Alexander Ulyanenkov

Structural Characterization of BiFeO3 Thin Films by Reciprocal Space Mapping

High-resolution X-ray diffraction reciprocal space mapping (HRXRD-RSM) was applied for the structural characterization of epitaxial BiFeO3 thin film grown on SrRuO3-coated (001) SrTiO3 single crystal substrate with a variety of film thicknesses ranging from 15 to 500 nm. Distinguishing monoclinic structure from rhombohedral or tetragonal structures was accomplished with a set of HRXRD-RSMs measured for several hkl diffraction conditions. The BiFeO3 thin films showed both monoclinic and tetragonal structures depending on film thickness. Tetragonal structure was observed for film thicknesses below 50 nm and was highly strained due to epitaxial strain, while films with film thickness thicker than 50 nm showed monoclinic structure. No BiFeO3 thin films showed bulk rhombohedral structure. This structural change in BiFeO3 thin film may play an important role in the enhanced ferroelectricity observed.

Two-level system in a one-mode quantum field: numerical solution on the basis of the operator method

Accurate eigenvalues and eigenfunctions of a two-level system interacting with a one-mode quantum field are calculated numerically. A special iteration procedure based on the operator method permits one to consider the solution within a wide range of the Hamiltonian parameters and to find the uniformly approximating analytical formula for the eigenvalues. Characteristic features of the model are considered, such as the level intersections, the population of the field states and the chaotization in the system through the doubling of the frequencies.

Theoretical concepts of X-ray nanoscale analysis

Basic principles of the interaction between X-rays and matter.- X-ray reflectivity.- High-resolution X-ray diffraction.- Grazing-incidence small-angle X-ray scattering.- Theory of X-ray scattering from imperfect crystals.- X-ray diffraction for evaluation of residual stresses in polycrystals.- Methods of mathematical and physical optimization of X-ray data analysis.

High-resolution x-ray diffraction investigation of relaxation and dislocations in SiGe layers grown on (001), (011), and (111) Si substrates

This work presents a detailed characterization, using high-resolution x-ray diffraction, of multilayered Si1-xGex heterostructures grown on (001), (011), and (111) Si substrates by reduced pressure chemical vapor deposition. Reciprocal space mapping has been used to determine both the strain and Ge concentration depth profiles within each layer of the heterostructures after initially determining the crystallographic tilt of all the layers. Both symmetric and asymmetric reciprocal space maps were measured on each sample, and the evaluation was performed simultaneously for the whole data set. The ratio of misfit to threading dislocation densities has been estimated for each individual layer based on an analysis of diffuse x-ray scattering from the defects.

Characterization of SiGe thin films using a laboratory X-ray instrument

This article reports the characterization of thin SiGe/Si(100) epilayers using reciprocal space maps measured by a laboratory X-ray instrument and a high-resolution X-ray diffraction study of partially relaxed SiGe/Si thin films.

Non-perturbative description of quantum systems

Capabilities of approximate methods in quantum theory.- Basics of the operator method.- Applications of OM for one-dimensional systems.- Operator method for quantum statistics.- Quantum systems with several degrees of freedom.- Two-dimensional exciton in magnetic field with arbitrary strength.- Atoms in the external electromagnetic fields.- Many-electron atoms.- Systems with infinite number of degrees of freedom.

Characterization of dislocations in germanium layers grown on (011)- and (111)-oriented silicon by coplanar and noncoplanar X-ray diffraction

The generalization of the theoretical approach suggested by Kaganer et al. [Phys. Rev. B, (1997 ▶), 55, 1793–1810] to an arbitrary surface orientation, arbitrary dislocation line direction and noncoplanar measurement scheme was developed. It was applied to study the dislocation microstructure of Ge films on Si(011) and Si(111) based on a set of reciprocal space maps and profiles measured in noncoplanar geometry.

Covariant description of X-ray diffraction from anisotropically relaxed epitaxial structures

A general theoretical approach to the description of epitaxial layers with essentially different cell parameters and in-plane relaxation anisotropy is presented.

Interference of parametric X-ray and coherent Bremsstrahlung radiation from nonrelativistic electrons: application to the phase analysis in crystallography

The intensity of coherent X-radiation (CXR) from a relativistic electron beam interacting with the crystal [Feranchuk, Ulyanenkov, Harada & Spence (2000). Phys. Rev. E, 62, 4225-4234] is studied in view of its application to the phase determination problem. The analysis of CXR spectra is shown to permit an independent measurement of unit-cell structure factors, defined by both the electron-density distribution and the nucleus positions. In relation to these structure factors, two new types of Patterson function are introduced that can simplify the solution of crystal structure.

Incorporation of interfacial roughness into recursion matrix formalism of dynamical X-ray diffraction in multilayers and superlattices

Interfacial roughness is considered as a transition layer. A method of calculation of diffraction scans from multilayered structures with interfacial roughness, which is both fast and free of numerical errors, is developed.