Stabilized Penta-silicene: An Elemental Ferroelectric Material with High Curie Temperature

The compatibility of Si semiconductor technology with current electronic devices has led to continuing search for new Si-based materials with novel properties. The recent synthesis of penta-Si nanoribbons is a new addition to this family. However, penta-silicene, a two dimensional (2D) sheet composed of only Si pentagons, was found to be unstable in penta-graphene-like configuration. Using first-principles calculations and a thorough analysis of its imaginary frequencies, we show that penta-silicene can be made dynamically stable by tilting the Si dimers to reduce the Coulomb repulsion between them. The consequence of this tilting leads to an interesting discovery: the stabilized penta-silicene breaks the centrosymmetry, resulting in intrinsic ferroelecticity with a high Curie temperature of 1190 K. This realizes the spontaneous electrical polarization in a pure 2D Si system, which has the potential to work as a future non-volatile phase change material.