Conductive polymer - AbsoluteAstronomy.com

Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

. Such compounds may have metallic conductivity or can be semiconductor

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

s. The biggest advantage of conductive polymers is their processability, mainly by dispersion

Dispersion (chemistry)

A dispersion is a system in which particles are dispersed in a continuous phase of a different composition . See also emulsion. A dispersion is classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not...

. Conductive polymers are generally not plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

s, i.e., they are not thermoformable. But, like insulating polymers, they are organic materials. They can offer high electrical conductivity but do not show mechanical properties as other commercially used polymers do. The electrical properties can be fine-tuned using the methods of organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

and by advanced dispersion techniques.

Types

The linear-backbone "polymer blacks" (polyacetylene

Polyacetylene

Polyacetylene is an organic polymer with the repeat unit n. The high electrical conductivity discovered for these polymers beginning in the 1960's accelerated interest in the use of organic compounds in microelectronics...

, polypyrrole

Polypyrrole

Polypyrrole is a chemical compound formed from a number of connected pyrrole ring structures. For example a tetrapyrrole is a compound with four pyrrole rings connected. Methine-bridged cyclic tetrapyrroles are called porphyrins. Polypyrroles are conducting polymers of the rigid-rod polymer host...

, and polyaniline

Polyaniline

Polyaniline is a conducting polymer of the semi-flexible rod polymer family. Although the compound itself was discovered over 150 years ago, only since the early 1980s has polyaniline captured the intense attention of the scientific community. This is due to the rediscovery of its high electrical...

) and their copolymers are the main class of conductive polymers. Historically, these are known as melanins. Poly(p-phenylene vinylene)

Poly(p-phenylene vinylene)

Poly is a conducting polymer of the rigid-rod polymer host family.PPV is the only polymer of this type that has so far been successfully processed into a highly ordered crystalline thin film. PPV and its derivatives are conducting polymers of rigid-rod polymer family...

(PPV) and its soluble derivatives have emerged as the prototypical electroluminescent semiconducting polymers. Today, poly(3-alkylthiophenes) are the archetypical materials for solar cells and transistors.

The following table presents some organic conductive polymers according to their composition. The well-studied classes are written in bold and the less well studied ones are in italic.

The main chain contains	\|Heteroatoms present
The main chain contains	No heteroatom	Nitrogen-containing Amine Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...	Sulfur Sulfur Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow... -containing
Aromatic cycles	Poly(fluorene)s Polyfluorene Polyfluorenes are a class of polymeric materials. They are of interest because similar to other conjugated polymers, they are currently being investigated for use in light-emitting diodes, field-effect transistors, and plastic solar cells. They are not a naturally occurring material, but are... polyphenylene Phenylene The phenylene group is based on a di-substituted benzene ring . For example, poly is a polymer built up from para-phenylene repeating units.... s polypyrene Pyrene Pyrene is a polycyclic aromatic hydrocarbon consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is . This colourless solid is the smallest peri-fused PAH... s polyazulene Azulene Azulene is an organic compound and an isomer of naphthalene. Whereas naphthalene is colourless, azulene is dark blue. Its name is derived from the Spanish word azul, meaning "blue"... s polynaphthalene Naphthalene Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings... s	The N is in the aromatic cycle: poly(pyrrole)s Polypyrrole Polypyrrole is a chemical compound formed from a number of connected pyrrole ring structures. For example a tetrapyrrole is a compound with four pyrrole rings connected. Methine-bridged cyclic tetrapyrroles are called porphyrins. Polypyrroles are conducting polymers of the rigid-rod polymer host... (PPY) polycarbazole Carbazole Carbazole is an aromatic heterocyclic organic compound. It has a tricyclic structure, consisting of two six-membered benzene ring fused on either side of a five-membered nitrogen-containing ring... s polyindole Indole Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an... s polyazepines The N is outside the aromatic cycle: polyaniline Polyaniline Polyaniline is a conducting polymer of the semi-flexible rod polymer family. Although the compound itself was discovered over 150 years ago, only since the early 1980s has polyaniline captured the intense attention of the scientific community. This is due to the rediscovery of its high electrical... s (PANI)	The S is in the aromatic cycle: poly(thiophene)s Polythiophene Polythiophenes result from the polymerization of thiophenes, a sulfur heterocycle, that can become conducting when electrons are added or removed from the conjugated π-orbitals via doping.... (PT) poly(3,4-ethylenedioxythiophene) Poly(3,4-ethylenedioxythiophene) Poly or PEDOT is a conducting polymer based on 3,4-ethylenedioxylthiophene or EDOT monomer. Advantages of this polymer are optical transparency in its conducting state, high stability and moderate band gap and low redox potential... (PEDOT) The S is outside the aromatic cycle: poly(p-phenylene sulfide) Poly(p-phenylene sulfide) Polyphenylene sulfide is an organic polymer consisting of aromatic rings linked with sulfides. Synthetic fiber and textiles derived from this polymer are known to resist chemical and thermal attack. PPS is used to make filter fabric for coal boilers, papermaking felts, electrical insulation,... (PPS)
Double bonds	Poly(acetylene)s Polyacetylene Polyacetylene is an organic polymer with the repeat unit n. The high electrical conductivity discovered for these polymers beginning in the 1960's accelerated interest in the use of organic compounds in microelectronics... (PAC)
Aromatic cycles and double bonds	Poly(p-phenylene vinylene) Poly(p-phenylene vinylene) Poly is a conducting polymer of the rigid-rod polymer host family.PPV is the only polymer of this type that has so far been successfully processed into a highly ordered crystalline thin film. PPV and its derivatives are conducting polymers of rigid-rod polymer family... (PPV)

