Editing Silicon (section)

==Applications==
===Compounds===
Most silicon is used industrially without being purified, often with comparatively little processing from its natural form. More than 90% of the Earth's crust is composed of [[silicate minerals]], which are compounds of silicon and oxygen, often with metallic ions when negatively charged silicate anions require cations to balance the charge. Many of these have direct commercial uses, such as clays, [[silica]] sand, and most kinds of building stone. Thus, the vast majority of uses for silicon are as structural compounds, either as the silicate minerals or silica (crude silicon dioxide). Silicates are used in making [[Portland cement]] (made mostly of calcium silicates) which is used in [[mortar (masonry)|building mortar]] and modern [[stucco]], but more importantly, combined with silica sand, and gravel (usually containing silicate minerals such as granite), to make the [[concrete]] that is the basis of most of the very largest industrial building projects of the modern world.{{sfn|Greenwood|Earnshaw|1997|p=356}}

Silica is used to make [[fire brick]], a type of ceramic. Silicate minerals are also in whiteware [[ceramic]]s, an important class of products usually containing various types of fired [[clay]] minerals (natural aluminium phyllosilicates). An example is [[porcelain]], which is based on the silicate mineral [[kaolinite]]. Traditional [[glass]] (silica-based [[soda–lime glass]]) also functions in many of the same ways, and also is used for windows and containers. In addition, specialty silica based [[glass fiber]]s are used for [[optical fiber]], as well as to produce [[fiberglass]] for structural support and [[glass wool]] for [[thermal insulation]].

Silicones often are used in [[waterproofing]] treatments, [[molding (process)|molding]] compounds, mold-[[release agent]]s, mechanical seals, high temperature [[lubricant|greases]] and waxes, and [[caulking]] compounds. Silicone is also sometimes used in [[breast implant]]s, contact lenses, [[explosive]]s and [[pyrotechnics]].<ref>{{cite journal |doi=10.1002/prep.200700021 |title=Special Materials in Pyrotechnics: VI. Silicon – An Old Fuel with New Perspectives |last1=Koch |first1=E.C. |last2=Clement |first2=D. |journal=Propellants, Explosives, Pyrotechnics |volume=32 |pages=205–212 |date=2007 |issue=3}}</ref> [[Silly Putty]] was originally made by adding [[boric acid]] to [[silicone oil]].<ref>{{cite book|chapter-url ={{google books |plainurl=y |id=jftapGDTmYUC|page=90}} |chapter=Silly Putty |title=Timeless toys: classic toys and the playmakers who created them |first=Tim |last=Walsh |publisher=Andrews McMeel Publishing |date=2005 |isbn=978-0-7407-5571-2}}</ref><!--Now name-brand Silly Putty also contains significant amounts of elemental silicon. (Silicon binds to the silicone and allows the material to bounce 20% higher.){{Citation needed|date=January 2008}} https://books.google.com/books?id=F2ApK7QnbPUC&pg=PA125 does not mention silicon--> Other silicon compounds function as high-technology abrasives and new high-strength ceramics based upon [[silicon carbide]]. Silicon is a component of some [[superalloy]]s.

===Alloys===
Elemental silicon is added to molten [[cast iron]] as [[ferrosilicon]] or silicocalcium alloys to improve performance in casting thin sections and to prevent the formation of [[cementite]] where exposed to outside air. The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steel, can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is grossly impure, it accounts for 80% of the world's use of free silicon. Silicon is an important constituent of [[transformer steel]], modifying its [[resistivity]] and [[ferromagnetic]] properties.

