TEMPERATURE-PROGRAMMED DESORPTION OF MOLECULAR-HYDROGEN FROM A SI(100)-2X1 SURFACE - THEORY AND EXPERIMENT

New experimental temperature programmed desorption (TPD) data have been obtained under carefully controlled conditions for atomic deuterium on the single crystal Si(100)-2 X 1 surface. A wide range of coverages from THETA = 1.5 to 0.05 ML was used. A kinetic lattice-gas model has been developed which describes atomic hydrogen (or deuterium) adsorbed on the Si(100)-2 X 1 surface in terms of four basic units: dihydride (SiH2), doubly occupied dimers (H-Si-Si-H), singly occupied dimers (Si-SiH), and unoccupied dimers (Si=Si). The equilibria between these species have been determined by considering both the lattice partition functions and the vibrational partition functions associated with the Si-H bonds. By using a quasiequilibrium approximation and two competing desorption routes corresponding to formation of the beta1 and beta2 peaks, the TPD spectra for hydrogen (deuterium) molecules are determined and compared with the new experimental data. Fitting the experimental curves with the simulated data from the afore-mentioned model showed that the desorption process which leads to the beta1 peak obeys first-order kinetics with an A factor of 2 X 10(15) s-1 and activation energy of 57 kcal mole-1, whereas the process giving the beta2 peak follows second-order kinetics with an activation energy of 47 kcal mole-1 and an A factor (expressed in 1 st order units) of 3 X 10(15) s-1.