NANOSCALE INDENTATION ON SI(111) SURFACES WITH SCANNING TUNNELING MICROSCOPE

We have investigated the mechanism of Si atom removal by measuring the current during formation of a point contact between the W tip of a sc anning tunneling microscope (STM) and the Si(111)-7 x 7 surface. The s tepwise drops observed in the current during tip retraction may be att ributed to the reduction of the contact area in an atom-by-atom manner . Based on the estimation of the contact size, it was concluded that t he adatoms were removed by chemical adhesion of the Si atoms with the W tip. The chemical adhesion was assisted by the mechanical force appl ied to the Si surface; contact potential and current induced local hea ting. A trilayer was removed by field evaporation with the assistance of electromigration on the Si surface.