Two-dimensional (2D) hexagonal boron nitride (hBN) has become integral to the fabrication of heterostructures based on van der Waals 2D crystals. It is a wide-bandgap insulator with a unique combination of properties, including exceptional strength, large oxidation resistance at high temperatures, and optical functionalities. Like many Group III-nitride materials, its covalent bonds are highly polar; presenting the possibility of spontaneous and piezoelectric polarisations in the correct crystalline configurations. In this work, we outline the observation of in-plane piezoelectricity for monolayer (one atom thick) hBN [1] - a property which does not exist for the bilayer or bulk systems. Furthermore, we report on the emergence of spontaneous polarisation and ferroelectricity in anomalously stacked hBN interfaces [2]. Throughout this work we utilise complimentary atomic force microscopy and Kelvin Probe force microscopy imaging to quantify the effects. As well as detailed modelling for in-plane strain profiles and interface relaxation. Both in-plane piezoelectricity and out-of-plane ferroelectricity present exciting possibilities for precise control over device properties.
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6 сен 2024
