Potassium hydroxide treatment of layered WSe2 with enhanced electronic performances.

2D WSe2-based electronic devices have received much research interest. However, it is still a challenge to achieve high electronic performance in WSe2-based devices. In this work, we report greatly enhanced performances of different thickness WSe2 ambipolar transistors and demonstrate homogeneous WSe2 inverter devices, which are obtained by using a semiconductor processing-compatible layer removal technique via chemical removal of the surface top WOx layer formed by O2 plasma treatment. Importantly, monolayer WSe2 was realised after several consecutive removal processes, demonstrating that the single layer removal is accurate and reliable. After subsequent removal of the top layer WOx by KOH, the fabricated WSe2 field-effect transistors exhibit greatly enhanced electronic performance along with the high electron and hole mobilities of 40 and 85 cm2 V-1 s-1, respectively. Our work demonstrates that the layer removal technique is an efficient route to fabricate high performance 2D material-based electronic devices.

Liquid-phase catalyst pre-seeding for controlled growth of layered MoS2 films over a large area via chemical vapor deposition.

We introduce an innovative method that facilitates precise control of high-quality molybdenum disulfide (MoS2) growth, extending up to three layers, on a large scale. This scalable growth is realized by employing solution-based catalysts and precursors in conjunction with chemical vapor deposition (CVD). The catalyst not only diminishes the precursor's activation energy and melting temperature but also augments the overall reaction rate. By regulating the concentration ratio, we directly manipulate the precursor concentrations, thereby promoting clean growth. This unique control mechanism, as delineated in this study, is unprecedented. Our findings confirm that the catalyst introduction does not compromise the quality of the resulting samples. Field effect transistors (FETs) fabricated from the synthesized MoS2 display superior electrical properties; they exhibit a high carrier mobility of 32.1 cm2 V-1 s-1 and an on/off current ratio of 108, signifying their promising electrical performance. Accordingly, our findings suggest that the solution-based CVD strategy presented herein can be potentially utilized for the integration of FETs into a multitude of practical applications.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites.

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

Transferring 2D TMDs through water-soluble sodium salt catalytic layer.

This study reports a clean and damage-free transfer method that enables the ultrafast transfer of two-dimensional (2D) transition metal dichalcogenides (TMDs) onto desired substrates with a remarkably high yield. We employ a water-soluble sodium salt as both a transfer sacrificial layer for facile transfer and a catalytic layer for the growth of high-quality large-area MoS2using liquid-phase chemical vapor deposition via a catalyzed kinetic growth. We show that the pristine structural and electrical properties of the grown MoS2can be reliably preserved by avoiding detrimental effects during the prolonged harsh-environment transfer process. We demonstrate the technological versatility of the proposed transfer method by fabricating as-transferred MoS2-based back-gated field-effect transistors (FETs). The MoS2FETs exhibit excellent charge mobility as high as 28.7 cm2V-1s-1and an on-off ratio up to ∼107at room temperature, indicating no performance degradation after the transfer process. The proposed transfer method offers universal applicability for various 2D TMDs, mechanical supporting polymers, and target substrates, thus facilitating the facile fabrication of 2D TMD-based electronics and optoelectronics.

High-Performance Flexible Energy Storage Devices Based on Graphene Decorated with Flower-Shaped MoS2 Heterostructures.

MoS2, owing to its advantages of having a sheet-like structure, high electrical conductivity, and benign environmental nature, has emerged as a candidate of choice for electrodes of next-generation supercapacitors. Its widespread use is offset, however, by its low energy density and poor durability. In this study, to overcome these limitations, flower-shaped MoS2/graphene heterostructures have been deployed as electrode materials on flexible substrates. Three-electrode measurements yielded an exceptional capacitance of 853 F g-1 at 1.0 A g-1, while device measurements on an asymmetric supercapacitor yielded 208 F g-1 at 0.5 A g-1 and long-term cyclic durability. Nearly 86.5% of the electrochemical capacitance was retained after 10,000 cycles at 0.5 A g-1. Moreover, a remarkable energy density of 65 Wh kg-1 at a power density of 0.33 kW kg-1 was obtained. Our MoS2/Gr heterostructure composites have great potential for the development of advanced energy storage devices.

