Farkhondeh H, Rahsepar FR, Zhang L, Leung KT. Structural and Chemical Evolution of l-Cysteine Nanofilm on Si(111)-√3×√3-Ag: From Preferential Growth at Step Edges and Antiphase Boundaries at Room Temperature to Adsorbate-Mediated Metal Cluster Formation at Elevated Temperature.
LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019;
35:16185-16200. [PMID:
31661626 DOI:
10.1021/acs.langmuir.9b02852]
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Abstract
The interaction of cysteine molecules with the Si(111)-√3×√3-Ag surface has been investigated over the submonolayer to multilayer regime using X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory calculations. With both upper step and lower step terraces, step edges, and antiphase boundaries, the √3×√3-Ag overlayer supported on Si(111) provides a rich two-dimensional template for studying site-specific biomolecular interactions. As an amino acid with three functional groups, cysteine is found to chemisorb through S-H bond cleavage and S-Ag bond linkage first at step edges and antiphase boundaries followed by island formation and expanded growth onto terraces. Intermolecular interactions are dominated by zwitterionic hydrogen bonding at higher coverages, producing a porous unordered interfacial layer composed of cysteine agglomerates at room temperature. Upon annealing, cysteine adsorbates induce structural transformation of the uniform √3×√3-Ag reconstructed surface lattice into metallic Ag clusters with a narrow size distribution and short-range ordering. Preferential nanoaggregate formation of cysteine at defect sites and cysteine-induced metal cluster formation promise a new approach to fabricating nanoclusters for potential applications in chemical sensing and catalysis.
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