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Title: CuInP2S6 Room Temperature Layered Ferroelectric

In this paper, we explore ferroelectric properties of cleaved 2-D flakes of copper indium thiophosphate, CuInP2S6 (CITP), and probe size effects along with limits of ferroelectric phase stability, by ambient and ultra high vacuum scanning probe microscopy. CITP belongs to the only material family known to display ferroelectric polarization in a van der Waals, layered crystal at room temperature and above. Our measurements directly reveal stable, ferroelectric polarization as evidenced by domain structures, switchable polarization, and hysteresis loops. We found that at room temperature the domain structure of flakes thicker than 100 nm is similar to the cleaved bulk surfaces, whereas below 50 nm polarization disappears. We ascribe this behavior to a well-known instability of polarization due to depolarization field. Furthermore, polarization switching at high bias is also associated with ionic mobility, as evidenced both by macroscopic measurements and by formation of surface damage under the tip at a bias of 4 V—likely due to copper reduction. Mobile Cu ions may therefore also contribute to internal screening mechanisms. Finally, the existence of stable polarization in a van-der-Waals crystal naturally points toward new strategies for ultimate scaling of polar materials, quasi-2D, and single-layer materials with advanced and nonlinear dielectric properties thatmore » are presently not found in any members of the growing “graphene family”.« less
 [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [1] ;  [4] ;  [2] ;  [5] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Inst. for Functional Imaging of Materials. Center for Nanophase Materials Sciences
  2. Vilnius Univ. (Lithuania). Faculty of Physics
  3. National Academy of Sciences of Ukraine (NASU), Kyiv (Ukraine). Inst. for Problems of Material Sciences
  4. National Academy of Sciences of Ukraine (NASU), Kyiv (Ukraine). Inst. of Physics
  5. Uzhgorod Univ. (Ukraine). Inst. of Solid State Physics and Chemistry
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 15; Journal Issue: 6; Journal ID: ISSN 1530-6984
American Chemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY 2D crystals; atomic force microscopy; ferroelectricity; layered materials