Revealing Fast Cu-Ion Transport and Enhanced Conductivity at the CuInP<sub>2</sub>S<sub>6</sub>-In<sub>4/3</sub>P<sub>2</sub>S<sub>6</sub> Heterointerface.

Checa, Marti; Jin, Xin; Millan-Solsona, Ruben; Neumayer, Sabine M; Susner, Michael A; McGuire, Michael A; O'Hara, Andrew; Gomila, Gabriel et al. · ACS Nano · 2022

basic_science · Level V

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Abstract

Van der Waals layered ferroelectrics, such as CuInP<sub>2</sub>S<sub>6</sub> (CIPS), offer a versatile platform for miniaturization of ferroelectric device technologies. Control of the targeted composition and kinetics of CIPS synthesis enables the formation of stable self-assembled heterostructures of ferroelectric CIPS and nonferroelectric In<sub>4/3</sub>P<sub>2</sub>S<sub>6</sub> (IPS). Here, we use quantitative scanning probe microscopy methods combined with density functional theory (DFT) to explore in detail the nanoscale variability in dynamic functional properties of the CIPS-IPS heterostructure. We report evidence of fast ionic transport which mediates an appreciable out-of-plane electromechanical response of the CIPS surface in the paraelectric phase. Further, we map the nanoscale dielectric and ionic conductivity properties as we thermally stimulate the ferroelectric-paraelectric phase transition, recovering the local dielectric behavior during this phase transition. Finally, aided by DFT, we reveal a substantial and tunable conductivity enhancement at the CIPS/IPS interface, indicating the possibility of engineering its interfacial properties for next generation device applications.