Abstract The need for sustainable mobility and renewable energy systems has been a major driving force for battery research in recent years. While ion batteries are in widespread application, there remain unsolved questions regarding fundamental processes occurring within batteries during use that ultimately limit their performance. The most important of such processes is intercalation, which describes the reversible incorporation of a guest species into a host lattice. The early stages of this process, when only a limited amount of guest material is present, are still barely understood. In this work, we use advanced transmission electron microscopy to directly observe the structure and host/guest interactions in a partially intercalated graphite model system. We show the three-dimensional layer occupancy and demonstrate that the established staging laws break down in this regime. Finally, we elucidate the impact of host lattice defects on the intercalation process using 4D-STEM, moiré imaging and in situ heating.

Transistors capable of operating at cryogenic temperatures are key components for the fast and energy-efficient control and readout of qubits. However, the ultra-low power requirements and performance metrics are not met by conventional complementary metal oxide semiconductor technology, which has been optimized for room-temperature operation. Here, we propose to enhance Si-based Schottky junction field-effect transistors with ultra-thin layers of SiGeSn to address these issues. By combining single-elementary Al contacts to avoid dopant freezeout and utilizing a multi-gate transistor architecture, which suppresses reverse junction leakage, a fivefold increase in oncurrent and a threefold increase in peak transconductance were achieved compared to a Si reference device. Measurements down to 5K revealed a drain current modulation over nine orders of magnitude with improved inverse subthreshold slopes of 20mV/dec below 50K and 50% reduced threshold voltages, while the on-currents remain mostly temperature-independent, making the system interesting for cryogenic computing.

While gas aggregation cluster sources can tailor the chemistry, size, and shape of nanoparticles (NPs), low NP yield and instability over time still limit the fabrication of nanoparticle-based coatings or nanocomposite films. In this work, we propose controlled addition of ambient air as a nucleation source to enhance the efficiency and stability of the process. Additionally, the type of power source is varied, juxtaposing direct current and high-power impulse magnetron sputtering. Quadruple mass spectrometry and high-resolution transmission electron microscopy are used to monitor the deposition rate and morphology of tungsten NPs (size, shape, microstructure) as a function of process parameters. We observe significant variations in the deposition rate, the average diameter (3-5 nm), and the microstructure (amorphous vs. single-crystalline) of produced W NPs. The enhanced NP flux was exploited to demonstrate fast deposition of 500 nm thick W nanoparticle films as well as 200 nm thick nanocomposite films, consisting of a Cu matrix with incorporated W nanoparticles. For the latter we attribute refinement of the Cu matrix microstructure to two competing mechanisms: Formation of growth twins facilitated by W NPs and grain refinement due to residual air.

Grain boundary networks and their evolution are strongly influenced by triple junctions. The defect nature of these line defects significantly affects the network's properties, but they have not been fully characterized to date. Here, we use scanning transmission electron microscopy combined with atomistic computer simulations to investigate a triple junction at the atomic scale in an Al thin film with texture. Using sampling methods, we were able to construct a computer model of the same junction as in the experiment. We present a technique to calculate the Burgers vector of the triple junction. This allows us to connect the junction's dislocation character to the microscopic degrees of freedom of the joining grain boundaries. The junction line energy can then be calculated using an embedded atom method potential. It follows the same laws as bulk dislocations. Finally, we discovered a range of possible triple junctions for the observed grain boundaries, which vary in the magnitude of their Burgers vector. Interestingly, the experimentally observed junction does not have the smallest possible Burgers vector and energy. This suggests that the kinetics of transforming the junction line are likely too slow to be driven by the small energy contribution of the triple junction.

