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 scanning tunneling microscope (STM) and the Si(111)-7 x 7 surface. The stepwise drops observed in the current during tip retraction may be attributed 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 the adatoms were removed by chemical adhesion of the Si atoms with the W tip. The chemical adhesion was assisted by the mechanical force applied to the Si surface; contact potential and current induced local heating. A trilayer was removed by field evaporation with the assistance of electromigration on the Si surface.