​Changes in the surface of a sapphire crystal

Changes in the surface of a sapphire crystal

Al3+:[O2-]6 type point and group defects appear in the layer adjacent to the crystal surface. Dislocation density rises and dislocation loops are created. The unique characteristics of defect formation in the electronic structure of the surface adjacent layer are determined by the type and energy of irradiation . Irradiation damage to the crystal surface affects the kinetics of atomic diffusion and other processes.

Surface relief. Bombardment of a sapphire crystal with 10keV Ar ions at a dose of 1020 cm-2 and an incident angle of 70º at room temperature resulted in the removal of ~40 μm of the surface adjacent layer. Irradiation of the polished crystal surface with a generally incident ion pair, the surface The roughness Rz decreased from 0.85 to 0.65 μm. For the polished crystal surface with surface removal of 6-μm, the roughness decreased from Rz = 0.03-0.04 μm to Rz = 0.01-0.02 μm[1]. Upon incidence, the surface roughness rises due to the formation of microstructures.

The increase of bombarding ion energy (Kr, 40 keV, dose over 1015cm-2) produces lattice radiation damage. The ratio of mobile Al and O atoms is about 1:3[2].

The amorphous sapphire surface is formed under irradiation with enriched energy of about 3 1023 keV/cm3 (~44 kJ/mm2), for example, under irradiation of Y ions (300 keV, dose of 5.8 1017 cm2) [3]. The thresholds for the formation of the amorphous layer under the irradiation of Zr and Zn ions are of the same order of magnitude. The depth of the amorphous layer can reach 40-100 nm. Consistent with the data [4], the saturation dose corresponding to the onset of the formation of the sapphire amorphous layer is 1014 ions/cm2 (85Kr, 10keV) (for zirconium and diamond this dose is 3•1013 ions/cm2 and 3•1014 ions/cm2, respectively). The depth of the amorphous layer determines the apparent load at <50 g. Microhardness values. Although the depth of ion incorporation is critical (up to 1000Å), lattice deformation can be partially eliminated by annealing in an oxygen atmosphere at 870-1,870K.

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