Evolution of the composition and structure of cleaved and heat-treated icosahedral Al-Pd-Mn quasicrystal surfaces

We investigated the changes in composition and structure induced by heat tr eatment of cleaved fivefold icosahedral Al-Pd-Mn quasicrystal surfaces by s canning electron microscopy and calibrated Auger electron spectroscopy. Wit h increasing temperature we observed five different composition ranges of t he surface coupled with distinct changes in the surface morphology. The cha nges in composition can be explained by successive evaporation and diffusio n processes occurring with increasing temperatures. First, Mn evaporates fr om the uppermost surface layer, then Al evaporation starts and induces a fu rther Mn evaporation leading to an enrichment in Pd. The enrichment is redu ced by Mn diffusion from the bulk, Al diffusion from the bulk, and probably simultaneously occurring Pd desorption. Finally, a recrystallization of th e surface is induced by the full diffusive mobility of all elements and pre ferential evaporation of Mn and to a lesser degree of Al. We also discuss t he signature of the bonding configuration of Al in the Auger spectra of all investigated compositions. [S0163-1829(99)02925-2].