Plasmonic metamaterials
Encyclopedia
Plasmonic metamaterials are negative index metamaterials
that exploit surface plasmons, which are produced from the interaction of light with metal-dielectric materials. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons
(SPPs). Once launched, the SPPs ripple along the metal-dielectric interface and do not stray from this narrow path. Compared with the incident light that triggered the transformation, the SPPs can be much shorter in wavelength.
Plasmonic metamterials are tailor made composites - combinations of materials designed to achieve optical properties
not seen in nature. The properties stem from the unique structure of the composites, with features smaller than the wavelength of light separated by subwavelength distances. By fabricating such metamaterials fundamental limits tied to the wavelength of light are overcome. Light hitting a metamaterial is transformed into electromagnetic waves of a different variety—surface plasmon polaritons, which are shorter in wavelength than the incident light. This transformation leads to unusual and counterintuitive properties that might be harnessed for practical use. Moreover, new approaches that simplify the fabrication process of metamaterials are under development. This work also includes making new structures specifically designed to enable measurements of the materials novel properties. Furthermore, nanotechnology applications of these nanostructures are currently being researched, including microscopy beyond the diffraction limit.
with dimensions that are fractions of the wavelength of light. Research groups are experimenting with a variety of geometric approaches in an effort to exploit surface plasmons, which are light-induced packets of electrical charges that collectively oscillate at the surfaces of metals at optical frequencies. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons
(SPPs). Once launched, the SPPs ripple along the metal-dielectric interface and do not stray from this narrow path. Compared with the incident light that triggered the transformation, the SPPs can be much shorter in wavelength.
, rather than traveling in lockstep, as is the case in positive index materials. As a result, when juxtaposed with a positive index material, negative index materials were predicted to exhibit counterintuitive properties, like bending, or refracting, light in unnatural ways.
Normally, light traveling from, say, air into water bends upon passing through the normal (a plane perpendicular to the surface) and entering the water. In contrast, light beaming from air toward a negative index material would not cross the normal. Rather, it would bend the opposite way, and, as yet, not occurring in nature.
Negative refraction was first reported for microwaves and infrared
radiation. In 2007, a collaboration team consisting of the Harry Atwater team at the California Institute of Technology, and the NIST reported narrow band, negative refraction of visible light in two dimensions.
To accomplish this a material platform that is a sandwich-like construction with exceedingly thin layers was fabricated. It consists of an insulating sheet of silicon nitride
topped by a film of silver and underlain by gold. The critical dimension is the thickness of the layers, which taken together are only a fraction of the wavelength of blue and green light. By incorporating this metamaterial into integrated-optics on an IC chip, negative refraction was demonstrated over blue and green frequencies. The design exploits bulk materials properties of each component, but the collective result is a relatively significant response to light.
To create this response incident light couples with the undulating, gas-like charges normally on the surface of metals. This photon-plasmon interaction results in SPPs that generate intense, localized optical fields. The waves are confined to the interface between metal and insulator. This narrow channel serves as a transformative guide that, in effect, traps, squeezes, and compresses the wavelength of incoming light.
deposition, focused ion beam
milling, and self-assembly
. In addition, nanomechanical systems incorporating metamaterials are specifically designed to show one of the unusual predicted properties of metamaterials, and that is negative radiation pressure.
Light falling on conventional materials, with a positive index of refraction, exerts a positive pressure, meaning that it can push an object away from the light source. In contrast, illuminating negative index metamaterials should generate a negative pressure that pulls an object toward light.
could exceed the diffraction limit, which prevents positive-index lenses from resolving objects small than one-half of the wavelength of visible light. Because plasmonic materials can literally pinch light to a fraction of its original wavelength, a superlens would capture subwavelength spatial information that is beyond the view of conventional optical microscopes. There are several approaches to building a non-diffraction-limited optical microscope based on the superlens concept. The subwavelength domian can be applied to optical switch
es, modulators, photodetectors, and directional light emitters. These planned devices are also based on plasmonic metamaterials.
. Hence, a type of thermoplastic
, known as a PMMA
, is placed on a gold
surface. This type of lithography is also used to apply three dimensional surface topographies to computer chips. This method has resulted in a plasmonic type of Luneburg lens and Eaton lens.
Light waves propagate by employing transformation optics
at surface plasmon
scales. In other words, transformation optics is applied to the science of plasmonics. The Luneburg and Eaton lenses interact with surface plasmon polaritons
rather than photons.
Possible applications are computers which will use light in place of electronic signals, enhanced optical microscopes, and carpet-cloaking devices.
and electroplating
, and tested using both near-field and far-field optical microscopy and spectroscopy
.
