DEPENDENCE OF IMPLANTED K+ CLUSTER FORMATION ON THE SHIFT OF THE W WORK FUNCTION

The large shift (up to 2 eV) of-the work function of polycrystalline t ungsten implanted by 30-100 keV K+ ions, observed experimentally, cann ot be explained only by the assumption of single implanted particles d istributed in full statistical disorder in the W matrix. Recent measur ements by grazing incidence x-ray-diffraction technique show the forma tion of small K clusters at the surface of the sample: A model is prop osed that describes a two-component system, a small sphere for implant ed metal and a homogeneous isotropic matrix, from which it is possible to estimate the dependence of the surface work-function shift on both the all;ali-ion implantation:rate and the dimension of the clusters. This model predicts the active surface-layer thickness in agreement wi th the effective implantation thickness.