Research on Micro-Thermal Materials Processing with Pulsed Field Emission Current

本课题通过基础实验，明确了高密度场发射电流下微米至纳米级精密热材料加工存在的问题及其机理。所得结果总结如下：1。采用Fowler-Nordheim方程，从理论上计算了表面镀有碳纳米管（CNT）的尖阴极在镍基体上发射出的电子电流分布场。假设阴极形状为轴对称双曲线。阳极表面的电流分布随间隙长度和阴极尖端半径的变化而变化。在阴极与不锈钢阳极间隙长度为0.1 ~ 2 μm的范围内，通过施加窦向波电压，精确测量了阴极与不锈钢阳极间的场发射电流。所测电流随外加电压的增加呈指数增长。利用FN图确定了该电流为场致发射电流。理论预测的场发射电流与间隙长度、针尖半径等参数的关系与实测结果定性一致。但是，测量得到的电流值高于计算得到的电流值。在下一阶段的研究中，有必要明确碳纳米管的等效功函数和/或仔细处理阴极形状。在SEM真空环境下，对碳纳米管涂层阴极进行了场发射电流精密加工。实验表明，只有当两电极之间发生电击穿时，才会在不锈钢阳极表面形成熔斑。因此，下一阶段的研究需要在阳极表面制造更高的电流密度。少

In this project the fundamental experiments were carried out to make clear the problems and the mechanisms of the precise thermal materials processing in micro-meter to nano-meter size with high density field emission current. The results obtained are summarized as follows :1.Theoretical prediction of field emission current from a pointed cathode coated with Carbon-Nano-Tube(CNT)The electron current distribution field-emitted from a pointed cathode, of which surface was coated by CNT on the substrate of nickel, was theoretically calculated using Fowler-Nordheim equation. The cathode shape was assumed to be axial symmetric hyperbola. The current distribution on the anode surface is varied depending on the gap length and the tip radius of the cathode.2.Measurement of field emission current from a pointed cathode coated with CNTThe field emission current was precisely measured in the range of 0.1 to 2 μm of the gap length between the cathode and stainless steel anode by applying the sinus … More oidal wave voltage. The current measured increases exponentially with increase of applied voltage. Then, the current was confirmed to be field emission current with the aid of FN plotting. The theoretical prediction of the relationship between the field emission current and the parameters such as gap length and tip radius qualitatively accorded with that by measurement. However, the current value by the measurement was higher than the calculation. It is necessary to make clear the equivalent work function of CNT and/or to treat the cathode shape carefully in the next stage of the research.3.Precise thermal materials processing by field emission currentThe precise materials processing by field emission current was tried with the CNT coated cathode in the SEM vacuum environment. The experiment showed that the melt spot was formed on the surface of stainless anode only when the electrical breakdown between both electrodes occurred. Then, it is necessary to make higher current density on the anode surface in the next stage of the research. Less