Photoelectric emission and work function of silver-zinc oxide Ag-ZnO (92/8) pseudo-alloy electrical contacts

Abstract

Abstract Arc roots models require a good knowledge of the physical constants characterizing the contact material used in various kinds of switchgears. Electron work function (EWF) is one of the most important parameters of electron emission for metals and has not yet been studied in detail for pseudo-alloy contact materials. For pure metals, the values of these constants are well known and can easily be found in tables. This is not the case for the new silver-based industrial materials recently available on the market, which are more efficient without the manufacturers knowing the cause. The main goal of this paper is to understand better the photoelectron emission occurring in silver-metal oxide Ag-ZnO (92/8) electrical contacts, before and after several heat treatments from room temperature up to 813 K, under UHV conditions. The photoelectric work function of Ag-ZnO (92/8) pseudo-alloy electrical contacts has been measured by photooelectric effect, using both Fowler’s methods, i.e. isothermal curves method and linearized plots method. It was demonstrated that after several heating treatments in vacuum, the EWF of the silver–zinc oxide, Ag–ZnO (92/8), determined at T = 300 K, is kept within the following interval limits ]ɸ(Ag), ɸ(ZnO)[ = ]4.26 eV, 4.68 eV[. This is due to the evaporation and/or diffusion phenomena which influences the surface composition of the pseudo-alloy electrical contact. Moreover, all the measurements carried out in this study give clearly a demonstrable proof that the EWF of the Ag-ZnO pseudo-alloy should be between the EWF values of each of the two components 4.26 eV for Ag and 4.64 eV for ZnO. Observations and surface analyses carried out under the scanning electron microscope illustrated the development of the surface composition of the Ag-ZnO contact material after several heating treatments in vacuum. Thus, surface analysis of two Ag–ZnO electrical contacts performed before and after VH treatments showed a significant increase of weight proportion for ZnO nanoparticles on the contact surface.