Metalization of thin graphite layers after Cs deposition oa 4H-SiC(0001) surfaces

摘要

The interaction of cesium atoms with graphitized 4H-SiC(0001) surfaces was investigated by use of Auger electron, ultraviolet photoemission and high-resolution electron energy-loss spectroscopy (HREELS) as well as work function measurements with a Kelvin probe. The samples were annealed at temperatures well above 1300 K resulting in a formation of about two graphite layers on top of the SiC substrates. The corresponding low-energy electron diffraction image shows a (6 3x6 3)R30 deg pattern. Cs deposition on graphitized SiC occurs in two subsequent stages. First, even small amounts of evaporated Cs lead to a spontaneous decrease in work function by 1.8 eV. The work function stays coonstant after further eevaporation corresponding to an intercalation of Cs into the graphite overalyer. In the second stage Cs atoms are adsorbed on top of the Cs-intercalated compound resulting in a futher decrease of work function. The grpahite laer is effectively metallized by Cs evaporation. This is confirmed by a Fermi edge which is observed in the photemission spectra even after the smallest dose applied. Moreover, the excitation of optical Fuchs-Kliewer phonons in SiC by HREELS is significantly quenched by the metallic overalyer and the electron energy-loss spectra exhibit features which are typical for thinhomogeneous metal layers on surfaces of heteropolar semiconductors.