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Abstract: Metal–organic frameworks have been intensively investigated for their ability to effectively control the growth and surface chemistry of nanosized guests, with their pores acting as templates and potentially providing anchoring sites. Since the speciation, as determined by the geometry and surface chemistry of hydride-forming metals, such as Pd, under particular conditions (T, p), is controlled by their size at and beyond the nanoscale, metal–organic frameworks are a prospective matrix for speciation or phase selection. This is of relevance because the role and characteristics of the phases in hydrogenation reactions involving hydride-forming Pd catalysts are open questions. In particular, it is a matter of debate which palladium phase is the most active and most selective, as they often occur simultaneously under catalytic conditions. For the first time, our thorough investigation, including operando XAFS and computer simulations, demonstrates that by embedding Pd nanoclusters, ≤1 nm in diameter, in the pores of the NH2–UiO-66 metal–organic framework, the speciation of subnanometric Pd particles can be controlled, such that the active particles only exist in their metallic state under reaction conditions; in fact, the Pd–H2 mixture only affords surface-bound hydrogen atoms. This control of Pd speciation consequently enables the direct probing of the phase activity and selectivity in the model reaction of 1,3-butadiene hydrogenation to butenes, wherein it showed no deactivation and improved selectivity compared to conventionally prepared catalytic systems. This result shows that the metallic phase can be stabilized through subnanometric size control and that it is more selective and less prone to overhydrogenating the butadiene reactant to butane, resulting in a purer product.

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Abstract: Titanium alloys owe their superior fatigue performance to a lack of extrinsic nucleation sites for cracking, but this also results in difficulty in developing fine, 10 nm scale precipitates to provide fatigue strength. Conventional Ti alloys used for large components such as jet engine discs must instead develop a hierarchical microstructure through successive waves of nucleation. Here we show that intermediate temperature deformation can result in the nucleation of nanoscale hcp α precipitates in between large μm thick α plates, and observe the precipitation of these in situ in the TEM using 4D-Scanning Transmission Electron Microscopy (4D-STEM) alongside the accompanying partially-relaxed transformation strain fields. This results in an improvement in the high cycle fatigue strength of the material by 95 MPa, to around 920 MPa in un-notched high cycle fatigue at 106 cycles, or 200 MJ kg−1, which is among the highest of all structural materials.

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Abstract: A correlative multi-technique approach, including electron microscopy and X-ray synchrotron work, has been used to obtain both structural and compositional information of a sulfur-bearing serpentine identified in several carbonaceous chondrites (Winchcombe CM2, Aguas Zarcas CM2, Ivuna CI, and Orgueil CI), and in Ryugu samples returned by the Hayabusa2 mission. S-K edge X-ray absorption spectroscopy was used to determine the oxidation state of sulfur in the serpentine in all samples except Ryugu. The abundance of this phase varies across these samples, with the largest amount in Winchcombe; ~12 vol% of phyllosilicates are identified as sulfur-bearing serpentine characterized by ~10 wt% SO3 equivalent. HRTEM studies reveal a d001-spacing range of 0.64–0.70 nm across all sulfur-bearing serpentine sites, averaging 0.68 nm, characteristic of serpentine. Sulfur-serpentine has variable S6+/ΣStotal values and different sulfur species dependent on specimen type, with CM sulfur-bearing serpentine having values of 0.1–0.2 and S2− as the dominant valency, and CIs having values of 0.9–1.0 with S6+ as the dominant valency. We suggest sulfur is structurally incorporated into serpentine as SH− partially replacing OH−, and trapped as SO42− ions, with an approximate mineral formula of (Mg Fe2+ Fe3+ Al)2-3(Si Al)2O5(OH)5-6(HS−)1-2(SO4)2−0.1-0.7. We conclude that much of the material identified in previous studies of carbonaceous chondrites as TCI-like or PCPs could be sulfur-bearing serpentine. The relatively high abundance of sulfur-bearing serpentine suggests that incorporation of sulfur into this phase was a significant part of the S-cycle in the early Solar System.

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Abstract: Decoherence in superconducting quantum circuits, caused by loss mechanisms like material imperfections and two-level system (TLS) defects, remains a major obstacle to improving the performance of quantum devices. In this work, we present atomic-level characterization of cross-sections of a Josephson junction and a spiral resonator to assess the quality of critical interfaces. Employing scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) and electron-energy loss spectroscopy (EELS), we identify structural imperfections associated with oxide layer formation and carbon-based contamination, and correlate these imperfections to the pattering and etching steps in the fabrication process and environmental exposure. These results help to understand that TLS imperfections at critical interfaces play a key role in limiting device performance, emphasizing the need for an improved fabrication process.

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Abstract: The electron beam for scanning transmission electron microscopy (STEM) provides rich information about the atomic structure and chemical composition of materials from micron to atomic scale. However, the electron probe can also damage the materials of interest, as the high-energy electrons are often focused on very small sample regions. These effects limit the quality of information which can be extracted from experiments on beam-sensitive materials, such as Li-ion battery materials and metal halide perovskites used in solar cell devices. However, with the increasing interest in these materials to address environmental and societal concerns, a detailed understanding of their microstructure and chemical composition at high spatial resolution is needed to improve their performance and stability. For these materials, the correlation between processing and nanoscale structure-property relationships has been difficult to firmly establish. As shown in Fig. 1a-1c, phase change or amorphisation in beam-sensitive materials can be easily caused by a focused electron probe. Fortunately, this problem can be solved through combined scanning electron nano-diffraction (SEND) and energy dispersive X-ray spectroscopy (EDX) with low electron dose conditions, providing nanoscale crystallographic and chemical information from the specimen. However, the signal-to-noise (SNR) of the EDX data is very poor - with just a few counts in any individual scan prohibiting comprehensive materials characterisation (Fig. 1d). To address this, we perform automated SEND-EDX data acquisition under low dose conditions utilising our automated data analysis workflow. By communicating with two different modalities, i.e., Aztec®; Oxford Instruments and MerlinEM; Quantum Detectors, and using our Python-based software, many SEND-EDX data pairs were simultaneously acquired from a metal halide perovskite. The radially flattened diffraction datasets were then be segmented into distinct phases by using an unsupervised learning approach, non-negative matrix factorisation, and the EDX spectra from identical phases classified earlier were summed across all datasets to enable chemical identification with a much higher SNR than one EDX spectrum image (Fig. 1d) as shown in Fig. 2. In this way we can determine the chemical and crystallographic structure of small phase domains in a highly beam-sensitive multi-phase metal halide perovskite. This research will both demonstrate a novel multi-modal, data-fusion based approach to imaging beam-sensitive materials and shed light on the processing and structure-property relationships of these materials on the nanometre length scale to improve their long-term operational stability.