Second Harmonic Generation in Van der Waals Ferroelectric CuInP 2 S 6 Nanoflakes under Uniaxial Strain

Abstract Van der Waals materials exhibit exotic physical properties, promising significant practical applications across various fields. The layered structure and its flexibility particularly stand out as significant advantages for wearable devices. Ferroelectricity (FE) is a notable phenomenon in some layered systems, with CuInP 2 S 6 (CIPS) identified as one of the few van der Waals materials exhibiting FE at room temperature. To explore its potential in flexible devices, the second harmonic generation (SHG) of CIPS nanoflakes is investigated under uniaxial strain. A method involving clamping and bending is employed to simulate strain effects as encountered in practical applications, achieving uniaxial strains up to 1.1% without slippage. The findings reveal that the SHG intensity of CIPS nanoflakes increases upon the application of strain in different directions, with enhancement correlating with both the magnitude of strain and the thickness of the nanoflakes. Additionally, polarization‐resolved SHG measurements indicate a slight rotation (≈5° maximum) of the central axis of the SHG pattern under strain, the direction and extent of which depend on the applied strain magnitude. This study provides crucial insights into the nonlinear optical behavior of typical ferroelectric vdW materials, with significant implications for the design and application of flexible electronics based on 2D ferroelectric materials.