Effect of Na adsorption on the structural and electronic properties of Si(111)[radical]3 x [radical]3-Au surface

Adsorption of ~0.1 ML of Na onto the Si(111)[radical]3 x [radical]3-Au surface held at 300 [degrees]C has been found to induce pronounced changes in its structural and electronic properties. Domain wall networks, characteristic of the pristine surface, are removed completely, leading to the formation of a highly ordered homogeneous surface. The original atomic arrangement of the Si(111)[radical]3 x [radical]3-Au is preserved and Na atoms occupy T sub(4) adsorption sites at the centers of surface Si trimers. Upon Na adsorption, a pronounced metallic S sub(1) surface-state band develops. It is characterized by a large spin splitting (momentum splitting at the Fermi level Delta k sub() = 0.027 A super(-1) and consequent energy splitting Delta E sub(F) = 110 meV), large electron filling (on the order of 0.5 electrons per [radical]3 x [radical]3 unit cell) and small effective electron mass of (0.028 + or - 0.006)m sub(e). The natural consequence of the latter properties is a high surface conductivity of the Si(111)[radical]3 x [radical]3-(Au, Na) surface.