Chemical doping of MoS2 multilayer by p-toluene sulfonic acid

Abstract

We report the tailoring of the electrical properties of mechanically exfoliated multilayer (ML) molybdenum disulfide (MoS₂) by chemical doping. Electrical charge transport and Raman spectroscopy measurements revealed that the p-toluene sulfonic acid (PTSA) imposes n-doping in ML MoS₂. The shift of threshold voltage for ML MoS₂ transistor was analyzed as a function of reaction time. The threshold voltage shifted toward more negative gate voltages with increasing reaction time, which indicates an n-type doping effect. The shift of the Raman peak positions was also analyzed as a function of reaction time. PTSA treatment improved the field-effect mobility by a factor of ~4 without degrading the electrical characteristics of MoS₂ devices.     

Chemical doping of MoS2 multilayer by p-toluene sulfonic acid

We report the tailoring of the electrical properties of mechanically exfoliated multilayer (ML) molybdenum disulfide (MoS₂) by chemical doping. Electrical charge transport and Raman spectroscopy measurements revealed that the p-toluene sulfonic acid (PTSA) imposes n-doping in ML MoS₂. The shift of threshold voltage for ML MoS₂ transistor was analyzed as a function of reaction time. The threshold voltage shifted toward more negative gate voltages with increasing reaction time, which indicates an n-type doping effect. The shift of the Raman peak positions was also analyzed as a function of reaction time. PTSA treatment improved the field-effect mobility by a factor of ~4 without degrading the electrical characteristics of MoS₂ devices.     

Highly Flexible and Transparent Multilayer MoS2 Transistors with Graphene Electrodes

A highly flexible and transparent transistor is developed based on an exfoliated MoS₂ channel and CVD‐grown graphene source/drain electrodes. Introducing the 2D nanomaterials provides a high mechanical flexibility, optical transmittance (～74%), and current on/off ratio (>10⁴) with an average field effect mobility of ～4.7 cm² V^?1 s^?1, all of which cannot be achieved by other transistors consisting of a MoS₂ active channel/metal electrodes or graphene channel/graphene electrodes. In particular, a low Schottky barrier (～22 meV) forms at the MoS₂/graphene interface, which is comparable to the MoS₂/metal interface. The high stability in electronic performance of the devices upon bending up to ±2.2 mm in compressive and tensile modes, and the ability to recover electrical properties after degradation upon annealing, reveal the efficacy of using 2D materials for creating highly flexible and transparent devices.     

Structurally Deformed MoS2 for Electrochemically Stable,Thermally Resistant,and Highly Efficient Hydrogen Evolution Reaction

The emerging molybdenum disulfide (MoS₂) offers intriguing possibilities for realizing a transformative new catalyst for driving the hydrogen evolution reaction (HER). However, the trade‐off between catalytic activity and long‐term stability represents a formidable challenge and has not been extensively addressed. This study reports that metastable and temperature‐sensitive chemically exfoliated MoS₂ (ce‐MoS₂) can be made into electrochemically stable (5000 cycles), and thermally robust (300 °C) while maintaining synthetic scalability and excellent catalytic activity through physical‐transformation into 3D structurally deformed nanostructures. The dimensional transition enabled by a high throughput electrohydrodynamic process provides highly accessible, and electrochemically active surface area and facilitates efficient transport across various interfaces. Meanwhile, the hierarchically strained morphology is found to improve electronic coupling between active sites and current collecting substrates without the need for selective engineering the electronically heterogeneous interfaces. Specifically, the synergistic combination of high strain load stemmed from capillarity‐induced‐self‐crumpling and sulfur (S) vacancies intrinsic to chemical exfoliation enables simultaneous modulation of active site density and intrinsic HER activity regardless of continuous operation or elevated temperature. These results provide new insights into how catalytic activity, electrochemical‐, and thermal stability can be concurrently enhanced through the physical transformation that is reminiscent of nature, in which properties of biological materials emerge from evolved dimensional transitions.     

The Semiconductor/Conductor Interface Piezoresistive Effect in an Organic Transistor for Highly Sensitive Pressure Sensors

The piezoresistive pressure sensor, a kind of widely investigated artificial device to transfer force stimuli to electrical signals, generally consists of one or more kinds of conducting materials. Here, a highly sensitive pressure sensor based on the semiconductor/conductor interface piezoresistive effect is successfully demonstrated by using organic transistor geometry. Because of the efficient combination of the piezoresistive effect and field‐effect modulation in a single sensor, this pressure sensor shows excellent performance, such as high sensitivity (514 kPa^?1), low limit of detection, short response and recovery time, and robust stability. More importantly, the unique gate modulation effect in the transistor endows the sensor with an unparalleled ability—tunable sensitivity via bias conditions in a single sensor, which is of great significance for applications in complex pressure environments. The novel working principle and high performance represent significant progress in the field of pressure sensors.     

