ANOMALOUS PERMEATION OF LOW ENERGY NEON ATOMS IN TUNGSTEN AT LOW TEMPERATURES.

Atomic depth profiles of tungsten tips irradiated with neon atoms of low thermal energy left bracket i) 77 K ii) 300 K right bracket were measured with the aid of an atom-probe field ion microscope. The tip temperature was maintained usually at 25 plus or minus 1 K during the course of atom-probe measurements to practically eliminate thermal diffusion. In the case of i), neon atoms were detected at locations as deep as 300 layers from the surface, a depth much greater than that predicted assuming the usual diffusion mechanism. In the case of ii), however, no neon atoms were detected in the matrix. At present no theory seems to have been established to explain such anomalous penetration of low energy neon atoms.