On the optical properties and dynamical and mechanical stability of 1T PdSSe, PdSTe, and PdSeTe monolayers under biaxial strain

In this work, the effects of compressive and tensile biaxial strain, applied to monolayered 1T Pd Janus PdSSe, PdSTe, and PdSeTe structures are investigated. For tensile strengths larger than 4%, the valence band maxima no longer occur at the high symmetry Gamma point; this phenomenon is accompanied by the emergence of a quasi-direct bandgap, where Dirac-like cones develop for large enough strain. A semiconductor-semimetal phase transition takes place for compressive strain strengths of -8%, -4%, and -2% in PdSSe, PdSTe, and PdSeTe respectively. Phonon dispersion calculations show that the Janus structures, subject to tensile strains, are dynamically stable; yet under compressive strains, they are only stable for values not exceeding -6% in PdSSe, -4% in PdSTe, and -2% in PdSeTe. All structures are mechanically stable except for PdSTe under a 14% tensile strain, registering negative in-plane stiffness constants of -9.36 and -7.62 N/m along the x and y directions respectively. Optical absorption/emission within the infrared region is possible when the materials are exclusively subject to tensile strain. Once the Pd Janus structures are synthesized, the results presented here can serve as a guide for the fabrication of optoelectronic devices of optimal performance.