硼烯和碱土金属硼化物二维纳米材料的制备、结构、物性及应用研究

随着石墨烯研究的兴起,二维纳米材料得以迅速发展.在众多的二维纳米材料中,硼烯和碱土金属硼化物二维材料由于具有高费米速度、高杨氏模量、高透光性、高延展性、高度的各向异性、大的泊松比和高的化学稳定性等独特的性质,成为研究人员关注的焦点.本文侧重介绍目前硼烯和碱土金属硼化物二维纳米材料的制备工艺、结构、物性和应用情况.首先总结了目前硼烯的主要结构构型和制备及掺杂工艺;其次介绍了碱土金属硼化物二维纳米材料的理论结构构型和可能的制备路线;最后对硼烯和二维碱土金属硼化物纳米材料的物理特性进行归纳总结,同时预测它们未来最可能实现应用的领域.     

An easy way to controllably synthesize one-dimensional Sm B_6 topological insulator nanostructures and exploration of their field emission applications

A convenient fabrication technique for samarium hexaboride(SmB_6) nanostructures(nanowires and nanopencils) is developed, combining magnetron-sputtering and chemical vapor deposition. Both nanostructures are proven to be single crystals with cubic structure, and they both grow along the [001] direction. Formation of both nanostructures is attributed to the vapor-liquid-solid(VLS) mechanism, and the content of boron vapor is proposed to be the reason for their different morphologies at various evaporation distances. Field emission(FE) measurements show that the maximum current density of both the as-grown nanowires and nanopencils can be several hundred μA/cm~2, and their FN plots deviate only slightly from a straight line. Moreover, we prefer the generalized Schottky-Nordheim(SN) model to comprehend the difference in FE properties between the nanowires and nanopencils. The results reveal that the nonlinearity of FN plots is attributable to the effect of image potential on the FE process, which is almost independent of the morphology of the nanostructures.All the research results suggest that the SmB_6 nanostructures would have a more promising future in the FE area if their surface oxide layer was eliminated in advance.     

Controlled growth and field emission of vertically aligned AlN nanostructures with different morphologies

The controllable growth of three different morphologies of AlN nanostructures (nanorod, nanotip and nanocrater) arrays are successfully realized by using chemical vapour deposition (CVD) technology. All three nanostructures are of single crystal h-AlN with a growth orientation of [001]. Their growth is attributed to the vapour-liquid-solid (VLS) mechanism. To investigate the factors affecting field emission (FE) properties of AlN nanostructures, we compare their FE behaviours in several aspects. Experimental results show that AlN nanocrater arrays possess the best FE properties, such as a threshold field of 7.2~V/μm and an emission current fluctuation lower than 4%. Moreover, the three AlN nanostructures all have good field emission properties compared with a number of other excellent cathode nanomaterials, which suggests that they are future promising FE nanomaterials.     

利用光电子能谱研究氩离子对三氧化钨纳米线的还原作用

三氧化钨是具有多功能的宽带隙半导体材料,它表现出许多独特的性质,具有广阔的应用前景,成为目前纳米材料的一个研究热点.三氧化钨有显著的电致变色、气致变色、热致变色、光致变色的特性,它们可以用来做成平板显示器[1]、灵巧窗口[2]、温湿度传感器[3]等等.此外,一些氧化钨低值氧化物(WO3-x)还有很好的电特性,尤其表现在超导及电荷输运能力方面[4].本文利用光电子能谱技术,对三氧化钨纳米线的还原进行深入细致的分析,力图阐明其还原所经历的复杂过程.     

碳纳米管冷阴极脉冲发射特性及仿真模型研究

针对碳纳米管场致发射冷阴极在微波、毫米波电真空辐射源器件中的应用需求,采用2μs,20 kV的脉冲高压对碳纳米管场致发射冷阴极的脉冲发射特性进行了实验研究.通过改变阴阳极间距,对碳纳米管冷阴极发射电流特性及发生脉冲高压打火后的碳纳米管冷阴极发射特性进行了测试研究.在直径为4 mm的圆形平面碳纳米管冷阴极上获得最大发射电流16 mA,电流密度为127 mA/cm~2.以实验测试数据为基础,结合粒子模拟软件建立碳纳米管冷阴极场致发射仿真模型,给出了该仿真模型的相关参数,为下一步设计研制碳纳米管冷阴极电子光学系统及相关辐射源器件奠定基础.     

