abstract
We consider nanoflakes of van der Waals ferrielectric CuInP2S6 covered by an ionic surface charge and reveal the appearance of polar states with a relatively large polarization of approximately 5 µC/cm2 and stored free charge of around 10 µC/cm2, which can mimic “midgap” states associated with a surface-field-induced transfer of Cu and/or In ions in the van der Waals gap. The change in the ionic screening degree and mismatch strains induce a broad range of the transitions between paraelectric phase, antiferroelectric, ferrielectric, and ferri-ionic states in CuInP2S6 nanoflakes. The states’ stability and/or metastability is determined by the minimum of the system free energy consisting of electrostatic energy, elastic energy, and a Landau-type four-well potential of the ferrielectric dipole polarization. The possibility of governing the transitions by strain and ionic screening can be useful for controlling the tunneling barrier in thin-film devices based on CuInP2S6 nanoflakes. Additionally, we predict that the CuInP2S6 nanoflakes reveal features of the controllable negative capacitance effect, which make them attractive for advanced electronic devices, such as nanocapacitors and gate oxide nanomaterials with reduced heat generation.
authors
Anna N. Morozovska , Sergei V. Kalinin, Eugene A. Eliseev, Svitlana Kopyl, Yulian M. Vysochanskii, and Dean R. Evans
our authors
Svitlana Kopyl
ResearcherProjects
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
Piezoelectricity in 2D-materials: materials, modeling, and applications (Piezo2D)
acknowledgements
This work of S.K. was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (Grant DOI: 10.54499/UIDB/50011/2020), UIDP/50011/2020 (Grant DOI: 10.54499/UIDP/50011/2020) and LA/P/0006/2020 (Grant DOI10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC). Part of S.K.’s work was funded by national funds (OE), through FCT: Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5, and 6 of article 23, of the Decree-Law 57/2016, of 29 August, changed by Law 57/2017, of 19 July. Y.M.V. and S.K. acknowledge support from the Horizon Europe Framework Programme (HORIZON-TMA-MSCA-SE), Project No. 101131229, Piezoelectricity in 2D-materials: materials, modeling, and applications (PIEZO 2D).