Dimension effect on ferroelectricity: a first-principles study on GeS nanoribbons.

Low-dimensional ferroelectricity has attracted enormous attention due to its applications in miniaturized devices and understanding the dimension effect on ferroelectricity is of significant importance. Based on first-principles calculations, we have investigated the dimension effect on the ferroelectricity of group-IV monochalcogenide MX nanoribbons. Our results reveal that H-terminated armchair GeSNRs exhibit large in-plane polarization along the ribbon direction which converges to the value of 2D GeS as the width increases, while out-of-plane polarization only arises in those with n = odd number. Interestingly, for bare A-GeSNRs, the structure with small n transforms into a paraelectric phase and the critical width for the PE/FE transition is calculated to be n = 10. On the side of zigzag GeSNRs, H-terminated ribbons possess polarization along both the out-of-plane and width directions, while bare Z-GeSNRs are expected to be polar ferromagnetic metals.