Electronics-Cooling.com have a fascinating article about metal-diamond matrix heat spreaders for the thermal solutions industry. Essentially, the new technique creates a mixture of silver and synthetic diamonds which possess a thermal conductivity on the order of 600W/mK at a relatively reasonable manufacturing cost. The article focuses on the Silver-Diamond matrix (best performing), but Aluminum-Diamond and Copper-Diamond are also tested.
Here's a quote from the article to whet your whistle;
"The metal-diamond interface plays an extremely crucial role in diamond composites in regards to the thermal properties and stability of the composites. The interface must provide a mechanically stable bond between the diamond and the metal matrix but is also responsible for the heat transfer between the diamond and the metal. The custom alloys with specific alloying additions build carbides at the diamond providing such a thermally stable interface."
"The cost of the diamond composites is determined by the features necessary in a given application. As a rule of thumb diamond composites cost a factor of 2-3 higher than existing composite materials, as seen in Figure 5. "
"Diamond composites have superior thermal conductivity and a CTE matching to that of the semiconductor materials. These advanced composite materials are capable of providing thermal management solutions at the heat spreader level for main applications such as lids for CPUs, heat sinks"