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Indium tin oxide (ITO) is a
ternary composition In inorganic chemistry and materials chemistry, a ternary compound or ternary phase is a chemical compound containing three different elements. While some ternary compounds are molecular, ''e.g.'' chloroform (), more typically ternary phases re ...
of
indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
, tin and
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
in varying proportions. Depending on the oxygen content, it can be described as either a
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, ...
or an
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
. Indium tin oxide is typically encountered as an oxygen-saturated composition with a formulation of 74% In, 18% Sn, and 8% O by weight. Oxygen-saturated compositions are so typical that unsaturated compositions are termed ''oxygen-deficient ITO''. It is transparent and colorless in thin layers, while in bulk form it is yellowish to gray. In the infrared region of the spectrum it acts as a metal-like mirror. Indium tin oxide is one of the most widely used transparent conducting oxides because of its
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
and
optical transparency In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable light scattering by particles, scattering of light. On a macroscopic scale ...
, the ease with which it can be deposited as a thin film, and its chemical resistance to moisture. As with all transparent conducting films, a compromise must be made between conductivity and transparency, since increasing the thickness and increasing the concentration of
charge carrier In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term i ...
s increases the film's conductivity, but decreases its transparency.
Thin film A thin film is a layer of material ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...
s of indium tin oxide are most commonly deposited on surfaces by
physical vapor deposition Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...
. Often used is electron beam evaporation, or a range of
sputter deposition Sputter deposition is a physical vapor deposition (PVD) method of thin film deposition by the phenomenon of sputtering. This involves ejecting material from a "target" that is a source onto a "substrate" such as a silicon wafer. Resputtering is ...
techniques.


Material and properties

ITO is a mixed oxide of
indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
and tin with a melting point in the range 1526–1926 °C (1800–2200 K, 2800–3500 °F), depending on composition. The most commonly used material is an oxide of a composition of ca. In4Sn. The material is a
n-type semiconductor An extrinsic semiconductor is one that has been '' doped''; during manufacture of the semiconductor crystal a trace element or chemical called a doping agent has been incorporated chemically into the crystal, for the purpose of giving it differen ...
with a large
bandgap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (i ...
of around 4 eV. ITO is both transparent to visible light and relatively conductive. It has a low electrical
resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
of ~10−4 Ω·cm, and a thin film can have an optical transmittance of greater than 80%. These properties are utilized to great advantage in
touch-screen A touchscreen or touch screen is the assembly of both an input ('touch panel') and output ('display') device. The touch panel is normally layered on the top of an electronic visual display of an information processing system. The display is ofte ...
applications such as
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whi ...
s.


