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Developing a sufficiently accurate classical force field representation of molecules is key to realizing the full potential of molecular simulation as a route to gaining fundamental insight into a broad spectrum of chemical and biological phenomena. This is only possible, however, if the many complex interactions between molecules of different species in the system are accurately captured by the model. Historically, the intermolecular van der Waals (vdW) interactions have primarily been trained against densities and enthalpies of vaporization of pure (single-component) systems, with occasional usage of hydration free energies. In this study, we demonstrate how including physical property data of binary mixtures can better inform these parameters, encoding more information about the underlying physics of the system in complex chemical mixtures. To demonstrate this, we re-train a select number of the Lennard-Jones parameters describing the vdW interactions of the OpenFF 1.0.0 (Parsley) fixed charge force field against training sets composed of densities and enthalpies of mixing for binary liquid mixtures as well as densities and enthalpies of vaporization of pure liquid systems, and assess the performance of each of these combinations. We show that retraining against the mixture data almost universally improves the force field's ability to reproduce both pure and mixture properties, reducing some systematic errors that exist when training vdW interactions against properties of pure systems only.

The effect of chromatic aberration (CC) on the spatial resolution in transmission electron microscopy (TEM) was studied in thick specimens in which the sample becomes the limiting factor in the resolution. The sample influences the energy spread of the electron beam, allows only a limited electron dose, and modulates electron scattering events. The experimental set-up consisted of a thin silicon nitride membrane and a silicon wedge containing gold nanoparticles. The resolution was measured as a function of electron dose and sample thickness for different sample configurations and for different microscopy modalities including regular TEM, energy filtered TEM (EFTEM) and CC-corrected TEM. Comparison with an analytical model aided the understanding of the experimental data applied over varied conditions. The general trend for all microscopy modalities was a transition from a noise-limited resolution at low electron dose to a CC-limited resolution at high-dose in the absence of beam blurring. EFTEM required an accurate energy slit offset and an optimal energy spread to energy-slit width ratio to surpass regular TEM. The key advantage of CC correction appeared to be the best possible resolution for larger sample thickness at low electron dose outperforming EFTEM by about fifty percent. Several hypothetical sample configurations relevant to liquid phase electron microscopy were evaluated as well to demonstrate the capabilities of the analytical model and to determine the most optimal microscopy modality for this type of experiment. The analytical model included an automated optimization of the EFTEM settings and may aid in optimizing the sample-limited resolution for experimental analysis and planning. The research was funded by the Deutsche Forschungsgemeinschaft project TFS-STEM

The basic principles of crystallography are reviewed, including the lattice, basis and reciprocal lattice. The Bragg diffraction law and Laue equation, which describe coherent scattering from a crystalline material, are derived, and the structure factor and differential cross-section are obtained in the static approximation. It is explained how the presence of defects, short-range order, and reduced dimensionality causes diffuse scattering. For non-crystalline materials, such as liquids and glasses, the pair distribution function and density-density correlation function are introduced, and their relation to the static structure factor established. For molecular fluids, the form factor is defined and calculated for a diatomic molecule, and the separation of intra- and inter-molecular scattering is discussed. The principles of small-angle neutron scattering are described.

Charcoal consists mostly of carbon materials prepared by carbonization, i.e., traditionally by pyrolysis [1,2] of wood pieces in a kiln. At a high enough temperature and an absence of oxygen [3], high-quality charcoal with low resistance can be produced. A possible application of the low-resistivity charcoal is as an electrode material for electrochemical devices. In this research, bamboo waste was used to produce low-resistance bamboo charcoal. During heating, the temperature gradually increased up to 700°C, was kept approximately constant overnight, and was left to cool down to room temperature. Then, the charcoal bamboo pieces were obtained. A rough temperature-resistivity map was constructed. The bamboo charcoals were divided into 3 resistivity ranges, namely, 20, 100 and 1000 ohm.cm-1. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and microEDX (energy dispersive X-ray spectroscopy), were conducted for charcoal morphology and spectroscopic characterization [4-6]. The morphological results from SEM did not show any significant differences among bamboo charcoals with different resistivity. DF-STEM and EDS-STEM mapping revealed impurities inside the bamboo charcoal. Elemental analysis of micro areas showed weight percentage of carbon and other impurities in the bamboo charcoals. The 20 ohm.cm-1 bamboo charcoal was the best among all resistivity studied in terms of purity and main carbon structure. Decreasing the impurity content was found to be one of the essential parameters to obtain low resistivity bamboo charcoal. It was concluded that improving the stability and condition of the burning process in the conventional kiln was necessary in order to get a high yield of low resistance bamboo charcoals.

