Alumina Nanostructures Formed by Electron Beam Irradiation

抄録

Two types of metastable δ- and θ-Al₂O₃ complex nanostructures, ‘nanoball’ and ‘nanowire’, were obtained from δ- and θ-Al₂O₃ particles by electron beam irradiation at an intensity of 1.0-5.5×10²² e/cm²sec by transmission electron microscopy (TEM). Their average dimensions were 20 nm diameter for the nanoball, and 15 nm diameter and approximately 50 nm length for the nanowire, which were changed by controlling the irradiation intensity. Nanoballs wrapped by an Al-O amorphous layer adhered to the tip of every nanowire, whereas nanowires grew dynamically in the process of flashing an electron beam. These nanostructures differ from the Al nanodecahedron obtained by lower electron beam irradiation, 3.0×10²⁰ e/cm²sec, to θ-Al₂O₃ particles reported by B.-S. Xu and S.-I. Tanaka in 1995. The intensity of more than 7.0×10²¹ e/cm²sec and a flashing mode of irradiation are required for the growth of nanowires. The grown nanowire and nanoball had the same crystal structure in two alumina polymorphs, θ-Al₂O₃ and δ-Al₂O₃. We observed in situ the dynamical growth of the nanowire and concluded that the nanowire grew epitaxially from the interface between the nanoball and the parent particle keeping the same crystallographic relations.