Common uses

Indium tin oxide (ITO) is an optoelectronic material that is applied widely in both research and industry. ITO can be used for many applications, such as flat-panel displays, smart windows, polymer-based electronics, thin film photovoltaics, glass doors of supermarket freezers, and architectural windows. Moreover, ITO thin films for glass substrates can be helpful for glass windows to conserve energy. ITO green tapes are utilized for the production of lamps that are electroluminescent, functional, and fully flexible. Also, ITO thin films are used primarily to serve as coatings that are anti-reflective and for liquid crystal displays (LCDs) and electroluminescence, where the thin films are used as conducting, transparent electrodes. ITO is often used to make transparent conductive coating for displays such as
liquid crystal display A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but ...
s,
OLED An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
displays,
plasma display A plasma display panel (PDP) is a type of flat panel display that uses small cells containing plasma: ionized gas that responds to electric fields. Plasma televisions were the first large (over 32 inches diagonal) flat panel displays to be rele ...
s, touch panels, and electronic ink applications. Thin films of ITO are also used in
organic light-emitting diode An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
s,
solar cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
s,
antistatic coating An antistatic agent is a compound used for treatment of materials or their surfaces in order to reduce or eliminate buildup of static electricity. Static charge may be generated by the triboelectric effect or by a non-contact process using a high ...
s and EMI shieldings. In
organic light-emitting diode An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
s, ITO is used as the
anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
(hole injection layer). ITO films deposited on windshields are used for defrosting aircraft windshields. The heat is generated by applying a voltage across the film. ITO is also used to reflect
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
. The
F-22 Raptor The Lockheed Martin F-22 Raptor is an American single-seat, twin-engine, all-weather stealth tactical fighter aircraft developed for the United States Air Force (USAF). As the result of the USAF's Advanced Tactical Fighter (ATF) program, th ...
's canopy has an ITO coating that reflects
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
waves, enhancing its
stealth Stealth may refer to: Military * Stealth technology, technology used to conceal ships, aircraft, and missiles ** Stealth aircraft, aircraft which use stealth technology **Stealth ground vehicle, ground vehicles which use stealth technology ** St ...
capabilities and giving it a distinctive gold tint. ITO is also used for various
optical coating An optical coating is one or more thin-film optics, thin layers of material deposited on an optical component such as a lens (optics), lens, prism (optics), prism or mirror, which alters the way in which the optic reflection (physics), reflects an ...
s, most notably
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
-reflecting coatings (
hot mirror A hot mirror is a specialized dielectric mirror, a dichroic filter, often employed to protect optical systems by reflecting infrared light back into a light source, while allowing visible light to pass. Hot mirrors can be designed to be inserted ...
s) for automotive, and
sodium vapor lamp A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589  nm. Two varieties of such lamps exist: low pressure and high pressure. Low-pressure sodium lamps are ...
glasses. Other uses include gas sensors,
antireflection coating An antireflective, antiglare or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses, other optical elements, and photovoltaic cells to reduce reflection. In typical imaging systems, this improves the effici ...
s,
electrowetting Electrowetting is the modification of the wetting properties of a surface (which is typically hydrophobic) with an applied electric field. History The electrowetting of mercury and other liquids on variably charged surfaces was probably first ex ...
on dielectrics, and
Bragg reflector A distributed Bragg reflector (DBR) is a reflector used in waveguides, such as optical fibers. It is a structure formed from multiple layers of alternating materials with varying refractive index, or by periodic variation of some characterist ...
s for VCSEL lasers. ITO is also used as the IR reflector for low-e window panes. ITO was also used as a sensor coating in the later
Kodak DCS The Kodak Digital Camera System is a series of digital single-lens reflex cameras and digital camera backs that were released by Kodak in the 1990s and 2000s, and discontinued in 2005. They are all based on existing 35mm film SLRs from Nikon, Canon ...
cameras, starting with the Kodak DCS 520, as a means of increasing blue channel response. ITO thin film
strain gauge A strain gauge (also spelled strain gage) is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports ...
s can operate at temperatures up to 1400 °C and can be used in harsh environments, such as
gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...
s,
jet engine A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...
s, and
rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accorda ...
s.


Alternative synthesis methods and alternative materials

Because of high cost and limited supply of indium, the fragility and lack of flexibility of ITO layers, and the costly layer deposition requiring vacuum, alternative methods of preparing ITO and alternative materials are being investigated. Promising alternatives based on zinc oxide doped with various elements.


Doped compounds

Several transition metal dopants in indium oxide, particularly molybdenum, give much higher electron mobility and conductivity than obtained with tin. Doped binary compounds such as aluminum-doped
zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement ...
(AZO) and indium-doped
cadmium oxide Cadmium oxide is an inorganic compound with the formula CdO. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride, with octahedral cation and anion centers. It occurs natura ...
have been proposed as alternative materials. Other inorganic alternatives include
aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
,
gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic table and is similar to ...
or indium-doped zinc oxide (AZO, GZO or IZO).


Carbon nanotubes

Carbon nanotube A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...
conductive coatings are a prospective replacement.


