Field-emission studies of the adsorption of chlorine and the dissociation of carbon-chlorine compounds on tungsten

Abstract

The adsorption/desorption of chlorine and the dissociation of carbon tetrachloride and chloroform on tungsten were studied in a field-emission microscope observing the pattern variations and changes in work function derived from the Fowler-Nordheim equation. Chlorine from the gasphase and from dissociated carbon-chlorine compounds gave rise to positive surface potentials at low coverages (oxygen was examined for comparison), accompanied by a reduction in emitting area. This was ascribed to chlorine penetration below the metal surface; final surface potentials were about –1 eV. The adsorption of methane and its attack on a chlorine-covered surface were also examined. Under a continuously applied field tungsten whiskers were formed in carbon tetrachloride or chloroform vapour, believed to arise from the migration of surface complexes involving both carbon and chlorine.