Thermal properties of ZrSe2 and HfS2/ZrSe2 heterojunctions subjected to tensile strain

Abstract

In this paper, the phonon spectra of ZrSe2, HfS2, and HfS2/ZrSe2 heterojunctions are calculated based on the density-functional perturbation method for biaxial tensile strains to study their stability and thermal properties. It was found that monolayers of ZrSe2 and HfS2 should not be subjected to >8 % biaxial tensile strain, and HfS2/ZrSe2 heterojunctions should not be subjected to >6 %. By looking at the graphs of enthalpy, entropy, free energy, and heat capacity under strain for the three systems, it is found that the effect on heat capacity is greater after destabilization in the monolayer system and after destabilization in the heterojunction structure, it is greater for the free energy. Enthalpy, entropy and free energy all increase continuously with increasing temperature, and heat capacity increases continuously with the rising temperature at temperatures <200 K and tends to remain constant when the temperature is >200 K.