Editing Indium tin oxide

{{Short description|Chemical compound}}
[[File:LHcockpitWindow.jpg|250px|thumb|[[Thin film interference]] caused by ITO coating on an [[Airbus]] cockpit window, used for defrosting.]]
'''Indium tin oxide''' ('''ITO''') is a [[ternary composition]] of [[indium]], [[tin]] and [[oxygen]] in varying proportions. Depending on the oxygen content, it can be described as either a [[ceramic]] or an [[alloy]]. Indium tin oxide is typically encountered as an oxygen-saturated composition with a formulation of 74% In, 8% Sn, and 18% 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 oxide]]s, not just for its [[electrical conductivity]] and [[optical transparency]], but also for the ease with which it can be deposited as a thin film, as well as 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]]s increases the film's conductivity, but decreases its transparency.

[[Thin film]]s of indium tin oxide are most commonly deposited on surfaces by [[physical vapor deposition]]. Often used is [[electron beam evaporation]], or a range of [[sputter deposition]] techniques.

==Material and properties==
[[File:Absorption of glass and ITO glass.svg|350px|thumb|Absorption of glass and ITO glass.]]
ITO is a mixed oxide of [[indium]] and [[tin]] with a melting point in the range 1526–1926&nbsp;°C (1800–2200 [[Kelvin|K]], 2800–3500&nbsp;°F), depending on composition. The most commonly used material is an oxide of a composition of ca. In<sub>4</sub>Sn. The material is a [[n-type semiconductor]] with a large [[bandgap]] of around 4 eV. ITO is both transparent to visible light and relatively conductive. It has a low electrical [[resistivity]] of ~10<sup>−4</sup> [[Ohm|Ω]]·cm, and a thin film can have an optical transmittance of greater than 80%.<ref name="Chen-2013">{{cite journal|doi=10.1021/la4033282 | pmid=24117323 | volume=29 | issue=45 | title=Fabrication of Highly Transparent and Conductive Indium–Tin Oxide Thin Films with a High Figure of Merit via Solution Processing | journal=Langmuir | pages=13836–13842 | last1 = Chen | first1 = Zhangxian| year=2013 }}</ref> These properties are utilized to great advantage in [[touch-screen]] applications such as [[mobile phone]]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.<ref name=j1>{{cite journal |last1=Kim |first1=H. |last2=Gilmore |first2=C. M. |last3=Piqué |first3=A. |last4=Horwitz |first4=J. S. |last5=Mattoussi |first5=H. |author-link5=Hedi Mattoussi |last6=Murata |first6=H. |last7=Kafafi |first7=Z. H. |last8=Chrisey |first8=D. B. |title=Electrical, optical, and structural properties of indium–tin–oxide thin films for organic light-emitting devices |journal=Journal of Applied Physics |date=December 1999 |volume=86 |issue=11 |pages=6451–6461 |doi=10.1063/1.371708 |bibcode=1999JAP....86.6451K }}</ref>

ITO [[Tape casting|green tapes]] are utilized for the production of lamps that are electroluminescent, functional, and fully flexible.<ref name=":0">{{cite journal |last1=Straue |first1=Nadja |last2=Rauscher |first2=Martin |last3=Dressler |first3=Martina |last4=Roosen |first4=Andreas |last5=Moreno |first5=R. |title=Tape Casting of ITO Green Tapes for Flexible Electroluminescent Lamps |journal=Journal of the American Ceramic Society |date=February 2012 |volume=95 |issue=2 |pages=684–689 |doi=10.1111/j.1551-2916.2011.04836.x }}</ref> 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.<ref name=":1">{{cite journal |last1=Du |first1=Jian |last2=Chen |first2=Xin-liang |last3=Liu |first3=Cai-chi |last4=Ni |first4=Jian |last5=Hou |first5=Guo-fu |last6=Zhao |first6=Ying |last7=Zhang |first7=Xiao-dan |title=Highly transparent and conductive indium tin oxide thin films for solar cells grown by reactive thermal evaporation at low temperature |journal=Applied Physics A |date=24 April 2014 |volume=117 |issue=2 |pages=815–822 |doi=10.1007/s00339-014-8436-x |bibcode=2014ApPhA.117..815D |s2cid=95720073 }}</ref>

