Epitaxial growth of YNi 2B 2C films on single crystal MgO substrates: an HRTEM investigation of the interface

Abstract

Epitaxial thin films of the superconducting borocarbide compound YNi 2B 2C have been grown on single-crystal MgO (001) substrates using pulsed laser deposition. The deposition temperature has a strong influence on the structural properties of the films, which in turn affect the superconducting transition temperature, T c. The resulting phases and their orientations with respect to the substrate have been investigated by X-ray diffraction and HRTEM, using cross-section samples. For deposition temperatures around 750 °C, c-axis oriented growth of YNi 2B 2C films occurs preferentially. At lower temperatures a weaker a-axis orientation was found by X-ray diffraction, whereas by HRTEM grains with a-axis and a weak c-axis orientation could be identified. An interfacial layer some 100 nm thick was formed bordering on the substrate, comprising mainly Y 2O 3 but also other epitaxially grown phases such as YNi 4B. The growth directions of Y 2O 3 are [001] at 750 °C and [111] at lower temperatures. The in-plane orientations and the lattice mismatches of the bordering phases were also investigated.