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In-depth modification of CrOSi 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 SiCr 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 SiCr bonds formed by the preceding Ar + bombardment and conversion of Cr and Si predominantly to Cr 3+ O, Cr 6+ O and Si 4+ O. With N 2 + bombardment formation of CrN and SiN 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. |
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