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Insight into the nucleation, growth and phase transformations of calcium sulphate could improve the performance of construction materials, reduce scaling in industrial processes and aid understanding of its formation in the natural environment. Recent studies have suggested that the calcium sulphate pseudo polymorph, gypsum (CaSO4·2H2O) can form in aqueous solution via a bassanite (CaSO4·0.5H2O) intermediate. Some in situ experimental work has also suggested that the transformation of bassanite to gypsum can occur through an oriented assembly mechanism. In this work, we have exploited liquid cell transmission electron microscopy (LCTEM) to study the transformation of bassanite to gypsum in an undersaturated aqueous solution of calcium sulphate. This was benchmarked against cryogenic TEM (cryo‐TEM) studies to validate internally the data obtained from the two microscopy techniques. When coupled with Raman spectroscopy, the real‐time data generated by LCTEM, and structural data obtained from cryo‐TEM show that bassanite can transform to gypsum via more than one pathway, the predominant one being dissolution/reprecipitation. Comparisons between LCTEM and cryo‐TEM also show that the transformation is slower within the confined region of the liquid cell as compared to a bulk solution. This work highlights the important role of a correlated microscopy approach for the study of dynamic processes such as crystallisation from solution if we are to extract true mechanistic understanding. [ABSTRACT FROM AUTHOR]

Summary: Formulation processing of organic crystalline compounds can have a significant effect on drug properties, such as dissolution rate or tablet strength/hardness. Transmission electron microscopy (TEM) has the potential to resolve the atomic lattice of these crystalline compounds and, for example, identify the defect density on a particular crystal face, provided that the sensitivity of these crystals to irradiation by high‐energy electrons can be overcome. Here, we acquire high‐resolution (HR) lattice images of the compound furosemide using two different methods: low‐dose HRTEM and bright‐field (BF) scanning TEM (STEM) scanning moiré fringes (SMFs). Before acquiring HRTEM images of furosemide, a model system of crocidolite (asbestos) was used to determine the electron flux/fluence limits of low‐dose HR imaging for our scintillator‐based, complementary metal‐oxide semiconductor (CMOS) electron camera by testing a variety of electron flux and total electron fluence regimes. An electron flux of 10 e−/(Å2 s) and total fluence of 10 e−/Å2 was shown to provide sufficient contrast and signal‐to‐noise ratio to resolve 0.30 nm lattice spacings in crocidolite at 300 kV. These parameters were then used to image furosemide which has a critical electron fluence for damage of ≥10 e−/Å2 at 300 kV. The resulting HRTEM image of a furosemide crystal shows only a small portion of the total crystal exhibiting lattice fringes, likely due to irradiation damage during acquisition close to the compound's critical fluence. BF‐STEM SMF images of furosemide were acquired at a lower electron fluence (1.8 e−/Å2), while still indirectly resolving HR details of the (001) lattice. Several different SMFs were observed with minor variations in the size and angle, suggesting strain due to defects within the crystal. Overall BF‐STEM SMFs appear to be more useful than BF‐STEM or HRTEM (with a CMOS camera) for imaging the crystal lattice of very beam‐sensitive materials since a lower electron fluence is required to reveal the lattice. BF‐STEM SMFs may thus prove useful in improving the understanding of crystallization pathways in organic compounds, degradation in pharmaceutical formulations and the effect of defects on the dissolution rate of different crystal faces. Further work is, however, required to quantitatively determine properties such as the defect density or the amount of relative strain from a BF‐STEM SMF image. [ABSTRACT FROM AUTHOR]

