  Non-equilibrium molecular dynamics (NEMD) simulations were performed on
Au-SAM (self-assembly monolayer)-Au junctions to study the thermal energy
transport across the junctions. Thermal conductance of the Au-SAM interfaces
was calculated. Temperature effects, simulated external pressure effects, SAM
molecule coverage effects and Au-SAM bond strength effects on the interfacial
thermal conductance were studied. It was found that the interfacial thermal
conductance increased with temperature increase at temperatures lower than
250K, but it did not have large changes at temperatures from 250K to 400K. Such
a trend was found to be similar to experimental observations on similar
junctions. The simulated external pressure did not affect the interfacial
thermal conductance. SAM molecule coverage and Au-SAM bond strength were found
to significantly affect on the thermal conductance. The vibration densities of
state (VDOS) were calculated to explore the mechanism of thermal energy
transport. Interfacial thermal resistance was found mainly due to the limited
population of low-frequency vibration modes of the SAM molecule. Ballistic
energy transport inside the SAM molecules was confirmed, and the anharmonicity
played an important role in energy transport across the junctions. A heat pulse
was imposed on the junction substrate, and heat dissipation inside the junction
was studied. Analysis of the junction response to the heat pulse showed that
the Au-SAM interfacial thermal resistance was much larger than the Au substrate
and SAM resistances separately. This work showed that both the Au substrate and
SAM molecules transported thermal energy efficiently, and it was the Au-SAM
interfaces that dominated the thermal energy transport across the Au-SAM-Au
junctions.
