Ferroelectric 2D ice under graphene confinement

Hao-Ting Chin,I-Fan Hu,Jiri Klimes,Shao-Wei Ma,Mario Hofmann,Ya-Ping Hsieh,Ding-Rui Chen,Chi-Te Liang,Hai-Thai Nguyen,Ting-Wei Chen

doi:10.1038/s41467-021-26589-x

Abstract

We here report on the direct observation of ferroelectric properties of water ice in its 2D phase. Upon nanoelectromechanical confinement between two graphene layers, water forms a 2D ice phase at room temperature that exhibits a strong and permanent dipole which depends on the previously applied field, representing clear evidence for ferroelectric ordering. Characterization of this permanent polarization with respect to varying water partial pressure and temperature reveals the importance of forming a monolayer of 2D ice for ferroelectric ordering which agrees with ab-initio and molecular dynamics simulations conducted. The observed robust ferroelectric properties of 2D ice enable novel nanoelectromechanical devices that exhibit memristive properties. A unique bipolar mechanical switching behavior is observed where previous charging history controls the transition voltage between low-resistance and high-resistance state. This advance enables the realization of rugged, non-volatile, mechanical memory exhibiting switching ratios of 106, 4 bit storage capabilities and no degradation after 10,000 switching cycles.

Highlights

We here report on the direct observation of ferroelectric properties of water ice in its 2D phase
No clear evidence of water ice with the necessary proton ordering has been reported leading to the coining of the term “UFI” in the literature[4]
Theoretical predictions suggest that the confined conditions between two graphene layers could generate atomic layers of ice with a preferential dipole orientation that results in ferroelectric ordering[10,11]

Summary

Introduction

We here report on the direct observation of ferroelectric properties of water ice in its 2D phase. We here demonstrate direct evidence for the formation of ferroelectric ice when water is actively confined to a monolayer between two layers of graphene. The robust and room-temperature stable ferroelectric response of ice at the graphene interface represents a new phase of water but can be applied to impart nanoelectromechanical devices with unexpected properties.

Results

Conclusion