Thermal conductivity of free-standing CVD diamond films by growing on both nuclear and growth sides

Polycrystalline CVD diamond typically has inhomogeneous structure in cross section, with grain size monotonically increasing from bottom (nucleation) side to top (growth) side, this resulting in a significant difference in local thermal conductivity in the layers adjacent to the two surfaces. The polycrystalline diamond films with both sides of similar structure with coarse-grains are of interest for thermal management applications. Here, we produced a double-side coarse-grain polycrystalline diamond film by microwave plasma assisted chemical vapor deposition (MPCVD), by a repeated diamond growth on nucleation side of a primary free-standing film. The grain size, texture, morphology and phase purity of the samples were characterized with SEM, XRD and Raman spectroscopy, while the thermal conductivity (TC) perpendicularly to the film plane was measured by a laser flash technique in the temperature range of 250–400 K. The thermal conductivity of a single layer and bi-layered films are found to be almost identical, while the local TC values for latter on both sides are expected to become similar. A simple model discretizing the film in two regions, “poor” and “good” diamond layers, is considered to explain the observed TC temperature dependences.