Delafossite CuFeO2 thin films via aerosol assisted CVD

Over the past few years, a tremendous increase in the population and industrialization have overstrained the presently available energy sources. As such development of alternative and efficient energy sources is highly desirable. This, however, has to be in line with the set regulations that have been recently set to mitigate the environmental pollution and climate changes associated with energy consumption. To this note, several approaches for developing clean and sustainable energy sources have been initiated. In a recently published literature, solar energy has been directly converted into chemical fuels through photo-assisted water splitting. Unfortunately, they are associated with low solar spectrum absorption efficiency that limits their large-scale utilization. Alternatively, delafossite materials, specifically CuFeO₂, have been used in hydrogen generation owing to its conductivity, electrical and optical properties.

Presently, several methods for CuFeO₂ synthesis including electrodeposition, spin coating spray pyrolysis among others have been developed. However, efficient techniques for synthesis of CuFeO₂ that will ensure proper control of the morphology, crystalline structure and composition have not been fully explored.

To this note, a group of researchers led by Dr. Mario Miki-Yoshida at CIMAV, where Ph.D. candidate Pedro Piza-Ruiz and Dr. Saenz-Trevizo investigated the optimal conditions for the synthesis of the delafossite CuFeO₂ based on the aerosol-assisted CVD approach. Technically, the synthesis process was repeated several times until a molar ratio of copper to iron in the synthesized films was recorded as one by using the titanium oxide coated borosilicate glass, as a substrate. Their fascinating research work is currently published in the research journal, Ceramics International.

In brief, the research team cross-examined the feasibility of using aerosol-assisted CVD method in synthesizing ternary oxide materials. Next, they utilized a one-step method that did not require any treatment processes after deposition. The initial average atomic ratio of copper to iron was approximated using the energy dispersive x-ray spectroscopy technique, which was also later used as an indicator in the synthesis of CuFeO₂. In addition, different characterization techniques such as Raman spectroscopy, atomic force microscopy and x-ray diffraction were utilized to control the composition, morphology, and microstructure for effective delafossite growth.

The authors observed that the polycrystalline CuFeO₂ was formed in the rhombohedral phase. The formation of the rhombohedral phase was attributed to the suitable combination of the copper and iron precursors, which transform during the complex reaction mechanisms initiated by the aerosol-assisted CVD method into the desire phase. Consequently, the copper oxide was observed coexisting with the formed CuFeO₂ even though in small amounts. Furthermore, a slight influence of titanium oxide and zinc oxide buffer layers on the deposited copper and iron, grain size and thickness were observed thus, confirming the existence of delafossite material.

In summary, CIMAV scientists successfully demonstrated the application of the synthesized CuFeO₂ in light absorption. Even though the influence in the coexisting copper oxide on the applications such as water splitting have not been fully presented, the method proves suitable for the synthesis of CuFeO₂. This will pave the way for developing alternative sustainable energy sources not only to meet the increasing demands but also to address the environmental concerns.