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Biominerals, such as nacreous bivalve shells, are important archives of environmental information. The processes explaining how the organisms code this information into the structure and composition of their shells are yet unknown. Most marine calcifiers form their shells from amorphous calcium carbonate by particle attachment and stepwise crystallisation of metastable precursor phases. However, the mechanism of this transformation including its incorporation of trace metal ions used for environmental reconstructions are poorly constrained. Using the nacreous shell of the Mediterranean mussel, we explore the formation of nacre from the meso- to the atomic scale. We use a novel combination of strontium pulse-chase labelling in aquaculture experiments and correlative micro- to sub-nanoscale analysis to show that nacre grows in a two-step process and crystallizes via localised dissolution and reprecipitation within nanogranules. Our findings elucidate how stepwise crystallization pathways affect trace element incorporation in natural biominerals, while preserving their intricate hierarchical structure.

Environmentally friendly earth-abundant Cd-free Cu2ZnSnS4 (CZTS) solar cells have recently achieved increasing power conversion efficiency by using ZnSnO as the buffer layer. However, the large open circuit voltage (Voc) deficit remains the key concern. Here, we report a Cd-free CZTS solar cell that exhibits an energy conversion efficiency of 10.2% resulting from the application of an aluminium oxide (Al2O3) passivation layer prepared by atomic layer deposition (ALD). We found that the application of full ALD cycles as well as trimethylaluminum (TMA) exposures resulted in a significant increase in Voc and relate this to the properties of the CZTS interface. Both processes facilitate the formation of a thicker Cu-deficient nanolayer with a higher concentration of Na and O, forming a homogeneous passivation layer across the CZTS surface. This nanolayer reduces the local potential fluctuation of band edges and leads to the widened electrical band gap and suppressed defects recombination at the heterojunction interface, thus improvement in Voc and device performance. The ability of nanolayers to alter the atomic composition in the near surface region of compound semiconductors might be beneficial for a wider range of semiconductor devices.

This work was supported by Australian Research Council funding to King (DP150104604 and FT130101524) that provided for the contributions from King, Renggli, Troitzsch, and Palm; Australian Synchrotron funding to King, Troitzsch, Mernagh, Yue and Palm; plus an Australian Commonwealth Supported Place and the Kerry and John Lovering scholarship to Palm

In this study atom probe tomography was used to determine the implantation depth of four different plasma FIB ion species – xenon, argon, nitrogen, and oxygen – implanted at different acceleration voltages. It was found that lowering the beam energy reduces the implantation depth, but significant implantation was still observed for N, O and Ar at beam energies as low as 2 kV. Furthermore, nitrides and oxides were observed that were formed when using N and O. Xe had the lowest implantation depth compared to Ar, N and O when using the same conditions. No Xe ions were detected in the sample prepared at 2 kV. Experimentally-determined implantation depths were compared to calculated implantation depths. The experiments exhibited deeper-than-predicted ion implantation into the microstructure, but lower-than-predicted ion concentrations.

Sulfide kesterite Cu2ZnSnS4 provides an attractive low-cost, environmentally benign and stable photovoltaic material, yet the record power conversion efficiency for such solar cells has been stagnant at around 9% for years. Severe non-radiative recombination within the heterojunction region is a major cause limiting voltage output and overall performance. Here we report a certified 11% efficiency Cu2ZnSnS4 solar cell with a high 730 mV open-circuit voltage using heat treatment to reduce heterojunction recombination. This heat treatment facilitates elemental inter-diffusion, directly inducing Cd atoms to occupy Zn or Cu lattice sites, and promotes Na accumulation accompanied by local Cu deficiency within the heterojunction region. Consequently, new phases are formed near the hetero-interface and more favourable conduction band alignment is obtained, contributing to reduced non-radiative recombination. Using this approach, we also demonstrate a certified centimetre-scale (1.11 cm2) 10% efficiency Cu2ZnSnS4 photovoltaic device; the first kesterite cell (including selenium-containing) of standard centimetre-size to exceed 10%. The emerging kesterite Cu2ZnSnS4 solar cell offers a potential low-cost, non-toxic, materially abundant platform for next-generation photovoltaics, yet its efficiency has been mired below 10%. Yan et al. now use post-heat treatment of the heterojunction to show device efficiencies that surpass 10%.

