Atomic-scale structure of the SrTiO3(001)-c(6x2) reconstruction: Experiments and first-principles calculations

The c(6x2) is a reconstruction of the SrTiO3(001) surface that is formed between 1050-1100oC in oxidizing annealing conditions. This work proposes a model for the atomic structure for the c(6x2) obtained through a combination of results from transmission electron diffraction, surface x-ray diffraction, direct methods analysis, computational combinational screening, and density functional theory. As it is formed at high temperatures, the surface is complex and can be described as a short-range ordered phase featuring microscopic domains composed of four main structural motifs. Additionally, non-periodic TiO2 units are present on the surface. Simulated scanning tunneling microscopy images based on the electronic structure calculations are consistent with experimental images

Epitaxial checkerboard arrangement of nanorods in ZnMnGaO4 films studied by x-ray diffraction

The intriguing nano-structural properties of a ZnMnGaO4 film epitaxially grown on MgO (001) substrate have been investigated using synchrotron radiation-based x-ray diffraction. The ZnMnGaO4 film consisted of a self-assembled checkerboard (CB) structure with perfectly aligned and regularly spaced vertical nanorods. The lattice parameters of the orthorhombic and rotated tetragonal phases of the CB structure were analyzed using H-K, H-L, and K-L cross sections of the reciprocal space maps measured around various symmetric and asymmetric reflections of the spinel structure. We demonstrate that the symmetry of atomic displacements at the phases boundaries provides the means for coherent coexistence of two domains types within the volume of the film

Low resistance Cu[3]Ge compounds formation by the lowtemperature treatment of Cu/Ge system in atomic hydrogen

The research deals with the regularities for Cu[3]Ge compound formation under the low temperature treatment of a double-layer Cu/Ge system deposited on i-GaAs substrate in atomic hydrogen flow. The treatment of a Cu/Ge/i-GaAs system with layer thicknesses, respectively, of 122 and 78 nm, in atomic hydrogen with a flow rate of 10{15} at.·сm{-2} s{-1} for a duration of 2.5{-10} min at room temperature, leads to an interdiffusion of Cu and Ge and formation of a polycrystalline film containing stoichiometric phase Cu[3]Ge. The film consists of vertically oriented grains of dimensions 100-150 nm and has a minimum specific resistance of 4.5 [mu omega] сm. Variation in the treatment duration of Cu/Ge/i-GaAs samples in atomic hydrogen affects Cu and Ge distribution profiles, the phase composition of films formed, and the specific resistance of the latter. As observed, Cu3Ge compound synthesis at room temperature demonstrates the stimulative effects characteristic of atomic hydrogen treatment for both Cu and Ge diffusion and for the chemical reaction of Cu[3]Ge compound generation. Activation of these processes can be conditioned by the energy released during recombination of hydrogen atoms adsorbed on the surface of a Cu/Ge/i-GaAs sample

Theory and Applications of X-ray Standing Waves in Real Crystals

Theoretical aspects of x-ray standing wave method for investigation of the real structure of crystals are considered in this review paper. Starting from the general approach of the secondary radiation yield from deformed crystals this theory is applied to different concreat cases. Various models of deformed crystals like: bicrystal model, multilayer model, crystals with extended deformation field are considered in detailes. Peculiarities of x-ray standing wave behavior in different scattering geometries (Bragg, Laue) are analysed in detailes. New possibilities to solve the phase problem with x-ray standing wave method are discussed in the review. General theoretical approaches are illustrated with a big number of experimental results.Comment: 101 pages, 43 figures, 3 table

Features of the course of coronavirus infection in patients after thoracic and cardiac surgery

