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.

The effect of concentration on the oxidative deposition of a monolayer of alkylthiolate on gold: from island formation to random adsorption

“…Recent studies revealed that alkylthiols adsorbed on gold form different ordered phases depending on the surface coverage [1][2][3]. A phase diagram was proposed for alkylthiols adsorbed on gold under ultra-high vacuum conditions [1,2].…”

“…A phase diagram was proposed for alkylthiols adsorbed on gold under ultra-high vacuum conditions [1,2]. It was found that at low coverage the alkyl chains were flat on the surface.…”

“…When the coverage increased the alkyl chains became upright and new ordered phases formed. The thermal stability of the various phases has been examined and rationalized using thermodynamic arguments [1,2].…”

Oxygen-free in situ scanning tunnelling microscopy

“…STM in UHV can give strong imaging signals [35,36]. Tunneling routes between substrate and tip through the substrate molecules is thus feasible and determined by the combined substrate/adsorbate/tip electronic properties.…”

Reflection anisotropy spectroscopy of decanethiol adsorbed at Au(110)/liquid interfaces

“…The self-assembly of alkanethiols into stable monolayers (SAMs) has been studied for many years with Ultra High Vacuum/Scanning Tunnelling Microscopy (UHV/STM) being the diagnostic tool most widely used to determine molecular orientation as a function of coverage (or lateral pressure) and temperature [1][2][3][4] through vapour phase deposition on Au(111). Other techniques employed to probe this system include X-ray Photoelectron Spectroscopy (XPS) [5,6], Low Energy He Atom Diffraction (LEAD) [5] and Atomic Force Microscopy (AFM) [7].…”