A central focus in high strain rate research is understanding the dynamic behavior of materials at strain rates where a strength upturn is observed. While strength upturns at strain rates of 10^3 to 10^4 s^-1 have been widely reported in the literature, their occurrence in certain materials remains controversial, and the underlying physics driving this phenomenon is not yet fully understood. Current mechanical testing methods are limited, as no single technique spans the full strain rate range of 10^1 to 10^5 s^-1 where this phenomenon is expected, and a unified technique would enable consistent post-deformation characterization with minimal error. To address this, we developed a customized piezoelectric in situ nanomechanical test setup, enabling constant indentation strain rates up to 10^5 s^-1 for the first time. Using this system, we examined rate-dependent hardness in single-crystalline molybdenum, nanocrystalline nickel, and amorphous fused silica over strain rates from 10^1 to 10^5 s^-1, remarkably revealing a hardness upturn in all three materials. Further, post-deformation analysis of single-crystalline molybdenum revealed that the hardness upturn was primarily driven by increased dislocation density, with phonon drag – traditionally considered a dominant contributor – playing a minimal role.

Zinc dialkyldithiophosphate (ZDDP), as the most prominent lubrication additive, forms tribofilms consisting primarily of zinc phosphate glasses containing sulfides. As sulfur is linked to environmental concerns, sulfur-free zinc phosphate coatings have been sputtered from a Zn3(PO4)2 target and investigated here. Based on the bridging to non-bridging oxygen ratio, determined by X-ray photoelectron spectroscopy (XPS), the as deposited coatings are classified as metaphosphates. As the annealing temperature is increased, the chain lengths are reduced, as witnessed by XPS data indicated by a loss of phosphorus and oxygen of the coating surface, likely due to hydrolysis with water from the atmosphere. Transmission electron microscopy energy-dispersive X-ray spectroscopy line scans show that the XPS-revealed composition change of the coating surface upon annealing occurs over the whole thickness of the coating. This alteration in composition and chain length reductions causes a rise in hardness, reduced Young's modulus, and wear resistance. Therefore, the properties of the artificial zinc phosphate tribofilms can be tailored via a thermally stimulated composition change, causing an alternation in chain length from meta- to orthophosphate and thereby enabling the design of coatings with desired mechanical properties.

Bone serves as an example of nature's architectured material with its characteristic blend of strength and toughness, all at a lightweight design. Given the hierarchical nature of these materials, it is essential to understand the governing mechanisms and organization of their constituents across length scales for bioinspired structural design. Despite recent advances in transmission electron microscopy (TEM) that have allowed us to witness the hierarchical arrangement of bone at micro-down to the nanoscale, we are still missing the details about the structural organization and mechanical properties of the main building blocks of bone─mineralized collagen fibrils (MCFs). Here, we present a method to extract individual MCFs from nature's model material, mineralized turkey leg tendon, using a dropcasting procedure. By isolating the MCFs onto TEM supporting grids, we visualized the arrangement of organic and mineral phases within individual MCFs at the nanoscale. Using a four-dimensional scanning transmission electron microscopy (4D-STEM) approach, the orientation of individual mineral crystals within the MCFs was examined. Furthermore, we conducted in situ tensile experiments, revealing exceptional tensile strains of at least 8%, demonstrating the intricate relationship between structural organization and the mechanical behavior of MCFs. These insights into the ultrastructure of mineralized tissue building blocks, as well as the proposed sample-extraction method compatible with in situ mechanical testing, provide a strong basis for research into nature-inspired material design.

The oxidation behavior of stoichiometric Ti0.12Al0.21B0.67 coatings is investigated by scanning transmission electron microscopy (STEM) after oxidizing for 1, 4 and 8 h at 700 degrees C and at 800 and 900 degrees C. In the as deposited state, a similar to 4 nm thick, native, amorphous oxide layer covers the surface of the coating, while the magnitude of incorporated O along the column boundaries decreases with depth. During oxidation, the formation of scale layers consisting predominantly of Al, O and B is observed, that appear to be amorphous at 700 degrees C, while after oxidation at 900 degrees C for 8 h, a (nano-)crystalline aluminoborate layer forms. Concurrently, within the unoxidized coating, the formation of Al- and Ti-rich boride regions, consistent with spinodal decomposition, is observed. Chemical environment dependent density functional theory (DFT) predictions of the energies required for mass transport on the metal sublattice indicate that Al diffusion is initiated before Ti diffusion. Hence, as the temperature is increased, the migration of Al is initiated first, leading to the formation of the oxide scale observed already after oxidation at 700 degrees C for 1 h. Below the oxidized region, the formation of Al-rich and Ti-rich regions by spinodal decomposition require the concurrent migration of Al and Ti. The fact that decomposition takes place at 900 degrees C and hence at larger temperatures than the Al diffusion mediated scale formation is consistent with DFT predictions as the average values of the predicted energies required for both, vacancy formation and migration for Ti, are larger than for Al.