Ultrafast blue light emission from SiC nanowires

Cubic silicon carbide (SiC) nanowires are synthesized in a catalyst-assisted process. The nanowires with diameter of - 40 nm exhibit strong blue light emission at room temperature under ultraviolet (UV) femtosecond laser excitation. The photon energy of peak emission is higher than the energy bandgap of cubic SiC which shows involvement of quantum confinement effect. The ultrafast fluorescence is deconvoluted by Monte-Carlo method. The results show two ultrafast decay processes whose lifetimes are about 26 and 567 ps respectively. The mechanisms of such ultrafast processes are discussed.     

Preparation of patterned boron nanowire films with different widths of unit-cell and their field emission properties

Large-area patterned films of boron nanowires(BNWs) are fabricated at various densities by chemical vapor deposition(CVD). Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell of Mo masks are100 μm, 150 μm, and 200 μm, respectively. The distance between unit cells is 50 μm. The BNWs have an average diameter of about 20 nm and lengths of 10 μm–20 μm. High-resolution transmission electron microscopy analysis shows that each nanowire has a β-tetragonal structure with good crystallization. Field emission measurements of the BNW films show that their turn-on electric fields decrease with width of unit-cell increasing.     

No-catalyst growth of vertically-aligned AlN nanocone field electron emitter arrays with high emission performance at low temperature

The AlN nanostructures with a wide band-gap of 6.28 eV are considered as ideal cold cathode materials because of their low electron-affinity. Many methods have been devoted to fabricating AlN nanostructures, but high growth temperature over 800°C and the use of the catalysts in most methods limit their practical application and result in their poor field-emission behaviours in uniformity. This paper reports that without any catalysts, a simple chemical vapour deposition method is used to synthesize aligned AlN nanocone arrays at 550°C on silicon substrate or indium tin oxide glass. Field emission measurements show that these nanocones prepared at low temperature have an average turn-on field of 6 V/μm and a threshold field of 11.7 V/μm as well as stable emission behaviours at high field, which suggests that they have promising applications in field emission area.     

Room-temperature strong coupling between dipolar plasmon resonance in single gold nanorod and two-dimensional excitons in monolayer WSe_2

All-solid-state strong coupling systems with large vacuum Rabi splitting energy have great potential applications in future quantum information technologies, such as quantum manipulations, quantum information storage and processing,and ultrafast optical switches. Monolayer transition metal dichalcogenides(TMDs) have recently been explored as excellent candidates for the observation of solid-state strong coupling phenomena. In this work, from both experimental and theoretical aspects, we explored the strong coupling effect by integrating an individual plasmonic gold nanorod into the monolayer tungsten diselenide(WSe_2). Evident anti-crossing behavior was observed from the coupled energy diagram at room temperature; a Rabi splitting energy of 98 meV was extracted.     

Towards an optical coupler using fine-wire: a study of the photovoltaic effect of a heterojunction formed in a single fine-wire of tungsten oxides

Nanodevices using the photovoltaic effect of a single nanowire have attracted growing interest. In this paper, we consider potential applications of the photovoltaic effect to optical signal coupling and optical power transmission, and report on the realization of a heterojunction formed between WO₂ and WO₃ in a fine-wire having a diameter on the micrometer scale. Using a laser beam of 514.5~nm as a signal source, the WO₂--WO₃ heterojunction yields a maximum output power of up to 37.4 pico watt per heterojunction. Fast responses (less than a second) of both photovoltaic voltage and current are also observed. In addition, we demonstrate that it is a simple and effective way to adapt a commercial Raman spectrometer for the combined functions of fabrication, material characterization and photovoltaic measurement of an optical signal coupler and optical power transmitter based on a fine-wire. Our results show an attractive perspective of developing nanowire or fine-wire elements for coupling optical signals into and for powering a nanoelectronic or nano-optoelectronic integrated circuit that works under the condition of preventing it from directly electrically connecting with the optical coupler.