Metamaterials scientists
Negative index metamaterials
Negative index metamaterials or negative index materials are artificial structures where the refractive index has a negative value over some frequency range. This does not occur in any known natural materials, and thus is only achievable with engineered structures known as metamaterials...
that exploit surface plasmons, which are produced from the interaction of light with metal-dielectric materials. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons
Surface plasmon polaritons
Surface plasmon polaritons , are infrared or visible frequency electromagnetic waves trapped at or guided along metal-dielectric interfaces. These are shorter in wavelength than the incident light...
(SPPs). Once launched, the SPPs ripple along the metal-dielectric interface and do not stray from this narrow path. Compared with the incident light that triggered the transformation, the SPPs can be much shorter in wavelength.
Plasmonic metamterials are tailor made composites - combinations of materials designed to achieve optical properties
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
not seen in nature. The properties stem from the unique structure of the composites, with features smaller than the wavelength of light separated by subwavelength distances. By fabricating such metamaterials fundamental limits tied to the wavelength of light are overcome. Light hitting a metamaterial is transformed into electromagnetic waves of a different variety—surface plasmon polaritons, which are shorter in wavelength than the incident light. This transformation leads to unusual and counterintuitive properties that might be harnessed for practical use. Moreover, new approaches that simplify the fabrication process of metamaterials are under development. This work also includes making new structures specifically designed to enable measurements of the materials novel properties. Furthermore, nanotechnology applications of these nanostructures are currently being researched, including microscopy beyond the diffraction limit.
Plasmonic materials
Plasmonic materials are composed of metals and dielectrics that are ordered in geometric arrangementsPeriodic function
In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,...
with dimensions that are fractions of the wavelength of light. Research groups are experimenting with a variety of geometric approaches in an effort to exploit surface plasmons, which are light-induced packets of electrical charges that collectively oscillate at the surfaces of metals at optical frequencies. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons
Surface plasmon polaritons
Surface plasmon polaritons , are infrared or visible frequency electromagnetic waves trapped at or guided along metal-dielectric interfaces. These are shorter in wavelength than the incident light...
(SPPs). Once launched, the SPPs ripple along the metal-dielectric interface and do not stray from this narrow path. Compared with the incident light that triggered the transformation, the SPPs can be much shorter in wavelength.
Negative index materials
Plasmonic metamaterials are incarnations of materials first proposed by a Russian theorist in 1967. Also known as left-handed or negative index materials, the proposed materials were theorized to exhibit optical properties opposite to those of glass, air. These have been termed positive index—materials of our everyday world. In particular, energy is transported in a direction opposite to that of propagating wavefrontsWave propagation
Wave propagation is any of the ways in which waves travel.With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves....
, rather than traveling in lockstep, as is the case in positive index materials. As a result, when juxtaposed with a positive index material, negative index materials were predicted to exhibit counterintuitive properties, like bending, or refracting, light in unnatural ways.
Normally, light traveling from, say, air into water bends upon passing through the normal (a plane perpendicular to the surface) and entering the water. In contrast, light beaming from air toward a negative index material would not cross the normal. Rather, it would bend the opposite way, and, as yet, not occurring in nature.
Negative refraction was first reported for microwaves and infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation. In 2007, a collaboration team consisting of the Harry Atwater team at the California Institute of Technology, and the NIST reported narrow band, negative refraction of visible light in two dimensions.
To accomplish this a material platform that is a sandwich-like construction with exceedingly thin layers was fabricated. It consists of an insulating sheet of silicon nitride
Silicon nitride
Silicon nitride is a chemical compound of silicon and nitrogen. If powdered silicon is heated between 1300° and 1400°C in an atmosphere of nitrogen, trisilicon tetranitride, Si3N4, is formed. The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen...
topped by a film of silver and underlain by gold. The critical dimension is the thickness of the layers, which taken together are only a fraction of the wavelength of blue and green light. By incorporating this metamaterial into integrated-optics on an IC chip, negative refraction was demonstrated over blue and green frequencies. The design exploits bulk materials properties of each component, but the collective result is a relatively significant response to light.
To create this response incident light couples with the undulating, gas-like charges normally on the surface of metals. This photon-plasmon interaction results in SPPs that generate intense, localized optical fields. The waves are confined to the interface between metal and insulator. This narrow channel serves as a transformative guide that, in effect, traps, squeezes, and compresses the wavelength of incoming light.
Three dimensional optical materials
Computer simulations are designing plasmonic metamaterials with a negative index in three dimensions. The experimental composites will be made using a variety of fabrication methods, including multilayer thin filmThin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
deposition, focused ion beam
Focused ion beam
Focused ion beam, also known as FIB, is a technique used particularly in the semiconductor industry, materials science and increasingly in the biological field for site-specific analysis, deposition, and ablation of materials. An FIB setup is a scientific instrument that resembles a scanning...
milling, and self-assembly
Self-assembly
Self-assembly is a term used to describe processes in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction...
