Phase-sensitive lock-in imaging of surface densities of states

Abstract

A new way of imaging the local density of states has been devised through a combination ofthe constant-height scanning tunnelling microscopy operational mode and lock-in techniques.We have obtained current images simultaneously with real space dynamical conductance maps(d I/d V) for energies around the Fermi level, on theSi(111)-(7 × 7) surface. We reconstructed the normalized dynamical conductancespectra—(d I/d V)/(I/V). Since the (d I/d V)/(I/V) curves are closely related to the local densities of states, we compared their sum over theunit cell to photoelectron spectra and theoretical calculations. We find that the results arein good agreement. Consequently, the extent of localization of surface electronic states atlattice positions was determined.