Interfacial Microenvironment Modulation Enhancing Catalytic Kinetics of Binary Metal Sulfides Heterostructures for Advanced Water Splitting Electrocatalysts.

Interfacial microenvironment modulation has been proven to be a promising route to fabricate highly efficient catalysts. In this work, the lattice defect-rich NiS2 /MoS2 nanoflakes (NMS NFs) electrocatalysts are successfully synthesized by a simple strategy. Benefiting from the abundant lattice defects and modulated interfacial microenvironment between NiS2 and MoS2 , the prepared NMS NFs show superior catalytic activity for water splitting. Particularly, the optimized NMS NFs (the molar ratio of Ni:Mo = 5:5) exhibit remarkable catalytic activity toward overall water splitting with a voltage of 1.60 V at 10 mA cm-2 in alkaline media, which is lower than that of the noble-metal-based electrocatalysts (1.68 V at 10 mA cm-2 ). The NMS NFs electrocatalysts also show exceptional long-term stability (>50 h) for overall water splitting. The density functional theory results demonstrate that the injection of NiS2 into MoS2 can greatly optimize the catalytic kinetics and reduce the energy barrier for hydrogen/oxygen evolution reactions. The work does not only offer a promising candidate for a highly efficient water splitting electrocatalyst but also highlights that interfacial microenvironment modulation is a potential strategy to optimize the catalytic kinetics.

Flexible Supercapacitor-Type Rectifier-free Self-Charging Power Unit Based on a Multifunctional Polyvinylidene Fluoride-ZnO-rGO Piezoelectric Matrix.

The development of an effective mechanical to electrical energy conversion device and its functional integration with an energy storage device for self-powered portable gadgets are cutting-edge research fields. However, the generated power and the mechanical stability of these integrated devices are still not efficient to power up portable electronics. We fabricated a rectifier-free piezoelectric nanogenerator (NG) integrated with a supercapacitor (SC). A multifunctional composite matrix was prepared by the incorporation of ultrathin (<10 nm) ZnO nanoflakes and reduced graphene oxide in polyvinylidene fluoride to enhance the piezoelectric output characteristics and mechanical stability of the device while minimizing the additional energy losses during the integration. The as-fabricated SC-based power unit through the energy conversion and storage processes showed a remarkable self-charging performance. We obtained the maximum output voltage, current density, and power density of about 44 V, 1000 nA cm-2, and 193.6 µW cm-2 under the applied mechanical force of 10 N, respectively. The self-charging behavior of the device showed that it can store 1.5 × 10-3 mC within 100 s without resorting to a rectifier. We obtained the total energy density of about 10.34 mW h kg-1 under palm impact. Our results present a step forward in the development of the NG and SC-based flexible and self-charging devices.

Synthesis and Enhanced Photocatalytic Activity of Porous SrTiO3/TiO2 Composites.

Porous photocatalysts have attracted significant attention for their large specific surface area, numerous surface catalytic active sites, and high photocatalytic activity. In this study, porous SrTiO3/TiO2 composites were successfully fabricated through a hydrothermal approach utilizing porous TiO2 as a substrate. The as-synthesized SrTiO3/TiO2 composites were then characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, Brunauer-Emmett-Teller (BET), and ultraviolet-visible spectroscopy (UV-Vis) analysis. The results of SEM and BET indicate that such composites have a porous structure and large surface area. Compared to unadulterated TiO2, SrTiO3 /TiO2 composites exhibit higher photocatalytic performance for the photodegradation of rhodamine B under UV-Vis irradiation. Additionally, it was found that when the content of SrTiO3 reaches 20%, it achieves the maximum photodegradation efficiency of 98.6% under UV-Vis irradiation over 60 min. These results demonstrate that SrTiO3/TiO2 composites are a promising material in terms of environmental cleanliness.

Ultrahigh Output Piezoelectric and Triboelectric Hybrid Nanogenerators Based on ZnO Nanoflakes/Polydimethylsiloxane Composite Films.

