THE INTERACTION OF N-2 WITH IRON ON W(110), PD(111) AND RH(111)

We have studied the interaction of molecular nitrogen with thin iron f ilms on W(110), Pd(111) and Rh(111) using angular resolved spectroscop y (ARUPS). Iron layers on W(110) with thicknesses of up to 2 layers ar e strained thereby acquiring the lattice constant of the substrate. Al so a moire like superstructure has been studied. In contrast to result s obtained for Fe(110) we find molecular adsorption at low temperature s as well as dissociation of nitrogen molecules on strained Fe/W(110). In agreement with calculations we find an upward shift of the iron 3d band density which might be the reason for the enhanced reactivity of Fe/W(110) as compared to Fe(110). In order to study the influence of the substrate on the interaction with nitrogen we have investigated fi lms with different thickness. Iron layers on Pd(111) and Rh(111) have been studied since the strain of pseudomorphic iron films on these sub strates is intermediate between that of Fe/W(110) and. unstrained Fe(1 10). We find the formation of surface compounds and iron diffusion int o the substrate at elevated temperatures. The chemical activity of the compound films is intermediate between those of pseudomorphic Fe on W (110) and Fe(110).