ITO is often used to make transparent conductive coating for displays such as [[liquid crystal display]]s, [[OLED]] displays, [[plasma display]]s, [[Touchscreen|touch panel]]s, and [[Electronic paper|electronic ink]] applications. Thin films of ITO are also used in [[organic light-emitting diode]]s, [[solar cell]]s, [[antistatic coating]]s and [[electromagnetic interference|EMI]] shieldings. In [[organic light-emitting diode]]s, ITO is used as the [[anode]] (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 or absorb [[electromagnetic radiation]]. The [[Lockheed Martin F-22 Raptor|F-22 Raptor]]'s canopy has an ITO coating that absorbs [[radar]] waves and reflects infrared waves, enhancing its [[Stealth technology|stealth]] capabilities and giving it a distinctive gold tint.<ref>{{cite book |last1=Sweetman |first1=Bill |author1-link=Bill Sweetman |title=F-22 Raptor |date=1998 |publisher=[[MBI Publishing Company]] |isbn=978-1-61060-143-6 |page=48 |language=en}}</ref><ref>{{cite journal |last1=Xu |first1=Yang |title=Indium tin oxide as a dual-band compatible stealth material with low infrared emissivity and strong microwave absorption |journal=Journal of Materials Chemistry C |date=2023-01-06 |volume=11 |issue=5 |pages=1754–1763 |doi=10.1039/D2TC04722E |url=https://pubs.rsc.org/en/content/articlehtml/2023/tc/d2tc04722e |access-date=2025-03-24|url-access=subscription }}</ref>

ITO is also used for various [[optical coating]]s, most notably [[infrared]]-reflecting coatings ([[hot mirror]]s) for automotive, and [[sodium vapor lamp]] glasses. Other uses include [[gas sensor]]s,<ref>{{Cite journal|last1=Mokrushin|first1=Artem S.|last2=Fisenko|first2=Nikita A.|last3=Gorobtsov|first3=Philipp Yu|last4=Simonenko|first4=Tatiana L.|last5=Glumov|first5=Oleg V.|last6=Melnikova|first6=Natalia A.|last7=Simonenko|first7=Nikolay P.|last8=Bukunov|first8=Kirill A.|last9=Simonenko|first9=Elizaveta P.|last10=Sevastyanov|first10=Vladimir G.|last11=Kuznetsov|first11=Nikolay T.|date=2021-01-01|title=Pen plotter printing of ITO thin film as a highly CO sensitive component of a resistive gas sensor|url=http://www.sciencedirect.com/science/article/pii/S0039914020307463|journal=Talanta|language=en|volume=221|pages=121455|doi=10.1016/j.talanta.2020.121455|pmid=33076078|s2cid=224811369|issn=0039-9140|url-access=subscription}}</ref> [[antireflection coating]]s, [[electrowetting]] on dielectrics, and [[Bragg reflector]]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]] cameras, starting with the Kodak DCS 520, as a means of increasing blue channel response.<ref>[http://www.kodak.com/global/en/service/professional/tib/tib4131.jhtml?pq-path=14567#SEC3 Increasing the Blue Channel Response]. ''Technical Information Bulletin''. kodak.com</ref>

ITO thin film [[strain gauge]]s can operate at temperatures up to 1400&nbsp;°C and can be used in harsh environments, such as [[gas turbine]]s, [[jet engine]]s, and [[rocket engine]]s.<ref>{{cite thesis |last1=Luo |first1=Qing |title=Indium tin oxide thin film strain gages for use at elevated temperatures |date=1 January 2001 |pages=1–146 |url=https://digitalcommons.uri.edu/dissertations/AAI3025561 |access-date=2 November 2019 |archive-date=2 November 2019 |archive-url=https://web.archive.org/web/20191102170845/https://digitalcommons.uri.edu/dissertations/AAI3025561/ |url-status=dead }}</ref>

