Scanning tunneling spectroscopy on clean and contaminated V(0 0 1)

Scanning tunneling spectroscopy measurements on clean V(0 0 1), carbon-covered V(0 0 1) and the oxygen-induced V(0 0 1) (1 × 5) reconstruction are reported. The clean V(0 0 1) surface shows a strong surface state 0.03 eV below the Fermi level. Isolated impurities shift the surface state 0.05 eV upwards in energy and broaden the peak observed in dI/dV. No significant influence of monoatomic steps on the surface state could be observed. For tunneling resistances down to about 1 MΩ the surface state is unaffected by the tip of the scanning tunneling microscope. A surface state is detected around +0.75 eV in small c(2 × 2) patches which are observed at higher carbon (and oxygen) coverages. The oxygen induced (1 × 5) reconstruction of V(0 0 1) shows a peak at similar energy (+0.63 eV) in the areas with O and C atoms in fourfold hollow sites and a peak around +0.91 eV above the rows of bridge-site oxygen. Ab initio band structure calculations confirm the existence of a surface state of d_z(2) symmetry with an energy close to that observed experimentally on clean V(0 0 1). This agreement provides strong evidence that the V(0 0 1) surface is not magnetic (at least at room temperature) as predicted by the calculations. We also compare the experimentally observed peak shifts on the carbon and oxygen covered surfaces with calculational results for carbon-covered geometries.