Effect of traps and conductive pathways on electron emission from copper broad-area composite emitters

Abstract

This paper offers an explanation of the process of electron emission from copper broad-area composite emitters (CBACEs) based on the principles of trapping and conductive pathways supported by experimental evidence. Emission current measurements were conducted on two CBACE, comprising copper coated with a 300-400μm epoxy resin, subjected to high voltages up to 15 kV. This study investigated the witch-on and collapse phenomena in the epoxy layer. Field electron microscopy (FEM) was operated under a high vacuum environment (10-6 mbar).
This helps to follow changes in the value of the emission current (breakdown current). Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FTIR) were used to comprehensively characterize the composite emitter before and after exposure to high voltages. The mechanism of electron emission from composite broad-area emitters is explained, as well as how the epoxy breaks down when exposed to high voltage. The results showed that the emission pattern of copper broad-area emitters (CBAEs) was brighter at the edges. The emission pattern of the CBACEs was centered on a single bright point. The effect of coating on the (I-V) curve was studied. A simulation of the electric field acting on the coating was also performed to understand the contribution of the high field to the epoxy breakdown. Furthermore, impedance spectroscopy at frequencies ranging from 1 to 106 Hz showed that the high electric field decreased both the impedance and permittivity of the epoxy resins, as the changes in the Nyquist and Cole-Cole plots were studied before and after exposing the samples to a high electric field.