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Benzenethiol adsorption from the liquid phase on Au(111) has been studied using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and electrochemistry. The absence of a S−H stretching vibration and the presence of benzene-like bands indicate that the sulfhydryl hydrogen is lost during adsorption, consistent with the formation of a thiolate intermediate. On the basis of the intensity of the out-of-plane C−H deformation, an adsorption geometry with a strong inclination of the plane of the phenyl ring toward an upright orientation on the Au(111) surface is favored. XPS provides further evidence that the primary adsorbate species is bonded to Au through the sulfur atom. The monolayer film thickness, absolute sulfur surface coverage and molecular packing density confirm a bonding arrangement in which the phenyl ring is aligned largely perpendicular to the substrate surface. Attenuation of a voltammetric peak, associated with reversible removal of the Au(111)−(√3×22) reconstruction, and inhibition of chloride anion adsorption, suggest that benzenethiol chemisorption gradually deconstructs the Au(111) surface to the (1×1) bulk truncated phase and self-assembles through a mechanism involving growth of two-dimensional islands. Specifically adsorbing anions leads to formation of a (1×1) surface structure, causing reorganization of the organic adlayer, reducing the ability of the Au(111) surface to undergo reversible reconstruction. The influence of benzenethiol on the underpotential deposition (UPD) of Cu on Au(111) is investigated. At sub-monolayer thiol coverages, a series of broad adsorption features are observed. In contrast, desorption peaks are readily identified from sub-monolayer to high thiol coverages. It appears that saturation coverage of benzenethiol passivates the surface toward Cu adsorption and desorption processes. A benzenethiol coverage-dependent study of Cu UPD supported by XPS uptake data suggests a multistep adsorption mechanism comprising an initial rapid adsorption step with benzenethiol adopting a flat-lying bonding geometry, followed by a slow orientational phase transition to form islands of densely packed upright adsorbate.

The kinetics of the adsorption system CO/Pt(111) has been studied by time-resolved high-resolution x-ray photoelectron spectroscopy using third generation synchrotron radiation at BESSY II. CO is dosed by a supersonic molecular beam device which allows for a high sample pressure (here up to 10−6 mbar) and a fast switching of the pressure. The site-specific occupation of CO adsorbed on on-top and bridge sites is determined quantitatively from C 1s spectra, which can be taken with a minimum collection time of 1.5 s per spectrum. Based on the observation of thermal equilibrium between the two sites, we perform a phenomenological analysis of the data, assuming a constant binding energy difference ΔE. From the on-top/bridge occupation ratio as a function of coverage obtained by uptake measurements we extract a value of ΔE=41 meV. With the same ansatz, ΔE is calculated from temperature-dependent measurements at a constant coverage. Finally, determination of the coverage during isothermal desorption is used to obtain the total binding energy of CO on Pt(111). Differences between our evaluation methods and literature reports are discussed.

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In this contribution we introduce a new apparatus combining high-resolution photoelectron spectroscopy and supersonic molecular beam techniques designed to follow simple surface reactions like adsorption, desorption or oxidation in situ in a time- and temperature-resolved manner. Using high brightness synchrotron radiation high resolution core-level spectra can be obtained in less than 3 s. The molecular beam allows for local pressures of up to 1 · 10-5 mbar and translational energies of the molecules of up to 2 eV in the case of CO. Preliminary examples of CO adsorption on Pt(111) are shown, where kinetic parameters can be derived from the coverage dependence of the different adsorption sites.