STUDY OF LEUKOSAPPHIRE SURFACE MORPHOLOGY CHANGE BY ARGON ION BEAM AT SMALL GRAZING ANGLE

Subject of Research. The paper presents the results of experimental study on the specific features of argon ion beam effect on a sapphire surface at small grazing angles. Mechanically ground and defective epipolished leucosapphire plates with 20 × 20 × 1.2 mm in size were used as experimental samples. The initial surface roughness of the polished samples was 0.250–1 μm and of the epipolished ones was 5–10 nm. Method. The ion beam deposition setup was used for research. It includes the ion source of CLAN-53M type with ion neutralizer. The ion source generates ion flux with energies in the range of 150–1500 eV, with an output ion current density up to 4 mA/cm2, with ion current from 10 to 80 mA. The studies were carried out at different technological parameters of ion-beam polishing: the ion energy and the angle between the sapphire surface and the ion beam axis α. Main Results. We have determined effects of sapphire surface morphology change both with preservation and change in the overall roughness level, and the effect of surface structuring during processing in two projections with the formation of flat peaks with a diameter of 2 μm. The experiment results have shown that the maximum efficiency (the highest value is a change in the arithmetic average surface roughness) during ion-beam polishing is observed at α equal to 15° and the ion beam energy of 400 eV. When α value changes from 25 to 30°, an oriented change of the surface morphology from the symmetrically ordered surface microrelief to an asymmetric one occurs. At the same time, the flat sides do not bleed much, and the effect of steep shadow smoothing of the local microrelief is observed with retention of the same general roughness level. After the sample surface processing with ion beam at the first stage of the experiment, it was re-processed at 90° angle relative to the previous treatment, which led to cross-spraying of the shadow sections and the design of gentle peaks with a diameter of about 2 μm (effect of the substrate surface structuring). Practical Relevance. After the ion-beam polishing of epipolished sapphire substrate samples, smoothing of the highest surface irregularities is observed, and the average arithmetic value of surface roughness has decreased from 5.7 nm to 0.9 nm for the polished sample.