Structural and Dynamic Properties of Gallium Alkoxides

Abstract

A comparison of chlorido-gallium functionalized alkoxides as precursors for aerosol-assisted chemical vapor deposition (AACVD) was carried out. Variable-temperature (VT)-NMR studies were used to probe the fluxional behavior of these alkoxides in solution, and hence their utility as precursors. The synthesis involved the initial isolation of the dimer [GaCl(NMe₂)₂]₂ via a salt metathesis route from GaCl₃ and 2 equiv of LiNMe₂. This dimer was then reacted with 4 equiv of HOCH₂CH₂CH₂NEt₂, resulting in the formation of Ga[μ-(OCH₂CH₂CH₂NEt₂)₂GaCl₂]₃ (<b>1</b>). Mass spectrometry and VT-NMR confirmed the oligomeric structure of <b>1</b>. Tuning of the ligand properties, namely, the chain length and substituents on N, resulted in formation of the monomers [GaCl(OR)₂] (R = CH₂CH₂NEt₂, (<b>2</b>); CH₂CH₂CH₂NMe₂, (<b>3</b>)). VT-NMR studies, supported by density functional theory calculations, confirmed that the ligands in both <b>2</b> and <b>3</b> possess a hemilabile coordination to the gallium center, owing to either a shorter carbon backbone (<b>2</b>) or less steric hindrance (<b>3</b>). Both <b>2</b> and <b>3</b> were selected for use as precursors for AACVD: deposition at 450 °C gave thin films of amorphous Ga₂O₃, which were subsequently annealed at 1000 °C to afford crystalline Ga₂O₃ material. The films were fully characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-visible spectroscopy, and energy dispersive X-ray analysis.