The bimetallic Pt/Mo(110) surface: Structural and CO chemisorption studies

Abstract

Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and temperature-programmed desorption (TPD) measurements were performed to monitor the growth, thermal stability, and CO adsorption characteristics of Pt layers on Mo(110). Pt grows in a layer-by-layer or Frank-van der Merwe fashion on the molybdenum surface below 600 K. The first monolayer of Pt is stable and no significant structural change is observed at higher substrate temperatures. A monolayer of Pt eliminates the dissociative adsorption of CO observed on the Mo(110) surface. The thermal desorption of CO from this Pt overlayer occurs at lower temperatures (in comparison to CO desorption from the bulk Pt(111) and Mo(110) surfaces), indicating a withdrawal of electron density from the Pt monolayer due to interactions with the Mo(110) surface. As the Pt coverage is increased above a monolayer, LEED measurements indicate the growth of Pt(111) layers at 300 K. The multilayers of Pt are thermally unstable and agglomerate into three-dimensional (3D) clusters upon heating to above ~ 600 K. The 3D clusters contribute little to the AES signal. The CO desorption spectra from the annealed layers are very similar to the CO desorption spectra from one monolayer of Pt on the Mo(110) surface, suggesting that Pt clustering occurs on top of a single Pt monolayer on Mo(110). The spatial distribution of Pt clusters is estimated from Auger intensity changes following annealing of a 6 monolayer Pt film.