STM and voltammetric studies on the structure of a 4-pyridinethiolate monolayer chemisorbed on Au(100)-(1 x 1) surface

The structure for a 4-pyridinethiolate monolayer chemisorbed on the Au(100) -(1 x 1) single crystal surface was characterized by in situ scanning tunne ling microscopy (STM) and cyclic voltammetry (CV). in situ STM observation showed a well-ordered p(root 2 R 45 degrees x5 R 53.1 degrees) structure (a bbreviated as root 2x5) for the surface modified with either 4-pyridinethio l (4-PySH) or bis(4-pyridyl)disulfide (4,4'-PySSPy) in a 0.05 M HClO4 solut ion. On the Au(100)-(1x1) surface, 4-PySH molecules formed a dimer structur e with the S-S bond length of about 2.4 nm. The observed dimer structure is similar to that previously reported on the Au(111) surface, and the orient ation of the pyridine ring is mostly perpendicular to the surface normal. H owever, the adsorbed molecules were more densely packed (root 3/root 2 time s) on the Au(100) surface than on the Au(111) surface. The surface excess w as estimated to be 5.8 (+/- 0.2) x 10(-10) mol cm based on the voltammetric charge for the reductive desorption. This value is in good agreement with that (5.7 x 10(-10) mol cm(-2)) calculated from the parallelogrammic (root 2 x 5) unit cell. The Au(100)-(1 x 1) surface modified with 4-PySH gave a w ell-defined electrochemical response of cytochrome c. (C) 2000 Elsevier Sci ence S.A. All rights reserved.