Adsorption of nitrogen on single crystal faces of iridium,studied by field emission microscopy

The adsorption of nitrogen on iridium was studied with a field emission microscope equipped with a probe-hole assembly to enable emission experiments on individual emitter regions. The adsorption of nitrogen is markedly face-specific. Temperature programmed desorption reveals three binding states: γ₁ on the (100) face with a maximum heat of adsorption of 7–8 kcal/mole, γ₂ on the regions around (110) with a maximum heat of adsorption of 10–11 kcal/mole and γ₃ on the roughest tip regions (210), (320), (531) and (731) with a maximum heat of adsorption of 13–14 kcal/mole. Nitrogen adsorbed in the γ₁ and γ₃ states causes a decrease, but in the γ₂ state a small increase, in the work function. These results are discussed in relation with data on nickel, palladium, platinum and rhodium. While nitrogen is only weakly adsorbed on all these metals there is a marked difference in the nature of the pertinent adsorption complex.