In this study, hydrothermal carbonization of carrot juice was conducted at 180 °C for 6 hours, followed by annealing at 500 °C for 6 hours. In the absence of a catalyst, hydrothermal carbonization of carrot juice produced hollow and solid carbon microspheres (CMS) with diameters ranging from 0.3 to 4.0 µm. SEM and TEM images of the CMS showed various morphologies and sizes. X-ray diffraction and Raman spectroscopy indicated the CMS had a disordered graphitic structure. A HAADF micrograph showed that although the majority of the CMS in this study were hollow, there were also solid spheres which had not previously been reported for hydrothermal carbonization. STEM EDS mapping of a solid CMS indicated approximately 95 wt% of C with traces of N, O, Si, P, S, Cl and K. The effect of the starting precursors on the hard sphere formation mechanism is discussed.

Dye sensitized solar cells (DSSCs) consist of photoanodes (dye adsorbed porous semiconductor film), electrolytes and counter electrodes. Nanostructured materials play important parts in both the photoanodes and the counter electrodes, while dyes are there to absorb photons and generate electron-hole pairs and electrolytes are there to transfer electrons from the photoanodes to the counter electrodes. In this study, to enhance light absorption and minimize electron-hole recombination, Ag nanoparticles and MgO nanolayer were coated on TiO2, respectively. To enable a long lifetime, i.e. avoiding liquid electrolyte leakage, quasi-solid-state (QSS) DSSCs were fabricated. PtSn nanoparticles were prepared by a simple chemical reduction method on graphene oxide (GO) to compare with conventional Pt catalyst on FTO substrates as counter electrodes. An average efficiency of the QSS DSSCs with PtSn/GO co-catalysts was found to outperform that of the QSS DSSCs with conventional Pt catalyst. A mixed microstructure of the PtSn/GO co-catalyst was observed. Although, PtSn2 and Pt2Sn3 phases were suggested by XRD, in a small region observed by EDX-STEM, it was found that C, O and Si were distributed uniformly on the graphene oxide film. Pt was also distributed uniformly, but the signal was low so there were only a few X-Ray counts across the image. There was no sign of Pt being concentrated in the particles. However, Sn was found to be concentrated in the particles without any other elements.

Solubility is a fundamental property of widespread significance. Despite its importance, its efficient and accurate prediction from first principles remains a major challenge. Here we propose a novel method to predict the solubility of molecules using a density of states (DOS) approach from classical molecular simulation. The method offers a potential route to solubility prediction for large (including drug-like) molecules over a range of temperatures and pressures, all from a modest number of simulations. The method was employed to predict the solubility of sodium chloride in water at ambient conditions, yielding a value of 3.77(5) mol kg-1. This is in close agreement with other approaches based on molecular simulation, the consensus literature value being 3.71(25) mol kg-1. The predicted solubility is about half of the experimental value, the disparity being attributed to the known limitation of the Joung-Cheatham force field model employed for NaCl. The proposed method also accurately predicted the NaCl model's solubility over the temperature range 298-373 K directly from the density of states data used to predict the ambient solubility.

We report on the structural, magnetic, and electronic properties of two new double-perovskites synthesized under high pressure; Pb2CaOsO6 and Pb2ZnOsO6. Upon cooling below 80 K, Pb2CaOsO6 simultaneously undergoes a metal--insulator transition and develops antiferromagnetic order. Pb2ZnOsO6, on the other hand, remains a paramagnetic metal down to 2 K. The key difference between the two compounds lies in their crystal structure. The Os atoms in Pb2ZnOsO6 are arranged on an approximately face-centred cubic lattice with strong antiferromagnetic nearest-neighbor exchange couplings. The geometrical frustration inherent to this lattice prevents magnetic order from forming down to the lowest temperatures. In contrast, the unit cell of Pb2CaOsO6 is heavily distorted up to at least 500 K, including antiferroelectric-like displacements of the Pb and O atoms despite metallic conductivity above 80 K. This distortion relieves the magnetic frustration, facilitating magnetic order which in turn drives the metal--insulator transition. Our results suggest that the phase transition in Pb2CaOsO6 is spin-driven, and could be a rare example of a Slater transition., Comment: 14 pages, 9 figures. Accepted as a regular article in Phys. Rev. B

