TENSILE-STRENGTH OF SYNTHETIC CHEMICAL-VAPOR-DEPOSITED DIAMOND

Pressure burst tests gave measured tensile strengths between 230 and 4 10 MPa for a total of six chemical-vapor-deposited (CVD) diamond disks in both transparent ''white'' and opaque ''black'' forms obtained fro m three different sources. The disks were nominally 0.635 cm in diamet er and 254 mu m thick. These strengths are explained by a theoretical model using a Young's modulus of 1.05x10(6) MPa and a fracture surface energy of 5.3 J/m(2), appropriate for natural diamond, and with criti cal crack lengths between 33 and 105 mu m. The latter lengths can fit, either on or inside, the tapered columnar crystal grains that grow ve rtically in synthetic CVD diamond films. The model is consistent with the observed inverse dependence of measured tensile strength on film t hickness and with tensile strengths between 180 and 5190 MPa reported by other workers for synthetic CVD diamond. (C) 1995 American Institut e of Physics.