Chemical short-range ordering is expected to be a key factor for tuning the electronic structure of semiconductors. However, experimental evidence of short-range ordering is still lacking due to the challenge of characterizing atomic-scale ordering motifs. Here, we determined the presence of short-range order in a ternary GeSiSn semiconductor system using advanced energy-filtered four-dimensional scanning transmission electron microscopy and large-scale atomistic models generated by a machine learning neuroevolution potential of first-principles accuracy. This approach revealed preferred ordering of different atomic species with the dominant occurrence of Si-Ge-Sn triplets. Our findings not only confirmed the presence of short-range order but also directly revealed the actual atomic structure, demonstrating the potential for informed atomic order-based band engineering as a third degree of freedom beyond composition and strain tuning.

Silver nanowire (AgNW) networks have emerged as one of the most promising materials for flexible transparent conductive electrodes. These wires offer excellent electrical, optical, and mechanical properties and can be applied using low-cost printing techniques with the potential for upscaling. To elucidate the mechanical properties of nanowire networks for use in flexible electronics, it is essential to first characterize the behavior of individual wires adhered to the polymer surface under mechanical loading of the polymer. This study investigates the mechanical response of isolated nanowires during uniaxial in situ tensile testing of the polymer using correlative microscopy, which combines the advantages of light and electron microscopy. By changing the orientation of the nanowires with respect to the tensile straining axis of the polymer, the nanowires experience either tensile (for parallel orientation) or compressive forces (for perpendicular orientation) according to the polymer's elastic-plastic Poisson's ratio, which links lateral contraction of the polymer to tensile strain. Aligned and isolated AgNWs were applied to flat surfaces of two polymers, PET and PDMS, which serve as model systems to investigate the effect of the substrate on the mechanical response of the nanowires. We observe a strong influence of the polymer type on the wire deformation behavior and fracture, which we attribute to the different adhesion strength of the wires on PET and PDMS. While the wires on PET undergo multiple fractures, breaking into segments of roughly equal length under tensile loading, those on PDMS typically fracture only once, accompanied by early sliding of the wire on the substrate. Compression tests revealed localized plastic deformation by nanowire kinking with the formation of new grain boundaries for both polymer substrates. Electron microscopy studies revealed different deformation configurations depending on the amount of load applied. In addition, cyclic compressive tests provided insight into the fatigue behavior of the wires. Here, newly formed grain boundaries acted as potential fracture sites, whereas the purely elastic deformation remained fully reversible up to 1000 cycles.

Metallic nanosponges are well known to exhibit distinct mechanical properties that are considered to originate from the interwoven mechanics of the nanoscale ligaments as individual units and as a network. A comprehensive understanding of the physical mechanisms behind these properties spanning over several length scales is to date lacking. Here, by employing a correlative and scale-bridging workflow combining non-destructive 3D electron and X-ray tomography, in situ mechanics and experimentally-informed real-size modelling, we reveal the atomic origins of size dependent deformation mechanisms of nanoporous gold ranging from sub-ten to hundreds of nanometers. A realistic distribution of geometries and sizes of the ligaments appears to be crucial to accurately capture the mechanical response of nanoporous gold, including deformation gradients and plasticity. Our workflow demonstrates the potential for exploring the atomistic mechanisms of material plasticity with geometrical complexity. The mechanical properties of nanoporous gold are tied to their topology and surface morphology. Here, a correlative and scale-bridging approach, combining non-destructive 3D tomography, mechanical testing and experimentally-informed modelling, reveals the origins of the size dependent deformation mechanisms.

