Title: Space-Filling Fractal Description of Ion-induced Local Thermal Spikes in Molecular Solid of ZnO,
Abstract: Anions of the molecules ZnO, O2 and atomic Zn and O constitute mass spectra
of the species sputtered from pellets of molecular solid of ZnO under Cs+
irradiation. Their normalized yields are independent of energy of the
irradiating Cs+. Collision cascades cannot explain the simultaneous sputtering
of atoms and molecules. We propose that the origin of the molecular
sublimation, dissociation and subsequent emission is the result of localized
thermal spikes induced by individual Cs+ ions. The fractal dimension of binary
collision cascades of atomic recoils in the irradiated ZnO solid increases with
reduction in the energy of recoils. Upon reaching the collision diameters of
atomic dimensions, the space-filling fractal-like transition occurs where
cascades transform into thermal spikes. These localized thermal spikes induce
sublimation, dissociation and sputtering from the region. The calculated rates
of the subliming and dissociating species due to localized thermal spikes agree
well with the experimental results.