In-plane Thermal Transport Characteristics Of Borophene Based On Molecular Dynamics Simulations

In recent years,the electronics industry has developed rapidly.With the development of technology,electronic devices have become more integrated,miniaturized and complex.However,the Joule heat generated by electronic devices has brought a great test to the safety performance of electronic devices.The problem of thermal management limiting the development of electronic devices needs to be solved urgently.Two-dimensional materials demonstrate superior thermal transport properties and have promising applications in the field of thermal management.Borophene is a new material with many good properties,but its thermal conductivity has not been studied in detail.Therefore,it is particularly important to modulate and study its thermal transport properties.In this paper,a systematic study of the in-plane thermal transport properties of hexagonal lattice borophene was carried out by molecular dynamics(MD)method.The results are summarized as follows.1.In this study,different sizes of borophene models were constructed by programming means,and the size effect of borophene was investigated.The thermal conductivity of borophene is significantly smaller at small sizes because the sample will intensify the boundary scattering at small sizes,resulting in a smaller phonon mean free range length,thus producing an obvious size effect.Meanwhile,the thermal transport properties of borophene under the temperature effect are studied,and the analysis of its PDOS diagram reveals that the optical branch part changes significantly more than the acoustic branch under the temperature effect.2.The results show that there exists a strong anisotropy in the in-plane thermal conductivity of borophene.The causes of the anisotropy of borophene material are analyzed qualitatively by phonon dispersion curves and phonon group velocities.Through the dispersion curves,it can be found that the slope of dispersion in the armchair direction is significantly larger than that in the zigzag direction as far as the optical branch is concerned.The total group velocity in the armchair direction is 1965.5 m/s,and the total group velocity in the zigzag direction is 1408.5 m/s.The larger the phonon group velocity,the higher the thermal conductivity of the sample,so the comparison of the phonon group velocity can qualitatively explain the reason for the anisotropy of the thermal conductivity in the borophene surface.3.In this study,a more in-depth mechanistic exploration of how random vacancy defects affect the in-plane thermal conductivity of borophene was carried out.First,five different models of random vacancy defect borophene with 1%～5% defect concentration were constructed.Then,the in-plane thermal conductivity was calculated and found to decrease and level off with the increase of defect concentration.Next,the phonon density of states analysis shows that the phonon group velocity and specific heat are constant,so it is concluded that the decrease of the phonon free range length is the main reason for the decrease of the thermal conductivity of the defected borophene.The analysis of the phonon participation rate shows that the phonon participation rate in the range of 0-10 THz and the whole high frequency part(26 THz～50 THz)shows a significant decreasing trend with the increase of the vacancy defect concentration.We make a quantitative definition of the localization intensity as 1-PR,and finally the phonon localization intensity cloud can be clearly found that the localization intensity of random vacancy defect atoms is much higher than that of other atoms.We can conclude that it is the defect-induced localization that causes the decrease of the thermal conductivity.