Large exciton binding energy, superior mechanical flexibility, and ultra-low lattice thermal conductivity in BiI3 monolayer

The exciton binding energy, mechanical properties, and lattice thermal conductivity of monolayer BiI3are investigated on the basis of first principle calculation. The excitation energy of monolayer BiI3is predicted to be 1.02 eV, which is larger than that of bulk BiI3(0.224 eV). This condition is due to the reduced dielectric screening in systems. The monolayer can withstand biaxial tensile strain up to 30% with ideal tensile strength of 2.60 GPa. Compared with graphene and MoS2, BiI3possesses superior flexibility and ductility due to its large Poisson's ratio and smaller Young's modulus by two orders of magnitude. The predicted lattice thermal conductivitykLof monolayer BiI3is 0.247 W m-1 K-1at room temperature, which is lower than most reported values for other 2D materials. Such ultralowkLresults from the scattering between acoustic and optical phonon modes, heavy atomic mass, and relatively weak chemical bond.