Search

Fast‐cooling after sintering or annealing of BiFeO3‐BaTiO3 mixed oxide ceramics yields core‐shell structures that give excellent functional properties, but their precise phase assemblage and nanostructure remains an open question. By comparing conventional electron energy loss spectroscopy (EELS) with scanning precession electron diffraction (SPED) mapping using a direct electron detector, we correlate chemical composition with the presence or absence of octahedral tilting and with changes in lattice parameters. This reveals that some grains have a 3‐phase assemblage of a BaTiO3‐rich pseudocubic shell; a BiFeO3‐rich outer core with octahedral tilting consistent with an R3c structure; and an inner core richer in Ba and even poorer in Ti, which seems to show a pseudocubic structure of slightly smaller lattice parameter than the shell region. This last structure has not been previously identified in these materials, but the composition and structure fit with previous studies. These inner cores are likely to be non‐polar and play no part in the ferroelectric properties. Nevertheless, the combination of EELS and SPED clearly provides a novel way to examine heterogeneous microstructures with high spatial resolution, thus revealing the presence of phases that may be too subtle to detect with more conventional techniques.

The use of fast pixelated detectors and direct electron detection technology is revolutionising many aspects of scanning transmission electron microscopy (STEM). The widespread adoption of these new technologies is impeded by the technical challenges associated with them. These include issues related to hardware control, and the acquisition, real-time processing and visualisation, and storage of data from such detectors. We discuss these problems and present software solutions for them, with a view to making the benefits of new detectors in the context of STEM more accessible. Throughout, we provide examples of the application of the technologies presented, using data from a Medipix3 direct electron detector. Most of our software is available under an open source licence, permitting transparency of the implemented algorithms, and allowing the community to freely use and further improve upon them., 16 pages, 7 figures, post revision

Interface-related phenomena have great potential to control the superconducting state in Fe-based superconductors. We propose a comprehensive classification of Fe-pnictide heterointerfaces based on electrostatic principles that allow the prediction of the interface microstructure, in particular, distinguishing between clean heterointerfaces and the formation of interfacial layers. The concept was successfully tested on a novel LnOFeAs/BaFe2As2 (Ln = La, Sm) Fe-pnictide heterostructure. With the addition of different cations/anions, it is possible to produce clean interfaces or interfacial layers. The impact of the microstructure on superconductivity in the Fe-pnictide heterostructures is discussed. A classification of Fe-pnictide heterointerfaces based on electrostatic principles into initially compensated and uncompensated interfaces is proposed and used for tailoring the interfacial microstructure and superconducting properties. We show that the heterointerface between LnOFeAs (Ln = La, Sm) and BaFe2As2 is nonpolar and remains clean and coherent with Co2+ addition. Co-diffusion results in superconductivity across the whole bilayer. In contrast, IFL formation occurs after adding O2−, and superconductivity with a 2D signature develops with time.

It is shown that higher order Laue zone (HOLZ) rings in high energy electron diffraction are specific to individual columns of atoms, and show different strengths, structure and radii for different atom columns along the same projection in a structure. An atomic resolution 4-dimensional STEM dataset is recorded from a direction in a perovskite trilayer, where only the central LaFeO3 layer should show a period doubling that gives rise to an extra HOLZ ring. Careful comparison between experiment and multislice simulations is used to understand the origins of all features in the patterns. A strong HOLZ ring is seen for the La-O columns, indicating strong La position modulation along this direction, whereas a weaker ring is seen along the O columns, and a very weak ring is seen along the Fe columns. This demonstrates that atomic resolution HOLZ-STEM is a feasible method for investigating the 3D periodicity of crystalline materials with atomic resolution.