Synthesis

There are many methods for the synthesis of conductive polymers. Most conductive polymers are prepared by oxidative coupling of monocyclic precursors. Such reactions entail dehydrogenation

Dehydrogenation

Dehydrogenation is a chemical reaction that involves the elimination of hydrogen . It is the reverse process of hydrogenation. Dehydrogenation reactions may be either large scale industrial processes or smaller scale laboratory procedures....

n H–[X]–H → H–[X]_n–H + 2(n–1) H⁺ + 2(n–1) e^–

The low solubility of most polymers presents challenges. Some researchers have addressed this through the formation of nanostructures and surfactant-stabilized conducting polymer dispersions in water. These include polyaniline nanofibers

Polyaniline nanofibers

Polyaniline nanofibers are the high aspect version of polyaniline created by several techniques including nanofiber seeding, electrochemical synthesis , electrospinning of composites and several oxidative polymerization methods. Most of these methods required templates that had to be removed,...

and PEDOT

Poly(3,4-ethylenedioxythiophene)

Poly or PEDOT is a conducting polymer based on 3,4-ethylenedioxylthiophene or EDOT monomer. Advantages of this polymer are optical transparency in its conducting state, high stability and moderate band gap and low redox potential...

:PSS

Sodium polystyrene sulfonate

Sodium polystyrene sulfonate is a type of polymer and ionomer based on polystyrene. It is the sodium salt of polystyrene sulfonic acid.-Chemical properties:...

. These materials have lower molecular weights than that of some materials previously explored in the literature. However, in some cases, the molecular weight need not be high to achieve the desired properties.

Molecular basis of electrical conductivity

The conductivity of such polymers is the result of several processes. E.g., in traditional polymers such as polyethylene

Polyethylene

Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

s, the valence electrons are bound in sp³ hybridized covalent bond

Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

s. Such "sigma-bonding electrons" have low mobility and do not contribute to the electrical conductivity of the material. However, in conjugated

Conjugated system

In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...

materials, the situation is completely different. Conducting polymers have backbones of contiguous sp² hybridized carbon centers. One valence electron on each center resides in a p_z orbital, which is orthogonal to the other three sigma-bonds. The electrons in these delocalized orbitals have high mobility when the material is "doped" by oxidation, which removes some of these delocalized electrons. Thus, the conjugated p-orbitals

Conjugated system

form a one-dimensional electronic band

Electronic band structure

In solid-state physics, the electronic band structure of a solid describes those ranges of energy an electron is "forbidden" or "allowed" to have. Band structure derives from the diffraction of the quantum mechanical electron waves in a periodic crystal lattice with a specific crystal system and...