=== Silver nanoparticle–ITO hybrid ===

ITO has been popularly used as a high-quality flexible substrate to produce flexible electronics.<ref>{{cite journal |last1=Lu |first1=Nanshu |last2=Lu |first2=Chi |last3=Yang |first3=Shixuan |last4=Rogers |first4=John |title=Highly Sensitive Skin-Mountable Strain Gauges Based Entirely on Elastomers |journal=Advanced Functional Materials |date=10 October 2012 |volume=22 |issue=19 |pages=4044–4050 |doi=10.1002/adfm.201200498 |s2cid=16369286 }}</ref> 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]].<ref>{{cite journal |last1=Kim |first1=Eun-Hye |last2=Yang |first2=Chan-Woo |last3=Park |first3=Jin-Woo |title=The crystallinity and mechanical properties of indium tin oxide coatings on polymer substrates |journal=Journal of Applied Physics |date=15 February 2011 |volume=109 |issue=4 |pages=043511–043511–8 |doi=10.1063/1.3556452 |bibcode=2011JAP...109d3511K }}</ref> Doping with silver (Ag) can improve this property, but results in a loss of transparency.<ref>{{cite journal |last1=Yang |first1=Chan-Woo |last2=Park |first2=Jin-Woo |title=The cohesive crack and buckle delamination resistances of indium tin oxide (ITO) films on polymeric substrates with ductile metal interlayers |journal=Surface and Coatings Technology |date=May 2010 |volume=204 |issue=16–17 |pages=2761–2766 |doi=10.1016/j.surfcoat.2010.02.033 }}</ref> An improved method that embeds Ag [[nanoparticles]] (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.<ref>{{cite journal |last1=Triambulo |first1=Ross E. |last2=Kim |first2=Jung-Hoon |last3=Na |first3=Min-Young |last4=Chang |first4=Hye-Jung |last5=Park |first5=Jin-Woo |title=Highly flexible, hybrid-structured indium tin oxides for transparent electrodes on polymer substrates |journal=Applied Physics Letters |date=17 June 2013 |volume=102 |issue=24 |pages=241913 |doi=10.1063/1.4812187 |bibcode=2013ApPhL.102x1913T }}</ref>

==Alternative synthesis methods==
ITO is typically deposited through expensive and energy-intensive processes that deal with physical [[vapor deposition]] (PVD). Such processes include [[sputtering]], which results in the formation of brittle layers.{{Citation needed|date=March 2016}} 
Because of the cost and energy of physical vapor deposition, with the required vacuum processing, alternative methods of preparing ITO are being investigated.<ref name="Fortunato 2007 242–247">{{cite journal|last=Fortunato|first=E. |author2=D. Ginley |author3=H. Hosono |author4=D.C. Paine|title=Transparent Conducting Oxides for Photovoltaics|journal=MRS Bulletin|date=March 2007|volume=32|issue=3 |pages=242–247|doi=10.1557/mrs2007.29|s2cid=136882786 }}</ref> 

===Tape casting process===
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]] [[phthalate]] [[plasticizer]] and [[polyvinyl]] butyral binder have been shown to be helpful in preparing nanoparticle [[Slurry|slurries]]. 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 and conductance|electrical resistance]] of 2 Ω·cm.<ref name=":0" />

===Laser sintering===
Using ITO [[nanoparticles]] imposes a limit on the choice of substrate, owing to the high temperature required for [[sintering]]. As an alternative starting material, In-Sn alloy [[nanoparticles]] allow for a more diverse range of possible substrates.<ref>{{cite journal |last1=Ohsawa |first1=Masato |last2=Sakio |first2=Susumu |last3=Saito |first3=Kazuya |title=ITO透明導電膜形成用ナノ粒子インクの開発 |trans-title=Development of nanoparticle ink for ITO transparent conductive film formation |language=ja |journal=Journal of Japan Institute of Electronics Packaging |date=2011 |volume=14 |issue=6 |pages=453–459 |doi=10.5104/jiep.14.453 |doi-access=free }}</ref> 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]] can be converted easily into a conductive metal film under the treatment of laser, laser [[sintering]] is applied to achieve products' homogeneous morphology. Laser sintering is also easy and less costly to use since it can be performed in air.<ref>{{cite journal |last1=Qin |first1=Gang |last2=Fan |first2=Lidan |last3=Watanabe |first3=Akira |title=Formation of indium tin oxide film by wet process using laser sintering |journal=Journal of Materials Processing Technology |date=January 2016 |volume=227 |pages=16–23 |doi=10.1016/j.jmatprotec.2015.07.011 }}</ref>

===Ambient gas conditions===
For example, using conventional methods but varying the ambient gas conditions to improve the optoelectronic properties<ref>{{cite journal |last1=Marikkannan |first1=M. |last2=Subramanian |first2=M. |last3=Mayandi |first3=J. |last4=Tanemura |first4=M. |last5=Vishnukanthan |first5=V. |last6=Pearce |first6=J. M. |title=Effect of ambient combinations of argon, oxygen, and hydrogen on the properties of DC magnetron sputtered indium tin oxide films |journal=AIP Advances |date=January 2015 |volume=5 |issue=1 |pages=017128 |doi=10.1063/1.4906566 |bibcode=2015AIPA....5a7128M |doi-access=free }}</ref> as, for example, [[oxygen]] plays a major role in the properties of ITO.<ref>{{cite journal |last1=Gwamuri |first1=Jephias |last2=Marikkannan |first2=Murugesan |last3=Mayandi |first3=Jeyanthinath |last4=Bowen |first4=Patrick |last5=Pearce |first5=Joshua |title=Influence of Oxygen Concentration on the Performance of Ultra-Thin RF Magnetron Sputter Deposited Indium Tin Oxide Films as a Top Electrode for Photovoltaic Devices |journal=Materials |date=20 January 2016 |volume=9 |issue=1 |pages=63 |doi=10.3390/ma9010063 |pmid=28787863 |pmc=5456523 |bibcode=2016Mate....9...63G |doi-access=free }}</ref>

