CHEMISORPTION OF L-CYSTEINE ONAu(111)/Si(111)AND$Si(111)\sqrt{3} \times \sqrt{3}-{\rm Au}$SURFACES

The electronic structures of L-cysteine adsorbed onAu(111)/Si(111)and$Si(111)\sqrt{3} \times \sqrt{3}-{\rm Au}$surfaces were studied by using X-ray photoelectron spectroscopy (XPS). L-cysteine multilayers onAu(111)/Si(111)and$Si(111)\sqrt{3} \times \sqrt{3}-{\rm Au}$surfaces were prepared under UHV condition. L-cysteine monolayers were obtained by annealing such multilayer sample up to 130°C. In the case of theAu(111)/Si(111)surface, we observed no chemical shift and no change in the peak intensity ratios amongC1s,N1s,O1sandS2p before and after annealing. On the other hand, the component attributed toCOOHgroup inC1sspectra decreased after annealing. In addition,O1sXPS spectra of monolayer on the$Si(111)\sqrt{3} \times \sqrt{3}-{\rm Au}$surface was composed of two distinct peaks, which indicates that there are two kinds ofOatoms in different conformations. These observations indicate that theCOOHgroup adsorbs directly to a surface atoms and dissociate by the interaction with the substrateSi(111)trimer atoms.