic Structure of Molybdenum Oxide Oxidized at Different Pressures P. A. Dementeva,*, E. V. Ivanovaa,**, M. N. Lapushkina,***, D. A. Smirnovb,****, and S. N. Timoshnevc,***** a
b
Ioffe Institute, St. Petersburg, 194021 Russia Institut für Festkörper- und Materialphysik, Technische Universität Dresden, Dresden, 01062 Germany c Alferov University, St. Petersburg, 194021 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected] *****e-mail: [email protected] Received June 23, 2020; revised July 23, 2020; accepted July 27, 2020
Abstract—Electronic structure of molybdenum oxides obtained by the oxidation of molybdenum at an oxygen pressure of 1 Torr (thin film) and air (thick film) was studied. It was shown that a thick oxide film is formed from MoO3 oxide, and a thin film from a mixture of MoO3 and MoO2 oxides, which is reflected in the form of valence band spectra. Oxygen on the surface belongs both in molybdenum oxide and in the hydroxyl group, which is associated with dissociative adsorption of water during the oxidation of molybdenum in air for a thick film. Keywords: molybdenum oxide, oxidation, valence band, photoelectron spectroscopy DOI: 10.1134/S1063782620120040
1. INTRODUCTION Molybdenum oxides are widely used in electronics, in designing various sensors and detectors, in energy storages, in electro- and photochromic systems, solar cells, catalysts in oxidation reduction reactions, etc. Molybdenum oxides are widely used as emitters at the thermal ionization of metals and organic molecules [1], and also in detectors of organic nitrogen-containing molecules operating in air at normal pressure. There are various methods of obtaining molybdenum oxide films: the evaporation of molybdenum oxides in vacuum by various methods, the liquid phase methods, including the electrochemical synthesis, and others [2]. A simple and low-cost method of preparing molybdenum oxide thin films is a heating of molybdenum in an oxygen atmosphere at various pressures. Of the great number of Mo oxides and their phases, the orthorhombic α-phase of MoO3 and the β-monoclinic phase of MoO2 are of the greatest interest. The band gap of the α-phase of MoO3 is about 3.0 eV. Calculations show that the valence band of MoO3 is formed from O 2p states with an insignificant admixture of Mo 4d states [3–7]. The electronic structure of
molybdenum oxide is well studied for samples obtained by various methods. It was shown that the shape of the spectrum of the valence band and the shape of the spectra of core oxygen levels depend on the preparation methods [7–10]. The purpose of this work was to study the effect of oxygen pressure on the electronic structure of a molybdenum oxide films obtained during heating at the temperature T = 1000 K and two pressures: in 1 atm and the oxygen pressure 1 Torr. 2. EXPERIMENTS Molybdenum foil was oxid
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