Influence of barium adsorption on the work function of hafnium grids cathode-grid assembly

The interaction of barium atoms with the surface of a hafnium grid located near the emitting surface of a metal-porous cathode is studied. The type of crystal lattice and the surface structure of hafnium used as a material for grid structures in cathode-grid units of vacuum tubes are determined using X-ray phase analysis. The adsorption of barium atoms on the surface of hafnium at the operating temperature of the cathode – 1080$^\circ$C – is studied using the density functional method with molecular dynamics. It is found that the first adsorbed layers of barium atoms are introduced into the crystal lattice of hafnium and increase the work function of electrons. After saturation of the near-surface layer of hafnium, barium atoms accumulate on the surface, forming a crystalline film. During its formation, the work function of the film decreases and, starting from the twentieth layer, stabilizes at the value of the work function of barium.