Editing Plasmon (section)

== Surface plasmons ==
{{Main article|Surface plasmon}}
[[Surface plasmon]]s are those plasmons that are confined to surfaces and that interact strongly with light resulting in a [[polariton]].<ref>{{cite journal|title=Size dependence of Au NP-enhanced surface plasmon resonance based on differential phase measurement |journal=Sensors and Actuators B: Chemical |date=2013|doi=10.1016/j.snb.2012.09.073|volume=176|pages=1128–1133|display-authors=4|last1=Zeng|first1=Shuwen|last2=Yu|first2=Xia|last3=Law|first3=Wing-Cheung|last4=Zhang|first4=Yating|last5=Hu|first5=Rui|last6=Dinh|first6=Xuan-Quyen|last7=Ho|first7=Ho-Pui|last8=Yong|first8=Ken-Tye |bibcode=2013SeAcB.176.1128Z |url=http://www.unilim.fr/pages_perso/zeng/a13.pdf }}</ref> They occur at the interface of a material exhibiting positive real part of their relative permittivity, i.e. [[dielectric constant]], (e.g. vacuum, air, glass and other dielectrics) and a material whose real part of permittivity is negative at the given frequency of light, typically a metal or heavily doped semiconductors. In addition to opposite sign of the real part of the permittivity, the magnitude of the real part of the permittivity in the negative permittivity region should typically be larger than the magnitude of the permittivity in the positive permittivity region, otherwise the light is not bound to the surface (i.e. the surface plasmons do not exist) as shown in the famous book by [[Heinz Raether]].<ref>{{Cite book|title = Surface Plasmons on Smooth and Rough Surfaces and on Gratings|last = Raether|first = Heinz|publisher = Springer|year = 1988|isbn = 978-3-540-17363-2|page = 119}}</ref> At visible wavelengths of light, e.g. 632.8&nbsp;nm wavelength provided by a He-Ne laser, interfaces supporting surface plasmons are often formed by metals like silver or gold (negative real part permittivity) in contact with dielectrics such as air or silicon dioxide. The particular choice of materials can have a drastic effect on the degree of light confinement and propagation distance due to losses. Surface plasmons can also exist on interfaces other than flat surfaces, such as particles, or rectangular strips, v-grooves, cylinders, and other structures. Many structures have been investigated due to the capability of surface plasmons to confine light below the diffraction limit of light. One simple structure that was investigated was a multilayer system of copper and nickel.  Mladenovic ''et al.'' report the use of the multilayers as if its one plasmonic material.<ref>{{cite journal |last1=Mladenović |first1=I. |last2=Jakšić |first2=Z. |last3=Obradov |first3=M. |last4=Vuković |first4=S. |last5=Isić |first5=G. |last6=Tanasković |first6=D. |last7=Lamovec |first7=J. |title=Subwavelength nickel-copper multilayers as an alternative plasmonic material |journal=Optical and Quantum Electronics |date=17 April 2018 |volume=50 |issue=5 |page=203 |doi=10.1007/s11082-018-1467-3 |bibcode=2018OQEle..50..203M |s2cid=125180142 |url=http://cer.ihtm.bg.ac.rs/bitstream/id/23832/bitstream_23832.pdf }}</ref> Oxidation of the copper layers is prevented with the addition of the nickel layers. It is an easy path the integration of plasmonics to use copper as the plasmonic material because it is the most common choice for metallic plating along with nickel. The multilayers serve as a diffractive grating for the incident light. Up to 40 percent transmission can be achieved at normal incidence with the multilayer system depending on the thickness ratio of copper to nickel. Therefore, the use of already popular metals in a multilayer structure prove to be solution for plasmonic integration.

Surface plasmons can play a role in [[surface-enhanced Raman spectroscopy]] and in explaining anomalies in diffraction from metal [[diffraction grating|gratings]] ([[Robert W. Wood|Wood's]] anomaly), among other things. [[Surface plasmon resonance]] is used by [[biochemist]]s to study the mechanisms and kinetics of ligands binding to receptors (i.e. a substrate binding to an [[enzyme]]). [[Multi-parametric surface plasmon resonance]] can be used not only to measure molecular interactions but also nanolayer properties or structural changes in the adsorbed molecules, polymer layers or graphene, for instance.

