Electronic Properties of Polymorphic Two-Dimensional Layered Chromium Disulphide
Two-dimensional (2D) Cr-based layered and non-layered materials such as CrI3, Cr2Ge2Te6, Cr2S3, CrSe, and CrOX (X=Cl, Br) have attracted considerable attention due to their potential application in spintronics. Despite few experimental study, theoretical studies reported that 2D chromium dichalcogenides (CrS2) materials show unique properties such as valley polarization, piezoelectric coupling, and phase dependent intrinsic magnetic properties. Here, we report for the first time the synthesis of 2D layered CrS2 flakes down to monolayer via chemical vapor deposition (CVD) method, its phase structures and electronic properties. We observe the 2H, 1T, and 1T′ phases coexisting in CVD grown monolayer CrS2. The formation of 1T′ phases from 1T phases are described by dimerization of metal atoms at room temperature according to our molecular dynamics studies. The coexistence of 1T and 1T′ phase with 2H phase is referred as 1T and 1T′puddling phenomenon. We theoretically show that the monolayer 2H-CrS2 is a direct bandgap semiconductor with a gap of approximately 0.95 eV predicted by PBE functional, while the 1T- and 1T’-CrS2 are metallic and semi-metallic with approximately 10 meV gap, respectively. Furthermore, 2H CrS2 exhibit nonmagnetic semiconducting property while 1T and 1T’ CrS2 show magnetic characteristics with 0.531μB and 2.206 μB magnetic moment per Cr atom respectively, as predicted from DFT+U calculation. Importantly, CrS2-based field-effect transistors exhibit a p-type behavior. Our study would stimulate further exploration of 2D layered CrS2 with astonishing properties and opens up a whole new venue for the urgent need for the developing of multifunctional 2D materials for nanoelectronics, valleytronics, and spintronics.