Bulk studies have revealed a first-order valence phase transition in Ba2PrRu1−xIrxO6 (0.10 ≤ x ≤ 0.25), which is absent in the parent compounds with x = 0 (Pr3+) and x = 1 (Pr4+), which exhibit antiferromagnetic order with transition temperatures TN = 120 and 72 K, respectively. In the present study, we have used magnetization, heat capacity, neutron diffraction, inelastic neutron scattering and x-ray absorption measurements to investigate the nature of the Pr ion in x = 0.1. The magnetic susceptibility and heat capacity of x = 0.1 show a clear sign of the first order valence phase transition below 175 K, where the Pr valence changes from 3+ to 4+. Neutron diffraction analysis reveals that x = 0.1 crystallizes in a monoclinic structure with space group P21/n at 300 K, but below 175 K two phases coexist, the monoclinic having the Pr ion in a 3+ valence state and a cubic one (Fm3m) having the Pr ion in a 4+ valence state. Clear evidence of an antiferromagnetic ordering of the Pr and Ru moments is found in the monoclinic phase of the x = 0.1 compound below 110 K in the neutron diffraction measurements. Meanwhile the cubic phase remains paramagnetic down to 2 K, a temperature below which heat capacity and susceptibility measurements reveal a ferromagnetic ordering. High energy inelastic neutron scattering data reveal well-defined highenergy magnetic excitations near 264 meV at temperatures below the valence transition. Low energy INS data show a broad magnetic excitation centred at 50 meV above the valence transition, but four well-defined magnetic excitations at 7 K. The high energy excitations are assigned to the Pr4+ ions in the cubic phase and the low energy excitations to the Pr3+ ions in the monoclinic phase. Further direct evidence of the Pr valence transition has been obtained from the x-ray absorption spectroscopy. The results on the x = 0.1 compound are compared with those for x = 0 and 1.

Organic–inorganic halide perovskites have attracted a lot of interest for applications such as light-emitting diodes (LEDs), photodetectors and lasers. As this group of materials is highly sensitive to moisture and oxygen, a simple in situ controlled synthesis of these nanoparticles (NPs) in a polymer matrix will open up the possibility for a wide range of light-emitting and color-conversion applications. This paper presents a simple in situ approach for controlled synthesis of organic–inorganic lead halide perovskite NPs as a function of halide composition in polymer matrix (polymethyl methacrylate, PMMA). Chemical mapping using scanning transmission electron microscopy (STEM) shows a varying of size distribution of the lead halide perovskite NPs. Mixed halide NP in PMMA were composed of grains of different compositions. Time-resolved photoluminescence (TRPL) correlated with compositional information from energy dispersive X-ray spectroscopy (EDX) provides evidence for the role of surfaces and grain boundaries on charge recombination in the nanoparticles. The annealing temperature and the molar ratio of the precursors were found to greatly affect the morphology and composition of the perovskite NP in polymer matrix.

The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT2Al10 (T=Fe, Ru and Os) possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu2Al10 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10 with a paramagnetic ground state down to 50 mK. We are investigating this family of compounds, both in polycrystalline and single crystal form, using inelastic neutron scattering to understand the role of anisotropic c-f hybridization on the spin gap formation as well as on their magnetic properties. We have observed a clear sign of a spin gap in all three compounds from our polycrystalline study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive gapped spin wave excitations below TN. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy, which prefers moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K. We will discuss the origin of the anisotropic hybridization gap in CeFe2Al10 based on theoretical models of heavy-fermion semiconductors.

In this paper, the growth kinetics of Cu–Al intermetallic compounds formed during isothermal annealing of Pd–Cu wire bonds with different palladium distribution at 175 °C are investigated by electron microscopy and compared to bare Cu wire bonds. Transmission electron microscopy (TEM) was used to provide high resolution imaging of the Cu–Al IMCs in the as-bonded state and TEM-EDX used to analyze the concentrations of Pd at the bond interface in the as-bonded state. Cu–Al IMCs were found to grow thicker with increasing annealing duration. The growth kinetics of the Cu–Al IMCs were correlated with the diffusion process during thermal annealing. The IMC thickness for Pd–Cu wire bonds with Pd at the bond interface was found to be thinner as compared to that for Pd–Cu wire bonds with no Pd at the bond interface. Thus, the presence of palladium at the bond interface has slowed down the IMC growth. Nano-voids were found in the Pd–Cu wire bonds with Pd at the bond interface, but not in the Pd–Cu wire bonds with no Pd at the bond interface. The IMC growth rate for the Pd–Cu bonds with no Pd was found to be close to that for bare Cu for the initial annealing durations. Corresponding bond pull testing showed that Pd–Cu wire bonds containing Pd have best preserved the bond strength after 168 h aging at 175 °C due to the beneficial presence of Pd.

