Electron Beam Source of Nanotube for Free Electron laser

众所周知，从金属/半导体针尖通过场发射发射出低发射度和低能量扩散的电子束。场发射体的这些特性对自由电子激光器（FEL）是有利的。本文采用电弧放电、激光烧蚀和化学气相沉积三种方法合成了碳纳米管。对其中一些进行了场发射实验。W针上单个多壁碳纳米管的电流为~ 9 μA，大量缠绕的碳纳米管发出的电子电流为2.5 mA，是普通W针阴极的~ 100倍。实验前后碳纳米管的SEM图像表明，缠结的碳纳米管受到高电场的磨损，电子主要从每个碳纳米管的尖端发射。特别是在不锈钢管上涂有极少量树脂的缠结CNTs，其电流波动幅度均< 4%。而当设置中心有空穴的电极以提取电子束时，电流降至~ 600 ~ 40 μA。这是由于大多数元素到达了第一个电极。在进一步的研究中，电极的几何优化设计将改善自由电子激光器的电流和电子束聚焦性能。除了场发射实验外，还取得了其他显著的成果，如XeCl准分子的紫外激光首次成功形成含碳纳米管的纳米产品，以及发现了含碳纳米管的聚乙烯片在远红外波段的优越透射滤光片。

It is well known that an electron beam with low emittance and low energy spread is emitted from a tip of metal/semiconductor needle by field emission. These characters of the field emitter are favorable for a free electron laser (FEL). In this study carbon nano-tubes (CNTs) were synthesized by three methods of arc discharge, laser ablation and chemical vapor deposition (CVD). Some of them were investigated for the field emission experiment.A single multiwalled CNT on a W needle gave the current of 〜9 μA and a mass of entangled CNTs emitted electrons with current of 2.5 mA which is 〜100 times as high as that of usual W needle cathode. The SEM images of CNTs in pre-/post-experiment suggested that the entangled tubes were frayed by the high electric field and then electrons were emitted mainly from the tip of each CNT. Especially the entangles CNTs coated on a stainless tube with a very small amount of resin presented similar high current with a fluctuation of <4 %. However the current decreased to 〜600 to 40 μA when the electrodes with a hole at the center were set in order to extract the electron beam. It was attributed to the arrival of most of the elements to the first electrode. In the further studies, the geometrical optimum design of the electrodes will improve the current and the focusing property of the electron beam for FEL. Besides the field emission experiment, other remarkable results were obtained such as the first success of forming nano-products including CNT by ultraviolet laser of XeCl excimer and finding the superior transmission filter of polyethylene sheet including CNT in the far-infrared.