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

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Alternating SiCl4 and H2O exposures were used to deposit SiO2 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 BNH2* surface species. SiCl4 exposure at 700 K converted these species to SiClx* surface species. The subsequent H2O exposure at 700 K converted the SiClx* species to SiOH* surface species. Alternate exposures of SiCl4 and H2O yielded SiClx* and SiOH* species, respectively, sequentially depositing silicon and oxygen with atomic layer control. By repeating the sequential surface reactions, the absorbance of SiO2 bulk vibrational modes on the BN particles increased versus the number of SiCl4 and H2O reaction cycles. Transmission electron microscopy studies revealed fairly uniform SiO2 films of ∼28−38 Å on the edge planes of the BN particles after 32 reaction cycles at 700 K. SiO2 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 SiO2 films on BN particles may be useful to enhance the loading of BN particles in composite materials.