目次
Theoretical Analyses of Thermal Desorption of Hydrogen from Si(100)-H Surface
Y.Yagi, H.Kaji, K.Kakitani, A.Yoshimori
Okayama University of Science, Okayama
Introduction of Hydrogen adsorbed Si(100)
Si(100) surface is reconstructed in 2×1 structure, where two adjacent surface Si atoms form dimers. Hydrogen molecules can adsorb on the top Si atoms; one H on each Si atom up to coverage 1 ML. Above this coverage, The dimer structure is rearranged to form local 3×1 structures.
| $\theta<1{\rm ML}$ 2×1 structure with mono-hydrides | $\theta<4/3{\rm ML}$ 3×1 structure di- and mono-hydrides* |
*Y. J. Chabal, et al., Phys. Rev. Lett. 54 (1985) 1055.
Experimental TPD Spectra
Experimental TPD Spectra, K. Sinniah et al., J. Chem. Phys. 92 (1990) 5700.
The TPD spectra feature two majour peaks. The alpha-peak appears for initial coverage over 1 ML. This peak is considered to correspond to the desorption from di-hydride states. Only the beta-peak is observed for initial coverage below 1 ML. This peak is considered to correspond to the desorption from mono-hydride states.
The peak position shifts little with coverage change. The peaks are almost symmetric in shape, which are typical characteristics of a first order non-interacting desorption. However, this desorption is known to be an associative desorption, which involves interactions between adsorbates. The interactions are expected to cause large peak shift and asymmetric peak shapes. The purpose of this study is to clarify the cause of this unusual behaviour.
Simple Model Analyses
1 Dimensional Interaction Model Analyses
2 Dimensional Interaction Model Analyses
Conclusion and Summary
Conclusion (important effects for TPD)
- Excited states for 2×1 structure: di-hydride/di-hydride pair
- Hydrogen-hydrogen interaction across dimers
Summary
- TPD spectra of H/Si(100) analyzed with 1D/2D interaction model
- Good agreement with experiment at low initial coverage
Future problem
- analyses for alpha-peak:
- Thermal desorption from non-equilibrium state!
- Discussion about interaction parameters
- Their origin?
- Negative J1, J2 : Unnatural ?