Atom probe tomography has developed into a technique that can provide atomic-scale three-dimensional information pertaining to corrosion products, with excellent chemical resolution. Like for most characterization techniques, use of atom probe tomography for analysis of corrosion products is not without its challenges. In the short time that this technique has been utilized for corrosion studies, complementary microscopy techniques have been extremely useful for production and analysis of oxide-containing atom probe samples. We review herein how correlative microscopy techniques such as electron microscopy, microanalysis techniques, and transmission Kikuchi diffraction have been utilized to overcome challenges associated with atom probe microscopy, including how information from correlative microscopy can be applied to inform three-dimensional reconstruction of atom probe data.

Atom probe tomography was used to analyze self-assembled monolayers of thiophene on different surfaces, including tungsten, platinum, and aluminum, where the tungsten was examined in both pristine and oxidized forms. A glovebag with controlled atmospheres was used to alter the level of oxidation for tungsten. It was shown that different substrates lead to substantial changes in the way thiophene adsorbs on the surface. Furthermore, the oxidation of the surface strongly influenced the adsorption behavior of the thiophene molecules, leading to clear differences in the amounts and compositions of field evaporated ions and molecular ions.

Correlative microscopy approaches offer synergistic solutions to many research problems. One such combination, that has been studied in limited detail, is the use of atom probe tomography (APT) and transmission Kikuchi diffraction (TKD) on the same tip specimen. By combining these two powerful microscopy techniques, the microstructure of important engineering alloys can be studied in greater detail. For the first time, the accuracy of crystallographic measurements made using APT will be independently verified using TKD. Experimental data from two atom probe tips, one a nanocrystalline Al–0.5Ag alloy specimen collected on a straight flight-path atom probe and the other a high purity Mo specimen collected on a reflectron-fitted instrument, will be compared. We find that the average minimum misorientation angle, calculated from calibrated atom probe reconstructions with two different pole combinations, deviate 0.7° and 1.4°, respectively, from the TKD results. The type of atom probe and experimental conditions appear to have some impact on this accuracy and the reconstruction and measurement procedures are likely to contribute further to degradation in angular resolution. The challenges and implications of this correlative approach will also be discussed.

Two Al-Sc alloys were examined to establish the relative influence of grain boundary segregation and precipitation of Sc on the microstructural evolution during equal channel angular pressing (ECAP). Due to the ultra-low Sc content in the low-Sc alloy additional measures were taken to ensure a homogenous distribution of the Sc. After casting, this alloy was swaged and homogenised. One ECAP pass and a solution treatment were undertaken before carrying out 10 ECAP passes. For the analysis with transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD), electron transparent thin foils were cut parallel to the ECAP extrusion axis and then thinned by using a Struers TenuPol5, at a voltage of 12 V in 30% nitric acid and 70% methanol at -30°C. To assess the grain size stability, the samples were heated to 550°C. Analysis of grain orientation maps obtained by TKD revealed that the grain size, defined by the HAGBs, is three times larger than expected. The distribution of Al3Sc precipitates after heat treatment indicated that recovery occurs.

In this study, a fully dense and crack-free alpha titanium alloy was fabricated using selective laser melting (SLM) of commercially pure titanium (CP Ti) blended with 1 vol.% micrometre-sized Mo2C powder. The microstructure and mechanical properties of the fabricated Ti alloy were systematically investigated. It was found that the fabricated Ti alloy consisted of both alpha (α) and beta (β) phases and exhibited a nest-like inhomogeneous microstructure with graded local phase formation, composition and crystallographic texture. This novel microstructure was formed through melting and rapid solidification of CP Ti and Mo2C during SLM, assisted by the high laser absorptivity and resultant high temperature rise of the Mo2C powder. The fabricated Ti alloy exhibited higher tensile strength (∼1250 ± 50 MPa) and improved ductility (elongation ∼17 ± 1%) when compared to CP Ti fabricated using the same SLM process. The underlying reasons were mainly attributed to (i) the nest-like inhomogeneous microstructure consisting of fine grained α-Ti and β-Ti, (ii) the overall solid solution strengthening of the Ti matrix by interstitial C, and (iii) the high dislocation density in the Ti matrix arising from the mismatch between α-Ti and β-Ti phases. This study not only provides a fundamental knowledge about the modification of CP Ti with minor addition of secondary particles through SLM but also provides insight into the fabrication of inhomogeneous Ti alloys with graded microstructure and local composition through SLM for enhanced mechanical properties.

