PROPERTIES OF BULK POLYCRYSTALLINE CVD DIAMOND

Properties are reported of bulk polycrystalline diamond synthesized by chemical vapour deposition (BPCVD diamond). It is shown that this material exhibits optical and thermal properties similar to those of high purity natural Type IIa diamond. The mechanical strength and elastic properties of this material have been measured by a disc-bursting technique and values of bursting strength of up to 1138 MPa and Young's modulus values of 986-1079 GPa have been observed. Indentation measurements indicate a value for fracture toughness K1c of 6 MP a m1/2. The dielectric constant and dielectric loss have been measured by an open resonator technique at frequencies of 36, 72 and 144 GHz. Bulk values of dielectric loss tangent as low as 73 x 10(-6) have been observed, the lowest so far reported for CVD diamond. The threshold to laser damage has been tested at laser wavelengths of 10.6, 1.06 and 0.532 mum. Damage thresholds are found to be influenced by bulk absorption. However, the best values measured in BPCVD diamond at 10.6 mum approach that of natural Type IIa diamond.