The study of ultrafast dynamics is a new tool to understand and control the properties of correlated oxides. By enhancing some properties and realizing new dynamically excited phrases, this tool has opened new routes for technological applications. LaCoO3 is one paradigmatic example where the strong electron, spin, and lattice coupling induced by electronic correlations results in a low-temperature spin transition and a high-temperature semiconductor-to-metal transition that is still not completely understood. Here, we monitor ultrafast metallization in LaCoO3 using time-resolved soft x-ray reflectivity experiments. While the process is entangled at the Co L-3 edge, the time information of the different channels is decrypted at different resonant energies of the O K edge. Metallization is shown to occur via transient electronic, spin, and lattice separation. Our results agree with the thermodynamical model and demonstrate the potential of femtosecond soft x-ray experiments at the O K edge to understand correlated oxides. We thank Karsten Holldack, Niko Pontius, and Christian Schuessler-Langeheine, for experimental support at the FemtoSpeX facility during the experiments. We acknowledge Alexander Folisch for supporting the realization of the experiments at the FEMTOSPEX and Kurt Ament for editing the manuscript. M. I. acknowledges BMBF Grant no. 05K12GU2 for financial support.

Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations. Classical spin ices provide the first context in which it is possible to control emergent magnetic monopoles, and anisotropic exchange leads to even richer behaviour associated with large quantum fluctuations. Whether the magnetic ground state of Yb2Ti2O7 is a quantum spin liquid or a ferromagnetic phase induced by a Higgs transition appears to be sample dependent. Here we have determined the role of structural defects on the magnetic ground state via the diffuse scattering of neutrons. We find that oxygen vacancies stabilise the spin liquid phase and the stuffing of Ti sites by Yb suppresses it. Samples in which the oxygen vacancies have been eliminated by annealing in oxygen exhibit a transition to a ferromagnetic phase, and this is the true magnetic ground state., Exploring the role of structural defect is essential to understand the exotic quantum spin phenoma in rare earth pyrochlores. Here the authors show oxygen vacancies can stabilise the spin liquid phase and reveal the ferromagnetic ground state when oxygen vacancies are eliminated in Yb2Ti2O7.

We describe a new approach for preparing organic-inorganic perovskite solar cells for electron beam-induced current (EBIC) measurements in plan-view geometry. This method substantially reduces sample preparation artefacts, provides good electrical contact and keeps the preparation steps as close as possible to those for real devices. Our EBIC images were acquired simultaneously with annular dark-field scanning transmission electron microscopy images using a home-made highly sensitive EBIC amplifier. High-angle annular dark-field images and energy dispersive X-ray maps were recorded from the same area immediately afterwards. This allowed the EBIC contrast to be correlated with regions containing N and a deficiency of O. The EBIC contrast was also found to be similar to secondary electron contrast recorded with a scanning electron microscope. By identifying the generation and absorption electron processes, we determine that EBIC cannot be separated from the secondary electron and absorbed currents. This means that careful analysis needs to be performed before conclusions can be made on the origin of the current measured across p-n or p-i-n junctions. Nanyang Technological University We are grateful to Thomas Duden for the fabrication and operation of the amplifier during the EBIC experiments. M.D. acknowledges fi- nancial support from Nanyang Technological University start-up grant M4081924

Exploiting graphene’s exceptional physical properties in polymer composites is a significant challenge because of the difficulty in controlling the graphene conformation and dispersion. Reliable processing of graphene polymer composites with uniform and consistent properties can therefore be difficult to achieve. We demonstrate distinctive regimes in morphology and nanocomposite properties, achievable through systematic control of shear rate and shear history. Remarkable changes in electrical impedance unique to composites of graphene nanoplates (GNPs) are observed. Low shear rates ≤ 0.1 s-1 break up the typical GNP agglomerates found in graphene composites, exfoliate the GNPs to fewer graphene layers and reduce orientation, enhancing electrical conductivi-ty in the composite materials. Whereas, at higher shear rates GNP orientation increases and the conductivity reduces by four orders of magnitude, as the graphene filler network is broken down. The structure of the composite continues to evolve, reflected in fur-ther changes in conductivity, after the shear force has been removed and the process temperature maintained. This work provides critical insights for understanding and controlling GNP orientation and dispersion within composites and will have important consequences in the industrial processing of graphene polymer composites via the informed design and choice of processing conditions.