===Chemical shaving for very thin films===
There has been numerical modeling of [[plasmonic]] metallic nanostructures have shown great potential as a method of light management in thin-film nanodisc-patterned [[hydrogenated amorphous silicon]] (a-Si:H) solar [[photovoltaic]] (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.<ref>{{cite journal |last1=Gwamuri |first1=Jephias |last2=Vora |first2=Ankit |last3=Mayandi |first3=Jeyanthinath |last4=Güney |first4=Durdu Ö. |last5=Bergstrom |first5=Paul L. |last6=Pearce |first6=Joshua M. |title=A new method of preparing highly conductive ultra-thin indium tin oxide for plasmonic-enhanced thin film solar photovoltaic devices |journal=Solar Energy Materials and Solar Cells |date=May 2016 |volume=149 |pages=250–257 |doi=10.1016/j.solmat.2016.01.028 |doi-access=free |bibcode=2016SEMSC.149..250G }}</ref>

==Constraints and trade-offs==
{{Unreferenced section|date=April 2011}}
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 film|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 cells|copper indium gallium selenide solar cell]] 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==
[[File:44665-11.png|thumb|Surface morphology changes in Al:ZnO and i-/Al:ZnO upon damp heat (DH) exposure ([[optical interferometry]])<ref name=dampheat>{{cite web|title=Stability Issues of Transparent Conducting Oxides (TCOs) for Thin-Film Photovoltaics|date=December 2008|author=Pern, John |publisher=U.S. National Renewable Energy Laboratory|url=http://www.nrel.gov/docs/fy09osti/44665.pdf}}</ref>]]
The primary advantage of ITO compared to AZO as a transparent conductor for [[liquid crystal display|LCDs]] is that ITO can be precisely etched into fine patterns.<ref name=Ginley>{{cite book|author=David Ginley|title=Handbook of Transparent Conductors|url=https://books.google.com/books?id=K0qjBlrAGYsC&pg=PA524|date=11 September 2010|publisher=Springer Science & Business Media|isbn=978-1-4419-1638-9|pages=524–}}</ref> AZO cannot be etched as precisely: It is so sensitive to acid that it tends to get over-etched by an acid treatment.<ref name=Ginley/>

Another benefit of ITO compared to AZO is that if moisture does penetrate, ITO will degrade less than AZO.<ref name=dampheat/>

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]] and correlative light.<ref>{{cite journal |last1=Pluk |first1=H. |last2=Stokes |first2=D.J. |last3=Lich |first3=B. |last4=Wieringa |first4=B. |last5=Fransen |first5=J. |title=Advantages of indium-tin oxide-coated glass slides in correlative scanning electron microscopy applications of uncoated cultured cells |journal=Journal of Microscopy |date=March 2009 |volume=233 |issue=3 |pages=353–363 |doi=10.1111/j.1365-2818.2009.03140.x |pmid=19250456 |s2cid=5489454 }}</ref>

==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.<ref>{{cite web|title=Energy Conversion and Storage: New Materials and Processes for Energy Needs |url=http://www.nano.gov/html/res/fy04-pdf/fy04%20-%20small%20parts/NNI_FY04_R_mode2_part8.pdf |author=National Nanotechnology Initiative |url-status=dead |archive-url=https://web.archive.org/web/20090512004243/http://www.nano.gov/html/res/fy04-pdf/fy04%20-%20small%20parts/NNI_FY04_R_mode2_part8.pdf |archive-date=May 12, 2009 }}</ref><ref>
{{cite web|title=National Nanotechnology Initiative Research and Development Supporting the next Industrial Revolution|work=nano.gov| page= 29|url=http://nano.gov/sites/default/files/pub_resource/nni04_budget_supplement.pdf}}</ref> Recent studies demonstrated that nanostructured ITO can behave as a miniaturized photocapacitor, combining in a unique material the absorption and storage of light energy.<ref>{{cite journal |title=Photodoping of metal oxide nanocrystals for multi-charge accumulation and light-driven energy storage |journal=Nanoscale  |date= 2021 |pages=8773–8783  |doi=10.1039/d0nr09163d|pmc=8136238 |last1=Ghini |first1=Michele |last2=Curreli |first2=Nicola |last3=Camellini |first3=Andrea |last4=Wang |first4=Mengjiao |last5=Asaithambi |first5=Aswin |last6=Kriegel |first6=Ilka |volume=13 |issue=19 |pmid=33959732 }}</ref>

