Lattice Dynamics Simulation Of Heat Conduction Properties Of Monolayer Films And Nanotubes

With the continuous progress of manufacturing technology,electronic devices have developed to the nanometer size,so the high integration leads to more serious thermal effect and more prominent heat dissipation problem,which puts forward higher requirements for the thermal stability and reliability of nanometer electronic devices.Mono-atomic layer films such as graphene are nanomaterials with excellent electronic and mechanical properties,which have broad application prospects in the application of micron and nano-electronic devices in the future.By virtue of its excellent heat conduction properties,nanotubes can be used as important components for the design of micro and nano electronic devices.The heat conduction properties of monolayer films and nanotubes determine their heat dissipation capacity and are closely related to their thermal stability and reliability.It can be seen that the study of the heat conduction properties of mono-atomic layer films and nanotubes is of great significance for the rational design and reliable use of micro-nano electronic devices.For a long time,the most commonly used methods to study the heat conduction properties of materials are the boltzmann transport equation method and the classical molecular dynamics simulation.However,due to the size development of electronic devices has reached the nanometer level,the device performance is more and more obviously affected by the quantum effect.However,the two classical methods above ignore the quantum effect,which will lead to certain errors when the quantum effect is obvious such as low temperature.Moreover,the molecular dynamics simulation method is complex and computations are large,which is not conducive to the simulation of systems with large particle number.Therefore,in this paper,the thermal conduction properties of single-atom thin films and nanotubes are studied by using the lattice dynamics simulation method which takes quantum effect into consideration and requires low computation and high speed.The following are the main research contents and conclusions of this paper:1.Lattice dynamics theory of mono-atomic layer films and nanotubesOn the basis of the existing lattice dynamics theory,this paper derived the single atomic layer film and nanotubes lattice dynamics of matrix,to solve the eigenvalue problem,and got their lattice vibration frequency of the phonon frequency formula,the atomic displacement formula,atomic momentum formula,the lattice vibration energy formula,the group velocity of lattice vibration formula,and on the basis of deriving the single atomic layer film and nanotubes interatomic interactions of third order non harmonious potential energy formula.Green function is derived for the phonon Green function of mono-atomic thin films and nanotubesby using the third order diharmonic potential energy as perturbation,and the iterative formula for the line width of phonon is obtained from the imaginary part of the pole of Green function.According to the result of the line width of phonon obtained by iterative calculation,the phonon free equation is also calculated.The results show that the spectral line width of the low-frequency phonons decreases with the decrease of the wave vector,that is,the phonon lifetime increases with the decrease of the wave vector.And the phonon free path of the low frequency phonon is much larger than that of the high frequency phonon.2.Heat conduction properties of mono-atomic layer films and nanotubesHardy energy flux formula is presented in this paper,on the basis of single atomic layer thin film was deduced and nanotubes lattice vibration energy flux formula,and the use of Green Kubo formula derivation single atomic layer film and the heat transfer coefficient formula of nanotubes,the formula shows that the single atomic layer film and heat transfer coefficient of the nanotubes is the sum of all the phonon heat conduction coefficient.The heat conduction coefficient of a single phonon is closely related to its velocity,phonon energy,phonon lifetime(or spectral line width)and free path.Of single atomic layer film respectively using Matlab and nanotubes heat transfer coefficient changing with the sizerelations are simulated,the results show that the single atomic layer of thin film heat transfer coefficient increases with the increase of size film,and the data fitting,found that when the size of more than 40 * 40 atomic layer,heat transfer coefficient has a linear relation and the logarithm of size order,thus,when size tends to infinity,the heat conduction coefficient showed a trend of divergent;The axial heat transfer coefficient of the nanotube increases with the increase of its length,and as the length approaches infinity,the heat transfer coefficient also tends to diverge.On the other hand,the heat transfer coefficient of the nanotube decreases with the increase of its diameter.These conclusions provide a theoretical basis for solving the problem of heat dissipation in the design of micron and nanometer electronic devices.