The properties of silicon may be used to modify alloys with metals other than iron. "Metallurgical grade" silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminium-silicon alloys ([[silumin]] alloys) for aluminium part [[Casting|casts]], mainly for use in the [[automotive industry]]. Silicon's importance in aluminium casting is that a significantly high amount (12%) of silicon in aluminium forms a [[eutectic mixture]] which solidifies with very little thermal contraction. This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidity. Silicon also significantly improves the hardness and thus wear-resistance of aluminium.<ref name="diecasting">{{cite web|last=Apelian |first=D.|date=2009 |url=http://www.diecasting.org/research/wwr/WWR_AluminumCastAlloys.pdf |title=Aluminum Cast Alloys: Enabling Tools for Improved Performance |publisher=North American Die Casting Association |location=Wheeling, Illinois|archive-url=https://web.archive.org/web/20120106013105/http://www.diecasting.org/research/wwr/WWR_AluminumCastAlloys.pdf|archive-date=2012-01-06}}</ref><ref name="USGS" /> Metallurgical grade silicon is made by melting quartz or quartzite in a large arc furnace, in a carbothermal reduction process with carbon-containing material such as coal, coke or charcoal and woodchips for gas circulation. This production technique without iron is often used for [[polysilicon]] production for photovoltaics and also semiconductors.<ref>Troszak T.A. (2021) The hidden costs of solar photovoltaic power, NATO ENSEC COE Energy highlights Vol 16, pp 22. Copyright 2021 NATO Energy Security Center of Excellence</ref><ref>{{cite web | url=https://hackaday.com/2021/11/15/mining-and-refining-pure-silicon-and-the-incredible-effort-it-takes-to-get-there/ | title=Mining and Refining: Pure Silicon and the Incredible Effort It Takes to Get There | date=15 November 2021 }}</ref><ref>{{cite web | url=https://magazine.elkem.com/material-science-insights/from-quartz-to-silicon-to-silicones/#:~:text=Metallurgical%2Dgrade%20silicon%20is%20produced,a%20submerged%20electric%20arc%20furnace | title=From quartz to silicon to silicones }}</ref><ref>{{Cite journal|title=Mass Production Test of Solar Cells and Modules Made of 100% UMG Silicon. 20.76% Record Efficiency|first1=Eduardo|last1=Forniés|first2=Bruno|last2=Ceccaroli|first3=Laura|last3=Méndez|first4=Alejandro|last4=Souto|first5=Antonio|last5=Pérez Vázquez|first6=Timur|last6=Vlasenko|first7=Joaquín|last7=Dieguez|date=April 19, 2019|journal=Energies|volume=12|issue=8|pages=1495|doi=10.3390/en12081495|doi-access=free }}</ref>

===Electronics===
{{Main|Semiconductor device fabrication}}
{{Further|Semiconductor industry}}
[[File:Silicon wafer with mirror finish.jpg|thumb|upright|Silicon wafer with mirror finish]]

Most elemental silicon produced remains as a ferrosilicon alloy, and only approximately 20% is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year). An estimated 15% of the world production of metallurgical grade silicon is further refined to semiconductor purity.<ref name="USGS" /> This typically is the "nine-9" or 99.9999999% purity,<ref>"Semi" SemiSource 2006: A supplement to Semiconductor International. December 2005. Reference Section: ''How to Make a Chip.'' Adapted from Design News. Reed Electronics Group.</ref> nearly defect-free single [[crystalline]] material.<ref>SemiSource 2006: A supplement to Semiconductor International. December 2005. Reference Section: ''How to Make a Chip.'' Adapted from Design News. Reed Electronics Group.</ref>

[[Monocrystalline silicon]] of such purity is usually produced by the [[Czochralski process]], and is used to produce [[Wafer (electronics)|silicon wafers]] used in the [[semiconductor industry]], in electronics, and in some high-cost and high-efficiency [[photovoltaic]] applications.<ref name="Ullmann590">{{harvnb|Zulehner|Neuer|Rau|p=590}}</ref> Pure silicon is an [[intrinsic semiconductor]], which means that unlike metals, it conducts [[electron hole]]s and electrons released from atoms by heat; silicon's [[electrical conductivity]] increases with higher temperatures. Pure silicon has too low a conductivity (i.e., too high a [[resistivity]]) to be used as a circuit element in electronics. In practice, pure silicon is [[doping (semiconductors)|doped]] with small concentrations of certain other elements, which greatly increase its conductivity and adjust its electrical response by controlling the number and charge ([[electron hole|positive]] or [[electron|negative]]) of activated carriers. Such control is necessary for [[transistor]]s, [[solar cell]]s, [[semiconductor detector]]s, and other [[semiconductor device]]s used in the computer industry and other technical applications.<ref name="Ullmann573">{{harvnb|Zulehner|Neuer|Rau|p=573}}</ref> In [[silicon photonics]], silicon may be used as a continuous wave [[Raman laser]] medium to produce coherent light.<ref name="dekker_2008">{{cite journal |title=Ultrafast nonlinear all-optical processes in silicon-on-insulator waveguides |journal=[[Journal of Physics D]] |year=2008 |volume=40 |issue=14 |page=R249–R271 |doi=10.1088/0022-3727/40/14/r01 |bibcode=2007JPhD...40..249D |last1=Dekker |first1=R |last2=Usechak |first2=N |last3=Först |first3=M |last4=Driessen |first4=A |s2cid=123008652 |url=https://ris.utwente.nl/ws/files/6730038/Dekker_R._Journ._Appl._Phys__Juni_2007.pdf |access-date=2024-04-15 |archive-date=2024-04-16 |archive-url=https://web.archive.org/web/20240416161929/https://ris.utwente.nl/ws/files/6730038/Dekker_R._Journ._Appl._Phys__Juni_2007.pdf |url-status=dead }}</ref>

