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The effect of low-energy Ar+ irradiation on the surface of monocrystalline α-Al2O3 (0001)

Single crystals α-Al2O3 (0001) were exposed to the energetic Ar+-ions for two periods of 4 min with kinetic energy of 2 keV and 4 min of 5 keV at an incident angle of 45°. The samples were studied by X-ray photoemission spectroscopy (XPS) before and after Ar+-ion beam exposure. The average values of the bandgap energy before and after Ar+-ion beam treatment were measured to be (7.8 ± 0.2) eV and (6.3 ± 0.2) eV, respectively. The dynamic change in the XPS spectra of the valence band (VB) region before and after Ar+-ion beam treatment were explained using the theoretical calculation of the density of state (DOS) and the molecular orbital (MO) theory. This change is attributed to the transformation of α-phase to γ-Al2O3 phase at the surface. The surface morphology of the samples before and after Ar+-ion bombardment was also examined using scanning electron microscopy (SEM). Creation of circular well-shaped nanoholes with diameters in the range of (20–550) nm was observed at the surface after exposure to 2 keV Ar+-ions. Whereas, a series of irregular nanovoids were observed on the surface of the sample which was exposed to 5 keV Ar+-ions.