Growth of alpha-Fe2O3 thin films by plasma deposition: Studies of structural, morphological, electrochemical, and thermal-optical properties

In this work, iron oxide thin films were grown on glass slides and AISI 304 austenitic steel substrates using carbon steel as the cathodic cage in the plasma deposition process. For the deposition on steel 304, the temperature, time and concentration of oxygen (O) and argon (Ar) gases were kept constant, with the only variable being the concentration of hydrogen (H). However, the deposition on glass substrate was performed at temperature and concentration of O, Ar, and H gases with varying the deposition time. Structural, morphological, electrochemical, and thermal-optical properties of the films were investigated. Raman analysis showed an iron oxide layer composed of a hematite crystalline structure (alpha-Fe2O3). The images obtained using a field emission scanning electron microscope showed the formation of thin films well-shaped, with thickness ranging from 1.90 to 2.56 mu m. The thermal-optical parameters showed that the thermal diffusivity of films grown on the glass slide varied with deposition time. Electrochemical experiments such as open circuit potential, electrochemical impedance spectroscopy, and polarization curves were performed, revealing that the iron oxide film formed with the gas flow rate of 4H(2)/4O(2)/4Ar improved the pitting corrosion resistance in the presence of corrosive saline solution. The electrochemical measurements highlighted that the steel treated in the above condition (gas flow rate of 4H(2)/4O(2)/4Ar) had a pitting potential (E-pit = +0.842 V vs. Ag/AgCl, KCl sat.) of similar to x223C 400 mV, higher than the untreated steel.