Evaluation of the Phonon Mean Free Path in Thin Films by using Classical Molecular Dynamics

A non-equilibrium molecular dynamic (NEMD) study has been performed to evaluate the phonon mean free path (MFP) of a solid material. Solid argon with a Lennard-Jones (L-J) potential is selected as a simulation material. The thermal conductivity of a thin film plays an important role in the design of nano-electro-mechanical systems (NEMS) or micro-electro-mechanical systems (MEMS) since heat removal from these devices is a crucial factor for their intended proper operations. The values calculated by using molecular dynamics (MD) simulations are compared with the available bulk experimental data when possible. It is confirmed that there is apparently a size effect on the thermal conductivity, which indicates that the microscale system has a lower thermal conductivity than that of the bulk material in the heat transfer direction. The dependence of the thermal conductivity on the system size is the result of a reduction in the phonon mean free path (MFP) as the system size becomes microscaled, and the MD simulations can be used to predict the phonon MFP of such a system.