Investigation of the electron emission properties of Silver: from technical Ag surface to ion- cleaned Ag surface
Résumé
Electron emission is at the origin of Multipactor effect that can occur in several rf devices under vacuum. To improve the estimation of Multipactor threshold, it is capital to know accurately some proprieties of the emitted electrons such as (i) the secondary electron emission yield, (ii) the electron backscattered yield and (iii) the energy distribution. The purpose of this paper is to study experimentally electron emission of technical silver. Indeed, Ag is widely used as coating material in waveguides. Measurements are performed in an UHV experimental facility named CELESTE and located at ONERA. A special experimental protocol was developed to extract many interesting properties. The total electron emission yield is investigated from very low incidence energy (few eV) to 2000eV. The energy distribution of the emitted electrons was monitored with a help of an electron analyser. The electron emission is a surface phenomenon; the emitted secondary electrons are generated in the 10 first nanometres depth of the material. Thus, the electron emission is hugely influenced by surface composition and morphology. Technical Ag surface (exposed to atmosphere) is mainly composed by Ag2S and other deposited compounds, like water and carbon compounds. Therefore the electron emission proprieties of the technical Ag are undoubtedly different from the tabulated ones, measured on pure and cleaned Ag samples. For, accurate physical modelling of the secondary electron emission phenomenon, it is important to link the proprieties of the pure material and those of the technical one. For this purpose, a step by step Ar ion “cleaning” in situ was performed. The surface composition is monitored by Auger electron spectroscopy during cleaning process and electron emission yields (backscattered and secondary electrons) as well as the energy distribution of the emitted electrons were measured. The results as well there analyses will be presented at this conference.
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