Annealing temperature-driven near-surface crystallization with improved luminescence in self‐patterned alumina films

The impact of annealing on luminescence properties of radio-frequency magnetron sputtering grown alumina films and their possible application in radiation measurement are presented. Here, grazing incidence X-ray diffraction study reveals the growth of amorphous alumina films, while the annealing treatment results in the gradual formation of nanocrystallites. They are found to be embedded in the amorphous matrix by cross-sectional Transmission Electron Microscopy for 1200 °C annealed thin film. The evolution of self-patterned wrinkles has also been observed at the surface by Scanning Electron Microscopy. A comprehensive analysis of optically active defect centers is carried out by room temperature photoluminescence (PL) measurement. This indicates a monotonic increase of oxygen vacancies (F centers) with increasing annealing temperature up to 1200 °C, though they are not directly correlated with the thermoluminescence (TL) results after exposing them to gamma radiation from a ⁶⁰Co source. Based on PL analysis, the TL glow curves with increasing annealing temperature are elucidated in the light of the involvement of both trap centers and F-type recombination centers residing at grain boundaries. In terms of TL results, 1200 °C annealed alumina film is found to be superior to both the as-grown film, and the one annealed at 1100 °C. Finally, the linear TL response curves in the 1200 °C annealed film after exposing to both gamma radiation (up to 5 kGy) and energetic charged particles (80 MeV carbon ions) are demonstrated up to 130 kGy.