第二相粒子大小对Mo-La_2O_3阴极电子发射性能的影响

Effects of Second Phase Particle Size on Electron Emission Ability of Mo-La_2O_3 Cathode

利用溶胶-凝胶、氢气还原及热压工艺制备了纳米复合Mo-4La2O3(质量分数,%)阴极材料,其显微组织中La2O3粒径小于100nm,而常规Mo-4La2O3阴极中La2O3粒径为200～300nm。在真空击穿实验中发现La2O3粒径对于阴极电子发射性能有显著的影响,纳米复合阴极的电子发射能力远高于常规阴极的发射能力,其电子发射点遍布整个阴极表面,而常规阴极电子发射点只是集中在一小块区域。通过建立金属-半导体电子相互作用模型,计算并绘制了Mo及La2O3中电子隧穿几率随La2O3粒径变化的关系曲线,解释了纳米复合阴极电子发射能力强的原因。

Nanocomposite Mo-4La2O3 (mass fraction) cathode was prepared by sol-gel method and hydrogen reduction process and then hot-pressing sintering technique. The microstructure of nanocomposite cathode is homogeneous and very fine; the lanthana particles are about 40-50 nm, while they are about 200-300 nm in the conventional Mo-4La2O3 cathode. The particle size of lanthana has a strong effect on the field electron emission ability of cathode. The nanocomposite cathode has superior field electron emission ability compared with that of the conventional cathode. The sites of field electron emission of the nanocomposite cathode nearly extend over the whole surface of cathode, whereas the emission sites of the conventional cathode concentrate on a small area of the cathode surface. By creating the electron interaction model between the metal and semiconductor, the relation curves between the tunneling probability of electrons in Mo and La2O3 and second phase size were calculated and plotted, respectively. The reasons that nanocompposite cathode has stronger electron emission performance were explained. Copyright © 2010, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.