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Air‐Stable Monolayer Cu 2 Se Exhibits a Purely Thermal Structural Phase Transition
Author(s) -
Qian Kai,
Gao Lei,
Chen Xiya,
Li Hang,
Zhang Shuai,
Zhang XianLi,
Zhu Shiyu,
Yan Jiahao,
Bao Deliang,
Cao Lu,
Shi JinAn,
Lu Jianchen,
Liu Chen,
Wang Jiaou,
Qian Tian,
Ding Hong,
Gu Lin,
Zhou Wu,
Zhang YuYang,
Lin Xiao,
Du Shixuan,
Ouyang Min,
Pantelides Sokrates T.,
Gao HongJun
Publication year - 2020
Publication title -
advanced materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.707
H-Index - 527
eISSN - 1521-4095
pISSN - 0935-9648
DOI - 10.1002/adma.201908314
Subject(s) - materials science , phase transition , electron diffraction , scanning tunneling microscope , monolayer , scanning transmission electron microscopy , density functional theory , phase (matter) , chemical physics , transmission electron microscopy , diffraction , molecular physics , condensed matter physics , nanotechnology , computational chemistry , chemistry , optics , physics , organic chemistry
Materials possessing structural phase transformations exhibit a rich set of physical and chemical properties that can be used for a variety of applications. In 2D materials, structural transformations have so far been induced by strain, lasers, electron injection, electron/ion beams, thermal loss of stoichiometry, and chemical treatments or by a combination of such approaches and annealing. However, stoichiometry‐preserving, purely thermal, reversible phase transitions, which are fundamental in physics and can be easily induced, have not been observed. Here, the fabrication of monolayer Cu 2 Se, a new 2D material is reported, demonstrating the existence of a purely thermal structural phase transition. Scanning tunneling microscopy, scanning transmission electron microscopy, and density functional theory (DFT) identify two structural phases at 78 and 300 K. DFT calculations trace the phase‐transition mechanism via the existence/absence of imaginary (unstable) phonon modes at low and high temperatures. In situ, variable‐temperature low‐energy electron diffraction patterns demonstrate that the phase transition occurs across the whole sample at ≈147 K. Angle‐resolved photoemission spectra and DFT calculations show that a degeneracy at the Γ point of the energy bands of the high‐temperature phase is lifted in the low‐temperature phase. This work opens up possibilities for studying such phase transitions in 2D materials.