XPS measurements of the thickness of thermal oxide on lead-indium alloys as a function of oxidation time and oxygen pressure

Abstract

Oxidation time and oxygen pressure relationships are investigated in thermal oxide growth on PbIn alloys by means of XPS. Alloy-side In2O3 layer growth dominates the oxide growth and its thickness follows an inverse-logarithmic function. On the other hand, surface-side PbOx layer growth follows an inverse-logarithmic function only after a long time (>or=10 min) or in the high-pressure range (>or=1 Pa). These critical values correspond to the point at which PbOx layer thickness reaches the one-monolayer thickness. Using the Langmuir concept, the oxide layer thickness can be expressed as a function of a product of oxygen pressure and oxidation time, and atomic oxygen is found to play a key role in the oxidation process at the alloy surface.