High stability Janus structures of two dimensional Fe3GeTe2 monolayer by first-principles investigations

In line with ongoing efforts on discovering new materials for the utilization in advanced nanotechnologies, in the present work, based on the original Fe${}_3$GeTe${}_2$ material, two-dimensional Janus Fe${}_3$Ge$X$Te ($X=$ S and Se) monolayers are constructed and analyzed by using first-principles calculations. All three monolayers of Fe${}_3$GeTe${}_2$, Fe${}_3$GeSTe, and Fe${}_3$GeSeTe exhibit hexagonal structures with good dynamical stability. No negative frequency is observed in the phonon dispersion spectra. During the ab initio molecular dynamics simulation at room temperature, the Fe${}_3$Ge$X$Te structures are predicted to be thermally stable without any reconstruction/fracture, suggesting the high thermal stability of these systems. In addition, the Fe${}_3$Ge$X$Te monolayers show high negative cohesive energy of about $-5$ eV/atom and the obtained elastic constants satisfy the Born and Huang condition. Their Young’s modulus and Poisson’s ratio exhibit isotropic elastic behaviors due to the isotropic structures. These results confirm that the Fe${}_3$Ge$X$Te monolayers are energetically and mechanically stable for experimental synthesis. Especially, the electronic properties of our studied structures are explored for applications in electronic devices. The Fe${}_3$Ge$X$Te monolayers show a metallic nature for both the spin-up and spin-down cases. The projected density of states reveals that the Fe${}_3$GeTe${}_2$, Fe${}_3$GeSTe, and Fe${}_3$GeSeTe are magnetic materials due to their different spin-up and-down configurations. The results of our study can provide more information for the Janus Fe${}_3$Ge$X$Te materials and stimulate future experimental studies for practical applications in magnetic and electronic devices.