By tuning the X-ray energy from synchrotron radiation very close to an absorption edge of a consituent atom in a crystal, it is possible to induce the X-ray resonant scattering as much as the normal scattering. Based on the latest dynamical theory for absorbing crystals, the diffraction from a perfect crystal is described.
General ideas of usages of anormalous dispersion effects are given in the limit of kinematical diffraction. They are categorized in two groups. One is to utilize phase effects due to imaginary part of anomalous dispersion. The other is to change the contrast of atoms which show dispersion effects. The latter is normally done by changing the real part of anomalous dispersion at the lower energy side of absorption edge where the backgroud is much lower than that of higher energy side.
This paper describes the principles to determine the distribution of metal elements in a crystal with an x-ray diffraction method. When the elements have similar atomic numbers, the metal distribution is not determined precisely with a conventional x-ray diffraction method. The precision can be improved if we use the anomalous dispersion effect. To determine the distribution of three kinds of elements we need two sets of diffraction data different in x-ray wavelength using anomalous dispersion effect. The anomalous dipersion method is also effective in determining the position of each element in a metal site.
The anomalous X-ray scattering method has recently received much attention for obtaining the fine structure of disordered materials, coupled with the synchrotron radiation source. This paper demonstrates the usefulness of the AXS method for determining the local environmental structure around a specific element as a function of distance, by providing fundamentals with some selected examples of high temperature CuBr liquid, 70GeO230Bi2O3 oxide glass and Zr-Y-Al-Ni metallic glasses.
Owing to linearly polarized nature of synchrotron radiations, X-ray absorption spectroscopy allows us to investigate anisotropic local structures and vibrations. The determination of surface structures of molecularly chemisorbed SO2 on Pd (100) and Ni (100) is briefly reviewed as a suitable demonstration of the technique. Anisotropic vibrations of the surface S-Ni bonds in S/Ni (110) - c (2×2) are also discussed.
We will describe a rather new X-ray structural technique, Diffraction Anomalous Fine Structure (DAFS), in which the Bragg diffraction intensities of a fixed momentum transfer is measured as a function of the incident X-ray energy. This technique can provide the same short-range structural information as XAFS. Because DAFS combines the capabilities of diffraction and XAFS into a single technique, it has two enhanced sensitivities compared to the separate technique. These are “spatial selectivity” and “ site selectivity”. In this chapter semiconductor interface structure study as an example for spatial selectivity and structural study of high Tc superconductor as an example for site selectivity will be shown.
Diffraction and scattering experiments at x-ray wavelengths close to an absorption edge has made it possible to distinguish even different valence states. Anomalous scattering factors derived from the XANES absorption data and the chemical shift show that the difference between f' (Fe2+) and f' (Fe3+) reaches up to 2.5. Here we demonstrate the possibility of va-lence-difference contrast methods.
The multiple wavelength anomalous dispersion (MAD), a powerful direct method, has been modified and applied for the first time to the interface structural analysis. This allows us to separate heavy and light atoms, and so deduce the structure.
Weak diffuse scattering intensitites due to the structural fluctuations in materials can be detected with the use of X-ray anomalous scattering phenomena. The study applied to the two alloy systems, which have constituent atoms nearby in atomic number, is presented.
Physical properties involved in X-ray polarization effects on X-ray diffraction near an absorption edge and the applications in crystallography and crystal-physics are briefly reviewed. Violence of the extinction rules by a screw axis and for a glide plane is described as introduction to X-ray diffraction using an anisotropic tensor of susceptibility. Experimental results concerning to the polarization effect are also surveyed.
This paper presents a white X-ray magnetic diffraction method, a new tool for studying microscopic magnetic moments in ferromagnetic materials which utilizes circulay polarized synchrotron radiation. First an overview is given on synchrotron radiation researches of magnetic materials, and then the white X-ray magnetic diffraction is introduced. Two examples of the application to ferromagnets are shown; one is the magnetic form factor measurement of Fe by Collins et al. who have developed the method, and the other is the measurement of form factors of the orbital and spin magnetic moments of uranium in UTe by the authors.
