HE-INDUCED CHEMICAL-CHANGES IN CR-O-SI LAYERS( AND AR+ BOMBARDMENT)

The effects of 2 keV He+ and Ar+ bombardment on the surface compositio n and on the short range chemical structure of sputter deposited amorp hous Cr-O-Si layers (with approx. 1: 1: 1 atomic ratio) have been stud ied by XPS. It was found that Arf bombardment causes an essentially co mplete reduction of chromium to metallic state (Cr-0) whereas it was p artly oxidized in the as-received sample. At the same time about 30% o f the oxidized silicon is converted to Si-0 which is stabilized by for ming Si-Cr bonds. He+ bombardment, on the contrary, lends to the disru ption of Si-Cr bonds formed by the preceding Arf bombardment, converti ng Cr-0 and Si-0 essentially to Cr3+-O, Cr4+-O and Si4+-O, and, at the same time raises the surface oxygen concentration up to three times o f the nominal bulk value. The observed transformations are discussed, in connection with the great differences in energy deposition, in term s of direct energy transfer and of ion induced diffusion, together wit h a significant contribution from thermodynamic driving forces.