Graphene

As another carbon-based alternative, films of
graphene Graphene () is an allotrope of carbon consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice nanostructure.
are flexible and have been shown to allow 90% transparency with a lower electrical resistance than standard ITO. Thin metal films are also seen as a potential replacement material. A hybrid material alternative currently being tested is an electrode made of
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
nanowires A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...
and covered with
graphene Graphene () is an allotrope of carbon consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice nanostructure.
. The advantages to such materials include maintaining transparency while simultaneously being electrically conductive and flexible.


Conductive polymers

Inherently
conductive polymers Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The biggest advantage of conductive polymers ...
(ICPs) are also being developed for some ITO applications. Typically the conductivity is lower for conducting polymers, such as
polyaniline Polyaniline (PANI) is a conducting polymer and organic semiconductor of the semi-flexible rod polymer family. The compound has been of interest since the 1980s because of its electrical conductivity and mechanical properties. Polyaniline is one o ...
and
PEDOT Poly(3,4-ethylenedioxythiophene) (PEDOT or PEDT; ''IUPAC'' name poly(2,3-dihydrothieno ,4-''b''1,4]dioxane-5,7-diyl)) is a conducting polymer based on 3,4-ethylenedioxythiophene or EDOT. It was first reported by Bayer AG in 1989. Polymer PEDOT p ...
:PSS, than for inorganic materials, but they are more flexible, less expensive and more environmentally friendly in processing and manufacture.


Amorphous indium–zinc oxide

In order to reduce indium content, decrease processing difficulty, and improve electrical homogeneity, amorphous transparent conducting oxides have been developed. One such material, amorphous indium-zinc-oxide maintains short-range order even though
crystallization Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...
is disrupted by the difference in the ratio of oxygen to metal atoms between In2O3 and ZnO. Indium-zinc-oxide has some comparable properties to ITO. The amorphous structure remains stable even up to 500 °C, which allows for important processing steps common in
organic solar cells An organic solar cell (OSC) or plastic solar cell is a type of photovoltaic that uses organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport t ...
. The improvement in
homogeneity Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, size, ...
significantly enhances the usability of the material in the case of
organic solar cells An organic solar cell (OSC) or plastic solar cell is a type of photovoltaic that uses organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport t ...
. Areas of poor electrode performance in organic solar cells render a percentage of the cell's area unusable.


Silver nanoparticle–ITO hybrid

ITO has been popularly used as a high-quality flexible substrate to produce flexible electronics. However, this substrate's flexibility decreases as its conductivity improves. Previous research have indicated that the mechanical properties of ITO can be improved through increasing the degree of
crystallinity Crystallinity refers to the degree of structural order in a solid. In a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic stru ...
. Doping with silver (Ag) can improve this property, but results in a loss of transparency. An improved method that embeds Ag
nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...
(AgNPs) instead of homogeneously to create a hybrid ITO has proven to be effective in compensating for the decrease in transparency. The hybrid ITO consists of domains in one orientation grown on the AgNPs and a matrix of the other orientation. The domains are stronger than the matrix and function as barriers to crack propagation, significantly increasing the flexibility. The change in resistivity with increased bending significantly decreases in the hybrid ITO compared with homogeneous ITO.


Alternative synthesis methods


Tape casting process

ITO is typically deposited through expensive and energy-intensive processes that deal with physical vapor deposition (PVD). Such processes include
sputtering In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and ca ...
, which results in the formation of brittle layers. An alternative process that uses a particle-based technique, is known as the tape casting process. Because it is a particle-based technique, the ITO nano-particles are dispersed first, then placed in organic solvents for stability.
Benzyl In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group. Nomenclature In IUPAC nomenclature, the prefix benzyl refers to a substi ...
phthalate Phthalates (, ), or phthalate esters, are esters of phthalic acid. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility, transparency, durability, and longevity. They are used primarily to soften ...
plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticiz ...
and
polyvinyl In polymer chemistry, vinyl polymers are a group of polymers derived from substituted vinyl () monomers. Their backbone is an extended alkane chain . In popular usage, "vinyl" refers only to polyvinyl chloride (PVC). Examples Vinyl polymers are ...
butyral binder have been shown to be helpful in preparing nanoparticle
slurries A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal pu ...
. Once the tape casting process has been carried out, the characterization of the green ITO tapes showed that optimal transmission went up to about 75%, with a lower bound on the
electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallel ...
of 2 Ω·cm.


