ELECTRIC-FIELD CONTROL OF THE RAPID DIFFUSION OF K ATOMS INTO A GRAPHITE SURFACE

We show that the steady-state diffusion rate of potassium atoms into a graphite surface in the temperature range 1100-1500 K is increased st rongly if the electric field outside the surface is directed so that n o positive ions can leave the surface. This means that the thermal pro cess of removing K atoms from a basal graphite surface is changed by t he direction of the external electric field. If ions are allowed to le ave the surface, most K atoms leave in the form of ions or easily ioni zable Rydberg species, but if the electric field is reversed the K ato ms disappear from the surface by diffusion into the material, not by d esorption. The mechanism is not yet understood in its details, but the thermal barrier for this process is the same as that required to form a Rydberg state, as shown in recent kinetic studies. We speculate tha t the rate of diffusion into a metal surface may be increased by a gra phite layer, which could greatly increase the hydrogen diffusion in me tals used for hydrogen storage.