Abstract
The work function, the effects of argon-ion bombardment, and the adsorption of oxygen and carbon monoxide were investigated for the (111) surface of niobium. Cleaning of the sample was accomplished in an ultra-high vacuum system by the process of argonion bombardment and annealing. In terms of the photoelectric behavior and the oxygen adsorption properties of the surface, it was determined that many cycles of this process were required before the most satisfactory surface was obtained. Oxygen was adsorbed at room temperature with a sticking coefficient of about 0.6. The coefficient for carbon monoxide was slightly lower. Attempts to remove adsorbed oxygen by heating up to 1500° C in vacuum were unsuccessful and indicated that some diffusion into the lattice took place. Adsorbed species could be removed by the ion-bombardment cleaning process. Argon-ion bombardment in the 500 eV range caused the work function to decrease from the initial clean, annealed surface value of 4.66 eV to 4.09 eV after a bombardment of 10 17 ions/cm 2. Following shorter bombardments, the surface seemed to be in a transition state in which the fit of experimental points to the Fowler curve was poor. These bombardment effects are discussed in terms of the possible nature of the ion-bombardment damage.
Published Version
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