One-dimensional delocalized adsorbate Bloch states on a semiconductor surface:: C2H4/Si(001)-(2x1)

We report the observation of a 1D molecular adsorbate band structure caused by direct adsorbate-adsorbate interactions on a semiconductor. For ethylene chemisorbed on Si(001)-(2 x 1) two adsorbate-derived electronic states, 1b(3u) and 1b(2g), are found to delocalize along the Si-Si dimer rows. The corresponding bands can be followed in reciprocal space from the <(Gamma)over bar> point into the third surface Brillouin zone. Density functional calculations for ethylene adsorbed on a silicon slab reproduce the experimental 1D band structure and allow us to identify the origin of the lateral interactions.