SURFACE-COMPOSITION OF PT-RH ALLOYS

Ion scattering spectroscopy has been used to determine the surface composition of Pt/Rh alloys as a function of temperature and bulk Pt/Rh atomic ratio. Three alloys, with bulk compositions of 90 at.% Pt, 50 at.% Pt and 10 at.% Pt were studied. The surfaces of the three alloys are enriched in platinum at temperatures between 800 K and 1400 K. At 1300 K the surfaces of the three alloys contain 97 at.% Pt, 77 at.% Pt, and 27 at.% Pt respectively. Segregation of Rh to these surfaces was expected from bond-breaking theories of surface segregation and no satisfactory explanation for the disparity has been found. The segregation of Pt to the surface shows a maximum near 1050 K and decreases to zero (bulk composition) at temperatures below 800 K. This behavior is attributed to a competition between non-preferential sputtering by the analysis beam and thermal diffusion. Sputter removal of quenched surface layers indicated that surface enrichment only occurs in the outer atomic layer. © 1979.