Abstract: Dielectric properties of materials are crucial in describing the electromagnetic response of materials. As devices are becoming considerably smaller than the optical wavelength, the conventional measuring methods based on optical response are limited by their spatial resolution. Electron energy loss spectroscopy performed in a scanning transmission electron microscope is a good alternative to obtain the dielectric properties with excellent spatial resolution. Due to the overlap of diffraction discs in scanning transmission electron microscopy, it is difficult to apply conventional experimental settings to suppress retardation losses. In this contribution, a relativistic dielectric model for the loss function is presented which is used in a model based optimization scheme to estimate the complex dielectric function of a material. The method is applied to experiments on bulk diamond and SrTiO3 and shows a good agreement with optical reference data when retardation effects are included. Application of this technique to nanoparticles is possible but several theoretical assumptions made in the model of the loss function are violated and interpretation becomes problematic.

Abstract: Diamond is a promising material for a number of bio-applications, including the fabrication of platforms for attachment and investigation of neurons and of neuroprostheses, such as retinal implants. In the current work ultrananocrystalline diamond (UNCD) films were deposited by microwave plasma chemical vapor deposition, modified by UV/O-3 treatment or NH3 plasma, and comprehensively characterized with respect to their bulk and surface properties, such as crystallinity, topography, composition and chemical bonding nature. The interactions of insect circadian pacemaker neurons with UNCD surfaces with H-, O- and NH2-terminations were investigated with respect to cell density and viability. The fast and strong attachment achieved without application of adhesion proteins allowed for advantageous modification of dispersion protocols for the preparation of primary cell cultures. Centrifugation steps, which are employed for pelletizing dispersed cells to separate them from dispersing enzymes, easily damage neurons. Now centrifugation can be avoided since dispersed neurons quickly and strongly attach to the UNCD surfaces. Enzyme solutions can be easily washed off without losing many of the dispersed cells. No adverse effects on the cell viability and physiological responses were observed as revealed by calcium imaging. Furthermore, the enhanced attachment of the neurons, especially on the modified UNCD surfaces, was especially advantageous for the immunocytochemical procedures with the cell cultures. The cell losses during washing steps were significantly reduced by one order of magnitude in comparison to controls. In addition, the integration of a titanium grid structure under the UNCD films allowed for individual assignment of physiologically characterized neurons to immunocytochemically stained cells. Thus, employing UNCD surfaces free of foreign proteins improves cell culture protocols and immunocytochemistry with cultured cells. The fast and strong attachment of neurons was attributed to a favorable combination of topography, surface chemistry and wettability. (C) 2016 Elsevier B.V. All rights reserved.

Abstract: Development of efficient production methods of nanodiamond (ND) particles containing substitutional nitrogen and nitrogen-vacancy (NV) complexes remains an important goal in the nanodiamond community. ND synthesized from explosives is generally not among the preferred candidates for imaging applications owing to lack of optically active particles containing NV centers. In this paper, we have systematically studied representative classes of NDs produced by detonation shock wave conversion of different carbon precursor materials, namely, graphite and a graphite/hexogen mixture into ND, as well as ND produced from different combinations of explosives using different cooling methods (wet or dry cooling). We demonstrate that (i) the N content in nanodiamond particles can be controlled through a correct selection of the carbon precursor material (addition of graphite, explosives composition); (ii) particles larger than approximately 20 nm may contain in situ produced optically active NV centers, and (iii) in ND produced from explosives, NV centers are detected only in ND produced by wet synthesis. ND synthesized from a mixture of graphite/explosive contains the largest amount of NV centers formed during synthesis and thus deserves special attention.

