A First-principles Study Of The Thermal Conductivity Of Monolayer Graphene-like IIA-VI Oxides

As we know,phonons are the main carriers of heat transport in semiconductors or insulators.In recent years,heat transport has become a hot topic in the field of energy.With the miniaturization of electronic integrated devices,the heat dissipation of nanoscale devices has become an important factor restricting their performance.Therefore,it is necessary to improve the thermal conductivity of materials.On the other hand,in order to improve the efficiency of thermoelectric conversion in thermoelectric devices,a lower thermal conductivity of material is required.Different from the heat transport of macroscopic systems,there are many unique physical phenomena in the heat transport of 2D systems,and revealing the mechanism behind them is of great importance for regulation.The regulation of heat transport in 2D materials is a practical problem in thermoelectric conversion,thermal equipment and electronic device refrigeration.It will also advance the development of energy nanotechnology in the future.In this work,we used first principles-calculations combined with phonon Boltzmann transport equation to study thermal properties of graphene-like?A-?monolayer oxides.As new 2D materials,graphene-like?A-?monolayer oxides have gradually attracted the interest of researchers.The characteristics of their wide band gap show that they have potential prospects in electronic devices.We first predicted the electronic and thermal properties of monolayer Be O.Compared with graphene and monolayer h-BN,the monolayer Be O is an insulator and its electrons are highly localized around O and Be atoms(ionic nature).More importantly,the thermal conductivity of monolayer Be O is found to be 266 Wm^-1K^-1 at 300 K,which is lower than that of graphene and h-BN but higher than most other 2D materials.Further analysis reveals that 75%of the thermal conductivity of monolayer Be O is contributed by phonons with a frequency from 0 to 5.4 THz.With the characteristics of wide bandgap and high thermal conductivity,monolayer Be O shows great potential for applications in electronic device packages.Then,we regulated the stability and thermal conductivity of other oxide materials in the main group(Mg O,Ca O,Sr O and Ba O)through strain engineering.The results show that the tensile strain can not only improve the dynamic and mechanical stability of these materials,but also effectively improve the thermal conductivity of the materials.The maximum thermal conductivity at 300K is increased by 3.25,3.07,1.50 and 1.53 times,respectively.We also discussed the enhancement of thermal conductivity from the perspectives of heat capacity,group velocity and phonon lifetime.Detailed analysis shows that the weakened phonon–phonon scattering strength is the behind physical mechanism.Our research can not only enrich the relevant studies on heat transport of 2D materials,but also provide guidance for experiments.It will also provide an important reference for the application of these materials in new devices.