Degradation Mechanisms of Scandate Cathodes in Nonideal Vacuum: Evaluation of Ion Bombardment and Surface Poisoning

The stringent high-vacuum requirement for scandate cathodes, leading to high costs and operational complexities, remains a critical bottleneck limiting their broader application in modern microwave vacuum electronic devices. This work systematically investigates the degradation mechanisms of scandate cathode emission performance in nonideal vacuum environments. Based on the test results of cathode emission current density decreasing with vacuum degree and conducting comparative assessments before and after atmosphere exposure, we separated the degradation mechanism into two distinct pathways: physical damage from ion bombardment and chemical property alteration from surface poisoning. The mechanisms were elucidated through a combination of surface morphology characterization in a scanning electron microscope (SEM), ion bombardment energy calculation via COMSOL/MATLAB simulation, and depth-profiling elemental analysis by argon ion sputtering-assisted X-ray photoelectron spectroscopy (XPS) of the cathode, combined with DFT calculations of the surface work function. The results show that the two damage pathways fundamentally disrupt the formation and stability of the surface dipole layer, impairing its ability to maintain low work function, which ultimately reduces the emission performance of the cathode. These findings provide valuable insights and a theoretical foundation for designing effective protection of scandate cathode emission performance.