. In addition, nanomechanical systems incorporating metamaterials are specifically designed to show one of the unusual predicted properties of metamaterials, and that is negative radiation pressure.
Light falling on conventional materials, with a positive index of refraction, exerts a positive pressure, meaning that it can push an object away from the light source. In contrast, illuminating negative index metamaterials should generate a negative pressure that pulls an object toward light.
Subwavelength focusing
Plasmonic negative-index metamaterials are also applicable to visible-light imaging of molecular and atomic scale objects. A theorized superlensSuperlens
A superlens, super lens or perfect lens is a lens which uses metamaterials to go beyond the diffraction limit. The diffraction limit is an inherent limitation in conventional optical devices or lenses. In 2000, a type of lens was proposed, consisting of a metamaterial that compensates for wave...
could exceed the diffraction limit, which prevents positive-index lenses from resolving objects small than one-half of the wavelength of visible light. Because plasmonic materials can literally pinch light to a fraction of its original wavelength, a superlens would capture subwavelength spatial information that is beyond the view of conventional optical microscopes. There are several approaches to building a non-diffraction-limited optical microscope based on the superlens concept. The subwavelength domian can be applied to optical switch
Optical switch
In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits to be selectively switched from one circuit to another....
es, modulators, photodetectors, and directional light emitters. These planned devices are also based on plasmonic metamaterials.
Gradient index plasmonics
Gradient index plasmonics works by placing a dielectric material on a metal substrate (composite material), along with electron beam lithographyElectron beam lithography
Electron beam lithography is the practice of emitting a beam of electrons in a patterned fashion across a surface covered with a film , and of selectively removing either exposed or non-exposed regions of the resist...
. Hence, a type of thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...
, known as a PMMA
PMMA
PMMA can refer to* Para-Methoxymethamphetamine, a stimulant drug* Philippine Merchant Marine Academy* Poly, a transparent thermoplastic often used as a glass substitute...
, is placed on a gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
surface. This type of lithography is also used to apply three dimensional surface topographies to computer chips. This method has resulted in a plasmonic type of Luneburg lens and Eaton lens.
Light waves propagate by employing transformation optics
Transformation optics
Transformation optics represents an advancement in the design of optical devices. It is the basis for conceptualizing complex tools in the electromagnetic regime which allows for novel control of light, also known as electromagnetic waves. The mathematics underpinning transformation optics is...
at surface plasmon
Surface plasmon
Surface plasmons , are coherent electron oscillations that exist at the interface between any two materials where the real part of the dielectric function changes sign across the interface...
scales. In other words, transformation optics is applied to the science of plasmonics. The Luneburg and Eaton lenses interact with surface plasmon polaritons
Surface plasmon polaritons
Surface plasmon polaritons , are infrared or visible frequency electromagnetic waves trapped at or guided along metal-dielectric interfaces. These are shorter in wavelength than the incident light...
rather than photons.
Possible applications are computers which will use light in place of electronic signals, enhanced optical microscopes, and carpet-cloaking devices.
Biological and chemical sensing
Other proof-of-concept applications that are being explored include high sensitivity biological and chemical sensing. This pertains to the development of optical sensors which exploit the confinement of surface plasmons within a certain type of Fabry-Perot nano-resonators. This tailored confinement will allow efficient detection of specific binding of target chemical or biological analyte molecules because of the strong spatial overlap between the optical resonator mode and the analyte ligands bound to the cavity sidewalls. Structures are optimized using finite difference time domain electromagnetic simulations, fabricated using a combination of electron beam lithographyElectron beam lithography
Electron beam lithography is the practice of emitting a beam of electrons in a patterned fashion across a surface covered with a film , and of selectively removing either exposed or non-exposed regions of the resist...
and electroplating
Electroplating
Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...
, and tested using both near-field and far-field optical microscopy and spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
.
See also
- History of metamaterialsHistory of metamaterialsHistory of metamaterials shares a common history with artificial dielectrics in microwave engineering, as it developed just after World War II. However, there are seminal explorations of artificial materials for manipulating electromagnetic waves at the end of the 19th century...
- Metamaterial cloakingMetamaterial cloakingMetamaterial cloaking is the scientific application of metamaterials in order to achieve invisibility-cloaking. This is accomplished by manipulating the paths traversed by light through a novel optical material....
- MetamaterialMetamaterialMetamaterials are artificial materials engineered to have properties that may not be found in nature. Metamaterials usually gain their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior....
- Metamaterial antennasMetamaterial antennasMetamaterial antennas are a class of antennas which use metamaterials to increase performance of miniaturized antenna systems. Their purpose, as with any electromagnetic antenna, is to launch energy into free space...