Abstract: Despite the enormous interest in the properties and applications of porous silica matrix, only a few attempts have been reported to deposit metal and metal oxide nanoparticles (NPs) inside the porous silica matrix. We report a simple approach (i.e. sol-gel hot injection) for insitu synthesis of ZnO NPs inside a porous silica matrix. Control of the Zn:Si molar ratio, reaction temperature, pH value, and annealing temperature permits formation of ZnO NPs (<= 10 nm) inside a porous silica particles, without additives or organic solvents. Results revealed that a solid state reaction inside the ZnO/SiO2 nanocomposites occurs with increasing the annealing temperature. The reaction of ZnO NPs with SiO2 matrix was insignificant up to approximately 500 degrees C. However, ZnO NPs react strongly with the silica matrix when the nanocomposites are annealed at temperatures above 700 degrees C. Extensive annealing of the ZnO/SiO2 nanocomposite at 900 degrees C yields 3D structures made of 500 nm rod-like, 5-7 pm tube-like and 35 pm needle-like Zn2SiO4 crystals. A possible mechanism for forming ZnO NPs inside porous silica matrix and phase transformation of the ZnO/SiO2 nanocomposites into 3D architectures of Zn2SiO4 are carefully discussed. (C) 2017 Elsevier Ltd. All rights reserved.

Abstract: Design and optimization of materials properties can only be performed through a thorough knowledge of the structure of the compound. In this feature article we illustrate the possibilities of advanced electron microscopy in materials science and solid state chemistry. The different techniques are briefly discussed and several examples are given where the structures of complex oxides, often with a modulated structure, have been solved using electron microscopy.

Abstract: Density functional theory calculations are used to study gas adsorption properties of a recently synthesized CaO monolayer, which is found to be thermodynamically stable in its buckled form. Due to its topology and strong interaction with the CO2 molecules, this material possesses a remarkably high CO2 uptake capacity (similar to 0.4 g CO2 per g adsorbent). The CaO + CO2 system shows excellent thermal stability (up to 1000 K). Moreover, the material is highly selective towards CO2 against other major greenhouse gases such as CH4 and N2O. These advantages make this material a very promising candidate for CO2 capture and storage applications.

Abstract: Cu-Pd alloys containing 10, 20, 30, 40, and 50 at. % Pd and quenched from a temperature just above the ordering temperature T-c are investigated by electron diffraction and high-resolution electron microscopy (HREM). The results show diffuse electron diffraction intensities at {100} and {110} positions for the alloy with 10 at. % Pd, but with a characteristic twofold and fourfold splitting for the alloys with more than 10 at. % Pd. High-resolution images show the formation of microdomains best developed between 20 and 30 at. % Pd. A real-space characterization has been performed by applying videographic real-structure simulations revealing that the splitting of the diffuse maxima depends on the average distance between microdomains of Cu3Au type in antiphase with each other. By applying image processing routines on the HREM images, correlation vectors are identified which correspond to correlations between microdomains.

Abstract: Crystal structure and magnetic properties of the layered vanadium phosphate PbZnVO(PO4)2 are studied using x-ray powder diffraction, magnetization and specific-heat measurements, as well as band-structure calculations. The compound resembles AA′VO(PO4)2 vanadium phosphates and fits to the extended frustrated square-lattice model with the couplings J1, J1′ between nearest neighbors and J2, J2′ between next-nearest neighbors. The temperature dependence of the magnetization yields estimates of averaged nearest-neighbor and next-nearest-neighbor couplings, J̅ 1≃−5.2 K and J̅ 2≃10.0 K, respectively. The effective frustration ratio α=J̅ 2/J̅ 1 amounts to −1.9 and suggests columnar antiferromagnetic ordering in PbZnVO(PO4)2. Specific-heat data support the estimates of J̅ 1 and J̅ 2 and indicate a likely magnetic ordering transition at 3.9 K. However, the averaged couplings underestimate the saturation field, thus pointing to the spatial anisotropy of the nearest-neighbor interactions. Band-structure calculations confirm the identification of ferromagnetic J1, J1′ and antiferromagnetic J2, J2′ in PbZnVO(PO4)2 and yield (J1′−J1)≃1.1 K in excellent agreement with the experimental value of 1.1 K, deduced from the difference between the expected and experimentally measured saturation fields. Based on the comparison of layered vanadium phosphates with different metal cations, we show that a moderate spatial anisotropy of the frustrated square lattice has minor influence on the thermodynamic properties of the model. We discuss relevant geometrical parameters, controlling the exchange interactions in these compounds and propose a strategy for further design of strongly frustrated square-lattice materials.