Laser sintering

Using ITO
nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...
imposes a limit on the choice of substrate, owing to the high temperature required for
sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...
. As an alternative starting material, In-Sn alloy
nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...
allow for a more diverse range of possible substrates. A continuous conductive In-Sn alloy film is formed firstly, followed by oxidation to bring transparency. This two step process involves thermal annealing, which requires special atmosphere control and increased processing time. Because metal
nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...
can be converted easily into a conductive metal film under the treatment of laser, laser
sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...
is applied to achieve products' homogeneous morphology. Laser sintering is also easy and less costly to use since it can be performed in air.


Ambient gas conditions

For example, using conventional methods but varying the ambient gas conditions to improve the optoelectronic properties as, for example,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
plays a major role in the properties of ITO.


Chemical shaving for very thin films

There has been numerical modeling of
plasmonic In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantiz ...
metallic nanostructures have shown great potential as a method of light management in thin-film nanodisc-patterned
hydrogenated amorphous silicon Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs. Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films onto ...
(a-Si:H) solar
photovoltaic Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...
(PV) cells. A problem that arises for plasmonic-enhanced PV devices is the requirement for 'ultra-thin' transparent conducting oxides (TCOs) with high transmittance and low enough resistivity to be used as device top contacts/electrodes. Unfortunately, most work on TCOs is on relatively thick layers and the few reported cases of thin TCO showed a marked decrease in conductivity. To overcome this it is possible to first grow a thick layer and then chemically shave it down to obtain a thin layer that is whole and highly conductive.


Constraints and trade-offs

A major concern with ITO is its cost. ITO costs several times more than aluminium zinc oxide (AZO). AZO is a common choice of transparent conducting oxide (TCO) because of its lower cost and relatively good optical transmission performance in the solar spectrum. However, ITO is superior to AZO in many other important performance categories including chemical resistance to moisture. ITO is not affected by moisture, and is stable as part of
copper indium gallium selenide solar cell A copper indium gallium selenide solar cell (or CIGS cell, sometimes CI(G)S or CIS cell) is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper indium gallium selenide solu ...
for 25–30 years on a rooftop. While the sputtering target or evaporative material that is used to deposit the ITO is significantly more costly than AZO, the amount of material placed on each cell is quite small. Therefore, the cost penalty per cell is quite small, too.


Benefits

The primary advantage of ITO compared to AZO as a transparent conductor for LCDs is that ITO can be precisely etched into fine patterns. AZO cannot be etched as precisely: It is so sensitive to acid that it tends to get over-etched by an acid treatment. Another benefit of ITO compared to AZO is that if moisture does penetrate, ITO will degrade less than AZO. The role of ITO glass as a cell culture substrate can be extended easily, which opens up new opportunities for studies on growing cells involving
electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
and correlative light.


Research examples

ITO can be used in nanotechnology to provide a path to a new generation of solar cells. Solar cells made with these devices have the potential to provide low-cost, ultra-lightweight, and flexible cells with a wide range of applications. Because of the nanoscale dimensions of the nanorods, quantum-size effects influence their optical properties. By tailoring the size of the rods, they can be made to absorb light within a specific narrow band of colors. By stacking several cells with different sized rods, a broad range of wavelengths across the solar spectrum can be collected and converted to energy. Moreover, the nanoscale volume of the rods leads to a significant reduction in the amount of semiconductor material needed compared to a conventional cell. Recent studies demonstrated that nanostructured ITO can behave as a miniaturized photocapacitor, combining in a unique material the absorption and storage of light energy.


