Variation of Sticking Probabilities with Temperature and Coverage, and Desorption Spectra for Nitrogen on Tungsten Films

D. O. Hayward, D. A. King, F. C. Tompkins
1967 Proceedings of the Royal Society A  
From 78 to 150 °K, and at coverages < 8 x 1014 molecules/cm2, the sticking probability s of nitrogen on tungsten films (= 0*9) is independent of both temperature and coverage, whereas at temperatures above 150 °K it is a function of both these variables. These results are interpreted in terms of a physically adsorbed precursor state with a heat of adsorption of ca. 3 kcal/mole. It is concluded that only a fraction of molecules colliding with the surface enter this state and that it is this
more » ... hat it is this fraction wdiich determines the initial value of s at low temperatures. The decrease of s with increasing temperature above 150 °K is a consequence of the inactivity of some planes, such as the (110), at the higher temperatures. Desorption spectra were obtained by warming films from 78 °K to room temperature and recording the subsequent pressure changes as a function of time. From these data the distribution of site energies for the weakly held adsorbate (the ay state) was evaluated, indicating a continuous distribution with heats of adsorption varying between 6 and 20 kcal/ mole.
doi:10.1098/rspa.1967.0070 fatcat:ogewymedzbcdhf3xva6ehecefe