Editing Surface wave (section)

===Surface plasmon polariton===

[[File:SPP silver-air interface 10um.gif|thumb|255px|right|The [[Electric field|E-field]] of a [[surface plasmon polariton]] at a silver–air interface, at a frequency corresponding to a free-space wavelength of 10μm. At this frequency, the silver behaves approximately as a [[perfect electric conductor]], and the SPP is called a Sommerfeld–Zenneck wave, with almost the same wavelength as the free-space wavelength. <!--The permittivity of silver at this frequency is {{nowrap|(−2700 + 1400i)}}. The picture is {{nowrap|(0.6 × 10μm)}} across horizontally.-->]]

The [[surface plasmon polariton]] (SPP) is an [[electromagnetic wave|electromagnetic surface wave]] that can travel along an interface between two media with different dielectric constants. It exists under the condition that the [[permittivity]] of one of the materials <ref name="Corum_2016"/> forming the interface is negative, while the other one is positive, as is the case for the interface between air and a lossy conducting medium below the [[plasma frequency]]. The wave propagates parallel to the interface and decays exponentially vertical to it, a property called evanescence. Since the wave is on the boundary of a lossy conductor and a second medium, these oscillations can be sensitive to changes to the boundary, such as the adsorption of molecules by the conducting surface.<ref>{{cite journal|author=S. Zeng|title=Nanomaterials enhanced surface plasmon resonance for biological and chemical sensing applications |journal=Chemical Society Reviews|volume=43 |pages=3426–3452 |date=2014|doi=10.1039/C3CS60479A|last2= Baillargeat|first2= Dominique|last3=Ho|first3=Ho-Pui|last4=Yong|first4=Ken-Tye |pmid=24549396 |issue=10 |hdl=10220/18851 |url=https://www.researchgate.net/publication/260252810|hdl-access=free}}</ref>