Health and safety

Inhalation of indium tin oxide may cause mild irritation to the respiratory tracts and should be avoided. If exposure is long-term, symptoms may become chronic and result in benign
pneumoconiosis Pneumoconiosis is the general term for a class of interstitial lung disease where inhalation of dust ( for example, ash dust, lead particles, pollen grains etc) has caused interstitial fibrosis. The three most common types are asbestosis, silico ...
. Studies with animals indicate that indium tin oxide is toxic when ingested, along with negative effects on the kidney, lung, and heart. During the process of mining, production and reclamation, workers are potentially exposed to indium, especially in countries such as China, Japan, the Republic of Korea, and Canada and face the possibility of
pulmonary alveolar proteinosis Pulmonary alveolar proteinosis (PAP) is a rare lung disorder characterized by an abnormal accumulation of surfactant-derived lipoprotein compounds within the alveoli of the lung. The accumulated substances interfere with the normal gas exchange and ...
,
pulmonary fibrosis Pulmonary fibrosis is a condition in which the lungs become scarred over time. Symptoms include shortness of breath, a dry cough, feeling tired, weight loss, and nail clubbing. Complications may include pulmonary hypertension, respiratory failu ...
,
emphysema Emphysema, or pulmonary emphysema, is a lower respiratory tract disease, characterised by air-filled spaces ( pneumatoses) in the lungs, that can vary in size and may be very large. The spaces are caused by the breakdown of the walls of the alv ...
, and
granulomas A granuloma is an aggregation of macrophages that forms in response to chronic inflammation. This occurs when the immune system attempts to isolate foreign substances that it is otherwise unable to eliminate. Such substances include infectious o ...
. Workers in the US, China, and Japan have been diagnosed with
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
clefts under indium exposure. Silver
nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...
existed in improved ITOs have been found
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology a ...
to penetrate through both intact and breached skin into the epidermal layer. Un-sintered ITOs are suspected of induce
T-cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...
-mediated sensitization: on an intradermal exposure study, a concentration of 5% uITO resulted in
lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic a ...
proliferation in mice including the number increase of cells through a 10-day period. A new occupational problem called indium lung disease was developed through contact with indium-containing dusts. The first patient is a worker associated with wet surface grinding of ITO who suffered from interstitial pneumonia: his lung was filled with ITO related particles. These particles can also induce
cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in au ...
production and
macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
dysfunction.
Sintered Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...
ITOs particles alone can cause
phagocytic Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is c ...
dysfunction but not
cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in au ...
release in
macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
cells; however, they can intrigue a
pro-inflammatory Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecu ...
cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in au ...
response in
pulmonary The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...
epithelial cells Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellu ...
. Unlike uITO, they can also bring
endotoxin Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer m ...
to workers handling the wet process if in contact with endotoxin-containing liquids. This can be attributed to the fact that sITOs have larger diameter and smaller surface area, and that this change after the
sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...
process can cause
cytotoxicity Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa''). Cell physiology Treating c ...
. Because of these issues, alternatives to ITO have been found.


Recycling

The
etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types ...
water used in the process of
sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...
ITO can only be used for a limited numbers of times before it has to be disposed. After degradation, the waste water should still contain valuable metals such as In and Cu as a secondary resource as well as Mo, Cu, Al, Sn and In, which can pose a health hazard to human beings.Yokel, R. A. (2014) pp. 116–119 in ''Encyclopedia of the Neurological Sciences'', ed. M. J. Aminoff and R. B. Daroff, Academic Press, Oxford, 2nd ed..


See also

* Transparent conducting film


References

{{reflist


External links


Spectroscopic studies of conducting metal oxides
with many slides about ITO Articles containing unverified chemical infoboxes Oxides Indium compounds Tin Display technology Transparent electrodes