矿物颗粒功函数及辐射环境对月尘电子发射带电特性的影响

Electron emission charging is an important mechanism for charging the lunar dust particle in lunar daytime, and it plays an important role in electrostatic adhesion and electrostatic migration of lunar dust. However, both of the difference of charging properties among lunar mineral grains and effect of work function and radiation environment on the lunar dust charging are not known clearly. For these reasons, we plan to measure the work function of mineral grains by non-contact atomic force microscopy in ultra-high vacuum and get the work function value of plagioclase grains, orthopyroxene grains, olivine grains, ilmenite grains, and volcanic glass grains. It might fill the blank of the knowledge of these mineral grains work function. With these experiments, the relationship between particle size and work function might be discussed. We also simulate the photoelectric emission and second electron emission processes by radiating the mineral grains with vacuum ultraviolet, extreme ultraviolet and electric gun. Then, we measure the charging character of the mineral grains with phase doppler particle analyzer in different radiation environment. Based on the multiple regression analysis of experimental results, the electron emission charge of mineral grains might relate to the work function and radiation environment. Then, a multiple parameters response model of photoelectric emission charge and second electron emission charge might be constructed, which termed with the grain work function and radiation environment. The study might provide a reference to electrostatic adhesion and electrostatic migration of lunar dust.

电子发射带电是月尘颗粒白昼带电的一个重要机制，对认识月尘静电粘附和静电迁移具有重要意义。但目前对月尘颗粒带电特性的差异及功函数和辐射环境对其影响研究还不够深入和系统。针对这一现状，项目拟在超高真空下利用nc-AFM开展矿物颗粒的功函数测量研究，获取斜长石、斜方辉石、橄榄石、钛铁矿等矿物颗粒以及火山玻璃颗粒的功函数，填补对这些矿物颗粒功函数认识的空白，并分析颗粒大小与功函数之间的关系；利用真空紫外、极紫外光源和电子枪对矿物颗粒进行辐射，模拟月球表面矿物颗粒的光电发射和二次电子发射带电过程，并利用激光相位多普勒粒子分析技术测量颗粒的在不同辐射环境条件下的带电量。通过对实验数据的多元回归分析，将颗粒功函数、辐射环境特征与电子发射带电量有效联系起来，建立月尘矿物颗粒和玻璃颗粒关于功函数和辐射环境参数的光电发射带电和二次电子发射带电多参数响应模型，为进一步探讨月尘的静电迁移和静电粘附问题提供参考。

随着我国月球探测的深入，航天员和航天器在月面开展巡视探测将受到带电月尘的严重威胁。电子发射带电是月球尘埃颗粒在白昼带电的一个重要机制，对认识月尘静电粘附和静电迁移具有重要意义。项目针对目前对月表不同矿物颗粒的带电特性差异及对影响电子发射过程的矿物颗粒功函数认识不足的现状，建立了超高真空条件下利用nc-AFM测量矿物颗粒功函数的方法，获得了斜长石、斜方辉石、橄榄石、钛铁矿等矿物颗粒的功函数分别为7.90±0.35eV、5.58±0.38eV、5.14±0.36eV和4.29±0.11eV，对应的光电效应阈值波长分别是164nm、238nm、259nm和297nm，填补了对这些矿物颗粒功函数认识的空白；通过地面模拟实验，利用激光相位多普勒粒子分析技术（PDPA）获得颗粒的带电特征，光电发射可使半径为0.1μm的单颗粒尘埃的荷电量可达到10^2-10^3量级个正电荷。根据实验结果，比较不同矿物颗粒的电子发射带电特征差异，分析其带电特征与功函数的关系，探讨实际月球白昼尘埃颗粒带电的基本特征，为后续月球尘埃环境探测和尘埃工程防护提供参考。