Carbide-induced reconstruction initiated at step edges on Ni(111)

We have studied the effect of step edges on carbide formation by the Boudouard reaction (2CO(g) --> C-a + CO2,g) over a Ni(1 1 1) surface using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and Low energy electron diffraction (LEED). The apparent activation energy of the initial reaction probability is positive (12.8 +/- 6.4 kJmol(-1)) in contrast to the negative value (-36.4 kJmol(-1)) previously measured for Ni(9 7 7), indicating a structure-sensitive reaction. The reconstruction of Ni(1 1 1) into square meshes is initiated at all the step edges by the carbide formation. The nearest-neighbor C-C distance (5.01-5.10 Angstrom) is twice the nearest-neighbor Ni-Ni distance (2.49 Angstrom). STM images show that the direction of a unit vector for the square lattice apparently agrees with that of the (1 (1) over bar 0) step edge, which is a unit vector of the Ni(1 1 1). LEED patterns show the single domain of the well-known (root 39 x root 39)R16.1 degrees super structure in consistent with the STM results. The carbide formation and the subsequent reconstruction of Ni(1 1 1) are thus strongly influenced by the presence of the step edge. (C) 2001 Elsevier Science B.V. All rights reserved.