ULTRA-THIN COBALT FILMS ON MO(110) - OVERLAYER GROWTH AND CHEMISORPTION OF CO AND D2

The overlayer growth of cobalt on Mo(110) and the adsorption of CO and deuterium on Co/Mo(110) have been studied by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and temperature-programmed desorption (TPD). Co grows layer by layer on Mo(110) at a sample temperature of 115 K. Annealing multilayers of Co on Mo(110) to > 400 K results in the formation of three-dimensional (3D) Co clusters. The TPD spectra of Co from Mo(110) reveal two desorption peaks, beta-1 and beta-2, with activation energies of 82 and 85 kcal/mol, corresponding to desorption from 3D Co clusters and the first uniform Co overlayer, respectively. Submonolayer Co (< 0.75 ML, where 1 ML corresponds to the atomic density of the Co(0001) surface) is believed to form a pseudomorphic layer on Mo(110) upon annealing to 400 K. Co coverages from 0.75 to multilayers, annealed to 500 K, exhibit the following LEED patterns: a 9 x 2 structure, a hexagonal structure, and a 2 x 2 structure. The 9 x 2 and hexagonal structures are interpreted to correspond to a distorted lattice of Co(0001) and to 3D Co clusters on Mo(110), respectively. The TPD spectra of CO or D2 on Co overlayers show desorption features with lower activation energies than the analogous desorption features from bulk Co(0001).