Abstract: Thin films of heavily B-doped nanocrystalline diamond (B:NCD) have been investigated by a combination of high resolution annular dark field scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy performed on a state-of-the-art aberration corrected instrument to determine the B concentration, distribution and the local B environment. Concentrations of [similar]1 to 3 at.% of boron are found to be embedded within individual grains. Even though most NCD grains are surrounded by a thin amorphous shell, elemental mapping of the B and C signal shows no preferential embedding of B in these amorphous shells or in grain boundaries between the NCD grains, in contrast with earlier work on more macroscopic superconducting polycrystalline B-doped diamond films. Detailed inspection of the fine structure of the boron K-edge and comparison with density functional theory calculated fine structure energy-loss near-edge structure signatures confirms that the B atoms present in the diamond grains are substitutional atoms embedded tetrahedrally into the diamond lattice.

Abstract: Spin selectivity in angle-resolved Auger photoelectron coincidence spectroscopy (AR-APECS) is used to probe electron correlation in ferromagnetic thin films. In particular, exploiting the AR-APECS capability to discriminate Auger electron emission events characterized by valence hole pairs created either in the high or in the low total spin state, a strong correlation effect in the Fe M2,3VV Auger line shape (measured in coincidence with the Fe 3p photoelectrons) of Fe/Cu(001) thin films is detected and ascribed to interactions within the majority spin subband. Such an assignment follows from a close comparison of the experimental AR-APECS line shapes with the predictions of a model based on spin polarized density functional theory and the Cini-Sawatzky approach.

Abstract: In this work, a detailed structural and spectroscopic study of nanocrystalline diamond (NCD) thin films grown by a continuous bias assisted CVD growth technique is reported. This technique allows the tuning of grain size and phase purity in the deposited material. The crystalline properties of the films are characterized by SEM, TEM, EELS, and Raman spectroscopy. A clear improvement of the crystalline structure of the nanograined diamond film is observed for low negative bias voltages, while high bias voltages lead to thin films consisting of diamond grains of only ∼10 nm nanometer in size, showing remarkable similarities with so-called ultrananocrystalline diamond. These layers arecharacterized by an increasing amount of sp2-bonded carbon content of the matrix in which the diamond grains are embedded. Classical molecular dynamics simulations support the observed experimental data, giving insight in the underlying mechanism for the observed increase in deposition rate with bias voltage. Furthermore, a high atomic concentration of hydrogen has been determined in these films. Finally, Raman scattering analyses confirm that the Raman line observed at ∼1150 cm−1 cannot be attributed to trans-poly-acetylene, which continues to be reported in literature, reassigning it to a deformation mode of CHx bonds in NCD.

Abstract: The aim of this paper is to provide a thorough study on the occurrence and importance of deformation twinning in simple shear deformed pure α-Ti. A statistically relevant inspection of the morphology of the deformation twins in relation to the applied strain/deformation is performed. The investigated microstructural aspects are the twin volume fraction, the twin thickness distribution and the resolved shear stress distribution on the twin plane. All these aspects are examined as a function of the twin types and two initial textures. Monotonic simple shear experiments are carried out for three different loading directions with respect to a direction linked to the initial crystallographic texture. EBSD and TEM observations reveal the presence of View the MathML source and View the MathML source twins. The statistical analysis reveals that View the MathML source and View the MathML source twins have a similar average thickness around 1.9 nm, but the View the MathML source twins show a far larger spread on their thickness and can grow to almost the size of the original parent grain. Correlation of the twin fractions with the RSS analysis shows that RSS is an acceptable method explaining the difference in twin fractions for different textures and orientations. A detailed analysis shows that View the MathML source twins occur in average with a smaller volume fraction but with a higher RSS, indicating they are more difficult to nucleate or grow compared to View the MathML source twinning. In general a higher RSS value on the twin plane is not connected to a higher twin thickness; only in the case of View the MathML source twins the highest RSS values show clearly thicker twins.

