Oxidation of Cs2Te with superficial Te clusters studied by XPS

Article abstract of DOI:10.1016/0039-6028(91)91153-O

The oxidation of alkali-metal (Cs, K) tellurides at room temperature and low oxygen pressure has been studied by X-ray photoelectron and Auger electron spectroscopies (XPS, XAES). The oxidation kinetics is faster than logarithmic and does not saturate for the exposures studied, while a migration of alkali ions to the surface is detected. These effects are strongly enhanced in a sample of overcaesiated telluride with elemental Te clusters on the surface. A strong gradient of the oxidation state (Te^2-, Te⁰, Te⁴⁺, Te⁶⁺) is formed in a depth of the order of the XPS analysis depth. The oxygen concentration shows a similar gradient. Cs₂O₂ is formed too. The surface layer remains as Cs₂Te; the Te clusters also remain unreactive at the surface; they only transform into telluride when heavy oxidation of the Cs₂Te film is reached.