Li-Induced Metal-Semiconductor-Metal Transitions On The Si(111)-(7x7) Surface: A Work Function, Photoemission, And Nmr Study

The metallic (7x7) reconstructed Si(111)-surface undergoes with increasing Li coverage a metal-semiconductor-metal transition as seen in work function changes, photoelectron spectra and T-1 times determined in NMR experiments. From zero coverage to about 0.12 ML the partly delocalized electron gas of the originally metallic Si(111)-(7x7) surface becomes increasingly localized. Around 1 ML Li coverage the surface becomes semiconducting and its properties may be understood in a simple local bonding picture in which the (sp)(3)-Si orbitals hybridize with the 2s-Li orbital. A further increase of coverage leads to a metallic overlayer.