Rapid development of cold spray technology has made it a viable option to remanufacture and repair damaged engineering components made of Ti-6Al-4V (Ti64). This solid-state deposition process contributes to the distinctive microstructure of Ti64 coatings. In this study, the microstructural evolution of Ti64 from feedstock powder to coating as a result of high strain rate deformation is evaluated. TEM lamellae were extracted from the particle-substrate and particle-particle interfaces of a cold sprayed coating by focused ion beam milling and a comprehensive microstructural analysis was carried out. The feedstock powder is predominantly composed of martensitic lathes. The microstructure of the coating at the particle-substrate interface is noticeably different from the microstructure of the feedstock powder. Narrow regions consisting of nanometre-sized grains are observed in both the particle and substrate in the vicinity of the interface. Adiabatic shear instability under localized high strain rate deformation and heat accumulation are believed to be responsible for this observation. However, the martensitic structure is partially retained in the less deformed region of the particles, further away from the interfaces. The formation mechanism of the microstructure observed from the inner region of particle, at the vicinity of the particle-substrate and particle-particle interfaces respectively is discussed in the light of microstructural observations and finite element modelling. NRF (Natl Research Foundation, S’pore) Accepted version

Strong spin-orbit coupling, resulting in the formation of spin-momentum-locked surface states, endows topological insulators with superior spin-to-charge conversion characteristics, though the dynamics that govern it have remained elusive. Here, we present an all-optical method that enables unprecedented tracking of the ultrafast dynamics of spin-to-charge conversion in a prototypical topological insulator Bi$_2$Se$_3$/ferromagnetic Co heterostructure, down to the sub-picosecond timescale. Compared to pure Bi$_2$Se$_3$ or Co, we observe a giant terahertz emission in the heterostructure than originates from spin-to-charge conversion, in which the topological surface states play a crucial role. We identify a 0.12-picosecond timescale that sets a technological speed limit of spin-to-charge conversion processes in topological insulators. In addition, we show that the spin-to-charge conversion efficiency is temperature independent in Bi$_2$Se$_3$ as expected from the nature of the surface states, paving the way for designing next-generation high-speed opto-spintronic devices based on topological insulators at room temperature., Comment: 19 pages, 4 figures

In this study, the atomic arrangement of the decagonal phase in a spark-plasma-sintered Al–Cr–Fe alloy has been studied by Cs-corrected high angle annular dark field scanning transmission electron microscopy (HAADF STEM) for the first time. We have found that three types of atomic clusters exist as basic structural units: star, flattened hexagon and decagon with an edge-length of 0.65 nm. These three types of units are linked to each other by sharing edges or inter-penetrating, with adjacent star clusters overlapping each other. The respective structural models of these structural units are proposed from the HAADF STEM images. MOE (Min. of Education, S’pore)

The separation of rare metals from the ores and commercially available compounds is an important issue due to the need of their high purity in advanced materials and devices. Important examples of two highly important elements that co-exist in the ores are scandium and thorium. Scandium containing ores and consequently also commercially available scandium compounds often contain traces of thorium which is very difficult to separate. We used graphene oxide for the selective sorption of thorium ions from scandium and thorium mixtures originating from the mined ores as well as from commercially available scandium salts. Our results showed that graphene oxide has an extreme affinity towards thorium ions. After the sorption process the graphene oxide contained over 20 wt% of thorium while the amount of scandium sorbed on GO was very low. This phenomenon of high sorption selectivity of graphene oxide can be applied in industry for the purification of various chemicals containing scandium and for separation of thorium containing mixtures. Alternatively, this methodology can be used for preconcentration of thorium from low-grade ores and its further use in the new generation of nuclear reactors.

We report growth of large single crystals of the triangular-lattice antiferromagnetic compound Ba3CoSb2O9 by the floating-zone technique in an image furnace. Evaporation of Sb due to its high volatility was controlled by high pressure and addition of excess Sb in the starting materials to compensate for the losses. The crystal quality was analysed using different X-ray techniques, and the magnetic transition temperature was confirmed by magnetization and heat capacity measurements.

