METALLIZATION ONSET IN K SI(100)-(2X1)

The electronic structure of single-domain K/Si(100)-(2 x 1) has been p robed by angle-resolved ultraviolet photoemission in order to investig ate the semiconducting or metallic nature of the surface as a function of K coverage. The surface undergoes a transition from a low-coverage semiconducting phase to a high-coverage metallic phase in a narrow co verage range (width less than or equal to 0.05 ML) close to room-tempe rature saturation. The metallization takes place by filling of a surfa ce band of s-p(z) symmetry which disappears away from <(Gamma)over bar > points. The binding energy of the K 3p core level changes during the process, reflecting the surface metallization.