利用探针法研究二次电子发射过程中介质材料的表面电位

Surface Potential Measurement of Dielectric Materials Using Metal Probe in Secondary Electron Emission Process

为研究介质材料二次电子发射过程中表面电位的测量手段及相关规律,以拒斥场会影响二次电子出射为基础,提出了能够原位测量介质材料表面电位的探针法。首先,利用专业电磁仿真软件对探针法原理进行了研究,计算了探针附近电位分布和探针偏压对二次电子发射系数的影响曲线,此曲线拐点处对应的探针偏压即为样品的表面电位;其次,用铜样品进行了实验研究,验证了探针法测量样品表面电位的可行性;最后,将探针法应用于介质材料聚甲基丙烯酸甲酯(PMMA),对其表面电位进行了实验测量和研究。结果表明:栅网偏压和入射电子能量对PMMA表面电位有直接的影响,PMMA表面电位总是高于栅网偏压,两者呈线性关系;随着入射电子能量的增加,PMMA表面电位呈现先升高后下降的趋势。实验结果与理论分析相一致,验证了探针法测量介质材料表面电位的可行性。该方法操作简便、成本低廉,而且实现了原位在线测量,减小了实验中的不稳定性,对介质材料二次电子发射机理的研究有一定的参考价值。

To study measurement methods and relevant rules of the surface potential in the process of secondary electron emission of dielectric materials,this paper proposes a new in situ online method for the measurement of the surface potential of insulating samples based on the fact that electric field will affect the secondary electron emission,and we call it probe method.Firstly,the principle of the probe method is studied by using a professional electromagnetic simulation software.The potential distribution near the probe and the influence of probe bias on the secondary electron emission coefficient are calculated.Then the probe bias at the knee of the curve is considered as the surface potential of the dielectric sample.Secondly,experiments are carried out with copper samples,and the feasibility of the probe method for measuring the surface potential of the samples is verified.Finally,the probe method is applied to the dielectric material polymethyl methacrylate (PMMA) to measure its surface potential.The results show that the grid bias voltage and the incident electron energy have direct influences on the surface potential of PMMA.The surface potential of PMMA is higher than the grid bias and they are in a linear relationship.With the increase of the incident electron energy,the surface potential of PMMA increases first and then decreases.This is consistent with the theoretical analysis,which further validates the feasibility of the probe method in measuring the surface potential of dielectric materials.This method is easy to operate and low in cost,and can realize in situ online measurement to reduce the instability in the experiment,therefore it is applicable to the study of the secondary electron emission of dielectric materials.