Bone serves as a remarkable example of nature's architectured material with its unique blend of strength and toughness, all at a lightweight design. Given the hierarchical nature of these materials, it is essential to understand the governing mechanisms and organization of its constituents across length scales for bio-inspired structural design. Despite recent advances in transmission electron miscoscopy (TEM) that have allowed us to witness the fascinating arrangement of bone at micro- down to the nano-scale, we are still missing the details about the structural organization and mechanical properties of the main building blocks of bone - mineralized collagen fibrils (MCFs). Here, we propose a novel approach for extracting individual MCFs from nature's model material via a dropcasting procedure. By isolating the MCFs onto TEM-compatible substrates, we visualized the arrangement of organic and mineral phases within the individual MCFs at the nanoscale. Using a 4D-STEM approach, the orientation of individual mineral crystals within the MCFs was examined. Furthermore, we conducted first-of-its-kind in situ tensile experiments, revealing exceptional tensile strains of at least 8%, demonstrating the intricate relationship between structural organization and the mechanical behavior of MCFs. The capabilities of TEM allow us to resolve MCF organization and composition down to the nanoscale level. This new knowledge of the ultrastructure of the bone-building blocks and the proposed sample extraction and in situ mechanical testing opens up new avenues for research into nature's inspired material design.

Integrating Ge onto SOI should enhance the drive currents and switching speeds of transistors. However, Ge on insulator platforms have fallen short of providing these benefits and are additionally facing processing issues and high fabrication costs. To cope with these issues, we use an ultra-low-temperature molecular-beam epitaxy growth of Ge layers on SOI and strained SOI substrates, as device prototyping platforms. Thereof, we obtain symmetric IV-on-states in Ge based reconfigurable transistors, enabling to investigate the temperature-dependent gating capabilities and identify the dominant transport mechanisms. In this respect, to give a comprehensive picture of the influence of different parameters on transport mechanisms, temperature-dependent gate- and biasdependent current-voltage data was evaluated constructing 2-D colormap representations.

Autonomous health tracking of coated components via electrical resistance measurements requires physical connections between coating and readout. Here, the proof of concept for contactless tracking of decomposition in autonomous self-reporting Cr-Al-B coatings is demonstrated. Contactless-monitored electrical resistance changes of Cr0.34Al0.31B0.35 coatings reveal decomposition of Cr2AlB2 and Cr3AlB4 to CrB and CrB2. Comparison of contactless-measured resistance data with in situ and ex situ high-resolution scanning transmission electron microscopy, as well as ex situ X-ray diffraction and elastic-recoil detection analysis, reveals the untapped potential of assessing materials health data in extreme environments. More sustainable materials consumption is enabled by continuous or periodic contactless tracking of materials health data as the individual remaining component lifetime is utilized instead of the much shorter lifetime prediction resulting from safety-factor-based design approaches.

Autonomous tracking of structural changes in coated components yields information on materials health and remaining lifetime; but until now, electrical resistance tracking required undesired physical connections between coating and readout. Here, the proof of concept for contactless tracking of phase transformations in autonomous self-reporting Cr-Al-B coatings is demonstrated. Contactless monitored electrical resistance changes of glassy Cr0.34Al0.31B0.35 coatings reveal crystallization, phase formation, and grain growth of Cr3AlB4 and Cr2AlB2. The hitherto untapped potential of contactless measured electrical resistance data for assessing materials health by tracking structural change is revealed by in situ high-resolution scanning transmission electron microscopy and selected area electron diffraction as well as ex situ X-ray diffraction, and elastic-recoil detection analysis. Continuous or periodic contactless tracking of material health data will enable more efficient and more sustainable materials service by utilizing the individual remaining component lifetime rather than the much shorter lifetime assessment emanating from safety factor-based design approaches.

Advancing SOI-based transistors with Ge-rich layers aims to increase device performance in terms of on-state operation and switching speed. Here, we investigate multi-heterojunction SiGe-based Schottky barrier FETs with Ge concentrations up to 75% by means of temperature- dependent electrical characterizations to identify the transport regimes and the effective barrier heights with a thermionic-emission-based model. Importantly, incorporating 33% Ge gives the best compromise for n- and p-type on-state symmetry. As the Ge concentration increases, the p-type on-state current becomes dominant, which is interesting for low-power p-type transistors.

