Oxidation of amorphous NiZr sputtered films

In this study the surface oxidation of a number of nickel-rich NiZr alloys is reported as a means to determine its role on the stability of amorphous zirconium-based metallic glasses. The evolution of the oxide layer was monitored by following the nickel and zirconium XPS peaks after exposure to an oxygen pressure of 10-5 mbar for various periods. The surface of the air-exposed films is characterized as ZrO2 even for bulk nickel concentrations over 80 at.%. After sputter cleaning, oxidation at room temperature under controlled oxygen exposure results in a several-stage oxidation towards ZrO2 accompanied by a systematic depletion of the nickel at the surface. This reaction saturates after exposures of the order of several thousand Langmuirs. Throughout this process, nickel remains primarily in a metallic state. There is, moreover, indirect transport evidence that a non-surface nickel-rich layer is produced.