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RESEARCH PRODUCT

Reactivity of H2S and H2S/H2 Mixture With Molybdenum Oxide Thin Films Epitaxied on CoO (100) : Characterization by Rheed and Auger Spectroscopy

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Molybdenum-Cobalt composite oxide films were prepared by the evaporation of molybdenum trioxide on a fresh cleaved CoO (100) surface (Thickness = 10 A). The MoO3-CoO interface has been characterized simultaneously by reflexion high electron diffraction (RHEED) and Auger Electron Spectroscopy (AES). The thin film structure and composition depend on the annealing temperature. After a 300°C treatment, metallic cobalt islands nucleate at the interface thin film - CoO (100) and crystallize with the cubic FCC symmetry. After a 700°C treatment cobalt molybdate (a CoMoO4) islands grow. The metastable crystallites are epitaxied on CoO (100). After a 900°C treatment, the thin film consists of flat two-dimensional crystallites with the following structures √5 × √5 R 26°, P (2 × 2), P (2 × 1), P (3 × 1) R 45°, P (4 × 2) R 45°. The sulphurization by H2S of the deposited thin film (300–400°C) is much slower than that of the CoO substrate (Pressure range : 0.1–15 Pa). The reaction products are epitaxied crystallites of Co9S8 and islands of amorphous MoS2.