Structural and electronic properties of adsorbed thiophene on Cu(111) studied by S K-edge x-ray absorption spectroscopy

The surface structure and electronic properties of 0.07 ML thiophene (C4H4S) adsorbed on Cu(111) have been investigated by means of S K-edge X-ray-absorption fine structure measurements. The results are comparatively discussed with the previously studied C4H4S/Cu(100) case. It is found that C4H4S molecules are adsorbed with the molecular plane parallel to the surface, as in the Cu(100) substrate. The S-Cu distance is 2.50+/-0.02 Angstrom, which is significantly longer than that of Cu(100) (2.42+/-0.02 Angstrom), while the S-C bond distance is 1.71+/-0.04 Angstrom, somewhat shorter than the Cu(100) one (1.74+/-0.04 Angstrom). Correspondingly, a smaller amount of charge transfer of (0.5+/-0.2) electron from the substrate to the C4H4S pi* orbital is estimated compared to the Cu(100) case of (1.0+/-0.2) electron. These findings indicate a considerably weaker interaction of thiophene with Cu(111) than with Cu(100), due to a more closely packed surface of Cu(111).