Low temperature atomic layer deposition of highly photoactive hematite using iron(III) chloride and water

Nanostructured hematite (alpha-Fe2O3) has been widely studied for use in a variety of thin film applications including solar energy conversion, water oxidation, catalysis, lithium-ion batteries, and gas sensing. Among established deposition methods, atomic layer deposition (ALD) is a leading technique for controlled synthesis of a wide range of nanostructured materials. In this work, ALD of Fe2O3 is demonstrated using FeCl3 and H2O precursors at growth temperatures between 200 and 350 degrees C. Self-limiting growth of Fe2O3 is demonstrated with a growth rate of similar to 0.6 angstrom per cycle. As-deposited, films are nanocrystalline with low chlorine impurities and a mixture of alpha- and gamma-Fe2O3. Post-deposition annealing in O-2 leads to phase-pure alpha-Fe2O3 with increased out-of-plane grain size. Photoelectrochemical measurements under simulated solar illumination reveal high photoactivity toward water oxidation in both as-deposited and post-annealed films. Planar films deposited at low temperature (235 degrees C) exhibit remarkably high photocurrent densities similar to 0.71 mA cm(-2) at 1.53 V vs. the reversible hydrogen electrode (RHE) without further processing. Films annealed in air at 500 degrees C show current densities of up to 0.84 mA cm(-2) (1.53 V vs. RHE).