Influence of Adsorbed Gas on Surface Diffusion and Nucleation

Experiments with the field-electron emission microscope show that residual gas pressures as low as 2×10−8 Torr increase the density of nucleation of copper on tungsten compared with the nucleation density at 4×10−10 Torr ambient pressure. The effect of adsorbed oxygen and nitrogen on the mobility of copper on tungsten depends on the relative amounts of gas and copper and on the local substrate crystallography. Generally stated, they increase the activation energy for surface diffusion.