Applied Surface Science, Vol.254, No.2, 436-440, 2007
Stress dependence of growth mode change of epitaxial layered cobaltite gamma-Na0.7CoO2
We report stress dependence of growth characteristics of epitaxial gamma-Na0.7CoO2 films on various substrates deposited by pulsed laser deposition method. On the sapphire substrate, the gamma-Na0.7CoO2 thin film exhibits spiral surface growth with multi-terraces and highly crystallized texture. For the gamma-Na0.7CoO2 thin film grown on the (1 1 1) SrTiO3 substrate, the nano-islands of similar to 30 nm diameter on the hexagonal grains are observed. These islands indicate that: the growth mode changes from step-flow growth mode to Stranski-Krastanow (SK) growth mode. On the (1 1 1) MgO substrate, the large grains formed by excess adatoms covering an aperture between hexagonal grains are observed. These experimental demonstrations and controllability could provide opportunities of strain effects of NaxCoO2, physical properties of thin films, and growth dynamics of heterogeneous epitaxial thin films. (c) 2007 Elsevier B.V. All rights reserved.