Theoretical Study On The Thermal Transport Properties Of Two-dimensional Borides

Since the successful synthesis of graphene in 2004,much more two-dimensional（2D）materials have received widespread attentions.2D borides,as a classical material,have attracted tremendous interest from researchers due to their novel physical phenomena and promising applications in nanoelectronics,superconductivity and Li/Na batteries.Considering the important impact of temperature on the stability,life-time and safety of devices in practice,we perform a comprehensive study on the thermal transport properties of 2D borides and further understand thermal transport process in low-dimensional systems.In this paper,based on the first-principles calculation we systematically study both diffusive and ballistic thermal transport properties in 2D borides via phonon Boltzmann transport equation（BTE）and non-equilibrium Green’s function（NEGF）methods.By analyzing the physical mechanism therein,we propose new strategies to improve the thermal transport performance in micro/nano devices and promotes the research of corresponding thermal management devices.Firstly,we studied the abnormal high thermal conductivity in h-BAs.By analyzing the contributions of different phonon modes thermal conductivity,we found the contribution of in-plane acoustic（IA）modes is up to 76%,which is rooted in the platform of phonon relaxation time.Besides,the contrastive study of h-BAs vs.h-Ga N shows that the trend of out-of-plane optical（ZO）branch is also an important factor impacting on the thermal conductivity.Secondly,we further researched the thermal transport properties in covalently bonded bi-layer BAs.Combining two types of stacking order and three possible bonding configurations,we can construct six types of hydrogenated bi-layer BAs.At 300K,the thermal conductivity of AA（As-As）configuration is about 80%higher than that of h-BAs.This result can be understood by the smaller scattering phase space and weaker phonon anharmonicity.The abnormal phenomenon of thermal conductivity increasing with thickness enriches control techniques of thermal transport in layered 2D materials.Finally,via intercalating the Al atoms to the interlayer ofδ₄borophene,we regulate the diffusive thermal transport properties.Then,Al atoms ionically bond with adjacent boron atoms,and the configuration changes into Al B₆ nanosheets.We found,at room temperature,the thermal conductivity of Al B₆significantly increases.Especially in the armchair direction,the thermal conductivity of Al B₆is about two times larger than that ofδ₄borophene and reach to 160.2 W/m K.This study proposed a new strategy to regulate the thermal transport performance in 2D materials.