Anisotropic Core-Shell Swift Heavy Ion Tracks in beta-Ga2O3

Abstract: Swift heavy ion (SHI) irradiation generates nanoscale ion tracks through intense electronic excitation, yet the microscopic mechanisms governing their morphology and phase stability in low symmetry oxides remain poorly understood. Here, a multiscale atomistic simulation framework is employed to investigate SHI-induced track formation and recovery in monoclinic beta-Ga2O3 over a wide range of electronic energy losses (Se) and crystallographic orientations. A sequence of distinct structural responses is identified with increasing Se: complete lattice recovery at low Se, recrystallization into a metastable gamma-Ga2O3 phase at intermediate Se, and the formation of core-shell ion tracks at high Se, consisting of an amorphous core surrounded by a recrystallized gamma-phase shell. Despite the essentially isotropic initial energy deposition, the final ion-track morphology exhibits pronounced crystallographic anisotropy, governed by orientation-dependent recovery dynamics. The superior recrystallization along [010] direction is attributed to its exceptionally high elastic stiffness. Notably, SHI irradiation perpendicular to the (100) plane induces a more severe structural response at low Se (less than 10 keV/nm), however, at higher Se, it yields a smaller residual ion track compared with the other orientations. The simulated ion-track sizes show excellent quantitative agreement with available experimental measurements over a broad range of Se values. These findings establish a unified atomic-scale picture of core-shell track formation and anisotropic recovery in beta-Ga2O3.