Analog switching in ferroelectric devices promises neuromorphic computing with the highest energy efficiency if limited device scalability can be overcome. To contribute to a solution, one reports on ...the ferroelectric switching characteristics of sub‐5 nm thin Al0.74Sc0.26N films grown on Pt/Ti/SiO2/Si and epitaxial Pt/GaN/sapphire templates by sputter‐deposition. In this context, the study focuses on the following major achievements compared to previously available wurtzite‐type ferroelectrics: 1) Record low switching voltages down to 1 V are achieved, which is in a range that can be supplied by standard on‐chip voltage sources. 2) Compared to the previously investigated deposition of ultrathin Al1−xScxN films on epitaxial templates, a significantly larger coercive field (Ec) to breakdown field ratio is observed for Al0.74Sc0.26N films grown on silicon substrates, the technologically most relevant substrate‐type. 3) The formation of true ferroelectric domains in wurtzite‐type materials is for the first time demonstrated on the atomic scale by scanning transmission electron microscopy (STEM) investigations of a sub‐5 nm thin partially switched film. The direct observation of inversion domain boundaries (IDB) within single nm‐sized grains supports the theory of a gradual domain‐wall driven switching process in wurtzite‐type ferroelectrics. Ultimately, this should enable the analog switching necessary for mimicking neuromorphic concepts also in highly scaled devices.
This study reports on sputter‐deposited ferroelectric sub‐5 nm thin Al0.74Sc0.26N. Scanning transmission electron microscopy (STEM) investigations reveal the formation of domain walls with a significant horizontal component and in‐grain partial switching on lateral dimensions below 10 nm2. The impact of the substrate type (silicon and sapphire) as well as a decrease in the coercive field (Ec) with thickness are discussed in detail and enable switching voltages as low as 1 V.
The conversion of SO
into arylsulfones under metal-free conditions was achieved for the first time by reacting SO
with (hetero)arylsilanes and alkylhalides in the presence of a fluoride source. The ...mechanism of this transformation was elucidated based on DFT calculations, which highlight the influence of SO
in promoting C-Si bond cleavage.
Novel energy and atom efficiency processes will be keys to develop the sustainable chemical industry of the future. Electrification could play an important role, by allowing to fine-tune energy input ...and using the ideal redox agent: the electron. Here we demonstrate that a commercially available Milstein ruthenium catalyst (
1
) can be used to promote the electrochemical oxidation of ethanol to ethyl acetate and acetate, thus demonstrating the four electron oxidation under preparative conditions. Cyclic voltammetry and DFT-calculations are used to devise a possible catalytic cycle based on a thermal chemical step generating the key hydride intermediate. Successful electrification of Milstein-type catalysts opens a pathway to use alcohols as a renewable feedstock for the generation of esters and other key building blocks in organic chemistry, thus contributing to increase energy efficiency in organic redox chemistry.
Electrification of the Milstein catalyst enabled successful molecular electrocatalytic oxidation of ethanol to the four-electron products acetate and ethyl acetate.
Films containing 8, 16, 24, 32 and 64 MoSe2 layers were synthesized using the modulated elemental reactants method. X-ray reflectivity patterns showed that the annealed films were the targeted number ...of MoSe2 layers thick with atomically smooth interfaces. In-plane x-ray diffraction (XRD) scans contained only hk0 reflections for crystalline MoSe2 monolayers. Specular XRD patterns contained only 00l reflections, also indicating that the hk0 plane of the MoSe2 layers are parallel to the substrate. Both XRD and electron microscopy techniques indicated that the hk0 planes are rotationally disordered with respect to one another, with all orientations equally probable for large areas. The rotational disorder between MoSe2 layers is present even when analyzed spots are within 10 nm of one another. Cross-plane thermal conductivities of 0.07-0.09 W m−1 K−1 were measured by time domain thermoreflectance, with the thinnest films exhibiting the lowest conductivity. The structural analysis suggests that the ultralow thermal conductivity is a consequence of rotational disorder, which increases the separation between MoSe2 layers. The bonding environment of the Se atoms also becomes significantly distorted from C3v symmetry due to the rotational disorder between layers. This structural disorder efficiently reduces the group velocity of the transverse phonon modes but not that of longitudinal modes. Since rotational disorder between adjacent layers in heterostructures is expected if the constituents have incommensurate lattices, this study indicates that these heterostructures will have very low cross-plane thermal conductivity.
Abstract
We report a C−C bond‐forming reaction between benzyl alcohols and alkynes in the presence of a catalytic amount of KO
t
Bu to form α‐alkylated ketones in which the C=O group is located on ...the side derived from the alcohol. The reaction proceeds under thermal conditions (125 °C) and produces no waste, making the reaction highly atom efficient, environmentally benign, and sustainable. Based on our mechanistic investigations, we propose that the reaction proceeds through radical pathways.
