Heteroepitaxial Growth of a Ta 3 N 5 Thin Film with Clear Anisotropic Optical Properties.

Ta 3 N 5 is a promising semiconductor photocatalyst which can generate H 2 gas from water under visible light illumination. It is expected that Ta 3 N 5 exhibits a strong anisotropy in its physical properties stemming from its highly anisotropic crystal structure. However, such anisotropic properties have not been verified experimentally due to the difficulty in synthesizing a large single crystal. Here, we report the synthesis of (010)-oriented Ta 3 N 5 single-crystalline thin films by solid phase epitaxy on the (110) plane of perovskite LaAlO 3 substrates. The obtained epitaxial thin films of Ta 3 N 5 exhibited clear optical anisotropy (pleochroism) as predicted by previous first-principles calculations. The optical gap for E ||[100] polarization (∼2.12 eV) was smaller than that for E ||[100] polarization (∼2.27 eV).