NEXAFS STUDY OF 2-MERCAPTOBENZOXAZOLE ADSORBED ON PT(111) - MULTILAYER AND MONOLAYER

The adsorption of 2-mercaptobenzoxazole on the Pt(111) surface has bee n studied, in both monolayer and multilayer regimes, by means of NEXAF S (near edge X-ray absorption fine structure). 2-Mercaptobenzoxazole r epresents a very interesting molecule because it contains an aromatic, benzene-like fragment as well as a heteroatom-rich part, chemically m ore reactive, containing N and S atoms, which can bond covalently to m etals. Spectra at normal and grazing incidence angle of the photon bea m with respect to the surface have been recorded. The carbon and nitro gen K-edges and the sulphur L-edge were measured. The C and N K-edges recorded for the multilayer system exhibit strong angular dependence i n the pi resonances region, indicating a clear preferential orientati on of the molecules on the surface. The angle between the molecular pl ane and the surface has been found to be about 35 degrees. The S L-edg e of the multilayer, instead, shows only a weak angular dependence. Fu rthermore, the C K-edge spectra of the monolayer reveal practically no change going from normal to grazing incidence. Hypotheses of random o r ''magic'' angle orientation in the monolayer are discussed. The cova lent nature of the bond between 2-mercaptobenzoxazole and Pt(111) surf ace has been hypothesized on the basis of the comparison between monol ayer and multilayer systems. (C) 1998 Elsevier Science B.V. All rights reserved.