== 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]]. Studies with animals indicate that indium tin oxide is toxic when ingested, along with negative effects on the kidney, lung, and heart.<ref>{{cite journal |last1=Hosono |first1=Hideo |last2=Kurita |first2=Masaaki |last3=Kawazoe |first3=Hiroshi |title=Excimer Laser Crystallization of Amorphous Indium-Tin-Oxide and Its Application to Fine Patterning |journal=Japanese Journal of Applied Physics |date=1 October 1998 |volume=37 |issue=Part 2, No. 10A |pages=L1119–L1121 |doi=10.1143/JJAP.37.L1119 |bibcode=1998JaJAP..37L1119H |s2cid=122207774 }}</ref>

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<ref>POLINARES (EU Policy on Natural Resources, 2012). [https://web.archive.org/web/20160313020355/http://www.polinares.eu/docs/d2-1/polinares_wp2_annex2_factsheet5_v1_10.pdf Fact sheet: Indium]. [last accessed 20 Mar 2013]</ref> and face the possibility of [[pulmonary alveolar proteinosis]], [[Pulmonary fibrosis /granuloma|pulmonary fibrosis]], [[emphysema]], and [[granulomas]]. Workers in the US, China, and Japan have been diagnosed with [[cholesterol]] clefts under indium exposure.<ref>{{cite journal |last1=Cummings |first1=Kristin J. |last2=Nakano |first2=Makiko |last3=Omae |first3=Kazuyuki |last4=Takeuchi |first4=Koichiro |last5=Chonan |first5=Tatsuya |last6=Xiao |first6=Yong-long |last7=Harley |first7=Russell A. |last8=Roggli |first8=Victor L. |last9=Hebisawa |first9=Akira |last10=Tallaksen |first10=Robert J. |last11=Trapnell |first11=Bruce C. |last12=Day |first12=Gregory A. |last13=Saito |first13=Rena |last14=Stanton |first14=Marcia L. |last15=Suarthana |first15=Eva |last16=Kreiss |first16=Kathleen |title=Indium Lung Disease |journal=Chest |date=June 2012 |volume=141 |issue=6 |pages=1512–1521 |doi=10.1378/chest.11-1880 |pmid=22207675 |pmc=3367484 }}</ref> Silver [[nanoparticles]] existed in improved ITOs have been found [[in vitro]] to penetrate through both intact and breached skin into the [[Epidermis|epidermal layer]]. Un-sintered ITOs are suspected of induce [[T cell|T-cell]]-mediated sensitization: on an intradermal exposure study, a concentration of 5% uITO resulted in [[lymphocyte]] proliferation in mice including the number increase of cells through a 10-day period.<ref>{{cite journal |last1=Brock |first1=Kristie |last2=Anderson |first2=Stacey E. |last3=Lukomska |first3=Ewa |last4=Long |first4=Carrie |last5=Anderson |first5=Katie |last6=Marshall |first6=Nikki |last7=Jean Meade |first7=B. |title=Immune stimulation following dermal exposure to unsintered indium tin oxide |journal=Journal of Immunotoxicology |date=29 October 2013 |volume=11 |issue=3 |pages=268–272 |doi=10.3109/1547691X.2013.843620 |pmid=24164313 |pmc=4652645 }}</ref>

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.<ref>{{cite journal |last1=Homma |first1=Toshiaki |last2=Ueno |first2=Takahiro |last3=Sekizawa |first3=Kiyohisa |last4=Tanaka |first4=Akiyo |last5=Hirata |first5=Miyuki |title=Interstitial Pneumonia Developed in a Worker Dealing with Particles Containing Indium-tin Oxide |journal=Journal of Occupational Health |date=4 July 2003 |volume=45 |issue=3 |pages=137–139 |doi=10.1539/joh.45.137 |pmid=14646287 |doi-access= }}</ref> These particles can also induce [[cytokine]] production and [[macrophage]] dysfunction. [[Sintered]] ITOs particles alone can cause [[phagocytic]] dysfunction but not [[cytokine]] release in [[macrophage]] cells; however, they can intrigue a [[pro-inflammatory]] [[cytokine]] response in [[pulmonary]] [[epithelial cells]]. Unlike uITO, they can also bring [[endotoxin]] 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]] process can cause [[cytotoxicity]].<ref>{{cite journal |last1=Badding |first1=Melissa A. |last2=Schwegler-Berry |first2=Diane |last3=Park |first3=Ju-Hyeong |last4=Fix |first4=Natalie R. |last5=Cummings |first5=Kristin J. |last6=Leonard |first6=Stephen S. |last7=Ojcius |first7=David M. |title=Sintered Indium-Tin Oxide Particles Induce Pro-Inflammatory Responses In Vitro, in Part through Inflammasome Activation |journal=PLOS ONE |date=13 April 2015 |volume=10 |issue=4 |pages=e0124368 |doi=10.1371/journal.pone.0124368 |pmid=25874458 |pmc=4395338 |bibcode=2015PLoSO..1024368B |doi-access=free }}</ref>

