Highly heterogeneous epitaxy of flexoelectric BaTiO3-δ membrane on Ge

Abstract

The integration of complex oxides with a wide spectrum of functionalities on Si, Ge and flexible substrates is highly demanded for functional devices in information technology. We demonstrate the remote epitaxy of BaTiO3 (BTO) on Ge using a graphene intermediate layer, which forms a prototype of highly heterogeneous epitaxial systems. The Ge surface orientation dictates the outcome of remote epitaxy. Single crystalline epitaxial BTO3-δ films were grown on graphene/Ge (011), whereas graphene/Ge (001) led to textured films. The graphene plays an important role in surface passivation. The remote epitaxial deposition of BTO3-δ follows the Volmer-Weber growth mode, with the strain being partially relaxed at the very beginning of the growth. Such BTO3-δ films can be easily exfoliated and transferred to arbitrary substrates like Si and flexible polyimide. The transferred BTO3-δ films possess enhanced flexoelectric properties with a gauge factor of as high as 1127. These results not only expand the understanding of heteroepitaxy, but also open a pathway for the applications of devices based on complex oxides.

Applications of remote epitaxy and van der Waals epitaxy

“…COMSOL FEM calculation with a tip-force model of the BTO film under applied force 28nN(up) and 196nN(down). The colors of blue to red correspond to lower to higher strain values [ 77 ] …”

“…The strength of flexoelectric polarization becomes stronger as the flexoelectric film becomes a freestanding film and possesses smaller dimensions because of the increase in strain gradient. As an example, a flexoelectric BaTiO 3 -δ (BTO) film with a cubic phase was remote-epitaxially grown on a graphene-covered Ge substrate [ 77 ]. In contrast to tetragonal BTO films, the cubic BTO film did not show piezoelectric property at room temperature, which was confirmed by piezo-response force microscopy (PFM) measurement.…”

Freestanding Perovskite Oxide Membranes: A New Playground for Novel Ferroic Properties and Applications

“…Dai et al reported the transferred BaTiO 3−𝛿 films, with the strain being partially relaxed at the very beginning of the growth, possess enhanced flexoelectric properties with a gauge factor of as high as 1127 (Figure 6c-e). [54] Along this line, the great flexibility and strain gradient tunability are of great interest for the exploration of intriguing flexo-effects, like flexoelectric and flexomagnetic effects, and the coupling between them. The interaction between flexo-and ferro-effects are also an interesting topic to be studied in oxide membranes.…”

Flexible strategy of epitaxial oxide thin films

“…deposited various oxide thin films (ZnO, NiO, STO, and CFO) on different crystalline oxide substrate with MoS 2 as the interlayer ( Ma et al., 2021 ). Other than that, epitaxial BaTiO 3-δ thin film on Ge ( Dai et al., 2022 ) and yttrium iron garnet film on gadolinium gallium garnet ( Leontsev et al., 2022 ) have been achieved by applying graphene as the interlayer. The remote epitaxy method has been employed more and more on fabricating freestanding epitaxy oxide thin films, which could be a critical approach toward both fundamental research and practical applications of epitaxial oxide thin films.…”