Structure and Dynamics of Tetramethylthiourea Adsorption on Au(111) Studied by in Situ Scanning Tunneling Microscopy

Abstract

We have examined tetramethylthiourea (TMTU) adsorption on Au(111) with cyclic voltammetry, capacitance measurements, and in situ scanning tunneling microscopy (STM). Capacitance measurements indicate that TMTU is adsorbed over a wide potential range. A capacitance peak at higher potentials (ca. 650 mV vs SCE) is interpreted as arising from the displacement of TMTU by bisulfate/sulfate ions. High-resolution STM images show an ordered structure of TMTU on the gold surface. Three distinctive spots for each molecule are seen in the STM images. From these molecular resolution images a (3 × 3) structure for the TMTU adsorbate is deduced. Large changes are observed in the step and terrace morphology of the Au(111) substrate at potentials (+400 mV) slightly before the capacitance maximum assigned to TMTU desorption. The STM images indicate a slow etching of the gold surface at potentials slightly before the onset of TMTU desorption. This deduction has been further supported by inductively coupled plasma optical e...