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Overcoming the difficulty in the precise definition of the metal phase of metal-Si heterostructures is among the key prerequisites to enable reproducible next-generation nanoelectronic, optoelectronic, and quantum devices. Here, we report on the formation of monolithic Al-Si heterostructures obtained from both bottom-up and top-down fabricated Si nanostructures and Al contacts. This is enabled by a thermally induced Al-Si exchange reaction, which forms abrupt and void-free metal-semiconductor interfaces in contrast to their bulk counterparts. The selective and controllable transformation of Si NWs into Al provides a nanodevice fabrication platform with high-quality monolithic and single-crystalline Al contacts, revealing resistivities as low as ρ = (6.31 ± 1.17) × 10

The study describes the creation of high-quality metal oxide nanotubes via a defined heat treatment process of core-shell nanowires. In situ TEM heating experiments and correlative ex situ observations unravel the dynamical processes at small scales.

Abstract Size effects decisively influence the properties of materials at small length scales. In the context of mechanical properties, the trend of ‘smaller is stronger’ has been well established. This statement refers to an almost universal trend of increased strength with decreasing size. A strong influence of size on the elastic properties has also been widely reported, albeit without a clear trend. However, the influence of nanostructure shape on the mechanical properties has been critically neglected. Here, we demonstrate a profound influence of shape and size on the elastic properties of materials on the example of gold nanowires. The elastic properties are determined using in-situ mechanical testing in scanning and transmission electron microscopy by means of resonance excitation and uniaxial tension. The combination of bending and tensile load types allows for an independent and correlative calculation of the Young's modulus. We find both cases of softening as well as stiffening, depending critically on the interplay between size and shape of the wires. Graphic abstract

Modern devices based on modular designs require versatile and universal sensor components which provide an efficient, sensitive, and compact measurement unit. To improve the space capacity of devices, miniaturized building elements are needed, which implies a turning away from conventional microcantilevers toward nanoscale cantilevers. Nanowires can be seen as high-quality resonators and offer the opportunity to create sensing devices on small scales. To use such a one-dimensional nanostructure as a resonant cantilever, a precise characterization based on the fundamental properties is needed. We present a correlative electron and light microscopy approach to characterize the pressure and environment sensing capabilities of single nanowires by analyzing their resonance behavior

Si

The interplay between microphase separation and crystallization in the semicrystalline PS-b-PEO system is investigated in the context of solution-based thin film formation. For this end, the film m...

Flexible electrodes using nanowires (NWs) suffer from challenges of long-term stability and high junction resistance which limit their fields of applications. Welding via thermal annealing is a common strategy to enhance the conductivity of percolated NW networks, however, it affects the structural and mechanical integrity of the NWs. In this study we show that the decoration of NWs with an ultrathin metal oxide is a potential alternative procedure which not only enhances the thermal and chemical stability but, moreover, provides a totally different mechanism to reduce the junction resistance upon heat treatment. Here, we analyze the effect of SnO x decoration on the conductance of silver NWs and NW junctions by using a four-probe measurement setup inside a scanning electron microscope. Dedicated transmission electron microscopy analysis in plan-view and cross-section geometry are carried out to characterize the nanowires and the microstructure of the junctions. Upon heat treatment the junction resistance of both plain silver NWs and SnO x -decorated NWs is reduced by around 80%. While plain silver NWs show characteristic junction welding during annealing, the SnO x -decoration reduces junction resistance by a solder-like process which does not affect the mechanical integrity of the NW junction and is therefore expected to be superior for applications.

