Interfacial effects on the structure of thin metal films

Three studies of thin metal films grown on semiconductor and insulator substrates are presented. Thin films grown on a substrate decorated by a periodic array of atomic wires can exhibit unusual properties such as stacking faults and electronic topological phase transitions due to the interfacial modulation. We report a study of Ag films grown on an array of atomic In chains on . Prior STM studies have suggested an array of stacking faults in the Ag films that allow the film lattice structure to match the interfacial modulations. STM however can only probe the surface. Our work uses x-ray diffraction to elucidate the internal 3-dimensional structure of this system. The measurements are found to be best explained by a model in which the unit cell contains a single stacking fault. When the thickness of a thin film approaches the nanoscale significant changes in its properties can occur known as quantum size effects. Bilayer oscillations in the preferred island heights as a function of thickness in Pb films grown on substrates is one example of a quantum size effect that is now well understood. Here we present a study of Pb films grown on sapphire substrates and present evidence of quantum size effects in a metal on insulator system. Intriguing difference between the Pb on Si system and this system are observed. The crossover between preferences for even and odd thicknesses is not observed in this system, over the range of thicknesses studied, as they are in the Pb on Si case. The preferred heights are found to have much greater thermal stability demonstrating a connection between the quantum growth of thin films and the substrate band gap. By growing thin films from materials with substantially different electronic properties interesting changes in the quantum growth behavior should also be observable. In the third study reported surface x-ray diffraction experiments on In films grown on Si substrates are presented. In films are grown on and substrates. The surface is found to persist upon burial by the film. Although preferences for island heights at low coverages have been observed no observation of preferred island heights above 7 monolayers (ML) have been made in previous studies of this system. Our experiments show that by annealing the sample a preference for islands 13 ML in height can be seen