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 b
y MDS (metastable deexcitation spectroscopy) and TDS (thermal desorpti
on 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 temper
ature simultaneously. It is found from the above experiments that no s
ilicide formation takes place by heating up to 800-degrees-C in the sy
stem of submonolayer Ba on Si(100)2 x 1 and that silicide is formed ve
ry easily by heating up to 250-degrees-C in the system of 2 ML Ba/Si(1
00)2 x 1. The Si-Ba bond is so tight that the Ba atoms bonded to the s
ubstrate Si atoms cannot move easily to form three-dimensional barium
silicide. Therefore more than a few Ba layers are necessary to form ba
rium silicide on the Si(100) surface.