transition metal dichalcogenides (TMDCs) have been extensively studied. Among them, vanadium dichalcogenides, a unique metallic family of the TMDCs, have been considered as potential room temperature ferromagnetic materials at the monolayer scale. However, further progress has been hampered by the difficulties growing monolayer and the challenges making high-quality single crystalline VSe 2 , free from artificial factors. Here, we report high-quality octahedral 1T-VSe 2 single crystals grown by chemical vapor transport. Spectroscopic analyses identified that as-grown VSe 2 crystals were a single phase of VSe 2 and highly oriented along the (00l) plane. High-resolution scanning transmission electron microscopy verified that as-grown VSe 2 crystals not only had single crystalline nature, the octahedral 1T phase, and AAA stacking order in atomistic real space, but also supported valuable lattice information that differed from the predicted values of the previous calculation model. Mechanical exfoliation allowed our VSe 2 crystals to turn into largesized VSe 2 flakes with various thicknesses. With in-depth structural analyses, our findings provide insight into further research of the fundamental calculation model and the crystallographic tailoring for intrinsic room-temperature 2D ferromagnetic materials.

Summary Tremendous efforts have been made to create significant energy storage devices using nanoscale design and hybrid techniques. Toward this end, herein, we have fabricated, a binder‐free, amorphous iron‐doped nickel‐cobalt phosphate (FexNiCo(PO4)2, ie, F‐NCP) thin film on stainless steel substrate using a facile successive ionic layer adsorption and reaction (SILAR) method. Furthermore, the influence of Fe doping concentration on physico‐chemical properties is investigated. The various F‐NCP‐series electrodes contain nanoparticle‐like morphology that is beneficial for charge transfer and efficient diffusion of electrolytes in supercapacitors. Such nanoparticle‐like morphology and the synergy among iron, cobalt, and nickel elements in the F‐NCP‐3 electrode deliver a maximum specific capacity of 987 C g−1 at a current density of 2.1 A g−1 with excellent cyclic retention of 95.3% after 5000 galvanostatic charge‐discharge cycles. Especially, when an asymmetric solid‐state supercapacitor (ASSS) is fabricated in polyvinyl alcohol‐KOH gel electrolyte with reduced graphene oxide (rGO) as a negative electrode, the designed F‐NCP‐3//rGO ASSS device shows the wide (1.6 V) potential window, and a maximum specific capacitance of 116 F g−1 at 1.5 A g−1. In addition, the ASSS device gives a higher energy density of 41.26 Wh kg−1 at 1.22 kW kg−1 power density and exhibits superior cyclic stability (93% after 5000 cycles). The suggested asymmetric configuration makes a promising alternative of the cathode material to construct energy storage devices for various portable electronic systems.

Resistive strain sensors (RSS) with ultrasensitivity have attracted much attention as multifunctional sensors. However, since most ultrasensitive RSS are designed by cracked conductive metals, the sensing performance is severely degraded due to accumulated structural deformation with consecutive cycles. To overcome such limitation, newly designed structures have been suggested, but the development of mechanosensors exhibiting superior stability and ultrasensitivity still remains a challenge. Here, we demonstrate that vertical graphene (VG) RSS with high sensitivity (gauge factor greater than 5000), remarkable durability (>10,000 cycles), and extraordinary resilience can serve multifunctional applications. We find that well-defined cracks on tufted network structure result in highly reversible resistance variation, especially revivable status even after broken current path, confirmed by microscopic in situ monitoring. The VG integrated with a wireless sensing system exhibits excellent timbre recognition performance. Our findings provide inspirable insights for mechanosensing system, making VG a promising component for future practicable flexible sensor technologies.

The limited energy density and cyclability of supercapacitors are major roadblocks to their development as energy storage devices. To address these issues, a binder-free nickel−manganese (Ni−Mn) phosphate composite (NMP series) microarchitecture has been synthesized by the hydrothermal method on a nickel foam (NF) substrate using various urea dosages. Due to the influence of urea, microrod-/microplate-like morphologies of NMP series thin films evolved to micropetals. This study demonstrates a synergy between Ni and Mn metal ions and also the influence of different urea contents on the physicochemical properties of mesoporous NMP series thin films. Notably, the NMP-4 microarchitecture has a large surface area (7.5 m 2 g −1 ), which provides more electroactive sites in electrochemical measurements. Accordingly, in the NMP series electrodes, the NMP-4 thin film demonstrated high electrochemical properties (the maximum specific capacity was found to be 901 C/g at a 5 mV/s scan rate) and retained 127% capacity over 6000 cycles, indicating good durability with a well-preserved microstructure throughout the cycling. Furthermore, a flexible asymmetric solid-state (FASS) supercapacitor was designed utilizing NMP-4 and reduced graphene oxide (rGO) as a cathode and an anode, respectively, in the poly(vinyl alcohol)-KOH (PVA-KOH) gel electrolyte with an extended operational voltage of +1.8 V. This FASS device provides a high specific capacity (192 C/g at 0.6 A/g current density), supreme energy density (48.2 Wh kg −1 ) at a power density of 575 W kg −1 , and a desirable longevity of 108% over 5000 cycles. Moreover, the FASS device also demonstrated its practical applicability. The long-term stability suggests that the binder-free urea-assisted Ni−Mn phosphate composite is a good candidate for energy storage devices.

All-optical coherent control of interlayer vibrations in layered Bi2Se3 is demonstrated in a highly precise manner by employing ultrafast pump and probe spectroscopy with two delay-variable pump beams.