, and the electrons within this band become mobile when it is partially emptied. The band structures of conductive polymers can easily be calculated with a tight binding model. In principle, these same materials can be doped by reduction, which adds electrons to an otherwise unfilled band. In practice, most organic conductors are doped oxidatively to give p-type materials. The redox doping of organic conductors is analogous to the doping of silicon semiconductors, whereby a small fraction silicon atoms are replaced by electron-rich (e.g., phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

) or electron-poor (e.g. boron

Boron

Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

) atoms to create n-type

N-type semiconductor

N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....

and p-type semiconductor

P-type semiconductor

A P-type semiconductor is obtained by carrying out a process of doping: that is, adding a certain type of atoms to the semiconductor in order to increase the number of free charge carriers ....

s, respectively.

Although typically "doping" conductive polymers involves oxidizing or reducing the material, conductive organic polymers associated with a protic solvent

Protic solvent

In chemistry a protic solvent is a solvent that has a hydrogen atom bound to an oxygen or a nitrogen . In general terms, any molecular solvent that contains dissociable H+ is called a protic solvent. The molecules of such solvents can donate an H+...

may also be "self-doped."

The most notable difference between conductive polymers and inorganic semiconductors is the electron mobility

Electron mobility

In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...

, which until very recently was dramatically lower in conductive polymers than their inorganic counterparts. This difference is diminishing with the invention of new polymers and the development of new processing techniques. Low charge carrier mobility is related to structural disorder. In fact, as with inorganic amorphous semiconductors, conduction in such relatively disordered materials is mostly a function of "mobility gaps" with phonon

Phonon

In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...

-assisted hopping, polaron

Polaron

A polaron is a quasiparticle composed of a charge and its accompanying polarization field. A slow moving electron in a dielectric crystal, interacting with lattice ions through long-range forces will permanently be surrounded by a region of lattice polarization and deformation caused by the moving...

-assisted tunneling

Tunneling

Tunneling may refer to:* Digging tunnels * Quantum tunneling, the quantum-mechanical effect where a particle crosses through a classically-forbidden potential energy barrier...

, etc., between localized states. Recently, it has been reported that Quantum Decoherence

Quantum decoherence

In quantum mechanics, quantum decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition. A consequence of this dephasing leads to classical or probabilistically additive behavior...

on localized electron states might be the fundamental mechanism behind electron transport in conductive polymers.

The conjugated polymers in their undoped, pristine state are semiconductors or insulators. As such, the energy gap can be > 2 eV, which is too great for thermally activated conduction. Therefore, undoped conjugated polymers, such as polythiophenes, polyacetylene

Polyacetylene

s only have a low electrical conductivity of around 10⁻¹⁰ to 10⁻⁸ S/cm. Even at a very low level of doping (< 1%), electrical conductivity increases several orders of magnitude up to values of around 0.1 S/cm. Subsequent doping of the conducting polymers will result in a saturation of the conductivity at values around 0.1–10 kS/cm for different polymers. Highest values reported up to now are for the conductivity of stretch oriented polyacetylene with confirmed values of about 80 kS/cm. Although the pi-electrons in polyactetylene are delocalized along the chain, pristine polyacetylene is not a metal. Polyacetylene has alternating single and double bonds which have lengths of 1.44 and 1.36 Å, respectively. Upon doping, the bond alteration is diminished in conductivity increases. Non-doping increases in conductivity can also be accomplished in a field effect transistor (organic FET or OFET

OFET

An organic field-effect transistor is a field effect transistor using an organic semiconductor in its channel. OFETs can be prepared either by vacuum evaporation of small molecules, by solution-casting of polymers or small molecules, or by mechanical transfer of a peeled single-crystalline organic...

