Dielectric Properties of Diamond Using an X-band Microwave Split Dielectric Resonator

This work presents an easy-to-use microwave split dielectric resonator (MSDR) for X-band dielectric measurements of free-standing unpolished poly-crystalline diamond (PCD). PCD grown with varying CH4/H2 and O2/ CH4/H2 in the gas phase show stark differences in dielectric loss. Low microwave dielectric loss PCD is found for CH4/H2 concentrations of less than 5% while PCD grown with O2 show very high loss tangents. Vacuum annealing introduces non-diamond carbon (NDC) impurities which increases the loss, however, even after significant discolouration the loss is still lower than the O2 grown PCD. The loss mechanism of O2 grown PCD is likely due to a high concentration of grain boundaries and grain boundary hopping conduction mechanisms as opposed to high concentrations of NDC impurities.