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In this work, we, for the first time, observed the remarkable thermoelectric properties of a few high-quality PtSe2 layered films fabricated by a post selenization of Pt thin films. An excellent po...

Real-time, daily health monitoring can provide large amounts of patient data, which may greatly improve the likelihood of diagnosing health conditions at an early stage. One potential sensor is a flexible humidity sensor to monitor moisture and humidity information such as dehydration. However, achieving a durable functional nanomaterial-based flexible humidity sensor remains a challenge due to partial desorption of water molecules during the recovery process, especially at high humidities. In this work, we demonstrate a highly stable resistive-type Pd/HNb3O8 humidity sensor, which exhibits a perdurable performance for over 100 h of cycle tests under a 90% relative humidity (RH) without significant performance degradation. One notable advantage of the Pd/HNb3O8 humidity sensor is its ability to regulate hydroniums due to the strong reducibility of H atoms dissociated on the Pd surface. This feature realizes a high stability even at a high humidity (99.9% RH). Using this superior performance, the Pd/HNb3O8 humidity sensor realizes wireless monitoring of the changes in the fingertip humidity of an adult under different physiological states, demonstrating a facile and reliable path for dehydration diagnosis.

Transition metal dichalcogenides (TMDCs) have recently attracted a tremendous amount of attention owing to their superior optical and electrical properties as well as the interesting and various na...

In this work, we demonstrated nano-scaled Laue diffractions by a focused polychromatic synchrotron radiation beam to discover what happens in MoS2 when van der Waals epitaxy is locally invalid. A stronger exciton recombination with a local charge depletion in the density of 1 × 1013 cm-2, extrapolated by Raman scattering and photoluminescence, occurs in grains, which exhibits a preferred orientation of 30° rotation with respect to the c-plane of a sapphire substrate. Else, the charge doping and trion recombination dominate instead. In addition to the breakthrough in extrapolating mesoscopic crystallographic characteristics, this work opens the feasibility to manipulate charge density by the selection of the substrate-induced disturbances without external treatment and doping. Practically, the 30° rotated orientation in bilayer MoS2 films is promoted on inclined facets in the patterned sapphire substrate, which exhibits a periodic array of charge depletion of about 1.65 × 1013 cm-2. The built-in manipulation of carrier concentrations could be a potential candidate to lateral and large-area electronics based on 2D materials.

Aluminum-sulfur batteries (ASBs) have attracted substantial interest due to their high theoretical specific energy density, low cost, and environmental friendliness, while the traditional sulfur cathode and ionic liquid have very fast capacity decay, limiting cycling performance because of the sluggishly electrochemical reaction and side reactions with the electrolyte. Herein, we demonstrate, for the first time, excellent rechargeable aluminum-selenium batteries (ASeBs) using a new deep eutectic solvent, thiourea-AlCl3, as an electrolyte and Se nanowires grown directly on a flexible carbon cloth substrate (Se NWs@CC) by a low-temperature selenization process as a cathode. Selenium (Se) is a chemical analogue of sulfur with higher electronic conductivity and lower ionization potential that can improve the battery kinetics on the sluggishly electrochemical reaction and the reduction of the polarization where the thiourea-AlCl3 electrolyte can stabilize the side reaction during the reversible conversion reaction of Al-Se alloying processes during the charge-discharge process, yielding a high specific capacity of 260 mAh g-1 at 50 mA g-1 and a long cycling life of 100 times with a high Coulombic efficiency of nearly 93% at 100 mA g-1. The working mechanism based on the reversible conversion reaction of the Al-Se alloying processes, confirmed by the ex situ Raman, XRD, and XPS measurements, was proposed. This work provides new insights into the development of rechargeable aluminum-chalcogenide (S, Se, and Te) batteries.

Recently, extracting hot electrons from plasmonic nanostructures and utilizing them to enhance the optical quantum yield of two-dimensional transition-metal dichalcogenides (TMDs) have been topics ...

Unlike common TMDCs such as MoS2, PtSe2 can be fabricated at temperatures below 600 °C, or even as low as 300 °C, while still maintaining high quality. By varying the selenization temperature from 300 °C to 600 °C, the electrical properties were changed significantly, resulting in superior gas sensing performance. Through comprehensive material analysis, an interesting phenomenon was found, namely that strain along the [001] direction existed in films grown at a low temperature rather than at a high temperature. Moreover, due to the layer-dependent property of PtSe2, a phase transition from metal-to-semiconductor occurs as the thickness is reduced. Hybridization of phase engineering and thermal strain engineering significantly enhances the gas sensing performance, resulting in PtSe2 with a dramatic increase in the response to 1 ppm NO2 from 25% to 550% once the thickness was reduced from 10 to 5 layers. In addition, PtSe2 showed good stability during exposure to not only 1 ppm but also 50 ppb NO2 for more than 5 cycles with responses of over 550% and 60%, respectively.