Abstract: Magnetoelectric multiferroics showing coupling between polarization and magnetic order are attracting much attention. For instance, they could be used in memory devices. Metal-transition oxides are provided several examples of inorganic magnetoelectric multiferroics. In the present short review, spinel and delafossite chromites are described. For the former, an electric polarization is evidenced in the ferrimagnetic state for ACr2O4 polycrystalline samples (A=Ni, Fe, Co). The presence of a JahnTeller cation such as Ni2+ at the A site is shown to yield larger polarization values. In the delafossites, substitution by V3+ at the Cr or Fe site in CuCrO2 (CuFeO2) suppresses the complex antiferromagnetic structure at the benefit of a spin glass state. The presence of cation disorder, probed by transmission electron microscopy, favors relaxor-like ferroelectricity. The results on the ferroelectricity of ferrimagnets and insulating spin glasses demonstrate that, in this research field, transition-metal oxides are worth to be studied.

Abstract: It is widely accepted that the physical properties of nanostructures depend on the type of surface facets1, 2. For Au nanorods, the surface facets have a major influence on crucial effects such as reactivity and ligand adsorption and there has been controversy regarding facet indexing3, 4. Aberration-corrected electron microscopy is the ideal technique to study the atomic structure of nanomaterials5, 6. However, these images correspond to two-dimensional (2D) projections of 3D nano-objects, leading to an incomplete characterization. Recently, much progress was achieved in the field of atomic-resolution electron tomography, but it is still far from being a routinely used technique. Here we propose a methodology to measure the 3D atomic structure of free-standing nanoparticles, which we apply to characterize the surface facets of Au nanorods. This methodology is applicable to a broad range of nanocrystals, leading to unique insights concerning the connection between the structure and properties of nanostructures.

Abstract: The development of new electrode materials, which are composed of Earth-abundant elements and that can be made via eco-efficient processes, is becoming absolutely necessary for reasons of sustainable production. The 3.9 V triplite-phase of LiFeSO4F, compared to the 3.6 V tavorite-phase, could satisfy this requirement provided the currently complex synthetic pathway can be simplified. Here, we present our work aiming at better understanding the reaction mechanism that govern its formation as a way to optimize its preparation. We first demonstrate, using complementary X-ray diffraction and transmission electron microscopy studies, that triplite-LiFeSO4F can nucleate from tavorite-LiFeSO4F via a reconstructive process whose kinetics are significantly influenced by moisture and particle morphology. Perhaps the most spectacular finding is that it is possible to prepare electrochemically active triplite-LiFeSO4F from anhydrous precursors using either reactive spark plasma sintering (SPS) synthesis in a mere 20 min at 320 degrees C or room temperature ball milling for 3 h. These new pathways appear to be strongly driven by the easy formation of a disordered phase with higher entropy, as both techniques trigger disorder via rapid annealing steps or defect creation. Although a huge number of phases adopts the tavorite structure-type, this new finding offers both a potential way to prepare new compositions in the triplite structure and a wealth of opportunities for the synthesis of new materials which could benefit many domains beyond energy storage.

Abstract: The calculation of defect levels in semiconductors within a density functional theory approach suffers greatly from the band gap problem. We propose a band gap correction scheme that is based on the separation of energy differences in electron addition and relaxation energies. We show that it can predict defect levels with a reasonable accuracy, particularly in the case of defects with conduction band character, and yet is simple and computationally economical. We apply this method to ZnO doped with group III elements (Al, Ga, In). As expected from experiment, the results indicate that Zn substitutional doping is preferred over interstitial doping in Al, Ga, and In-doped ZnO, under both zinc-rich and oxygen-rich conditions. Further, all three dopants act as shallow donors, with the +1 charge state having the most advantageous formation energy. Also, doping effects on the electronic structure of ZnO are sufficiently mild so as to affect little the fundamental band gap and lowest conduction bands dispersion, which secures their n-type transparent conducting behavior. A comparison with the extrapolation method based on LDA+U calculations and with the HeydScuseriaErnzerhof hybrid functional (HSE) shows the reliability of the proposed scheme in predicting the thermodynamic transition levels in shallow donor systems.