A carbon‐rich melt fragment from the Gardnos impact structure has been studied for a better understanding of the preservation and structural form(s) of carbon that have been processed by impact melting. The carbon was analyzed in situ in its original petrographic context within the melt fragment, using high‐resolution techniques including focused ion beam‐transmission electron microscopy and electron energy loss spectroscopy. Results show that the carbon is largely uniform and has a nanocrystalline grain size. The Gardnos carbon has a graphitic structure but with a large c/a ratio indicating disorder. The disorder could be a result of rapid heating to high temperatures during impact, followed by rapid cooling, with not enough time to crystallize into highly ordered graphite. However, temperature distribution during impact is extremely heterogenous, and the disordered Gardnos carbon could also represent material that avoided extreme temperatures, and thus, it was preserved. Understanding the structure of carbon during terrestrial impacts is important to help determine if the history of carbon within extraterrestrial samples is impact related. Furthermore, the degree of preservation of carbon during impact is key for locating and detecting organic compounds in extraterrestrial samples. This example from Gardnos, together with previous studies, shows that not all carbon is lost to oxidation during impact but that impact melting can encapsulate and preserve carbon where it is available.

A scanning precession electron diffraction system has been integrated with a direct electron detector to allow the collection of improved quality diffraction patterns. This has been used on a two-phase α–β titanium alloy (Timetal® 575) for phase and orientation mapping using an existing pattern-matching algorithm and has been compared to the commonly used detector system, which consisted of a high-speed video-camera imaging the small phosphor focusing screen. Noise is appreciably lower with the direct electron detector, and this is especially noticeable further from the diffraction pattern center where the real electron scattering is reduced and both diffraction spots and inelastic scattering between spots are weaker. The results for orientation mapping are a significant improvement in phase and orientation indexing reliability, especially of fine nanoscale laths of α-Ti, where the weak diffracted signal is rather lost in the noise for the optically coupled camera. This was done at a dose of ~19 e−/Å2, and there is clearly a prospect for reducing the current further while still producing indexable patterns. This opens the way for precession diffraction phase and orientation mapping of radiation-sensitive crystalline materials.

Detectors are revolutionizing possibilities in scanning transmission electron microscopy because of the advent of direct electron detectors that record at a high quantum efficiency and with a high frame rate. This allows the whole back focal plane to be captured for each pixel in a scan and the dataset to be processed to reveal whichever features are of interest. There are many possible uses for this advance of direct relevance to understanding the nano- and atomic-scale structure of materials and heterostructures. This article gives our perspective of the current state of the field and some of the directions where it is likely to go next. First, a wider overview of the recent work in this area is given before two specific examples of its application are given: one is imaging strain in thin films and the other one is imaging changes in periodicity along the beam direction as a result of the formation of an ordered structure in an epitaxial thin film. This is followed by an outlook that presents future possible directions in this rapidly expanding field.

The argon content of titanium dioxide doped tantalum pentoxide thin films was quantified in a spatially resolved way using HAADF images and DualEELS. Films annealed at 300$^{\circ}$C, 400$^{\circ}$C and 600$^{\circ}$C were investigated to see if there was a relationship between annealing temperature and bubble formation. It was shown using HAADF imaging that argon is present in most of these films and that bubbles of argon start to form after annealing at 400$^{\circ}$C and coarsen after annealing at 600$^{\circ}$C. A semi-empirical standard was created for the quantification using argon data from the EELS atlas and experimental data scaled using a Hartree Slater cross section. The density and pressure of argon within the bubbles was calculated for 35 bubbles in the 600$^{\circ}$C sample. The bubbles had a mean diameter, density and pressure of 22\r{A}, 870kg/m$^3$ and 400MPa, respectively. The pressure was calculated using the Van der Waals equation. The bubbles may affect the properties of the films, which are used as optical coatings for mirrors in gravitational wave detectors. This spatially resolved quantification technique can be readily applied to other small noble gas bubbles in a range of materials., Comment: 14 pages, 5 figures, data avilable at Enlighten: Research Data at 10.5525/gla.researchdata.1074

