Long-range plasmons in lossy metal films on photonic crystal surfaces.

A one-dimensional (1D) photonic crystal structure with a terminal palladium layer supporting long-range surface plasmon polariton (LRSPP) waves in any gaseous environment is described. We show that LRSPP propagation may be achieved not only along "good plasmonic" metals such as Ag and Au but also along lossy metals such as Pd, which does not usually support plasmon propagation in the visible spectral range with ordinary Kretschmann excitation. The possibility of the LRSPP propagation along catalytically active metals such as Pd or Pt opens up new perspectives for studying of (photo)chemical surface reactions and offers the potential for more applications in the general area of catalysis, photocatalysis, and plasmon-mediated chemistry. We present experimental results that demonstrate the hydrogen sensitivity of this photonic structure incorporating a catalytically active 8-nm-thick Pd final layer. A 3% hydrogen concentration in nitrogen is detected with a signal-to-noise ratio of approximately 300, with a response time of about 10 s at room temperature.