Epitaxial growth of LiCoO2 thin films with (001) orientation

The layered structure of LiCoO2 implies anisotropic ionic conduction; however, experimental data have never demonstrated this. The anisotropy can be observed clearly in epitaxial films with controlled orientations. Our previous study had reported that LiCoO2 grows epitaxially on Nb-doped SrTiO3 (100) and (110) substrates with complete (104) and (018) orientations, respectively. On the other hand, the growth on SrTiO3 (111) substrates with (001) orientation was accompanied by the inclusion of (012)-oriented domains, although the (012) orientation is higher in the energy state than the (001). The present study reveals that lower laser energy density (fluence) and lower substrate temperature decrease the amount of inclusions; that is, the occurrence of the (012) orientation in spite of its higher energy is governed by these factors. Higher fluence leading to higher deposition rates does not provide sufficient time for the cations to be rearranged into the (001) orientation, and the higher substrate temperature increases the nucleation frequency for the (012) orientation. A micrograph of the final (001)-oriented film reveals that the LiCoO2 film grows in an island growth mode.