Composition profiles at initial stage of altered layer formation on Cu-Pt alloy surfaces under Ar+ ion bombardment

Abstract

The dynamic process of subsurface altered layer formation in a Cu-Pt alloy under Ar+ ion bombardment has been studied by sequential Auger electron spectroscopy (AES) and ion scattering spectroscopy (ISS) measurements. For this study, we recently developed a compact coevaporator, which enables Cu and Pt to be deposited at a constant composition ratio (within ±3 at. %) onto a Si substrate cooled to liquid-nitrogen temperature. The average surface composition of the alloy film was monitored by AES throughout the deposition procedure, and the composition of the topmost atomic layer was measured by ISS right after the end of the film deposition. The data show that the topmost atomic layer was considerably Cu-rich while subsurface atomic layers were of constant composition. During Ar+ ion bombardment, however, the surface composition of Cu, measured by sequential AES and ISS, gradually decreased with time toward a steady-state value. The temporal evolution of the composition profile is described. The surface-segregation constant and radiation-enhanced diffusion coefficient for the Cu-Pt alloy under Ar+ ion bombardment are inferred from the measured composition profile.