空气环境中镀银表面二次电子发射劣化机理

暴露于空气中的金属受环境影响，表面会产生吸附、沾污和氧化等表面改性作用，引起二次电子产额（secondary electron yield,SEY）变化。为探究银表面改性对SEY的影响，使用加热、有机清洗、离子清洗实现了多种银表面状态。实验结果显示，加热能够去除部分表面吸附和沾污，并使得SEY降低；离子清洗在去除表面吸附和沾污的同时还能够剥离表面氧化层，获得高度洁净的表面。离子清洗10/30分钟后SEY峰值由2.61降至1.73/1.70，说明剥离银表面的吸附、沾污和氧化层能使得SEY明显降低。为验证氧化对SEY的影响，使用磁控溅射制备氧化银薄膜。结果表明，氧化银SEY仅比银高0.1左右，且在斜入射下两者SEY差异更小，该结果证明银表面发生氧化不会使得SEY明显升高，并间接说明表面吸附和沾污是使得银表面SEY升高的主要因素。

Degradation mechanism of secondary electron emission for the silver-plated surfaces exposed to the air environment

Metals exposed to air are affected by the environment and cause surface modification including adsorption, contamination, and oxidation, resulting in changes of secondary electron yield (SEY). To investigate the effect of surface modification on SEY, a variety of silver surface conditions were achieved using heating, organic cleaning, and ionic cleaning processes. Experimental results show that heating can remove adsorption and contamination to a certain extent, achieving a decrease in SEY, ion cleaning can not only remove surface adsorption and contamination but also strip the surface oxide layer to achieve a highly clean surface. The SEY peak value decreased from 2.61 to 1.73/1.70 after 10/30 min of ion cleaning, which indicates that removing the surface layer formed by adsorption, contamination, and oxidation can remarkably decrease the surface SEY of silver. To verify the effect of surface oxidation on silver SEY, silver oxide films were prepared using magnetron sputtering. The results showed that SEY of the silver oxide film was only 0.1 higher than that of silver film at most energy points, and the difference in SEY between the two was even smaller under oblique incidence. The results demonstrate that the surface oxidation cannot raise the SEY of silver obviously, and indirectly suggest that surface adsorption and contamination are the main factors that increase the SEY of the silver surface.