Ti/TiO_xN_y thin films as highly efficient photoelectrode via engineered interfacial facet on plasmonic schottky barriers

Titanium nitride (TiN) is recognized for enhancing semiconductor photocatalytic activity due to its plasmonic properties, similar to those of gold and silver nanoparticles. Changing the stoichiometry of TiN enhances free carrier density, resulting in metallic characteristics and optical properties resembling gold in the visible spectrum. New Ti/TiO_xN_y thin films were synthesized with the aid of the Arc-PVD technique under some conditions, including low temperatures and various concentrations of N₂ gas. Under zero and maximum amounts of N₂ gas, nonstoichiometric and highly conductive N-rich phases of TiN were created, respectively. A TiO₂ semiconductor interlayer was specifically coated on a Ti substrate which served both as a co-catalyst layer and as a means to reduce residual stress in the TiN film. Our results demonstrate that the defects and resistance to oxidation in the TiN structure, dependent on the N₂ input, may significantly influence the orientation of stable crystal facet ( [111]) and the excitation of plasmonic-photonic hybrid modes. The highest photocurrent was recorded at about 8.2 mA cm^‒2 at 1.4 V vs. RHE for gold-colored Ti/TiO_xN_y oriented along [111] facet, which is 4.3 and 54.6 times more than samples adjusted along [110] and [001] facets, respectively. The employed PVD method at low temperatures as a strong designing technique for tailoring the metal-semiconductor interface simplifies the creation of highly activated photoelectrodes within the water-splitting performance. This applicable technique brings interesting eco-friendly benefits, including energy efficiency, low environmental footprint, and optimized material utilization, in accordance with green chemistry principles.