DIFFUSION OF LARGE POTASSIUM DEPOSIT ON SULFUR-PRECOVERED NICKEL FIELD EMITTER

The surface diffusion of a large potassium deposit corresponding to th e average coverage <(theta)over bar>(K) = 1.5 on sulfur precovered nic kel with <(theta)over bar>(S) = 0.2 and 0.4 was measured using the fie ld emission method in the temperature range 186-482 K. In general the presence of sulfur strongly reduces mobility of potassium on the Ni su bstrate. For the sulfur coverage <(theta)over bar>(S) = 0.2 the diffus ion of a large potassium deposit (<(theta)over bar>K = 1.5) occurs wit h a sharp boundary on the rough surface region with the total activati on energy Q = 0.94 eV which exceeds that for the small deposit. The re sults are discussed taking into account the strong interaction between sulfur and potassium which leads to the appearance of sulfur-potassiu m complexes disturbing (moderating) the diffusion of K atoms.