XPS measurements on L-cysteine and 1-octadecanethiol self-assembled films:a comparative study

The adsorption of D-cysteine on Au(111) surfaces from the solution phase ha s been investigated by X-ray photoelectron spectroscopy (XPS). To check the reliability of the XPS analysis, we performed measurements on D-cysteine/A u(lll) and alkanethiol/Au(111) interfaces paying particular attention to sp ectra time evolution during X-ray exposure. In both systems, X-ray irradiat ion increases the Au-4f intensity, but while in L-cysteine the line shape o f the S2p spectra does not change. in 1-octadecanethiol it dots. The analys is of the Au4f and S2p core level regions indicates the occurrence of a dis sociative molecular chemisorption on the metal surface for both systems. In the case of L-cysteine, the S2p spectra indicate the presence of a minor s ulphur component attributed to the presence of unbound cysteine molecules p hysisorbed on the first chemisorbed layer. (C) 2001 Elsevier Science B,V. A ll rights reserved.