Irradiation of smart functional thermochromic Vanadium dioxide thin films by gamma rays

What is it about?

This paper is about using thermochromic vanadium dioxide thin films as smart radiotor devices for cubesats

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Why is it important?

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. The parent structure of VO2 thin films remained unchanged upon irradiation. Gamma irradiation causes defects and crystal lattice imperfections on the structure of VO2 thin films. We suggest that the UPS intensity peak at 5eV and shoulder at around 7-8 eV observed from 60 eV to 125 eV excitation energies for the irradiated films originates from structural defects caused by the intense λ-radiation. This radiation damage creates new electronic states which have their signature in the valence band. The electric properties and potentially optical properties are slightly affected by this radiation treatment.

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