S.J.M acknowledges the EPSRC-funded CDT in Photonic Integration and Advanced Data Storage (EP/L015323/1) for his PhD studentship under which the work at the University of Glasgow was carried out. The work carried out at Queen’s University Belfast and the University of St Andrews was carried out as part of an EPSRC-funded collaboration (EP/P02453X/1 and EP/P024637/1). The improper ferroelectric CsNbW2O9 has recently been highlighted as the first material outside the manganite family to exhibit a similar meandering, six-fold domain structure to that responsible for enhanced and diminished conduction at charged domain walls in the rare earth manganites. While there is no current evidence for variation in domain wall conduction relative to bulk in CsNbW2O9, the similarities in microstructure strongly suggest that charged domain walls are present in this material. Herein, we report a comprehensive study of the domain microstructure of CsNbW2O9 using both piezoresponse force microscopy and transmission electron microscopy to reveal that there are, in fact, clear distinctions in the domain structure of the two systems. Constraints arising from the crystal structure of CsNbW2O9, namely, the connectivity of the BO6 polyhedra and atomic displacements occurring purely along the c axis, mean that domain walls preferentially run parallel to the c direction (the polar axis of the material) and thus remain uncharged. The characteristic cloverleaf domain structure reminiscent of the manganites is still present, however, the structure meanders predominantly in the ab plane and, therefore, appears differently depending on the projection direction from which it is viewed. As a result of this microstructural constraint, charged domain walls are not prevalent in this material. Publisher PDF

Fast pixelated detectors incorporating direct electron detection (DED) technology are increasingly being regarded as universal detectors for scanning transmission electron microscopy (STEM), capable of imaging under multiple modes of operation. However, several issues remain around the post acquisition processing and visualisation of the often very large multidimensional STEM datasets produced by them. We discuss these issues and present open source software libraries to enable efficient processing and visualisation of such datasets. Throughout, we provide examples of the analysis methodologies presented, utilising data from a 256$\times$256 pixel Medipix3 hybrid DED detector, with a particular focus on the STEM characterisation of the structural properties of materials. These include the techniques of virtual detector imaging; higher order Laue zone analysis; nanobeam electron diffraction; and scanning precession electron diffraction. In the latter, we demonstrate nanoscale lattice parameter mapping with a fractional precision $\le 6\times10^{-4}$ (0.06%)., 23 pages, 12 figures, add open data zenodo doi and revise precision discussion

Accelerated de novo formation of bone is a highly desirable aim of implants targeting musculoskeletal injuries. To date, this has primarily been addressed by biologic factors. However, there is an unmet need for robust, highly reproducible yet economic alternative strategies that strongly induce an osteogenic cell response. Here, we present a surface engineering method of translating bioactive nanopatterns from polymeric in vitro studies to clinically relevant material for orthopedics: three-dimensional, large area metal. We use a titanium-based sol-gel whereby metal implants can be engineered to induce osteoinduction both in vitro and in vivo. We show that controlled disordered nanotopographies presented as pillars with 15-25 nm height and 100 nm diameter on titanium dioxide effectively induce osteogenesis when seeded with STRO-1-enriched human skeletal stem cells in vivo subcutaneous implantation in mice. After 28 days, samples were retrieved, which showed a 20-fold increase in osteogenic gene induction of nanopatterned substrates, indicating that the sol-gel nanopatterning method offers a promising route for translation to future clinical orthopedic implants.

We outline a simple routine to correct for non-uniformities in the energy dispersion of a post-column electron energy-loss spectrometer for use in scanning transmission electron microscopy. We directly measure the dispersion and its variations by sweeping a spectral feature across the full camera to produce a calibration that can be used to linearize datasets post-acquisition, without the need for reference materials. The improvements are illustrated using core excitation electron energy-loss spectroscopy (EELS) spectra collected from NiO and diamond samples. The calibration is rapid and will be of use in all EELS analysis, particularly in assessments of the chemical states of materials via the chemical shift of core-loss excitations.

