A phase transition-induced photocathodic p-CuFeO2 nanocolumnar film by reactive ballistic deposition

초록

In the present study, Cu-Fe-O vertical nanocolumnar structured arrays are deposited on fluorine-doped tin oxide substrates by the reactive ballistic deposition technique in an oxygen atmosphere by fixing the deposition angle at 85 degrees. The scanning electron microscopy images show the presence of arrays of individual columns. The photocurrent density of the Cu-Fe-O sample annealed at 650 degrees C for 2 h in argon (CuFeO2) 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 of 0.12 mA cm(-2) at 1.23 V versus RHE. Here, the film annealed in an argon atmosphere at 650 degrees C exhibits a p-type characteristic with cathodic photocurrent, while the film annealed in air depicts an n-type characteristic with anodic photocurrent. The switch in conductivity from n-type to p-type is induced by the phase transition from amorphous Cu-Fe-O to delafossite CuFeO2. The generation of cathodic photocurrent from p-CuFeO2 is also expected to be from the presence of the Cu2+/Cu+ redox couple, which is evidenced by X-ray photoelectron spectroscopy.

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