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In antiferromagnetic spintronics control of the domains and corresponding spin axis orientation is crucial for devices. Here we investigate the antiferromagnetic axis in (111)-oriented LaFeO3/SrTiO3, which is coupled to structural twin domains. The structural domains have either the orthorhombic a- or b-axis along the in-plane 110 cubic directions of the substrate, and the corresponding magnetic domains have the antiferromagnetic axis in the sample plane. Six degenerate antiferromagnetic axes are found corresponding to the 110 and 112 in-plane directions. This is in contrast to the biaxial anisotropy in (001)-oriented films and reflects how crystal orientation can be used to control magnetic anisotropy in antiferromagnets.

We observe an induced switchable magnetic moment of 1.6±0.40μB/Fe for the nominally antiferromagnetic LaFeO3 extending two to four interface layers into the non-charge transfer system La0.7Sr0.3MnO3/LaFeO3/SrTiO3(111). Simultaneously a mismatch of oxygen octahedra rotations at the interface implies an atomic reconstruction of reduced symmetry at the interface, reaching two to five layers into LaFeO3. Density functional theory of a structure with atomic reconstruction and different correlation strength shows a ferrimagnetic state with a net Fe moment at the interface. Together these results suggest that engineered oxygen octahedra rotations, affecting the local symmetry, affect electron correlations and can be used to promote magnetic properties.

Lithium bis(trifluoromethanesulfonyl)imide (LiFSI) is a promising alternative salt for Li‐ion batteries. Unlike the conventional LiPF6, it is not prone to HF formation, and thus resistant to moisture. However, for cell voltages relevant for high energy cathodes (>4.2 V), the aluminium current collector will corrode in electrolytes based on this salt, and mitigation strategies are needed. Here, the use of Lithium tetrafluoroborate (LiBF4) and Lithium difluoro(oxalato)borate (LiDFOB) salts as additives is investigated, in order to enable the use of LiFSI‐based electrolytes. The performance of the electrolytes is evaluated separately for high content silicon anodes, (NMC442) cathodes and the aluminium current collector by electrochemical methods and post mortem analysis by SEM imaging and X‐ray photoelectron spectroscopy (XPS). Electrolytes with LiDFOB as additive showed the best performance for all components, and were therefore selected for cycling in full cells, composed of silicon anodes and NMC442. Results show that LiFSI‐based electrolytes with LiDFOB additive has an electrochemical performance similar to conventional electrolytes, and is thus a competitive, alternative electrolyte with a low fluorine content. Furthermore, it is verified that the good SEI forming properties of LiFSI based electrolytes known from cycling in half cells, is also preserved during cycling in full cells [ABSTRACT FROM AUTHOR]

Chemical solution deposition (CSD) is a versatile method to fabricate oxide films. Here, the structure and local variations in the chemical composition of BaTiO 3 (BTO) films prepared by CSD on (100), (110), and (111) SrTiO 3 (STO) substrates were examined by transmission electron microscopy. The films were shown to be epitaxial and the relaxation of the films occurred by the formation of edge dislocations at the substrate–film interfaces. The Burgers vectors of the dislocations were determined to be a ⟨ 010 ⟩ , a [ 1 1 ¯ 0 ] and a [ 001 ] , and a ⟨ 110 ⟩ for the (100), (110), and (111) films, respectively. Due to the difference in thermal expansion between STO and BTO, the films are demonstrated to be under tensile strain. Furthermore, the boundaries between each deposited layer in the BTO films were found to be Ba-deficient in all cases. In the case of the (111) oriented film, defects like an anti-phase boundary or a thin layer with a twinned crystal structure were identified at the boundary between each deposited layer. Moreover, a larger grain was observed at the film surface with a twinned crystal structure. The interdiffusion length of A-cations at the STO–BTO interface, studied by electron energy-loss spectroscopy, was found to be 3.4, 5.3, and 5.3 nm for the (100), (110), and (111) oriented films, respectively. Interdiffusion of cations across the STO–BTO interface was discussed in relation to cation diffusion in bulk BTO and STO. Despite the presence of imperfections demonstrated in this work, the films possess excellent ferroelectric properties, meaning that none of the imperfections are detrimental to the ferroelectric properties. [ABSTRACT FROM AUTHOR]