As the only stable binary compound formed between an alkali metal and nitrogen, lithium nitride possesses remarkable properties and is a model material for energy applications involving the transport of lithium ions. Following a materials design principle drawn from broad structural analogies to hexagonal graphene and boron nitride, we demonstrate that such low dimensional structures can also be formed from an s-block element and nitrogen. Both one- and two-dimensional nanostructures of lithium nitride, Li3N, can be grown despite the absence of an equivalent van der Waals gap. Lithium-ion diffusion is enhanced compared to the bulk compound, yielding materials with exceptional ionic mobility. Li3N demonstrates the conceptual assembly of ionic inorganic nanostructures from monolayers without the requirement of a van der Waals gap. Computational studies reveal an electronic structure mediated by the number of Li-N layers, with a transition from a bulk narrow-bandgap semiconductor to a metal at the nanoscale., Lithium nitride is the only stable binary alkali metal-nitrogen compound and shows promise for energy applications involving the transport of lithium ions. Here, the authors demonstrate that lithium nitride nanostructures can be grown as fibres and sheets despite the absence of a van der Waals gap.

Nanometre-sized TixV(1−x)CyNz precipitates in an Fe20%Mn steel matrix with a thickness range from 14 to 40 nm are analysed using DualEELS. Their thicknesses, volumes and compositions are quantified using experimental binary standards and the process used to give robust results is described. Precisions of a few percent are achieved with accuracies that are estimated to be of a similar magnitude. Sensitivities are shown to be at 0.5–1 unit cells range in the thinnest matrix region, based on the assumption that a sub-lattice is fully populated by the element. It rises to the 1–2 unit cell range for the metals and 2–3 unit cells for the non-metal in the thickest matrix region. The sensitivities for Ti and N are greater than those for V and C respectively because the O K-edge from surface oxide needs to be separated from the V L2,3-edge, and the C K-edges from C in the matrix and amorphous C on the surface have to be separated from the C in the precipitate itself. Separation of the contributions from the bulk and the surface is demonstrated, showing that there is significant and detectable C in the matrix but no O, while there is significant O but little C in the surface oxide. Whilst applied to precipitates in steel in this work, the approach can be adapted to many multi-phase systems.

In this study, it is proposed that coarsening austenitic grains is a key criterion for achieving giant recovery strains in polycrystalline Fe-Mn-Si based shape memory alloys. In order to verify the hypothesis, the relationship between recovery strains and austenitic grain-sizes in cast and processed Fe-Mn-Si based shape memory alloys was investigated. The recovery strain of cast Fe-19Mn-5.5Si-9Cr-4.5Ni alloy with the coarse austenitic grains of 652 µm reached 7.7% while the recovery strain of one with the relatively small austenitic grains of 382 µm was only 5.4%. Moreover, a recovery strain of 5.9%, which is the highest previously published value for solution-treated processed Fe-Mn-Si based shape memory alloys, was obtained by coarsening the austenitic grains through only solution treatment at 1483 K for 360 min in a processed Fe-17Mn-5.5Si-9Cr-5.5Ni-0.12C alloy. However, its recovery strain was still 5.9% after thermo-mechanical treatment consisting of 10% tensile strain at room temperature and annealing at 1073 K for 30 min. This happens because annealing twins play a negative role, refining the austenitic grains, limiting the recovery strains to below 6%. In summary, coarse austenitic grains enable the achievement large recovery strains by two mechanisms. Firstly, the grains are bigger, and consequently there are fewer grain boundaries, and thus their suppressive effects of grain boundaries on stress-induced e martensitic transformation is reduced. Secondly, coarse austenitic grains are advantageous to introduce e martensite with single orientation and reduce the collisions of different martensite colonies, especially when the deformation strain is large. As such, the ceiling of recovery strains is dependent on the austenitic grain-sizes.

Ray tracing is used to find improved set-ups of the projector system of a JEOL ARM 200CF TEM/STEM for use in coupling it to a Gatan 965 Quantum ER EELS system and to explain their performance. The system has a probe aberration corrector but no image corrector. With the latter, the problem would be more challenging. The agreement between the calculated performance and that found experimentally is excellent. At 200kV and using the 2.5mm Quantum entrance aperture, the energy range over which the collection angle changes by a maximum of 5% from that at zero loss has been increased from 1.2keV to 4.7keV. At lower accelerating voltages, these energy ranges are lower e.g. at 80kV they are 0.5keV and 2.0keV respectively. The key factors giving the improvement are an increase in the energy-loss at which the projector cross-over goes to infinity and a reduction of the combination aberrations that occur in a lens stack. As well as improving the energy-loss range, the new set-ups reduce spectrum artefacts and minimise the motion of the diffraction pattern at low STEM magnification for electrons that have lost energy. Even if making the pivot points conjugate with the film plane gives no motion for zero-loss electrons, there will be motion for those electrons that have lost energy, leading to a false sense of security when performing spectrum imaging at low magnifications. De-scanning of the probe after the objective lens is a better way of dealing with this problem.

