Temperature dependence of atomic hydrogen-induced surface processes on Ge(100): Thermal desorption, abstraction, and collision-induced desorption

The temperature effect on the atomic hydrogen-induced surface processes on Ge(100) has been studied from a desorption point of view. The experiments are carried out for temperature-programmed-desorption (TPD) of H-2 and D-2 and collision-induced desorption (CID) of D-2 and abstraction of HD in the reaction system H(g)+D/Ge(100). The D-2 and H-2 TPD spectra exhibit two clear peaks, assigned as beta (1) and beta (2) TPD arising from a monohydride and a dihydride phase, respectively. There are isotope effects on the TPD spectra; D-2 TPD peaks shift to higher surface temperature (T-s) compared to the peaks of H-2, and the ratio of the beta (2) to the beta (1) TPD peak intensity is smaller for H-2 than for D-2. It is found that the kinetics of the abstraction and CID reactions are similar to those on Si(100), indicating that the mechanism for the abstraction and CID on Ge(100) is same to that on Si(100). The observed D-2 rate curves show up a strong T-s dependence. The CID of D-2 versus T-s curve exhibits a peak at T(s)similar or equal to 480 K corresponding to the leading edge of the beta 2TPD spectra. For T(s)greater than or equal to 530 K, CID of D-2 is fully replaced by the spontaneous desorption ascribed to the beta (1) TPD. This fact suggests that the mechanism of CID is same to that of the beta (2) TPD. For T(s)similar to 480 K, the D-2 rate curves can be fitted with a fourth-order kinetics in a momentary D adatom coverage. The transiently created dihydride species that are considered to be mobile across the surface via a dihydride-monohydride isomerization reaction to exchange their sites, are invoked to explain the observed fourth-order kinetics. Probing H atoms reveals that the thermal desorption from the isolated dideuterides is not allowed, suggesting that for the beta (1) TPD the concerted desorption from hydrogen-prepared Ge dimers is preferred to the desorption from isolated dihydrides. (C) 2000 American Institute of Physics. [S0021-9606(00)71040-3].