This work focuses on the low temperature fabrication process of InN thin films via microwave plasma-assisted reactive high power impulse magnetron sputtering (MAR-HiPIMS). The influence of microwave plasma on the HiPIMS discharge process at various nitrogen flows and microwave powers was monitored and characterised through in situ diagnostics, including following HiPIMS I(V,t) curves, optical emission spectroscopy (OES), as well as performing time-resolved Langmuir probe and time-of-flight mass spectroscopy (ToF-MS) measurements. This was followed by the deposition of InN films via standard reactive HiPIMS (reference sample) and MAR-HiPIMS and their characterisation via X-ray diffraction (XRD), reflectometry (XRR), as well as scanning and transmission electron microscopy (SEM, TEM). It was found that the microwave plasma facilitates the dissoci-ation/activation of nitrogen species and supplies seed electrons to the magnetron discharge plasma. Furthermore, the energy of the incoming ions was determined via ToF-MS, and it was possible to identify their plasma origin and temporal behaviour. The produced R-HiPIMS sample was highly metallic, with no nitride phase detected. The MAR-HiPMS film, however, was stoichiometric and exhibited (0002) direction texturing, with an optical bandgap of approx. 1.5 eV, electron concentration of 2.72 x 1020 cm -3 and electron mobility of 7.16 cm2V- 1s- 1 (in the range for polycrystalline InN).

The strain rate (epsilon ) and temperature ( T ) dependent mechanical response of single crystal magnesium (Mg) micropillars compressed along the [ 2 over line 110 ] direction ( a-axis) is investigated from room temperature to 573 K and from 10-3 to 100 s-1 . The loading direction was chosen to disfavour basal slip activation by a low Schmid factor, allowing the investigation of the rate-sensitivities of extension twinning and prismatic slip. For T 423 K and for epsilon 10 s-1 , however, the accommodation of the plastic deformation by activation of prismatic slip is not enough to match the applied deformation rate, favouring again deformation twinning. The first part of this work provides a complete overview of the mutual effects of T and epsilon on the transition points of deformation modes in Mg at the microscale. In a second stage, the influence of thermal and kinetic contributions on the evolution of the flow stress leading to the slip to twin transition at 573 K has been assessed in more detail. Within the slip-dominated plasticity regime, this work provides a quantitative assessment of the increases in the saturation stress (stage III) with epsilon at high temperature, showing how the strain rate dependency of the dislocation generation rate in the pillar and escape rate at the free surfaces of the structure controls the stress evolution in Mg microcrystals.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Mn3O4 and Mn2O3 were synthesized by potentiostatic electrodeposition from a de-aerated manganese acetate and sodium sulfate electrolytic bath, followed by annealing. The electrodeposition parameters (including applied potential, precursor concentration, pH, temperature) and the thermal treatment conditions were investigated to obtain the best control over microstructure and stoichiometry of manganese oxides. We found that the applied voltage is the key parameter affecting the valence state of initial amorphous manganese while the thermal treatment leads to crystallization and tuning of optical properties without substantially changing the morphology. The as-electrodeposited manganese oxides are X-rays amorphous, while two different crystalline phases, Mn3O4 and Mn2O3, were obtained after the thermal treatment depending on the applied voltage. Through the analysis of TEM cross section images, a fiber-like growth was observed for Mn3O4, while Mn2O3 presented a less porous-more compact microstructure. The optical properties were investigated, resulting in an enhancement in the charge separation properties of the thermally treated manganese oxides, reflected by nearly a 40 % reduction in the photoluminescence peak intensity. We believe that these finding will be useful in the future development of environmental friendly manganese oxide-based photoelectrochemical systems.

ACS nano 15(1), 362-376 (2021). doi:10.1021/acsnano.0c06480, Published by American Chemical Society, Washington, DC