We demonstrated a hybrid nanogenerator (NG) exploiting both piezoelectric and triboelectric effects induced from ZnO nanoflakes (NFs)/polydimethylsiloxane (PDMS) composite films through a facile, cost-effective fabrication method. This hybrid NG exhibited not only high piezoelectric output current owing to the enhanced surface piezoelectricity of the ZnO NFs but also high triboelectric output voltage owing to the pronounced triboelectrification of Au-PDMS contact, producing a peak-to-peak output voltage of ∼470 V, a current density of ∼60 µA·cm-2, and an average power density of ∼28.2 mW·cm-2. Without additional energy storage devices, the hybrid NGs with an area of 3 × 3 cm2 instantaneously lit up 180 commercial green light-emitting diodes through periodic hand compression. This approach may provide an innovative design for constructing high-performance and portable energy harvesting devices with enhanced power output, scavenging ambient mechanical energy from human motions in our daily life.

Poly(dimethylsiloxane)/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High-Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation.

Herein, we report the successful synthesis of poly(dimethylsiloxane)/ZnO nanoflakes/three-dimensional graphene (PDMS/ZnO NFs/3D Gr) heterostructures using Ni foams as the template substrate via a facile route, while adapting a rational material design for a high-performance energy-harvester application. The PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester simultaneously exploits the piezoelectric effect and triboelectrification and shows peak-to-peak output voltages up to 122 V and peak-to-peak current densities up to 51 µA cm-2, resulting in an ultrahigh power density of 6.22 mW cm-2. Furthermore, we have evaluated the performance of the PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester by demonstrating its capacity to instantaneously power up 68 commercially available light-emitting diodes without the need for an additional energy-storage device. The excellent performance of these energy harvesters suggests that PDMS/ZnO NFs/3D Gr heterostructures present a viable strategy for the development of high-performance, flexible, wearable energy-harvesting devices.

Large-Area High-Quality AB-Stacked Bilayer Graphene on h-BN/Pt Foil by Chemical Vapor Deposition.

Large-area, high-quality bilayer graphene (BLG) has attracted great interest because of its immense potential for many viable applications. However, its growth is still greatly limited owing to its small size and low carrier mobility. In this article, we report the successful growth of large-area, high-quality AB-stacked BLG on hexagonal boron nitride (h-BN)/Pt foil by chemical vapor deposition (CVD). Optical microscopy and scanning electron microscopy observations reveal the formation of uniform and continuous BLG films with sizes of up to 500 µm, which are 4-5 times larger than those reported elsewhere for CVD-grown BLG films. A large carrier mobility of up to 9000 cm2 V-1 s-1 is observed for the BLG films grown on h-BN/Pt foils under ambient conditions. We also propose a plausible growth mechanism of BLG growth on h-BN/Pt foils. Our findings will contribute for the better understanding of the fundamental BLG physics and the development of BLG-based devices.

Growth of Graphene/h-BN Heterostructures on Recyclable Pt Foils by One-Batch Chemical Vapor Deposition.

High-quality large-area graphene/h-BN vertical heterostructures are promising building blocks for many viable applications such as energy harvesting/conversion, electronics and optoelectronics. Here, we successfully grew high-quality large-area graphene/h-BN vertical heterostructures on Pt foils by one-batch low-pressure chemical vapor deposition (LPCVD). We obtained the high quality of about 200-µm-wide graphene/h-BN film having uniform layer thickness. Moreover, the obtained graphene/h-BN heterostructures exhibited field effect mobility of up to 7,200 cm2V-1s-1 at room temperature. These results suggest that such graphene/h-BN heterostructures on recyclable Pt foils grown by LPCVD are promising for high-performance graphene-based electronics.

PMMA-Etching-Free Transfer of Wafer-scale Chemical Vapor Deposition Two-dimensional Atomic Crystal by a Water Soluble Polyvinyl Alcohol Polymer Method.

We have explored a facile technique to transfer large area 2-Dimensional (2D) materials grown by chemical vapor deposition method onto various substrates by adding a water-soluble Polyvinyl Alcohol (PVA) layer between the polymethyl-methacrylate (PMMA) and the 2D material film. This technique not only allows the effective transfer to an arbitrary target substrate with a high degree of freedom, but also avoids PMMA etching thereby maintaining the high quality of the transferred 2D materials with minimum contamination. We applied this method to transfer various 2D materials grown on different rigid substrates of general interest, such as graphene on copper foil, h-BN on platinum and MoS2 on SiO2/Si. This facile transfer technique has great potential for future research towards the application of 2D materials in high performance optical, mechanical and electronic devices.