Summary: For many nanoparticle applications it is important to understand dispersion in liquids. For nanomedicinal and nanotoxicological research this is complicated by the often complex nature of the biological dispersant and ultimately this leads to severe limitations in the analysis of the nanoparticle dispersion by light scattering techniques. Here we present an alternative analysis and associated workflow which utilises electron microscopy. The need to collect large, statistically relevant datasets by imaging vacuum dried, plunge frozen aliquots of suspension was accomplished by developing an automated STEM imaging protocol implemented in an SEM fitted with a transmission detector. Automated analysis of images of agglomerates was achieved by machine learning using two free open‐source software tools: CellProfiler and ilastik. The specific results and overall workflow described enable accurate nanoparticle agglomerate analysis of particles suspended in aqueous media containing other potential confounding components such as salts, vitamins and proteins. Lay Description: In order to further advance studies in both nanomedicine and nanotoxicology, we need to continue to understand the dispersion of nanoparticles in biological fluids. These biological environments often contain a number of components such as salts, vitamins and proteins which can lead to difficulties when using traditional techniques to monitor dispersion. Here we present an alternative analysis which utilises electron microscopy. In order to use this approach statistically relevant large image datasets were collected from appropriately prepared samples of nanoparticle suspensions by implementing an automated imaging protocol. Automated analysis of these images was achieved through machine learning using two readily accessible freeware; CellProfiler and ilastik. The workflow presented enables accurate nanoparticle dispersion analysis of particles suspended in more complex biological media. [ABSTRACT FROM AUTHOR]

In this paper, the chemical interaction between catalyst and support was studied to understand the observed different growth rate of CNTs in our previous paper. Both pure MgO and Mg(NO3)2 • 6H2O as sources of the MgO catalyst support and Fel(SO4)3 • xH2O as the source of the Fe catalyst, were employed. A Fe catalyst supported on MgO was synthesized using the wet impregnation method followed by calcination. To compare the catalyst grain size and its distribution, the sample were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), BET specific surface area (SSA) measurement, and X-ray photoelectron spectroscopy (XPS). XPS technique was utilized complementary to demonstrate the existence of chemical interaction between MgO support and Fe catalyst. Results revealed that the type of precursor used to prepare the support had a significant infuence on the morphology of the support and the associated distribution of the Fe catalysts. The highest yield of MgFe2O4 phase was obtained using a pure MgO precursor which after calcination resulted in a homogenous distribution of nano-sized Fe particles over the support surface. [ABSTRACT FROM AUTHOR]

Annealing is necessary to achieve giant tunneling magnetoresistance (TMR) values in sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). In this study three complementary techniques were used to study the resulting changes in junction microstructure. The as-deposited TMR was modest, 5%, but rose to 101% after annealing at 325 °C for 1 h, corresponding to the tunneling spin polarization rising from 16% to 58%. Soft x-ray resonant magnetic scattering showed a roughening of the magnetic interfaces of the MTJ free layer, confirmed by transmission electron microscopy, which also showed the changes in the CoFeB and MgO to a lattice-matched polycrystalline form. [ABSTRACT FROM AUTHOR]

Materials with the pyrochlore/fluorite structure have diverse technological applications, from magnetism to nuclear waste disposal. Here we report the observation of structural instability present in the pyrochlores A2Zr2O6O' (A = Pr, La) and Yb2Ti2O6O', that exists despite ideal stoichiometry, ideal cation-ordering, the absence of lone pair effects, and a lack of magnetic order. Though these materials appear to have good long-range order, local structure probes find displacements, of the order of 0.01 nm, within the pyrochlore framework. The pattern of displacements of the A2O' sublattice mimics the entropically-driven fluxional motions characteristic of and well-known in the silica mineral β-cristobalite. The universality of such displacements within the pyrochlore structure adds to the known structural diversity and explains the extreme sensitivity to composition found in quantum spin ices and the lack of ferroelectric behavior in pyrochlores. [ABSTRACT FROM AUTHOR]

Both photons and electrons may be used to excite surface plasmon polaritons, the collective charge density fluctuations at the surface of metal nanostructures. By virtue of their nanoscopic and dissipative nature, a detailed characterization of surface plasmon (SP) eigenmodes in real space-time ultimately requires joint nanometer spatial and femtosecond temporal resolution. The latter realization has driven significant developments in the past few years, aimed at interrogating both localized and propagating SP modes. In this mini-review, we briefly highlight different techniques employed by our own groups to visualize the enhanced electric fields associated with SPs. Specifically, we discuss recent hyperspectral optical microscopy, tip-enhanced Raman nano-spectroscopy, nonlinear photoemission electron microscopy, as well as correlated scanning transmission electron microscopy-electron energy loss spectroscopy measurements targeting prototypical plasmonic nanostructures and constructs. Through selected practical examples from our own laboratories, we examine the information content in multidimensional images recorded by taking advantage of each of the aforementioned techniques. In effect, we illustrate how SPs can be visualized at the ultimate limits of space and time. [ABSTRACT FROM AUTHOR]

