https://doi.org/10.1351/goldbook.08688
Measurement method of infrared spectroscopy by which the intensity of absorption bands of molecules within a few nanometers of the surface of metal particles is increased by interactions with surface plasmons (the collective resonance of electrons near the surface of metal islands).
Note: The metals that give the largest enhancement are silver and gold, but this phenomenon has been reported to occur with at least eight other metals.