Forming of CdZnTe thin films grown by hot wall epitaxy and their properties

In this work morphological, X-ray structural and optical studies of CdZnTe films grown by hot wall epitaxy method at relatively low substrate temperatures were performed. Possible mechanisms and processes of self-organization that occur during the growth of such structures are considered. It is shown that at thickness of film more than 130 nm on the surface, large (lateral size 150 - 200 nm, height - up to 10 nm) and small crystals are observed. The thicknesses and energy of the band gap width of the CdZnTe films grown at different growth times were determined. It is shown that the film absorption edge in the transmission spectra depends on the film thickness and the reasons for the shift of the film absorption edge are discussed.

Hydrogen properties in an organic molecule revealed by XFEL and electron crystallography

Structure analysis of small crystals is important in synthetic organic chemistry, pharmaceutical and material sciences, and related areas, as the conformation of these molecules may differ in large and small crystals, thus affecting the interpretation of their functional properties and drug efficacy. From small crystals, X-ray and electron beams could furnish electron densities and Coulomb potentials of target molecules, respectively. The two beams provide distinctly different information, and this potential has not been fully explored. Here we present the detailed structure of an organic molecule, rhodamine-6g by X-ray free-electron laser (XFEL) and electron crystallography from the same sample batch of microcrystals. This is the first organic molecular structure determined using XFEL at subatomic resolution. Direct comparison between the electron-density and the Coulomb-potential maps together with theoretical models based on Poisson’s equation shows that the position of hydrogen atoms depends on bond type and charge distribution. The combined approach could lead to better insights into their chemical and/or binding properties for a broad range of organic molecules.

Innovative Ag–TiO2 Nanofibers with Excellent Photocatalytic and Antibacterial Actions

Ag–TiO2 nanostructures were prepared by electrospinning, followed by calcination at 400 °C, and their photocatalytic and antibacterial actions were studied. Morphological characterization revealed the presence of one-dimensional uniform Ag–TiO2 nanostructured nanofibers, with a diameter from 65 to 100 nm, depending on the Ag loading, composed of small crystals interconnected with each other. Structural characterization indicated that Ag was successfully integrated as small nanocrystals without affecting much of the TiO2 crystal lattice. Moreover, the presence of nano Ag was found to contribute to reducing the band gap energy, which enables the activation by the absorption of visible light, while, at the same time, it delays the electron–hole recombination. Tests of their photocatalytic activity in methylene blue, amaranth, Congo red and orange II degradation revealed an increase by more than 20% in color removal efficiency at an almost double rate for the case of 0.1% Ag–TiO2 nanofibers with respect to pure TiO2. Moreover, the minimum inhibitory concentration was found as low as 2.5 mg/mL for E. coli and 5 mg/mL against S. aureus for the 5% Ag–TiO2 nanofibers. In general, the Ag–TiO2 nanostructured nanofibers were found to exhibit excellent structure and physical properties and to be suitable for efficient photocatalytic and antibacterial uses. Therefore, these can be suitable for further integration in various important applications.

Structure of the active pharmaceutical ingredient bismuth subsalicylate

Structure determination of pharmaceutical compounds is invaluable for drug development but is challenging for those that form as small crystals with defects. Bismuth subsalicylate (BSS), among the most commercially significant bismuth compounds, is an active ingredient in over-the-counter medications such as Pepto-Bismol, used to treat dyspepsia and H. pylori infections. Despite its century-long history, the structure has remained unknown. Three-dimensional electron diffraction and hierarchical clustering analysis were applied on select data from ordered crystals, revealing a layered structure. In other less ordered crystals, high-resolution scanning transmission electron microscopy revealed variations in the stacking of layers. Together, these modern electron crystallography techniques provide a new toolbox for structure determination of active pharmaceutical ingredients and drug discovery, demonstrated by this study of BSS.

Electrosynthesis and characterization of lead dioxide–perfluorobutanesulfonate composite

The effect of potassium perfluorobutanesulfonate on the kinetic features of electrodeposition of lead dioxide from methanesulfonate electrolytes has been investigated. The introduction of C4F9SO3K into the lead dioxide deposition electrolyte leads to insignificant inhibition of the Pb2+ electrooxidation process, while the mechanism of the process does not change. A composite coating is formed upon deposition of coatings from electrolytes containing surfactants. The surface of a composite material consists of a mixture of clearly expressed large crystalline blocks with sharp angles and small crystals. Energy dispersive X-ray analysis revealed the satisfactory distribution of modifying elements in the entire sample bulk, and not only on the coating surface. It was shown that the electrocatalytic activity of lead dioxide–perfluorobuthanesulfonate composite differs from the undoped sample. The oxygen evolution reaction slightly decelerates on a PbO2–C4F9SO3K composite. The Tafel slopes in 1 M HClO4 calculated from these curves plotted in semilogarithmic coordinates are 136 and 145 mV dec–1 for undoped sample and lead dioxide-surfactant composite, respectively. The reaction of electrochemical oxidation of p-chlorophenol is characterized by the pseudo-first order kinetics with respect to the initial compound. The use of doped C4F9SO3K lead dioxide as an anode leads to the inhibition of the process of oxygen evolution and an almost one and a half higher rate of electrochemical conversion of 4-chlorophenol to aliphatic compounds.

