Crystallization, Phase Stability, Microstructure, and Chemical Bonding in Ga₂O₃ Nanofibers Made by Electrospinning

We report on the crystal structure, phase stability, surface morphology, microstructure, chemical bonding, and electronic properties of gallium oxide (Ga₂O₃) nanofibers made by a simple and economically viable electrospinning process. The effect of processing parameters on the properties of Ga₂O₃ nanofibers were evaluated by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Thermal treatments in the range of 700-900 °C induce crystallization of amorphous fibers and lead to phase stabilization of α-GaOOH, β-Ga₂O₃, or mixtures of these phases. The electron diffraction analyses coupled with XPS indicate that the transformation sequence progresses by forming amorphous fibers, which then transform to crystalline fibers with a mixture of α-GaOOH and β-Ga₂O₃ at intermediate temperatures and fully transforms to the β-Ga₂O₃ phase at higher temperatures (800-900 °C). Raman spectroscopic analyses corroborate the structural evolution and confirm the high chemical quality of the β-Ga₂O₃ nanofibers. The surface analysis by XPS studies indicates that the hydroxyl groups are present for the as-synthesized samples, while thermal treatment at higher temperatures fully removes those hydroxyl groups, resulting in the formation of β-Ga₂O₃ nanofibers.