Synthetic diamond heat spreaders

A synthetic diamond heat spreader comprising a first layer of synthetic diamond material forming a base support layer, a second layer of synthetic diamond material disposed on the first layer and forming a diamond surface layer, wherein the diamond surface layer has a thickness equal to/less than a thickness of the base support layer and a nitrogen content less than that of the base support layer, and wherein the nitrogen content of the diamond surface layer and the diamond surface layer is selected such that the thermal conductivity layers are 1000 W/mK to 1800 W/mK and 1900 W/mK to 2800 W/mK respectively. The heat spreader may include a metal, silicon/silicon carbide, semiconductor or an adhesive layer. A method of manufacturing a synthetic diamond heat spreader comprising growing a synthetic diamond material in a chemical vapour deposition (CVD) reactor using a carbon source gas, controlling nitrogen concentration in the CVD reactor during growth to form a two layer diamond structure including a base support layer and a diamond surface layer wherein the nitrogen content of the layers are selected such that the layer thermal conductivities are 1000 W/mK to 1800 W/mK and 1900 W/mK to 2800 W/mK respectively.