STUDIES OF LOW-COVERAGE ADSORPTION OF LI ON SI(001) - OBSERVATION OF NEGATIVE DIFFERENTIAL RESISTANCE AND ELECTRON TRAPPING

We have studied the initial stages of Li adsorption onto the Si(001) s urface with scanning tunneling microscopy and spectroscopy (STM/S). On p-type silicon samples, STS on the Li sites shows a region of strong negative differential resistance (NDR). In addition, with the tip held stationary above the Li sites, a digital switching is observed in the tunneling current, which we attribute to the existence of thermally a ctivated electron traps. The changing occupation statistics of these t raps as the voltage changes causes the NDR. Screening of the traps mea ns that weaker NDR is also observed when the tip is positioned over un modified Si dimers. Thus, Very small amounts of Li have a dramatic eff ect on both local and extended length scales. (C) 1996 American Vacuum Society.