Nanoscale in-depth modification of Cr-O-Si layers

In-depth modification of Cr-O-Si layers on a nanoscale has been performed by low energy inert (Ar+, He+) and reactive (N-2(+)) ions. Chemical and short range structural investigations were done by XPS. Cr and Si were essentially oxidised in the as-prepared (i.e. virgin) samples. Ar+ bombardment led to a nearly complete reduction of Cr to Cr-0. At the same time, about one third of the oxidised Si was converted to Si-0, which was shown to form Si-Cr bonds. Also, silicide type clusters, predicted earlier by XPS, have been identified by glancing angle electron diffraction. He+ bombardment led to an increase of the surface O concentration. This was manifested also in the disruption of Si-Cr bonds formed by the preceding Ar+ bombardment and conversion of Cr and Si predominantly to Cr3+-O, Cr6+-O and Si4+-O. With N-2(+) bombardment formation of Cr-N and Si-N bonds was observed. The thickness of the transformed surface layers were about 5 nm, 9 nm and 30 nm for Ar, N and He projectiles as estimated by TRIM calculations. The observed transformations were interpreted in terms of the relative importance of sputtering or ion induced mixing for Ar+ and He+, and also by the role of thermodynamic driving forces.