Yukishige Kitano

Characterization of long-periodic layered structures by X-ray diffraction IV: Small angle X-ray diffraction from a superlattice with non-ideal interfaces

Abstract The small angle X-ray diffraction intensity of superlattices (SLs) has been formulated on the basis of a trapeziform composition profile. The analysis using this model enables us to estimate the interface width as well as the layer thicknesses. A GaAs/AlAs SL was characterized according to this method, and the SL period was precisely determined with consideration of the effect of refraction. The scheme presented here has been shown to be useful for studies on structural modifications of SLs with a long period as large as tens of nanometres.

Characterization of long-periodic layered structures by X-ray diffraction III: Structure of a Langmuir-Blodgett film of cadmium arachidate at elevated temperatures

Abstract The thermal behavior of a Langmuir-Blodgett (LB) multilayer of cadmium arachidate (CdA) was investigated by small-angle X-ray diffraction. Before melting, the LB multilayer underwent a three-step structural change: (1) from room temperature to 60°C, rearrangement of the CdA layers; (2) between 60 and 80°C, onset of the pretransitional disordering; (3) above 80°C, conformational change from trans to gauche state in the hydrocarbon chain. The 001 reflection intensity, a measure of the short-range disorder of the multilayer structure, is sensitive to these changes. In contrast, the lattice distortion parameter tends to increase monotonously up to 100°C. This indicates that the long-range order of the multilayer structure is well preserved at temperatures close to the melting point. On cooling down to room temperature after melting, the crystallites of a periodic lamellar structure grow. Their lattice distortion and dimension in the [001] direction are much larger than those of the multilayer before melting.

Characterization of long-periodic layered structures by X-ray diffraction II: Lattice distortion of Langmuir-Blodgett films of lead stearate

X-ray 00l reflections from three kinds of 25-layer Langmuir-Blodgett films of lead stearate were measured, using a high resolution reflection Kratky camera system. The accurate thicknesses of a bilayer were evaluated by the modified Bragg law. According to the microstrain, the paracrystalline and the Wilson models, line breadths of the reflections were separated into broadening due to crystallite size and lattice distortion. The crystallite sizes thus obtained agree well with those calculated from the thickness and number of bilayers. Regardless of which distorion model is used, gaussian profiles always give a larger lattice distortion than Cauchy profiles. To describe the lattice distortion of the present specimens, the microstrain and the Wilson models are more favourable than the paracrystalline model. The lattice distortion has been proven to be very sensitive to preparation conditions such as surface pressure and surface treatment of the substrate.

Characterization of long-periodic layered structures by X-ray diffraction I: A system for small angle and intermediate angle X-ray diffraction using a reflection kratky camera

Abstract A high resolution camera has been developed for the small angle X-ray diffraction measurement of long-periodic layered structures such as Langmuir-Blodgett multilayers, superlattices and liquid crystals. A block collimation system known as a Kratky camera is used to produce a very narrow incident beam. The camera is mounted on a computer-controlled goniometer whose sample holder is rotated around a vertical Θ axis by a pulse motor. Measurements can be carried out in a θ-2θ scan, and also in θ or 2θ scans. Processing of the collected data includes smoothing, and correction for absorption, polarization factor and instrumental broadening. The performance of the present system has been demonstrated by observation of diffraction patterns of a Langmuir-Blodgett film of cadmium arachidate and a GaAs/AlAs superlattice.

Characterization of industrial materials by small angle X-ray scattering

Small angle X-ray scattering (SAXS) techniques have enabled remarkable progress to be made in both the experimental devices and algorithms of data processing. We have applied SAXS to the characterization of common industrial materials such as carbon fibres,γ-alumina, and poly-propylene films. For carbon fibres, the microporosity has been investigated by estimating the cross-sectional dimensions of the microvoids in the powdered specimens as well as in the aligned fibre bundles. The average particle size ofγ-alumina has been evaluated, and related to the heat-treatment conditions. Correlation-function analysis has revealed the changes in lamellar structure of polypropylene films induced by annealing. SAXS is shown to have the potential to be widely used as a practical method for characterizing materials of industrial importance.