Abstract: SrFe0.75Mo0.25O3-delta has been recently discovered as an extremely efficient electrode for intermediate temperature solid oxide fuel cells (IT-SOFCs). We have performed structural and magnetic studies to fully characterize this multifunctional material. We have observed by powder neutron diffraction (PND) and transmission electron microscopy (TEM) that its crystal symmetry is better explained with a tetragonal symmetry (I4/mcm space group) than with the previously reported orthorhombic symmetry (Pnma space group). The temperature dependent magnetic properties indicate an exceptionally high magnetic ordering temperature (T-N similar to 750 K), well above room temperature. The ordered magnetic structure at low temperature was determined by PND to be an antiferromagnetic coupling of the Fe cations. Mossbauer spectroscopy corroborated the PND results. A detailed study, with X-ray absorption spectroscopy (XAS), in agreement with the Mossbauer results, confirmed the formal oxidation states of the cations to be mixed valence Fe3+/4+ and Mo6+.

Abstract: Under ultrasonication, the production of high quality graphene layers by exfoliation of graphite was achieved via addition of tiopronin as an antioxidant.

Abstract: Recent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS-TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/Delta E = 104 and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS-TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs.

Abstract: We use density functional theory within the local density approximation to investigate the structural, electronic, and optical properties of Al-doped MgO. The concentrations considered range from 6% to 56%. In the latter case, we also compare the optical properties of the amorphous and crystalline phases. We find that, overall, the electronic properties of the crystalline phases change qualitatively little with Al concentration. On the other hand, the changes in the electronic structure in the amorphous phase are more important, most notably because of deep impurity levels in the band gap that are absent in the crystalline phase. This leads to observable effects in, e.g., the optical absorption edge and in the refractive index. Thus, the latter can be used to characterize the crystalline to amorphous transition with Al doping level.

Abstract: N-Lewis base mediated room temperature synthesis of covalent organic frameworks (COFs) starting from a solution of building blocks instead of partially soluble building blocks was developed. This protocol shifts COF synthetic chemistry from sealed tubes to open beakers. Non-conventional inclusion compounds of COF-1 were obtained by vapor phase infiltration of ferrocene and azobenzene, and solvation like effects were established.

Abstract: Single crystals of Bi3Mn1.9Te1.1O11 were prepared from NaCl+KCl flux. This compound adopts KSbO3-type crystal structure as evidenced by electron and single crystal X-ray diffraction analysis. The three-dimensional channel structure is formed by corner-sharing octahedral (Mn0.63Te0.37)2O10 dimers and two identical (Bi1)4(Bi2)2 interpenetrating lattices. The intra-dimer Mn/TeMn/Te distances in Bi3Mn1.9Te1.1O11 are short and are consistent with weak metalmetal interactions. The mixed oxidation state of manganese and the edge-sharing octahedral features are confirmed by X-ray near edge absorption spectroscopy measurements, which indicate Bi3(MnIII1.1MnIV0.8)TeVI1.1O11 with 57.7% Mn3+ and 42.3% Mn4+. The partial substitution of Te for Mn perturbs long-range magnetic interactions, thereby destroying the ferromagnetic ordering found in Bi3Mn3O11 (TC=150 K).

Abstract: We demonstrate site-specific mapping of the oxygen coordination number for transition metals in complex oxides using atomically resolved electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope. Pb2Sr2Bi2Fe6O16 contains iron with a constant Fe3+ valency in both octahedral and tetragonal pyramidal coordination and is selected to demonstrate the principle of site-specific coordination mapping. Analysis of the site-specific Fe-L2,3 data reveals distinct variations in the fine structure that are attributed to Fe in a six-fold (octahedron) or five-fold (distorted tetragonal pyramid) oxygen coordination. Using these variations, atomic resolution coordination maps are generated that are in excellent agreement with simulations.