High-angular-resolution powder-diffraction-experiments for the crystal structure analysis using synchrotron radiation are described. Topics discussed in this chapter are: 1) long horizontal parallel slits and crystal analyzer, 2) the accurate measurement of unit-cell parameters in the p.p.m. order, 3) the multiple-detector system for powder diffractometer and 4) the high-angular-resolution diffraction data and the accuracy of crystal structure analysis.
Structural studies on a sub-micrometer-sized crystal grain and on micrometer-sized area are introduced on the equipment and method of structure refinement based on the Laue intensities obtained with polychromatic synchrotron radiation. Some examples of analyses are also given.
Recent developments of X-ray optics for fabrication of synchrotron X-ray microprobe in hard X-ray region were reviewed. Potentail ability of X-ray microprobe was demonstrated through the XRF analysis of biological samples and μ-XANES analysis of meteorite samples.
Characterization of thin films with x-ray total reflection is introduced. Titanium silicite thin films are studied by grazing incidence x-ray diffraction. The epitaxial C49-TiSi2 grains are formed on heavily BF2 ion implanted Si (001) substrate after low temperature annealing, and they suppress the phase transition from C49 to C54 during high temperature annealing. SiO2 thin films are investigated by x-ray reflectivity analysis. Thermal oxides have always the high density interface layer of -1 nm in thickness. Extremely thin native oxides on Si is also characterized in a function of chemical cleaning solutions.
The structure of crystal surfaces is studied by X-Ray diffraction. The Si (111) √3×√3-Bi structure was analyzed in terms of reflectivity, and the coverage-dependent structures were unambiguously distinguished. The structure of the dimer in Si (001) 2×1 was determined.
Characterization by high precision lattice spacing measurement using synchrotron radiation is reviewed, Relationship between lattice spaciing and residual strain, dislocation density, composition of raw material and cell structures are given.
The ultra-small-angle X-ray scattering (USAXS) is a very powerful technique for a structural study in the order of several thousand Å to micrometers. In this study, the colloidal crystal structure in aqueous dispersion of latex particle has been studied by USAXS using the advantage that USAXS can be applied to turbid systems. The nearest neighbor interparticle distance in colloidal crystal first increased with increasing ionic strength, and passing through a maximum then decreased. This observation was never reported both by other experimental technique such as microscope and theoretical considerations. It was found that the maximum position was well scaled by product of inverse Debye screening length and particle radius for various kinds of latex particles and that this maximum is the solid-liquid transition point of colloidal crystal. This observation may mean that some additional factor for interparticle interaction should be taken into account.
Recent studies on lattice defects in silicon single crystals using synchrotron radiation topography are reviewed. Two types of methods are described, the plane wave topography using highly collimated x-rays with an angular divergence of less than 0.01 arcsec and the Lang topography using high energy x-rays of 60keV. Experiments of imaging of grown-in microdefects in FZ- and CZ-silicon crystals and growth striations in MCZ-Si crystals show that these methods are highly sensitive to minute lattice strain of the order of 10-7 which could not be measured by the conventional x-ray topograpy.
The X-ray diffraction has a long histry of being used for observation of electron-density distributions in crystalline substances. However, the accuracy of resulting densities remains still unsatisfactory except the special cases where the Pendellösung fringe method has been applied. In the process to derive accurate structure factors, the Fourier coefficients of electron-density distributions, from integrated intensities, the extinction effects act as the largest impediments. In order to avoid the extinction effects, it is suggested to use very short wavelength radiations and/or very small specimens in the intensity collections. Synchrotron radiations with high energy and high brilliance have possibility to realize such measurements. The present review describes outlines of studies carried out along this line employing synchrotron radiations.
Recent developments of powder diffraction studies under pressure are introduced. Two types of high pressure apparatuses, a multi anvil type and a diamond anvil type, are successfully applied to give various interesting results such as topological mechanism of transition, structural transition of ionic melts, structure determination of high pressure unknown phase, phonon related structural transition, pressure dependence of electron density distribution by maximum entropy method in conjunction with the development of high pressure and detecting techniques.The studies are performed at high and low temperature as well as at room temperature.