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 SiC siligraphene. The plausibility of the SiC siligraphene is verified by the low formation energy, positive phonon spectrum and high mechanical stability. The unique framework of sp carbon and sp silicon atoms leads to unusual in-plane negative Poisson's ratios and electronic properties superior to both graphene and silicene. SiC siligraphene possesses a natural band gap of 0.73 eV and a high carrier mobility. The theoretical mobility in the order of 10 cm V s 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 SiC siligraphene can be tuned by applying external strain. A possible synthetic route is also proposed. The exotic properties make SiC siligraphene a versatile and promising 2D material for applications in nanomechanics and nanoelectronics.
Using first-principles calculations, we investigated the photocatalytic mechanism of two-dimensional van der Waals CdS/InSe heterostructures (HSs). Our results show that the buckling distortion of a CdS monolayer sheet in the CdS/InSe HSs induces a built-in polarized electric field, which significantly changes the band edge positions of the InSe layer. The band alignment indicated that the photogenerated electrons in the conduction band (CB) of the InSe monolayer have a high possibility of recombining with the holes in the valence band (VB) of the CdS sheet, resulting in the electrons in the CB of CdS participating in a reduction reaction and the holes in the VB of InSe taking part in an oxidation reaction. This direct Z-scheme photocatalytic system can lead to spatial separation of photogenerated carriers and excellent redox ability, thus enhancing the photocatalytic efficiency. Meanwhile, CdS/InSe HSs can significantly extend the range of light harvesting from visible light to infrared light. Similar results can also be found in the CdS/InSe@2 HSs constructed by InSe bilayer deposit on a CdS nanosheet. These results indicate that CdS/InSe HSs are promising photocatalysts for water splitting.
Two-dimensional (2D) lattices composed exclusively of pentagons represent an exceptional structure of materials correlated to the famous pentagonal tiling problem in mathematics, but their π-conjugation and the related electronic properties have never been reported. Here, we propose a tight-binding (TB) model for a 2D Cairo pentagonal lattice and demonstrate that p-d π-
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