A Method for Measuring the Photoelectric Work Function of Contact Materials Versus Temperature

Abstract

The nature of the contact material plays a key role to determine the characteristics of electrical arcs and particularly those related to electronic emission. Mechanical and thermodynamic properties as well as electronic 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 functions of contact materials. Also reported in this paper are the results of experimental work whose purpose has been the buildup of a reliable photoelectric system and associated monochromatic ultraviolet radiations source, and the photoelectric measurement of the EWF of contact materials. As a first test of the experimental Ultra High Vacuum setup, the electron work functions (EWF) of silver contacts, namely pure polycrystalline metals that are actually used in relays, were measured photoelectrically, using both Fowler's method of isothermal curves and linearized Fowler plots. Ultrahigh vacuum techniques were employed to obtain residual gas pressure of about 5×10 −9 mbar that allows accurate and reliable photoelectric work function measurements. The EWF measured at room temperature of polycrystalline Ag contact (as commercially available) increased from 3.70 eV before heating, to 4.30 eV, and finally, stabilized at the vicinity of 4.26 eV after several vacuum heat treatments at 533 and 773 K. The EWF value obtained, i.e., 4.26 ± 0.03 eV, is in good agreement with the results found in the literature. This shows that the experimental method is valid and the experimental setup is usable. Furthermore, new photoelectric measurements versus temperature have shown a linear decrease of the EWF of silver contacts with increasing temperature, i.e., the temperature coefficient α = dφ/d t is constant and negative α = −4.58 · 10 −4 eV/K in the experiment temperature range 300-780 K.Index Terms-Contact materials, electron work function (EWF), Fowler's Methods, photoemission, temperature dependence, vacuum heat treatment.

Electrodes for Semiconductor Gas Sensors

“…Neglecting Δ Ф , Equation (3) reduces to Equation (2) when Ds = 0. In the literature, there are numerous experimental date [ 33 , 134 , 135 , 136 ] on Ф M . Table 4 gives the most preferred experimental values of work function for important metals.…”

Searching for evidence of optical rectification: optically induced nonlinear photovoltage in a capacitor configuration

“…Published values show that the work function of gold may change as much as 0.7 eV at 770 K due to high oxygen absorption at high temperatures [29]. However, a different mechanism suggests that the work function of silver changes about 0.2-0.3 eV at 700 K [36]. These numbers suggest that the work function of the electrode consisting of a thin gold layer on top of ITO glass will decrease by a couple of tenths of an electron volt for a one-hundred-degree temperature increment.…”