Carbide-induced reconstruction initiated at step edges on Ni(1 1 1)

We have studied the effect of step edges on carbide formation by the Boudouard reaction (2COg→Ca+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 kJ mol−1) in contrast to the negative value (−36.4 kJ mol−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 Å) is twice the nearest-neighbor Ni–Ni distance (2.49 Å). STM images show that the direction of a unit vector for the square lattice apparently agrees with that of the 〈1 1̄ 0〉 step edge, which is a unit vector of the Ni(1 1 1). LEED patterns show the single domain of the well-known (39×39)R16.1° 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.