Tunneling of hydrogen in surface diffusion on the tungsten (110) plane

The diffusion coefficients of 1H and 2H on the (110) plane of W have been measured by the field-emission fluctuation method. Below 140 K 1H diffusion corresponds to pure tunneling. The barrier is shown to be 0.21 eV high and approx. 0.5 A wide, and probably corresponds to passage over the saddle formed by two nearest-neighbor W atoms. Evidence for a phase transition at 89 K (at theta=0.6) is also presented