Thermophysical behaviour of diamond composites for diode laser heat sink applications at temperatures between 4K and ambient

In the frame of an ESA Basic Research Technology Program (TRP) activity experimental work was performed on "clean model" systems, i.e. well-defined synthetic diamond mono-crystal surfaces, which were functionalized and characterized by XPS. In a second approach those results were transformed onto synthetic diamond particles in Al- and Ag-diamond composites and the measurement of thermal conductivity in the temperature range between roughly 4 K and 298 K. Knowledge of thermal transport between diamond and metal surfaces and the thermal conductivity behavior of composites in that temperature range is essential for the development of improved thermal management applications and of heat sink materials to be operated in cryo-lasers and in space LIDAR applications and similar. The results obtained show an influence of matrix composition, diamond particle size and diamond surface treatment on thermal conductivity behavior, which can be as high as 1050 W m-1 K-1 at around 150 K. The surface treatment results in oxygenated diamond surfaces and can influence interfacial thermal conductance h. Furthermore, the h(T)-values in our findings on “real” composites can be close to values determined on clean model systems, i.e. sputtered and evaporated metal layers on even diamond mono-crystal substrates. In a next approach laser crystal materials were directly joined to the heat sink material to minimize strains.