Selenium, Benzeneselenol, and Selenophene Interaction with Cu(100)

A high-resolution synchrotron photoemission study of selenium, selenophene (Seph), and benzeneselenol (BSe) adsorption on a Cu(100) surface was performed, to investigate the film structure, chemical adsorption properties, and molecular orientation. Complementary measurements for selenophene adsorption on Au(111) were also performed. The investigation is based on determination of core level binding energies (CLBEs) by X-ray photoelectron spectroscopy (XPS) and near-edge adsorption fine structure (NEXAFS). Se chemisorption was studied as a complement to the work on molecules in order to obtain data on the CLBEs for the atomic case. Se adsorption was performed from a Na2Se solution and thereafter annealing in vacuum. Annealing leads to appearance of ordered structures in LEED. Se 3d CLBEs were determined for the different cases. Fits of Se 3d XPS spectra show existence of several components attributable to different adsorption configurations. Also coadsorption with S was studied, which leads to changes in adsorption configurations depending upon the coadsorption procedure: simultaneous or preadsorption of S. Annealing after simultaneous adsorption leads to S elimination, while it is retained after preadsorption suggesting a higher reactivity of Se. In the case of both BSe and selenophene, XPS spectra indicate that Se-C bond scission occurs, which leads to appearance of some atomic Se on the surface and coadsorption of molecules. This is accompanied by attenuation of characteristic aromatic ring peaks in NEXAFS. In the case of selenophene single Se-C bond scission leads to appearance of alkenechain selenol molecules bound with the Se atom to the surface. A similar situation is encountered for selenophene on Au(111). NEXAFS did not show dichroism possibly partly because of dissociation processes.