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The thermal conductivity of the silicon nanowire was calculated using nonequilibrium molecular dynamics method. The dependence of thermal conductivity on the wire length, cross-sectional area, and temperature was investigated. The Stillinger-Weber potential model and the Nose-Hoover thermostat were used. The surfaces at the wire ends were set free boundary conditions and potential boundaries in other directions. The cross-sectional area range of the nanowires under research is from about 5 nm2 to 19 nm2 and the length range is from about 6 nm to 54 nm. The results agree well with experimental results. The reciprocal of thermal conductivity was found to be linear with that of nanowire length. And our results quantitatively showed that decreasing the cross-sectional area can reduce the phonon mean free path of the nanowire.

Thermal rectification as a new phenomenon is attracting great attention. Thermal rectification in silicon nanowires with axial mass gradient is investigated by molecular dynamics simulation. The results of the simulations show that the thermal conductivities are different for the heat flux with opposite directions. The rectification efficiency becomes larger when the mass gradient increases. The effect of temperature gradient on the thermal rectification is also considered. The phonon density of states is calculated to explain the phenomenon. It is found that the interface is responsible to the thermal rectification.

A thermal rectifier has such nature that its thermal conductance or thermal conductivity has different values with reversed heat flux direction. This work investigates the rectification of the cross-plane thermal conductivity and interfacial thermal resistance of nanoscale bi-layered films using the nonequilibrium molecular dynamics (NEMD) method. The effects of the thickness of the single layer with the total thickness constant, the ratio of the atomic mass and temperature difference in the two ends on the thermal rectification are all considered. The results of the simulations show that the thermal conductivity and the interfacial thermal resistance are different for the heat flux with opposite directions. For the composite film with two layers of the same thicknesses, the thermal conductivity is larger when the heat flux direction is from the light layer to the heavy one. The difference becomes larger when the ratio of the atomic mass in the two layers increases. Increasing the heat flux makes the rectification of thermal conductivity larger, which means that the rectification is dependent on the temperature. For the composite film with fixed total thickness, the rectification becomes smaller when the thickness of the light layer increases. When the light layer is thick enough, the rectification is found reversed, which means that the thermal conductivity is larger with the heat flux direction from the heavy layer to the light one. The phonon density of states is also calculated to explain the phenomenon, and it is found that the overlap of the phonon density of states for the two layers is almost same even if the rectification of the thermal conductivity is reversed.