深紫外激光光发射与热发射电子显微镜在热扩散阴极研究中的应用

对热扩散阴极表面微区发射状态进行原位观察和分析一直是热阴极研究的重要课题.本文着重介绍深紫外激光光发射电子/热发射电子显微镜的基本原理及其在热扩散阴极研究中的典型实例.系统配备了高温激活所用的加热装置,样品可被加热至1400℃.系统具有光发射电子、阴极热发射电子、光发射电子和阴极热发射电子联合三种电子成像模式.应用表明,对于热扩散阴极而言,深紫外激光光发射电子像适于呈现阴极表面的微观结构形貌;热发射电子像适于反映阴极表面的本征热电子发射及均匀性;光电子和热电子联合成像适于对阴极表面的有效发射点做出精确定位.

Applications of deep ultraviolet laser photo-and thermal-emission electron microscope in thermal dispenser cathode research

The research of micro-region emission state for thermal dispenser cathode surface,especially in-situ observation and analysis,is an important subject in the field of thermal cathode.A newly developed instrument aiming at meeting the special operation requirements of thermal dispenser cathode is used to carry out this research.This instrument combines the functions of deep ultraviolet laser photo-emission electron microscope and thermal-emission electron microscope,so it is called DUV-PEEM/TEEM.In this paper,its basic principle is introduced emphatically.In addition,the actual applications of the microscope system to the electron emission investigation of thermal dispenser cathode are displayed. This system is equipped with the heating unit,which is used for activating the thermal dispenser cathode sample,and the temperature of sample can reach 1400℃.The system has three imaging modes,namely,photoemission electron imaging, cathode thermal emission electron imaging,and united imaging by integrating cathode thermal emission electron and photoemission electron.By applying new microscope system to traditional thermal dispenser cathode,we acquire the photoemission electron images of impregnated barium aluminate cathode surface at room temperature.In the heating process,we observe the thermal electron emission phenomenon originating from thermal dispenser cathode and record the variation process with temperature change.A high emission cathode which we developed before,is also studied with DUV-PEEM/TEEM.Fortunately,we find that some bright stripes appear on the surface of high emission cathode when the cathode temperature reaches 800℃.The widths of these bright stripes are about 100 nm.We calculate the thermal emission electron imaging resolution of this system by using these thermal electron emission stripes and the obtained resolution reaches 28 nm.Conveniently,the emission performance and uniformity of this high emission cathode are compared with those of traditional impregnated barium aluminate cathode directly at same temperature. Using united imaging mode of the system,in-situ observation and analysis of thermal electron emission spots on high emission cathode surface are carried out successfully.The results indicate as follows.For thermal dispenser cathode,the deep ultraviolet laser photoemission electron imaging can be used to show the surface fundamental micro-morphology of cathode;cathode thermal emission electron imaging is suitable for revealing the intrinsic emission uniformity of the thermal dispenser cathode;with the united imaging by integrating cathode thermal emission electron and photoemission electron,the positions of effective emission points on cathode surface can be fixed accurately.Based on these applications and findings,we believe that DUV-PEEM/TEEM also has ability to investigate the processes of cathode poisoning and recovery.