SURFACE OXIDATION OF AN AL-PD-MN QUASI-CRYSTAL, CHARACTERIZED BY X-RAY PHOTOELECTRON-SPECTROSCOPY

X-ray photoelectron spectroscopy (XPS) is used to determine the extent of oxidation of each of the three metals which comprise a quasicrysta lline alloy. A single-grain sample, oriented with the fivefold axis pe rpendicular to the surface plane, and with nominal bulk composition Al 70Pd21Mn9 is used. The oxide which results from exposure to ambient ga s at room temperature is compared with that which results from exposur e to pure oxygen in ultrahigh vacuum at temperatures up to 870 K. XPS probes the near-surface region (ca. top 100 Angstrom), and shows that only the Al can be oxidized. The depth of the oxide layer depends syst ematically upon the conditions of treatment, but is always very thin - in the range of about 5-30 Angstrom. Taken together, the data suggest that the surface forms a thin, passivating, surface layer of aluminum oxide.