The surface composition of binary substitutional alloys and its change caused by environmental oxygen

• Published in: Surface science Vol. 251-252; pp. 819 - 824
• Main Authors: Mezey, L.Z., Hofer, W., Varga, P., Giber, J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.1991
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(91)91105-7

In view of the large practical importance of the subject, several valuable attempts were made for the theoretical description of the surface chemical composition of solids, especially during the last ten years. However, the problem is not solved so far even in the relatively most simple case of — qualitatively — just predicting, which of the components of a dilute binary substitutional alloy composed of transition metals segregates to its free surface in the thermodynamic equilibrium state. E.g. for Pt(Ni) in the polycrystalline form and for the (111) surface Ni segregation is predicted by most of the theories, while that of Pt was observed in all experiments. A new theory, the MTCIP-1A (Modern Thermodynamic Calculation of Interface Properties — First Approximation) is applied here for the description of binary substitutional alloys even in the general case of surface reactions with environmental (e.g. oxygen) atoms. It is shown, in agreement with our ISS (Ion Scattering Spectroscopy) measurements and with those of others, that for Pt(Ni) Pt segregates to the polycrystalline and the (111) free surface, while Ni to the oxidized one. Similar agreement with ISS and other experimental data is mentioned for AuPd, CuPd and CuFe.