The effect of low-energy Ar+ irradiation on the surface of monocrystalline α-Al2O3 (0001) Faramarz Sahra Gard and Elena Forlerer Eur. Phys. J. Appl. Phys., 85 2 (2019) 21302 Published online: 08 March 2019 DOI: 10.1051/epjap/2019180241