Adsorbtion and emission properties of the barium-germanium-tungsten system

Results of barium adsorbtion investigation on tungsten coated with germanium by an autoelectron microscope are presented. A tungsten spike with a usual set of faces visible on emission image served as a substrate. Barium beryllate was used as a barium source. Germanium evaporated out of a tungsten spiral coated with alundum. Work function during germanium adsorbtion was determined from the slope of volt-ampere characteristics of autoelectron current. It reached the value phisub(Ge-W)=5.1+-0.05 eV with coating increase. The variation of work function in the process of barium adsorption was controlled from the dependence of anode voltage necessary for sustaining the given current. Substrate temperature was determined from the filament current of a bow with the spike. Germanium coating was made with distribution of a sputtered batch in the process of adatom migrations at T=1130 K. It was established that a germanium atom layer of monoatomic thickness on tungsten has a high saturation degree of valence bonds. In connection with this fact the electron interaciton of adatoms and a substrate is weakened, what manifests in change of adsorbtion anisotropy and considerable decrease of barium desorption heat