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

Abstract

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 H2 and D2 and collision-induced desorption (CID) of D2 and abstraction of HD in the reaction system H(g)+D/Ge(100). The D2 and H2 TPD spectra exhibit two clear peaks, assigned as β1 and β2 TPD arising from a monohydride and a dihydride phase, respectively. There are isotope effects on the TPD spectra; D2 TPD peaks shift to higher surface temperature (Ts) compared to the peaks of H2, and the ratio of the β2 to the β1 TPD peak intensity is smaller for H2 than for D2. 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 D2 rate curves show up a strong Ts dependence. The CID of D2 versus Ts curve exhibits a peak at Ts≃480 K corresponding to the leading edge of the β2TPD spectra. For Ts⩾530 K, CID of D2 is fully replaced by the spontaneous desorption ascribed to the β1 TPD. This fact suggests that the mechanism of CID is same to that of the β2 TPD. For Ts∼480 K, the D2 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 β1 TPD the concerted desorption from hydrogen-prepared Ge dimers is preferred to the desorption from isolated dihydrides.