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 treatment of cleaved fivefold icosahedral Al-Pd-Mn quasicrystal surfaces by scanning electron microscopy and calibrated Auger electron spectroscopy. With increasing temperature we observed five different composition ranges of the surface coupled with distinct changes in the surface morphology. The changes in composition can be explained by successive evaporation and diffusion processes occurring with increasing temperatures. First, Mn evaporates from the uppermost surface layer, then Al evaporation starts and induces a further Mn evaporation leading to an enrichment in Pd. The enrichment is reduced by Mn diffusion from the bulk, Al diffusion from the bulk, and probably simultaneously occurring Pd desorption. Finally, a recrystallization of the surface is induced by the full diffusive mobility of all elements and preferential evaporation of Mn and to a lesser degree of Al. We also discuss the signature of the bonding configuration of Al in the Auger spectra of all investigated compositions. [S0163-1829(99)02925-2].