Single‐Crystal Pd and its Alloy Nanowires for Plasmon Propagation and Highly Sensitive Hydrogen Detection

In this work plasmon propagation and highly sensitive hydrogen sensing are demonstrated in single‐crystal Pd and its alloy nanowires, based on an evanescent wave coupling technique using optical fiber tapers. The plasmon propagation losses of Pd nanowires on an MgF₂ substrate are measured to be ∼2 dB/μm (at 635 nm). Using a suspension scheme of the nanowire, the propagation losses decrease to ∼0.6 dB/μm in air. Utilizing an alloying technique, single‐crystal PdAg nanowires are fabricated and exhibit decreasing and tunable propagation losses. Furthermore, Pd nanowires are used for plasmonic gas sensing with amplitude sensitivity of ∼11 dB to 3.6% hydrogen gas, which is much higher than those in photonic nanowire sensors. The concentration detection limit is about 0.2%, which is lower than those in photonic nanowire sensors and most surface plasmon resonance sensors. The hysteresis effect of the Pd nanowire in hydrogen sensing is suppressed by using single‐crystal PdAu alloy nanowires. This work may find widespread application, ranging from sensing and integrated circuits to materials research.