STRUCTURAL AND ELECTRONIC-PROPERTIES OF K/SI(100)2X1

The interface K/Si(100)2 X 1 has been investigated by using a variety of surface techniques sensitive to both structural and electronic properties. The adsorption site of potassium was determined by using Xe titration and Xe photoelectron spectroscopy. Potassium atoms are preferentially adsorbed between the rows of dimers of the 2 X 1 reconstruction (cave-valley sites). Controversy exists about the degree of ionicity of the K-Si bond, and the way the surface is metallized after K adsorption. Using work-function change, thermal desorption, and ultraviolet photoemission measurements, we determined that the potassium overlayer has metallic character above 0.5-monolayer (ML) coverage. We have studied by means of photoemission of adsorbed xenon the way the surface potential is affected by K adsorption. The charge transfer from K to Si gives rise to a reduction of the local work function at sites close to K atoms. In addition, a long-range reduction affects the whole surface from coverages of 0.2 ML on.