Thickness-dependent in-plane polarization and structural phase transition in van der Waals Ferroelectric CuInP2S6

Abstract

Van der Waals (vdW) layered materials have rather weaker interlayer bonding than the intra-layer bonding, therefore the exfoliation along the stacking direction enables the achievement of monolayer or few layers vdW materials with emerging novel physical properties and functionalities. The ferroelectricity in vdW materials recently attracts renewed interest for the potential use in high-density storage devices. As the thickness going thinner, the competition between the surface energy, depolarization field and interfacial chemical bonds may give rise to the modification of ferroelectricity and crystalline structure, which has limited investigations. In this work, combining the piezoresponse force microscope scanning, contact resonance imaging, we report the existence of the intrinsic in-plane polarization in vdW ferroelectrics CuInP2S6 (CIPS) single crystals, whereas below a critical thickness between 90-100 nm, the in-plane polarization disappears. The Young's modulus also shows an abrupt stiffness at the critical thickness. Based on the density functional theory calculations, we ascribe these behaviors to a structural phase transition from monoclinic to trigonal structure, which is further verified by transmission electron microscope technique. Taken together, these findings demonstrate the foundational importance of structural phase transition for enhancing the rich functionality and broad utility of vdW ferroelectrics.

References in corpus (6)

• Photovoltaic effect in an electrically tunable van der Waals heterojunction
• Out-of-plane Piezoelectricity and Ferroelectricity in Layered $\alpha$-In2Se3 Nano-flakes
• Determination of band alignment in the single layer MoS2/WSe2 heterojunction
• Quantum engineering of transistors based on 2D materials heterostructures
• Asymmetric phase diagram of mixed $CuIn{P}_2(S_{x}S{e}_{1-x}{)}_6$ crystals
• Non-monotonic thickness dependence of Curie temperature and ferroelectricity in Two-dimensional SnTe film

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• Opportunities in Electrically Tunable 2D Materials Beyond Graphene: Recent Progress and Future Outlook
• Unconventional ferroelectric domain switching dynamics in CuInP2S6 from first principles
• Interface-tuning of ferroelectricity and quadruple-well state in CuInP${}_2$S${}_6$ via ferroelectric oxide
• Tunable photochemical deposition of silver nanostructures on layered ferroelectric CuInP${}_2$S6
• Deciphering the lattice vibrational behaviors of CuInP2S6 by angle-resolved polarized Raman scattering
• The ground state of CuInP${}_2$S${}_6$ thin films: A study of the deep potential method