Surface plasmons may also be observed in the X-ray emission spectra of metals. A dispersion relation for surface plasmons in the X-ray emission spectra of metals has been derived (Harsh and Agarwal).<ref>{{cite journal | doi=10.1016/0378-4363(88)90078-2 | volume=150 | issue=3 | title=Surface plasmon dispersion relation in the X-ray emission spectra of a semi-infinite rectangular metal bounded by a plane | journal=Physica B+C | pages=378–384|bibcode = 1988PhyBC.150..378H | last1=Harsh | first1=O. K | last2=Agarwal | first2=B. K | year=1988 }}</ref>

[[File:GothicRayonnantRose003.jpg|thumb|[[Gothic architecture|Gothic]] [[stained glass]] [[rose window]] of [[Notre-Dame de Paris]]. Some colors were achieved by [[colloid]]s of gold nano-particles.]]
More recently surface plasmons have been used to control colors of materials.<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/4443854.stm | work=[[BBC News]] | title=LEDs work like butterflies' wings | date=November 18, 2005 | access-date=May 22, 2010}}</ref> This is possible since controlling the particle's shape and size determines the types of surface plasmons that can be coupled into and propagate across it. This, in turn, controls the interaction of light with the surface. These effects are illustrated by the historic [[stained glass]] which adorn medieval cathedrals. Some stained glass colors are produced by metal nanoparticles of a fixed size which interact with the optical field to give glass a vibrant red color. In modern science, these effects have been engineered for both visible light and [[microwave radiation]]. Much research goes on first in the microwave range because at this wavelength, material surfaces and samples can be produced mechanically because the patterns tend to be on the order of a few centimeters.  The production of optical range surface plasmon effects involves making surfaces which have features <400&nbsp;[[nanometer|nm]]. This is much more difficult and has only recently become possible to do in any reliable or available way.

Recently, graphene has also been shown to accommodate surface plasmons, observed via near field infrared optical microscopy techniques<ref>{{cite journal |author=Jianing Chen |author2=Michela Badioli |author3=Pablo Alonso-González |author4=Sukosin Thongrattanasiri |author5=Florian Huth |author6=Johann Osmond |author7=Marko Spasenović |author8=Alba Centeno |author9=Amaia Pesquera |author10=Philippe Godignon |author11=Amaia Zurutuza Elorza |author12=Nicolas Camara |author13=F. Javier García de Abajo |author14=Rainer Hillenbrand |author15=Frank H. L. Koppens |title=Optical nano-imaging of gate-tunable graphene plasmons |journal=Nature |volume=487 |issue=7405 |pages=77–81 |doi=10.1038/nature11254 |date=5 July 2012 |arxiv = 1202.4996 |bibcode = 2012Natur.487...77C |pmid=22722861|s2cid=4431470 }}</ref><ref>{{cite journal |title=Gate-tuning of graphene plasmons revealed by infrared nano-imaging |author=Z. Fei |author2=A. S. Rodin |author3=G. O. Andreev |author4=W. Bao |author5=A. S. McLeod |author6=M. Wagner |author7=L. M. Zhang |author8=Z. Zhao |author9=M. Thiemens |author10=G. Dominguez |author11=M. M. Fogler |author12=A. H. Castro Neto |author13=C. N. Lau |author14=F. Keilmann |author15=D. N. Basov |journal=Nature |volume=487 |issue=7405 |pages=82–85 |date=5 July 2012 |doi=10.1038/nature11253 |bibcode=2012Natur.487...82F|arxiv = 1202.4993 |pmid=22722866|s2cid=4348703 }}</ref> and infrared spectroscopy.<ref>{{cite journal |title=Damping pathways of mid-infrared plasmons in graphene nanostructures |author=Hugen Yan |author2=Tony Low |author3=Wenjuan Zhu |author4=Yanqing Wu |author5=Marcus Freitag |author6=Xuesong Li |author7=Francisco Guinea |author8=Phaedon Avouris |author9=Fengnian Xia |journal=Nature Photonics |volume=7 |issue=5 |pages=394–399 |date=2013 |doi=10.1038/nphoton.2013.57 |bibcode = 2013NaPho...7..394Y |arxiv=1209.1984 |s2cid=119225015 }}</ref> Potential applications of graphene plasmonics mainly addressed the terahertz to midinfrared frequencies, such as optical modulators, photodetectors, biosensors.<ref>{{cite journal |title=Graphene Plasmonics for Terahertz to Mid-Infrared Applications |author=Tony Low |author2=Phaedon Avouris |journal=ACS Nano |volume=8 |issue=2 |pages=1086–1101 |date=2014 |doi=10.1021/nn406627u |pmid=24484181|arxiv=1403.2799 |bibcode=2014arXiv1403.2799L |s2cid=8151572 }}</ref>