Achieving Large Uniaxial and Homogeneous Strain in Two-Dimensional Materials

Strain is a powerful tool for tuning the electronic, magnetic, and topological properties of 2D materials - particularly at high values of strain ( $>3\%$ ) where many electronic, magnetic, and structural transitions are predicted. However, most approaches to straining 2D materials are limited below 1.5%, with poor repeatability when cycling strain and low strain transfer upon cooling. Here, we report a high-yield sample preparation and device strain platform that overcomes these limitations, enabling repeatable and reversible strain tuning up to the intrinsic strain-to-failure of the materials tested herein. We furthe r use this platform to controllably design uniform linear strain gradients, revealing a novel route for investigating flexoelectric and flexomagnetic phenomena. Using CrSBr as a standard for gauging strain, we demonstrate uniform uniaxial strain, up to $\sim$ 4%, with negligible slippage and linear strain gradients of up to 0.06%/ $\mu m$ . Our strain approach is applicable to a broad class of 2D materials, as validated by its performance for three different phases of transition metal dichalcogenides: 2H- ${\mathrm{MoTe}}_2$ , 1 $T^{\text{'}}$ - ${\mathrm{MoTe}}_2$ and $T_d$ - ${\mathrm{WTe}}_2$ . In $T_d$ - ${\mathrm{WTe}}_2$ , we show for the first time splitting of the $A_1^3$ and $A_1^2$ modes, starting at 2% strain, and record-breaking strain up to 5.5% strain.