OPTICAL AND CRYSTALLOGRAPHIC PROPERTIES OF POTASSIUM-IMPLANTED TUNGSTEN

Ion implantation has been demonstrated as a valuable new tool to impro ve the photoelectric emission of pure metals. An enhancement of the ph otoelectric sensitivity by a factor from 3 to 50 was measured in potas sium ion-implanted tungsten irradiated by 450 fs laser pulses with a p eak intensity of a few GW cm(-2). Investigation of the chemical and ph ysical properties al the origin of this enhancement is reported in thi s paper. The dose and the profile of the implanted ions were controlle d by Rutherford backscattering spectroscopy. The chemical structure of the surface was determined by X-ray photoelectron spectroscopy, Grazi ng incidence X-ray diffraction measurements have shown the presence of metallic potassium. The changes on the reflectivity R(lambda) and the ellipsometric measurements N(lambda) and K(lambda) can be interpreted both by the presence of an interface layer due to the radiation damag e and by a modification of the dielectric function of W in the presenc e of the K+ impurity.