The multilayer 1T-TaSe2 is successfully synthesized by annealing a Se-implanted Ta thin film on the SiO2/Si substrate. Material analyses confirm the 1T (octahedral) structure and the quasi-2D nature of the prepared TaSe2. Temperature-dependent resistivity reveals that the multilayer 1T-TaSe2 obtained by our method undergoes a commensurate charge-density wave (CCDW) transition at around 500 K. This synthesis process has been applied to synthesize MoSe2 and HfSe2 and expanded for synthesis of one more transition-metal dichalcogenide (TMD) material. In addition, the main issue of the process, that is, the excess metal capping on the TMD layers, is solved by the reduction of thickness of the as-deposited metal thin film in this work.

Non-layered e-Ti2N with a work function of ∼4.75 eV, synthesized by a rapid process assisted by N2 plasma immersion, is successfully applied as the anode material of lithium-ion batteries with good performance; it exhibits discharge capacity of ∼450 mA h g−1, which is close to the theoretical value, coulombic efficiencies of >85%, and capacity retentions (≥80%).

The rechargeable aluminum-ion battery (AIB) is a promising candidate for next-generation high-performance batteries, but its cathode materials require more development to improve their capacity and cycling life. We have demonstrated the growth of MoSe

A suitable electrocatalyst plays an essential role in room-temperature Na–S (RT/Na–S) batteries owing to the more severe dissolution of polysulfides and sluggish kinetics of the conversion of polysulfides during charging and discharging processes. In this study, a novel MoS2/MoN heterostructure synthesized via NH3 annealing was introduced as an electrocatalyst into RT/Na–S batteries to promote the evolution of polysulfides in the catholyte with an initial specific capacity of 703 mA h g–1 and retains 392 mA h g–1 after 300 cycles. The density-functional theory (DFT) calculations, ex-situ XPS and Raman spectra were utilized to reveal moderate anchoring and the fast redox kinetics of polysulfides, significantly enhancing the cycling performance and electrochemical performance of the RT-Na/S batteries when compared with those of the RT-Na/S batteries containing pure MoS2 or MoN as the catalyst. The work provides a new strategy for guiding the design of high‐performance catalysts with manipulated chemical components and optimized adsorption ability.

In this work, three-dimensional (3D) CoMoSe4 nanosheet arrays on network fibers of a carbon cloth denoted as CoMoSe4@C converted directly from CoMoO4 nanosheet arrays prepared by a hydrothermal process followed by the plasma-assisted selenization at a low temperature of 450 °C as an anode for sodium-ion battery (SIB) were demonstrated for the first time. With the plasma-assisted treatment on the selenization process, oxygen (O) atoms can be replaced by selenium (Se) atoms without the degradation on morphology at a low selenization temperature of 450 °C. Owing to the high specific surface area from the well-defined 3D structure, high electron conductivity, and bi-metal electrochemical activity, the superior performance with a large sodium-ion storage of 475 mA h g−1 under 0.5–3 V potential range at 0.1 A g−1 was accomplished by using this CoMoSe4@C as the electrode. Additionally, the capacity retention was well maintained over 80 % from the second cycle, exhibiting a satisfied capacity of 301 mA h g−1 even after 50 cycles. The work delivered a new approach to prepare a binary transition metallic selenide and definitely enriches the possibilities for promising anode materials in SIBs with high performances. Electronic supplementary material The online version of this article (10.1186/s11671-019-3035-6) contains supplementary material, which is available to authorized users.

Transition metal dichalcogenides (TMDCs) have not only recently attracted tremendous attention due to their unique optical and electrical properties but also the interesting and various nanostructures created by different synthesis process. These atomically thin TMDCs materials possess great potential in sensing, optoelectronic, energy harvesting and Li-ion battery applications. However, the atomic thickness of TMDCs will limit the light absorption and result in weak performance of optoelectronic devices, such as photodetectors. Here, we demonstrate a novel approach to increase the surface area of TMDCs in the one-step synthesis process of TMDC nanowalls from WOx into WS2 nanowalls. By utilizing the rapid heating and rapid cooling process, we can achieve the formation of nanowalls with the height of ~150 nm standing perpendicularly on top of the substrate. Our method provides a rapid synthesis process with enhanced aspect ratio compared to the conventional solid-vapor phase CVD process, which is commonly used for the synthesis of planar TMDCs with few atomic layers. Moreover, the combination of colloidal quantum dots (QDs) with three different emission wavelength and WS2 nanowalls will further improve the performance of WS2-based photodetector devices, including 3.5~4 times photocurrent enhancement and shorter response time. The remarkable results of the QD-WS2 hybrid devices to the high NRET efficiency between QDs and our nanostructured material are caused by the spectral overlap between the emission of QDs and the absorption of WS2. Additionally, the outstanding NO2 gas-sensing properties of QDs/WS2 devices were demonstrated with a remarkably low detection limit down to 50 ppb with a fast response time of 26.8 s contributed by tremendous local p-n junctions generated from p-type WS2 nanowalls and n-type CdSe-ZnS QDs. Our work successfully reveals the energy transfer phenomenon in QD-WS2 hybrid devices and shows great potential in commercial multifunctional sensing applications.