Wepresent a critical review of the commonmethods for determining the dispersion state of nanoparticulate samples particularly in liquid media, including the determination of particle size and morphology; particle size distributions and polydispersity and equilibrium particle structure and chemistry. We highlight the potential contributions of both scanning probe and electron microscopies in this analysis which is of benefit in understanding nanoparticulate formulations and their behaviour applied across a very wide range of technologies and industry sectors. [ABSTRACT FROM AUTHOR]

Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications. [ABSTRACT FROM AUTHOR]

Synchrotron X-ray diffraction was used to study the phase transformation processes during the magnetostructural transition in a B2-ordered FeRh (001)-oriented epilayer grown on MgO by sputtering. Out-of-plane lattice constant measurements within the hysteretic regime of the transition reveal a microstructure consistent with the coexistence of lattice-expanded and contracted phases in spatially distinct regions. It was found that the phase separation is more pronounced during cooling than heating. Furthermore, whilst lattice-expanded domains that span the height of the film can be undercooled by several kelvins, there is no equivalent superheating. This asymmetry between the cooling and heating processes in FeRh is consistent with the difference in the kinetics of generic freezing and melting transitions. [ABSTRACT FROM AUTHOR]

There is uncertainty concerning the potential toxicity of zinc oxide (ZnO) nanoparticles, which may be attributed in part to a lack of understanding with regard to the physiochemical properties of the nanoparticles used in toxicological investigations. This paper reports the synthesis of a ZnO nanopowder by flame spray pyrolysis and demonstrates that the typically employed characterisation techniques such as specific surface area measurement and X-ray diffraction provide insufficient information on the sample, especially if it is intended for use in toxicity studies. Instead, a more elaborate characterisation protocol is proposed that includes particle morphology as well as detailed compositional analysis of the nanoparticle surface. Detailed transmission electron microscopy analysis illustrated the polydispersity within the sample: particles were elongated in the c-crystallographic direction, with average Ferret length ~23 nm and Ferret width ~14 nm. Dynamic light scattering (0.1 w/v% in deionised water, pH 7.4) revealed the particles were agglomerated with a modal secondary particle size of ~1.5 μm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated the presence of carbonate and hydroxide impurities on the surface of the ZnO nanoparticles and an increase of such impurities was observed as the sample was aged, which might influence the nanoparticle dissolution and/or cellular uptake behaviour. These data will be utilised, in order to facilitate the interpretation and understanding of results from toxicological investigations using in vitro cell lines. [ABSTRACT FROM AUTHOR]

The rod-shaped plant virus tobacco mosaic virus (TMV) is widely used as a nano-fabrication template, and chimeric peptide expression on its major coat protein has extended its potential applications. Here we describe a simple bacterial expression system for production and rapid purification of recombinant chimeric TMV coat protein carrying C-terminal peptide tags. These proteins do not bind TMV RNA or form disks at pH 7. However, they retain the ability to self-assemble into virus-like arrays at acidic pH. C-terminal peptide tags in such arrays are exposed on the protein surface, allowing interaction with target species. We have utilized a C-terminal His-tag to create virus coat protein-templated nano-rods able to bind gold nanoparticles uniformly. These can be transformed into gold nano-wires by deposition of additional gold atoms from solution, followed by thermal annealing. The resistivity of a typical annealed wire created by this approach is significantly less than values reported for other nano-wires made using different bio-templates. This expression construct is therefore a useful additional tool for the creation of chimeric TMV-like nano-rods for bio-templating. [ABSTRACT FROM AUTHOR]

