OBSERVATION OF THE INTERFACE OF BA/SI(100) BY MDS AND TDS

The interaction of Ba overlayers with Si(100)2 x 1 surfaces and barium silicide formation are studied for Ba coverages up to theta = 10 ML by MDS (metastable deexcitation spectroscopy) and TDS (thermal desorption spectroscopy). TDS spectra of Ba from Ba/Si(100) are observed as a function of Ba coverage. The process of Ba dosing on Si(100)2 x 1 and the annealing process are observed by MDS as a function of Ba coverage and as a function of sample annealing temperature, respectively. The work function change is measured as a function of the annealing temperature simultaneously. It is found from the above experiments that no silicide formation takes place by heating up to 800-degrees-C in the system of submonolayer Ba on Si(100)2 x 1 and that silicide is formed very easily by heating up to 250-degrees-C in the system of 2 ML Ba/Si(100)2 x 1. The Si-Ba bond is so tight that the Ba atoms bonded to the substrate Si atoms cannot move easily to form three-dimensional barium silicide. Therefore more than a few Ba layers are necessary to form barium silicide on the Si(100) surface.