THE GROWTH AND REMOVAL OF MOLYBDENUM FILMS AT PLATINUM(111) SURFACES

LEED, AES, work function measurements and low-energy (<30 eV) electron reflectivity spectra were used to characterise films of 1 to 5 monolayers thickness of Mo on a Pt(lll) surface. With the Pt surface at 300 K, vapour deposition of Mo produced poorly ordered multilayer films, which gave no LEED pattern but showed the electron reflectivity properties of a Mo(110) surface after completion of the first monolayer. The evolution of surface microstructure during annealing at T > 750 K was dominated by diffusion of Mo into Pt. A new surface phase was seen only during removal of Mo films thicker than three monolayers. The distinctive electron reflectivity features and strong (root 3 x root 3)R30 degrees LEED pattern characteristic of this phase are attributed to separation of the ordered alloy Pt2Mo when the concentration of Mo diffusing into the Pt surface layers reaches the solubility limit. The electron reflectivity spectral features of the alloy were also seen during deposition of Mo on Pt(lll) at 600 K.