This investigation focuses on the austenite formation process during continuous heating, over a wide range of heating rates (0.05 to 20 K/s), in three low carbon-manganese steels alloyed with different levels of aluminum (0.02, 0.48, and 0.94, wt pct Al). High resolution dilatometry, combined with metallographic observations, was used to determine the starting ( Ac) and finishing ( Ac) temperatures of this transformation. It is shown that both the aluminum content and the applied heating rate have a strong influence on this process. During fast heating (>1 K/s), the pearlite phase present in the initial microstructure remains almost unaffected up to temperature Ac. On the contrary, during slow heating, cementite lamellas inside pearlite partially dissolve, this dissolution effect being more pronounced for the lower carbon and higher aluminum content steels. The changes in the initial microstructure during slow heating affect the austenite nucleation and growth processes. Furthermore, in the aluminum alloyed steels, slow heating conditions shift the Ac temperature to higher values. This shift is suggested to be due to aluminum partitioning from austenite to ferrite, which stabilizes ferrite and delays its transformation to higher temperatures. Thermodynamic calculations carried out with MTDATA software seem to support some of the experimental observations carried out under very low heating conditions close to equilibrium (0.05 K/s). [ABSTRACT FROM AUTHOR]

The article focuses on the study that investigates the influence of aluminum (Al) in solid solution on austenite formation during continuous heating. It shows that partitioning of magnesium to austenite takes place during slow heating. It reveals that the heat treated steel contains a mixture of large ferrite grains and relatively fine ferrite grains.

All biological tissues are three dimensional and contain structures that span a range of length scales from nanometres through to hundreds of millimetres. These are not ideally suited to current three-dimensional characterization techniques such as X-ray or transmission electron tomography. Such detailed morphological analysis is critical to understanding the structural features relevant to tissue function and designing therapeutic strategies intended to address structural deficiencies encountered in pathological states. We show that use of focused ion beam milling combined with scanning electron microscopy can provide three-dimensional information at nanometre resolution from biologically relevant volumes of material, in this case dentine. [ABSTRACT FROM AUTHOR]

The influence of aluminium on steel microstructure has been examined in low nitrogen steels. There is a lack of knowledge in the literature about the effect of aluminium on steel microstructure at levels greater than 0.1 wt-%. This has not been important as aluminium additions are typically low, with the aluminium being added as a deoxidant and grain refining element. However, recently aluminium has been added at significantly higher levels (0.5-2 wt-%) in new types of transformation induced plasticity (TRIP) steels to delay the bainitic transformation and give a dual phase microstructure. Furthermore, recent studies have shown that aluminium can be considered as a solid solution strengthener in low nitrogen steels. To investigate the effect of aluminium on steel microstructure, steels of differing aluminium composition between 0.02 and 0.98 wt-% have been prepared and investigated by metallography and EBSD. The results show that aluminium has a significant effect on ferrite grain size and ferrite grain size distribution. [ABSTRACT FROM AUTHOR]

We have evaluated a combined transmission electron microscopy (TEM)–scanning tunnelling microscopy (STM) (hence TEM-STM) sample holder for the investigation of the mechanical and electrical properties of individual bundles of single-walled carbon nanotubes (SWCNTs) together with their simultaneous observation, analysis and mechanical modification in the TEM. Current-voltage (I–V) measurements from bundles of SWCNTs were observed to change as the bundles were deformed both reversibly and irreversibly, although the observed behaviour was somewhat complex. Electron energy loss spectroscopy (EELS) analysis revealed measurable changes in the bonding of the carbon atoms within the graphene layers upon bundle deformation, with measurable changes in the π*/(π*+σ*) peak ratios observed at the carbon K-edge. Reversible deformation of the bundles was consistent with the sensitivity of σ bonding to deviations from nonplanarity, whereas irreversible deformation was consistent with the introduction of nonhexagonal defects into the graphene sheets. [ABSTRACT FROM AUTHOR]

The authors present aberration corrected scanning transmission electron microscopy (SuperSTEM) and electron energy loss spectroscopy (EELS) spectrum imaging data for the iron hydroxide mineral cores of cytosolic ferritin molecules in situ within human liver sections measured at a controlled electron dose. The authors have quantified the absolute iron content in individual cores using EELS and have checked the results against similar data obtained from synthetic maghemite nanoparticles of known composition and dimensions. Using these results the authors have then determined the quantitative relationship between the STEM high angle annular dark field (HAADF) image intensity of a ferritin core normalised to the background matrix intensity and the absolute iron content of the core as determined by EELS. This procedure then allows us to perform a rapid assessment of the iron content of any core within a tissue section based on the STEM HAADF image intensity. [ABSTRACT FROM AUTHOR]

