Change in the work function of zirconium by oxidation at high temperatures and low oxygen pressures

Abstract

Changes in the work function of zirconium on oxidation are measured at oxygen pressures of 3.0 × 10^–6– 3.0 × 10^–4 Pa and at temperatures in the range 426–775 K. The work function first decreases then increases until a final saturation stage is reached. Use of secondary-ion mass spectroscopy (SIMS) shows that the changes correspond to oxygen adsorption, oxide nucleation and oxide growth, respectively. The initial decrease in work function is interpreted by the incorporation of oxygen adatoms into the subsurface. The oxygen adsorption potential of zirconium is evaluated by an effective medium theory, and the physical origin of the incorporation of oxygen adatoms is discussed. The positive change in the work function caused by oxide formation and the temperature and pressure dependences of the change in the work function by oxidation are explained qualitatively.