AbstractThe oxidation resistance of Hf0.28B0.72 and Hf0.11Al0.20B0.69 thin films was investigated comparatively at 700 °C for up to 8 h. Single-phase solid solution thin films were co-sputtered from HfB2 and AlB2 compound targets. After oxidation at 700 °C for 8 h an oxide scale thickness of 31 $$\pm$$ ± 2 nm was formed on Hf0.11Al0.20B0.69 which corresponds to 14% of the scale thickness measured on Hf0.28B0.72. The improved oxidation resistance can be rationalized based on the chemical composition and the morphology of the formed oxide scales. On Hf0.28B0.72 the formation of a porous, O, Hf, and B-containing scale and the formation of crystalline HfO2 is observed. Whereas on Hf0.11Al0.20B0.69 a dense, primarily amorphous scale containing O, Al, B as well as approximately 3 at% of Hf forms, which reduces the oxidation kinetics significantly by passivation. Benchmarking Hf0.11Al0.20B0.69 with Ti–Al-based boride and nitride thin films with similar Al concentrations reveals superior oxidation behavior of the Hf-Al-based thin film. The incorporation of few at% of Hf in the oxide scale decelerates oxidation kinetics at 700 °C and leads to a reduction in oxide scale thickness of 21% and 47% compared to Ti0.12Al0.21B0.67 and Ti0.27Al0.21N0.52, respectively. Contrary to Ti–Al-based diborides, Hf0.11Al0.20B0.69 shows excellent oxidation behavior despite B-richness.

We present a study directly measuring the electron-beam-induced plasticity of amorphous Al2O3 coatings. Core-shell nanostructures are employed as small-scale model systems for two-dimensional coatings made by atomic layer deposition (ALD). Copper nanowires (NWs) are used as substrates for ALD deposition, representing a model system for interconnects commonly found in integrated circuits. Experiments are performed in situ in a transmission electron microscope (TEM) and further analyzed with electron energy loss spectroscopy (EELS). Our in situ TEM tensile experiments reveal the highly plastic behavior of the ALD shell, which withstands a maximum strain of 188%. Comparable samples under beam-off conditions show a brittle fracture, which underlines the effect of electron irradiation. The electron-beam-activated bond switching within the amorphous network enables compensation of the applied tensile strain, leading to viscous flow. By incorporating an intermediate nanocrystalline layer within the Al2O3 shell, the plasticity is suppressed and brittle fracture occurs. This work directly demonstrates the tuning of mechanical properties in amorphous ALD structures through electron irradiation. This article presents a systematic study on intentionally induced highly plastic flow in amorphous Al2O3 coatings. In situ transmission electron microscopy tensile experiments showcase the plastic behavior, enduring a maximum strain of 188%. The impact of electron irradiation, compensatory mechanisms, and the role of an intermediate nanocrystalline layer are explored, providing valuable insights into tuning mechanical properties through electron irradiation.image (c) 2024 WILEY-VCH GmbH

A promising approach to advance electronics beyond static operations is to enhance state-ofthe- art systems by the functional diversification of transistors. Here, we experimentally demonstrate that an ultra-thin Ge channel implemented on a Si on insulator platform enables run-time switchable symmetric pand n-type field-effect transistor operability as well as the prominent feature of distinct room-temperature negative differential resistance. Temperature dependent bias spectroscopy is utilized to map electronic transport in these so called negative differential resistance mode reconfigurable transistors. Thereof, a profound understanding of the involved transport physics and electrostatic gating mechanisms is obtained and evaluated. Further, we show that a multi-gate negative differential resistance reconfigurable transistor can effectively replace a cascode of negative differential resistance devices, contributing to a smaller area footprint, and reduced latency of critical paths. Notably, the experimentally obtained multi-heterojunction transistors constitute the first chip-scale platform that combines efficient polarity control as well as sizeand energy-efficient room-temperature negative differential resistance, providing an inherent component of emerging neuromorphic computing.