Fracture surface analysis of free-standing diamond films

Free-standing CVD diamond disk-shaped films of varying thicknesses between ∼40 and 1000 μm were fractured in ball-on-ring flexure using a high-precision hydraulic testing machine. Some of the films were smooth on the side formerly in contact with the substrate and rough (large crystallites) on the reverse side and some of the films were polished. Raman spectroscopic examination showed some of the films to be of high quality and others to be of lower quality (higher levels of non-diamond carbon mixed with diamond phase). All fracture surfaces were examined to identify the origin of failure. Strength varied between 650 and 971 MPa, and the fracture toughness was determined from fracture surface analysis to average 8 ± 1 MPam^1/2.