Objective: To study the features of the coronavirus infection course in cardiosurgical and thoracic patients to determine the factors potentially affecting the possibility of lethal outcome. To identify the predictors of fatal outcome based on the analyses of the features of the coronavirus infection course in this category of patients.Material and methods: During the analyzed period 80 patients from the departments of thoracic surgery and cardiac surgery were transferred to the infectious diseases department: 20 patients from the cardiac surgery department (CSD) – group 1; 60 patients from the thoracic surgery departments (TSD) – group 2. A control group number 3 consisting of 59 non-thoracic and non-cardiosurgical patients was also formed. According to the disease outcome the patients were divided into two groups: group 1 – fatal outcome, group 2 – recovery.Results: Out of 80 patients, lethal outcome was recorded in 25 cases: 22 patients of the thoracic profile (36% of the total number of transferred from this department) and 3 patients of the cardiosurgical profile (15% of the total number of those transferred from the cardiac surgery department). 20 out of 20 cardiac patients had been operated on the day before, 49 out of 60 thoracic patients also underwent surgery. 3 people from the group of non-operated patients transferred from departments of thoracic surgery died. Moreover, after pneumonectomy, fatal outcome was recorded in 7 out of 8 cases (87.5%).Conclusion: During the analyses of indicators it was revealed that the number of fatal outcomes in patients of the thoracic profile with COVID-19 infection is higher than of the cardiosurgical profile and in the infectious diseases department. Presumably, this is due to the fact that coronavirus infection affects the lungs to a greater extent, and in patients with a thoracic profile (in particular, those who have undergone resection interventions), the volume of the lung parenchyma is initially reduced. This is confirmed particularly by the highest percentage of fatal outcomes after pneumonectomy. Cardiosurgical patients after surgical interventions do not have a reduction in the functioning lung parenchyma, which creates an additional “reserve” for recovery. Moreover, men predominate among patients of the thoracic profile, with the survival rate lower in all groups compared to women. Patients transferred from thoracic departments showed higher rates of systemic inflammation, which indicates a more severe course of the viral infection and the possible development of complications.When analyzing the predictors of lethal outcome, the following factors were identified: male gender and, in general, a more severe course of a viral infection (low saturation, a high percentage of lung lesions on CT, more pronounced changes in laboratory screening). The studied factors are associated with a large number of fatal outcomes in thoracic and cardiac surgery patients. Among the factors that do not affect the prognosis are diabetes mellitus, stroke and myocardial infarction in history.Thus, patients diagnosed with coronavirus infection that developed after thoracic surgery had the most unfavorable prognosis. The revealed patterns are of interest for optimizing the routing of this category of patients in order to prevent coronavirus infection

Triple‐crystal x‐ray diffraction analysis of reactive ion etched gallium arsenide

This is the published version. Copyright 1994 American Institute of PhysicsThe effect of BCl3 reactive ion etching on the structural perfection of GaAs has been studied with diffuse x‐ray scattering measurementsconducted by high‐resolution triple‐crystal x‐ray diffraction. While using a symmetric 004 diffraction geometry revealed no discernible differences between etched and unetched samples, using the more surface‐sensitive and highly asymmetric 113 reflection revealed that the reactive ion etched samples etched displayed less diffusely scattered intensity than unetched samples, indicating a higher level of structural perfection. Increasing the reaction ion etch bias voltage was found to result in decreased diffuse scattering initially, until an apparent threshold voltage was reached, after which no further structural improvement was observed. Furthermore, we have shown that this reduction in process‐induced surfacestructural damage is not due merely to the removal of residual chemical‐mechanical polishing damage

High-resolution study of dynamical diffraction phenomena accompanying the Renninger (222/113) case of three-beam diffraction in silicon

The effect of the total reflection of the incident beam into the 222 reflected beam in the Renninger (222/113) case in Si was experimentally observed by using a highly monochromatic beam with high angular collimation in both the vertical and horizontal planes

A novel thick-layer electrochemical cell for in situ X-ray diffraction.

In this article we describe an electrochemical cell allowing x-ray diffraction from the working electrode in situ. The key feature of our novel design is a hemispherical fused silica dome serving as the x-ray window. The electrode is covered with a thick layer of electrolyte during the x-ray measurement, avoiding mass transport limitations inherent to common setups, where the thickness of the electrolyte layer is strongly reduced for the diffraction experiment. This allows in particular the monitoring of electrode processes which are associated with the consumption of species from solution and/or generation of a significant amount of reaction products. All solid angles in the hemisphere above the sample surface are accessible for the incoming and outgoing x-ray beam at a constant path length in the electrolyte. Thus, our cell is perfectly suitable for in situ surface x-ray diffraction, truncation rod scattering, and specular reflectivity measurements. We demonstrate the performance of the new cell by monitoring the electrochemical stripping of a 50 nm thick amorphous As layer on GaAs(001) in 0.5 M H22SO44 in situ with x rays