Ferroelectric thin films of wurtzite-type aluminum scandium nitride (Al1−xScxN) are promising candidates for non-volatile memory applications and high-temperature sensors due to their outstanding ...functional and thermal stability exceeding most other ferroelectric thin film materials. In this work, the thermal expansion along with the temperature stability and its interrelated effects have been investigated for Al1−xScxN thin films on sapphire Al2O3(0001) with Sc concentrations x (x = 0, 0.09, 0.23, 0.32, 0.40) using in situ X-ray diffraction analyses up to 1100 °C. The selected Al1−xScxN thin films were grown with epitaxial and fiber textured microstructures of high crystal quality, dependent on the choice of growth template, e.g., epitaxial on Al2O3(0001) and fiber texture on Mo(110)/AlN(0001)/Si(100). The presented studies expose an anomalous regime of thermal expansion at high temperatures >~600 °C, which is described as an isotropic expansion of a and c lattice parameters during annealing. The collected high-temperature data suggest differentiation of the observed thermal expansion behavior into defect-coupled intrinsic and oxygen-impurity-coupled extrinsic contributions. In our hypothesis, intrinsic effects are denoted to the thermal activation, migration and curing of defect structures in the material, whereas extrinsic effects describe the interaction of available oxygen species with these activated defect structures. Their interaction is the dominant process at high temperatures >800 °C resulting in the stabilization of larger modifications of the unit cell parameters than under exclusion of oxygen. The described phenomena are relevant for manufacturing and operation of new Al1−xScxN-based devices, e.g., in the fields of high-temperature resistant memory or power electronic applications.
A Pd-catalyzed Hiyama cross-coupling reaction using SO2 is described. The use of silicon-based nucleophiles leads to the formation of allyl sulfones under mild conditions with a broad functional ...group tolerance. Control experiments coupled with DFT calculations shed light on the key steps of the reaction mechanism, revealing the crucial role of a transient sulfinate anion.
Monolithic integration of permanent micromagnets into MEMS structures offers many advantages in magnetic MEMS applications. A novel technique called PowderMEMS, based on the agglomeration of ...micron-sized powders by atomic layer deposition (ALD), has been used to fabricate permanent micromagnets on 8-inch wafers. In this paper, we report the fabrication and magnetic characterization of PowderMEMS micromagnets prepared from two different NdFeB powder particle sizes. A remanence of 423 mT and intrinsic coercivity of 924 mT is achieved at the low ALD process temperature of 75 °C, making this process compatible with MEMS technology. The magnetic reversible mechanism in the micromagnets is discussed with the help of the Wohlfarth equation. To ensure the operability of such integrated micromagnets in different application environments, we conducted a set of experiments to systematically investigate the thermal and corrosive stability. NdFeB micromagnets with larger powder particle size (d50 = 25 µm) exhibit high thermal stability in air. Furthermore, the corrosion stability of the micromagnets is significantly improved by an additional silicon oxide passivation layer deposited by plasma-enhanced chemical vapor deposition (PECVD). The presented results demonstrate the durability of PowderMEMS micromagnets, enabling their application in various fields, e.g., microfluidics, sensors, actuators, and microelectronics.
Supercapacitors are energy storage devices with the ability to rapidly charge and discharge, making them a valuable complement to battery systems. To maximize their fast‐charging capabilities, ...identifying materials and methods to enhance their energy density is crucial. In this work, we carried out a comprehensive study of an emerging 2D dichalcogenide, CrSe2, as a supercapacitor material. We demonstrate that CrSe2 can be obtained at ambient temperature through deintercalation of a relevant KCrSe2 precursor using a 0.5 M solution of I2 in acetonitrile. Although CrSe2 decomposed in 1 M KOH, it was found to be chemically stable in common electrolytes such as H2SO4, Li2SO4, and Na2SO4. Despite low surface area CrSe2 reached a specific capacitance of 27 F g−1 in 1 M H2SO4 and, thus consistently outperformed high surface carbon black. Computational studies suggested that the metallic conductivity of CrSe2 was likely the primary factor contributing to the superior performance of this 2D chalcogenide over high surface carbon analogues.
The response of individual grain boundaries in polycrystalline ZnO nano‐ and microstructure platelets to visible light illumination is studied using scanning probe microscopy. The grain boundaries ...show enhanced photoconductivity even in the visible range of light below the band gap, suggesting that they can be potentially used as transparent conducting oxide electrodes.
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