Diamond is the material with the highest thermal conductivity in nature. It can be divided into single crystal and polycrystalline. The thermal conductivity of single crystal diamond at room temperature is as high as 2400 W / ( m·K ), and the thermal conductivity of polycrystalline diamond at room temperature is close to 2000 W / ( m· K ). What is the principle of diamond with such high thermal conductivity ? Next, let 's reveal the mystery together !
Firstly, the crystal structure of diamond is analyzed, which is determined by its unique crystal structure : diamond is a crystal of carbon, in which the carbon atoms are combined by covalent bonds, so it is called covalent bond crystal. There is a strong Coulomb attraction between the electrons in the covalent bond and the nucleus, so the energy of the covalent bond is the highest among all the valence bonds. Therefore, the covalent bond crystal has a high melting point and a high elastic modulus ( i.e., not prone to elastic deformation ), brittle and hard. The covalent bond energy of diamond is very high, insoluble in almost all solvents, and difficult to extend, that is, non-plastic and fragile.
The atomic structure of diamond
Combined with the principle of crystal heat conduction-phonon heat conduction through lattice vibration, and crystal thermal conductivity is determined by heat capacity, phonon mean free path and phonon velocity. The anharmonic vibration of diamond lattice is weak, and the anharmonic effect will make the vibration between atoms couple with each other, thus frequently changing the propagation direction of vibration and hindering the free propagation of vibration, which is precisely the important reason for reducing the thermal conductivity. The anharmonic effect of diamond vibration is weak, so the thermal conductivity is naturally high. Similarly, when the temperature increases, the vibration amplitude increases, the anharmonic effect increases, and the thermal conductivity decreases.
In addition, described in the language of phonons : U-shaped phonon scattering reduces the average free path of phonons, thereby reducing thermal conductivity. However, such scattering requires the sum of the wave vectors of two phonons to fall outside the first Brillouin zone, so the participation of long wave vector phonons is required. Because the Debye temperature of diamond is very high ( ~ 2200 K ), the number of phonons in the long wave vector of diamond is much less than that of other materials at the same temperature, so the probability of U-shaped phonon scattering is low and the thermal conductivity is high.
Heat conduction of lattice vibration
Due to its excellent thermal conductivity, diamond has broad application prospects in military, aerospace, heat transfer and other fields. It can be used as a heat sink for high-power microwave devices, lasers and semiconductor switching devices, and as an insulating heat dissipation substrate for large-scale integrated circuits. At present, most heat sinks are made of copper, and the thermal conductivity of diamond is 5 times that of copper. It can be imagined that using diamond instead of copper to prepare heat sinks can greatly improve efficiency. The application of diamond film in heat sink is also remarkable. First, a layer of diamond film with a thickness of 0.5 ~ 1.0 mm is prepared by laser cutting into the required shape and size. After polishing, it is coated with metal coatings such as gold and other metals, which can be used as heat sink. In addition, diamond is also used in high-tech fields such as 5G chips, laser diode arrays, high-speed computer CPU chips, multi-dimensional integrated circuits, high-power radar microwave traveling wave tube heat conduction support rods, satellite expansion plates, and microwave integrated circuit substrates.
CSMH focuses on the research and production of diamond wafers. At present, it has diamond wafers, diamond heat sinks, GaN on diamond, AlN on diamond and other products. Among them, high-power semiconductor lasers packaged by diamond heat sinks have been used in optical communications. In the fields of laser diodes, power transistors, and electronic packaging materials, it can provide customers with diamond thermal management solutions.
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