DETERMINATION OF THE RATES OF BOTH WORK FUNCTION CHANGE AND RESIDUAL-GAS ADSORPTION ON A TUNGSTEN SURFACE HEATED IN A HIGH-VACUUM

The work functions (phi(+) and phi(e)) effective for thermal positive-ionic and electronic emissions from a heated tungsten surface were measured as a function of the time (t) elapsing immediately after the surface made essentially clean by flashing was adjusted to a working temperature (similar to 1800-1500 K). The quantities (Q) of residual gases (RG) adsorbed during t were also measured by flash desorption mass spectrometry of O+ and CO+ produced by electron impact of desorbed gases. Analysis of the data thus obtained yielded the rate expressions of Y-n = A(n)-B-n exp [-C(n)t], where Y-1-Y-3 are phi(+), phi(e) and Q, respectively, and A(n)-C-n are the constants corresponding to respective ns. Comparison among the expressions indicates that the work function increases (by up to similar to 0.7 eV) generally observed by the temperature decrease from similar to 2300 K to 1500 K is caused mainly by adsorption of oxygen and/or oxygen compounds included in RG.