Abstract
Local electronic structure around the adatom vacancies on Si(111)-7 x 7 surface has been investigated using the methods of STM (scanning tunneling microscopy), STS (scanning tunneling spectroscopy) and the molecular orbital calculation for the cluster of local structure around each adatom vacancy. In view of the difference of surrounding local structure, the adatoms are classified into four types, i.e., the corner-and center-adaioms in a faulted half (F) cell, and the comer- and center-adatoms in an unfaulted half (UF) cell. The brightness for the nearest neighbor adatom of each adatom vacancy differs from that of each adatom in the STM images. In the STS spectra for each type of adatom vacancies, characteristic state is revealed. The new state forms at about 0.15eV above the HOMO (highest occupied molecular orbital) level for the adatom. The change of the local electronic structure by the presence of a vacancy is shown by the MO calculation using the cluster models with and without a vacancy. The new state also is observed in the calculated LDOS (local density of states).
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