Graphoepitaxial growth of CeO2 thin films on tilted-axes NdGaO3 substrates by pulsed laser deposition

Abstract

CeO₂ thin films were grown on NdGaO₃ tilted-axes substrates by pulsed laser deposition (PLD) showing three-dimensional graphoepitaxial (3DGE) growth in the whole studied range of substrate tilt angles γ = 5-27º. Deviations from the tangent dependence can be divided into a systematic negative part and local deviations near certain film tilt angles. The systematic deviation may be explained as the effect of completely-strained coherent growth of the bottom layers of CeO₂ film. Minimization of the surface energy near the small-index crystallographic planes (012) and (013) may account for the local deviations from the calculated dependence. The width of the rocking curve and the lattice constant variation for the 3DGE CeO₂ films increase almost linearly with the substrate tilt angle until 19º and decrease for higher γ.

At different deposition rates the 3DGE CeO₂ film exhibits three possible structures: (i) relaxed completely oxygenated films at very low deposition rate, (ii) completely strained well-oxygenated films at moderate deposition rates, and (iii) oxygen-deficient films consisting of two layers at high deposition rates. The deviations of orientation of the film from the 3DGE formula are set by the lattice constant c in the direction normal to the (110) SICP of the substrate, which, in turn, depends on oxygen deficiency and the level of strain, introduced into the film by lattice mismatch with the substrate.