AN ELECTRON SPECTROSCOPIC STUDY OF THE ADSORPTION OF BENZENETHIOL AND 1,2-BENZENEDITHIOL ON THE CU(110) SURFACE

The adsorption of benzenethiol and 1,2-benzenedithiol on Cu(110) is studied over wide exposure and temperature ranges using UPS, DELTAphi, XPS and vibrational-EELS. Both compounds lose their thiol hydrogen atom(s) when chemisorbed on Cu, forming mono- and di-phenyl mercaptide respectively. At room temperature and low surface coverage the chemisorbed phenyl mercaptide species further undergoes limited desulfurization, with the build-up of the resulting chemisorbed atomic sulfur on the surface self-inhibiting continued C-S bond dissociation. At low exposure the phenyl ring of both the adsorbates lies flat on the Cu surface, but takes a standing-up (though not strictly perpendicular) orientation at high exposures. Whereas the monomercaptide adsorbate appears highly ordered, the dimercaptide does not. UPS was employed to monitor the adsorbate thermo-evolution. Although direct observation of the interaction between the first adsorbate monolayer and the substrate was not possible, analysis of the spectral changes indicates that the loss of the thiol hydrogen of the first layer benzenethiol and 1,2-benzenedithiol were complete at - 112 and - 90-degrees-C, respectively, significantly below the final multilayer desorption temperatures of - 89 and - 46-degrees-C.