The C–S–H present in water and alkali activated hardened pastes of neat white Portland cement (WPC) and blends of WPC with 30% fly ash hydrated at 85°C has been characterised. The chemical composition of C–S–H could not be determined by SEM–EDX because of intermixing with other phases; TEM–EDX was necessary. The mean Ca/(Al–Si) atomic ratio of C–S–H was lower in the water activated blend than in the neat cement paste due to the reaction of the fly ash. The fibrillar morphology of outer product C–S–H in the water activated neat cement paste was coarser than that formed at lower temperatures. The mean length of the aluminosilicate anions in the C–S–H was much higher than in C–S–H formed at lower temperatures and was higher in the blended pastes than with neat cement. The composition–structure data are discussed in terms of models for the nanostructure of C–S–H. The lattice parameter a inferred from compositional data for the hydrogarnet phase in the water activated blend was in good agreement with the value measured directly by XRD. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effects of age on calcium silicate hydrate (C–S–H) present in two cement pastes: one in which the C–S–H at a younger age had a high Ca/Si ratio and another that had a low ratio. The study involved characterising a 20 year old neat ordinary Portland cement (OPC) paste (high Ca/Si) and a blend of the OPC with 90% ground granulated blast furnace slag (GGBS; low Ca/Si); the results are compared with data on the same mixes at 14 months old. The morphology of the outer product (Op) C–S–H in the blend was essentially the same as at 14 months, whereas that in the neat OPC paste appeared to be finer. The mean aluminosilicate chain length of the C–S–H was considerably longer in both pastes than in similar systems at younger ages. The chemical composition of the C–S–H in both pastes was significantly different than at 14 months: in the neat OPC paste, the Ca/Si ratio of the outer product C–S–H had increased with age, whereas that of the inner product C–S–H had decreased; the Ca/Si ratio of Op C–S–H in the blended paste had decreased with age. An entirely tobermorite based nanostructural model can account for the data for the C–S–H in the blend, whereas the data for the neat paste require some jennite or calcium hydroxide based structure; the distribution of the TEM–EDX analyses favours the T/CH model. [ABSTRACT FROM AUTHOR]

Electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) is explored as a useful characterization technique in the study of carbonization and graphitization of organic precursors. A model series of carbon materials was prepared from highly graphitizable petroleum pitch heat treated in the range 200-2730°C. Initial characterization was performed using the established techniques of X-ray diffraction (XRD), He pycnometry, TEM, electron diffraction and high-resolution lattice imaging (HREM). EELS in the TEM was then examined. Two routes are presented to quantify the change in the proportion of sp2 type hybridization accompanying the heat treatment as the material transforms to the graphitic state. Both routes suggest an initial relative sp2 content of ∼70%, rapidly increasing to ∼90% during mesophase development and carbonization, and then slowly increasing to 100% during graphitization. The peak position of the bulk valence plasmon (π + σ) is shown to be an excellent measure of the degree of graphitic character, and its fundamental dependence upon sample density (ρ) is confirmed. The appearance and definition of features within the core loss region representing the density of unoccupied σ* states are demonstrated to be an excellent measure of the extent of order. Finally, a method is established by which to extract the C-C bond length from core loss EELS spectra with an accuracy of ±0.1 pm. This method suggests an average bond length of 1.44 Å in samples with low heat treatment temperatures, decreasing to the theoretical length of 1.42 Å as both the heteroatom content and proportion of non-sp2-type hybridized carbon atoms decrease. [ABSTRACT FROM AUTHOR]

