Ostenfeld, Christopher Worsøe1; Davies, Jonathan Conrad1; Vegge, Tejs4; Chorkendorff, Ib1
1 Department of Physics, Technical University of Denmark2 Center for Individual Nanoparticle Functionality, Center, Technical University of Denmark3 Center for Nanoteknologi, Center, Technical University of Denmark4 Department of Energy Conversion and Storage, Technical University of Denmark
The growth and hydrogenation of ultra-thin magnesium overlayers have been investigated on a Mo(1 1 1) single crystal substrate. For increasing magnesium coverages we observe intermediate stages in the TPD and LEISS profiles, which illustrate the transition from one monolayer to multilayer growth. Hydrogen cannot be adsorbed on magnesium films under UHV conditions. However, when evaporating Mg in a hydrogen background, a hydrogen overlayer is seen to adsorb at the Mg surface, due to the catalytic interaction with the Mo(1 1 1) substrate and subsequent spill-over. We show that two monolayers of Mg are necessary to sustain this purely adsorbed state. Using predissociated hydrogen we show that the hydride formation is self-stabilizing and the hydride only decomposes at a temperature where a considerable desorption of magnesium occurs.