Surface EXAFS study of the p4g(2×2) reconstruction of C on Ni(100) and C on Ni films

We report temperature- and angular-dependent surface extended X-ray absorption fine structure spectroscopy (SEXAFS) measurements of the p4g(2×2)C/Ni(100) system. Both a Ni(100) single crystal and a 4 monolayer Ni film evaporated on a Cu(100) single crystal were used as substrates. The k-space used for the data analysis needs to be truncated at low k values. This is due to a strong increase of the atomic background close to the edge, which prevents a clear separation of near-edge features from the SEXAFS oscillations. For both substrates the local structure can be described by the ’clockwise’ reconstruction of the surface. This leads to a strong anisotropy of the vibrational amplitudes: the vibrational amplitude for the out-of-plane CNi bond at room temperature is determined to be twice as large as that for the in-plane motion.