A study of O2 and CO adsorption on thin evaporated chromium films

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Abstract
Internal stress measurements have been used to study oxygen and CO chemisorption and the oxidation of polycrystalline evaporated chromium films. The chemisorption of these gases on the chromium film gives rise to a compressive stress depending on the strength of the interaction between the metal and the respective gas. If the oxygen exposure of the chromium film exceeds 20 L a tensile stress superimposed on the compressive stress indicates the formation of a protective layer of chromium bulk oxide. The influence of the film structure as well as the film temperature during adsorption were investigated. The room-temperature adsorption behavior depends on the film deposition temperature up to about 150 °C but changes little at higher deposition temperatures. The temperature of adsorption has only a small effect on the compressive stress in the low-exposure regime but the subsequent tensile stress measured during the high oxygen exposure regime significantly increases with adsorption temperature. This is interpreted as indicating an increase in the thickness of the protective oxide layer formed.
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