Because of these issues, alternatives to ITO have been found.<ref>{{cite journal |first1=Akira |last1=Ichiki |first2=Yuichi |last2=Shirasaki |first3=Tadashi |last3=Ito |first4=Tadahiro |last4=Sorori |first5=Tadahiro |last5=Kegasawa |title=タッチパネル用薄型両面センサーフィルム「エクスクリア」の開発 |trans-title=Development of a Thin Double-sided Sensor Film 'EXCLEAR' for Touch Panels via Silver Halide Photographic Technology |language=ja |year=2017 |journal=Fuji Film Research & Development |id={{NAID|40021224398}} }}</ref><ref>{{Cite web|url=https://www.fujifilmholdings.com/en/sustainability/valuePlan2016/process/policy01/environment2016/02.html|title=Environment: [Topics2] Development of Materials That Solve Environmental Issues EXCLEAR thin double-sided sensor film for touch panels &#124; FUJIFILM Holdings|website=www.fujifilmholdings.com}}</ref>

== Recycling ==
[[File:ITO waste-water recycling.jpg|thumb|Process of indium-tin-oxide (ITO) etching wastewater treatment]]
The [[Etching (chemical)|etching]] water used in the process of [[sintering]] 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.<ref>{{cite journal |last1=Fowler |first1=Bruce A |last2=Yamauchi |first2=Hiroshi |last3=Conner |first3=EA |last4=Akkerman |first4=M |title=Cancer risks for humans from exposure to the semiconductor metals |journal=Scandinavian Journal of Work, Environment & Health |date=1993 |volume=19 |pages=101–103 |jstor=40966384 |pmid=8159952 }}</ref><ref>{{cite journal |last1=Chonan |first1=T. |last2=Taguchi |first2=O. |last3=Omae |first3=K. |title=Interstitial pulmonary disorders in indium-processing workers |journal=European Respiratory Journal |date=27 September 2006 |volume=29 |issue=2 |pages=317–324 |doi=10.1183/09031936.00020306 |pmid=17050566 |doi-access=free }}</ref><ref>{{cite journal |last1=Barceloux |first1=Donald G. |last2=Barceloux |first2=Donald |title=Molybdenum |journal=Journal of Toxicology: Clinical Toxicology |date=6 August 1999 |volume=37 |issue=2 |pages=231–237 |doi=10.1081/clt-100102422 |pmid=10382558 }}</ref><ref>{{cite journal |last1=Barceloux |first1=Donald G. |last2=Barceloux |first2=Donald |title=Copper |journal=Journal of Toxicology: Clinical Toxicology |date=6 August 1999 |volume=37 |issue=2 |pages=217–230 |doi=10.1081/clt-100102421 |pmid=10382557 }}</ref><ref>{{cite journal |last1=Gupta |first1=Umesh C. |last2=Gupta |first2=Subhas C. |title=Trace element toxicity relationships to crop production and livestock and human health: implications for management |journal=Communications in Soil Science and Plant Analysis |date=11 November 2008 |volume=29 |issue=11–14 |pages=1491–1522 |doi=10.1080/00103629809370045 |s2cid=53372492 }}</ref><ref>[http://nj.gov/health/eoh/rtkweb/documents/fs/1025.pdf Hazardous substance factsheet]. New Jersey Department of Health and Senior Services.</ref><ref>Lenntech [http://www.lenntech.com/periodic/elements/sn.htm Health effects of tin].</ref><ref>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.</ref>

