Atomic layer deposition of ultrathin and conformal Al 2O 3 films on BN particles

Abstract

Ultrathin and conformal Al 2O 3 films were deposited on BN particles using alternating exposures of Al(CH 3) 3 and H 2O. Transmission Fourier transform infrared spectroscopy performed in vacuum on high surface area BN particles was used to monitor the surface chemistry during the sequential exposures. The initial vibrational modes were consistent with BOH* and BNH 2* surface species on the BN particles. These species were converted to AlCH 3* species during Al(CH 3) 3 exposure. Subsequently, H 2O exposure was used to convert the AlCH 3* species into AlOH* species. Alternating Al(CH 3) 3 and H 2O exposures yielded AlCH 3* and AlOH* species, respectively, that sequentially deposited aluminum and oxygen with atomic layer control. The repetition of the Al(CH 3) 3 and H 2O exposures in an ABAB… reaction sequence led to the appearance of bulk Al 2O 3 vibrational modes. The intensity of these bulk vibrational modes increased with the number of AB reaction cycles. Following Al 2O 3 deposition, the BN particles were also examined with transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM studies revealed extremely uniform and conformal Al 2O 3 films on the BN particles with a thickness of ∼90 Å after 50 AB reaction cycles. The absence of observable B and N photoelectron signals during XPS analysis was consistent with a continuous and conformal Al 2O 3 coating. These ultrathin Al 2O 3 films should help to increase BN particle loading in composite materials for thermal management applications without degrading the high thermal conductivity of the BN particles.