FE-SEM observation of dotted hillocks formed by irradiation at grazing incidence of swift heavy ions

Kitamura, Akane; Ishikawa, Norito   ; Kondo, Keietsu  ; Fujimura, Yuki; Yamamoto, Shunya*

Swift heavy ions can create nanosized hillocks on the surfaces of various ceramics. When these materials are irradiated with swift heavy ions at normal incidence, each ion impact results in the formation of a single hillock on the surfaces. In contrast, irradiation at grazing incidence forms chains of multiple hillocks on the surface such as strontium titanate (SrTiO). So far, chains of multiple hillocks have been investigated using atomic force microscopy (AFM). It should be noted that AFM measurements involve systematic errors of several nanometers due to the finite size of the probe tip. Consequently, it is possible that the image of one hillock may merge with that of a neighboring hillock even if the two hillocks are well separated. In contrast to AFM, field-emission scanning electron microscopy (FE-SEM) is a useful technique for obtaining higher-resolution images. In this study, we observed multiple nanohillocks on the surfaces of SrTiO using FE-SEM. Crystals of SrTiO(100) and 0.5 wt% Nb-doped SrTiO(100) were irradiated with 200 MeV Xe ions, respectively. The irradiated angle between the sample surface and the beam was less than 2. On the SrTiO 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 SrTiO surface. As a result, we proposed a new model of formation process for the hillock chains in the framework of Rayleigh instability.