Scanning tunneling spectroscopy of c(2 x 2) reconstructed Fe thin-film surfaces

Fe thin films with flat surfaces are obtained on a MgO(001) substrate at a growth temperature of 550K. The surfaces with atomically flat and wide terraces exhibit a c(2x2) reconstructed structure. To evaluate the effect of impurity atoms at the surface on the surface structures, scanning tunneling spectroscopy (STS), reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS) studies were performed. The differential conductivity (dI/dV) spectrum of the c(2x2) Fe(001) thin-film surfaces indicates an intense peak at the sample bias voltage of 0.4V. Since there is no clear evidence of impurity adatoms forming such a surface structure, we expect that the topmost atoms are Fe, and that the observed peak originates from surface states.