Probe-Hole Fem and TDS Studies of No Adsorbed on Individual Tungsten Planes

Abstract

The adsorption, migration and desorption of NO on single tungsten planes was studied by means of probe-hole field emission and thermal desorption techniques over a wide range of coverages and temperatures. A molecular beam system that enabled deposition of strictly controlled doses of gas was employed. The system was connected to a probe-hole field emission tube in which the electron emission from individual planes was measured by means of a photoelectric method. Work function changes were measured for the (211), (100) and (111) planes as a function of coverage and temperature. Thermal desorption spectra were obtained for polycrystalline ribbon and single W (100) plane. It has been concluded from the results obtained that at 77K NO is adsorbed as molecular species, being a precursor to dissociative adsorption at higher temperatures. The adsorbed nitrogen resulting from dissociation exists mainly in the s1 state on the (100) plane. The corresponding desorption peak is very narrow and well defined as compared with the much weaker s2 peak. The desorption spectrum of the s1 state was satisfactorily compared with the computed one from the Wigner-Polanyi first order desorption kinetics and a lateral interaction dependent activation energy.