Structural and compositional analysis of two ordered near-surface alloys produced by adsorption and thermal decomposition of Mo(CO)6 on Ni{111}

The adsorption and thermal decomposition of Mo(CO)6 is reported on Ni{1 1 1}. At room temperature, Mo(CO)6 has an extremely low sticking probability. At 450–550 K, Mo(CO)6 adsorbs dissociatively via loss of one or more CO ligands to produce a surface intermediate stable up to about 675 K. Desorption of the remaining CO ligands leaves an essentially contaminant free NiMo surface. Two distinct NiMo near-surface alloys were synthesised by this route. These bimetallic surfaces were characterised by a combination of STM, LEED, AES, MEIS and TPD. In each case, the alloys were Ni rich and, in each case, are found to be very close to the structure of fcc nickel. The first alloy gives a (3×3) LEED pattern and has the composition Ni8Mo. The second structure gives a (5×5) LEED pattern and has the composition Ni24Mo.