Atomic Layer Deposition of SiO₂ Films on BN Particles Using Sequential Surface Reactions

Alternating SiCl 4 and H 2 O exposures were used to deposit SiO 2 films with atomic layer control on BN particles. The high surface area of the BN particles facilitated the use of transmission Fourier transform infrared (FTIR) spectroscopy to monitor the sequential surface reactions. The BN particles initially displayed vibrational modes consistent with BOH* and BNH 2 * surface species. SiCl 4 exposure at 700 K converted these species to SiCl x * surface species. The subsequent H 2 O exposure at 700 K converted the SiCl x * species to SiOH* surface species. Alternate exposures of SiCl 4 and H 2 O yielded SiCl x * and SiOH* species, respectively, sequentially depositing silicon and oxygen with atomic layer control. By repeating the sequential surface reactions, the absorbance of SiO 2 bulk vibrational modes on the BN particles increased versus the number of SiCl 4 and H 2 O reaction cycles. Transmission electron microscopy studies revealed fairly uniform SiO 2 films of ∼28−38 Å on the edge planes of the BN particles after 32 reaction cycles at 700 K. SiO 2 films on the basal planes of the BN particles were thinner and occurred in patches. X-ray photoelectron spectroscopy analysis was consistent with some uncoated regions on the BN particles. These ultrathin SiO 2 films on BN particles may be useful to enhance the loading of BN particles in composite materials.