DEAP-3600 is a single-phase liquid argon (LAr) direct-detection dark matter experiment, operating 2 km underground at SNOLAB (Sudbury, Canada). The detector consists of 3279 kg of LAr contained in a spherical acrylic vessel. This paper reports on the analysis of a 758 tonne · day exposure taken over a period of 231 live-days during the first year of operation. No candidate signal events are observed in the WIMP-search region of interest, which results in the leading limit on the WIMP-nucleon spin-independent cross section on a LAr target of 3.9 × 10 −45 cm 2 (1.5 × 10 −44 cm 2 ) for a 100 GeV=c 2 (1 TeV=c 2 ) WIMP mass at 90% C.L. In addition to a detailed background model, this analysis demonstrates the best pulseshape discrimination in LAr at threshold, employs a Bayesian photoelectron-counting technique to improve the energy resolution and discrimination efficiency, and utilizes two position reconstruction algorithms based on the charge and photon detection time distributions observed in each photomultiplier tube.

For mass production of high‐purity hydrogen fuel by electrochemical water splitting, seawater electrolysis is an attractive alternative to the traditional freshwater electrolysis due to the abundance and low cost of seawater in nature. However, the undesirable chlorine ion oxidation reactions occurring simultaneously with seawater electrolysis greatly hinder the overall performance of seawater electrolysis. To tackle this problem, electrocatalysts of high activity and selectivity with purposely modulated coordination and an alkaline environment are urgently required. Herein, it is demonstrated that atomically dispersed Ni with triple nitrogen coordination (Ni‐N3) can achieve efficient hydrogen evolution reaction (HER) performance in alkaline media. The atomically dispersed Ni electrocatalysts exhibit overpotentials as low as 102 and 139 mV at 10 mA cm–2 in alkaline freshwater and seawater electrolytes, respectively, which compare favorably with those previously reported. They also deliver large current densities beyond 200 mA cm–2 at lower overpotentials than Pt/C, as well as show negligible current attenuation over 14 h. The X‐ray absorption fine structure (XAFS) experimental analysis and density functional theory (DFT) calculations verify that the Ni‐N3 coordination, which exhibits a lower coordination number than Ni‐N4, facilitates water dissociation and hydrogen adsorption, and hence enhances the HER activity.

Realization of high-density and reliable resistive random access memories based on two-dimensional semiconductors is crucial toward their development in next-generation information storage and neuromorphic computing. Here, wafer-scale integration of solution-processed two-dimensional MoS2 memristor arrays are reported. The MoS2 memristors achieve excellent endurance, long memory retention, low device variations, and high analog on/off ratio with linear conductance update characteristics. The two-dimensional nanosheets appear to enable a unique way to modulate switching characteristics through the inter-flake sulfur vacancies diffusion, which can be controlled by the flake size distribution. Furthermore, the MNIST handwritten digits recognition shows that the MoS2 memristors can operate with a high accuracy of >98.02%, which demonstrates its feasibility for future analog memory applications. Finally, a monolithic three-dimensional memory cube has been demonstrated by stacking the two-dimensional MoS2 layers, paving the way for the implementation of two memristor into high-density neuromorphic computing system.

