SURFACE SELF-DIFFUSION ANISOTROPY OF TUNGSTEN ATOMS ON W(112) PLANE

Surface self-diffusion anisotropy of tungsten on W(112) plane has been measured along (||) and across (⊥) channels existed on this plane by using the field emission fluctuation method in two forms of the probeholes. In the round probehole the thermal activation energy E=13.0kcal, and the prefactor of the surface self-diffusion coefficient D₀ = 4.8x10^-7 cm² s^-1; in the long narrow rectangular slit, E(||) =13.2kcal, D₀(||)= 7.1x10^-7 cm² s^-1 and E (⊥) =6.2kcal, D₀(⊥) =1.8X 10^-9 cm² s^-1 at T=500～700K. The experimental data suggest that a W atom diffusing across channels should not climb over the channel wall, which would certainly require a much higher activation energy, but instead, displace an atom in the wall. This process requires a much smaller activation energy; however, since it involves concerted motion of at least two atoms, it will also have a much smaller prefactor.