ATOM MANIPULATION ON SI(111)-7X7 SURFACE BY CONTACT FORMATION OF BIASED SCANNING TUNNELING MICROSCOPE TIP - SURFACE-STRUCTURES AND TIP CURRENT VARIATION WITH ATOM REMOVAL

A novel technique of Si atom removal by approaching biased scanning tu nneling microscopy tip to the surface to the point contact region foll owed by retraction to the tunneling region was applied to Si(lll)-7X7 surface to reveal (i) the atomic structures on the newly exposed surfa ces, (ii) tip-substrate current variation in relation with the Si atom removal. When the adatoms were removed, the second layer of the diame ter-adatom-stacking fault model structure appeared without reconstruct ion except the relaxation of dimer rows. When a higher biased tip (>2 V) was contacted, the top three layers were removed. Clear metastable structures such as c(2X4) and root 3X root 3 are observed in the holes , and the shape of these structures was easily changed with the expans ion of the size of the hole. A staircase shape current drop was observ ed in the tip retraction process when the adatoms were removed. This i s considerably related to the decrease of the number of Si atoms in th e tip-substrate junction with atom-by-atom manner, which shows a clear contrast to the nanowire formation in the metal surface indentation. The last drop of the current to return to the tunneling region might c orrespond to a junction with a single atom between tip and substrate, which corresponds to 4X10(5) Ohm. A part of the Si atoms in the juncti on remains on the tip which resulted in the removal of Si adatoms, whi ch occurs with certain probability. (C) 1997 American Vacuum Society.