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 presence of ethyl (–CH2CH3) or hydroxyl (-OH) groups on the surface of the growing ZnO film. The infrared absorbance was higher with hydroxyl (-OH) groups and lower with ethyl (–CH2CH3) groups on the ZnO surface. The background absorbance changes were not linear with surface coverage. The large changes in absorbance after low reactant exposure suggested that the most reactive surface sites may be most influential in affecting the film conductance. Transmission electron microscopy (TEM) was used to examine the ZnO films deposited on the ZrO2 and BaTiO3 particles. The TEM images revealed ZrO2 and BaTiO3 particles encapsulated by conformal ZnO films. The ZnO films had a thickness of ∼43Å after 20 AB reaction cycles and ∼65Å after 30 AB reaction cycles, respectively. These TEM images are consistent with a ZnO ALD growth rate at 450K of ∼2.2Å∕AB cycle.