On the Temperature Dependence of the Photoelectric Work Function of Contact Materials

The nature of the contact material plays a key role to determine the characteristics of the electric arcs and particularly those of the electronic emission. Mechanical and thermodynamic properties as well as electron emission of such complicated alloys present a lack of reliable and accurate experimental data. The purpose of this paper is to present the development of a method for measuring photoelectric work function of pure contact materials that are actually used in relays. Also reported in this manuscript are the results of experimental work whose purpose has been the buildup of a reliable photoelectric system and associated monochromatic ultra-violet radiations source, and the photoelectric measurement of the electron work functions (EWF) of contact materials. In order to study the influence of temperature on the EWF, a vacuum furnace was used for heating the metallic samples up to 700 K. The Fowler's method of isothermal curves was used for the photoelectric measurement of the EWF. As a first test of the experimental UHV set-up, the EWF of the silver contact materials, namely pure polycrystalline metals (Ag, Cu, Ni, Sn and Zn) were investigated to study the influence of surface cathode temperature on the EWF. In the present study, the photoelectric measurements about silver contacts have shown a linear decrease of the EWF with increasing temperature, i.e. the temperature coefficient alpha = dphi : dt is constant and negative: alpha = -4.58 x 10(exp -4) eV / K in the experiment temperature range [300 K - 780 K].