​Changes in the surface of sapphire crystal (2)

Changes in the surface of sapphire crystal (2)

The composition of the layer adjacent to the surface may change under electron irradiation. Partial loss of oxygen ions results in an excess of aluminum ions.

The sapphire samples were diluted with 6 keV Ar+ ions accompanied by the formation of an amorphous surface layer. Subsequent irradiation in electron microscopy resulted in the appearance of the non-equilibrium phase γ-Al2O3 [5].

The absorption bands at 3,450 cm-1 (2.1•1019 protons/cm2) and 2,570 cm-1 (1.7•1019 deuterons/cm2) in the IR region are attributed to the formation of hydroxyl groups (deuterium groups) in the adjacent layers of the surface. The depth of the adjacent layer in seconds is determined by the ion energy and amount.

The hygroscopicity of the surface was determined after irradiation with 15 keV H+, D+, He+ ions at a dose exceeding 2•1017 ions/cm2 [6].

Due to the bonding between vacancies and hydrogen, blisters (gas-containing pores) are formed in the adjacent layer of the surface irradiated by hydrogen ions. When the hydrogen concentration is higher than 1018cm-2, the density of the bubbles reaches a saturation state. At a certain critical value of the hydrogen pressure of hydrogen in the pores and under heating, the thermal activation and desorption of hydrogen (foaming) were observed in sapphire [7]. The resistance to surface foaming is the highest on the (1010) plane, ( The 0001) plane is centered and the (1012) plane is the lowest. The resistance is determined by the interplanar spacing rather than the density of atoms.

Surface oxygen ion bombardment can also lead to the formation of oxygen bubbles in the surface adjacent layers [8] and the appearance of excess aluminum on the surface.

The intra-bulk changes in the surface-adjacent layer caused by the incorporation of 1H, 12C, 14N, 24Mg and 40Ar ions (100-500 keV, 1016cm-2 dose) are defined by the lattice anisotropy. Observed along the C-axis to a greater expansion.

Changes in the structure. After O+ irradiation (200keV energy, 5•105 cm-2 dose) and annealing at 1,170 K in vacuum for 30 min, small dislocation loops with a density of ~5•1015 cm-3 were observed (30 nm). As the annealing time increases, the dislocation loop density decreases by two orders of magnitude, while point defect complexes appear (these complexes are ~15 nm black dots in electron microscopy) [9].

The desorption of surface-adsorbed atoms and matrix ions is excited by electron and neutron irradiation.

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