Yasuharu Kashihara

Atomic Displacements at Surface of Si-Wafer(111)

The rod shaped distribution of X-ray scattered intensity observed from the (111) surface of Si-wafer shows asymmetry in its intensity profile with respect to the Bragg point. Such asymmetry is closely related to the lattice distortion near the crystal surface. From the analysis of the observed asymmetric intensity distribution the Si lattice plane at the interface region between the Si-wafer and the adsorbed amorphous SiO2 layer is shown to be expanded by about 3% from the bulk spacing.

Upper and Lower Critical Fields of TaS2(Pyridine)1/2

The temperature dependences of the upper critical fields, H c2//,⊥ , and the lower critical field, H c1// , have been measured on the single crystal of the layer structure TaS 2 intercalated with p...

High Resolution Investigation of the Rod-Shaped Scattering from a (111) Si Surface by a Synchrotron Radiation Source

By using a high resolution X-ray spectrometer in conjunction with a synchrotron radiation source, the rod-shaped scattering due to crystal truncation (RSCT), which is elongated along the normal of a crystal surface through a Bragg point, was investigated for two (111) silicon wafers of which the surfaces were differently processed. It is shown that the characterization of a crystal surface, on the basis of surface roughness on an atomic scale and the misorientation of mosaic blocks, is really possible by the precise measurement of the RSCT.

Determination of Lattice Distortion in (GaAs)28(AlAs)24 Superlattice Layers by X-Ray Diffraction

The structure of a (GaAs)28(AlAs)24 superlattice grown by MBE has been characterized in detail by X-ray diffraction. By applying a new method of Fourier analysis (Harada et al.: Jpn. J. Appl. Phys. 24 (1985) L62), both the concentration and lattice distortion modulations existing in the multilayer were determined on the basis of the integrated intensities of the satellite reflections around the (400) fundamental Bragg reflection. Both modulations were found to be like a step function. It is pointed out that the width of the boundary between the two regions should be narrow and less than two intermolecular layers. The spacings between successive cation layers were 2.827 and 2.835 A in the regions of GaAs and AlAl, respectively, along the (001) direction. This is in good agreement with the values calculated from the Poisson expansion model.

Orientation of Pyridine in TaS2(Py)1/2

X-ray diffraction measurements on TaS 2 (Py) 1/2 single crystals of the single phase with the layer spacing 12.03 A showed that the intercalated pyridine molecules lay with aromatic ring planes perpendicular to the TaS 2 layers, and the nitrogen atom located midway between the TaS 2 layers with the long C–N axis parallel to the layers.

X-ray crystal truncation rod scattering : general intensity formula for no lateral displacements of surface atoms

Abstract We present a fundamental formula to analyze the X-ray intensity distributions along the crystal truncation rod (CTR) scattered from the surface of a crystal. By introducing the model functions for the surface roughness and the lattice distortion near the surface, we provide general analytical methods for determining the surface structure from the CTR scattering. These methods can be used for the investigation of intensity profiles of the CTR scattering observed around any Bragg point.

Measurement of Elastic Constants of MBE Grown (Ga0.5Al0.5)As Mixed Thin Film Crystal by Diffuse X-Ray Scattering

By a measurement of X-ray thermal diffuse scattering and an analysis based on a least squares fitting procedure, it was demonstrated that a set of elastic constants could be determined for an MBE grown (Ga0.5Al0.5)As mixed crystal of 4 µm thickness. The absolute value of C11 and the ratios of the elastic constants, C12/C11 and C44/C11, were determined to be 13.32±0.35 [×1011 dyn/cm2], 0.418±0.021 and 0.473±0.013, respectively, for the sample. It turned out that the elastic constants of the mixed thin film crystal was slightly higher than that expected from the linear interpolation between GaAs and AlAs.

X-Ray Diffraction from GaAs/AlAs/GaAs Grown on GaAs(001) by MBE

The structure of a GaAs/AlAs/GaAs multilayer grown on a GaAs(001) substrate by MBE was investigated by X-ray diffraction. The lattice spacing in such a single bunch of AlAs layers was found to expand along the epitaxial-growth direction due to a Poisson expansion. The lattice mismatch between GaAs and AlAs perpendicular to the growth direction is compensated.

Cation and Anion Displacements at Hetero-Interfaces of (GaAs)28(AlAs)24 Superlattice Layers

By developing a new method of Fourier analysis the local cation and anion displacements in a superlattice, especially near the hetero-interface boundary between the GaAs and the AlAs, were determined from the X-ray integrated intensities of the satellite reflections observed around the two fundamental Bragg reflections, namely the 002 and 004 reflections. The interlayer distance of successive cation layers was found to be 2.827 A in the GaAs region and 2.835 A in the AlAs region, except near the hetero-interface boundary. The anion layers are, therefore, located at the mid-point between the cation layers in these regions. However, near the hetero-interface region, which consists of eight molecular layers, anion layers are not located at the mid-point between them but are slightly shifted to the GaAs side. The value of the shift at the boundary between GaAs and AlAs was 0.016 A.

Determination of Atomic Displacement Modulation in Multi-Layer Structure by X-Ray Diffraction

A new method of Fourier analysis is shown by which both concentration and atomic displacement modulations existing in multilayer structures can be reproduced from the measurement of the integrated intensities of satellite reflections. By applying the present method to a molecular beam epitaxy grown (GaAs)8(AlAs)8 superlattice, the atomic displacement modulation in interface region is given as well as concentration modulation.