In common [[integrated circuit]]s, a wafer of monocrystalline silicon serves as a mechanical support for the circuits, which are created by doping and insulated from each other by thin layers of [[silicon dioxide|silicon oxide]], an insulator that is easily produced on Si surfaces by processes of [[thermal oxidation]] or [[LOCOS|local oxidation (LOCOS)]], which involve exposing the element to oxygen under the proper conditions that can be predicted by the [[Deal–Grove model]]. Silicon has become the most popular material for both high power semiconductors and integrated circuits because it can withstand the highest temperatures and greatest electrical activity without suffering [[avalanche breakdown]] (an [[electron avalanche]] is created when heat produces free electrons and holes, which in turn pass more current, which produces more heat). In addition, the insulating oxide of silicon is not soluble in water, which gives it an advantage over [[germanium]] (an element with similar properties which can also be used in semiconductor devices) in certain fabrication techniques.<ref>[http://www.mpoweruk.com/semiconductors.htm Semiconductors Without the Quantum Physics] {{Webarchive|url=https://web.archive.org/web/20210813034833/https://mpoweruk.com/semiconductors.htm |date=2021-08-13 }}. Electropaedia</ref>

Monocrystalline silicon is expensive to produce, and is usually justified only in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. For other uses, other types of pure silicon may be employed. These include [[hydrogenated amorphous silicon]] and upgraded metallurgical-grade silicon (UMG-Si) used in the production of low-cost, [[large-area electronics]] in applications such as [[liquid crystal display]]s and of large-area, low-cost, thin-film [[solar cells]]. Such semiconductor grades of silicon are either slightly less pure or polycrystalline rather than monocrystalline, and are produced in comparable quantities as the monocrystalline silicon: 75,000 to 150,000 metric tons per year. The market for the lesser grade is growing more quickly than for monocrystalline silicon. By 2013, polycrystalline silicon production, used mostly in solar cells, was projected to reach 200,000 metric tons per year, while monocrystalline semiconductor grade silicon was expected to remain less than 50,000 tons per year.<ref name="USGS">Corathers, Lisa A. [http://minerals.usgs.gov/minerals/pubs/commodity/silicon/myb1-2009-simet.pdf 2009 Minerals Yearbook] {{Webarchive|url=https://web.archive.org/web/20180622193033/https://minerals.usgs.gov/minerals/pubs/commodity/silicon/myb1-2009-simet.pdf |date=2018-06-22 }}. USGS</ref>

