First Principle Investigation Of Opto-mechatronics And Thermoelectricity In Transition Metal Dichalcogenides

Graphene is the first true 2-dimensional(2D)material.However,the closed bandgap of graphene limits its applications in opto-mechanical devices and thermoelectric devices.In this context,many other 2D materials were discovered like hexagonal boron nitride(h-BN),transition metal dichalcogenides(TMDs),phosphorene(BP)and so on.TMDs monolayer exhibit direct bandgap between 1.0and 2.0 eV,which generates great potentials for them to be made into opto-mechanical devices and thermoelectric devices.In order to have a thorough understanding on material properties of low dimensional TMDs nanostructures and design high performance thermoelectric devices,we investigate the electronic,optical and mechanical properties for TMDs nanostructures by first principles methods.We investigate the electron and phonon transport on nano devices by first-principles methods with non-equilibrium Green's function and the Landauer equation.The main innovations of this work are follows:1.We investigate the electronic and mechanical properties of the monolayer MoS2,MoSe2,WS2 and WSe2 together.We have found that this direct bandgap range is inversely proportional to the Young's modulus.2.This is the first study on piezoelectric properties of the orthorhombic Pd S2 under tensile strains.Results show that the orthorhombic Pd S2 with 4% tensile strain has the strongest piezoelectric effect of 1.33 C/m2.3.We investigate that interlayer twisting modulates optical properties in MoS2/Pt S2 heterostructures,which reveals its high absorption coefficient in near infrared.Under the 30.0 degree twisting angle,the absorption coefficient in the absorption spectrum can reach to or above 1×105/cm with the tensile strain,from roughly450 nm to 1050 nm.4.We build some novel structures of Mo SSe and graphene nanoribbon thermoelectric devices.Results indicate that figure of merit(ZT)values of 2.01 and 1.64 can be achieved for the graphene/Se Mo S and Mo SSe nanoribbon at300 K.In bilayer graphene nanoribbons,peak ZT value of 6.11 can be achieved in the 21.8o twisted bilayer graphene nanoribbons.Moreover,bilayer graphene nanoribbons with holes exhibit high ZT values of 9.65 at 300 K.Overall,the results indicate in the TMDs that monolayer MoS2,MoSe2,WS2 and WSe2 will have potential applications in strain tunable opto-mechanical devices,PdS2 bulk will have potential applications in piezoelectric devices.In the TMDs heterostructures,MoS2/Pt S2 heterostructure will have potential applications in high absorption devices,graphene/MoXY heterostructure can induce tunable homogeneous doping of graphene.In the TMDs nano devices,MoSSe and bilayer graphene nanoribbons will have potential applications in thermoelectric devices.