Synthesis of Iron Oxide Nanostructures via Carbothermal Reaction of Fe Microspheres Generated by Infrared Pulsed Laser Ablation

Iron oxide nanostructures were synthesized using the carbothermal reaction of Fe microspheres generated by infrared pulsed laser ablation. The Fe microspheres were successfully deposited on Si(100) substrates by laser ablation of the Fe metal target using Nd:YAG pulsed laser operating at lambda = 1064 nm. By varying the deposition time (number of pulses), Fe microspheres can be prepared with sizes ranging from 400 nm to 10 mu m. Carbothermal reaction of these microspheres at high temperatures results in the self-assembly of iron oxide nanostructures, which grow radially outward from the Fe surface. Nanoflakes appear to grow on small Fe microspheres, whereas nanowires with lengths up to 4.0 mu m formed on the large Fe microspheres. Composition analyses indicate that the Fe microspheres were covered with an Fe3O4 thin layer, which converted into Fe2O3 nanowires under carbothermal reactions. The apparent radial or outward growth of Fe2O3 nanowires was attributed to the compressive stresses generated across the Fe/Fe3O4/Fe2O3 interfaces during the carbothermal heat treatment, which provides the chemical driving force for Fe diffusion. Based on these results, plausible thermodynamic and kinetic considerations of the driving force for the growth of Fe2O3 nanostructures were discussed.