α-Fe 2O 3 thin films prepared by metalorganic deposition (MOD) from Fe(III) 2-ethylhexanoate

Abstract

α-Fe 2O 3 thin films were prepared by metalorganic deposition (MOD) using Fe(III) 2-ethylhexanoate as the metalorganic precursor. A series of experiments were conducted on the metalorganic spin-coated films and their correspondingly annealed samples by employing experimental techniques ranging from thermal gravimetric analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) to optical property characterization. In this way a better understanding has been achieved regarding the decomposition process of the metalorganic precursor, the solid state α-Fe 2O 3 film formation and crystallization process, and the relationship between the structure and the optical properties of the prepared films. The conclusions of our experiments are the following. The decomposition of Fe(III) 2-ethylhexanoate is a multistep process that is characterized by distinct transition temperatures and thermogravimetric loss rates. Amorphous α-Fe 2O 3 film is formed at an annealing temperature of around 460°C, further annealing at higher temperatures induces the amorphous-to-crystalline phase transition and grain growth. FTIR, XRD and SEM data for structural characterization are correlated and in good agreement. A new FTIR absorption band, peaking at 1085 cm -1, is assigned to the vibration of crystalline Fe-O mode, therefore this peak is useful in monitoring the amorphous-to-crystalline phase transition of α-Fe 2O 3 material. Instead of columnar structure in physical vapour deposition-prepared films a granular structure is typical of MOD prepared films, the grain size is much larger near the surface of the film than near the substrate. Optical characterization shows that the refractive index and extinction coefficient of the α-Fe 2O 3 thin films increase with the increase of annealing temperatures. The potential interesting applications of the MOD-prepared α-Fe 2O 3 thin films include gas sensor materials, photoelectrodes and storage media.