Iron island films on sapphire grown by pulsed laser deposition with in situ electrical resistance monitoring

Abstract

Iron island films were grown on sapphire by pulsed laser deposition with in situ electrical resistance control, which made it possible to precisely determine the percolation transition. Four growth stages can be distinguished: initial nucleation, independent island growth, ripening with channel formation, and island coalescence into a labyrinth structure. The morphology of the iron island films corresponded to these stages, depending on the time and deposition rate at a given temperature. At growth temperatures of T ≥ 350 °C, the percolation thickness exponentially depended on the temperature. The electrical response time τ of the system to a single pulse was<1 s, and the temperature dependence of 1/τ was linear in Arrhenius coordinates with a slope corresponding to an activation energy of 0.41 eV. The dependence of the film thickness and island diameter on the pulse frequency before the onset of the percolation transition reached a maximum, which can be explained by two competing factors: diffusion stimulation owing to the high kinetic energy of the incident particles and an increase in the number of initial nuclei in the substrate regions without islands.