Recently, two-dimensional materials are considered as potential materials for future electronic devices. Moreover, fabrication of two-dimensional heterojunction attract lots of attention. Here, we use a laser with metal-assisted oxidation method to construct WSe2/WO3 heterostructure. In the experiment, a plasma-assisted chemical vapor reduction (PACVR) process was applied to synthesis large area WSe2 layer. A layer of nickel metal was deposited as a first layer which will absorb the heat of laser and oxidize the top WSe2 layer, then a additional oxide layer was deposited between nickel layer and WSe2 layer to prevent the nickel metal layer from getting selenized when we used PACVR process to selenize the amorphous WO3 precursor. In the laser oxidation process, we choose 808 nm wavelength continuous wave laser as the laser source which will not absorb by WSe2 layer cause the laser energy is lower than bandgap of WSe2. Therefore, the nickel metal layer will absorb most of the laser energy then heat the top WSe2 layer under atmosphere. The top area of WSe2 heated by the metal layer will get oxidized into WO3 hence formed a heterojunction with the outer area which was not expose by laser. We also used photolithography to get different pattern of nickel layer which could control and limit the oxidized area by the metal layer but not by the laser exposure area. After the laser oxidation process, this WSe2/WO3 structure was further fabricated into photodetector showed its great possibility in future electronic applications.

Recent advances in the use of organic–inorganic hybrid perovskites have been investigated in a variety of applications, such as solar cells, photodetector, light emitting devices (LEDs), and lasers because of their outstanding semiconductor properties. Furthermore, the perovskite structure has the ability to host extrinsic elements, making it a promising candidate for battery field. Previous studies have shown that organic–inorganic hybrid perovskites can be a suitable anode material for both lithium- and sodium-ion batteries. However, the multivalent rechargeable batteries with perovskite material have not yet been realized. Herein, we studied the electrochemical performance of three-dimensional (3D) CH3NH3PbI3 and quasi-two dimensional (C4H9NH3)2(CH3NH3)3Pb4I13 thin films as electrode materials for rechargeable Al-ion batteries. In this work, these electrodes were successfully synthesis on carbon cloth through a feasible solution process. The (C4H9NH3)2(CH3NH3)3Pb4I13 electrode yield a specific capacity of 210 mAh g–1 at the current density of 50mA g−1 . It still delivered 81 mAh g–1 after 250 cycles at the current density of 200mA g−1 with a retention of as high as 95%, indicating a long cycling stability. Compared with the CH3NH3PbI3, the (C4H9NH3)2(CH3NH3)3Pb4I13 presented higher initial capacities, better reversibility, and more excellent high-rate capabilities, all demonstrating the vitally prominent role of isobutyl amine (C4H9NH3). which can be attributed to the unique hydrogen-bonding interaction of isobutyl amine could effectively hinder the shuttle effect of polyiodide. We anticipate that these results open a new direction for the use of organic–inorganic hybrid perovskites for new secondary aluminum ion batteries.

A facile approach for the synthesis of Au- and Pt-decorated CuInS2 nanocrystals (CIS NCs) as sensitizer materials on the top of MoS2 bilayers is demonstrated. A single surfactant (oleylamine) is used to prepare such heterostructured noble metal decorated CIS NCs from the pristine CIS. Such a feasible way to synthesize heterostructured noble metal decorated CIS NCs from the single surfactant can stimulate the development of the functionalized heterostructured NCs in large scale for practical applications such as solar cells and photodetectors. Photodetectors based on MoS2 bilayers with the synthesized nanocrystals display enhanced photocurrent, almost 20-40 times higher responsivity and the On/Off ratio is enlarged one order of magnitude compared with the pristine MoS2 bilayers-based photodetectors. Remarkably, by using Pt- or Au-decorated CIS NCs, the photocurrent enhancement of MoS2 photodetectors can be tuned between blue (405 nm) to green (532 nm). The strategy described here acts as a perspective to significantly improve the performance of MoS2 -based photodetectors with the controllable absorption wavelengths in the visible light range, showing the feasibility of the possible color detection.