Single Cs adatoms at Si(001)2 x 1 surfaces: a local surface photovoltage imaging study

Local surface photovoltage (SPV) and current imaging, using a scanning tunn eling microscope (STM), were utilized in order to elucidate the effect of a single adsorbed cesium atom on the local electronic structure of p- and n- type Si(001)2 x 1 surfaces, in its vicinity. The Cs adatom gives rise to a small depression at negative sample bias constant current topography (CCT) image. The opposite sides of two adjacent Si dimers appear as protrusions. SPV and current imaging show that the Fermi level is 'softly' pinned at the surface in the location of these protrusions, possibly because of a downsh ift and/or broadening of the pi* band and its screening of the Cs positive charge. (C) 1999 Elsevier Science B.V. All rights reserved.