Chemisorption of Nitrogen on Tungsten

Abstract

Chemisorption studies are made in a closed system by a mass spectrometer operated statically and it is found that tungsten surface has three chemisorption states α, ε , and ζ for nitrogen. These chemisorption states have properties as follows; α is about 5% of the total saturation coverage and an unstable dissociative adsorption state of which the heat of chemisorption is 0.7 8 eV, ε is 60%∼65% and a non-dissociative adsorption of 3.6 5 eV, and ζ is 35%∼30% and a dissociative adsorption of 3.0 eV. “Activation energies” of chemisorption for ζ and ε -states are -0.07 5 and about -0.08 eV, respectively. The sticking probabilities are 0.5 for ζ and 0.02∼0.04 for ε and about 0.2 for the apparent value of ε at room temperature. At room temperature, adsorption to the three states occurs simultaneously at low coverages and the average sticking probability is 0.2. At the vicinity of the completion of the monolayer, however, the ε -adsorption only takes place. As it is verified that the strongest chemisorption state consists of the ε and ζ-states, previous reports of other authors for chemisorption of nitrogen on tungsten are reconsidered.