The interfacial structure of coincidence site lattice grain boundaries in multi-crystalline silicon plays a decisive role in their electrical behavior as revealed by high-resolution (scanning) transmission electron microscopy investigations. Considering only the global misorientation of the adjacent grains can lead to a false correlation between the structural and electrical properties of a grain boundary. The grain boundary habit plane as well as local deviations in the orientation and misorientation that induce additional structural defects need to be analyzed. Indeed, a Σ9 {221} grain boundary, presenting a perfect coincidence and periodicity at the atomic scale, appears electrically non-active. However, a grain boundary also identified as Σ9 {221} at the mesoscale is found to be composed of nano-sized triangular structures involving Σ3 {111} and Σ3 {112} facets at the nano-scale. This leads to the formation of grain boundary kinks and triple junctions that induce additional structural defects and turn the overall grain boundary interface electrically active. The possible origin of such a grain boundary dissociation, as well as its impact on the electrical activity, is discussed. [ABSTRACT FROM AUTHOR]

We report on the stability of the La0.7Sr0.3MnO3 thin film surface when deposited on (111)-oriented SrTiO3. For ultrathin La0.7Sr0.3MnO3 films, an initial 3-dimensional morphology is observed, which becomes 2-dimensional with increasing film thickness. For even thicker samples, we show that the surface morphology evolves from 2-dimensional to 3-dimensional and that this observation is consistent with an Asaro-Tiller-Grinfeld instability, which can be controlled by the deposition temperature. This allows for synthesis of films with step-and-terrace surfaces over a wide range of thicknesses. Structural characterization by x-ray diffraction and transmission electron microscopy shows that the films are strained to the SrTiO3 substrate and reveals the presence of an elongated out-of-plane lattice parameter at the interface with SrTiO3. [ABSTRACT FROM AUTHOR]

In antiferromagnetic spintronics control of the domains and corresponding spin axis orientation is crucial for devices. Here we investigate the antiferromagnetic axis in (111)-oriented LaFeO3/SrTiO3, which is coupled to structural twin domains. The structural domains have either the orthorhombic a- or b-axis along the in-plane 〈110〉 cubic directions of the substrate, and the corresponding magnetic domains have the antiferromagnetic axis in the sample plane. Six degenerate antiferromagnetic axes are found corresponding to the 〈110〉 and 〈112〉 in-plane directions. This is in contrast to the biaxial anisotropy in (001)-oriented films and reflects how crystal orientation can be used to control magnetic anisotropy in antiferromagnets. [ABSTRACT FROM AUTHOR]

An oxygen vacancy driven structural response at the epitaxial interface between La0.7Sr0.3MnO3/SrTiO3 films and SrTiO3 substrates is reported. A combined scanning transmission electron microscopy and electron energy loss spectroscopy study reveal the presence of an elongated out-of-plane lattice parameter, coupled to oxygen vacancies and reduced manganese oxidation state at the La0.7Sr0.3MnO3/SrTiO3 side of the interface. Density functional theory calculations support that the measured interface structure is a disordered oxygen deficient brownmillerite structure. The effect of oxygen vacancy mobility is assessed, revealing an ordering of the vacancies with time. [ABSTRACT FROM AUTHOR]

Twin structures in rhombohedrally distorted polycrystalline LaCoO3, La0.8Ca0.2CoO3-δ and La0.5Sr0.5Co0.5Fe0.5O3-δ have been studied by transmission electron microscopy. Normal {100} and {110} twinning was predominant in LaCoO3 and La0.8Ca0.2CoO3-δ. In addition, ferroelastic domains with a one-dimensional superstructure corresponding to a tripling of the pseudocubic lattice parameter, ac, were found in some grains. The monoclinic superstructure vanished over time and was sensitive to external mechanical stress. In La0.5Sr0.5Co0.5Fe0.5O3-δ no normal twinning was observed, but domains with a one-dimensional superstructure of two times ac were observed. The superstructures have been interpreted as atomic scale twinning, which reduce the crystal symmetry from rhombohedral to monoclinic. [ABSTRACT FROM AUTHOR]

We report current-voltage and spectral response characteristics of high density InAs/GaAs quantum dot (QD) solar cells with different positions where dots are located. The short circuit current density (Jsc), open circuit voltage (Voc), and external quantum efficiency of these cells under air mass 1.5 are presented and compared with a GaAs reference cell. An extended photoresponse in contrast to the GaAs reference cell was confirmed for all these cells. The effect of inserting QD layers into emitter and base region on device performance is shown. The Jsc is reduced, while the Voc is maintained. The cell with QDs located toward the base side shows better performance, confirmed by both current-voltage and spectral response measurements. [ABSTRACT FROM AUTHOR]

