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4); Comparison of X-ray diffraction and first-principles calculationTakahashi, Masamitsu; Kratzer, P.*; Penev, E.*; Mizuki, Junichiro
Surface Science, 600(18), p.4099 - 4102, 2006/09
Times Cited Count：1 Percentile：6.14(Chemistry, Physical)The GaAs(001)-c(44) has been studied by synchrotron surface X-ray diffraction. The atomic coordinates and Debye-Waller factors were determined up to the sixth layer from the surface. The results support the formation of the Ga-As heterodimers. The resultant atomic coordinates were compared with those given by a first-principle calculation. In spite of the theoretical prediction of the stability of the single-heterodimer structure, our data fit best a three-heterodimer model where three heterodimers are present in one unit cell. The preference of the formation of the three heterodimers will be discussed in the relationship with the transition process from the 24 to the c(44) structures.
4 surfaces under molecular-beam epitaxy conditionsTakahashi, Masamitsu; Yoneda, Yasuhiro; Mizuki, Junichiro
Applied Surface Science, 237(1-4), p.219 - 223, 2004/10
Times Cited Count：5 Percentile：28.90(Chemistry, Physical)The GaAs(001)-
reconstructed surface was investigated by in situ surface X-ray diffraction. The sample was subjected to measurements under molecular-beam epitaxy conditions without being transferred another chamber. Several X-ray diffraction patterns were measured with increasing the substrate temperature within the 
-phase of GaAs(001)- in a constant As flux of 510
Torr. At relatively low temperatures up to 545
C, the observed X-ray diffraction patterns agree well to the 2(24) surface. However, a different X-ray diffraction pattern was obtained at 585C, while the 
periodicity still persited. This change is explained by partial As-dimer desorption which results in a mixture of the 2(24) and 
2(24) structures.
Takahashi, Masamitsu; Yoneda, Yasuhiro; Inoue, Hirotane*; Yamamoto, Naomasa*; Mizuki, Junichiro
Journal of Crystal Growth, 251(1-4), p.51 - 55, 2003/04
Times Cited Count：3 Percentile：21.58(Crystallography)The reflection high energy electron diffraction (RHEED) oscillation has been widely adopted for studies on growth kinetics and dynamics in molecular beam epitaxy (MBE). Recent development in brilliant X-ray source has enabled similar experiments with X-rays, which has great advantage in a straightforward interpretation of results and in a high angular resolution. In general, the diffracted intensity from surface is proportional to the surface structure factor associated with the surface reconstruction, F, multiplied by a damping factor associated with the surface roughness, m. We show that the two factors, F and m, can be obtained separately by measuring diffuse scattering around the two-dimensional Bragg peak during growth.
Takahashi, Masamitsu; Yoneda, Yasuhiro; Inoue, Hirotane*; Yamamoto, Naomasa*; Mizuki, Junichiro
Japanese Journal of Applied Physics, Part 1, 41(10), p.6247 - 6251, 2002/10
Times Cited Count：55 Percentile：84.74(Physics, Applied)An X-ray diffractometer connected with a molecular-beam epitaxy (MBE) system has been constructed for in situ studies on the growing surfaces of III-V compound semiconductors. This diffractometer is based on the (4+2) type and equipped with an axis for rotating the receiving slit about the normal of the slit plane. This additional axis is used to align the resolution of the receiving slit properly for the surface X-ray diffraction measurement. For the alignment of the sample and the whole setup with respect to the X-ray beam, an XYZ-stage and an adjustable base plate are available. X-rays enter and leave the chamber through two cylindrical Be windows welded onto the MBE chamber. A graphite sheet which can be heated up to 250C is placed along the inside of the Be windows to protect the Be windows from being coated with evaporated materials. Preliminary data are presented to demonstrate the feasibility of static and dynamic measurements of growing surfaces using this instrument.
