Plasmonic TiN, ZrN, and HfN Nanofluids for Solar-to-Heat Conversion

Group IV transition metal (III) nitrides (MeN) are plasmonic materials that possess high optical absorption cross-sections and fast electron-phonon coupling that make them attractive in solar energy harvesting. Nanoparticles (NPs) of MeN dispersed in host liquids were predicted to be useful in photothermal energy conversion, although such nanofluids have never been systematically studied, mainly because of the complexity of their preparation. This research introduces reactive magnetron sputtering of Ti, Zr, and Hf targets in Ar/N-2 mixtures that can be tailored to produce beams of MeN NPs and load them into vacuum-compatible host liquids of polyethylene glycol, paraffin, and pentaphenyl trimethyl trisiloxane to produce MeN nanofluids in a single process. The NPs are cubic in shape, have a mean size of 10-12 nm, and exhibit a rock salt crystal structure characteristic of Me(III)N. The nanofluids based on these NPs reveal a turquoise color, given by a narrow optical transmittance window in the blue-green region and strong absorption at shorter and longer wavelengths caused by interband transitions and localized surface plasmon resonance in MeN NPs. These results open a path toward the synthesis of advanced plasmonic nanofluids without the involvement of aggressive compounds, high temperatures, or multiple chemical steps.