Initial deposition stage of LiNb0.5Ta0.5O3 films in thermal plasma CVD

Lithium niobate-tantalate (LiNb1−xTaxO3) epitaxial thin films have been prepared on sapphire (0 0 1) (i.e. c-plane) substrates by the thermal plasma spray chemical vapor deposition (TPS CVD) method. In order to achieve better control on the nanometer scale, it is necessary to gain detailed knowledge of the film formation mechanisms involved in film crystallinity and their relationship with the initial stage of film formation. In this work, the initial deposition stage of LiNb0.5Ta0.5O3 films in TPS CVD was studied. The growth mode of LiNb0.5Ta0.5O3 on sapphire (0 0 1) substrates was island growth (the Volmer–Weber mode). The islands with a triangular-pyramid-like shape formed under optimal conditions contributed to the high-crystallinity and high c-axis orientation of epitaxial LiNb0.5Ta0.5O3 films. On the other hand, the nucleation of islands with a dome like shape resulted in LiNb0.5Ta0.5O3 films with poorer both crystallinity and c-axis orientation. Moreover, the energy required for nucleation decreased as the liquid feed rate increased. This suggests that the deposited species might change with the liquid feed rate.