Anomalous scattering method in crystallography on the basis of parametric X-radiation

Spectra of parametric X-radiation (PXR) in the range of anomalous dispersion of atoms of a crystallographic unit cell are theoretically analyzed. Characteristics of PXR are calculated for both ultrarelativistic (E>=50 MeV) and nonrelativistic (E~=100 keV) electrons interacting with complex organic crystals. The analysis of the PXR angular distribution is shown to permit the realization of the anomalous scattering method for the direct measurement of structure amplitude phases

Radical increase of the parametric X-ray intensity under condition of extremely asymmetric diffraction

Parametric X-ray radiation (PXR) from relativistic electrons moving in a crystal along the crystal-vacuum interface is considered. In this geometry the emission of photons is happening in the regime of extremely asymmetric diffraction (EAD). In the EAD case the whole crystal length contributes to the formation of X-ray radiation opposed to Laue and Bragg geometries, where the emission intensity is defined by the X-ray absorption length. We demonstrate that this phenomenon should be described within the dynamical theory of diffraction and predict a radical increase of the PXR intensity. In particular, under realistic electron-beam parameters, an increase of two orders of magnitude in PXR-EAD intensity can be obtained in comparison with conventional experimental geometries of PXR. In addition we discuss in details the experimental feasibility of the detection of PXR-EAD.Comment: 9 pages, 5 figure

Dynamical diffraction theory for the parametric X-rays and coherent bremsstrahlung

The various mechanisms of X-ray radiation from relativistically charged particles in a crystal are analyzed from a common point of view, based on quantum electrodynamics in a medium. Parametric X-rays (PXR), diffraction radiation (DR) and coherent bremsstrahlung (CB) lead to different contributions to the amplitude of the radiation process but because of their interference they cannot be considered separately in the radiation intensity. The role of the dynamical diffraction effects and the coherent bremsstrahlung is considered to be dependent on the crystal parameters and particle energy. The conception of the high resolution parametric X-rays (HRPXR) is introduced and the universal radiation distribution, which can simplify the analysis of the results for this case is also considered. The possible applications of HRPXR are discussed

Self-consistent approach to x-ray reflection from rough surfaces

A self-consistent analytical approach for specular x-ray reflection from interfaces with transition layers I. D. Feranchuk et al., Phys. Rev. B 67, 235417 2003 based on the distorted-wave Born approximation DWBA is used for the description of coherent and incoherent x-ray scattering from rough surfaces and interfaces. This approach takes into account the transformation of the modeling transition layer profile at the interface, which is caused by roughness correlations. The reflection coefficients for each DWBA order are directly calculated without phenomenological assumptions on their exponential decay at large scattering angles. Various regions of scattering angles are discussed, which show qualitatively different dependence of the reflection coefficient on the scattering angle. The experimental data are analyzed using the method developed

Bunches of misfit dislocations on the onset of relaxation of Si0.4_{0.4}Ge0.6_{0.6}/Si(001) epitaxial films revealed by high-resolution x-ray diffraction

The experimental x-ray diffraction patterns of a Si$_{0.4}$Ge$_{0.6}$/Si(001) epitaxial film with a low density of misfit dislocations are modeled by the Monte Carlo method. It is shown that an inhomogeneous distribution of 60$^\circ$ dislocations with dislocations arranged in bunches is needed to explain the experiment correctly. As a result of the dislocation bunching, the positions of the x-ray diffraction peaks do not correspond to the average dislocation density but reveal less than a half of the actual relaxation

Description of x-ray reflection and diffraction from periodical multilayers and superlattices by the eigenwave method

The analytical solution of recurrent equations for amplitudes of electromagnetic field is found for description of x-ray reflection and diffraction from periodical multilayered media. The method proposed uses the Bloch eigenwaves approach for periodical structure, which reduces considerably the computer time required for simulation of diffracted/reflected x-ray intensity and, therefore, accelerates the fitting trial-and-error procedure for sample model parameters. Numerical examples and fit results for experimental x-ray data are provided to demonstrate the effectiveness of method. A new parameter describing the fluctuation of superlattice period is introduced and its influence on experimental data interpretation is discussed

Parametric x-ray radiation and coherent bremsstrahlung from nonrelativistic electrons in crystals

A theoretical analysis of radiation spectra produced during the coherent interaction of nonrelativistic electrons with crystals has been carried out. The output intensity has been found to be the result of interference between two distinguishable phenomena, coherent Bremsstrahlung and parametric x-ray radiation. The latter is determined by a coherent summation of transition radiation from electrons interacting with successive crystallographic planes. The interference is shown to be considerable for the case of nonrelativistic electrons, and so allows us to describe quantitatively the experiments of Korobochko et al. Zh. Eksp. Teor. Fiz. 48, 1248 (1965) [Sov. Phys. JETP 21, 834 (1965)] and Reese et al. Philos. Mag. A 49, 697 (1984). The conditions for possible application of coherent x-ray radiation, a comparison with synchrotron radiation, and the requirements for experimental setup are discusse