Single crystal growth, transport and scanning tunneling microscopy and spectroscopy of FeSe1-xSx

Single crystals of sulfur-substituted iron selenide, FeSe1-xSx, were grown within eutectics of molten halides, AlCl3/KCl, AlCl3/KCl/NaCl or AlCl3/KBr, under permanent temperature gradient. The innovative "ampoule in ampoule" design of a crystallization vessel allows obtaining mm-sized plate-like single crystals with a sulfur content up to x ∼ 0.19. The sharp anomalies in the physical properties indicate the superconducting and nematic phase transitions in FeSe0.96 at TC = 8.4 K and TN = 90 K, respectively. Scanning tunneling microscopy reveals the presence of dumbbell defects associated with Fe vacancies and dark defects at the chalcogen site associated with S within the FeSe1-xSx series of compounds. Scanning tunneling spectroscopy shows the presence of two different superconducting gaps at both hole and electron pockets of the Fermi surface for low S content levels. As a function of sulfur content, TC follows the conventional dome-shaped curve while TN decreases with x. The overall appearance of the T-x phase diagram of FeSe1-xSx suggests the importance of nematic fluctuations for the formation of the superconducting state in these compounds. © 2018 The Royal Society of Chemistry

NANOSTRUCTURES (Cu,Zn)/h-BN FOR HETEROGENEOUS CATALYSIS

(Cu,Zn)/h-BN heterogeneous nanostructures were successfully synthesized by wet chem-istry reaction. Metal nanopartciles, 10-20 nm in dimension, were homogeneously distributed over the BN support. Nanocatalysts showed high catalytic activity in CO oxidation reaction.Работа выполнена при финансовой поддержке Российского Научного Фонда (соглашение № 20-79-10286)

Different concepts for creating antibacterial yet biocompatible surfaces: Adding bactericidal element, grafting therapeutic agent through COOH plasma polymer and their combination

Antibacterial coatings have become a rapidly developing field of research, strongly stimulated by the increasing urgency of identifying alternatives to the traditional administration of antibiotics. Such coatings can be deposited onto implants and other medical devices and prevent the inflammations caused by hospital-acquired infections. Nevertheless, the design of antibacterial yet biocompatible and bioactive surfaces is a challenge that biological community has faced for many years but the "materials of dream" have not yet been developed. In this work, the biocompatible yet antibacterial multi-layered films were prepared by a combination of magnetron sputtering (TiCaPCON film), ion implantation (Ag-doped TiCaPCON film), plasma polymerization (COOH layer), and the final immobilization of gentamicin (GM) and heparin (Hepa) molecules. The layer chemistry was thoroughly investigated by means of FTIR and X-ray photoelectron spectroscopies. It was found that the immobilization of therapeutic components occurs throughout the entire thickness of the plasma-deposited COOH layer. The influence of each type of bactericide (Ag+ ions, GM, and Hepa) on antibacterial activity and cell proliferation was analyzed. Our films were cytocompatible and demonstrated superior bactericidal efficiency toward antibioticresistant bacterial E. coli K261 strain. Increased toxicity while using the combination of Ag nanoparticles and COOH plasma polymer is discussed

PT/H-BN NANOSTRUCTURES DEVELOPMENT FOR HETEROGENEOUS CATALYSIS

Pt/h-BN hybrid nanostructures were successfully synthesized by the impregnation method. Pt nanopartciles, 3-10 nm in size, were homogeneously distributed on over the BN support. Nanocatalysts showed high catalytic activity in CO oxidation, full conversion was achieved at 184 °С.Работа выполнена при финансовой поддержке Российского научного фонда (проект № 20-79-10286)

Catalytic properties of the framework-structured zirconium-containing phosphates in ethanol conversion

