Oxidation of Nb(110) thin films on a-plane sapphire substrates: an X-ray study

We studied the oxidation of Nb(1 1 0) thin films on a-plane sapphire substr ates at elevated temperatures with X-ray scattering techniques. Comparing a tmospheric versus dry oxidation, we observe a different behaviour resulting in the formation of chemically and structurally different oxides. Under at mospheric conditions ae obtain an unlimited growth 1 of an amorphous Nb2O5 layer, while dry oxidation results ir 1 the growth of a crystalline and pas sivating NbO(1 1 1) layer with a final thickness of about 50 Angstrom. In a ddition atmospherically oxidised samples show the formation of an oxygen la ttice gas in the remaining Nb(1 1 0) film, which is not observed after dry oxidation. (C) 2000 Elsevier Science B.V. All rights reserved.