Size effects and chemical tunability in the 2D namo-film catalysts

Ultrathin metal films may be used as well-defined model catalysts for studies in surface catalysis. In the two-dimensional(2D) catalyst systems the film thickness, as the main tunable structural parameter, can be well controlled down to nanometer or atomic-layer scales such that unusual catalytic propertieds apppear due to quantum-confinement at the size of film thickness. Here, the well-defined 2D Al overlayers and atomically flat Pb quantum well films have been grown on Si(111) by molecularbeam wpitaxy. the surface adsorption and reaction were studied by X-ray photelectron spectroscopy(XPS), scanning tunneling microscopy(STM), and high-resolution electron energy loss spectroscopy (HREELS). We could show that the 2D nanostructured Al overlayers on Si including the 2D array of indentical Al nanoclusers and 2D quasi-monolayer Al have much higher reactivity to CH3OH dissociation than the bulk Al films. The 23 and 25 ML Pb films have stronger surface adsorption to O2 in Comparison to the 24 and 26 ML Pb films. It is the quantum confinement at the film thickness that leads to these novel catalytic properties, wihch indicates that the surface reacticity can by tuned via controlling of the size of film thickness.