Binding of nanoparticles (NPs) to mineral surfaces influences their transport through the environment. The potential, however, for growing minerals to immobilize NPs via occlusion (the process of trapping particles inside the growing mineral) has yet to be explored in environmentally relevant systems. In this study, the ureolytic bacteria Sporosarcina pasteurii was used to induce calcium carbonate precipitation in the presence of organo-metallic manufactured nanoparticles. As calcite crystals grew the nanoparticles in the solution became trapped inside these crystals. Capture of NPs within the calcite via occlusion was verified by transmission electron microscopy of thin foils. Nanoparticles with a negative surface charge were captured with greater efficiency than those with a positive surface charge, resulting from stronger attachment of negative nanoparticles to the positively charged calcite surfaces, which in turn facilitated occlusion. Thermodynamic and kinetic analysis, however, did not reveal a significant difference in kp (calcite precipitation rate constant) or the critical saturation at which precipitation initiates (Scrit), indicating the presence of different charged nanoparticles did not influence calcite precipitation at the concentrations used here. Overall, these findings demonstrate that microbially driven mineral precipitation has potential to immobilize nanoparticles in the environment via occlusion Binding of nanoparticles (NPs) to mineral surfaces influences their transport through the environment. The potential, however, for growing minerals to immobilize NPs via occlusion (the process of trapping particles inside the growing mineral) has yet to be explored in environmentally relevant systems. In this study, the ureolytic bacteria Sporosarcina pasteurii was used to induce calcium carbonate precipitation in the presence of organo-metallic manufactured nanoparticles. As calcite crystals grew the nanoparticles in the solution became trapped inside these crystals. Capture of NPs within the calcite via occlusion was verified by transmission electron microscopy of thin foils. Nanoparticles with a negative surface charge were captured with greater efficiency than those with a positive surface charge, resulting from stronger attachment of negative nanoparticles to the positively charged calcite surfaces, which in turn facilitated occlusion. Thermodynamic and kinetic analysis, however, did not reveal a significant difference in kp (calcite precipitation rate constant) or the critical saturation at which precipitation initiates (Scrit), indicating the presence of different charged nanoparticles did not influence calcite precipitation at the concentrations used here. Overall, these findings demonstrate that microbially driven mineral precipitation has potential to immobilize nanoparticles in the environment via occlusion.

We have investigated the use of DualEELS in elementally sensitive tilt series tomography in the scanning transmission electron microscope. A procedure is implemented using deconvolution to remove the effects of multiple scattering, followed by normalisation by the zero loss peak intensity. This is performed to produce a signal that is linearly dependent on the projected density of the element in each pixel. This method is compared with one that does not include deconvolution (although normalisation by the zero loss peak intensity is still performed). Additionally, we compare the 3D reconstruction using a new compressed sensing algorithm, DLET, with the well-established SIRT algorithm. VC precipitates, which are extracted from a steel on a carbon replica, are used in this study. It is found that the use of this linear signal results in a very even density throughout the precipitates. However, when deconvolution is omitted, a slight density reduction is observed in the cores of the precipitates (a so-called cupping artefact). Additionally, it is clearly demonstrated that the 3D morphology is much better reproduced using the DLET algorithm, with very little elongation in the missing wedge direction. It is therefore concluded that reliable elementally sensitive tilt tomography using EELS requires the appropriate use of DualEELS together with a suitable reconstruction algorithm, such as the compressed sensing based reconstruction algorithm used here, to make the best use of the limited data volume and signal to noise inherent in core-loss EELS.

