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Thiols adsorbed on noble metals are prominent model systems for self-assembly and nanotechnology research. l-cysteine is the only proteinogenic amino acid containing a thiol group. A detailed knowledge of the interaction of this molecule with well-defined surfaces is essential to rationalize and advance interfacial amino acid self-assembly and the metal-mediated anchoring of proteins. Here, we address the exemplary system l-cysteine on Ag(111) in UHV, examined by direct STM observations, synchrotron-based XPS, and NEXAFS. Following adsorption, the molecules build up a dense-packed layer of zwitterions, attached to the surface via their sulfur atom. Upon annealing to 390 K, the cysteine molecules undergo pronounced chemical and conformational transformation, leading to a more complex assembly, driven by the deprotonation of the ammonium group.
Fischer et al. (Mon,) studied this question.