ADSORPTION OF CS ON TUNGSTEN - MEASUREMENTS ON SINGLE-CRYSTAL PLANES

The adsorption of immobilely deposited and thermally equilibrated Cs layers has been studied on the (110), (211), (100), (111), (103), and (115) regions of a tungsten field emitter. The work-function-vscoverage data permit resolution into adsorbate charge and effective dipole length, at least on the high work-function planes. The results indicate ionic adsorption on (110) and probably (211) at low coverage, with charge diminishing on all planes as θ increases. Dipole lengths exceed the ionic radius of Cs by 1.4-2 Å, indicating the effect of finite screening at the metal surface. The adsorption energies and their change with θ can be interpreted in terms of metallet" model."