Intrinsic Properties of Ferroic Materials Independent of Substrate Effects

Substrates are essential in thin-film deposition, yet they do not always meet the specific requirements of a given experiment or application and, in some cases, may even hinder in intrinsic measurements of epitaxial thin films. For example, SrTiO₃, one of the most widely used substrates, goes through an antiferrodistortive transition at 105 K which can lead to substrate artefacts extrinsic to the thin film properties grown atop the substrate. However, the bulk of the substrate in its single crystal form is not required to support epitaxy, as only the top few unit cells near the surface define the epitaxial template for thin film growth. We introduce the novel concept of "vector substrates" where the template layer for epitaxy can be chosen independently of the bulk of the substrate. Thus, by choosing the right combination of a bulk carrier substrate and the template layer, we can reduce, if not eliminate artefacts resulting from the behaviour of the bulk substrate. The fabrication of vector substrates leverages thin-film membrane technology by growing a template layer on a parent substrate and then transferring it onto a carrier substrate, thereby generating the vector substrate. By comparing the magnetism of La_0.67Sr_0.33MnO₃grown on a conventional SrTiO₃ substrate and a SrTiO₃-on-sapphire vector substrate, we show that we can indeed eliminate the extrinsic antiferrodistortive artefact on a vector substrate. Therefore, the concept of vector substrates can provide a platform to measure ferroic thin films and the characteristics independent of substrate effects.<br/><br/><b>References:</b><br/>V. Harbola et al., Vector Substrates: Idea, Design, and Realization, Adv. Func. Mater. (In press) Article DOI: 10.1002/adfm.202306289 (2023).