Surface nanostructures on Nb-doped SrTiO irradiated with swift heavy ions at grazing incidence
Ishikawa, Norito ; Fujimura, Yuki; Kondo, Keietsu ; Szabo, G. L.*; Wilhelm, R. A.*; Ogawa, Hiroaki ; Taguchi, Tomitsugu*
A single crystal of SrTiO doped with niobium (Nb-STO) was irradiated with 200 MeV Au ions at grazing incidence. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to study the relation between irradiation-induced change of surface topography and corresponding material property changes. As expected, multiple hillocks as high as 5-6 nm are imaged by AFM observation. It is also found that the region in between the adjacent hillocks is slightly elevated rather than depressed. Line-like contrasts along the ion paths are found in both AFM phase images and SEM images, indicating the formation of continuous ion tracks in addition to multiple hillocks. Cross-sectional transmission electron microscopy (TEM) observation shows that the ion tracks in the near-surface region are found to be relatively large, whereas buried ion tracks in the deeper region are relatively small. The results suggest that recrystallization plays an important role in the formation of small ion tracks in the deep region, whereas formation of large ion tracks in the near-surface region is likely due to the absence of recrystallization.