Long-range surface plasmons on ultrathin membranes.

A waveguide structure supporting long-range surface plasmon waves in any gaseous or liquid environment is described. The waveguide comprises a large area dielectric membrane of nanometric thickness upon which thin metal stripes and features are deposited. This structure allows the environment to surround the stripe thus ensuring that an essentially symmetric dielectric background is always present, as required to support the wave. The membrane perturbs the wave in a manner that significantly increases its surface sensitivity. The high surface sensitivity in concert with the ability to create long optical interaction length plasmonic structures leads to high sensitivity (bio)chemical sensors. Theoretical results describing the operation of the structure are given along with experimental results demonstrating the propagation of long-range surface plasmons in air and in liquid. The structure opens up a wealth of opportunities for research and application across many fields, including plasmonics, photonics, material science, surfaces, and solid-liquid interfaces.