Incident Angle Dependent Formation of Ion Tracks in Quartz Crystal with C₆₀⁺ Ions: Big Ions in Small Channels

Quartz (SiO2) crystals possess intrinsic columnar pores perpendicular to (0001) surfaces, consisting of three- and six-membered ring (3MR and 6MR) structures of Si and O atoms. The diameters of the larger pores, i.e., 6 MRs, are ~0.49 nm, while the diameters of fullerene (C60) ions are 0.7 nm, i.e., larger than either type of the pores. Transmission electron microscopy observation evidenced approximately two times longer ion tracks in the channeling condition, i.e., 0° incidence to (0001) surface, than an off-channeling condition, i.e., 7° incidence in this case, under 6 MeV C60 ion injection. The track length at the 0° incidence decreases more steeply than that at the 7° incidence with decreasing the energy from 6 MeV to 1 MeV. Finally, the track lengths at the 0° and 7° incidences become comparable, i.e., the channeling-like effect disappears at 1 MeV irradiation. This study experimentally indicates that the channeling-like effect of C60 ions is induced in quartz crystals, while the sizes of the channels are smaller than the C60 ions.