Atomic structures of iron-silicide ultra-thin films epitaxial grown on Si(111) were investigated by x-ray crystaltruncation-rod scattering measurements. Two films, each of them respectively exhibited 1×1 and 2×2 periodicities in ultra high vacuum, were measured with the x-ray diffraction under ambient air. Both of the films showed essentially the same Laue peaks. The Laue peaks directly indicate that both films have the CsCl-type (so-called c-FeSi) structure whose stacking orientation is rotated by 180 • with respect to the substrate. Quantitative structural analysis, which includes degree of the film roughness as fit parameters, reveals that the interfacial Fe atom is 8-fold coordinated to Si atoms (so-called B8 model). The determined interlayer spacing in the silicide film and the Fe-Si bond length at the interface are respectively ∼6 % and ∼9 % larger than those in the hypothetical c-FeSi.

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The atomic structure of the Si(111)-(5 × 2)-Au surface, a periodic gold chain on the silicon surface, has been a long-debated issue in surface science. The recent three candidates, the so-called Erwin-Barke-Himpsel (EBH) model [S. C. Erwin, I. Barke, and F. J. Himpsel, Phys. Rev. B 80, 155409 (2009)], the Abukawa-Nishigaya (AN) model [T. Abukawa and Y. Nishigaya, Phys. Rev. Lett. 110, 036102 (2013)], and the Kwon-Kang (KK) model [S. G. Kwon and M. H. Kang, Phys. Rev. Lett. 113, 086101 (2014)] that has one additional Au atom than the EBH model are tested by surface x-ray diffraction data. A two-dimensional Patterson map constructed from the in-plane diffraction intensities rejects the AN model and prefers the KK model over the EBH model. On the basis of the arrangement of Au obtained from the Patterson map, all the reconstructed Si atoms, such as the so-called honeycomb chain structure, are directly imaged out by utilizing a holographic method. The KK model reproduces out-of-plane diffraction data as well.

We have studied the metal-insulator transition near room temperature on the Si(553)-Au surface with surface X-ray diffraction. Diffraction intensities due to the ×2 superstructure developing in the transition were collected at 86 K. The Patterson map calculated from the experimental intensities shows that only a few atoms are involved in the transition. The atoms are displaced mostly in the surface plane. The temperature dependence of the intensity and width of one reflection due to the low temperature superstructure was measured as well. The changes in the intensity of this reflection below the transition temperature are consistent with the predictions by the mean-field theory for a Peierls transition at 336 K. The changes of the intensity above the transition temperature and the temperature dependence of the width of the reflection can be explained by the influence of defects.