This figure shows the ferromagnetic curve and inset the zero-field cooling (ZFC) and field cooling (FC) curves of Ce0.95Cr0.05O2 particles prepared by solid state reaction. This result was indicated that the sample is an intrinsic ferromagnetism. The ZFC and FC curves showed smooth curves and no signal of secondary phase in the range of 2-350K which conformed that magnetic behavior in our sample is not supported by magnetic impurities.Display Omitted The pure phase of Cr-doped CeO2 particles have been successfully prepared by solid state reaction.The ferromagnetism (FM) at room temperature (RT) was observed in Cr-doped CeO2 particles.Oxygen vacancy defect played an important role in the magnetism of Cr-doped CeO2 particles.The lattice distortion observed on shift of the diffraction peaks that causes from oxygen vacancy.The RT-FM is enhanced after annealing in argon (Ar) atmosphere. This work reports the room-temperature ferromagnetism of Cr-doped CeO2 (Ce1-xCrxO2 when 0≤x≤0.07) particles prepared by solid state reaction. The precursors were calcined in air at 1350?C for 10h to obtain nanoparticles. The prepared samples were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID). The XRD results showed a single phase nature with cubic structure without any impurity phase for all Cr-doped CeO2 samples and the lattice distortion observed on shift of the diffraction peaks that causes from defects/oxygen vacancy. Room temperature (RT) ferromagnetism (FM) is observed in samples with a maximum saturation magnetization of 8.82×10-4emu/g at 2kOe for x=0.05. In addition, the RT-FM is enhanced after annealing in argon atmosphere at 700?C for 3h. The F-center exchange interaction has been proposed to play in the magnetic properties of Cr-doped CeO2 particles.

We show that the thermoelectric compound Ag 0.5 Bi 1.5 Se 0.15 Te 2.85 can be prepared by mechanical alloying from elemental Ag, Bi, Se and Ag powers. By using complementary microstructural characterization techniques, i.e. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy and energy dispersive X-ray spectroscopy, it was possible to find the exact composition of each phase formed in the compound. The phases formed were Bi 2 Se 0.01 Te 2.99 and polymorphs of AgTe including an unusual β-Ag 2 Te phase.

Doping of graphene via low energy ion implantation could open possibilities for fabrication of nanometer-scale patterned graphene-based devices as well as for graphene functionalization compatible with large-scale integrated semiconductor technology. Using advanced electron microscopy/spectroscopy methods, we show for the first time directly that graphene can be doped with B and N via ion implantation and that the retention is in good agreement with predictions from calculation-based literature values. Atomic resolution high-angle dark field imaging (HAADF) combined with single-atom electron energy loss (EEL) spectroscopy reveals that for sufficiently low implantation energies ions are predominantly substitutionally incorporated into the graphene lattice with a very small fraction residing in defect-related sites.

Metals cannot exhibit ferroelectricity because static internal electric fields are screened by conduction electrons, but in 1965, Anderson and Blount predicted the possibility of a ferroelectric metal, in which a ferroelectric-like structural transition occurs in the metallic state. Up to now, no clear example of such a material has been identified. Here we report on a centrosymmetric (R-3c) to non-centrosymmetric (R3c) transition in metallic LiOsO3 that is structurally equivalent to the ferroelectric transition of LiNbO3. The transition involves a continuous shift in the mean position of Li+ ions on cooling below 140K. Its discovery realizes the scenario described by Anderson and Blount, and establishes a new class of materials whose properties may differ from those of normal metals., Manuscript of published version, including Supplementary Information. See also News & Views article by V. Keppens, Nature Materials 12, 952 (2013)

Transmission electron microscopy (TEM) in combination with electron tomography is widely used to obtain nanometer scale three-dimensional (3D) structural information about biological samples. However, studies of whole eukaryotic cells are limited in resolution and/or contrast on account of the effect of chromatic aberration of the TEM objective lens on electrons that have been scattered inelastically in the specimen. As a result, 3D information is usually obtained from sections and not from whole cells. Here, we use chromatic aberration-corrected TEM to record bright-field TEM images of nanoparticles in a whole mount macrophage cell. Tilt series of images are used to generate electron tomograms, which are analyzed to assess the spatial resolution that can be achieved for different vertical positions in the specimen. The uptake of gold nanoparticles coated with low-density lipoprotein (LDL) is studied. The LDL is found to assemble in clusters. The clusters contain nanoparticles taken up on different days, which are joined without mixing their nanoparticle cargo.

