Abstract
The interaction of NH3 with a stepped Fe(100) surface has been studied using electron stimulated desorption ion angular distributions (ESDIAD), thermal desorption spectroscopy (TDS), and low energy electron diffraction (LEED). The goal has been to provide insights into the molecular structure of adsorbed NH3 and the influence of steps on NH3 orientation and dissociation. For low NH3 coverages, θ(NH3)≈0.02, both molecular and dissociative adsorption occurs at step sites. The adsorbed species are believed to include oriented NHx fragments as well as NH3 species which are inclined due to interaction between the NH3 dipole and the dipolar charge distribution at the steps. For higher coverages, up to saturation of the first monolayer (θ(NH3)≈0.34), ESDIAD is dominated by a “halo” H+ pattern indicating the NH3 is bonded via the N atom and the H atoms (with random azimuthal orientation) are pointed away from the surface. The ESDIAD data correlate well with TDS data, where different binding states due to fractional monolayer, second layer and multilayer adsorption are observed. Using Auger electron spectroscopy (AES), it is found that only a small amount of residual nitrogen, θ(N)
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