==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 materials are being investigated.<ref name="Fortunato 2007 242–247">{{cite journal|last=Fortunato|first=E. |author2=D. Ginley |author3=H. Hosono |author4=D.C. Paine|title=Transparent Conducting Oxides for Photovoltaics|journal=MRS Bulletin|date=March 2007|volume=32|issue=3 |pages=242–247|doi=10.1557/mrs2007.29|s2cid=136882786 }}</ref> Promising alternatives based on zinc oxide doped with various elements.<ref>{{Cite journal |last1=Akhmedov |first1=Akhmed |last2=Abduev |first2=Aslan |last3=Murliev |first3=Eldar |last4=Asvarov |first4=Abil |last5=Muslimov |first5=Arsen |last6=Kanevsky |first6=Vladimir |date=January 2021 |title=The ZnO-In2O3 Oxide System as a Material for Low-Temperature Deposition of Transparent Electrodes |journal=Materials |language=en |volume=14 |issue=22 |pages=6859 |doi=10.3390/ma14226859 |issn=1996-1944 |pmc=8618142 |pmid=34832261|bibcode=2021Mate...14.6859A |doi-access=free }}</ref>

=== Doped compounds ===

Promising alternatives based on zinc oxide doped with various elements.<ref>{{Cite journal |last1=Akhmedov |first1=Akhmed |last2=Abduev |first2=Aslan |last3=Murliev |first3=Eldar |last4=Asvarov |first4=Abil |last5=Muslimov |first5=Arsen |last6=Kanevsky |first6=Vladimir |date=January 2021 |title=The ZnO-In2O3 Oxide System as a Material for Low-Temperature Deposition of Transparent Electrodes |journal=Materials |language=en |volume=14 |issue=22 |pages=6859 |doi=10.3390/ma14226859 |issn=1996-1944 |pmc=8618142 |pmid=34832261|bibcode=2021Mate...14.6859A |doi-access=free }}</ref>

Several transition metal dopants in indium oxide, particularly molybdenum, give much higher electron mobility and conductivity than obtained with tin.<ref name="Swallow 2019">{{cite journal |last1=Swallow |first1=Jack E. N. |last2=Williamson |first2=Benjamin A. D. |last3=Sathasivam |first3=Sanjayan |last4=Birkett |first4=Max |last5=Featherstone |first5=Thomas J. |last6=Murgatroyd |first6=Philip A. E. |last7=Edwards |first7=Holly J. |last8=Lebens-Higgins |first8=Zachary W. |last9=Duncan |first9=David A. |last10=Farnworth |first10=Mark |last11=Warren |first11=Paul |last12=Peng |first12=Nianhua |last13=Lee |first13=Tien-Lin |last14=Piper |first14=Louis F. J. |last15=Regoutz |first15=Anna |last16=Carmalt |first16=Claire J. |last17=Parkin |first17=Ivan P. |last18=Dhanak |first18=Vin R. |last19=Scanlon |first19=David O. |last20=Veal |first20=Tim D. |title=Resonant doping for high mobility transparent conductors: the case of Mo-doped In<sub>2</sub>O<sub>3</sub> |journal=Materials Horizons |date=2019 |volume=7 |pages=236–243 |doi=10.1039/c9mh01014a |doi-access=free }}</ref> Doped binary compounds such as aluminum-doped [[zinc oxide]] (AZO) and indium-doped [[cadmium oxide]] have been proposed as alternative materials. Other inorganic alternatives include [[aluminum]], [[gallium]] or indium-doped zinc oxide (AZO, GZO or IZO).

=== Carbon nanotubes ===
[[Carbon nanotube]] conductive coatings are a prospective replacement.<ref>{{cite news |title=Researchers find replacement for rare material indium tin oxide
 |url=http://www.rdmag.com/News/2011/04/Materials-Researchers-find-replacement-for-rare-material-indium-tin-oxid/
 |newspaper=R&D Magazine |format=online |publisher=Advantage Business Media |date=11 April 2011 |access-date=11 April 2011 }}</ref><ref>{{cite journal |last1=Kyrylyuk |first1=Andriy V. |last2=Hermant |first2=Marie Claire |last3=Schilling |first3=Tanja |last4=Klumperman |first4=Bert |last5=Koning |first5=Cor E. |last6=van der Schoot |first6=Paul |title=Controlling electrical percolation in multicomponent carbon nanotube dispersions |journal=Nature Nanotechnology |date=10 April 2011 |volume=6 |issue=6 |pages=364–369 |doi=10.1038/nnano.2011.40 |pmid=21478868 |bibcode=2011NatNa...6..364K }}</ref>