Bioinspired molecular self-assembly is a popular route to novel functional materials for industrial applications. Here we explore, for the first time, the possibility of using organogel and hydrogels of short self-assembling β-sheet-forming peptides, as starting states for the creation of nanostructured peptide aerogels. The effects of supercritical fluid drying (SCF) and freeze-drying (FD) on the nanofibrillar peptide gel network were investigated. SCF processing was found to cause collapse of peptide organogel networks, presumably because of peptide insolubility in carbon dioxide (CO2). Freeze-drying of peptide hydrogels proved a more efficient method of removing the solvent without destroying the self-assembled fibrillar network, leading to a microscopic aligned lamellar structure consisting of thousands of stacked peptide nanofibrils. These chiral, nanostructured, low-density aerogels are characterised by chemical versatility and regular display of functional groups on their surface. Appropriately designed peptides can also be triggered to self-assemble in situ inside other porous structures and impart biological-like functionality for catalysis, sensing, separation and filtration applications, or tissue engineering. [ABSTRACT FROM AUTHOR]

The evolution of microstructure and composition of the Fe3C iron carbide phase (cementite) during a graphitisation anneal of a quenched, medium carbon steel has been studied by analytical electron microscopy, including energy dispersive X-ray spectroscopy (EDX), electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM) imaging. During heat treatment at 680 °C, dissolution of the cementite particles dispersed in the martensitic matrix was completed within a time period of 1.5 h, during which time graphite nodules began to form. However, a non-graphitic carbon-rich amorphous phase was also detected during this heat treatment. It is postulated that these amorphous particles could be an intermediate stage during the overall graphitisation process. [ABSTRACT FROM AUTHOR]

Titanium-doped chromium oxide has been successfully employed in the form of thick film gas sensing devices where the porosity and surface conditioning are key aspects in providing a measurable gas response. Under normal gaseous atmospheres, where the partial oxygen pressure (p(O2)) is approximately 0.2 atm, sintering of the host material (α-Cr2O3) to high densities is not possible, instead, significant grain growth occurs through evaporation-condensation transport mechanisms owing to the volatility of non-sesquioxide phases formed at high temperatures. The doping of α-Cr2O3 with Ti does not significantly affect the sintering behaviour of the host oxide under atmospheric conditions, but instead tends to form a nanodimensional, surface-segregated ternary phase of a nominal composition: Cr2Ti2O7, whilst the composition of grain interiors is close to pure α-Cr2O3. By reducing the p(O2) to ∼10-15 atm during sintering, thereby reducing the formation of volatile phases, solid state diffusion mechanisms have been encouraged allowing the densification of green bodies to a density >99% of the theoretical value. Ceramic bodies obtained by sintering in reduced p(O2) atmospheres display a single phase solid solution, isostructural with α-Cr2O3 (space group R3c). [ABSTRACT FROM AUTHOR]

This paper presents electron energy-loss near-edge structure (ELNES) data for the N K edges of vanadium nitrides. By rapid thermal processing of vanadium layers in pure nitrogen at high temperatures the two known vanadium nitrides, VN and V2N, have been prepared. The phases have been checked by electron diffraction and quantitative electron energy-loss spectroscopy (EELS) analysis. Because their crystallographical structures are different, they also exhibit different ELNES features, which can be used as fingerprints for rapidly distinguishing between VN and V2N. The experimental findings are supported by modelling the N K edge using a band structure approach (full linearized augmented plane wave method). [ABSTRACT FROM AUTHOR]

Electron energy-loss near-edge structure (ELNES) is a technique that can be used to measure the electronic structure (i.e. bonding) in materials with subnanometre spatial resolution. This review covers the theoretical principles behind the technique, the experimental procedures necessary to acquire good ELNES spectra, including potential artefacts, and gives examples relevant to materials science. [ABSTRACT FROM AUTHOR]

The microstructures of low carbon steels with Sn additions were investigated using scanning electron microscopy, electron probe microanalysis, transmission electron microscopy and energy dispersive X-ray spectroscopy. Four steels based on Fe-0.9Nb-0.3Sn-0.05C (wt%) with different levels of Al and Si additions were prepared by arc melting under an argon atmosphere. The effects of heat treatment and the level of alloying elements Al and Si on the precipitation of Sn-rich phases were studied. After ageing at 1150°C and 850°C, NbC precipitates were found in all samples, as well as AlN in the higher Al content steels. The concentration of Al in steel was also found to affect the formation of Sn-rich compounds after heat treatment at 850°C for 96 hours. In the lower Al or Al-free steels, a η-Fe2Nb3 phase, which dissolves a significant amount of Si, was observed. In the higher Al steels, a Fe2Nb-based Laves phase, which dissolves both Si and Sn was detected. A mechanism based on both size factors and thermodynamic considerations is described, which accounts for the experimental observations. [ABSTRACT FROM AUTHOR]

