The ability to increase the thermal stability of protective coatings under work load gives rise to scientific and industrial interest in age hardening of complex nitride coating systems such as ceramic-like Ti1−xAlxN. However, the decomposition pathway of these systems from single-phase cubic to the thermodynamically stable binary nitrides (cubic TiN and wurtzite AlN), which are essential for age hardening, are not yet fully understood. In particular, the role of decomposition kinetics still requires more detailed investigation. In the present work, the combined effect of annealing time and temperature upon the nano-structural development of Ti0.46Al0.54N thin films is studied, with a thermal exposure of either 1 min or 120 min in 100 °C steps from 500 °C to 1400 °C. The impact of chemical changes at the atomic scale on the development of micro-strain and mechanical properties is studied by post-annealing investigations using X-ray diffraction, nanoindentation, 3D-atom probe tomography and high-resolution transmission electron microscopy. The results clearly demonstrate that the spinodal decomposition process, triggering the increase of micro-strain and hardness, although taking place throughout the entire volume, is enhanced at high diffusivity paths such as grain or column boundaries and followed within the grains. Ab initio calculations further show that the early stages of wurtzite AlN precipitation are connected with increased strain formation, which is in excellent agreement with experimental observations.

Computationally guided high-throughput synthesis is used to explore the Zn–V–N phase space, resulting in the synthesis of a novel ternary nitride Zn2VN3. Following a combinatorial PVD screening, we isolate the phase and synthesize polycrystalline Zn2VN3 thin films with wurtzite structure on conventional borosilicate glass substrates. In addition, we demonstrate that cation-disordered, but phase-pure (002)-textured, Zn2VN3 thin films can be grown using epitaxial stabilization on α-Al2O3 (0001) substrates at remarkably low growth temperatures well below 200 °C. The structural properties and phase composition of the Zn2VN3 films are studied in detail using XRD and (S)­TEM techniques. The composition as well as chemical state of the constituent elements are studied using RBS/ERDA and XPS/HAXPES methods. These analyses reveal a stoichiometric material with no oxygen contamination, besides a thin surface oxide. We find that Zn2VN3 is a weakly doped p-type semiconductor demonstrating broad-band room-temperature photoluminescence spanning the range between 2 and 3 eV. In addition, the electronic properties can be tuned over a wide range via isostructural alloying on the cation site, making this a promising material for optoelectronic applications.

Lithium dendrites have become a roadblock in the realization of solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk defects in crystalline electrolytes such as the garnet Li7La3Zr2O12 (LLZO) facilitates the growth of these hazardous lithium filaments. Here we explore the amorphous phase of LLZO as a lithium dendrite shield owing to its grain-boundary-free microstructure, stability against lithium metal, and high electronic insulation. By tuning the lithium stoichiometry, the ionic conductivity can be increased by 4 orders of magnitude while retaining a negligible electronic conductivity. In symmetric cells, plating-stripping shows no signs of lithium penetration up to 3.2 mA cm−2. The dense conformal nature of the films enables microbatteries with an electrolyte thickness of only 70 nm, which can be cycled at 10C for over 500 cycles. The application of this material as a coating on crystalline LLZO lowers the interface resistance and increases the critical current density. The effectiveness of the amorphous Li-La-Zr-O as dendrite blocking layer can accelerate the development of better solid-state batteries.

No abstract

We document the hygroscopic swelling and shrinkage of the central and the thickest secondary cell wall layer of wood (named S2) in response to changes in environmental humidity using synchrotron radiation-based phase contrast X-ray tomographic nanoscopy. The S2 layer is a natural fibre-reinforced nanocomposite polymer and is strongly reactive to water. Using focused ion beam, micropillars with a cross section of few micrometres are fabricated from the S2 layer of the latewood cell walls of Norway spruce softwood. The thin neighbouring cell wall layers are removed to prevent hindering or restraining of moisture-induced deformation during swelling or shrinkage. The proposed experiment intended to get further insights into the microscopic origin of the anisotropic hygro-expansion of wood. It is found that the swelling/shrinkage strains are highly anisotropic in the transverse plane of the cell wall, larger in the normal than in the direction parallel to the cell wall's thickness. This ultrastructural anisotropy may be due to the concentric lamellation of the cellulose microfibrils as the role of the cellulose microfibril angle in the transverse swelling anisotropy is negligible. The volumetric swelling of the cell wall material is found to be substantially larger than the one of wood tissues within the growth ring and wood samples made of several growth rings. The hierarchical configuration in wood optimally increases its dimensional stability in response to a humid environment with higher scales of complexity.

No abstract

The mechanistic understanding of structure–function relationships in biological systems heavily relies on imaging. While fluorescence microscopy allows the study of specific proteins following their labeling with fluorophores, electron microscopy enables holistic ultrastructural analysis based on differences in electron density. To identify specific proteins in electron microscopy, immunogold labeling has become the method of choice. However, the distinction of immunogold-based protein labels from naturally occurring electron dense granules and the identification of several different proteins in the same sample remain challenging. Correlative cathodoluminescence electron microscopy (CCLEM) bioimaging has recently been suggested to provide an attractive alternative based on labels emitting characteristic light. While luminescence excitation by an electron beam enables subdiffraction imaging, structural damage to the sample by high-energy electrons has been identified as a potential obstacle. Here, we investigate the feasibility of various commonly used luminescent labels for CCLEM bioimaging. We demonstrate that organic fluorophores and semiconductor quantum dots suffer from a considerable loss of emission intensity, even when using moderate beam voltages (2 kV) and currents (0.4 nA). Rare-earth element-doped nanocrystals, in particular Y2O3:Tb3+ and YVO4:Bi3+,Eu3+ nanoparticles with green and orange-red emission, respectively, feature remarkably high brightness and stability in the CCLEM bioimaging setting. We further illustrate how these nanocrystals can be readily differentiated from morphologically similar naturally occurring dense granules based on optical emission, making them attractive nanoparticle core materials for molecular labeling and (multi)­color CCLEM.

No abstract