Self-organized formation of a-few-nanometer sized nanocolumns in chalcogenide-oxide nanocomposite film

Abstract

Nanocomposite films are thin films with the addition of nano-sized second phases, and they are very promising for improving properties of chalcogenide films, such as superconducting vortex pinning. However, there are very few reports on the chalcogenide nanocomposite films, although many researchers are studying the oxide nanocomposite films. Since the process conditions for chalcogenide films are different from those for oxide films, the chalcogenide nanocomposite films are expected to have a characteristic structure. Here, we show fabrication of chalcogenide nanocomposite films containing self-organized oxide nanocolumns. FeSe+SrTiO3(STO) nanocomposite films were prepared using pulsed laser deposition, where the FeSe target with the STO sector was laser-ablated. The FeSe matrix kept the epitaxial relationship with LaAlO3 substrates even in the nanocomposite films, but the crystallinity and orientation of FeSe were degraded. Transmission electron microscopy observation clarified that Sr-Ti-O nanocolumns with the diameter of 2-5 nm and the spacing of <10 nm were formed at the deposition temperature of 450-550 ºC and the STO content of <25areal%. The formation of the FeSe+STO nanocomposite was affected by the low deposition temperature and interface instability. As a result, the nanocolumn diameter in the present chalcogenide-oxide nanocomposite was smaller than that in the oxide-oxide nanocomposites. This nanocolumn morphology (shape, diameter, and spacing) is expected to effectively influence the properties of chalcogenides.