A new in situ synthesis method for the growth of MoO2 nanowires via controlled thermal oxidation of MoS2 flakes is presented, going from a 2D transition metal chalcogenide to a transition metal oxide nanostructure. The wire growth is performed under an optical microscope using a heating stage with adjustable atmospheric conditions. In contrast to prevalent syntheses, this templated growth leads to highly directional wires along defined MoS2 crystallographic directions. We examine the growth kinetics of the wires in dependence of the process temperature. In the temperature regime from 650 °C to 710 °C high quality MoO2 nanowires are formed in a reaction-limited growth process with an activation energy of 596 kJ mol−1. The functional properties of the nanowires are studied by a combination of in situ electron microscopy techniques. Four point measurements in an SEM reveal outstanding metal-like behavior of the nanowires with resistivity values as low as 3.5 × 10−6 Ω m. Surprisingly, junctions between intergrown nanowires show hardly any increase in resistivity which can be attributed to the well-defined orientational relationship of the nanowires resulting from their templated growth on MoS2. Elastic properties of the nanowires are studied by complementary in situ bending and resonance measurements in SEM yielding consistent values of 383 GPa for the Young's modulus. Finally, field emission of single MoO2 nanowires is studied in situ inside the TEM, and an emission current of 500 nA is achieved. The combination of simple synthesis route with outstanding functional properties make the MoO2 nanowires promising candidates for functional devices in the field of novel 1D-oxide/2D-chalcogenide hybrids. The presented synthesis can be generalized and applied to other metal chalcogenides such as WS2, as well.

A new in situ synthesis method for the growth of MoO2 nanowires via controlled thermal oxidation of MoS2 flakes is presented, going from a 2D transition metal chalcogenide to a transition metal oxide nanostructure. The wire growth is performed under an optical microscope using a heating stage with adjustable atmospheric conditions. In contrast to prevalent syntheses, this templated growth leads to highly directional wires along defined MoS2 crystallographic directions. We examine the growth kinetics of the wires in dependence of the process temperature. In the temperature regime from 650 °C to 710 °C high quality MoO2 nanowires are formed in a reaction-limited growth process with an activation energy of 596 kJ mol-1. The functional properties of the nanowires are studied by a combination of in situ electron microscopy techniques. Four point measurements in an SEM reveal outstanding metal-like behavior of the nanowires with resistivity values as low as 3.5 × 10-6 Ω m. Surprisingly, junctions between intergrown nanowires show hardly any increase in resistivity which can be attributed to the well-defined orientational relationship of the nanowires resulting from their templated growth on MoS2. Elastic properties of the nanowires are studied by complementary in situ bending and resonance measurements in SEM yielding consistent values of 383 GPa for the Young's modulus. Finally, field emission of single MoO2 nanowires is studied in situ inside the TEM, and an emission current of 500 nA is achieved. The combination of simple synthesis route with outstanding functional properties make the MoO2 nanowires promising candidates for functional devices in the field of novel 1D-oxide/2D-chalcogenide hybrids. The presented synthesis can be generalized and applied to other metal chalcogenides such as WS2, as well.

Quantum size-confined CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

The transition of a thin film into an energetically favorable set of particles at temperatures below the melting point of the bulk material is known as solid-state dewetting. In this work the dewetting behavior of 16 nm thick discontinuous Au thin films on amorphous silicon nitride membranes is quantitatively studied by complementary in situ transmission electron microscopy techniques taking advantage of the unique capabilities of a chip-based heating system. The combination of dedicated imaging and diffraction techniques is used to investigate the interplay of grain growth and texture evolution with the process of dewetting. The results show an initial coarsening of the microstructure preceding the other processes. Texture evolution is highly correlated to material retraction and agglomeration during the following dewetting process. In-plane grain rotation has been observed, acting as an additional mechanism for orientation changes. From a methodological perspective this work demonstrates the capabilities of today’s transmission electron microscopy in combination with state-of-the-art in situ instrumentation. In particular the combination of complementary information from different dedicated techniques in one and the same setup is demonstrated to be highly beneficial.

