Compositional changes in the surface layers of the Cu3Au(100) below the bulk transition temperature

The surface compositional changes in the surface layers of Cu3Au(100) have been studied by medium-energy ion-scattering spectroscopy (MEIS). Using 100 keV N+ ions in a MEIS experiment, single atomic layer depth resolution was obtained. At a temperature starting at about 500 K, the Au atoms in the su rface layer of Cu3Au(100) apparently began to move to the second layer with increasing temperature. The atomic concentration of Au in the first layer as measured by MEIS then decreased from 50% at room temperature (RT) to 32% at 720 K. This decrease in the atomic concentration of Au atoms in the fir st layer was continuous, rather than abrupt at the critical temperature. Mo reover, it was found that the compositional change between the first and th e second layers was reversible at temperatures up to 720 K, The atomic conc entration of Au atoms in the third layer remained constant over the tempera ture range from RT to 720 K. The difference between this result, where the first layer Au concentration decreases, and the previous low-energy ion-sca ttering spectroscopy (LEIS) measurements which show a relatively constant A u concentration, lies in the production of surface vacancies and adatoms at elevated temperatures. These defects have no significant effect on yield i n LEIS experiments but are seen using MEIS. (C) 2001 Published by Elsevier Science B.V.