Dopants adsorbed as single atoms prevent degradation of catalysts

The design of catalysts with desired chemical and thermal properties is viewed as a grand challenge for scientists and engineers. For operation at high temperatures, stability against structural transformations is a key requirement. Although doping has been found to impede degradation, the lack of atomistic understanding of the pertinent mechanism has hindered optimization. For example, porous gamma-Al2O3, a widely used catalyst and catalytic support, transforms to non-porous alpha-Al2O3 at ~1,100C. Doping with La raises the transformation temperature to ~1,250C, but it has not been possible to establish if La atoms enter the bulk, adsorb on surfaces as single atoms or clusters, or form surface compounds. Here, we use direct imaging by aberration-corrected Z-contrast scanning transmission electron microscopy coupled with extended X-ray absorption fine structure and first-principles calculations to demonstrate that, contrary to expectations, stabilization is achieved by isolated La atoms adsorbed on the surface. Strong binding and mutual repulsion of La atoms effectively pin the surface and inhibit both sintering and the transformation to alpha-Al2O3. The results provide the first guidelines for the choice of dopants to prevent thermal degradation of catalysts and other porous materials.Comment: RevTex4, 4 pages, 4 JPEG figures, published in Nature Material

Current State of the Development of Next-Generation Vaccines against Ebola Virus Disease

Representative of Ebolavirus gender, Filoviridae family, Ebola virus is an etiological agent of particularly dangerous viral fever, the lethality of which comes up to 88 %. According to the leading specialists and experts in the sphere, vaccination is the most effective and cost-efficient method for the protection from epidemic spread. Objective of the review is to analyze current state of the development of next generation vaccines against Ebola fever. It is established that focus areas of the activities are the construction of vaccines on the basis of alpha-virus replicons, virus-like particles, and the development of DNA-vaccines and vector recombinant vaccines. The paper discusses the most significant achievements in the sphere of obtainment of potent therapies for prophylaxis as regards Ebola fever. To date manufactured, using various approaches, have been the next-generation vaccine preparations, for a number of which high protective capacity is demonstrated in the course of experiments on the nonhuman primates. The most advanced and prospective prototype is the vector recombinant vesicular stomatitis virus-based vaccine

Analysis of phase distributions in the Li\u3csub\u3e2\u3c/sub\u3eO–Nb\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e5\u3c/sub\u3e–TiO\u3csub\u3e2\u3c/sub\u3e system by piezoresponse imaging

The M-phase solid solutions Li1+x-yNb1-x-3yTix+4yO3) (0.1 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.175) in the Li2O–Nb2O5–TiO2 system have promising microwave dielectric properties. However, these compounds can contain small quantities of ferroelectric impurities that affect the polarization response of the material. Due to their low concentration and their chemical similarity to the host material, the impurities cannot be detected by x-ray diffraction or local elemental analysis. Scanning surface potential microscopy and piezoresponse imaging were used to analyze phase compositions in this system. Piezoresponse imaging demonstrated the presence of thin (\u3c200–300 nm) ferroelectric layers on the grain boundaries oriented along the c-axis of the M-phase. Differences between the surface potential and the piezoresponse of ferroelectric multicomponent systems are discussed

Identification of phases, symmetries and defects through local crystallography

Advances in electron and probe microscopies allow 10 pm or higher precision in measurements of atomic positions. This level of fidelity is sufficient to correlate the length (and hence energy) of bonds, as well as bond angles to functional properties of materials. Traditionally, this relied on mapping locally measured parameters to macroscopic variables, for example, average unit cell. This description effectively ignores the information contained in the microscopic degrees of freedom available in a high-resolution image. Here we introduce an approach for local analysis of material structure based on statistical analysis of individual atomic neighbourhoods. Clustering and multivariate algorithms such as principal component analysis explore the connectivity of lattice and bond structure, as well as identify minute structural distortions, thus allowing for chemical description and identification of phases. This analysis lays the framework for building image genomes and structure–property libraries, based on conjoining structural and spectral realms through local atomic behaviour