High resolution XPS of bithiophene on clean and S modified Ni(110)

In this contribution we demonstrate the usefulness of HR-XPS with synchrotron radiation by applying it to reveal the nature of various bonding configurations of bithiophene monolayers on clean Ni(110) and the sulphur c(2 X 2)S (Theta(S) = 0.5) and p(4 x 1)S (Theta(S), = 0.75) overlayer structures. The resolution was only limited by natural line widths and allowed two sulphur sites in the p(4 X 1)S reconstruction to be distinguished from the c(2 X 2)S sulphur site in agreement with proposed models for the reconstructions. For the molecule the linking carbons could be identified. Only small differences in C-K and S L(2,3) XPS energies were observed despite strong differences in bonding being suggested by the thermal evolution of the monolayers. It is argued that the differences in the observed S/C XPS intensity ratios are due to differences in adsorbate geometry for the three substrates.