[en] Titanium tri-aluminide (Al₃Ti) particles were dispersed homogeneously into a castable aluminium alloy matrix by the aluminothermic reduction of hexafluorotitanate (K₂TiF₆) under different conditions. Al₃Ti particles in different morphologies and sizes were produced by changing the fabrication conditions, such as composition of the flux, the temperature and holding time. The coarsening and growth of the Al₃Ti particulates are principally affected by other elements present in the flux during fabrication. The effects of the temperature and holding time, alloying elements and the composition of flux on the dispersion of the reinforcement were examined by using SEM and X-ray diffraction techniques. The observed results are explained in terms of the different growth behaviour of the Al₃Ti particles under different conditions. The dispersion of the Al₃Ti particles and the Al/Al₃Ti interfacial bonding are explained by the solidification of aluminium

[en] We present experimental measurements of the C K-ELNES of high temperature pyrolysed graphite and related crystalline materials as a function of collection angle and sample tilt. These results together with a corresponding theoretical analysis indicate that the so-called 'magic angle' for EELS measurements of an anisotropic crystal such as graphite, where spectra are independent of sample orientation, is approximately two times the characteristic scattering angle. We briefly discuss the implications of this result for the experimental measurement of anisotropic structures, including interfaces, as well as for the detailed modelling of ELNES structures using advanced electronic structure calculations

[en] In this study, fibre laser welds of alloy Ti-6%Al-2%Sn-4%Zr-6%Mo have been characterised. It has been found that although the microstructure of the welds is important in predicting properties, it is not enough to simply characterise the welds based on the microstructure, as crystallographic texturing is also important in determining mechanical properties. The texturing of the fibre laser welds is being characterized using EBSD mapping, with light microscopy to characterize the microstructure. This has been carried out for a weld that has been heat treated for 3 hours at 550 deg. C. At this temperature, relaxation of residual stress will occur, but changes to the microstructure will be minimal. It is planned that EBSD will now be carried out on the as received sample, and the results will be presented, along with a comparison with the heat treated weld

[en] We present the results of theoretical modeling studies of the electron energy loss near-edge structure (ELNES) of Group-IVA (Ti, Zr, Hf) and Group-VA (V, Nb, Ta) transition-metal carbides exhibiting a cubic NaCl structure. Calculations of the unoccupied densities of states at both metal and nonmetal sites have been performed using both multiple scattering (MS) and full linearized-augmented-plane-wave (FLAPW) band-structure calculations. The effects of self-consistency and the inclusion of the core hole produced during the ELNES excitation process have been investigated for the case of the MS calculations, while the size of the basis set and the effect of charge transfer have been examined for the case of the FLAPW calculations. The results are compared to high-energy-resolution ELNES measurements. We demonstrate the sensitivity of ELNES features to quantities such as the lattice parameter, chemical composition, and stoichiometry

[en] The application of nanoparticles (NPs) within medicine is of great interest; their innate physicochemical characteristics provide the potential to enhance current technology, diagnostics and therapeutics. Recently a number of NP-based diagnostic and therapeutic agents have been developed for treatment of various diseases, where judicious surface functionalization is exploited to increase efficacy of administered therapeutic dose. However, quantification of heterogeneity associated with absolute dose of a nanotherapeutic (NP number), how this is trafficked across biological barriers has proven difficult to achieve. The main issue being the quantitative assessment of NP number at the spatial scale of the individual NP, data which is essential for the continued growth and development of the next generation of nanotherapeutics. Recent advances in sample preparation and the imaging fidelity of transmission electron microscopy (TEM) platforms provide information at the required spatial scale, where individual NPs can be individually identified. High spatial resolution however reduces the sample frequency and as a result dynamic biological features or processes become opaque. However, the combination of TEM data with appropriate probabilistic models provide a means to extract biophysical information that imaging alone cannot. Previously, we demonstrated that limited cell sampling via TEM can be statistically coupled to large population flow cytometry measurements to quantify exact NP dose. Here we extended this concept to link TEM measurements of NP agglomerates in cell culture media to that encapsulated within vesicles in human osteosarcoma cells. By construction and validation of a data-driven transfer function, we are able to investigate the dynamic properties of NP agglomeration through endocytosis. In particular, we statistically predict how NP agglomerates may traverse a biological barrier, detailing inter-agglomerate merging events providing the basis for predictive modelling of nanopharmacology. (paper)

[en] The systematic EELS analysis of a series of naturally occurring, synthetic and biological samples has provided a framework from which Fe valence of unknown materials can be determined and the relative ratios of the valences present can be calculated. The quantification of the relative ratios of Fe³⁺/Fe²⁺ is possible via the fitting of Gaussian or Voigt (with 89.3% Gaussian contribution) line profiles to the Fe L₃-edge. The ratio of Fe³⁺/ΣFe is determined from the areas under the fitted peaks. The method is robust and has an error in the range of <10% on Fe³⁺/ΣFe for samples with >2 atom% Fe. We present applications of this method including the investigation of polaron hopping in calcic amphibole, the quantification of Fe³⁺/ΣFe in clay minerals from deep water sediments, quantification of Fe valence in human liver tissue and the determination of Fe valence in airborne particulate matter

