热阴极表面微观发射结构的密度泛函研究  

Density Functional Study of Surface Microscopic Emission Structures of Thermionic Cathodes

作　　者：李泽鹏 郭根材 郝广辉 于志强[1] 张珂[1] 邵文生[1] 王如志[2] LI Ze-peng;GUO Gen-cai;HAO Guang-hui;YU Zhi-qiang;ZHANG Ke;SHAO Wen-sheng;WANG Ru-zhi(The 12 th Research Institute of China Electronics Technology Group Corporation,Beijing 100015,China;Beijing University of Technology,Beijing 100124,China)

机构地区：[1]中国电子科技集团公司第十二研究所,北京100015 [2]北京工业大学,北京100124

出　　处：《真空电子技术》2019年第6期72-79,共8页Vacuum Electronics

摘　　要：经过一百多年的发展,对热阴极发射水平的提升和发射机理的研究方兴未艾。研究人员致力于寻找低功函数的发射材料来提升阴极发射能力,并采用多种表面分析方法对热阴极表面进行表征,以解释热电子发射的工作机理。B型扩散阴极由于Ba-O偶极层的存在降低了钨表面的功函数,并增强了电子发射;在B型阴极中引入过渡金属Os,Ir,Re等得到具有较低功函数,较高发射能力的M型阴极;含Sc扩散阴极因具有更低的功函数和更高的发射电流密度引起广泛关注。普遍认为这是由于阴极表面形成的低功函数结构引起的。本文基于密度泛函理论,对B型阴极、M型阴极、钪型阴极表面的微观发射结构进行了建模计算,结果表明Ba原子覆盖度影响阴极表面功函数的变化;过渡金属Os的引入会进一步降低表面功函数;随着Sc的掺杂,表面存在形成半导体属性层的趋势;并对不同表面结构的功函数进行加权平均求解,得到了计算阴极表观功函数的计算方程。After more than one hundred years development,researches on the improvement of the emission capability and the emission mechanism of thermionic cathodes are still in ascendant.Researchers are looking for materials with low work function to enhance the emission,and various surface analysis methods are used to characterize the surface of thermionic cathodes to explain the working mechanism.B-type dispenser cathodes reduce the work function of tungsten due to the presence of Ba-O dipole layer on the surface;M-type cathodes have lower work function and higher emission capability with the addition of transition metal osmium,iridium,rhenium into B-type cathodes;the scandia doped thermionic cathodes have received great attention because of their high electron emission density owing to the further reduction of work function.It is generally believed that this is due to the low work function structure formed on the cathode surface.Based on the density functional theory,the microscopic emission structures of B-type,M-type and Sc-type cathode surfaces are modeled and calculated.The results show that the coverage of barium atom affects the surface work function;with the introduction of transition metal osmium,the surface work function is further reduced.With the doping of scandate,the surface has a tendency to form a semiconductor layer.The weighted average work function of different surface is solved,and the calculating equation of the apparent work function is obtained.

关 键 词：阴极 密度泛函 热电子发射 功函数 

分 类 号：O462[理学—电子物理学]