Structure determination of Si(001)-c(4×2) 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(4×2) surfaces using low-energy electron diffraction analysis at 80 K. The asymmetric dimer model was optimized, and obtained structural parameters were almost identical with those previously reported by theoretical calculations. We analyzed both n-type and p-type samples and obtained almost the same structural parameters. 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, as in the recent study [Matsumoto et al., Phys. Rev. Lett. 90, 106103 (2003)]. However, we confirmed that the intensity changes below 40 K are caused by the incident electron beam. We observed clear c(4×2) patterns immediately after irradiation of electron beam at 24 K, and concluded that the phase transition at 40 K, which was proposed by Matsumoto et al., is improbable.