[en] Quantitative analysis of nanoparticle dispersion state within biological media is essential to understanding cellular uptake and the roles of diffusion, sedimentation, and endocytosis in determining nanoparticle dose. The dispersion of polymer-coated CdTe/ZnS quantum dots in water and cell growth medium with and without fetal bovine serum was analyzed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. Characterization by TEM of samples prepared by plunge freezing the blotted solutions into liquid ethane was sensitive to the dispersion state of the quantum dots and enabled measurement of agglomerate size distributions even in the presence of serum proteins where DLS failed. In addition, TEM showed a reduced packing fraction of quantum dots per agglomerate when dispersed in biological media and serum compared to just water, highlighting the effect of interactions between the media, serum proteins, and the quantum dots. The identification of a heterogeneous distribution of quantum dots and quantum dot agglomerates in cell growth medium and serum by TEM will enable correlation with the previously reported optical metrology of in vitro cellular uptake of this quantum dot dispersion. In this paper, we present a comparative study of TEM and DLS and show that plunge-freeze TEM provides a robust assessment of nanoparticle agglomeration state.

[en] Silicon nanoparticles (SiNPs) can be synthesized by a variety of methods. In many cases these routines are non-scalable with low product yields or employ toxic reagents. One way to overcome these drawbacks is to use one-pot synthesis based on the chemical reduction of micelles. In the following study trichloroalkylsilanes of differing chain lengths were used as a surfactant, and the level of capping, surface bonding and size of the nanoparticles formed has been investigated. FTIR results show that the degree of alkyl capping for SiNPs with different capping layers was constant, although SiNPs bound with shorter chains display a much higher level of Si–O owing to the reaction of the ethanol used in the method with uncapped sites on the particle. SiNPs with longer chain length capping show a sharp Si–H peak on the FTIR, these were heated at reflux with the corresponding 1-alkene to fully cap these particles, resulting in a reduction/disappearance of this peak with a minimal change in the intensity of the Si–O peak. Other techniques used to analyze the surface bonding and composition, XPS, ¹H-NMR, and TEM/EDX, show that alkyl-capped SiNPs have been produced using this method. The optical properties showed no significant changes between the different capped SiNPs.

[en] A potential methodology is presented for the systematic prediction of EELS edges using DFT, suitable for codes that calculate ELNES for a specific atom in a unit cell. The method begins with the selection of a unit cell, chosen as the smallest cell that still provides a physically valid representation of the bulk material. Within this small cell, a single electron core-hole is included in the atom for which the EELS ionisation edge is to be calculated. The basis-set size and k-point mesh of the DFT calculation are converged specifically against the predicted EELS result. Subsequently, the cell size is increased until the theoretical core-holes no longer interfere. At this point one can then modify the exact core-hole approximation. This methodology was applied to the new EELS module of the CASTEP pseudopotential DFT code, as well as the all-electron code Wien2k. Aluminium K edges were investigated for various aluminium metal systems. It was observed that as the cell size was increased the predicted EELS result became less sensitive to the exact core-hole approximation used. It was noted however that due to high screening in metals a ground state single cell calculation is often acceptable. The semiconductor aluminium nitride (wurtzite form) was also investigated. It was observed that for both Wien2k and CASTEP, with careful convergence of the key DFT code parameters, single cell ground state calculations gave a reasonable agreement with experiment, contrary to what might be expected for a semiconductor with a large band gap. This was particularly true of the Wien2k result. Given the greater computational effort required for supercell calculations, these results are likely to form the beginnings of a detailed investigation into accepted methods of ELNES predictions.

[en] This work quantitatively evaluates the contrast in phase contrast images of thin vermiculite crystals recorded by TEM and aberration-corrected bright-field STEM. Specimen movement induced by electron irradiation remains a major problem limiting the phase contrast in TEM images of radiation-sensitive specimens. While spot scanning improves the contrast, it does not eliminate the problem. One possibility is to utilise aberration-corrected scanning transmission electron microscopy (STEM) with an Angstrom-sized probe to illuminate the sample, and thus further reduce irradiation-induced specimen movement. Vermiculite is relatively radiation insensitive in TEM to electron fluences below 100,000 e^-/A² and this is likely to be similar for STEM although different damage mechanisms could occur. We compare the performance of a TEM with a thermally assisted field emission electron gun (FEG) and charge coupled device (CCD) image capture to the performance of STEMs with spherical aberration correction, cold field emission electron sources and photomultiplier tube image capture at a range of electron fluences and similar illumination areas. We show that the absolute contrast of the phase contrast images obtained by aberration-corrected STEM is better than that obtained by TEM. Although the STEM contrast is higher, the efficiency of collection of electrons in bright field STEM is still much less than that in bright field TEM (where for thin samples virtually all the electrons contribute to the image), and the SNR of equivalent STEM images is three times lower. This is better than expected, probably due to the absence of a frequency dependent modulation transfer function in the STEM detection system. With optimisation of the STEM bright field collection angles, the efficiency may approach that of bright field TEM, and if reductions in beam-induced specimen movement are found, STEM could surpass the overall performance of TEM.