Single-layer Cu 2 X (X = O, S, Se): auxetic materials modulated by strain engineering

Auxetic materials have shown significant potential for information, medicine, and aerospace applications. This work predicts a series of single-layer (SL) Cu 2 X (X = O, S, Se) with negative Poisson’s ratio (single) using first-principles calculations. It is found that SL Cu 2 O has an intrinsic ultrawide range of large NPR, which is less discovered in auxetic materials. By strain engineering, we not only reveal the maintainable in-plane NPR of SL Cu 2 O over a large strain range, but also modulate out non-intrinsic in-plane and out-of-plane NPRs of SL Cu 2 X. These exotic properties of SL Cu 2 X could lead to their favorable mechanical potential.