Jimpei Harada

X‐ray crystal truncation rod scattering measurement of AsH3‐exposed InP/InPAs/InP single heterostructures

The atomic‐level heterointerface structures of InP samples that contain growth interrupted and AsH3‐exposed surface, with 20 A thick cap layer, were revealed by x‐ray crystal truncation rod scattering measurement. The As atom distribution, the thickness of the cap layer, and the tetragonal distortion of the lattices were obtained from the samples that have only single modified layer in the whole InP wafer. The calculated total amounts of As matched well with the value obtained by fluorescence x‐ray analysis.

X-Ray Studies of the Lattice Vibration in Tetragonal Barium Titanate

Thermal diffuse scattering of X-rays by tetragonal barium titanate is studied. Two kinds of diffuse streaks, S A and S O , are observed in addition to thermal diffuse spots F near reciprocal lattice points. S A and F , which show intensity modulation in phase with the static structure factor, are due to acoustic lattice vibration. S O , which shows a different intensity modulation from them, is concluded to be due to low frequency transverse optic lattice vibration which plays an important role in the ferroelectric transition of the substance. The mode is a streching type vibration in which all the oxygen atoms vibrate to the oposite direction against barium and titanium atoms, and the frequency is estimated to be of the order of 10 12 cm -1 . The atomic shifts of ferroelectric polarization are discussed in relation to the vibration.

X-ray diffraction study of fine gold particles prepared by gas evaporation technique

Abstract From the analysis of the X-ray Debye-Scherrer lines of the fine gold particles of which sizes are in a range from 60 to 230 A, it was found that the thermal expansion coefficient as well as the lattice parameter are not different from those of the bulk crystal, while the characteristic temperature decreases monotonously with the decrease of the particle size. The particle size dependence of the characteristic temperature can be explained by introducing two characteristic temperatures θ core and θ shell , on the assumption that the particles are composed of the core and the shell. θ core and θ shell were found in good agreement with the characteristic temperature for the bulk crystal and that for the surface obtained by LEED experiment, respectively.

Direct Observation of Covalency between O and Disordered Pb in Cubic PbZrO3

In cubic PbZrO 3 , which undergoes an antiferroelectric phase transition, the distinct disorder of Pb at twelve sites toward the neighboring O is detected for the first time by analyzing high-energ...

Neutron Scattering Study of Lattice Dynamics in CuBr. II. Anharmonic Effect on Debye-Waller Factor

Integrated intensities for the Bragg reflections of neutrons from CuBr single crystal with zincblende structure were measured at several temperatures. The experimental data both at room temperature and higher temperatures were interpreted consistently in terms of Matsubaras representations for anharmonic Debye-Waller factor. The harmonic and cubic anharmonic potential parameters for each atom obtained by the least squares refinement are α Cu =0.937, α Br =1.49 (×10 -12 erg A -2 ) and β Cu =1.00 (×10 -12 erg A -3 ). A discrepancy was found between the harmonic component of the mean square displacement of the Cu atom and that calculated from the phonon dispersion relation reported in Part I. In view of the lattice dynamical study by inelastic neutron scattering, the effects of the quartic anharmonicity which were ignored are considered to be included in the harmonic component determined in this analysis.

Neutron diffraction study of asymmetric anharmonic vibration of the copper atom in cuprous chloride

Neutron diffraction measurements of CuCl with the zincblende structure were carried out at room temperature and the results examined on the basis of three possible structure models: (1) harmonic thermal vibration of atoms, (2) asymmetric anharmonic vibrations and (3) statistical disorder arrangement of the copper atom. It was found that the anharmonic model was the most plausible for the structure of CuCl. The final R value in the least-squares analysis was 0.037. The parameters in the effective one-atomic-potential fields for the zincblende structure Vj(r) = V0j + ½αj(u21 + u22 + u23) + βju1u2u3 + . . . were obtained as αCu = 0.74 ± 0.01, αC1 = 1.35 ± 0.02 × 10-12erg A-2, and βCu = 1.15 ± 0.66, βC1 = 0.0 ± 1.6 × 10-12erg A-3. It is also shown that the temperature dependence of the Bragg reflexion observed from room temperature to 523°K can be explained very well with the use of the above parameters.

Neutron Diffraction Study of the Structure in Cubic CsPbCl3

The crystal structure of cubic CsPbCl 3 was reinvestigated by neutron diffraction technique at 55°C. Two structure models were examined: (i) perovskite structure with anisotropic thermal vibration and (ii) disordered structure having several potential minima for the Cs and Cl atoms, originally proposed by Moller (1959). Both models explain the present neutron data equally well with a reliability index of about 9%. A set of parameters refined on the basis of the structure factor proposed by Moller is, however, revealed to be simply another representation of the perovskite model. As for the perovskite model, anomalously large thermal vibrations were obtained for the Cs and Cl atoms. It is concluded that such anomalous thermal vibrations are characteristics of the phase transitions of this substance.

X-ray diffraction evidence for epitaxial microcrystallinity in thermally oxidized SiO2 thin films on the Si(001) surface

In the X-ray diffraction pattern from a thermally oxidized thin film on an Si(001) surface, very weak Bragg peaks have been observed. The thermally oxidized thin film is, therefore, not purely amorphous but many small crystallites are dispersed within it, maintaining an epitaxial relation with the Si substrate. It is difficult to determine the structure of the crystalline phase because of the limited number of observable Bragg peaks. The pseudo-cristobalite structure proposed by Iida et al. was selected as a possible model. The atomic arrangement is similar to that of the cristobalite structure, while the unit cell is tetragonal so as to match the lattice spacing to that of the Si substrate. A least-squares fitting analysis of the profile of the newly observed Bragg peak reveals that the crystallites are located not only at the interface between the Si substrate and the amorphous layer, but also widely distributed in the amorphous layer, preserving an epitaxial relation among the crystallites. The proportion of such crystallites is estimated to be a few percent of the whole volume of the amorphous layer.

X-ray evidence for a deformation of CDW during the sliding motion in K0.30MoO3

Abstract The wave vector and the correlation length of the CDW ordering in K 0.30 MoO 3 are studied by x-ray diffraction as functions of electric fields applied along the one-dimensional axis. Several samples change their CDW-ordering above a threshold field. The change of the wave vector occurs mainly in the (2a ∗ -c ∗ ) - direction, which is perpendicular to the one-dimensional b ∗ - axis. It depends also on the field direction and magnitude. Time resolved x-ray experiments show that characteristic time of this change is of the order of 1 ms. The correlation length becomes longer along the (2a ∗ -c ∗ )-direction in the transient period.

Determination of the normal vibrational displacements in several perovskites by inelastic neutron scattering

Relative displacements of the atoms corresponding to the lowest frequency long wavelength transverse optic phonon of several materials with the perovskite structure were determined directly by a least-squares refinement of the integrated intensity of inelastic neutron scattering. The modes of KTaO3 and SrTiO3 were identified as being of the Slater type, in which oxygen atoms vibrate against Ta and Ti atoms. In the case of RbMnF3, however, an entirely different vibrational motion was obtained, in which Rb ions vibrate out of phase with the rigid MnF3 group.