Cation off-stoichiometric SrMnO3−δ thin film grown by pulsed laser deposition

The laser energy density (laser fluence) dependency of the Sr/Mn ratio was investigated for SrMnO3−δ (SMO) thin films grown by pulsed laser deposition (PLD). It was found that the Sr/Mn ratio showed a steep increase followed by a gradual increase as the laser fluence was increased. However, the Sr/Mn ratio always showed Mn-excess under the present laser fluence condition as long as stoichiometric SrMnO3 targets were used. In order to obtain cation stoichiometric SMO films, it was necessary to use Sr-excess SrMnO3 targets in addition with laser fluence tuning. The crystal quality of the SMO thin film was found to vary with the Sr/Mn ratio. In stoichiometric or Sr-excess SMO thin films, epitaxial thin films could be obtained, whereas Mn-excess thin films showed very low crystallinity. Sr-excess films were also found to have some extra SrO planes. In addition, they exhibited out-of-plane lattice expansion which electron energy loss spectroscopy analysis revealed was due to Mn vacancies. The variation of film growth was closely related to point defects due to excess cations included in growing thin films.