Abstract: Conventional CO2 separation in the petrochemical industry via cryogenic distillation or amine-based absorber-stripper units is energy-intensive and environmentally unfriendly. Membrane-based gas separation technology, in contrast, has contributed significantly to the development of energy-efficient systems for processes such as natural gas purification. The implementation of commercial polymeric membranes in gas separation processes is restricted by their permeability-selectivity trade-off and by their insufficient thermal and chemical stability. Herein, we present the fabrication of a Matrimid-based membrane loaded with a breathing metal-organic framework (MOF) (NH2-MIL-53(Al)) which is capable of separating binary CO2/CH4 gas mixtures with high selectivities without sacrificing much of its CO2 permeabilities. NH2-MIL-53(Al) crystals were embedded in a polyimide (PI) matrix, and the mixed-matrix membranes (MMMs) were treated at elevated temperatures (up to 350 degrees C) in air to trigger PI cross-linking and to create PI-MOF bonds at the interface to effectively seal the grain boundary. Most importantly, the MOF transitions from its narrow-pore form to its large-pore form during this treatment, which allows the PI chains to partly penetrate the pores and cross-link with the amino functions at the pore mouth of the NH2-MIL-53(Al) and stabilizes the open-pore form of NH2-MIL-53(Al). This cross-linked MMM, with MOF pore entrances was made more selective by the anchored PI-chains and achieves outstanding CO2/CH4 selectivities. This approach provides significant advancement toward the design of selective MMMs with enhanced thermal and chemical stabilities which could also be applicable for other potential applications, such as separation of hydrocarbons (olefin/paraffin or isomers), pervaporation, and solvent-resistant nanofiltration.

Abstract: Controlled in-plane rotation of the magnetic easy axis in manganite heterostructures by tailoring the interface oxygen network could allow the development of correlated oxide-based magnetic tunnelling junctions with non-collinear magnetization, with possible practical applications as miniaturized high-switching-speed magnetic random access memory (MRAM) devices. Here, we demonstrate how to manipulate magnetic and electronic anisotropic properties in manganite heterostructures by engineering the oxygen network on the unit-cell level. The strong oxygen octahedral coupling is found to transfer the octahedral rotation, present in the NdGaO3 (NGO) substrate, to the La2/3Sr1/3MnO3 (LSMO) film in the interface region. This causes an unexpected realignment of the magnetic easy axis along the short axis of the LSMO unit cell as well as the presence of a giant anisotropic transport in these ultrathin LSMO films. As a result we possess control of the lateral magnetic and electronic anisotropies by atomic-scale design of the oxygen octahedral rotation.

Abstract: Control of interactions between nanomaterials and cells remains a biomedical challenge. A strategy is proposed to modulate the intralysosomal distribution of nanoparticles through the design of 3D suprastructures built by hydrophilic nanocrystals (NCs) coated with alkyl chains. The intracellular fate of two water-dispersible architectures of self-assembled hydrophobic magnetic NCs: hollow deformable shells (colloidosomes) or solid fcc particles (supraballs) is compared. These two self-assemblies display increased cellular uptake by tumor cells compared to dispersions of the water-soluble NC building blocks. Moreover, the self-assembly structures increase the NCs density in lysosomes and close to the lysosome membrane. Importantly, the structural organization of NCs in colloidosomes and supraballs are maintained in lysosomes up to 8 days after internalization, whereas initially dispersed hydrophilic NCs are randomly aggregated. Supraballs and colloidosomes are differently sensed by cells due to their different architectures and mechanical properties. Flexible and soft colloidosomes deform and spread along the biological membranes. In contrast, the more rigid supraballs remain spherical. By subjecting the internalized suprastructures to a magnetic field, they both align and form long chains. Overall, it is highlighted that the mechanical and topological properties of the self-assemblies direct their intracellular fate allowing the control intralysosomal density, ordering, and localization of NCs.

