Negative Poisson's ratio and high-mobility transport anisotropy in SiC₆ siligraphene

The diverse forms of silicon carbides lead to versatile properties, but an auxetic allotrope at zero pressure has never been reported. Here, using first-principles calculations we propose a two-dimensional (2D) auxetic silicon carbide material, namely SiC₆ siligraphene. The plausibility of the SiC₆ siligraphene is verified by the low formation energy, positive phonon spectrum and high mechanical stability. The unique framework of sp² carbon and sp³ silicon atoms leads to unusual in-plane negative Poisson's ratios and electronic properties superior to both graphene and silicene. SiC₆ siligraphene possesses a natural band gap of 0.73 eV and a high carrier mobility. The theoretical mobility in the order of 10⁴ cm² V^-1 s^-1 for electrons along the [1[combining macron]10] direction is comparable to the hole mobility in black phosphorene, whereas the hole transport along the [110] direction is blocked. Both the electronic band structure and carrier mobility of the SiC₆ siligraphene can be tuned by applying external strain. A possible synthetic route is also proposed. The exotic properties make SiC₆ siligraphene a versatile and promising 2D material for applications in nanomechanics and nanoelectronics.