Mechanical and dynamic stability of ZnX chalcogenide (X=O, S, Se, Te) monolayers and their electronic, optical, and thermoelectric properties

Abstract

Graphene-like ZnX (X=O, S, Se, Te) structures are studied using the DFT+U method to address in detail the questions regarding the dynamical stability and also their utility in optoelectronic devices. The layer modulus, the Young's modulus, the shear modulus, and the Poisson coefficient demonstrate the stability of all ZnX in the presence of the Hubbard parameter U. Cohesion energy calculations show ZnO to be the most stable one and ZnSe to be the least stable one among the four systems. The presence of a direct bandgap in all the systems makes them suitable for use in optoelectronic devices. The gap values range between 2.13 eV in ZnTe and 3.50 eV in ZnO. U values tend to increase the bandgap in all the systems. This increase is seen to be as high as 100% in ZnO. A detailed study of the band structure and partial density of states is carried out. The electronic, optical, and thermoelectric properties of the ZnX monolayers are exhibited. The superior limit of the figure of merit increases with temperature and the highest value is found to be of the order of 0.6 in ZnO at 900 °C. Overall, the inclusion of the Hubbard parameter demonstrates better stability and also its importance in technological applications.

Theoretical Study of ZnS Monolayer Adsorption Behavior for CO and HF Gas Molecules

“…The electronic band structures of pristine ZnS ML and the adsorbed systems are shown in Figure . The band structure of the pristine ZnS ML shows a band gap of 3.34 eV (Figure a), which is consistent with previous DFT + U studies and much larger than that obtained using GGA-PBE (2.54 eV). The presence of Fermi energy closer to the valence band maximum indicates p -type behavior.…”

“…36 Therefore, the Hubbard parameter, U , was added to the PBE functional to define the on-site Coulomb interaction in d orbitals 37 and also to correct SIE in the d and p orbitals. 38 We have adopted U parameters from Monteiro et al 39 as U eff (Zn:3d) = 14.36 eV and U eff (S:3p) = 3.69 eV, which are obtained from the ACBN0 method, developed by Agapito et al, 40 calculated directly from the Coulomb and exchange integrals.…”

Graphene Induced High Thermoelectric Performance in ZnO/Graphene Heterostructure

“…[17] Also, the TE property of the free-standing ZnO monolayer was investigated theoretically. [18,19] However, the validity of the ZT value is questionable because both lattice thermal conductivity and relaxation time effect were ignored in these theoretical studies. Thus, no clear thermoelectric performance of the ZnO monolayer has yet been reported.Since the 2D flat ZnO monolayer has a large band gap, the ZnO layer will have very low electrical conductivity.…”

Highly sensitive sensing of CO and HF gases by monolayer CuCl

“…44 So, for this purpose, the addition of the Hubbard parameter (U), is carried out in the PBE functional. 45,46 The U parameters were adopted according to Monteiro et al 47 as U (Cu:3d) = 7.0 eV and U (Cl:3p) = 7.0 eV, which are attained using the ACBN0 method. 48 A CuCl monolayer with a 3 × 3 supercell is used, comprising 18 atoms of Cu and Cl (nine for each).…”