for piezoelectric devices was estimated to be worth $25.1 billion with a projected compounded annual growth rate (CAGR) of 6.2%. [6] However, the development of piezoelectrics took more than a century to evolve from quartz, which is among the first known piezoelectric materials, [7,8] to their current forms in the modern era. The evolution of piezoelectrics is, hence, rich with the exciting discoveries in fundamental physics, paving the way to the development of applications that changed the course of history. One such example is the invention of sonar by Paul Langevin and team in 1917 [9] which is still essentially implemented today for underwater acoustics and navigation. Later, the discovery of ferroelectricity in BaTiO 3 polycrystal in 1946 [10,11] and phase transition (now referred to as a morphotropic phase boundary (MPB)) in PbZrO 3 -PbTiO 3 solid solution in 1954 [12] stimulated a worldwide interest in gaining fundamental understanding of electromechanical coupling in ferroelectric materials to develop better and more reliable piezoelectric devices. [13][14][15] By contrast, the research on piezoelectrics in the past two decades has been driven mainly by the environmental and health concerns related to the toxicity of lead, which is a primary constituent of the widely used lead-based piezoelectric ceramics, [16,17] where the best known example is lead zirconium titanates (PZT). Consequently, the stringent regulations all over the world to restrict the use of lead [18] have resulted in the rise of "lead-free" ceramics which further gained popularity after Saito et al.'s discovery of large piezoelectric response in a lead-free piezoceramic. [19] These eco-friendly materials represent now although a relatively small part of the current piezoelectrics market, with a total estimate of around $172 million, but, their sales are projected to reach $443 million by 2024 with a CAGR of 20.8%. [6] ABO 3 -type perovskite oxide ferroelectrics hold great technical value owing to their large spontaneous polarization, which makes them highly suitable for piezoelectric applications. [1,3,20] In recent years, the research efforts have been primarily focused on developing new strategies to produce high-performance lead-free oxide piezoelectrics with properties at least comparable to or surpassing those of the lead-based counterparts, such as PZT. [20] These strategies have mainly Piezoelectric materials are known to mankind for more than a century, with numerous advancements made in both scientific understandings and practical applications. In the last two decades, in particular, the research on piezoelectrics has largely been driven by the constantly changing technological demand, and the drive toward a sustainable society. Hence, environmental-friendly "lead-free piezoelectrics" have emerged in the anticipation of replacing lead-based counterparts with at least comparable performance. However, there are still obstacles to be overcome for realizing this objective, while the efforts in this direction already seem to culminat...

Electrolyte-accessibly porous yet densely packed MXene composite electrodes with high ion-accessible surface and rapid ion transport rate have shown exceptional promise for high-volumetric-performance supercapacitors (SCs), but they are largely limited by the insufficient rate capability and poor electrochemical cyclability, in association with the instability in mechanical robustness of the porous network structures. Taking advantage of chemical bonding design, herein a black phosphorus (BP)@MXene compact film of 3D porous network structure is successfully made by in situ growth of BP nanoparticles on crumbled MXene flakes. The strong interfacial interaction (Ti−O−P bonds) formed at the BP− MXene interfaces not only enhances the atomic charge polarization in the BP−MXene heterostructures, leading to efficient interfacial electron transport, but also stabilizes the 3D porous yet dense architecture with much improved mechanical robustness. Consequently, fully packaged SCs using the BP@MXene composite films with a practical-level of mass loading (∼15 mg cm −2 ) deliver a high stack volumetric energy density of 72.6 Wh L −1 , approaching those of lead-acid batteries (50−90 Wh L −1 ), together with a long-term stability (90.58% capacitance retention after 50000 cycles). The achievement of such high energy density bridges the gap between traditional batteries and SCs and represents a timely breakthrough in designing compact electrodes toward commercial-level capacitive energy storage.

Traditional strategies for improving piezoelectric properties have focused on phase boundary engineering through complex chemical alloying and phase control. Although they have been successfully employed in bulk materials, they have not been effective in thin films due to the severe deterioration in epitaxy, which is critical to film properties. Contending with the opposing effects of alloying and epitaxy in thin films has been a long-standing issue. Herein we demonstrate a new strategy in alkali niobate epitaxial films, utilizing alkali vacancies without alloying to form nanopillars enclosed with out-of-phase boundaries that can give rise to a giant electromechanical response. Both atomically resolved polarization mapping and phase field simulations show that the boundaries are strained and charged, manifesting as head-head and tail-tail polarization bound charges. Such charged boundaries produce a giant local depolarization field, which facilitates a steady polarization rotation between the matrix and nanopillars. The local elastic strain and charge manipulation at out-of-phase boundaries, demonstrated here, can be used as an effective pathway to obtain large electromechanical response with good temperature stability in similar perovskite oxides.

al. (2019) Electromagnetic backgrounds and potassium-42 activity in the DEAP-3600 dark matter detector. Physical Review D, 100 (7). pp. 1-17.

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