| We made measurements of the sheet conductance of the Si(111) 7 x 7 reconstructed surface and its metallization with Ag-overlayers. The experiment employs a STM-tip point tunneling probe coupled to a second spring-contact electrode to evaluate charge-carrier injection and transport via surface states prepared in-situ in UHV. The electron transport can be controlled by different bias voltage using our method. The measurements distinguish a surface-state contribution, a Schottky diode contribution, and a metallic-overlayers dependence on thickness, ranging from submonolayer coverage to 10 monolayers. The thin film conductance shows a strong dependence on the interface conductance of the semiconductor. It is important that the conductance is affected by scatterings in the thin film and tip spacing, and the tip and the semiconductor generate a tip-induced Schottky barrier when measurements are done on a M-S system which has a poor metallic surface. |
