Thermal Conductivity Of Diamond Nanowires: A None-quilibrium Molecular Dynamics Study

As far as devices for microelectronics systems are concerned, the volume energy density increases with the integration increasing. It is important to export heat timely and efficiently to ensure the stability of device performance. Diamond has excellent mechanical and electrical properties, such as high thermal conductivity. So diamond nano-materials are the thermal material of top choice for micro-system device. Therefore, diamond nano-materials thermal conductivity is into the current research focuses.In the nanometer scale, many thermal measurement techniques will not be able to reach the spatial resolution and temporal resolution limits, and nano-scale experimental productions of measuring instruments are also more difficult. Therefore, it is more difficult to measure nano-materials thermal conductivity in the experimental measurement.At present, molecular dynamics method is a more mature approach to research in nano-material thermal conductivity. Thermal conductivities for relatively small scale of nano-materials have been reported by molecular dynamics calculations. However, thermal conductivities for nano-scale diamond, which close to line practical application, have few studies by the calculation of the limitations.With the development of the computer and parallel computing, it is possible to calculate diamond nanowires thermal conductivity by molecular dynamics for practical application of nano-scale. In this study, a large grid of Canada Sharcnet parallel computer is used, we study the cross-sectional area, length, orientation and temperature on the diamond nanowires thermal conductivity, using non-equilibrium molecular dynamics method. Size effect, temperature effect of diamond nanowires thermal conductivity and the different orientations of diamond nanowires thermal conductivity were investigated, and the major findings are in the following:When the temperature is 300 K, diamond nanowires thermal conductivity are investigated, with different cross-sectional areas ranging from 2 to 30 nm2 and length 85.6 nm. Three crystal orientations of diamond nanowires have been considered, that is<001>,<011> and<111> crystal orientations. Density of states with phonon spectrum of the thermal conductivity of nano-diamond wire mechanism. And with the help of phonon density of states, the mechanism of cross-sectional area dependence of thermal conductivity is investigated. The result shows that:For the same orientation of the diamond nanowires, its thermal conductivity increase with the cross-sectional area increasing, with obvious size effect; for the same cross-sectional area of the diamond nanowires, thermal conductivity has the maximum in<011> orientation, minimum in<001> orientation; diamond nanowires thermal conductivity much lower than the corresponding block-oriented diamond.When the temperature is 300 K, diamond nanowires thermal conductivity are investigated, with different length ranging from 20 to 350 nm and cross-sectional areas 2.2 nm2. Three crystal orientations of diamond nanowires have been considered, that is<001> <011> and<111> crystal orientations. The result shows that:For the same orientation of the diamond nanowires, its thermal conductivity increase with the length increasing, with obvious size effect; and so, for the same length of the diamond nanowires, thermal conductivity has the maximum in<011> orientation, minimum in<001> orientation; diamond nanowires thermal conductivity much lower than the corresponding block-oriented diamond.Diamond nanowires thermal conductivity are investigated in the temperature range 0 to 1000 K, with cross sectional area of 2.2 nm2, the length of 53 nm,125 nm,250 nm,320 nm respectively, three crystal orientations of diamond nanowires have been considered, that is <001>,<011> and<111> crystal orientations. The result shows that:diamond nanowires thermal conductivity have the dominant temperature effect. It can be seen that initially all diamond nanowires thermal conductivities increase with the increasing temperature, and then decrease. For all crystal orientations of diamond nanowires, the temperature position for maximum thermal conductivity decreases with increasing diamond nanowires length.