Understanding the local atomic order in amorphous thin film coatings and how it relates to macroscopic performance factors, such as mechanical loss, provides an important path towards enabling the accelerated discovery and development of improved coatings. High precision x-ray scattering measurements of thin films of amorphous zirconia-doped tantala (ZrO_{2}-Ta_{2}O_{5}) show systematic changes in intermediate range order (IRO) as a function of postdeposition heat treatment (annealing). Atomic modeling captures and explains these changes, and shows that the material has building blocks of metal-centered polyhedra and the effect of annealing is to alter the connections between the polyhedra. The observed changes in IRO are associated with a shift in the ratio of corner-sharing to edge-sharing polyhedra. These changes correlate with changes in mechanical loss upon annealing, and suggest that the mechanical loss can be reduced by developing a material with a designed ratio of corner-sharing to edge-sharing polyhedra.

Determining the three-dimensional (3D) crystallography of a material with subnanometer resolution is essential to understanding strain effects in epitaxial thin films. A scanning transmission electron microscopy imaging technique is demonstrated that visualizes the presence and strength of atomic movements leading to a period doubling of the unit cell along the beam direction, using the intensity in an extra Laue zone ring in the back focal plane recorded using a pixelated detector method. This method is used together with conventional atomic resolution imaging in the plane perpendicular to the beam direction to gain information about the 3D crystal structure in an epitaxial thin film of LaFeO3 sandwiched between a substrate of (111) SrTiO3 and a top layer of La0.7Sr0.3MnO3. It is found that a hitherto unreported structure of LaFeO3 is formed under the unusual combination of compressive strain and (111) growth, which is triclinic with a periodicity doubling from primitive perovskite along one of the three ⟨110⟩ directions lying in the growth plane. This results from a combination of La-site modulation along the beam direction, and modulation of oxygen positions resulting from octahedral tilting. This transition to the period-doubled cell is suppressed near both the substrate and near the La0.7Sr0.3MnO3 top layer due to the clamping of the octahedral tilting by the absence of tilting in the substrate and due to an incompatible tilt pattern being present in the La0.7Sr0.3MnO3 layer. This work shows a rapid and easy way of scanning for such transitions in thin films or other systems where disorder-order transitions or domain structures may be present and does not require the use of atomic resolution imaging, and could be done on any scanning transmission electron microscopy instrument equipped with a suitable camera.

Planned cryogenic gravitational-wave detectors will require improved coatings with a strain thermal noise reduced by a factor of 25 compared to Advanced LIGO. We present investigations of HfO_{2} doped with SiO_{2} as a new coating material for future detectors. Our measurements show an extinction coefficient of k=6×10^{-6} and a mechanical loss of ϕ=3.8×10^{-4} at 10 K, which is a factor of 2 below that of SiO_{2}, the currently used low refractive-index coating material. These properties make HfO_{2} doped with SiO_{2} ideally suited as a low-index partner material for use with a-Si in the lower part of a multimaterial coating. Based on these results, we present a multimaterial coating design which, for the first time, can simultaneously meet the strict requirements on optical absorption and thermal noise of the cryogenic Einstein Telescope.

An overview of recent progress in high loss electron energy loss spectroscopy is presented. This covers the instrumental aspects of how to best set up a scanning transmission electron microscope and post-column spectrometer combination to provide best performance, a survey of a range of results that are possible in EELS with a good setup, and a brief investigation of the current limitations imposed by the current mainstream detector technology. In the first section, detailed consideration is given to the coupling optics between microscope and spectrometer, the effects on the EELS spectrum, the need for spectrometer refocusing, and the problems with gun anodes in some field emission gun designs. In the second section, a survey of the absolute cross sections for the L edges of 4d transition elements is set out, these are used for absolute quantification in two cases, and the extended energy loss fine structure beyond the Si–K edge is used for atomic structure investigation. The final section comprises an investigation of noise levels on the Rh L3 edge with a standard CCD detector in the spectrometer with a comparison to simulated shot noise, and shows that in this case, RMS noise was 7 times worse than the fundamental limit, illustrating clearly how much improvement would be possible with electron counting detectors.