=== Graphene ===
As another carbon-based alternative, films of [[graphene]] are flexible and have been shown to allow 90% transparency with a lower electrical resistance than standard ITO.<ref>{{cite news |last1=ServiceJun. 20 |first1=Robert F. |title=Graphene Finally Goes Big |url=https://www.science.org/content/article/graphene-finally-goes-big |work=Science |publisher=AAAS |date=20 June 2010 }}</ref>  Thin metal films are also seen as a potential replacement material. A hybrid material alternative currently being tested is an electrode made of [[silver]] [[nanowires]] and covered with [[graphene]]. The advantages to such materials include maintaining transparency while simultaneously being electrically conductive and flexible.<ref>{{cite journal |last1=Chen |first1=Ruiyi |last2=Das |first2=Suprem R. |last3=Jeong |first3=Changwook |last4=Khan |first4=Mohammad Ryyan |last5=Janes |first5=David B. |last6=Alam |first6=Muhammad A. |title=Co-Percolating Graphene-Wrapped Silver Nanowire Network for High Performance, Highly Stable, Transparent Conducting Electrodes |journal=Advanced Functional Materials |date=6 November 2013 |volume=23 |issue=41 |pages=5150–5158 |doi=10.1002/adfm.201300124 |s2cid=97512306 }}</ref>

=== Conductive polymers ===
Inherently [[conductive polymers]] (ICPs) are also being developed for some ITO applications.<ref>{{cite journal |last1=Xia |first1=Yijie |last2=Sun |first2=Kuan |last3=Ouyang |first3=Jianyong |title=Solution-Processed Metallic Conducting Polymer Films as Transparent Electrode of Optoelectronic Devices |journal=Advanced Materials |date=8 May 2012 |volume=24 |issue=18 |pages=2436–2440 |doi=10.1002/adma.201104795 |pmid=22488584 |s2cid=205244148 |doi-access=free |bibcode=2012AdM....24.2436X }}</ref><ref>{{cite journal |last1=Saghaei |first1=Jaber |last2=Fallahzadeh |first2=Ali |last3=Saghaei |first3=Tayebeh |title=ITO-free organic solar cells using highly conductive phenol-treated PEDOT:PSS anodes |journal=Organic Electronics |date=September 2015 |volume=24 |pages=188–194 |doi=10.1016/j.orgel.2015.06.002 }}</ref>  Typically the conductivity is lower for conducting polymers, such as [[polyaniline]] and [[PEDOT]]: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]] is disrupted by the difference in the ratio of oxygen to metal atoms between In<sub>2</sub>O<sub>3</sub> and ZnO. Indium-zinc-oxide has some comparable properties to ITO.<ref>{{cite journal |last1=Ito |first1=N. |last2=Sato |first2=Y. |last3=Song |first3=P.K. |last4=Kaijio |first4=A. |last5=Inoue |first5=K. |last6=Shigesato |first6=Y. |title=Electrical and optical properties of amorphous indium zinc oxide films |journal=Thin Solid Films |date=February 2006 |volume=496 |issue=1 |pages=99–103 |doi=10.1016/j.tsf.2005.08.257 |bibcode=2006TSF...496...99I }}</ref> The amorphous structure remains stable even up to 500&nbsp;°C, which allows for important processing steps common in [[organic solar cells]].<ref name="Fortunato 2007 242–247"/> The improvement in [[Homogeneity (physics)|homogeneity]] significantly enhances the usability of the material in the case of [[organic solar cells]]. Areas of poor electrode performance in organic solar cells render a percentage of the cell's area unusable.<ref>{{cite journal |last1=Irwin |first1=Michael D. |last2=Liu |first2=Jun |last3=Leever |first3=Benjamin J. |last4=Servaites |first4=Jonathan D. |last5=Hersam |first5=Mark C. |last6=Durstock |first6=Michael F. |last7=Marks |first7=Tobin J. |title=Consequences of Anode Interfacial Layer Deletion. HCl-Treated ITO in P3HT:PCBM-Based Bulk-Heterojunction Organic Photovoltaic Devices |journal=Langmuir |date=16 February 2010 |volume=26 |issue=4 |pages=2584–2591 |doi=10.1021/la902879h |pmid=20014804 |s2cid=425367 }}</ref>


==See also==
*[[Transparent conducting film]]

==References==
{{reflist}}

==External links==
*[https://archive.today/20121214205349/http://www.ncsu.edu/chemistry/franzen/public_html/sf/ito/index.htm Spectroscopic studies of conducting metal oxides], with many slides about ITO

[[Category:Articles containing unverified chemical infoboxes]]
[[Category:Oxides]]
[[Category:Indium compounds]]
[[Category:Tin]]
[[Category:Display technology]]
[[Category:Transparent electrodes]]