- Nonlinear metamaterialsNonlinear metamaterialsA nonlinear metamaterial is an artificially constructed material that can exhibit properties not found in nature. Its response to electromagnetic radiation can be characterized by its permittivity and material permeability. The product of the permittivity and permeability results in the refractive...
- Photonic metamaterialsPhotonic metamaterialsPhotonic metamaterials, also known as Optical metamaterials, are a type of electromagnetic metamaterial, which are designed to interact with optical frequencies which are terahertz , infrared , and eventually, visible wavelengths. As a type of metamaterial, the periodic structures are made up of...
- Photonic crystalPhotonic crystalPhotonic crystals are periodic optical nanostructures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons...
- Seismic metamaterialsSeismic metamaterialsSeismic metamaterials, are metamaterials which are designed to counteract the adverse effects of seismic waves on artificial structures, which exist on or near the surface of the earth...
- Split-ring resonator
- SuperlensSuperlensA superlens, super lens or perfect lens is a lens which uses metamaterials to go beyond the diffraction limit. The diffraction limit is an inherent limitation in conventional optical devices or lenses. In 2000, a type of lens was proposed, consisting of a metamaterial that compensates for wave...
- Acoustic metamaterialsAcoustic metamaterialsAcoustic metamaterials are artificially fabricated materials designed to control, direct, and manipulate sound in the form of sonic, infrasonic, or ultrasonic waves, as these might occur in gases, liquids, and solids. The hereditary line into acoustic metamaterials follows from theory and research...
- Metamaterial absorberMetamaterial absorberA metamaterial absorber manipulates the loss components of the complex effective parameters, permittivity and magnetic permeability of metamaterials, to create a material with particularly high absorption...
- Terahertz metamaterialsTerahertz metamaterialsTerahertz metamaterials are a new class of composite, artificial materials which interact at terahertz frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz...
- Tunable metamaterialsTunable metamaterialsA tunable metamaterial is a metamaterial with a variable response to an incident electromagnetic wave. This includes remotely controlling how an incident electromagnetic wave interacts with a metamaterial. This means the capablitity to determine whether the EM wave is transmitted, reflected, or...
- Negative index metamaterialsNegative index metamaterialsNegative index metamaterials or negative index materials are artificial structures where the refractive index has a negative value over some frequency range. This does not occur in any known natural materials, and thus is only achievable with engineered structures known as metamaterials...
- Transformation opticsTransformation opticsTransformation optics represents an advancement in the design of optical devices. It is the basis for conceptualizing complex tools in the electromagnetic regime which allows for novel control of light, also known as electromagnetic waves. The mathematics underpinning transformation optics is...
- Theories of cloaking
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- Academic journals
- Metamaterials (journal)Metamaterials (journal)Metamaterials is a peer-reviewed scientific journal that was established in March 2007. It is published by Elsevier in association with the Metamorphose Network of Excellence. The Coordinating Editor is Mikhail Lapine. The journal is published quarterly, with occasional special issues...
- Metamaterials (journal)
- Metamaterials books
- Metamaterials HandbookMetamaterials HandbookMetamaterials Handbook is a two-volume handbook on metamaterials edited by Filippo Capolino .The series is designed to cover all theory and application topics related to electromagnetic metamaterials. Disciplines have combined to study, and develop electromagnetic metamaterials...
- Metamaterials: Physics and Engineering ExplorationsMetamaterials: Physics and Engineering ExplorationsMetamaterials: Physics and Engineering Explorations is a book length introduction to the fundamental research and advancements in electromagnetic composite substances known as electromagnetic metamaterials. The discussion encompasses examination of the physics of metamaterial interactions, the...
- Metamaterials Handbook
- Academic journals
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-
Metamaterials scientists
- John PendryJohn PendrySir John Brian Pendry, FRS FInstP is an English theoretical physicist known for his research into refractive indexes and creation of the first practical "Invisibility Cloak"...
- David R. SmithDavid R. SmithDavid R. Smith is a renowned American physicist and professor of electrical and computer engineering at Duke University in North Carolina. Smith's research focuses on electromagnetic metamaterials, or materials with a negative index of refraction...
- Richard W. ZiolkowskiRichard W. ZiolkowskiRichard W. Ziolkowski is a past president of the IEEE Antennas and Propagation Society , and a former vice president of this same society . In 2006 he was awarded OSA Fellow. He is also an IEEE Fellow....
- Nader EnghetaNader EnghetaNader Engheta is an Iranian scientist and engineer. He has significantly contributed to novel artificial materials, photonics, nano-structured materials, novel graphene materials, and plasmonics....
External links
- Plasmonic metamaterials - From microscopes to invisibility cloaks. Jan 21, 2011. PhysOrg.com.