Molybdenum(100) surface reconstruction and effects due to hydrogen and alkali metal adsorption

The clean Mo(100) surface exhibits a two dimensional reversible phase transition upon cooling. Previous low energy electron diffraction (LEED) studies have shown a high temperature phase with the same periodicity as the bulk and a low temperature reconstructed phase that has been called incommensurate. Lateral displacements have been shown to account for the low temperature phase, but determination of their magnitude by LEED is prohibitive due to the large size of the reconstructed unit mesh. The high temperature structure has not been previously investigated, and there is debate as to whether the phase transition is order-disorder or displacive. Further debate concerns the reconstruction's driving mechanism; charge-density-wave and local bonding descriptions have been proposed. Hydrogen adsorption has been shown to induce many substrate phases for which the displacements are unknown.;Perturbation of the low temperature structure by the adsorption of K, Na, and Li is also studied. Adsorbing minute quantities of these alkalis dramatically changes the substrate periodicity; these changes indicate a local bonding mechanism for the reconstruction and the presence of substrate mediated adatom-adatom interactions. Alkali bonding sites are determined by stabilization/destabilization of the Mo reconstruction. Study of these adsorption systems throughout the sub-monolayer coverage range is also carried out using Auger electron spectroscopy, thermal desorption, and work function measurements.;The present work, the most careful Mo(100) LEED study to date, reveals that the low temperature phase is in fact commensurate with a c(7...