The composition of films produced by ion beam sputtering of an amorphous chalcogenide glass (Tl2SeAs2Te3) target was investigated. Changes in the target surface temperature during the sputter process by means of changes in the ion energy or the total number of ions colliding with the target revealed that the target surface temperature is an important parameter in determining the film composition. When target temperature is kept low, the arsenic content of the film is less than the target (preferential sputtering). Raising the target temperature has, initially, only a small effect on the composition, but when it becomes so high that the target material begins to soften, its influence increases exponentially. This effect may possibly be explained by assuming the presence of thermal spikes, created by the ions. It was also noted that the compositions of multiple, thick, sputter‐deposited films are very constant provided the process parameters have not changed. Examination of the target surfaces show that the...