Structural precursor to adsorbate-induced reconstruction: C on Ni(100)

The local structure around adsorbed carbon atoms on Ni(100) has been determ ined at low coverage as well as in the 0.5 monolayer (2 x 2)p4g ''clock'' r econstruction by scanned energy mode photoelectron diffraction. At low cove rage, there is no radial strain of the Ni atoms surrounding the adsorbed ca rbon, contrary to previous suggestions. None of the C-Ni near-neighbor dist ances are changed by reconstruction, but the Ni-Ni nearest-neighbor distanc e in the top layer increases significantly, showing that the adsorbate-indu ced compressive stress is associated with Ni-Ni, rather than Ni-C, repulsio n. [S0163-1829(99)01739-7].