Spectroscopy of Si vacancies formed with a scanning tunneling microscope

The electronic structure of adatom vacancies on a Si (111)-7×7 surface is described based on their observation by scanning tunneling spectroscopy. Differential conductance (dI/dV) images show that electrons with energies 0.4 and 1.3 eV below the Fermi energy (EF) completely fill the vacancies. Spectra of (dI/dV)/(I/V ) versus bias voltage and the differential conductance images show characteristic bands at 0.4 and 1.3 eV below EF, which are associated with the dangling bonds and back bonds of vacancies, respectively. The electron densities associated with these bonds are lower at vacancies of center adatom sites than at those of corner adatom sites. This provides a possible explanation for the site-selective extraction of adatoms from a Si surface.