Phase Transition Induced Photocathodic p-CuFeO2 Nanocolumnar Film by Reactive Ballistic Deposition

In the present study, CuFeO vertical nanocolumnar structured arrays are deposited on fluorine-doped tin oxide substrates by reactive ballistic deposition technique in an oxygen atmosphere by fixing the deposition angle at 85°. Scanning electron microscopy images shows the presence of arrays of individual columns. The photocurrent density of the CuFeO2 annealed at 650 oC for 2 h in argon is determined to be -0.22 mA cm-2 at 0.4 V versus RHE in 1 M NaOH under AM 1.5 G illumination, while the same annealed in air exhibits a photocurrent density value of 0.12 mA cm-2 at 1.23 V versus RHE. Here, the film annealed in an argon atmosphere at 650 °C exhibits a p-type characteristic with cathodic photocurrent, while the same annealed in air depicts an n-type characteristic with anodic photocurrent. The p-type character was induced by the Cu vacancies and the shift in the conductivity from n-type to p-type is induced by phase transition formation of delafossite CuFeO2 from copper modfied FeO. The generation of photocurrent density from p-CuFeO2 is expected to be from the presence of Cu2+/Cu+ redox couple which is evidenced by X-ray photoelectron spectroscopy.