CIF Facilitates Client Breakthrough: Electric-Field-Controlled Ion Migration Recovers Mechanical Fatigue Resistance in 2D Ferroelectric CuInP₂S₆, Published in Small!

Time：2026-05-26 Click Count：25

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Recently, a research team led by Professor Zhong Zhang and Professor Guorui Wang from the University of Science and Technology of China (USTC), in collaboration with Professor Chongjian Zhou’s team from Northwestern Polytechnical University, published significant findings in the journal Small. The study reveals the exceptional mechanical fatigue resistance of the two-dimensional (2D) ferroelectric material CuInP₂S₆ (CIPS) and demonstrates the reversible recovery of its properties under electric-field regulation.

In the critical processes of patterned silicon substrate preparation and sample surface cleaning/activation, the CIF CPC-G Plasma Cleaning System was utilized to complete the core fabrication steps.

Research Background: The "Fatigue Bottleneck" of Traditional Ferroelectric Materials

Ferroelectric materials are widely used in core fields such as non-volatile memory, sensors, and optoelectronic devices due to their tunable spontaneous polarization. However, traditional ferroelectric oxides face an insurmountable bottleneck: during repeated polarization switching, irreversible accumulation of ionic defects leads to polarization fatigue and continuous performance degradation. Furthermore, at the nanoscale, polarization is prone to collapse, resulting in poor mechanical durability, which severely limits the long-term operation of flexible and wearable electronic devices.

Two-dimensional van der Waals (vdW) ferroelectric materials have emerged as ideal candidates for next-generation ferroelectric devices, thanks to their defect-suppressed interfaces and weak interlayer coupling. Nevertheless, systematic and in-depth experimental studies on their long-term mechanical fatigue behavior and reliability have been lacking.

Research Breakthroughs

This study systematically investigates the dynamic mechanical fatigue behavior of the 2D vdW ferroelectric material CIPS. It was found that CIPS can withstand over 10⁷ cyclic loading cycles under high stress approaching 7 GPa, demonstrating significantly superior fatigue resistance compared to existing ferroelectric materials.

The research confirms that material fatigue originates from cyclic stress-induced flexoelectric field-driven migration and local aggregation of Cu⁺ ions. This process leads to surface protrusions and lattice distortion. Crucially, this damage process can be completely reversed by applying an external electric field. The electric field redistributes the aggregated Cu⁺ ions, restoring the crystal integrity and mechanical fatigue resistance, thereby extending the material's service life by nearly an order of magnitude. These findings provide a novel principle and technical pathway for designing durable, self-healing, and reconfigurable 2D ferroelectric devices.

Figure 1 | Mechanical properties of CIPS under cyclic loading.
a) Schematic diagram of the atomic force microscopy (AFM)-based fatigue testing setup.
b) Evolution of the probe amplitude and deflection. The continuously growing protrusion structures correspond to damage accumulation.
c) Functional relationship between Young's modulus and the dimensions of the protrusion structures.
d) Fatigue life of CIPS under different stress conditions. The AFM images illustrate the distinct failure modes under static loading and dynamic loading, respectively.

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Figure 2 | Characterization of the protrusion structures.
a) EDS elemental mapping of CIPS containing protrusion structures.
b) Morphology image of the protrusion structures.
c) Electrostatic force microscopy (EFM) image.
d) Scanning Kelvin probe microscopy (SKPM) image.
e) Conductivity performance.
f) Raman spectra of CIPS in regions A and B, as marked in (b).

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Figure 3 | Ion migration dynamics within CuInP₂S₆ (CIPS) under cyclic loading.
Under cyclic loading, a distinct aggregation region of Cu⁺ ions forms beneath the AFM tip. The bending of the CIPS nanosheets generates strain gradients and flexoelectric fields internally, providing the driving force for ion migration. Current–voltage curves under different stress levels indicate that ion redistribution significantly alters the local conductivity. Molecular dynamics (MD) simulations intuitively present the dynamic response of the material under cyclic nanoindentation. The gradual decrease in the tip feedback force over time reflects the structural softening caused by ion migration. The density of Cu⁺ in the core region beneath the tip continuously increases with loading time. The in-plane and out-of-plane mean square displacements (MSD) of Cu⁺ are significantly greater than those of In, P, and S atoms. The substantial difference in diffusion coefficients directly confirms the high migration activity of Cu⁺, while the lattice framework atoms remain essentially stable.

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Figure 4 | Electromechanical control of CIPS fatigue.
a) Programmable writing and erasing of Cu⁺ ions on suspended CIPS thin films, demonstrating the reversible ion aggregation achieved via electric-field regulation.
b) Schematic diagram of the fatigue regulation pathways: cyclic stress causes continuous aggregation of Cu⁺ ions until ultimate failure (Pathway 1); an electric field disperses the ion cluster structures and restores fatigue resistance, thereby extending the service life (Pathway 2); repeated write-erase cycles enable multiple recovery processes (Pathway 3).
c) Schematic illustration of the mechanically loading-induced ion aggregation and the recovery process of fatigue performance driven by an applied electric field.

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Figure 5 | Comparison of fatigue life among different piezoelectric materials.