Laser photochemical deposition of magnetite nanograins in a-Fe/C/O composite: High-pressure metal oxide polymorph surviving ambient conditions

摘要

UV laser-induced gas-phase photolysis of Fe(CO)5 results in deposition of Fe/C/O nanocomposite film which was analyzed by Raman, Fourier transform infrared, X-ray photoelectron and laser-induced breakdown spectroscopy and electron microscopy. The nanocomposite film was revealed as an amorphous phase composed of iron oxides (FeO and Fe2O3) and carbonaceous constituents possessing C-O and C=O bonds. This phase contains crystalline nanograins of ambient cubic and high-pressure orthorhombic magnetite. The survival of the high-pressure Fe3O4 nanograins at ambient conditions is tentatively ascribed to their Laplace pressure and/or to stabilizing effect of the amorphous Fe/C/O phase. The o-Fe3O4 nanograins represent a very rare example of high-pressure nanosized polymorph surviving at ambient conditions and not retrieving ambient-pressure-stable phase upon decompression.