Structure determination of Si(001)-c(4x2) surfaces at 80 K and electron beam effect below 40 K studied by low-energy electron diffraction

We have studied the structures of the Si(001)-c(4x2) surfaces using low-energy electron diffraction analysis at 80 K. The asymmetric dimer model was optimized as Fig. 1.

Fig. 1. Determined structure model of Si(001)-c(4x2) clean surface by LEED.

Using the same samples, we measured changes in the intensity of diffraction spots in a temperature range of 24-120 K. The intensities of the quarter-order spots decreased significantly below 40 K, caused by the incident electron beam.

Fig. 2. LEED patterns of the clean Si(001)-c(4x2) surface at 20 K. (a) Just after the observation. (b) 1 minute later.

A quantitative analysis of decreasing rates of the spot intensity at various conditions of beam current, beam energy, and substrate temperature leads to a proposal for a mechanism of the disordering in the buckled-dimer arrangement in terms of electronic excitation, electron-phonon coupling, and carrier concentration.
=== Original papers ===
Electron-Beam-Induced Disordering of the Si(001)-c(4x2) Surface Structure. Phys. Rev. Lett. 94 (2005) 195502. 
Structure determination of Si(001)-c(4x2) surfaces at 80 K and electron beam effect below 40 K, studied by LEED. Phys. Rev. B 69 (2004) 241306(R). 
Ground state of the Si(001) surface revisited - is seeing believing? Prog. Surf. Sci. 76 (2004) 147-162. 
Structural analysis of the c(4x2) reconstruction in Si(001) and Ge(001) surfaces by LEED. Surf. Sci. 600 (2006) 815-819.
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