Recent Progress in Obtaining Semiconducting Single‐Walled Carbon Nanotubes for Transistor Applications

High purity semiconducting single‐walled carbon nanotubes (s‐SWCNTs) with a narrow diameter distribution are required for high‐performance transistors. Achieving this goal is extremely challenging because the as‐grown material contains mixtures of s‐SWCNTs and metallic‐ (m‐) SWCNTs with wide diameter distributions, typically inadequate for integrated circuits. Since 2000, numerous ex situ methods have been proposed to improve the purity of the s‐SWCNTs. The majority of these techniques fail to maintain the quality and integrity of the s‐SWCNTs with a few notable exceptions. Here, the progress in realizing high purity s‐SWCNTs in as‐grown and post‐processed materials is highlighted. A comparison of transistor parameters (such as on/off ratio and field‐effect mobility) obtained from test structures establishes the effectiveness of various methods and suggests opportunities for future improvements.     

微波绿色合成N,S共掺杂碳点及其在Fe3+检测和温度传感方面的应用

以韭菜为前驱体,采用微波法一步绿色合成N,S共掺杂的粒径均匀、分散性好的碳点。所合成的碳点近似球状,粒径2.0-5.0 nm。在365 nm的紫外灯照射下发明亮的蓝色荧光,发射峰具有激发波长依赖性。Fe³⁺对所制备的碳点有明显选择性荧光猝灭现象。在5-300μmol/L的范围内,荧光猝灭程度(F/F₀)与Fe³⁺浓度呈现良好的线性关系(R=0.9930),检测限为4.0μmol/L。同时探测温度对制备碳点的影响,在20-55℃范围内,碳点荧光强度与温度具有较好的线性响应。由于生理温度范围在此温度范围内,所制备的碳点可用于细胞温度传感。     

荧光碳点的制备和性质及其应用研究进展

荧光碳点是继碳纳米管、纳米金刚石和石墨烯之后,最受关注的碳纳米材料之一。与传统半导体量子点相比,碳点具有优异的荧光性能、小尺寸特性、良好的生物相容性、低毒性以及表面易于化学修饰等特点,在环境检测、生物成像、药物载体、光催化及电催化技术等领域具有很好的潜在应用价值。总结了碳点合成方法、结构与性能及应用面进展,剖析了目前制约碳点应用发展的瓶颈问题,并展望了其未来的研究发展重点方向。      

Chemical Modulation of Metal–Insulator Transition toward Multifunctional Applications in Vanadium Dioxide Nanostructures

The metal–insulator transition (MIT) of vanadium dioxide (VO₂) has been of great interest in materials science for both fundamental understanding of strongly correlated physics and a wide range of applications in optics, thermotics, spintronics, and electronics. Due to the merits of chemical interaction with accessibility, versatility, and tunability, chemical modification provides a new perspective to regulate the MIT of VO₂, endowing VO₂ with exciting properties and improved functionalities. In the past few years, plenty of efforts have been devoted to exploring innovative chemical approaches for the synthesis and MIT modulation of VO₂ nanostructures, greatly contributing to the understanding of electronic correlations and development of MIT-driven functionalities. Here, this comprehensive review summarizes the recent achievements in chemical synthesis of VO₂ and its MIT modulation involving hydrogen incorporation, composition engineering, surface modification, and electrochemical gating. The newly appearing phenomena, mechanism of electronic correlation, and structural instability are discussed. Furthermore, progresses related to MIT-driven applications are presented, such as the smart window, optoelectronic detector, thermal microactuator, thermal radiation coating, spintronic device, memristive, and neuromorphic device. Finally, the challenges and prospects in future research of chemical modulation and functional applications of VO₂ MIT are also provided.     

