Spherical aluminum oxide nanoparticle synthesis and monolayer film assembly

Aluminum oxide is an important ceramic material for coatings and catalyst support for high-temperature applications. In this work, spherical aluminum oxide (AlO_x) nanoparticles (NPs) are synthesized via the thermal decomposition of aluminum oleate using oleic acid as a stabilizing agent. X-ray diffraction analysis confirms its crystallization to γ-Al₂O₃ and α-Al₂O₃ after annealing at 700 and 1100 °C, respectively, revealing their gradual phase transition. Morphological and crystallinity changes of spherical nanoparticles upon annealing were investigated by transmission electron microscopy. The chemical composition and phase transitions to Al₂O₃ NPs were supported by X-ray photoelectron spectroscopy as a function of temperature. Monolayer assembly of as-synthesized NPs onto quartz substrate was performed using organic linker molecules (11-phosphonoundecanoic acid), which was confirmed by atomic force microscopy imaging. The optical band gap of the monolayer assembly was evaluated after annealing at different temperatures along with transmittance properties to compare with the current literature by UV–visible spectroscopy.