Semitransparent solar cells (SSCs) can open photovoltaic applications in many commercial areas, such as power-generating windows and building integrated photovoltaics. This study successfully demonstrates solution-processed small molecule SSCs with a conventional configuration for the presently tested material systems, namely BDTT-S-TR:PC70BM, N(Ph-2T-DCN-Et)3:PC70BM, SMPV1:PC70BM, and UU07:PC60BM. The top transparent cathode coated through solution processes employs a highly transparent silver nanowire as electrode together with a combination interface bilayer of zinc oxide nanoparticles (ZnO) and a perylene diimide derivative (PDINO). This ZnO/PDINO bilayer not only serves as an effective cathode buffer layer but also acts as a protective film on top of the active layer. With this integrated contribution, this study achieves a power conversion efficiency (PCE) of 3.62% for fully solution-processed SSCs based on BDTT-S-TR system. Furthermore, the other three systems with various colors exhibited the PCEs close to 3% as expected from simulations, demonstrate the practicality and versatility of this printed semitransparent device architecture for small mole­cule systems. This work amplifies the potential of small molecule solar cells for window integration.

Electron diffraction is a powerful characterization method that is used across different fields and in different instruments. In particular, the power of transmission electron microscopy (TEM) largely relies on the capability to switch between imaging and diffraction mode enabling identification of crystalline phases and in-depth studies of crystal defects, to name only examples. In contrast, while diffraction techniques have found their way into the realm of scanning electron microscopy (SEM) in the form of electron backscatter diffraction and related techniques, on-axis transmission diffraction is still in its infancy. Here we present a simple but versatile setup that enables a ‘diffraction mode’ in SEM using a fluorescent screen and a dedicated in vacuo camera. With this setup spot-like nano-beam diffraction patterns of thin samples can be acquired with electron energies as low as 500 eV. We therefore coin the name Low Energy Nano Diffraction (LEND). Diffraction patterns can be recorded from single positions on the sample or integrated over selected areas by adjustable scan patterns. Besides showing the principal application of the technique to standard materials such as gold and silicon we also explore the application to graphene and other 2D materials. Besides single pattern measurements, also full 4D-STEM diffraction mappings are demonstrated. Finally, we show how the integration of a versatile diffraction mode in SEM enables a thorough analysis performed with a single instrument.

Despite major technological advances within the field of cardiovascular engineering, the risk of thromboembolic events on artificial surfaces in contact with blood remains a major challenge and limits the functionality of ventricular assist devices (VADs) during mid- or long-term therapy. Here, a biomimetic blood-material interface is created via a nanofiber-based approach that promotes the endothelialization capability of elastic silicone surfaces for next-generation VADs under elevated hemodynamic loads. A blend fiber membrane made of elastic polyurethane and low-thrombogenic poly(vinylidene fluoride- co-hexafluoropropylene) was partially embedded into the surface of silicone films. These blend membranes resist fundamental irreversible deformation of the internal structure and are stably attached to the surface, while also exhibiting enhanced antithrombotic properties when compared to bare silicone. The composite material supports the formation of a stable monolayer of endothelial cells within a pulsatile flow bioreactor, resembling the physiological in vivo situation in a VAD. The nanofiber surface modification concept thus presents a promising approach for the future design of advanced elastic composite materials that are particularly interesting for applications in contact with blood.

A materials scientist’s dream come true: manipulating and controlling individual dislocations in situ., Topological defects in crystalline solids are of fundamental interest in physics and materials science because they can radically alter the properties of virtually any material. Of particular importance are line defects, known as dislocations, which are the main carriers of plasticity and have a tremendous effect on electronic and optical properties. Understanding and controlling the occurrence and behavior of those defects have been of major and ongoing interest since their discovery in the 1930s. This interest was renewed with the advent of two-dimensional materials in which a single topological defect can alter the functionality of the whole system and even create new physical phenomena. We present an experimental approach to directly manipulate dislocations in situ on the nanometer scale by using a dedicated scanning electron microscope setup. With this approach, key fundamental characteristics such as line tension, defect interaction, and node formation have been studied. A novel switching reaction, based on the recombination of dislocation lines, was found, which paves the way for the concept of switches made of a bimodal topological defect configuration.