Abstract: Confinement of electrons in ultrathin metallic films leads to subbands. By increasing the thickness of the electron layer, the subbands will dissolve into a quasicontinuum, with the number of electrons per unit volume kept constant. Within the random-phase approximation, the two-dimensional plasmon, which originally follows Stern's dispersion relation, becomes a longitudinal surface plasmon. The plasmon excitations of a model metallic film are investigated by including all subbands. Single-particle excitations, which exhibit the depolarization shift, converge into the plasma excitation spectrum. With further increases in the film thickness, the bulk plasmon arises and the surface plasmon remains. Our analysis shows how quantum size effects evolve into hydrodynamical classical size effects with increasing thickness of the film.

Abstract: Composite (La0.67Ca0.33MnO3)(1-x):(MgO)(x) films were prepared by metalorganic aerosol deposition on a (100)MgO substrate for different concentrations of the (MgO) phase (0less than or equal toxless than or equal to0.8). At xapproximate to0.3 a percolation threshold in conductivity is reached, at which an infinite insulating MgO cluster forms around the La0.67Ca0.33MnO3 grains. This yields a drastic increase of the electrical resistance for films with x>0.3. The film structure is characterized by x-ray diffraction and transmission electron microscopy. The local structure of the La0.67Ca0.33MnO3 within the film depends on the MgO concentration which grows epitaxially along the domain boundaries. A different structural phase transition from the orthorhombic Pnma structure to an unusual rhombohedral R (3) over barc structure at the percolation threshold xapproximate to0.3 is found for La0.67Ca0.33MnO3. A three-dimensional stress accommodation in thick films through a phase transition is suggested.

Abstract: Colloidal CsPbBr3 nanocrystals (NCs) have emerged as promising candidates for various opto-electronic applications, such as light-emitting diodes, photodetectors, and solar cells. Here, we report on the self-assembly of cubic NCs from an organic suspension into ordered cuboidal supraparticles (SPs) and their structural and optical properties. Upon increasing the NC concentration or by addition of a nonsolvent, the formation of the SPs occurs homogeneously in the suspension, as monitored by in situ X-ray scattering measurements. The three-dimensional structure of the SPs was resolved through high-angle annular dark-field scanning transmission electron microscopy and electron tomography. The NCs are atomically aligned but not connected. We characterize NC vacancies on superlattice positions both in the bulk and on the surface of the SPs. The occurrence of localized atomic-type NC vacancies-instead of delocalized ones-indicates that NC-NC attractions are important in the assembly, as we verify with Monte Carlo simulations. Even when assembled in SPs, the NCs show bright emission, with a red shift of about 30 meV compared to NCs in suspension.

Abstract: Colloidal 2D semiconductor nanocrystals, the analogue of solid-state quantum wells, have attracted strong interest in material science and physics. Molar quantities of suspended quantum objects with spectrally pure absorption and emission can be synthesized. For the visible region, CdSe nanoplatelets with atomically precise thickness and tailorable emission have been (almost) perfected. For the near-infrared region, PbS nanosheets (NSs) hold strong promise, but the photoluminescence quantum yield is low and many questions on the crystallinity, atomic structure, intriguing rectangular shape, and formation mechanism remain to be answered. Here, we report on a detailed investigation of the PbS NSs prepared with a lead thiocyanate single source precursor. Atomically resolved HAADF-STEM imaging reveals the presence of defects and small cubic domains in the deformed orthorhombic PbS crystal lattice. Moreover, variations in thickness are observed in the NSs, but only in steps of 2 PbS monolayers. To study the reaction mechanism, a synthesis at a lower temperature allowed for the study of reaction intermediates. Specifically, we studied the evolution of pseudo-crystalline templates towards mature, crystalline PbS NSs. We propose a self-induced templating mechanism based on an oleylamine-lead-thiocyanate (OLAM-Pb-SCN) complex with two Pb-SCN units as a building block; the interactions between the long-chain ligands regulate the crystal structure and possibly the lateral dimensions.