Cold sintering of iron nanoparticles

Changes in the morphology and composition of a metal-oxide iron nanoparticle obtained by reactive pulse sputtering of iron in an oxygen atmosphere (10−4 mmHg) on glass followed by low-temperature annealing in air atmosphere in a temperature range from 20 to 100°C were studied with the use of atomic-force microscopy with digital processing of images and infrared spectroscopy. During annealing of a particle, accelerated sintering (up to 50% of the volume) is found to take place due to the compaction and possible spreading over the glass surface. Judging from data of infrared spectroscopy, annealing is accompanied by oxidation of the nanoparticle and the accumulation of hematite phase formed as a result of magnetite oxidation. The activation energy of the deformation of a nanoparticle seemingly determined by the viscous flow at low-temperature annealing was estimated from the kinetic curves of volume degradation based on AFM data.