Core–Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na–S Batteries

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium–sulfur (RT Na–S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S₈→Na₂S_x→Na₂S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core–shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N₄), where isolated Ni–N₄ sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S₈ into Na₂S_x (4 < x ≤ 8), while Ni–N₄ sites realize the efficient conversion of Na₂S_x into Na₂S, bridged by the diffusion of Na₂S_x from the core to shell. Besides, Ni–N₄ sites on the shell can also induce an inorganic-rich cathode–electrolyte interface (CEI) on ZnS-NC@Ni-N₄ to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N₄/S cathode exhibits an excellent rate-performance (650 mAh g⁻¹ at 5 A g⁻¹) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na–S batteries.     

Coordination Engineering of Defective Cobalt–Nitrogen–Carbon Electrocatalysts with Graphene Quantum Dots for Boosting Oxygen Reduction Reaction

Developing efficient and robust metal–nitrogen–carbon electrocatalysts for oxygen reduction reaction (ORR) is of great significance for the application of hydrogen–oxygen fuel cells and metal–air batteries. Herein, a coordination engineering strategy is developed to improve the ORR kinetics and stability of cobalt–nitrogen–carbon (Co–N–C) electrocatalysts by grafting the oxygen-rich graphene quantum dots (GQDs) onto the zeolite imidazole frameworks (ZIFs) precursors. The optimized oxygen-rich GQDs-functionalized Co–N–C (G-CoNOC) electrocatalyst demonstrates an increased mass activity, nearly two times higher than that of pristine defective Co–N–C electrocatalyst, and retains a stability of 90.0% after 200 h, even superior to the commercial Pt/C. Comprehensive investigations demonstrate that the GQDs coordination can not only decrease carbon defects of Co–N–C electrocatalysts, improving the electron transfer efficiency and resistance to the destructive free radicals from H₂O₂, but also optimize the electronic structure of atomic Co active site to achieve a desired adsorption energy of OOH⁻, leading to enhanced ORR kinetics and stability by promoting further H₂O₂ reduction, as confirmed by theoretical calculations and experimental results. Such a coordination engineering strategy provides a new perspective for the development of highly active noble-metal-free electrocatalysts for ORR.     

Critical assessment of the fatigue performance of additively manufactured Ti–6Al–4V and perspective for future research

To realize the potential benefits of additive manufacturing technology in airframe and ground vehicle applications, the fatigue performance of load bearing additively manufactured materials must be understood. Due to the novelty of this rapidly developing technology, a very limited, yet swiftly evolving literature exists on the topic. Motivated by these two points, we have attempted to catalog and analyze the published fatigue performance data of an additively manufactured alloy of significant technological interest, Ti–6Al–4V. Focusing on uniaxial fatigue performance, we compare to traditionally manufactured Ti–6Al–4V, discussing failure mechanisms, defects, microstructure, and processing parameters. We then attempt to identify key knowledge gaps that must be addressed before AM technology can safely and effectively be employed in critical load bearing applications.     

Fatigue lifetime and tearing resistance of AA2198 Al–Cu–Li alloy friction stir welds: Effect of defects

The fatigue strength and failure mechanisms of defect-free (“sound”) and flaw bearing friction stir butt-welds of 3.1 mm-thick AA2198-T8 Al–Li–Cu alloy have been investigated via S–N curves at R = 0.1 using cross weld specimens. The fatigue strength of sound welds is only reduced by 10–15% at the aimed lifetime of 10⁵ cycles compared to the base material. Joint Line Remnant (JLR) bearing welds have a similar fatigue strength as sound welds and the JLR is not the crack initiation site. Kissing Bond (KB) bearing welds that have undergone a weld root polishing show a reduction in fatigue strength by 17% compared to sound welds. For specimens loaded at or above yield strength of the weld nugget the crack systematically initiates from the KB during the first cycle, which is interpreted further using fracture mechanics. The strongest reduction, about 28% in fatigue strength, is found for welds with an initial gap between the parent sheets (GAP welds) along with initiation at intergranular surface microcracks. Kahn tear tests show a reduction in tearing resistance for the flaw bearing welds with a similar ranking as for the fatigue strength.