Growth of 1,4-Benzenedimethanethiol Films on Au, Ag and Cu: Effect of Surface Temperature on the Adsorption Kinetics and on the Single versus Multi-layer Formation

Abstract

We report a study of 1,4-benzenedimethanethiol (BDMT) adsorption on the (111) surface of the noble metals Au, Ag, and Cu performed from the vapor phase by ion scattering. The better known case of BDMT on the Au(111) surface is used for comparison. Ion scattering carried out in the forward direction to detect both scattering and recoiling atoms allowed us to delineate the two main different film configurations: with both S atoms attached to the surface and with S exposed at the vacuum interface. The experiments were carried out at room temperature (RT) and around 250 K. At RT we found that a monolayer of standing-up molecules can be formed on all of the surfaces at very high exposures, that is, approaching the Mega Langmuir for Au and Ag. Comparison with experiments of adsorption of S2 on the Au(111) bare surface allowed us to estimate that the S content at the BDMT-vacuum interface is ∼0.3 of a monolayer. The adsorption at lower temperatures has two main effects: it enhances the sticking coefficient and results in the formation of a multilayer at lower exposures. The discrimination of the mono- versus the multilayer film formation with the ion scattering technique is discussed. Once the multilayer is formed, the increase of the surface temperature to 270 K is sufficient to obtain a monolayer with spectral features that are similar to those obtained at RT with much higher exposures.