Extending nanoscale spectroscopy with titanium nitride probes

We present a means of controlling the stoichiometry of titanium nitride (TiN) coatings on probes for tip‐enhanced Raman spectroscopy measurements made using sputtering so that outstanding enhancements can be obtained. This provides a more robust alternative to gold‐coated tips that also has potential for tuning the plasmon resonance and working in new environments. Proof of concept measurements on poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonate) thin films demonstrate increases in the observed intensity with contrast values up to 3.1. TiN is mechanically, chemically, and thermally robust. When deposited under appropriate conditions it has optical properties, including a plasmon resonance, very similar to those of gold. However, the spontaneous formation of a surface TiN_xO_y layer with relatively high values of y has prevented attaining enhancements in tip‐enhanced Raman spectroscopy beyond that provided by the lightning rod effect. Depositing a thin layer of aluminum to form a passivating Al₂O₃ layer over the TiN plasmonic structure allows the stoichiometry achieved in the vacuum deposition to be maintained. Copyright © 2016 John Wiley & Sons, Ltd.