A Study On Quantum Thermal Transport Properties Of Borophene

Graphene has a wide application prospect in the field of electronic devices due to its unique electronic and mechanical properties,as well as ultra-high thermal conductivity.Boron,as a neighbor of carbon in the periodic table,has been widely concerned by researchers for a long time.Many theoretical studies have shown that boron also has a two-dimensional structure of single atom thickness,but due to the lack of electrons of boron elements,it is difficult to fabricate monolayer boron two-dimensional materials in experiments.Recently,2D boron sheets,also called borophene,have been successfully synthesized on a Ag?111?surface.Subsequently,more and more researchers have studied borophene through experimental and theoretical methods,and found that this new two-dimensional material has a lot of excellent properties.However,the atomic mass of boron and carbon is almost the same,and the structure of borophene is very similar to that of graphene,so what about the thermal transport properties of borophene compared with graphene?In this paper,the thermal transport properties of borophene have been studied in combination with first principles and non-equilibrium Green's function,which provides a theoretical basis for finding new thermal conductive materials.The main conclusions of this paper are as followsFirstly,we investigated the thermal transport properties of???₆ borophane.It is found that the quantum thermal conductance of borophane along the armchair at room temperature is greater than that of graphene.And there is a dimensionality crossover phenomenon,there are two-dimensional transmission of low-frequency phonons and one-dimensional transmission of high-frequency phonons(950¹450cm^-1),which is also the reason for the high thermal conductance in the direction of armchair.In addition,We found that the thermal conductance of borophane increases with the increase of uniaxial tensile strain,reasonable explanation is given through structural changes and bonding characteristics.Secondly,we investigated the thermal transport properties of 2D hydrogen boride.The contribution of phonons and electrons to thermal conductance is given.The phonon thermal conductance of 2D hydrogen boride is close to that of graphene,while its electrical thermal conductance is almost ten times over graphene.So the total thermal conductance is twice as high as graphene.This is also the largest two-dimensional material of thermal conductance at present.In addition,we have studied the strain effect of thermal transport properties.At the Fermi level,the tensile strain along armchair-direction gives a higher electronic density of states,which effectively brings more states toward electrical thermal conductance.The increase of electrical thermal conductance in this direction makes up for the decrease of phonon thermal conductance,so that the total thermal conductance increases with the increase of tensile strain.In contrast,zigzag-direction tensile strain induces bandgap opening at the?-point under,which can fully“close”the electron channel,leading to zero electrical thermal conductance.This is the opposite of the armchair-direction strain effect.Thirdly,we studied the quantum thermal conductance of hydrogenated boron nanotube.It was found that the room temperature thermal conductance of?5,0?H-BNT is as high as 3.84nWK^-1nm^-2,which is comparable to that of single-walled carbon nanotubes with the similar diameter.Theoretical analysis of phonon transmission is also provided to understand the high thermal conductance in this new type of 1D nanomaterial.