Novel bonding patterns and optoelectronic properties of the two-dimensional SixCy monolayers
The search for new two-dimensional (2D) materials with novel optical and electronic properties is always desirable for material development. Herein, we report a comprehensive theoretical prediction of 2D SiC compounds with different stoichiometries from C-rich to Si-rich. In addition to the previously known hexagonal SiC sheet, we identified two types of hitherto-unknown structural motifs with distinctive bonding features. The first type of 2D SiC monolayer, including t-SiC and t-Si2C sheet, can be described by tetragonal lattice. Among them, t-SiC monolayer sheet is featured by each carbon atom binding with four neighboring silicon atoms in almost the same plane, constituting a quasi-planar four-coordinated rectangular moiety. More interestingly, our calculations demonstrate that this structure exhibits a strain-dependent insulator–semimetal transition, suggesting promising applications in strain-dependent optoelectronic sensors. The second type of 2D SiC sheet is featured by silagraphyne with acetylenic linkages (–CC–). Silagraphyne shows both high pore sizes and Poisson's ratio. These properties make it a potentially important material for applications in separation membranes and catalysis. Moreover, one of the proposed structures, γ-silagraphyne, is a direct-band-gap semiconductor with a bandgap of 0.89 eV, which has a strong absorption peak in the visible-light region, giving a promising application in ultra-thin transistors, optical sensor devices and solar cell devices.