Formation and thermal stability of aluminium nanoparticles synthesized via yttrium ion implantation into sapphire

Abstract

Yttrium ion implantation of 1 1 2 3 alumina resulted in the formation of metallic aluminium–yttrium, face centred cubic (a0=0.41 nm) spherical nanocrystals (∼ 12 nm in diameter) embedded in an amorphous matrix. A fluence of 5×1016Y+/cm2 implanted at ambient temperature and accelerating energies of 150 or 170 keV yielded this result. Crystalline nanoparticles were not present in the amorphous matrix for implantations done with identical conditions but lower energy (100 keV). Substrates implanted at 150 keV were annealed in laboratory air for times ranging from 20 to 90 min and temperatures ranging from 1000 to 1400°C. A clear progression of morphologies resulted from these annealing treatments. A 1000°C, 90 min anneal produced ∼13% recrystallization of the amorphous region and induced the formation of crystallites of a metastable Y–Al alloy. An 1100°C, 90 min anneal demonstrated ∼40% recrystallization of the amorphous region, accompanied by the formation of partially aligned internal grains of Y2O3. Electron diffraction shows that the Y–Al alloy crystallites which formed in the 1000°C anneal are also present at 1100°C. A highest temperature anneal of 1400°C, 60 min induced essentially complete recrystallization of the amorphous phase, the dissolution of the metastable Y–Al alloy, the retention of the internal yttria grains, and the formation of partially oriented external grains of yttria resulting from the segregation of yttrium to the substrate surface.