Geometric phase analysis has been applied to high resolution aberration corrected (scanning) transmission electron microscopy images of InAs/GaAs quantum dot (QD) materials. We show quantitatively how the lattice mismatch induced strain varies on the atomic scale and tetragonally distorts the lattice in a wide region that extends several nanometers into the GaAs spacer layer below and above the QDs. Finally, we show how V-shaped dislocations originating at the QD/GaAs interface efficiently remove most of the lattice mismatch induced tetragonal distortions in and around the QD., Comment: 11 pages, 3 figures

Molten-salt reactors (MSRs) can provide inexpensive industrial process heating in addition to generating electricity. In most cases, this can be best accomplished by design simplification, which results in improvements to MSR’s already existing and inherently strong safety characteristics. This is just one of a number of possible future scenarios that will influence the way in which MSR technology can develop and become marketable. The emphasis in this paper is to develop a reactor with application to the widest possible range of industries. This paper concentrates on the need to develop the inherent safety characteristics of the single fluid thermal reactor with the expectation that sufficient reliability and safety will be achieved in design so that these power generators will eventually be accepted for close integration into the fabric of modern society. It seems inevitable that the required licensing procedures needed for MSRs will vary considerably depending on their type because different designs vary so much. Those used for low-temperature process heat in addition to power generation require much less demanding regulatory procedures than those operating at higher temperatures. This is largely because long-term corrosion is more problematic at higher temperatures and present-day construction materials limit the development of MSRs from reaching their full potential. With appropriate experience with operating early designs of MSRs it is reasonable to expect that lower temperature versions will become certifiable for use in close proximity to a large range of human activities. Ultimately these reactors will be controllable remotely without the local attendance of technical staff.

We have measured the lifetime and frequency of acoustic phonons in niobium by triple-axis neutron spectroscopy over a range of temperatures spanning the superconducting transition temperature, and have extracted quantitative information on the q and polarisation dependence of the electron-phonon interaction. The behaviour of the transverse modes supports a simple calculation based on the BCS theory of superconductivity, but the damping of a longitudinal mode appears to be unusually severe.

We examined the terahertz magnetoelectric response of cupric oxide, a high-temperature multiferroic with a cycloidal spin structure that induces an electrical polarisation. Terahertz time-domain spectroscopy at various temperatures and magnetic fields uncovered electromagnon and magnon modes, providing insights into the spin Hamiltonian. © 2013 IEEE.

We have applied the technique of polarised neutron reflectometry (PNR) to investigate the magnetic held penetration in different superconducting phases of Nb, namely the Meissner state (H < H-c1), the mixed state (H-c1 < H < H-c2) and the surface superconductivity state (H-c2 < H < H-c3) around 4 K. The sample was a sputtered him of Nb with a 3 mu m thickness on a 5 mm Si crystal substrate. The measurements were carried out on the CRISP reflectometer at the ISIS facility, with field strengths between 400 and 4500 Oe. We present preliminary data for the spin-dependent reflectivity as a function of applied field. (C) 1998 Elsevier Science B.V. All rights reserved.

The magneto-electric multiferroic TbMn 2O 5 has a complex magnetic structure in three different magnetically ordered phases. We have determined the nature of the induced magnetic order on the oxygen sites in the commensurate magnetic phase through full linear X-ray polarisation analysis at the oxygen K edge. This has been achieved rotating the linear polarisation of the incident beam at the source, and using multilayers to analyse the polarisation state of the scattered X-ray beam. We have confirmed that the anisotropy of the magnetic scattering at the oxygen edge is consistent with the anisotropy of the manganese magnetic structure. © 2012 EDP Sciences, Springer-Verlag.

The influence of electrostatic interactions on the ordering of sodium ions in Na$_x$CoO$_2$ is studied theoretically through Monte-Carlo simulations. For large $x$ small di- or tri-vacancy clusters are stable with respect to isolated Na vacancies. At commensurate fillings these small clusters order in triangular superstructures. These results agree with recent electron diffraction data at $x=1/2$ and 3/4. We have performed neutron La\"ue diffraction experiments at higher $x$, which confirm the predictions of this simple model. The consequences on the properties of the electronic charges in the Co layers are discussed., Comment: Talk at LT24 International Conference, Orlando, FLO, USA. August 2005. Accepted for publication in LT24 Conference Proceedings (AIP. Proc.). 2 pages, 4 figures

We have studied the temperature dependence of crystal field (CF) excitation linewidths of lanthanide ions (Er and Ho) in YBa 2 Cu 3 O 7 by neutron scattering. The Ho data reveal an anomaly in the CF damping around T c with no evidence of a coherence peak below T c . We have applied the theory of Becker, Fulde and Keller to derive the reduced s - f coupling constants from the CF linewidth data for the ions Er, Ho and Tm.

