Morphology of ion tracks and nanopores in LiNbO3 produced by swift-ion-beam irradiation

The surface of LiNbO3 crystals after swift ion irradiation in the low velocity regime has been investigated by optical and atomic force microscopy (AFM). Samples were irradiated with Cu 50 MeV, Cl 46 MeV and Br 12 MeV ions. Before any additional treatment the surface of the sample irradiated with Cu ions shows hillocks of a 5–8 nm diameter and of 5 nm in height. The latent tracks were subsequently etched at room temperature with HF:HNO3 solutions during a few minutes. The shape of the surface pore caused by etching was strongly anisotropic for the Cu irradiations and only slightly anisotropic for the Br irradiations. The larger track length and surface stopping power for the Cu 50 MeV ions is most likely the origin of the final difference in pore shape via the induced swelling and enhanced etching rate. Optical waveguide measurements were also performed in the case of Cl irradiations to obtain in-depth averaged values of internal amorphization and track radius.