Phase and polarization modulation in two-dimensional In ₂ Se ₃ via in situ transmission electron microscopy

Abstract

Phase transitions in two-dimensional (2D) materials promise reversible modulation of material physical and chemical properties in a wide range of applications. 2D van der Waals layered In 2 Se 3 with bistable out-of-plane ferroelectric (FE) α phase and antiferroelectric (AFE) β′ phase is particularly attractive for its electronic applications. However, reversible phase transition in 2D In 2 Se 3 remains challenging. Here, we introduce two factors, dimension (thickness) and strain, which can effectively modulate the phases of 2D In 2 Se 3 . We achieve reversible AFE and out-of-plane FE phase transition in 2D In 2 Se 3 by delicate strain control inside a transmission electron microscope. In addition, the polarizations in 2D FE In 2 Se 3 can also be manipulated in situ at the nanometer-sized contacts, rendering remarkable memristive behavior. Our in situ transmission electron microscopy (TEM) work paves a previously unidentified way for manipulating the correlated FE phases and highlights the great potentials of 2D ferroelectrics for nanoelectromechanical and memory device applications.

Polymorphism and Ferroelectricity in Indium(III) Selenide

“…The decomposed In from In 2 O 3 reacts with sublimed Se to form In 2 Se 3 on a substrate placed downstream. When the high-temperature as-grown β-In 2 Se 3 is cooled to room temperature, β′-In 2 Se 3 is obtained. , CVD has also been shown to synthesize specific polymorphs and polytypes of In 2 Se 3 via the regulation of growth temperatures, heating positions, and substrates . Samples prepared using CVD are usually polycrystalline in nature.…”

“…The phase conversions of In 2 Se 3 can be driven by thermal, strain, and electric field. Zheng and co-workers demonstrated strain-modulated reversible β′-to-α phase conversion of In 2 Se 3 on an amorphous carbon substrate . By applying a compressive stress with a tungsten tip in TEM, an in situ β′-to-α phase transition was observed as wrinkles developed on a flat sample.…”

“…(c) Joule heating by electric field modulation to transform α-In 2 Se 3 to β′- and γ-In 2 Se 3 . Adapted with permission from ref . Copyright 2022 American Association for the Advancement of Science.…”

Bend-Induced Ferroelectric Domain Walls in α-In2Se3

“…Here, we investigate the impact of nanoscale bending in α-In 2 Se 3 , a room-temperature van der Waals ferroelectric with a thickness-dependent Curie temperature of 533–700 K. − α-In 2 Se 3 has been used in field-effect transistors, memristors, neural computing, and nonvolatile memories . Moreover, α-In 2 Se 3 exhibits rich electromechanical behavior, such as strain-induced phase changes and flexoelectric effects . We utilize bending in α-In 2 Se 3 to probe electromechanical coupling in a previously unstudied limit: in a strongly polarized, ferroelectric material under extreme bending down to a 0.3 nm radius of curvature, where electromechanical coupling should be the strongest.…”

Oscillatory Order–Disorder Transition during Layer-by-Layer Growth of Indium Selenide

“…16 A β polymorph variant, named β′, manifests as a one-dimensional (1D) periodic nanostriped domain and has been proposed to be antiferroelectric. 17 The α and β polymorphs can also be electrically switched, and the conversion of the domains has been observed in situ using transmission electron microscopy (TEM) 18 and scanning tunneling microscopy (STM). 19 The β phase appears to be structurally reconfigurable between a crystalline phase and an amorphous phase, although the mechanism involved is not clear.…”