Photoemission study of stepped surface, thin film and nanowire growth
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Steps on a high index metal or semiconductor surface may play a fundamental role for electronic structure, adsorption, film growth, chemical reaction and catalysis. The surface atomic and electronic structures of stepped W(110) surfaces have been investigated by a few research groups during the past 20 years. But there is still a lot of controversy. We use high resolution core level photoemission to study several different stepped tungsten surfaces. Curve fittings of the spectra permit tests of core-level binding- energy shift models that relate local atomic coordination to binding -energy differences associated with terrace and step-edge atoms. For the first time we find a well resolved W4f₂/₇ peak associated with step edge atoms. We attribute previous failure to directly detect the step-edge effects in core level photoemission to contamination by hydrogen. The well resolved peaks for surface atoms with different coordinations can serve as a “finger print” for specific atoms. Experiments in which stepped surfaces are systematically dosed by H₂ clarify the role played by H contamination. We also grow Ag nanowires on the stepped W(110) surface and use angle resolved photoemission to study the band structure. We find distinct dispersion for the nanowires along the step edge direction while there is only little dispersion perpendicular to the wires. The second part of the research is core level photoemission study on Cesium film growth on Cu(100) surface. We study the phonon broadening effect for Cs at different temperatures. We compare our data with previous theoretical models and get good results on surface and bulk Debye temperatures and zero temperature phonon broadening. The binding energy shifts for the Cs 5p₂/₇ at different temperatures have also been investigated. The results fit the lattice expansion model very well except at temperature higher than 200 K. The higher temperature deviation is caused by thermal evaporation of Cs films. This conclusion is checked by the following coverage dependent core level peaks study on the Cs/Cu(100) system.