Graphene, having a perfect two-dimensional crystal structure, has many excellent features such as a high specific surface area, and extraordinary electrical, thermal and mechanical properties. However, during the production process, lattice defects will inevitably be produced. Therefore, the performance of graphene with various defects is much lower than its theoretical value. We summarize the major advances of research into graphene defects in engineering in this paper. Firstly, the main types and causes of defects in graphene are introduced. Secondly, the influence of different defects in graphene on the chemical, electronic, magnetic and mechanical properties is discussed. Also, the control methods of graphene defects are reviewed. Finally, we propose the future challenges and prospects for the study of the defects of graphene and other nano-carbon materials.
Featured Application: gas sensors based on graphene and its derivatives have brilliant development prospects on innovating composite material and designing appropriate structure.Abstract: Gas sensors are devices that convert a gas volume fraction into electrical signals, and they are widely used in many fields such as environmental monitoring. Graphene is a new type of two-dimensional crystal material that has many excellent properties including large specific surface area, high conductivity, and high Young's modulus. These features make it ideally suitable for application for gas sensors. In this paper, the main characteristics of gas sensor are firstly introduced, followed by the preparation methods and properties of graphene. In addition, the development process and the state of graphene gas sensors are introduced emphatically in terms of structure and performance of the sensor. The emergence of new candidates including graphene, polymer and metal/metal oxide composite enhances the performance of gas detection significantly. Finally, the clear direction of graphene gas sensors for the future is provided according to the latest research results and trends. It provides direction and ideas for future research.2 of 21 excellent conductivity, and easy adsorption of gas molecules, and the surface can easily be modified by functional groups, so it has good gas sensing properties.Graphene, a monolayer of graphite sheet consisting of sp 2 hybridized carbon atoms covalently bonded to three other atoms which was first isolated by Geim and Novoselov using micro-mechanical peeling of graphite in 2004, so they won the 2010 Nobel Prize in Physics [8]. Graphene is the thinnest and highest strength material in nature at present and has the advantages of strong electric conductivity and heat conductivity, and is almost transparent and dense, thus attracts people's attention [9].Nowadays, there are many studies about graphene gas sensors focused on the performance improvement in the field of composite materials, computational chemistry and Micro-Electro-Mechanical System (MEMS). Considering the practical application of graphene gas sensor, we need to find the most potential direction. In this article, the development process and the state of art of graphene gas sensors are introduced. The direction of graphene gas sensors for the future is also provided. The review provides important reference for follow-up research work. Gas Sensor Key Parameters of Gas SensorGas sensors are the crucial components to detect the type and concentration of gas. The components can transform gas composition, gas concentration and other information from non-electricity to electricity to achieve the measurement of gas [10].The key parameters of gas sensor measuring performance include the following aspects [11]:
Topological insulator (TI), a promising quantum and semiconductor material, has gapless surface state and narrow bulk band gap. Firstly, the properties, classifications and compounds of TI are introduced. Secondly, the preparation and doping of TI are assessed. Some results are listed. (1) Although various preparation methods are used to improve the crystal quality of the TI, it cannot reach the industrialization. Fermi level regulation still faces challenges; (2) The carrier type and lattice of TI are affected by non-magnetic impurities. The most promising property is the superconductivity at low temperature; (3) Magnetic impurities can destroy the time-reversal symmetry of the TI surface, which opens the band gap on the TI surface resulting in some novel physical effects such as quantum anomalous Hall effect (QAHE). Thirdly, this paper summarizes various applications of TI including photodetector, magnetic device, field-effect transistor (FET), laser, and so on. Furthermore, many of their parameters are compared based on TI and some common materials. It is found that TI-based devices exhibit excellent performance, but some parameters such as signal to noise ratio (S/N) are still lower than other materials. Finally, its advantages, challenges and future prospects are discussed. Overall, this paper provides an opportunity to improve crystal quality, doping regulation and application of TI.
WTe2 as a candidate of transition metal dichalcogenides (TMDs) exhibits many excellent properties, such as non-saturable large magnetoresistance (MR). Firstly, the crystal structure and characteristics of WTe2 are introduced, followed by a summary of the synthesis methods. Its thermodynamic properties are highlighted due to the insufficient research. Finally, a comprehensive analysis and discussion are introduced to interpret the advantages, challenges, and future prospects. Some results are shown as follows. (1) The chiral anomaly, pressure-induced conductivity, and non-saturable large MR are all unique properties of WTe2 that attract wide attention, but it is also a promising thermoelectric material that holds anisotropic ultra-low thermal conductivity (0.46 W·m−1·K−1). WTe2 is expected to have the lowest thermal conductivity, owing to the heavy atom mass and low Debye temperature. (2) The synthesis methods influence the properties significantly. Although large-scale few-layer WTe2 in high quality can be obtained by many methods, the preparation has not yet been industrialized, which limits its applications. (3) The thermodynamic properties of WTe2 are influenced by temperature, scale, and lattice orientations. However, the in-plane anisotropy cannot be observed in the experiment, as the intrinsic property is suppressed by defects and boundary scattering. Overall, this work provides an opportunity to develop the applications of WTe2.
In this paper, electrical characteristic analysis and corresponding experimental tests on gold bonding wire are presented. Firstly, according to EIA (Electronic Industries Association)/JEDEC97 standards, this paper establishes the electromagnetic structure model of gold bonding wire. The parameters, including flat length ratio, diameter, span and bonding height, were analyzed. In addition, the influence of three kinds of loops of bonding wire is discussed in relation to the S parameters. An equivalent circuit model of bonding wire is proposed. The effect of bonding wire on signal transmission was analyzed by eye diagram as well. Secondly, gold bonding wire design and measurement experiments were implemented based on radio frequency (RF) circuit theory analysis and test methods. Meanwhile, the original measurement data was compared with the simulation model data and the error was analyzed. At last, the data of five frequency points were processed to eliminate the fixture error as much as possible based on port embedding theory. The measurement results using port extension method were compared with the original measurement data and electromagnetic field simulation data, which proved the correctness of the simulation results and design rules.
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