Amorphization and recrystallization of single-crystalline hydrogen titanate nanowires by N+ ion irradiation

We report the phase transformation of hydrogen titanate (H2Ti3O7) nanowires induced by 50 keV N+ ion irradiation at room temperature with fluencies of 1×1015 ions/cm2 and 1×1016 ions/cm2. By high resolution transmission electron microscopy the internal structure of the ion irradiated nanowires is analyzed. While at lower fluence a transformation from crystalline H2Ti3O7 to amorphous TiO2 is observed, at higher fluence a remarkable crystalline-amorphous TiO2 core-shell structure is formed. At this higher fluence the recrystallization occurs in the core of the nanowire and the outer layer remains amorphized. The phase transformation and formation of core-shell structure is explained using the thermal spike model and non-equilibrium thermodynamics. X-ray Photoelectron Spectroscopy and Raman Scattering reveale further insight into the structure of the nanowires before and after ion irradiation.