He+ and Ar+ bombardment induced chemical changes in Cr-O-Si layers

The effects of 2 keV He+ and Ar+ bombardment on the surface composition and on the short range chemical structure of sputter deposited amorphous Cr-O-Si layers (with approx. 1: 1: 1 atomic ratio) have been studied by XPS. It was found that Arf bombardment causes an essentially complete reduction of chromium to metallic state (Cr-0) whereas it was partly oxidized in the as-received sample. At the same time about 30% of the oxidized silicon is converted to Si-0 which is stabilized by forming Si-Cr bonds. He+ bombardment, on the contrary, lends to the disruption of Si-Cr bonds formed by the preceding Arf bombardment, converting 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 of the nominal bulk value. The observed transformations are discussed, in connection with the great differences in energy deposition, in terms of direct energy transfer and of ion induced diffusion, together with a significant contribution from thermodynamic driving forces.