A460

B.E, N I E U W E N H U Y S

Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands

Received 28 March 1987; accepted for publication 15 May 1987

AES has been used to investigate the variation of the surface composition of a polycrystalline Pt0.62-Rh0,38 foil with the equilibration temperature. The results show that an ultraclean surface exhibits a Pt enrichment that increases with increasing equilibration temperature from 80 to 89 at% Pt in the 800-1000 K range. In the range 1000-1500 K an almost constant surface concentration of 89 at% Pt was found. The influence of small amounts of impurities such as P, C and Sn is discussed. The surface enrichment in Pt is in agreement with a number of literature data, but it cannot be understood with the classical models of surface segregation. The Pt enrichment in the surface and its temperature dependence are qualitatively in line with a model based on vibrational entropy contributions in addition to the enthalpy contributions used in classical surface segregation models.

Surface Science 189/190 (1987) 1135-1142 1135 North-Holland, Amsterdam

S U R F A C E SEGREGATION IN T R A N S I T I O N - M E T A L A L L O Y S

A N D IN B I M E T A L L I C A L L O Y C L U S T E R S

S. M U K H E R J E E

lnstitut de Physique Experimentale, Ecole Polytechnique Fdddrale de Lausanne, CH-1015 Lausanne, Switzerland

a n d

J .L. M O R A N - L O P E Z

lnstituto de FJsica, Universidad Autfnoma de San Luis Potosi, 78000 San Luis Potosi, Mexico

Received 30 March 1987; accepted for publication 15 April 1987

Surface segregation in transition-metal binary alloys, belonging to 3d, 4d and 5d series, is studied using a simple tight-binding scheme. Predictions about general segregation trends are made for over 700 alloys in the dilute limit. The predictions agree for a large number of systems that have been studied experimentally. Furthermore, an extension of this theory is made to study segregation behavior in small bimetallic alloy clusters and results are given for the Cu-Ru system.

Surface Science 189/190 (1987) 1143-1149 North-Holland, Amsterdam

F O R M A T I O N O F V A N A D I U M S I L I C I D E

BY HIGH D O S E I O N I M P L A N T A T I O N V,P. S A L V I , A . M . N A R S A L E *, S.V. V I D W A N S , A . A . R A N G W A L A

Physics Department, Bombay University, Bombay 400098, India

1143