Theoretical prediction of stress-tunable optoelectronic properties of GaSeI: a novel 1D helical van der Waals crystal

One-dimensional (1D) van der Waals materials demonstrate exceptional application potential due to their unique electronic and mechanical properties. Among them, the recently synthesized 1D GaSeI nanochain features a non-centrosymmetric helical structure with individual helical chains interconnected by weak van der Waals interactions. Remarkably, these nanochains can be readily isolated from the bulk crystal using a straightforward micromechanical exfoliation method. Using first-principles calculations, we predicted the dynamic stability as well as the mechanical, electronic and optical properties of 1D GaSeI nanochains. 1D GaSeI exhibits an indirect band gap of 2.44 eV, with hole carrier mobility (20.23 cm² V^-1 s^-1) approximately five times higher than the electron mobility (4.06 cm² V^-1 s^-1). Furthermore, 1D GaSeI can withstand a tensile strain of 22.5% along the chain direction, with a Young's modulus of ∼25.6 GPa. Such mechanical flexibility endows the nanochains with exceptional stress tunability, motivating further investigation into the effects of strain on their electronic structures. Notably, under a compressive strain of 7.5%, the 1D GaSeI nanochain undergoes a band gap transition from indirect to direct. The electronic localization function and optical properties of 1D GaSeI under various deformations are further analyzed. The nanochain exhibits a high absorption coefficient of ∼10⁵ cm^-1 in the ultraviolet range along the chain direction. These remarkable properties of the 1D GaSeI nanochain highlight the application potential of helical nanostructures in nonlinear optics and electronic devices.