First-principles study of two-dimensional puckered and buckled honeycomb-like carbon sulfur systems

The stability and geometrical, mechanical, and electronic properties of monolayer carbon sulfur (CS) systems with honeycomb-like structure are studied by using first-principles calculations based on density functional theory. The results demonstrate that the honeycomb-like CS systems with two types of structure (buckled and puckered) are quite stable. It is found that such puckered and buckled CS nanosheets possess indirect gaps of 1.952 and 2.325 eV, respectively. Interestingly, both puckered and buckled CS monolayer materials exhibit negative out-of-plane Poisson's ratio, most likely originating from their puckered and buckled nature. Moreover, their bandgap can be effectively modulated by altering bond and bond lengths under uni- and biaxial strains. Meanwhile, an indirect-to-direct gap transition occurs in both monolayers, which is a useful feature for addressing the electron transition difficulties observed for intrinsic indirect nanosheets, thereby enabling their use in solar cells and light-emitting diodes. In particular, the Dirac-like cones of the puckered CS monolayer are identified in the band structure on the application of appropriate zigzag tensile strain. The results of the present calculations are very interesting for the selection of monolayer CS materials for use in electronic devices and provide a promising method to engineer their electronic characteristics for potential applications in future electronic and optoelectronic devices.