Resonant photoemission spectroscopy of gamma irradiated VO 2 films
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.356
Resonant photoemission spectroscopy of gamma irradiated VO2 films I.G. Madiba1-4, A. Braun4, N. Émond6, M. Chaker6, S.I. Tadadjeu5, B.S. Khanyile1,3, M. Maaza1,3 1
UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, PO Box 392, Pretoria, South Africa. 2
ETH Zurich, Swiss Federal Institute of Technology CH-8057 Zurich, Switzerland
3
iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO Box 722, Somerset West, Western Cape Province, South Africa 4
Empa, Swiss Federal Laboratories Materials Science and Technology, CH-8600 Dübendorf, Switzerland
5
Department of Electrical, Electronics and Computer Engineering, French South African Institute of Technology/Cape Peninsula University of Technology, Bellville campus, PO Box 1906, Bellville, 7530, South Africa 6
Institut National de la Recherche Scientifique (INRS), 1650 Blvd. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada
Abstract
Vanadium dioxide thin films are considered as smart functional coatings for thermal shielding, and are attractive as a passive thermal shield for spacecrafts. In space they would, however, be subjected to bombardment by interstellar dust particles and electromagnetic radiation. Materials subjected to irradiation will suffer damages induced by the displacement cascades initiated by nuclear reaction. Such cosmic radiation can severely impact the structure and function of materials. To study this effect in the laboratory, we have deposited VO2 films on silicon wafers and exposed them to γ-radiation of doses up to 100 kGy by using a 60Co nuklid source with 1.17 and 1.33 MeV photon energy. We anticipate that the γ-radiation causes local structural perturbations which can amount to defects with a corresponding change in electronic structure and thermal shielding property. We report on the photo emission spectroscopy of gamma irradiated VO2 thin films.
INTRODUCTION Thermal shielding protective coatings in spacecraft will be increasingly important as the spacecraft become smaller and more compact. Such spacecraft with low thermal mass like CubeSats must be designed to retain or reject heat more efficiently [1]. The protective coating radiation device (PCR) is a new type of thermal control material for spacecraft. Current space thermal control systems require heaters with an additional power penalty to maintain spacecraft temperatures during cold swings. Because its emissivity can be changed without electrical instruments or mechanical part, the use of PCR decreases the request of spacecraft power budget [2]. The PCR based on VO2 films is one of the most important structures of the functional thermal control surface, being lighter, more advanced and without any moving component. A large portion of the heat exchange between an object in space and the environment is performed throughout radiation, which is in turn determined by the object’s surface properti
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