) and by irradiation

Photoconductivity

Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation....

. Some materials also exhibit negative differential resistance and voltage-controlled "switching" analogous to that seen in inorganic amorphous semiconductors.

Despite intensive research, the relationship between morphology, chain structure and conductivity is still poorly understood. Generally, it is assumed that conductivity should be higher for the higher degree of crystallinity and better alignment of the chains, however this could not be confirmed for PEDOT

Poly(3,4-ethylenedioxythiophene)

and polyaniline

Polyaniline

, which are largely amorphous.

Properties and applications

Conductive polymers enjoy few large-scale applications due to their poor processability. They have been known to have promise in antistatic materials and they have been incorporated into commercial displays and batteries, but there have had limitations due to the manufacturing costs, material inconsistencies, toxicity, poor solubility in solvents, and inability to directly melt process. Literature suggests they are also promising in organic solar cells, printing electronic circuits

Printed electronics

Printed electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment or other low-cost equipment suitable for defining patterns on material, such as screen printing, flexography, gravure, offset lithography and...

, organic light-emitting diodes, actuator

Actuator

An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...

s, electrochromism

Electrochromism

Electrochromism is the phenomenon displayed by some materials of reversibly changing color when a burst of charge is applied. Various types of materials and structures can be used to construct electrochromic devices, depending on the specific applications....

, supercapacitors, biosensors, flexible transparent displays, electromagnetic shielding

Electromagnetic shielding

Electromagnetic shielding is the process of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive and/or magnetic materials. Shielding is typically applied to enclosures to isolate electrical devices from the 'outside world' and to cables to isolate...

and possibly replacement for the popular transparent conductor indium tin oxide

Indium tin oxide

Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey...

. Conducting polymers are rapidly gaining attraction in new applications with increasingly processable materials with better electrical and physical properties and lower costs. The new nanostructured forms of conducting polymers particularly, provide fresh air to this field with their higher surface area and better dispersability.

With the availability of stable and reproducible dispersions, PEDOT and polyaniline

Polyaniline

have gained some large scale applications. While PEDOT (poly(3,4-ethylenedioxythiophene)

Poly(3,4-ethylenedioxythiophene)

) is mainly used in antistatic applications and as a transparent conductive layer in form of PEDOT:PSS dispersions (PSS=polystyrene sulfonic acid

Sodium polystyrene sulfonate

Sodium polystyrene sulfonate is a type of polymer and ionomer based on polystyrene. It is the sodium salt of polystyrene sulfonic acid.-Chemical properties:...

), polyaniline is widely used for printed circuit board manufacturing – in the final finish, for protecting copper from corrosion and preventing its solderability.

Electroluminescence

Electroluminescence is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field...

is light emission stimulated by electrical current. In organic compounds, electroluminescence has been known since the early 1950s, when Bernanose and coworkers first produced electroluminescence in crystalline thin films of acridine orange and quinacrine. In 1960, researchers at Dow Chemical developed AC-driven electroluminescent cells using doping. In some cases, similar light emission is observed when a voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

is applied to a thin layer of a conductive organic polymer film. While electroluminescence was originally mostly of academic interest, the increased conductivity of modern conductive polymers means enough power can be put through the device at low voltages to generate practical amounts of light. This property has led to the development of flat panel display

Flat panel display

Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...

s using organic LEDs, solar panel

Photovoltaic module

A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...

s, and optical amplifier

Amplifier

Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...

Barriers to applications

Since most conductive polymers require oxidative doping, the properties of the resulting state are crucial. Such materials are salt-like (polymer salt), which diminishes their solubility in organic solvents and water and hence their processability. Furthermore, the charged organic backbone is often unstable towards atmospheric moisture. Compared to metals, organic conductors can be expensive requiring multi-step synthesis. The poor processability for many polymers requires the introduction of solubilizing or substituents, which can further complicate the synthesis.

