Preparation And Functional Properties Of Diamond Polycrystalline Materials

Diamond has many advantages compared with other semiconductor materials, such as low dielectric constant, high band gap, good electron hole mobility, high thermal conductivity and optical properties. The potential use of polycrystalline diamond as ceramic substrate, heat sink materials, and microwave window materials needs an urgent research and development. In this paper, polycrystalline diamond was prepared by the high-temperature and high-pressure method, pressureless sintering of sol-gel and solid state reaction method, respectively. The microstructure and electrical, thermal, optical and other properties and the effects of different sintering method had been investigated by SEM, PL spectroscopy and impedance analyzer.The main findings of this paper were as follows: the near ultraviolet light-emitting properties of polycrystalline diamond materials prepared by high-temperature and high-pressure and rapid sintering. It had been shown that the metal element Zn with high boiling and low melting point could promote the sintering and densification of diamond below the Co eutectic temperature by different phases of transition metals addition. Zn-containing polycrystalline diamond material photoluminescence spectra was investigated, it had been found that a series of sharp fluorescence spectra with the emission line width at half maximum was less than 0.5 nm when the excitation wavelength was 200nm and PL spectra was in the UV range of 310 to 390nm. The Si-containing polycrystalline diamond composite material had high resistivity and high volage resistance stability under this condition. The diamond composite material prepared by sol-gel and low-temperature pressureless sintering method had a slightly larger resistance and smaller dielectric loss than thin diamond film. The dielectric constant and the dielectric loss of diamond/ceramic polycrystalline composites materials with good high-frequency dielectric stability prepared by citric acid as complexing agent reduced to 2.55 and 10-3, respectively. Compared with the polycrystalline diamond prepared by sol-gel method, the polycrystalline diamond prepared by solid-phase reaction and high temperature sintering needed high sintering temperature and it had larger porosity, dielectric constant and dielectric loss.