Aliphatic alcohols C1–C4 can serve as raw material for the production of essential organic products, such as olefins, aldehydes, ketones and ethers. For the development of catalysts of alcohols’ conversion, the authors considered two families of framework phosphate compounds with significant chemical, thermal and phase stability: NaZr2(PO4)3 (NZP/NASICON) and Sc2(WO4)3 (SW). Variation in the composition of zirconium-containing NZP- and SW-complex phosphates allows one to vary the number and strength of Lewis acid centers and incorporate oxidative-reducing centers (such as d-transition metals) into the structure. The phosphates M0.5+xNixZr2 − x(PO4)3 (where M are Mn and Ca) were studied in the reactions of ethanol conversion. From the results of complex investigation, the compounds with M–Mn (x = 0, 0.3 and 0.5) were crystallized in the SW-type (monoclinic symmetry), while the phosphates with M–Ca (x = 0, 0.2 and 0.4) were characterized as the NZP-structured compounds (trigonal symmetry). The surface areas and pore volumes of synthesized catalysts varied, with different compositions, from 14 to 32 m2/g and 0.03 to 0.12 mL/g, respectively. From the catalytic experiments, the main direction of conversion on all the studied catalysts was ethanol dehydrogenization with acetaldehyde formation. The other conversion products—diethyl ether and ethylene—were produced with small yields. Based on the results obtained, the NZP-sample Ca0.5Zr2(PO4)3 can be considered as a selective catalyst for producing acetaldehyde at 400 °C with a yield of 55% from its theoretical amount. © 2021, The Author(s), under exclusive licence to Springer Nature B.V

High-strength aluminum-based composites reinforced with BN, AlB2 and AlN particles fabricated via reactive spark plasma sintering of Al-BN powder mixtures

Light (density 350 MPa) metal matrix composites (MMCs) are highly anticipated for aerospace and automotive industries. The MMCs application fields can be significantly expanded if they possess enhanced strength at elevated temperatures also. In the present study, Al-based composites loaded with either micro- or BN nanoparticles (BNMPs and BNNPs) with up to 10 wt% of BN phase were produced via spark plasma sintering (SPS) of ball-milled Al-BN powder mixtures. A dramatic increase in the composite tensile strength compared to pure Al samples (up to 415%) was demonstrated during tensile tests both at 20 °C and 500 °C. BNMPs were found to be a more preferred additive compared with BNNPs due to the formation of more homogeneous and uniform morphologies within the ball-milled powder mixtures and resultant SPS products. The most impressive tensile strength of 170 MPa at 500 °C was achieved for an Al-7 wt% BNMPs SPS composite, as compared to a value of only 33 MPa for a pure Al SPS-produced sample. The reinforcement mechanism was uncovered based on detailed X-ray diffraction analysis, differential scanning calorimetry, Raman spectroscopy, scanning and high-resolution transmission electron microscopy and energy-dispersion X-ray analysis. Microscale BN, AlB2 and AlN inclusions acting within Al-matrices in the frame of Orowan strengthening mechanism, and pre-formed during ball-milling-induced pre-activation of Al-BN powder mixtures, finally crystallized during SPS processing and ensured the dramatically improved tensile strength and hardness of the resultant composites

Structural analysis and atomic simulation of Ag/BN nanoparticle hybrids obtained by Ag ion implantation

The present paper describes fabrication of Ag/BN nanoparticle hybrids by means of Ag ion implantation into the hollow BN nanoparticles (BNNPs) with a petal-like surface. The structural transformations occurring during Ag ion implantation into BNNPs are studied by low- and high-resolution transmission electron microscopy (TEM), high angle annular dark field scanning TEM (HAADF-STEM) paired with energy-dispersive X-ray (EDX) spectroscopy mapping. The experimental results are theoretically verified in the framework of the classical molecular dynamics (MD) method. Our results have demonstrated that by changing Ag ion energy in the range of 2-20 kV it is possible to selectively fabricate Ag/BNNP nanohybrids with crystalline or amorphous BNNP structures and various Ag NPs distributions over the BNNP thicknesses. © 2016 Elsevier Ltd

Hollow spherical and nanosheet-base BN nanoparticles as perspective additives to oil lubricants: Correlation between large-scale friction behavior and in situ TEM compression testing

In the present study we utilized h-BN nanoparticles (NPs) with different morphologies (hollow NPs with smooth surface (H-BNNPs), solid NPs with “pompon”-like or petalled structure (P-BNNPs), and globular NPs formed by numerous thin h-BN nanosheets (N-BNNPs)) as additives to PAO6 oil. Two sliding 100Cr6 surfaces were tested in the presence of PAO6+BNNP lubricants with 0.1% and 0.01% of BNNPs. The positive effect of BNNP additives increased along the row P-BNNPs → H-BNNPs → N-BNNPs. Utilization of N-BNNPs permitted to decrease noticeably the friction coefficient from 0.1 to 0.06 and reduce significantly the wear rate. In situ mechanical TEM tests were also performed to visualize and correlate the mechanical properties of individual h-BN NPs to their large-scale friction behavior.</p