Electronic structure of Cs multilayer and monolayer adsorbed on Ru(001): A photoemission study

The electronic structure of Cs adsorbed on Ru(001) at multilayer and monolayer coverages has been investigated with high resolution photoelectron spectroscopy (PES) using synchrotron radiation. It is found that at multilayer coverage, the electron distribution curve (EDC) of the Cs overlayer is essentially the same as that of the Cs metal reported previously except that, with the high resolution, a surface atom core-level (Cs 5p32) binding-energy shift of +0.24 eV is observed for the first time. It is also found that at monolayer coverage which exhibits a ( 78 x 78 )-R300 LEED pattern, the Cs 5p32 level shifts by 1.0 eV to lower binding energy relative to that of the multilayer; this shift is accompanied by a significant linewidth broadening and a nearly complete suppression of O3VV Auger emission. These results are interpreted on the basis of the volume effect and a rehybridization mechanism in which the compression of the Cs atom and the interplay of conduction and 5d electrons at the Cs site are crucial to the 5p binding energy shift, core hole lifetime, and Auger transition