The oxide films formed on iron-chromium alloys in superheated steam have been investigated using a variety of microanalytical techniques, most notably electron energy loss spectroscopy. The addition of boron dopants leads to the rapid formation of a microcrystalline film of composition (Cr) B O, which resists further oxidation. Analysis of the near-edge structures associated with each core-loss edge after different oxidation times allows us to postulate various mechanisms for the observed behavior. [ABSTRACT FROM AUTHOR]

An analysis of variations in the Auger parameters of vapour deposited Mg-V alloys with nominal compositions 0.48, 2.95, 8.9 and 15 at.% V has been undertaken in order to investigate the electronic changes that take place upon alloying Mg with V. The presence of vanadium in the Mg-V system required certain assumptions to be made in the calculations as a result of the electronic configuration of the valence band of V. Charge transfer from Mg to V as well as changes in the V d charge were calculated by measuring the Mg and V Auger parameters and using the charge transfer model of Thomas and Weightman. The application of Thomas and Weightman's approach is shown to have advantages over the use of core ionization energy shifts in combination with the potential model. With the use of the Auger parameter there is no need for explicit energy referencing of the core levels and, moreover, in the improved model the Madelung or surface dipole contributions are not required unlike in the potential model. An attempt has also been made to understand the metallurgical significance of charge transfer in terms of the tendency for ordering or disordering of solid solutions. [ABSTRACT FROM AUTHOR]

Evidence of boron diffusion into the MgO barrier of a CoFeB/MgO based magnetic tunnel junction has been identified using analytical scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy. Structures were deposited by DC/RF-magnetron sputtering, where defective, sub-stoichiometric MgO barriers degrading device performance have been previously mitigated against by deposition of thin Mg layers prior to MgO deposition. We show that despite the protection offered by the Mg layer, disorder in the MgO barrier is still evident by STEM analysis and is a consequence of the oxidation of the Co40Fe40B20 surface during MgO deposition. Evidence of boron diffusion from CoFeB into the MgO barrier in the as-deposited and annealed structure is also presented, which in the as-deposited case we suggest results from the defective structures at the barrier interfaces. Annealing at 375 °C results in the presence of B in the trigonal coordination of [BO3]3- in the MgO barrier and partial crystallization of the top electrode (we presume there is also some boron diffusion into the Ta capping layer). The bottom electrode, however, fails to crystallize and much of the boron is retained in this thicker electrode. A higher annealing temperature or lower initial boron content is required to crystallize the bottom electrode. [ABSTRACT FROM AUTHOR]

It is common to find a thin (∼0.5 nm) layer of Mg deposited prior to the MgO tunnel barrier in crystalline CoFe(B)/MgO/CoFe(B) magnetic tunnel junctions, due to the improved device performance that results. However, despite their common usage, the reasons why such layers are effective are unclear. We use structures that model the lower electrode of such devices to show that a suitably thick Mg insert layer enhances the crystal quality of both MgO and CoFe(B), permits interfacial oxides to reduce back to a metallic ferromagnetic state, and hence improves magnetic switching of the CoFe(B) electrode, properties which are inextricably linked to device performance. [ABSTRACT FROM AUTHOR]

High-resolution (scanning) transmission electron micrographs taken on both aberration corrected and uncorrected microscopes, and indirect reconstructed images of mixed phase magnetite—maghemite nanoparticles all show the presence of {111} facets that terminate with enhanced contrast. This enhanced contrast is shown to be a real effect caused by the presence of additional octahedrally coordinated iron cations occupying the {111} terminating layers of these nanoparticle surfaces. [ABSTRACT FROM AUTHOR]