Metal supported low-dimensional oxide nanostructures: strain effects, electronic interactions and magnetic behaviour

Full text: The interfacial coupling of a nanoscale oxide material to a metal surface creates a hybrid system with novel and often unprecedented physical and chemical properties that are not shared by the individual components of the system. The dimensionality of the oxide phase adds a further parameter to a oxide-metal hybrid system, which may be used as a tunable model for the study of emergent phenomena of low-dimensional (low-D) materials. Low-D oxide nanostructures on well-defined metal surfaces can be fabricated with atomic-scale design control using bottom-up directed self-assembly and a surface science methodology. Here we discuss the elastic and electronic effects introduced by the oxide-metal interface and how they determine the novel structure concepts that are encountered in low-D oxide nanophases on metal surfaces. The systems of interest are the oxides of Mn, Co, and Ni, which in monoxide form share a common rock-salt structure in the bulk and antiferromagnetic ordering behaviour. Their properties in low-D hybrid systems on noble metal surfaces are investigated here. The phase diagrams of 2-D oxide nanolayers reflect the flexibility of the oxidation states of the respective metals cations: this is illustrated by Mn oxides on Pd surfaces, which display a very complex phase behaviour, whereas the Ni oxide phases on Pd or Ag substrates are much simpler. A complex nanoscale morphology as a result of the interplay of elastic and electronic effects has been found for Mn oxide nanostripes on stepped Pd surfaces and for 2-D Ni oxide nanostructures embedded in a Ag(100) substrate. The magnetic response of 2-D Mn oxides show emergent behaviour and the high chemical reactivity of 1-D Mn and Ni oxide nanowires is emphasized. Finally, some preliminary results on the growth of low-D ceria nanostructures on Au will be briefly presented. (author)