Electron emission properties of silver oxide and its impact on the secondary emission yield of air-exposed silver

Surface oxidation, contamination and adsorption are commonly considered as three leading factors of secondary electron yield (SEY) increase for metals exposed to various environments. Whereas, the influence of these three factors on SEY is different for diverse metal materials. To discover the SEY dependence on surface oxidation for silver, a group of silver oxide (Ag2O) and silver coatings are therefore prepared. Experimental results show the SEY of Ag2O is just about 0.1 higher than that of silver coating whether before or after ion cleaning, and SEY difference becomes smaller under oblique incidence, which indicates the surface oxidation may not be the major causes of SEY increase for air-exposed silver. To further verify the speculation, various surface conditions are achieved on silver surface. Microscopic analysis reveals the adsorptions and contaminations can be effectively removed by heating treatment, meanwhile, SEY is remarkably decreased. Furthermore, the treatment of ion cleaning eliminates all the surface additions and achieves a superlative cleanliness for silver sample, the SEY peak value of air-exposed silver decreases from 2.61 to 1.73 after ion cleaning for 10 min, and to 1.70 after ion cleaning for 30 min, which indicates the surface oxidation contributes little to the SEY raise of air-exposed silver. The SEY dependence on the thickness of contamination layer is also theoretically explained. This work does a systematic research on how the surface oxidation and modification influence SEY of silver, which makes significant sense for comprehending the SEE characteristics of silver with various surface conditions.