We observe an induced switchable magnetic moment of 1.6±0.40μB/Fe for the nominally antiferromagnetic LaFeO3 extending two to four interface layers into the non-charge transfer system La0.7Sr0.3MnO3/LaFeO3/SrTiO3(111). Simultaneously a mismatch of oxygen octahedra rotations at the interface implies an atomic reconstruction of reduced symmetry at the interface, reaching two to five layers into LaFeO3. Density functional theory of a structure with atomic reconstruction and different correlation strength shows a ferrimagnetic state with a net Fe moment at the interface. Together these results suggest that engineered oxygen octahedra rotations, affecting the local symmetry, affect electron correlations and can be used to promote magnetic properties. [ABSTRACT FROM AUTHOR]

Scanning precession electron diffraction (SPED) enables the local crystallography of materials to be probed on the nanoscale by recording a two-dimensional precession electron diffraction (PED) pattern at every probe position as a dynamically rocking electron beam is scanned across the specimen. SPED data from nanocrystalline materials commonly contain some PED patterns in which diffraction is measured from multiple crystals. To analyse such data, it is important to perform nanocrystal segmentation to isolate both the location of each crystal and a corresponding representative diffraction signal. This also reduces data dimensionality significantly. Here, two approaches to nanocrystal segmentation are presented, the first based on virtual dark-field imaging and the second on non-negative matrix factorization. Relative merits and limitations are compared in application to SPED data obtained from partly overlapping nanoparticles, and particular challenges are highlighted associated with crystals exciting the same diffraction conditions. It is demonstrated that both strategies can be used for nanocrystal segmentation without prior knowledge of the crystal structures present, but also that segmentation artefacts can arise and must be considered carefully. The analysis workflows associated with this work are provided open-source. LAY DESCRIPTION: Scanning precession electron diffraction is an electron microscopy technique that enables studies of the local crystallography of a broad selection of materials on the nanoscale. The technique involves the acquisition of a two-dimensional diffraction pattern for every probe position in an area of the sample. The four-dimensional dataset collected by this technique can typically comprise up to 500 000 diffraction patterns. For nanocrystalline materials, it is common that single diffraction patterns contain signals from overlapping crystals. To process such data, we use nanocrystal segmentation, where a representative diffraction pattern is constructed for each individual crystal, together with a real space image showing its morphology and location in the data. This reduces the dimensionality of the data and allows unmixing of signals from overlapping crystals. In this work, we demonstrate two methods for nanocrystal segmentation, one based on creating virtual dark-field images, and one based on unsupervised machine learning. A model system of partly overlapping nanoparticles is used to demonstrate the segmentation, and a demanding case for segmentation is highlighted, where some crystals are not discernible based on their diffraction patterns. To obtain a more complete nanocrystal segmentation, we add an image segmentation routine to both methods, and we discuss benefits and limitations of the two methods. The demonstration data and the used code are provided open-source, so that it can be used by everyone for analysis of nanocrystalline materials or as a starting point for further development of nanocrystal segmentation in scanning precession electron diffraction data., (© 2019 The Authors. Journal of Microscopy published by John Wiley & Sons Ltd on behalf of Royal Microscopical Society.)

Beryl in different varieties (emerald, aquamarine, heliodor etc.) displays a wide range of colours that have fascinated humans throughout history. Beryl is a hexagonal cyclo-silicate (ring-silicate) with channels going through the crystal along the c-axis. The channels are about 0.5 nm in diameter and can be occupied by water and alkali ions. Pure beryl (Be 3 Al 2 Si 6 O 18 ) is colourless (variety goshenite). The characteristic colours are believed to be mainly generated through substitutions with metal atoms in the lattice. Which atoms that are substituted is still debated it has been proposed that metal ions may also be enclosed in the channels and that this can also contribute to the crystal colouring. So far spectroscopy studies have not been able to fully answer this. Here we present the first experiments using atomic resolution scanning transmission electron microscope imaging (STEM) to investigate the channel occupation in beryl. We present images of a natural beryl crystal (variety heliodor) from the Bin Thuan Province in Vietnam. The channel occupation can be visualized. Based on the image contrast in combination with ex situ element analysis we suggest that some or all of the atoms that are visible in the channels are Fe ions., (© 2016 The Authors. Journal of Microscopy published by JohnWiley & Sons, Ltd on behalf of the Royal Microscopical Society.)