Strong Pyramidal Growth of Metal Films Studied with IR Transmittance and Surface Enhanced IR Absorption of CO

Metal-film surfaces show well ordered facets if grown at sufficiently high temperature and at relatively small deposition rate. Such films may grow as pyramids that become increasingly steep with more coverage. On MgO(001) at about 400 °C iron forms nanoparticles with a shape like cuboids. These cuboids avoid coalesce with further deposition, and therefore they are an interesting system for effects that involve field enhancement, like for example surface enhanced infrared absorption of adsorbate vibrations. In this work we show that for such films the percolation is extended over a broad coverage range. Surface enhanced infrared absorption of CO adsorbed on the film shows the asymmetry of the C−O stretch line, which is typical for films near the percolation threshold. Both the line shape and the line intensity do not change remarkably above a certain average film thickness.