层间共价键和拉伸应变对双层石墨烯纳米带热导率的调控

Regulation of thermal conductivity of bilayer graphene nanoribbon through interlayer covalent bond and tensile strain

石墨烯的层间键合是一种石墨烯的改性方式,能够改变石墨烯的机械和导电等性能,同时也会对其热学性质产生影响.本文采用非平衡分子动力学方法,以层间局部碳原子sp^(3)杂化(层间形成共价键)的双层石墨烯纳米带为研究对象,研究了层间共价键呈链状分布时,其浓度、角度以及拉伸应变对双层石墨烯纳米带热导率的调控,并通过声子态密度对具有层间共价键的双层石墨烯纳米带热导率变化的原因进行机理分析.研究发现:双层石墨烯纳米带的热导率随层间共价键浓度的增加而减小,且依赖于共价键链的分布角度.随着层间共价键浓度的增加,层间共价键链与热流方向平行时,双层石墨烯纳米带热导率下降的速率最慢,层间共价键链与热流方向呈现一定角度时,热导率下降的速率变快,且角度越大,热导率下降的速率越快.此外研究还发现,拉伸应变会导致具有层间共价键的双层石墨烯纳米带的热导率进一步降低.研究结果表明,可以通过层间键合和拉伸应变共同对双层石墨烯纳米带的热导率进行调控.这些结论对石墨烯基纳米器件的设计及热管控具有重要的意义.

The interlayer bonding of graphene is a method of modifying graphene,which can change the mechanical property and conductivity of graphene,but also affect its thermal properties.In this paper,the non-equilibrium molecular dynamics method is used to study the thermal conductivity of bilayer graphene nanoribbon which is local carbon sp^(3) hybridization(covalent bond formed between layers)under different concentration and angle of interlayer covalent bond chain and different tensile strain.The mechanism of the change of the thermal conductivity of bilayer graphene nanoribbon is analyzed through the density of phonon states.The results are as follows.The thermal conductivity of bilayer graphene nanoribbon decreases with the increase of the interlayer covalent bond concentration due to the intensification of phonon scattering and the reduction of phonon group velocities and effective phonon mean free path.Moreover,the decrease rate of thermal conductivity depends on the distribution angle of covalent bond chain.With the increase of interlayer covalent bond concentration,when the interlayer covalent bond chain is parallel to the direction of heat flow,the thermal conductivity decreases slowest because the heat transfer channel along the heat flow direction is gradually affected;when the interlayer covalent bond chain is at an angle with respect to the direction of heat flow,the thermal conductivity decreases more rapidly,and the larger the angle,the faster the thermal conductivity decreases.The rapid decline of thermal conductivity is due to the formation of interfacial thermal resistance at the interlayer covalent bond chain,where strong phonon-interface scattering occurs.In addition,it is found that the thermal conductivity of bilayer graphene nanoribbon with interlayer bonding will be further reduced by tensile strain due to the intensification of phonon scattering and the reduction of phonon group velocity.The results show that the thermal conductivity of bilayer graphene nanoribbon can be controlled by interlayer bonding and tensile strain.These conclusions are of great significance in designing and thermally controlling of graphene based nanodevices.