Effects of thermal annealing of thin Au film on Fe₄₀Ni₃₈Mo₄B₁₈

Thin films (∼20 nm) of Au were vapour-deposited at room temperature on melt-spun amorphous ribbon specimens of the alloy Fe₄₀ Ni₃₈ Mo₄B₁₈ . The specimens were subsequently annealed at 823 and 873 K in a flowing nitrogen atmosphere and in low vacuum conditions (∼10^-1-10^-3 mbar) in order to observe any dispersion of Au in the alloy matrix. The depth profiles of Au from annealed specimens were obtained by XPS and showed depth distribution of Au up to several hundred nanometres in the alloy in sharp contrast to those obtained from specimens annealed in ultra-high vacuum. An analysis of the XPS peaks of the alloy constituents suggests strong surface segregation of the matrix elements and the growth of an oxide film on the surface during thermal annealing. It is suggested that the driving force for Au dispersion in the alloy is provided by the reactivity of matrix elements with oxygen present in the annealing media.