Metastable Few-Layer GeS van der Waals Ferroelectrics Stabilized in SnS-GeS Heterostructures

2D and layered van der Waals semiconductors have attracted interest as alternatives to conventional oxide ferroelectrics, combining attributes such as facile materials integration, distinct symmetry-breaking and polarization mechanisms, and bandgaps in the visible and near-infrared spectral region. Often, growth processes that produce high-quality ferroelectrics of a layered crystal are not easily adaptable to other materials, even within the same family. Here, we show that in such cases, a nonequilibrium ferroelectric crystal phase can be templated from one material into another across interfaces in heterostructures. Growing two types of layered SnS-GeS heterostructures, using seed crystals of equilibrium (centrosymmetric) SnS or a metastable (distorted) phase of SnS, respectively, we find that the distorted noncentrosymmetric phase can be templated from SnS to GeS. This templating effect is identified both across vertical (van der Waals) interfaces and at lateral (covalent) interfaces of the synthetic heterostructures. Furthermore, in vertically stacked regions, the GeS layers also inherit the ferroelectric stripe domain patterns from the underlying SnS seed. Heterostructures using centrosymmetric SnS seeds, on the other hand, incorporate the nonferroelectric equilibrium phase of GeS throughout. Within the studied materials system, the findings point to a rational route for obtaining ferroelectric Ge monochalcogenides. More broadly, the results indicate that interfaces in heterostructures between van der Waals crystals allow transcribing nonequilibrium crystal structures between dissimilar materials, which can be used to access distinct structures and functional properties.