John D. Ferguson

Atomic layer deposition of ultrathin and conformal Al2O3 films on BN particles

Abstract Ultrathin and conformal Al2O3 films were deposited on BN particles using alternating exposures of Al(CH3)3 and H2O. 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 BNH2* surface species on the BN particles. These species were converted to AlCH3* species during Al(CH3)3 exposure. Subsequently, H2O exposure was used to convert the AlCH3* species into AlOH* species. Alternating Al(CH3)3 and H2O exposures yielded AlCH3* and AlOH* species, respectively, that sequentially deposited aluminum and oxygen with atomic layer control. The repetition of the Al(CH3)3 and H2O exposures in an ABAB… reaction sequence led to the appearance of bulk Al2O3 vibrational modes. The intensity of these bulk vibrational modes increased with the number of AB reaction cycles. Following Al2O3 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 Al2O3 films on the BN particles with a thickness of ∼90 A after 50 AB reaction cycles. The absence of observable B and N photoelectron signals during XPS analysis was consistent with a continuous and conformal Al2O3 coating. These ultrathin Al2O3 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.

ALD of SiO2 at Room Temperature Using TEOS and H 2 O with NH 3 as the Catalyst

Amine catalysts can reduce the high temperatures and long exposure times required for SiO 2 atomic layer deposition (ALD) using SiCl 4 and H 2 O reactants. One problem is that the reaction product, HCI, readily reacts with the amine catalysts to form a salt. Salt formation can be avoided by using organometallic silicon precursors. This study investigated catalyzed SiO 2 ALD on BaTiO 3 and ZrO 2 particles using alternating exposures of tetraethoxysilane (TEOS) and H 2 O at 300 K with NH3 as the catalyst. The sequential surface chemistry was monitored in a vacuum chamber using in situ transmission Fourier transform infrared (FTIR) spectroscopy. Alternating TEOS/NH 3 and H 2 O/NH 3 exposures yielded Si(OCH 2 CH 3 ) x * and SiOH* surface species, respectively, that sequentially deposited silicon and oxygen. Repetition of the TEOS and H 2 O exposures in an ABAB... reaction sequence led to the appearance of bulk SiO 2 vibrational modes. The infrared absorbance of these bulk SiO 2 vibrational modes increased with the number of AB reaction cycles. After SiO 2 deposition, the BaTiO 3 and ZrO 2 particles were examined using transmission electron microscopy (TEM). The TEM images revealed extremely uniform and conformal SiO 2 films. The measured SiO 2 film thicknesses were consistent with SiO 2 ALD growth rates of 0.7-0.8 A per AB reaction cycle. The NH 3 catalysis mechanism was also explored by monitoring the FTIR spectra of hydroxylated SiO 2 particles vs. NH 3 pressure at constant temperature and vs. temperature at constant NH 3 pressure. The spectra revealed strong hydrogen bonding between NH 3 and SiOH* surface species that activates the oxygen in SiOH* for nucleophilic attack. Catalyzed SiO 2 at room temperature should be useful for deposition of inorganic and insulating films on thermally fragile organic, polymeric, or biological substrates.

Atomic layer deposition of boron nitride using sequential exposures of BCl3 and NH3

Abstract The atomic layer deposition (ALD) of boron nitride (BN) was demonstrated on ZrO 2 particles. The BN ALD was accomplished by splitting the binary chemical vapor deposition reaction, BCl 3 +NH 3 →BN+3HCl, into BCl 3 and NH 3 half-reactions. BCl 3 and NH 3 were alternately applied in an ABAB… reaction sequence at 500 K. Fourier transform infrared (FTIR) spectroscopy observed that the OH stretching vibration of the ZrOH* surface species on the initial ZrO 2 particles was removed by the first BCl 3 exposure. NH 2 asymmetric and symmetric stretching vibrations attributed to BNH 2 * dihydride species and NH stretching vibrations assigned to B 2 NH* monohydride species were observed after the subsequent NH 3 exposure. The BNH 2 * and B 2 NH* species were removed and added after the BCl 3 and NH 3 exposures, respectively. The surface species were monitored during the first 26 AB cycles. FTIR spectroscopy was also used to monitor the bulk BN vibrational feature that grew progressively throughout the 26 AB cycles. After the 26 AB cycles at 500 K, transmission electron microscopy studies revealed uniform and conformal BN films with a thickness of ∼25 A on the ZrO 2 particles.

Atomic layer deposition of Al2O3 and SiO2 on BN particles using sequential surface reactions

Abstract Al2O3 and SiO2 were deposited on BN particles with atomic layer control using alternating exposures of Al(CH3)3/H2O and SiCl4/H2O, respectively. The sequential surface chemistry was monitored in vacuum using transmission Fourier transform infrared (FTIR) spectroscopy studies on high surface area BN particles. The initial BN particles displayed vibrational modes consistent with BOH* and BNH2* surface species. These species reacted with Al(CH3)3 or SiCl4 and were converted to AlCH3* or SiCl* surface species. The subsequent reaction with H2O converted the surface species to AlOH* or SiOH*. By repeating the sequential surface reactions, the absorbance of Al2O3 and SiO2 bulk vibrational modes on the BN particles increased vs. the number of reaction cycles. Transmission electron microscopy (TEM) studies revealed extremely uniform and conformal Al2O3 coatings on the BN particles. X-ray photoelectron spectroscopy (XPS) analysis was consistent with conformal Al2O3 coatings. In contrast, TEM investigations observed fairly uniform SiO2 coatings on the edge planes of the BN particles and only patches of SiO2 on the basal planes. XPS measurements were consistent with some uncovered regions on the SiO2-coated BN particles. These results illustrate the capability of sequential surface reactions to deposit ultrathin Al2O3 and SiO2 films on BN particles.

Surface chemistry and infrared absorbance changes during ZnO atomic layer deposition on ZrO2 and BaTiO3 particles

ZnO atomic layer deposition (ALD) was achieved using sequential exposures of Zn(CH2CH3)2 and H2O on ZrO2 and BaTiO3 particles at 450K. The surface chemistry of ZnO ALD was monitored in vacuum using Fourier transform infrared spectroscopy. The BaTiO3 and ZrO2 particles initially displayed vibrational features consistent with surface hydroxyl (-OH) groups. Zn(CH2CH3)2 exposure removed the surface hydroxyl groups and created Zn(CH2CH3)* surface species. The subsequent H2O exposure removed the Zn(CH2CH3)* surface species and produced ZnOH* surface species. Repeating the Zn(CH2CH3)2 and H2O exposures in an ABAB… reaction sequence at 450K progressively deposited ZnO. Because ZnO is a semiconductor, the background infrared absorbance increased with the number of AB cycles during the deposition of the ZnO film. The increasing background infrared absorbance during long Zn(CH2CH3)2 exposures also revealed that the Zn(CH2CH3)2 reaction is not self-limiting. The background absorbance was modulated dramatically by the...