Silver Nanoflower Decorated Graphene Oxide Sponges for Highly Sensitive Variable Stiffness Stress Sensors

Soft conductive materials should enable large deformation while keeping high electrical conductivity and elasticity. The graphene oxide (GO)‐based sponge is a potential candidate to endow large deformation. However, it typically exhibits low conductivity and elasticity. Here, the highly conductive and elastic sponge composed of GO, flower‐shaped silver nanoparticles (AgNFs), and polyimide (GO‐AgNF‐PI sponge) are demonstrated. The average pore size and porosity are 114 µm and 94.7%, respectively. Ag NFs have thin petals (8–20 nm) protruding out of the surface of a spherical bud (300–350 nm) significantly enhancing the specific surface area (2.83 m² g^?1). The electrical conductivity (0.306 S m^?1 at 0% strain) of the GO‐AgNF‐PI sponge is increased by more than an order of magnitude with the addition of Ag NFs. A nearly perfect elasticity is obtained over a wide compressive strain range (0–90%). The strain‐dependent, nonlinear variation of Young's modulus of the sponge provides a unique opportunity as a variable stiffness stress sensor that operates over a wide stress range (0–10 kPa) with a high maximum sensitivity (0.572 kPa^?1). It allows grasping of a soft rose and a hard bottle, with the minimal object deformation, when attached on the finger of a robot gripper.     

无机杂质对改善纳米BaTiO_3湿敏特性的作用

用硬酯酸盐法合成了纳米ＢａＴｉＯ３材料，它对湿度有良好的敏感性能。在纳米ＢａＴｉＯ３中掺入少量杂质，会影响其感湿性能。本文研究了掺杂方法、掺杂种类及掺杂浓度对纳米ＢａＴｉＯ３湿敏元件的电阻和湿滞的影响。混合掺入Ｎａ２ＣＯ３和ＮａＨ２ＰＯ４可以使纳米ＢａＴｉＯ３湿敏元件的电阻为１０６～１０３Ω，湿滞＜３％。     

钛酸钡纳米材料的压力效应及其对湿敏性能的影响

采用硬酯酸法合成了ＢａＴｉＯ３纳米晶材料（１８￣８０ｎｍ）,在０￣１．５ＧＰａ的压力范围内考察了压力对材料性能尤其是对湿度敏感性能的影响,并用ＸＲＤ、ＩＲ等手段材料的压力效应进行了表征。     

A Hierarchically Porous Carbon Fabric for Highly Sensitive Electrochemical Sensors

The hierarchically porous carbon fabrics with controlled conductivity and hydrophilicity have been fabricated by dual templating method of soft templates nested on hard templates. A non‐woven fabric coated with a solution of F127/resol has been carbonized for the synthesis of both macro‐porous structures of 10–15 µm in diameter having meso‐porous carbon structures of 4–6 nm, respectively. After carbonization treatment, not only conductivity is significantly improved, the hierarchically porous carbon also shows superhydrophilicity or water‐absorbing nature due to mild hydrophilic material and its dual scale roughness. The porous carbon becomes conductive with resistivity widely tuned from 5.4 × 10³ Ωm to 3.1 × 10^?3 Ωm by controlling the carbonization temperature. As the increased wettability for organic liquids could lead organic molecules deep into carbonized fabrics, the sensitivity of hierarchically porous carbon fabrics benefits the detection for methanol(CH₃OH) or hydrogen peroxide (H₂O₂). This new design concept of hierarchically porous structures having the multi‐functionality of high wettability and conductivity can be highly effective for electroanalytical sensors.

     

Highly Sensitive and Stretchable Resistive Strain Sensors Based on Microstructured Metal Nanowire/Elastomer Composite Films

High sensitivity and high stretchability are two conflicting characteristics that are difficult to achieve simultaneously in elastic strain sensors. A highly sensitive and stretchable strain sensor comprising a microstructured metal nanowire (mNW)/elastomer composite film is presented. The surface structure is easily prepared by combining an mNW coating and soft‐lithographic replication processes in a simple and reproducible manner. The densely packed microprism‐array architecture of the composite film leads to a large morphological change in the mNW percolation network by efficiently concentrating the strain in the valley regions upon stretching. Meanwhile, the percolation network comprising mNWs with a high aspect ratio is stable enough to prevent electrical failure, even under high strains. This enables the sensor to simultaneously satisfy high sensitivity (gauge factor ≈81 at >130% strain) and high stretchability (150%) while ensuring long‐term reliability (10 000 cycles at 150% strain). The sensor can also detect strain induced by bending and pressure, thus demonstrating its potential as a versatile sensing tool. The sensor is successfully utilized to monitor a wide range of human motions in real time. Furthermore, the unique sensing mechanism is easily extended to detect more complex multiaxial strains by optimizing the surface morphology of the device.     

二硫化钼用作不对称型电化学电容器的负极材料

利用二硫化钼(MoS₂)在较低电势范围内可逆储锂的现象, 采用二硫化钼作为负极材料,和活性炭(AC)正极材料配伍, 组装成混合型电化学电容器, 在锂基有机系电解液中其电压可高达3.4 V。使用XRD和SEM等测试手段对负极材料的物性进行了表征,探讨了负极材料的储能机理, 并考察了正负极质量比对负极储锂容量的影响。电化学性能测试结果显示电容器具有较高能量密度和功率密度, 分别达到28.7 Wh/kg和1203.4 W/kg, 电容器也表现出较好的循环稳定性, 在0.4 A/g电流密度下, 经1000次循环后容量保持率高达76.6%。     

Surface Engineering of MoS2 via Laser‐Induced Exfoliation in Protic Solvents

With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS₂) is considered a promising nonprecious candidate to substitute Pt‐based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one‐step exfoliation of bulk 2H‐MoS₂ to ultrastable few‐layer MoS₂ nanosheets. Such prepared MoS₂ nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H‐to‐1T phase transition under laser irradiation. MoS₂ exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm^?2 and Tafel slope of 54 mV dec^?1.