Hydrogen-induced stabilization and tunable electronic structures of penta-silicene: a computational study
Using first-principles calculations, we have systematically investigated the structural stability and electronic properties of penta-silicene nanosheets, which are the Si analogues of recently proposed penta-graphene [S. Zhang et al., Proc. Natl. Acad. Sci. U.S.A., 2015, 112, 2372]. We find that unlike penta-graphene, the pristine penta-silicene sheet has soft modes from the unfavourable high-buckled configuration for tricoordinated Si atoms. The dynamic stability of penta-silicene is restored by surface hydrogen decoration, which also gives it good energetic and mechanical stability. The hydrogenated penta-silicene (p-SiH) sheet is a soft material with superior flexibility, which can endure large biaxial and uniaxial strains up to 25% and 31%, respectively. The two-dimensional p-SiH nanosheet is an indirect-band-gap semiconductor, while for one-dimensional nanoribbons, the edge states induce flat bands at the Fermi level, causing a spontaneous spin-polarization in the system. In narrow nanoribbons, the antiferromagnetic (AFM) state is more favorable than the ferromagnetic (FM) one, while they become degenerate in wide nanoribbons. More interestingly, the FM p-SiH nanoribbons are bipolar magnetic semiconductors that can be altered to half-metals with opposite conducting spin channels by p-type and n-type doping. Our study demonstrates that the hydrogenated penta-silicene possesses robust structural stabilities and promising mechanical and electronic properties, which gives the Si-based nanostructure many potential applications in future nanodevices.