The Sputter-Based Synthesis Of Tantalum Oxynitride Nanoparticles With Architecture And Bandgap Controlled By Design

Among strategies of fuel production, photoelectrochemical water splitting for hydrogen generation is garnering significant attention. The challenge for solar energy harvesting is material development with intense photocatalytic activity, efficient free-charge generation, separation, and transport. Tantalum nitride (Ta3N5) and oxynitrides (Ta3NyOx) are recognized as promising candidates for this role. This research suggests a new route to engineer Ta3NyOx nanoparticles (NPs) with structure, crystallinity, chemical, and optoelectronic properties controlled by design. This work employs a single-step plasma-based technique that takes advantage of dc reactive magnetron sputtering of tantalum in Ar/N2 mixtures. The NPs with the chemical composition of Ta3N3.9O0.6 are synthesized; however, they become partially oxidized when exposed to air, providing an inwardly-directed gradient of the nitrogen concentration. The core-region consists of n-type sub-stoichiometric Ta3Ny with a band gap of <2.0 eV partially filled with mid-gap states, whereas the outermost region belongs to Ta3NyOx, with oxygen enhancing the n-character of the material. The nitridation and the amorphous/crystalline ratio enhance with the concentration of N2. The NPs exhibit plasmonic and photoluminescent properties in the visible range and are therefore attractive for numerous interdisciplinary fields. In particular, additional annealing in ammonia improves crystallinity and nitridation, making the NP-assembled deposits perform as advanced anodes for photoelectrochemical water splitting.