Experimental and theoretical thermodynamical evidence suggests that conductive polymers may even be completely and principally insoluble so that they can only be processed by dispersion

Dispersion (chemistry)

Trends

Most recent emphasis is on organic light emitting diodes and organic polymer solar cell

Polymer solar cell

Polymer solar cells are a type of flexible solar cell. They can come in many forms including: organic solar cell , or organic chemistry photovoltaic cell that produce electricity from sunlight using polymers. There are also other types of more stable thin-film semiconductors that can be deposited...

s. The Organic Electronics Association is an international platform to promote applications of organic semiconductors. Conductive polymer products with embedded and improved electromagnetic interference (EMI) and electrostatic discharge (ESD) protection have led to both prototypes and products. For example, Polymer Electronics Research Center at University of Auckland is developing a range of novel DNA sensor technologies based on conducting polymers, photoluminescent polymers and inorganic nanocrystals (quantum dots) for simple, rapid and sensitive gene detection. Typical conductive polymers must be "doped" to produce high conductivity. To date, there remains to be discovered an organic polymer that is intrinsically electrically conducting.

History

There are multiple reviews of the history of the field. The first report on polyaniline goes back to the discovery of aniline. In the mid-19th century, Letheby reported the electrochemical and chemical oxidation products of aniline in acidic media, noting that reduced form was colourless but the oxidized forms were deep blue. In the early 20th century, German chemists named several compounds "aniline black" and "pyrrole black" and used them industrially. Classically, such polymer "blacks", their parent compound polyacetylene, and their co-polymers were called "Melanins".

The first highly-conductive organic compounds were the charge transfer complex

Charge transfer complex

A charge-transfer complex or electron-donor-acceptor complex is an association of two or more molecules, or of different parts of one very large molecule, in which a fraction of electronic charge is transferred between the molecular entities. The resulting electrostatic attraction provides a...

es. In the 1950s, researchers reported that polycyclic aromatic compounds formed semi-conducting charge-transfer complex salts with halogens. In 1954, researchers at Bell Labs and elsewhere reported organic charge transfer complexes with resistivities as low as 8 ohms-cm. In the early 1970s, salts of tetrathiafulvalene

Tetrathiafulvalene

Tetrathiafulvalene is a organosulfur compound with the formula 2. Studies on this heterocyclic compound contributed to the development of molecular electronics. TTF is related to the hydrocarbon fulvalene, 2, by replacement of four CH groups with sulfur atoms...

were shown to exhibit almost metallic conductivity, while superconductivity was demonstrated in 1980. Broad research on charge transfer salts continues today. While these compounds were technically not polymers, this indicated that organic compounds can carry current. While organic conductors were previously intermittently discussed, the field was particularly energized by the prediction of superconductivity

Superconductivity

Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...

following the discovery of BCS theory

BCS theory

BCS theory — proposed by Bardeen, Cooper, and Schrieffer in 1957 — is the first microscopic theory of superconductivity since its discovery in 1911. The theory describes superconductivity as a microscopic effect caused by a "condensation" of pairs of electrons into a boson-like state...

.

In 1963 Australians Bolto, DE Weiss, and coworkers reported iodine-doped oxidized polypyrrole

Polypyrrole

blacks with resistivities as low as 1 ohm·cm. This Australian group eventually claimed to reach resistivities as low as 0.03 ohm·cm with other conductive organic polymers. This resistivity is roughly equivalent to present-day efforts. The 1964 monograph Organic Semiconductors cites multiple reports of similar high-conductivity oxidized polyacetylenes. With the notable exception of Charge transfer complex

Charge transfer complex

es (some of which are even superconductors), organic molecules were previously considered insulators or at best weakly conducting semiconductors. Subsequently, DeSurville and coworkers reported high conductivity in a polyaniline. Likewise, in 1980, Diaz and Logan reported films of polyaniline that can serve as electrodes.