===Quantum dots===
[[Silicon quantum dots]] are created through the thermal processing of hydrogen [[silsesquioxane]] into nanocrystals ranging from a few nanometers to a few microns, displaying size dependent [[Luminescence|luminescent]] properties.<ref>{{Cite journal|last1=Clark|first1=Rhett J.|last2=Aghajamali|first2=Maryam|last3=Gonzalez|first3=Christina M.|last4=Hadidi|first4=Lida|last5=Islam|first5=Muhammad Amirul|last6=Javadi|first6=Morteza|last7=Mobarok|first7=Md Hosnay|last8=Purkait|first8=Tapas K.|last9=Robidillo|first9=Christopher Jay T.|last10=Sinelnikov|first10=Regina|last11=Thiessen|first11=Alyxandra N.|date=2017-01-10|title=From Hydrogen Silsesquioxane to Functionalized Silicon Nanocrystals|url=https://doi.org/10.1021/acs.chemmater.6b02667|journal=Chemistry of Materials|volume=29|issue=1|pages=80–89|doi=10.1021/acs.chemmater.6b02667|issn=0897-4756|url-access=subscription}}</ref><ref>{{Cite journal|last1=Hessel|first1=Colin M.|last2=Henderson|first2=Eric J.|last3=Veinot|first3=Jonathan G. C.|date=2007|title=Hydrogen Silsesquioxane: A Molecular Precursor for Nanocrystalline Si—SiO2 Composites and Freestanding Hydride-Surface-Terminated Silicon Nanoparticles.|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/chin.200710014|journal=ChemInform|language=en|volume=38|issue=10|doi=10.1002/chin.200710014|issn=1522-2667|url-access=subscription}}</ref> The nanocrystals display large [[Stokes shift]]s converting photons in the ultraviolet range to photons in the visible or infrared, depending on the particle size, allowing for applications in [[quantum dot display]]s and [[luminescent solar concentrator]]s due to their limited self absorption. A benefit of using silicon based [[quantum dot]]s over [[cadmium]] or [[indium]] is the non-toxic, metal-free nature of silicon.<ref>{{Cite journal|last1=Lim|first1=Cheol Hong|last2=Han|first2=Jeong-Hee|last3=Cho|first3=Hae-Won|last4=Kang|first4=Mingu|date=2014|title=Studies on the Toxicity and Distribution of Indium Compounds According to Particle Size in Sprague-Dawley Rats|url=http://koreascience.or.kr/article/JAKO201416747604676.page|journal=Toxicological Research|volume=30|issue=1|pages=55–63|doi=10.5487/TR.2014.30.1.055|issn=1976-8257|pmc=4007045|pmid=24795801|bibcode=2014ToxRe..30...55L }}</ref><ref>{{Cite journal|date=2020-03-15|title=Cadmium-induced cytotoxicity in mouse liver cells is associated with the disruption of autophagic flux via inhibiting the fusion of autophagosomes and lysosomes|url=https://www.sciencedirect.com/science/article/abs/pii/S0378427419304126|journal=Toxicology Letters|language=en|volume=321|pages=32–43|doi=10.1016/j.toxlet.2019.12.019|issn=0378-4274|last1=Zou |first1=Hui |first2=Tao |last2=Wang |first3=Junzhao  |last3=Yuan |first4=Jian  |last4=Sun |first5=Yan |last5=Yuan|first6=Jianhong  |last6=Gu |first7=Xuezhong  |last7=Liu |first8=Jianchun  |last8=Bian |first9=Zongping  |last9=Liu|pmid=31862506|s2cid=209435190|url-access=subscription}}</ref>
Another application of silicon quantum dots is for sensing of hazardous materials. The sensors take advantage of the luminescent properties of the quantum dots through [[Quenching (fluorescence)|quenching]] of the [[photoluminescence]] in the presence of the hazardous substance.<ref>{{Cite journal|last1=Nguyen|first1=An|last2=Gonzalez|first2=Christina M|last3=Sinelnikov|first3=Regina|last4=Newman|first4=W|last5=Sun|first5=Sarah|last6=Lockwood|first6=Ross|last7=Veinot|first7=Jonathan G C|last8=Meldrum|first8=Al|date=2016-02-10|title=Detection of nitroaromatics in the solid, solution, and vapor phases using silicon quantum dot sensors|url=https://doi.org/10.1088/0957-4484/27/10/105501|journal=Nanotechnology|language=en|volume=27|issue=10|pages=105501|doi=10.1088/0957-4484/27/10/105501|pmid=26863492|bibcode=2016Nanot..27j5501N|s2cid=24292648 |issn=0957-4484|url-access=subscription}}</ref> There are many methods used for hazardous chemical sensing with a few being electron transfer, [[Förster resonance energy transfer|fluorescence resonance energy transfer]], and photocurrent generation.<ref>{{Cite journal|last1=Gonzalez|first1=Christina M.|last2=Veinot|first2=Jonathan G. C.|date=2016-06-02|title=Silicon nanocrystals for the development of sensing platforms|url=https://pubs.rsc.org/en/content/articlelanding/2016/tc/c6tc01159d|journal=Journal of Materials Chemistry C|language=en|volume=4|issue=22|pages=4836–4846|doi=10.1039/C6TC01159D|issn=2050-7534|url-access=subscription}}</ref> Electron transfer quenching occurs when the [[lowest unoccupied molecular orbital]] (LUMO) is slightly lower in energy than the conduction band of the quantum dot, allowing for the transfer of electrons between the two, preventing recombination of the holes and electrons within the nanocrystals. The effect can also be achieved in reverse with a donor molecule having its [[highest occupied molecular orbital]] (HOMO) slightly higher than a valence band edge of the quantum dot, allowing electrons to transfer between them, filling the holes and preventing recombination. Fluorescence resonance energy transfer occurs when a complex forms between the quantum dot and a quencher molecule. The complex will continue to absorb light but when the energy is converted to the ground state it does not release a photon, quenching the material. The third method uses different approach by measuring the [[photocurrent]] emitted by the quantum dots instead of monitoring the photoluminescent display. If the concentration of the desired chemical increases then the photocurrent given off by the nanocrystals will change in response.<ref>{{Cite journal|last1=Yue|first1=Zhao|last2=Lisdat|first2=Fred|last3=Parak|first3=Wolfgang J.|last4=Hickey|first4=Stephen G.|last5=Tu|first5=Liping|last6=Sabir|first6=Nadeem|last7=Dorfs|first7=Dirk|last8=Bigall|first8=Nadja C.|date=2013-04-24|title=Quantum-Dot-Based Photoelectrochemical Sensors for Chemical and Biological Detection|url=https://doi.org/10.1021/am3028662|journal=ACS Applied Materials & Interfaces|volume=5|issue=8|pages=2800–2814|doi=10.1021/am3028662|pmid=23547912|issn=1944-8244|url-access=subscription}}</ref>

===Thermal energy storage===
{{excerpt|Thermal energy storage|Hot silicon technology}}