Thin films of C/Mo/W deposited using combined UBM/HIPIMS sputtering show 2–8 nm clusters of material richer in Mo and W than the matrix (found by EDS microanalysis), with structures that resemble graphitic onions with the metal atoms arranged regularly within them. EELS microanalysis showed the clusters to be rich in W and Mo.\ud \ud \ud \ud As the time averaged power used in the pulsed HIPIMS magnetron was increased, the clusters became more defined, larger, and arranged into layers with amorphous matrix between them. Films deposited with average HIPIMS powers of 4 kW and 6 kW also showed a periodic modulation of the cluster density within the finer layers giving secondary, wider stripes in TEM. By analysing the ratio between the finer and coarser layers, it was found that this meta-layering is related to the substrate rotation in the deposition chamber but in a non-straightforward way. Reasons for this are proposed. The detailed structure of the clusters remains unknown and is the subject of further work.\ud \ud \ud \ud Fluctuation electron microscopy results indicated the presence of crystal planes with the graphite interlayer spacing, crystal planes in hexagonal WC perpendicular to the basal plane, and some plane spacings found in Mo2C. Other peaks in the FEM results suggested symmetry-related starting points for future determination of the structure of the clusters.

The recently developed precession electron diffraction (PED) technique in scanning transmission electron microscopy has been used to elucidate the local strain distribution and crystalline misorientation in a CMOS fabricated strained Ge microdisk structure grown on a Si substrate. Tensile strained Ge and GeSn structures are considered to be potential CMOS compatible optical sources, as both Sn alloying and strain can lead to a direct band-structure and lasing. The ability to take nanometer resolution, experimental measurements of the cross-sectional strain distribution, is important to understand modal gain and, therefore, ultimate device performance. In this work, we demonstrate PED techniques to measure the cross-sectional strain field in tensile Ge microdisks strained by SiN stressors. The strain maps are interpreted and compared with a finite element model of the strain in the investigated structure, which shows good agreement, and, therefore, highlights the applicability of PED techniques for mapping strained photonic structures. The technique also allows for the observation of strain relaxation due to dislocation pileup, further demonstrating the benefit of such experimental techniques.

The atomic structure of mixtures of titania (TiO_2) and tantala (Ta_2O_5) ion-beam sputtered amorphous thin film coatings at various post-deposition annealing temperatures have been studied using Ta LIII and Ti K edge Extended X-ray Absorption Fine Structure (EXAFS). The results indicate that post-deposition annealing produces subtle changes in the short range order (< 1 nm) for samples which remain amorphous. We also show that titania–tantala mixtures maintain a structure similar to that of pure tantala, with the titanium atoms preferring to sit at the second shell distance, which is similar to the Ta–Ta distance seen in the pure tantala structure. A discussion is also included on interpretation of the general trends identified in the EXAFS data and how this relates to previous and ongoing studies of the structure and mechanical loss measurements of titania–tantala coatings.

TIMETAL® 575, developed by Titanium Metals Corporation (TIMET), is a high strength forgeable α+β titanium alloy with comparable density, beta transus temperature and processing characteristics to Ti-6Al-4V but with enhanced static and fatigue strength primarily aimed at aero-engine disc or blade applications. Recent research on this alloy has focussed on microstructure evolution as a means to optimise mechanical behaviour and it has been concluded that a solution heat treatment followed by an ageing step yields a resulting “tri-modal” microstructure, consisting of equiaxed primary α and bi-lamellar transformation product containing nano-scale “tertiary alpha” laths, which appear to provide an excellent balance of strength and ductility. The key objective of the work presented here is to characterise this complex nanoscale microstructure in detail at various stages of alloy processing. For that purpose various advanced and recently developed transmission electron microscopy (TEM) techniques have been used. These include alpha and beta phase mapping Precession Electron Diffraction (PED), overall microstructure imaging with conventional BF and DF TEM, distinction of fine phase detail with high angle annular dark field (HAADF) scanning TEM (STEM), and correlation of the nanostructure to the elemental distribution using scanned Electron Energy Loss Spectroscopy (EELS).