L-CYSTEINE ADSORBED ON GOLD AND COPPER - AN X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY

l-Cysteine adsorbates and multilayer films on gold and copper surfaces have been investigated by X-ray photoelectron spectroscopy. Both adsorbates, prepared by vapor deposition in UHV and prepared from solution, strongly indicate a dissociative chemisorption through the thiol group (-SH) on the metal surface. We suggest that an organized double layer is formed on gold, for the UHV-prepared layer. In the case of copper, evidence is found for the coordination of both amino and carboxyl groups to the surface, in addition to chemisorption through the thiol group. When l-cysteine is adsorbed from solution on copper, all of the thiol groups interact with copper ions, even in a 25-Å-thick layer. This indicates copper ion diffusion and copper complex formation through the entire layer. © 1992.