Scanning tunneling spectroscopy of Fe/W(110) using iron covered probe tips

We have used iron covered tungsten probe tips to study the electronic structure of thin films of Fe on a W(110) substrate by means of scanning tunneling spectroscopy. In contrast to earlier experiments which were performed with tungsten tips we have found a minimum in the differential conductivity dI/dV at submonolayer Fe coverage just above the Fermi level. At a coverage of 1.3 ML a pronounced peak is measured above Fe islands of the second layer approximately 0.9 eV above the Fermi level, i.e., in the empty sample states. This empty state peak was found to be extremely sensitive to contamination from the residual gas which is also known to influence the magnetic state of the second layer islands. (C) 1997 American Vacuum Society.