Similarly, much early work on the physics and chemistry of conductive polymers was done under the melanin rubrick. This was because of the medical relevance of this material. For example, in the 1960s Blois et al. showed semiconduction in melanins, as well as further defining their physical structures and properties Nicolaus et al. further defined the conductive polymer structures. Classically, all polyacetylenes, polypyrroles and polyanilines are melanins, "The most simple melanin can be considered the acetylene-black from which it is possible to derive all the others.. Substitution does not qualitatively influence the physical properties like conductivity, colour, EPR, which remain unaltered."

However, while mostly operating in the quantum realm

Quantum realm

Quantum realm is a term of art in physics referring to scales where quantum mechanical effects become important . Typically, this means distances of 100 nanometers or less. Not coincidentally, this is the same scale as nanotechnology....

of less than 100 nanometers, "molecular" electronic processes can collectively manifest on a macro scale. Examples include quantum tunneling, negative resistance

Negative resistance

Negative resistance is a property of some electric circuits where an increase in the current entering a port results in a decreased voltage across the same port. This is in contrast to a simple ohmic resistor, which exhibits an increase in voltage under the same conditions. Negative resistors are...

, phonon

Phonon

In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids...

-assisted hopping, polaron

Polaron

s, and the like. Thus, macro-scale active organic electronic devices were described decades before molecular-scale ones. E.g., in 1974, John McGinness

John McGinness

John Edward McGinness , is an American physicist and physician. McGinness worked as a in the field of Organic electronics and Nanotechnology.-Education:McGinness studied physics at the University of Houston and after his B.S...

and his coworkers described the putative "first experimental demonstration of an operating molecular electronic device". This was an "active" organic-polymer electronic device, a voltage-controlled bistable switch. As its active element, this device used DOPA-melanin, a well-characterized self-doping copolymer of polyaniline

Polyaniline

, polypyrrole

Polypyrrole

, and polyacetylene

Polyacetylene

. The "ON" state of this device exhibited almost metallic conductivity, and exhibited low conductivity with switching, with as much as five orders of magnitude shifts in current. Their material also exhibited classic negative differential resistance.

In 1977, Alan J. Heeger

Alan J. Heeger

Alan Jay Heeger is an American physicist, academic and Nobel Prize laureate in chemistry.Heeger was born in Sioux City, Iowa to a Jewish family. He earned a B.S. in physics and mathematics from the University of Nebraska-Lincoln in 1957, and a Ph.D in physics from the University of California,...

, Alan MacDiarmid

Alan MacDiarmid

Alan Graham MacDiarmid ONZ was a chemist, and one of three recipients of the Nobel Prize for Chemistry in 2000.-Early life:He was born in Masterton, New Zealand as one of five children - three brothers and two sisters...

and Hideki Shirakawa

Hideki Shirakawa

Hideki Shirakawa is a Japanese chemist and winner of the 2000 Nobel Prize in Chemistry for his discovery of conductive polymers together with physics professor Alan J. Heeger and chemistry professor Alan G...

reported similar high conductivity in oxidized iodine-doped polyacetylene. This research earned them the 2000 Nobel prize in Chemistry "For the discovery and development of conductive polymers." The Nobel citation made no reference to Weiss et al.'s similar earlier work (see Nobel Prize controversies

Nobel Prize controversies

Subsequent to his death in 1896, the will of Swedish industrialist Alfred Nobel established the Nobel Prizes. Annual prizes were to be awarded for service to humanity in the fields of physics, chemistry, physiology or medicine, literature, and peace. Similarly, the Bank of Sweden Prize in Economic...

). Because of the numerous earlier reports of similar compounds, reviewers question the Nobel citation's discovery assignment. Thus, Inzelt notes that, while the Nobelists deserve credit for publicising and popularizing the field, conductive polymers were " ..produced, studied and even applied " well before their work.

External links

Conducting Polymers for Carbon Electronics – a Chem Soc Rev themed issue with a foreword from Alan Heeger

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Types

Synthesis

Molecular basis of electrical conductivity

Properties and applications

Electroluminescence

Barriers to applications

Trends

History

Further reading

External links