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

Abstract

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.