The kinetics of the tetragonal to monoclinic (t-m) transformation of zirconia in a hydrous environment at 134°C and 3 bar pressure was studied. As surface X-ray diffraction, which is conventionally used to explore the progress, has a very limited depth of information, it distorts the quantitative results in a layer-on-layer situation and by itself is ill suited for this reason. Analyzing cross sections is more suitable; therefore, focused ion beam techniques were used to prepare artifact-free cuts. The material was subsequently investigated by scanning electron microscopy, electron backscatter diffraction and Raman spectroscopy. Only the combination of methods makes it possible to resolve the quantifiable details of the process. The transformation starts in the near-surface areas, forms a layer, and the growth of this layer proceeds into the bulk material following a simple linear time law (0.0624 μm h(-1) for material in the chosen condition), without apparent retardation or limit. The progress yields a gradientless layer with a fixed amount of residual tetragonal zirconia (~27% for 3Y-TZP in the present conditions) separated from unaffected material by a boundary, which has a roughness only in the grain size range. The kinetics indicates a reaction rate control, where the hydration reaction is the key factor, but is modified by the stepwise access of water to the reaction front opened by the autocatalytic transformation of zirconia with a critical hydration level.

Due to their unique properties, nano-sized materials such as nanoparticles and nanowires are receiving considerable attention. However, little data is available about their chemical makeup at the atomic scale, especially in three dimensions (3D). Atom probe tomography is able to answer many important questions about these materials if the challenge of producing a suitable sample can be overcome. In order to achieve this, the nanomaterial needs to be positioned within the end of a tip and fixed there so the sample possesses sufficient structural integrity for analysis. Here we provide a detailed description of various techniques that have been used to position nanoparticles on substrates for atom probe analysis. In some of the approaches, this is combined with deposition techniques to incorporate the particles into a solid matrix, and focused ion beam processing is then used to fabricate atom probe samples from this composite. Using these approaches, data has been achieved from 10-20 nm core-shell nanoparticles that were extracted directly from suspension (i.e. with no chemical modification) with a resolution of better than ±1 nm., SCOPUS: ar.j, info:eu-repo/semantics/published

OBJECTIVES: The purpose of this study was to evaluate the potential of 3-dimensional ultrasonographic planar and nonplanar reslicing techniques. METHODS: Fetuses with severe brain anomalies diagnosed by means of 2-dimensional ultrasonography were prospectively included in the study. Good-quality 3-dimensional volumes of the fetal head were obtained in each case. Subsequently, these volumes were reviewed with use of 3-dimensional extended imaging with Oblique View and DynamicMR (Medison Co, Ltd, Seoul, Korea). RESULTS: Eight fetuses (mean gestational age, 23 weeks; range, 20-30 weeks) with the following central nervous system anomalies were examined: semilobar holoprosencephaly, absent cavum septum pellucidum, porencephaly in twin-to-twin transfusion syndrome, partial agenesis of the corpus callosum, Dandy-Walker variant, open-lip schizencephaly, aneurysm of the vein of Galen, and dilated cavum vergae. CONCLUSIONS: Planar and nonplanar reslicing of the volumes delivered informative images in any reconstructed plane. One important prerequisite, however, was the absence of acoustic shadowing during data acquisition.

Objectives: The aim of this study was to evaluate whether fetuses with trisomy 21 and detectable nasal bones have a distinct facial anthropometry that can be objectively defined using three-dimensional (3D) ultrasonography. Methods: A prospective cross-sectional study of 40 fetuses in the second trimester, 17 with trisomy 21 and 23 controls, was performed. The 3D volume datasets of each case were evaluated for documentation of the nasal bones using the multiplanar and the maximum mode. The nasal bone length and the angle formed by the two maxillary bones at the level of the frontal process were then measured. Results: The nasal bones were absent in 7 (41%) of the 17 fetuses with Down syndrome. All of the 23 normal fetuses had detectable nasal bones. The difference between nasal bone length in trisomy 21 fetuses and controls did not reach statistical significance (p = 0.087). The mean maxillary angle in trisomy 21 fetuses with nasal bones was significantly wider compared to controls (p = 0.029). Conclusions: The nasal bones are present in the majority of fetuses with trisomy 21 in the second trimester. This group of fetuses has a characteristic mid-facial anthropometry (wider maxillary angle) that can be assessed by means of 3D ultrasonography.