Ultrafast Field‐Emission Electron Sources Based on Nanomaterials

The search for electron sources with simultaneous optimal spatial and temporal resolution has become an area of intense activity for a wide variety of applications in the emerging fields of lightwave electronics and attosecond science. Most recently, increasing efforts are focused on the investigation of ultrafast field‐emission phenomena of nanomaterials, which not only are fascinating from a fundamental scientific point of view, but also are of interest for a range of potential applications. Here, the current state‐of‐the‐art in ultrafast field‐emission, particularly sub‐optical‐cycle field emission, based on various nanostructures (e.g., metallic nanotips, carbon nanotubes) is reviewed. A number of promising nanomaterials and possible future research directions are also established.     

Enhanced Field‐Emission Behavior of Layered MoS2 Sheets

Field emission studies are reported for the first time on layered MoS₂ sheets at the base pressure of ～1 × 10^?8 mbar. The turn‐on field required to draw a field emission current density of 10 μA/cm² is found to be 3.5 V/μm for MoS₂ sheets. The turn‐on values are found to be significantly lower than the reported MoS₂ nanoflowers, graphene, and carbon nanotube‐based field emitters due to the high field enhancement factor (～1138) associated with nanometric sharp edges of MoS₂ sheet emitter surface. The emission current–time plots show good stability over a period of 3 h. Owing to the low turn‐on field and planar (sheetlike) structure, the MoS₂ could be utilized for future vacuum microelectronics/nanoelectronic and flat panel display applications.     

Micrometer‐ and Nanometer‐Sized Organic Single‐Crystalline Transistors

The use of micrometer and nanometer‐sized organic single crystals to fabricate devices can retain all the advantages of single crystals, avoid the difficulties of growing large crystals, and provide a way to characterize organic semiconductors more efficiently. Moreover, the effective use of such “small” crystals will be beneficial to nanoelectronics. Here we review the recent progress of organic single‐crystalline transistors based on micro‐/nanometer‐sized structures, namely fabrication methods and related technical issues, device properties, and current challenges.     

Carbon‐Nanotube–Polymer Nanocomposites for Field‐Emission Cathodes

The electron field‐emission (FE) characteristics of functionalized single‐walled carbon‐nanotube (CNT)–polymer composites produced by solution processing are reported. It is shown that excellent electron emission can be obtained by using as little as 0.7% volume fraction of nanotubes in the composite. Furthermore by tailoring the nanotube concentration and type of polymer, improvements in the charge transfer through the composite can be obtained. The synthesis of well‐dispersed randomly oriented nanotube–polymer composites by solution processing allows the development of CNT‐based large area cathodes produced using a scalable technology. The relative insensitivity of the cathode's FE characteristics to the electrical conductivity of the composite is also discussed.     

Mg掺杂ZnO纳米棒阵列的场发射性能研究

采用水热法在硝酸锌(Zn(NO3)2·6H2O)与硝酸镁(Mg(NO3)2·6H2O)的生长液中制备了Mg掺杂的Mg/ZnO(MZO)纳米棒,其中生长液中Mg2+的物质的量浓度c(Mg2+)分别为0.05 mol/L、0.10 mol/L、0.25 mol/L和0.50 mol/L.利用场发射电子显微镜(FESEM)、X射线光电子能谱仪(XPS)、X射线衍射仪(XRD)、光致发光谱(PL)测试及场发射测试对所制备的MZO纳米棒的表面形貌、成分、晶体结构、光学性能及场发射性能进行了研究.结果表明:随着生长液中c(Mg2+)的增加,MZO纳米棒的直径逐渐减小、缺陷逐渐增加;且掺入的Mg含量与c(Mg2+)并不成正比关系;当生长液中的c(Mg2+)为0.10 mol/L时,所制备的MZO纳米棒的场发射性能最好,其开启场强为2.85 V/μm.     

Cl‐Doped ZnO Nanowire Arrays on 3D Graphene Foam with Highly Efficient Field Emission and Photocatalytic Properties

An environmentally friendly, low‐cost, and large‐scale method is developed for fabrication of Cl‐doped ZnO nanowire arrays (NWAs) on 3D graphene foam (Cl‐ZnO NWAs/GF), and investigates its applications as a highly efficient field emitter and photocatalyst. The introduction of Cl‐dopant in ZnO increases free electrons in the conduction band of ZnO and also leads to the rough surface of ZnO NWAs, which greatly improves the field emission properties of the Cl‐ZnO NWAs/GF. The Cl‐ZnO NWAs/GF demonstrates a low turn‐on field (≈1.6 V μm⁻¹), a high field enhancement factor (≈12844), and excellent field emission stability. Also, the Cl‐ZnO NWAs/GF shows high photocatalytic efficiency under UV irradiation, enabling photodegradation of organic dyes such as RhB within ≈75 min, with excellent recyclability. The excellent photocatalytic performance of the Cl‐ZnO NWAs/GF originates from the highly efficient charge separation efficiency at the heterointerface of Cl‐ZnO and GF, as well as improved electron transport efficiency due to the doping of Cl. These results open up new possibilities of using Cl‐ZnO and graphene‐based hybrid nanostructures for various functional devices.     

CVD法和丝印法制作的碳纳米管场致发射冷阴极的研究

本文研究了丝网印刷法和CVD生长法制备的碳纳米管冷阴极的场致发射性能.结果表明,在没有模板的情况下,通过CVD生长的碳纳米管的直径与催化剂颗粒的直径有关,随催化剂颗粒的直径变化而变化,生长方向是随机的,但大电流发射稳定性较差;用丝网印刷方法制作的碳纳米管致发射冷阴极,场发射电流发射较稳定.