Probing electric polarization at solid-liquid and solid-solid interfaces in van der Waals heterostructures

Session

Poster Session 2

Authors

Ms Harriet Nevison-Andrews (1), Dr Pablo Ares (1), Mr James Dougherty (1), Dr Rui Wang (1), Dr Rene Fabregas (1), Dr Thomas Dufils (1), Dr Laura Fumagalli (1)

Affiliations

1. University of Manchester

Keywords

Scanning probe microscopy, scanning dielectric microscopy, electrostatic force microscopy, Kelvin probe force microscopy, 2D materials, permittivity, interfacial water, hexagonal boron nitride

Abstract text

Electric polarization is a fundamental physical property, represented by the dielectric constant, or permittivity, which quantifies how materials respond to an electric field. It is of great significance when seeking to understand the properties of materials, and has major technological applications in a variety of fields, including energy storage, electronics, electrochemistry, biochemistry, micro/nanofluidics, and molecular sensing. However, our understanding of polarization has traditionally been limited to bulk systems, with sizes down to the microscale, as such systems can be probed by standard dielectric spectroscopy equipment. Probing electric polarization at the nano- and atomic scale, particularly at the interface between materials and liquids, has remained a technical challenge due to the lack of sufficiently sensitive tools. 

 

In this work, we used advanced scanning probe methods to probe electric polarization at the atomic scale, focusing on solid/liquid and solid/solid interfaces in van der Waals (vdW) heterostructures. First, we followed up our recent study [1] in which we applied scanning dielectric microscopy [2] to nanoslits constructed from vdW crystals and filled with water [3]. We succeeded in probing the dielectric polarization properties of water confined inside slits made of various vdW crystals. Our experiments revealed an anomalously low out-of-plane polarization of water at the solid-liquid interface with vdW crystals, irrespective of the composition of the slits. Secondly, by using electrostatic force microscopy and Kelvin probe force microscopy, we probed the electric polarization properties of solid-solid interfaces in vdW heterostructures. We found that heterostructures made of twisted hBN crystals - that is, two crystals stacked at a small twist angle - show ferroelectric-like domains arranged in triangular superlattices, which we attributed to out-of-plane dipoles forming at the interface of the two crystals [4]. These findings open up interesting new avenues for the design of heterostructures with ferroelectric properties, based on vdW crystals and confined water.

References

[1] L. Fumagalli, A. Esfandiar, R. Fabregas, S. Hu, P. Ares, A. Janardanan, Q.Yang, B. Radha, T. Taniguchi, K. Watanabe, G. Gomila, K. S. Novoselov, A. K. Geim Anomalously low dielectric constant of confined water. Science 360, 1339-1342 (2018).

[2] L. Fumagalli, D. Esteban-Ferrer, A. Cuervo, J.L. Carrascosa, G. Gomila Label-free identification of single dielectric nanoparticles and viruses with ultraweak polarization forces. Nature Mater. 11, 808-816 (2012).

[3] B. Radha, A. Esfandiar, F. C. Wang, A. P. Rooney, K. Gopinadhan, A. Mishchenko, A. Janardanan, P. Blake, L. Fumagalli, M. Lozada-Hidalgo, S. J. Haigh, I. V. Grigorieva, H. A. Wu, A. K. Geim Designer capillaries made with atomic scale precision. Nature 538, 222 (2016).

[4] C. R. Woods, P. Ares, H. Nevison-Andrews, M. J. Holwill, R. Fabregas, F. Guinea, A. K. Geim, K. S. Novoselov, N. R. Walet, L. Fumagalli Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride Nat. Commun. 12, 347 (2021).