Improved diamond particle reactivity by alumina coating

Diamond has the highest thermal conductivity of all bulk materials, making it one of the most promising thermally conductive fillers for thermal interface materials (TIMs). However, the commercial use of diamond for this purpose remains limited because the chemically inert diamond surface prevents mixing with polymer matrices. Hence, it would be helpful to improve the reactivity of the diamond surface without reducing the thermal conductivity of the diamond particles themselves. The present work used atomic layer deposition (ALD) to selectively modify the surface characteristics of diamond particles by applying an ultrathin conformal alumina film. Film thicknesses of 0.6–0.8 nm and 1.0–1.4 nm were obtained after five and ten ALD cycles, respectively. The deposited alumina had an amorphous structure and the modified diamond surfaces exhibited greatly enhanced chemical reactivity as demonstrated using a labeling agent. A TIM fabricated using alumina-coated diamond particles with a polydimethylsiloxane matrix showed improved thermal conductivity and flow rate. The alumina film effectively interacted with surfactants in the polymer matrix to improve the miscibility of the TIM components.