Unidirectional crystallization and 3D structure of ternary four-component eutectic of B4C-NbB2-SiC system

Purpose. To investigate the laws of crystallization and formation of 3D morphology of ternary eutectics in system B4C-NbB2-SiC. Research methods. SEM (SE, BSE), РСМА (EDS, WDS), XRD. Results. The micro- and macro-morphology of eutectic colonies in alloys of the system NbB2-SiC-В4С formed during directional crystallization have been investigated. The obtained patterns are embodied in a 3D structural model of (B4C+NbB2+SiC) eutectic cell and from these result, a microscopic kinetics of crystallization of this cell was proposed. The continuity of eutectic phase dendrites from nucleation to the end of growth and inadequacy of ideas about eutectic as a mechanical mixture of small crystals of eutectic phases were shown. Scientific novelty. For the first time a 3D model of a three-phase 4-component eutectic cell of eutectic colony was built. For the first time the possibility of combined microscopic crystallization kinetics of a three-phase eutectics was revealed, including both paired cooperative microscopic kinetics of (SіC+ NbB2) growth and the kinetics of autonomous growth of the third eutectic phase B4C. Practical value. Revealing the pattern of micro and macrostructure formation of a three-phase eutectics, which was formed in the course of directional crystallization, opens up technological prospects for purposeful control of the structure and properties of eutectic alloy due to the change of micro and macro morphological constituents, including the method of modification.

Pyrite Morphology and δ34S as Indicators of Deposition Environment in Organic-Rich Shales

This study is focused on the mineralogical, chemical, and isotopic characterization of pyrites from the rocks of the Bazhenov Formation (Upper Jurassic–Lower Cretaceous organic-rich shales, Western Siberia, Russia). Scanning electron microscopy (SEM) revealed pyrites of different morphologies: small and large framboids, small crystals, and large euhedral crystals; all morphotypes were usually combined into aggregates. Isotope ratio mass spectrometry (IRMS) and secondary ion mass spectrometry (SIMS) showed that small framboids and microcrystalline pyrite are isotopically light, with δ34SCDT varying from −55 to −20‰. Large framboids and euhedral crystals of pyrite are isotopically heavy with δ34SCDT up to +26‰. Both morphology and δ34S were suggested to be controlled by the redox conditions and sedimentation regime. The abundance of small framboids suggests that pyrite sedimentation occurred under anoxic conditions; the presence of the large framboids and euhedral crystals of pyrite suggest the accumulation of sediments occurred at suboxic conditions, possibly in the presence of oxygen.

Textural and genetic relationships between glauconite and celadonite at the nanoscale: two different structural-compositional fields

Glauconite and celadonite coexist at the nanometre scale in Early Jurassic submarine volcanic rocks of the Betic Cordillera (southern Spain) as a result of microbial activity. Samples from the limit between the two micas, recognizable in scanning electron microscopy, have been extracted using the focussed ion beam technique and studied by high-resolution analytical electron microscopy. Both micas are present as randomly oriented differentiated small crystals in the boundary area. They define clearly distinct compositional fields with gaps affecting to Fe, Mg and K. At the lattice scale, celadonite shows a high degree of order, with homogeneous orientation of the visible lattice parameters being a difference from glauconite, formed by packets no more than 10-layers thick. Smectite layers were also detected alongside glauconite packets, in accordance with X-ray diffractograms which indicate that glauconite is a mica–smectite interstratification being more than 90 % mica layers. The compositional gap indicates that celadonite is not the endmember of the glauconitic series and the two micas represent two different structural tendencies of mica, with glauconite having more distorted octahedral sheets, indicated by systematically higher b parameters than celadonite.

Crystallisation in a two-dimensional granular system at constant temperature

We study the crystallisation processes occurring in a nonvibrating two-dimensional magnetic granular system at various fixed values of the effective temperature. In this system, the energy loss due to dissipative effects is compensated by the continuous energy input coming into the system from a sinusoidal magnetic field. When this balance leads to high values of the effective temperature, no aggregates are formed, because particles’ kinetic energy prevents them from aggregating. For lower effective temperatures, formation of small aggregates is observed. The smaller the values of the applied field’s amplitude, the larger the number of these disordered aggregates. One also observes that when clusters form at a given effective temperature, the average effective diffusion coefficient decreases as time increases. For medium values of the effective temperature, formation of small crystals is observed. We find that the sixth bond-orientational order parameter and the number of bonds, when considering more than two, are very sensitive for exhibiting the order in the system, even when crystals are still very small.