A TiN@Au-NR Plasmonic Structure with Tunable Surface Plasmon Resonance Depending on TiN to Au Thickness Ratio

TiN nanostructures have been shown to exhibit promising plasmonic properties and are potential candidates for various applications, including energy harvesting. However, these properties also show a strong dependence on the processing conditions which have been reported to affect metallicity of TiN. Herein, we report on layered TiN@Au-nanorods (NRs) nanostructures consisting of 20 nm TiN thin layer that is magnetron sputtered on Au-NRs of variable length, yielding different TiN/Au thickness ratios (R). While a 20 nm TiN layer sputtered on the same substrate on which the Au-NRs are grown shows a weak absorption peak in the near IR region, an intense and broad plasmonic peak that lies red from the transverse plasmonic peak of monolithic Au-NRs layer is observed for TiN@Au-NRs. The red-shift is shown to increase with increasing R, attaining 100 nm for R = 1, together with an intense tail in the IR region. These results are interpreted in terms of a strong coupling between TiN and Au that drastically affects the plasmonic behavior of the structure. The results are contrasted with those on Pd@Au-NRs where only a slight blue-shift of few nanometers from the Au peak is observed. Potential applications of the TiN@Au-NRs are mainly in energy harvesting such as water splitting and photocatalysis using electromagnetic radiation in a broad wavelength range, as well as medical applications. Pd@Au-NRs may be used as electrocatalysts with plasmonic enhancement, e.g., for the hydrogen evolution reaction.