掺氮N型超纳米金刚石薄膜阴极的强流脉冲发射性能及发射机制

Because of generation and closure of plasma and out-gassing of materials, most of high-current pulsed cathodes could not obtain electron beam source with long pulsewidth and high rep-rate. This project takes diamond thin films as research subject and is planning to prepare nitrogen-doped N-type ultrananocrystalline diamond (N-UNCD) thin films, which will be employed as cathode, via microwave-enhanced plasma chemical vapor deposition technology, using saturated solution of melamine in methanol as doping source. The effect of deposition parameters on the microstructure of N-UNCD thin films, such as size and structure of grain and grain boundary, and amount and location of doping nitrogen atom, will be systematically investigated through experimental characterizations. Moreover, high-current pulsed-emission performances of N-UNCD thin films with different microstructures will be investigated in detail. Based on the microstructure characterizations of N-UNCD thin films after the emission, and the observations of lightening at the cathode surface and pressure-changing of diode during the emission, high-current pulsed-emission mechanisms of N-UNCD thin films will be explored, which can be provide theoretical fundaments for obtaining long pulsewidth and high rep-rate electron sources for high power microwave devices.

针对现有强流脉冲发射阴极材料由于存在等离子体产生、闭合以及放气问题从而难以获得长脉冲宽度、高重复频率电子束源的问题，本项目拟以金刚石薄膜为研究对象，采用三聚氰胺的甲醇饱和溶液为液态掺杂源，通过微波等离子体化学气相沉积法制备掺氮N型超纳米金刚石薄膜阴极，并通过多种实验表征方法系统地研究掺氮N型超纳米金刚石薄膜的微观结构（如晶粒/晶界尺寸、晶粒/晶界结构、掺氮量及位置等）随沉积工艺参数的变化；在此基础上，详细研究具有不同微观结构的掺氮N型超纳米金刚石薄膜阴极的强流脉冲发射性能；结合脉冲发射过程中阴极表面发光、真空二极管气压变化以及脉冲发射后薄膜阴极的微观结构表征，探索掺氮N型超纳米金刚石薄膜阴极的强流脉冲发射物理机制，为获得可用于高功率微波器件的长脉冲宽度、高重复频率电子束源提供理论基础。

本项目旨在探索掺氮N型超纳米金刚石薄膜作为一种新型的阴极材料为高功率微波器件提供长脉冲宽度、高重复频率电子束源的理论可行性。在本项目的研究中，我们首先以三聚氰胺的甲醇饱和溶液为液态掺氮源，采用微波等离子体化学气相沉积技术制备了掺氮N型超纳米金刚石（UNCD）薄膜，详细研究了沉积气压、沉积温度、CH4浓度等因素对所制备的掺氮N型UNCD薄膜的形貌和微观结构的影响，并比较了不同微观结构的掺氮N型UNCD薄膜阴极的S波段微波场强流脉冲发射特性，提出了相应的发射机制；在此基础上，以高温去润湿化所形成的金属Ni纳米粒子为掩膜，采用不同比例的O2/Ar等离子体刻蚀技术，制备了表面纳米结构化的掺氮N型UNCD薄膜，以此为阴极详细研究了其S波段微波场强流脉冲发射特性及机制；同时，我们又开发了以有机胺小分子为液态源制备高导电率掺氮N型UNCD薄膜的新工艺，详细研究所制备的薄膜的形貌和微观结构，并研究了其直流发射性能；最后，我们运用基于第一性原理的VASP软件掺氮N型UNCD薄膜进行了态密度、能带结构计算，从理论上分析掺氮N型UNCD薄膜的导电机制，有望为研究掺氮N型UNCD阴极的强流脉冲发射机制提供理论依据。