Direct observation of ferroelectricity in two-dimensional MoS2

Alexey Lipatov, Pradeep Chaudhary, Zhao Guan, Haidong Lu, Gang Li, Olivier Crégut, Kokou Dodzi Dorkenoo, Roger Proksch, Salia Cherifi-Hertel, Ding Fu Shao, Evgeny Y. Tsymbal, Jorge Íñiguez, Alexander Sinitskii, Alexei Gruverman

Research output: Contribution to journalArticlepeer-review

Abstract

Recent theoretical predictions of ferroelectricity in two-dimensional (2D) van der Waals materials reveal exciting possibilities for their use in scalable low-power electronic devices with polarization-dependent functionalities. These prospects have been further invigorated by the experimental evidence of the polarization response in some transition metal chalcogenides (TMCs)—a group of narrow-band semiconductors and semimetals with a wealth of application potential. Among the TMCs, molybdenum disulfide (MoS2) is known as one of the most promising and robust 2D electronic materials. However, in spite of theoretical predictions, no ferroelectricity has been experimentally detected in MoS2, while the emergence of this property could enhance its potential for electronics applications. Here, we report the experimental observation of a stable room-temperature out-of-plane polarization ordering in 2D MoS2 layers, where polarization switching is realized by mechanical pressure induced by a tip of a scanning probe microscope. Using this approach, we create the bi-domain polarization states, which exhibit different piezoelectric activity, second harmonic generation, surface potential, and conductivity. Ferroelectric MoS2 belongs to the distorted trigonal structural 1T” phase, where a spontaneous polarization is inferred by its P3m1 space-group symmetry and corroborated by theoretical modeling. Experiments on the flipped flakes reveal that the 1T”-MoS2 samples consist of the monolayers with randomly alternating polarization orientation, which form stable but switchable “antipolar” head-to-head or tail-to-tail dipole configurations. Mechanically written domains are remarkably stable facilitating the application of 1T”-MoS2 in flexible memory and electromechanical devices.

Original languageEnglish (US)
Article number18
Journalnpj 2D Materials and Applications
Volume6
Issue number1
DOIs
StatePublished - Dec 2022

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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