SURFACE STRAIN IMPROVES MOLECULAR ADSORPTION BUT HAMPERS DISSOCIATION FOR N2 ON THE FE/W(110) SURFACE
Surface strain, which brings important changes in the original electronic structure, can effectively be used to alter the adsorption properties and reactivity on surfaces.
In most cases, as known from both theory and experiments, the adsorption of gas species increases with tensile stretching, while decreases with crystal lattice compression. There are exceptions to this simplified picture, but what it is common to all the examples reported so far is that the overall adsorption properties of the surface are equally modified from the unstrained to the strained surface. However, in the work published in Physical Review Letters, Goikoetxea et al. show an intriguing case that highly contrasts with the existing understanding on this matter.
Their comparative study on the adsorption dynamics of N2 on Fe(110) and on the strained Fe/W(110) surfaces explains previous experiments showing that the inertness of Fe(110) towards N2molecular adsorption disappears on Fe/W(110). As an unexpected outcome, the authors find that the number of dissociation events are on the contrary considerably reduced on Fe/W(110) and, therefore, that the atomic N observed experimentally on Fe/W(110) cannot be the direct result of surface strain as originally thought. The atypical observation of a combined molecular adsorption improvement and dissociative adsorption reduction contravenes the common notion that associated surface strain with either an overall increase or an overall reduction of all kind of adsorption events. As the authors argue in this letter, the reasons behind this unusual behavior are ultimately related with the large (10%) tensile stretching of the Fe monolayer that hampers the efficiency of the N-Fe interaction in triggering dissociation. This work opens a new perspective on the role of surface strain to control the adsorption properties on surfaces, since the central condition of a large tensile stretching can be achieved with many heteroepitaxial surfaces.