Reflection High-energy Electron Diffraction Apparatus Research Articles

Temperature dependence of reflection high-energy electron diffraction intensity from Si(111)-7×7 superlattice

Rocking curves of reflection high-energy electron diffraction (RHEED) were observed from Si(111)-(7×7) surface at temperature of 293, 523, and 653 K by a RHEED apparatus with a magnetic deflector to change the glancing angle. The temperature dependence of RHEED intensity was calculated with change of the real and imaginary part of the potential corresponding to the thermal diffuse scattering arising from a thermal vibration of atoms, which was obtained by the way proposed by Dudarev et al. [Surf. Sci. 330, 86 (1995)]. We assumed that the amplitude of the thermal vibration (Debye parameter) increases with temperature according to the Einstein model. By comparing with the experimental results, the atomic positions of the (7×7) structure satisfying the observed RHEED rocking curves in this temperature range is determined. The positions of the surface atoms are almost coincident with the results obtained by using ab initio molecular-dynamics scheme (Brommer et al. [Phys. Rev. Lett. 68, 1355 (1992)]) within the difference of 0.01 nm.

Surface Superstructures of Ce Thin Films on an Mo(100) Surface

Surface structures of Ce thin films on an Mo(100) single crystal substrate were investigated using a molecular beam epitaxy system equipped with a reflection high-energy electron diffraction apparatus. Five kinds of surface superstructures (√2×√2 R45°, one-dimensional √2a Mo periodicity, 3×3/√2×4√2 R45°, C√2×5√2 R45° and 4×4 structures) were observed in the regions with low Ce coverage and their phase diagram was obtained. Four out of five surface superstructures (except the 4×4 structure) showed the same √2a Mo periodicity along Mo[011]. This periodicity is also dominant in the case of Ce thin films on an Mo(110) surface when the Ce film thickness is smaller than 0.5 nm. This Ce structure with one-dimensional √2a Mo periodicity along Mo[011] is considered to be very stable.