Field-Emission-Current Fluctuations from a (100) Vicinal Plane of Tungsten with Adsorbed Xenon Molecules

The surface diffusion of Xe molecules on an atomically rough (110) vicinal plane of W was studied by the field-emission current-fluctuation method. The probed area was located in a brightly-emitting region around a dark (110) plane. The autocorrelation function of the current fluctuation was measured for temperatures ranging from 80 to 87 K. The apparent surface diffusion coefficients deduced from the correlation time are strongly coverage-dependent and show a maximum at θ=0.4. The activation energy E d and the pre-exponentials D 0 of the surface diffusion coefficient at θ=0.7 are 2.5 kcal/mol and 2×10 -6 cm 2 /s, respectively. For θ<0.5, the apparent value of D 0 is more than 6×10 2 cm 2 /s and is much larger than the value estimated from the hopping model of surface diffusion.