Highly oriented epitaxial CaFe2O4 thin films on TiO2 substrates grown by pulsed-laser deposition

CaFe2O4 (CFO) is an oxide semiconductor being usable for a photocathode, but its single crystal is so far grown only by a high-pressure bulk synthesis method. Using pulsed-laser deposition, we have obtained the (010)-oriented CFO films on TiO2 (100) substrates. The epitaxial structure included twin domains with 1.5° tilting from the surface normal and sixfold domains with in-plane rotations of ± 70° with respect to the b axis of TiO2, which was explained by taking a number of probable arrangements between FeO6 and TiO6 octahedra into account. X-ray absorption spectroscopy and ultra-violet-visible-near-infrared spectroscopy measurements revealed the electronic properties similar to those of bulk and thus the CFO films would be suitable to the investigation of photocathodic performance.