Structure Investigations of Islands with Atomic-Scale Boron-Carbon Bilayers in Heavily Boron-Doped Diamond Single Crystal: Origin of Stepwise Tensile Stress.

The detailed studies of the surface structure of synthetic boron-doped diamond single crystals using both conventional X-ray and synchrotron nano- and microbeam diffraction, as well as atomic force microscopy and micro-Raman spectroscopy, were carried out to clarify the recently discovered features in them. The arbitrary shaped islands towering above the (111) diamond surface are formed at the final stage of the crystal growth. Their lateral dimensions are from several to tens of microns and their height is from 0.5 to 3 µm. The highly nonequilibrium conditions of crystal growth enhance the boron solubility and, therefore, lead to an increase of the boron concentrations in the islands on the surface up to 1022 cm-3, eventually generating significant stresses in them. The stress in the islands is found to be the volumetric tensile stress. This conclusion is based on the stepwise shift of the diamond Raman peak toward lower frequencies from 1328 to 1300 cm-1 in various islands and on the observation of the shift of three low-intensity reflections at 2-theta Bragg angles of 41.468°, 41.940° and 42.413° in the X-ray diffractogram to the left relative to the (111) diamond reflection at 2theta = 43.93°. We believe that the origin of the stepwise tensile stress is a discrete change in the distances between boron-carbon layers with the step of 6.18 Å. This supposition explains also the stepwise (step of 5 cm-1) behavior of the diamond Raman peak shift. Two approaches based on the combined application of Raman scattering and X-ray diffraction data allowed determination of the values of stresses both in lateral and normal directions. The maximum tensile stress in the direction normal to the surface reaches 63.6 GPa, close to the fracture limit of diamond, equal to 90 GPa along the [111] crystallographic direction. The presented experimental results unambiguously confirm our previously proposed structural model of the boron-doped diamond containing two-dimensional boron-carbon nanosheets and bilayers.

[The use of hybrid CAD/CAM materials for rehabilitation of patients with dental hard tissues defects]. / Osobennosti ispol'zovaniia gibridnykh CAD/CAM-materialov dlia reabilitatsii patsientov s defektami tverdykh tkanei zubov.

The article presents a clinical case demonstrating the effectiveness of hybrid materials for rehabilitation of patients with dental hard tissues defects. The patient presented with insufficient restoration of teeth 1.3, which was replaced by hybrid material Lava Ultimate fixed with adhesive protocol. The use of hybrid material allowed minimally invasive preparation of dental hard tissues and perfect marginal fit, as well as prevented the attrition of antagonists. The important issue in oral rehabilitation with hybrid materials is to respect adhesion protocol details.

Refraction and ultra-small-angle scattering of X-rays in a single-crystal diamond compound refractive lens.

In this work a double-crystal setup is employed to study compound refractive lenses made of single-crystal diamond. The point spread function of the lens is calculated taking into account the lens transmission, the wavefront aberrations, and the ultra-small-angle broadening of the X-ray beam. It is shown that, similarly to the wavefront aberrations, the ultra-small-angle scattering effects can significantly reduce the intensity gain and increase the focal spot size. The suggested approach can be particularly useful for the characterization of refractive X-ray lenses composed of many tens of unit lenses.

[Clinical-experimental study of efficacy of tablets "corega tаbs for partial dentures" in individuals with arc dentures]. / Kliniko-éksperimental'noe izuchenie éffektivnosti primeneniia tabletok "corega tabs dlia chastichnykh protezov" u patsientov s dugovymi zubnymi protezami.

The aim of the study was to assess clinical efficacy of corega tabs cleaning tablets for dentures in 36 somatically intact patients aged 35 to 64 years with Class I and II defects of the lower jaw dentition treated with partial arc dentures. Control group included 30 persons of similar age and condition of the oral cavity using traditional oral hygiene means. The results of the study proved the absence of pathological galvanical phenomenas in metallic parts of arc dentures after exposure to a solution obtained by dissolving the cleansing tablets for partial dentures corega tabs. The shown effect of passivation of the metallic parts of the arc prostheses may be seen as a preventive measure for the development of oral galvanosis in this group of patients.