FE-SEM observation of chains of nanohillocks in SrTiO3 and Nb-doped SrTiO3 surfaces irradiated with swift heavy ions

Single crystals of SrTiO3 (1 0 0) and 0.05% Nb-doped SrTiO3 (1 0 0) were irradiated with 200 MeV Au-197(32+) swift heavy ions and 350 MeV Xe-129(26+) ions, respectively. The angle between the sample surface and the beam was less than 2 degrees. The irradiated surfaces were examined by field-emission scanning electron microscopy (FE-SEM). On the SrTiO3 surface, a chain of periodic nanohillocks is created along the ion path. In contrast, black lines accompanied by hillocks are observed on the Nb-doped SrTiO3 surface. The observation of the edge effect in FE-SEM strongly suggests that the black lines observed for Nb-doped SrTiO3 can be attributed to groove formation. The dark contrast between the adjacent hillocks observed for ion-irradiated SrTiO3 suggests that the area correspond to the depressed region. On this basis, a formation process for the hillock chains in the framework of Rayleigh instability is proposed.