Molecular Dynamics Simulation Of Thermophysical Properties Of Nanoscale Thin Film

As indispensable components of various micro-devices, thin films with thickness in microscale and nanoscale are playing vital roles in the application areas such as microelectronics, optoelectronics, MEMS and the burgeoning nanotechnology. Since the performance and reliability of the devices are strongly dependent on the heat conduction in thin films, exploring thin film thermal conductivity and understanding the heat transport mechanism are of great significance for the thermal management and thermal-electrical coupling optimization design of devices. When the film thickness is reduced below 100nm, however, it is extremely difficult to measure thin film thermal conductivity. In this case, molecular dynamics (MD) technique is valuable and promising tool and it is particularly a good alternative for the study of microscale heat conduction in solids.The present dissertation elucidates the process of the material micromation, the theory of thermoelectricity cooling, and the recent research of micro-scale thermal transport; discusses the basic theory, detailed steps of molecular dynamics simulation, the classification and application conditions. By means of constant-temperature, constant-pressure molecular dynamics techniques, the melting and crystallization process of a model system are simulated. It is found that the melting temperature of bulk argon not only depends on the external pressure, but also relies on the heating rate. And crystallization may reduce thermal conductivity over the temperature range of 20–70K, but it is somewhat higher than that of thermal expansion while the variational trend of thermal conductivity relative to temperature is close to the experimental. Results also show that for the same defect density, the thermal conductivity of crystallized material is smaller than that of non-crystallized one under high temperature, and vice verse, that the thermal conductivity of crystallized material is higher than that of non-crystallized under low temperature. However, under each case, the thermal conductivity increases with the increase of defect density.In the second part of the thesis, the thermal properties of superlattices is simulated by non-equilibrium molecular dynamics method. With the increase of the well depth, the phonon mean free path and thermal conductivity of a solid material increase. The results indicate that the thermal conductivity of superlattice has a minimum value at a specific periodic length when lattice matched, otherwise the thermal conductivity increases with the increasing of periodic length.