L-cysteine chemisorption on gold: an XPS and STM study

L-Cysteine has been deposited on Au(lll) surfaces from the solution phase. Chemical and structural information on the L-cysteine/Au(lll) interface hav e been obtained by X-ray photoelectron spectroscopy (XPS) and scanning tunn elling microscopy (STM). XPS measurements provided a chemical characterisat ion of the interface. The deconvolution of the Au4f and S2p core level regi ons reveals a peak splitting, which can be explained by the formation of a chemical bond between the cysteine thiol group and the gold surface. The an alysis of the N1s spectrum indicates that L-cysteine is present in the zwit terionic state. The STM structural characterisation performed in air at roo m temperature reveals that the molecular chemisorption results in the lifti ng of the (22 x root 3) gold reconstruction accompanied by the formation of depressions, a few nm in size, one gold layer in depth, as in alkanethiol/ Au(lll) systems. Molecular resolution images show that the L-cysteine overl ayer forms a hexagonal lattice, which, in a few regions, presents a striped modulation. (C) 2000 Elsevier Science B.V. All rights reserved.