Formation, growth and dissociation of He bubbles in Al2O3
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms(2004)
摘要
The formation and dissociation of helium bubbles and helium desorption are investigated in sapphire Al2O3(0001) implanted with 30 keV He ions to four different doses of 0.1, 0.3, 1.0 and 2.0×1016 ions cm−2. The samples were annealed isochronally up to 1850 K in steps of 100 K. The techniques of Doppler broadening positron beam analysis (PBA) and neutron depth profiling (NDP) were used to investigate defect evolution and helium retention, respectively, during the annealing procedure. It was observed that the maximum bubble volume is found after 1250 K annealing, after which a process of bubble shrinkage sets in. Cross-sectional transmission electron microscopy (XTEM) was performed on the sample that was implanted with the highest-dose (2.0×1016 He ions cm−2) after annealing at 1250 K. It was found that the bubbles are shaped as discs lying parallel with the surface and that the average bubble size is 5.5 nm. In all samples, helium is released mainly at a temperature of 1750 K. The desorption curves were analyzed by means of a permeation model. The activation energy for permeation was found as 4.0 eV.
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61.46.+w,61.80.−x,68.43.Vx,68.55.Ln
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