Fabrication of alpha-iron and iron carbide nanostructures by electron-beam induced chemical vapor deposition and postdeposition heat treatment

We succeeded in fabricating crystalline alpha-iron nanostructures with desired shapes. Electron-beam-induced chemical vapor deposition with iron carbonyl gas, Fe(CO)₅, was carried out at room temperature in a field-emission-gun scanning electron microscope to fabricate nanodots, nanorods and square frames. The as-deposited structures exhibited an amorphous phase containing iron, carbon and oxygen in their entire volumes and iron oxide nanocrystals existed near their surfaces. Postdeposition heat treatment at about 600°C resulted in the formation of crystalline alpha-iron and iron carbide phases in their structures, while maintaining their shapes. Quantitative elemental analyses using electron energy loss spectroscopy suggested that the original as-deposited iron-to-carbon compositional ratio is crucial in determining the stoichiometry of the produced structures after the heat treatment.