We demonstrate for the first time that small-angle neutron scattering can be used as a direct and accurate method to determine the temperature dependence of the unperturbed dimensions of a polymer. The sensitivity of the technique arises from the remarkable accuracy with which the random walk model can be used to describe the single-chain structure factor, and enables us to detect changes in the polymer radius of gyration of less than 0.5%. We present results for molten polyethylene and verify the accepted value of the temperature coefficient of thermal expansion.

The dispersion of the low-energy magnetic excitations of the Pr sublattice in PrBa2Cu3O6.2 is determined by inelastic neutron scattering measurements on a single crystal. The dispersion, which shows the effect of interactions with the Cu spin-waves, is well described by a model of the coupled Cu-Pr magnetic system. This enables values for the principal exchange constants to be determined, which suggest that both Pr-Pr and Cu-Pr interactions are important in producing the anomalously high ordering temperature of the Pr sublattice. Measurements of the Cu optic spin wave mode show that the inter-layer Cu-Cu exchange is significantly lower than in YBa2Cu3O6.2., To be published Phys. Rev. Lett

An impurity-driven magnetic phase transition has been investigated in LaCoO3 at temperatures below that of the thermally induced spin state transition of the Co3+ ion. We have discovered a saturating component of the magnetisation, which we attribute to previously unobserved interactions between magnetic excitons. These conclusions are confirmed by muon spin spectroscopy which indicates an ordering temperature of 50 K in both the transverse and zero-field configurations. Low-energy muon measurements demonstrate that the magnetic behaviour is independent of implantation energy and hence a property of the bulk of the material. The magnetic exciton formation is attributed to the interaction between electrons bound at oxygen vacancies and neighbouring cobalt ions, and is proposed as the precursor to the magneto-electronic phase separation recently observed in doped lanthanum cobaltite. © EDP Sciences.

We report the discovery of incommensurate magnetic order in non-superconducting single crystals PrBa2Cu3O6.92. Resonant X-ray magnetic scattering at the Pr L-II and L-III edges and high resolution neutron diffraction were used to characterise the magnetic order on the different magnetic sublattices. The data reveal that the Pr sublattice orders at a temperature of 19 K in an incommensurate structure with ordering wavevector (0.5 +/- delta, 0.5, 0) or (0.5, 0.5 +/- delta, 0), delta approximate to 0.006-0.008, A spin reorientation in the Pr sublattice to a commensurate antiferromagnetic structure with ordering wavevector (0.5, 0.5, 0.5) takes place at a temperature close to 9 K. (C) 1999 Elsevier Science B.V. All rights reserved.

The thermal diffusivity in the vicinity of the magnetic transition of a set of La1-xSrxMnO3 (0less than or equal toxless than or equal to0.3) single crystals has been measured using the photopyroelectric technique. Taking into account that the inverse of the thermal diffusivity behaves as the specific heat, the critical exponent alpha has been obtained. In the pure and lightly doped samples (x=0,0.05) where the transition is antiferromagnetic-paramagnetic, the critical exponent is consistent with the Heisenberg model (alpha=-0.115). For Sr concentration higher than 0.20, where the low temperature phase is ferromagnetic, a drastic change in the critical exponent has been observed, approaching Ising behavior (alpha=+0.11) at the highest concentration. (C) 2004 American Institute of Physics.

We use ultrafast resonant x-ray diffraction to study the magnetic order in CuO under conditions of high electronic excitation. By measuring changes in the spectral shape of the Cu2+ magnetic (1/2 0 â1/2) reflection we investigate how an intense optical pump pulse perturbs the electronic and magnetic states. We observe an energy shift in the magnetic resonance at short times after the pump pulse. This shift is compared with expectations from band structure calculations at different electronic temperatures. This spectral line shift indicates that although the electrons are heated to effective electron temperatures far above TN on a time scale faster than the experimental resolution, magnetic order persists in this highly excited state for several hundred femtoseconds. © 2014 American Physical Society.