Thermodynamics of Decanethiol Adsorption on Au(111): Extension to 0 °C

Abstract

The coverage-dependent phase behavior of the thiolate formed from decanethiol, CH3(CH2)9SH, on Au(111) was studied at 0 °C using variable-temperature scanning tunneling microscopy and compared to analogous results for temperatures between 25 and 65 °C. At 0 °C, the lowest density striped phase, β, converts to higher density striped phases, δ and χ, at exposures that are significantly less than those required at room temperature. The upright saturation phase, φ, is also obtained with a lower relative exposure. We discuss these results using an extrapolation of the schematic two-dimensional pressure (π) versus temperature phase diagram developed in previous work. The observed low-temperature phase behavior is rationalized on the basis of thermodynamic considerations. By use of a schematic plot of phase chemical potential versus lateral pressure, the range of exposures over which various phases are thermodynamically stable is assessed as a function of temperature between 0 and 65 °C.