Editing Metalloid (section)

==Common applications==
:''The focus of this section is on the recognised metalloids. Elements less often recognised as metalloids are ordinarily classified as either metals or nonmetals; some of these are included here for comparative purposes.''
Metalloids are too brittle to have any structural uses in their pure forms.<ref>[[#Russell2005|Russell & Lee 2005, pp.&nbsp;421, 423]]; [[#Gray2009|Gray 2009, p.&nbsp;23]]</ref> They and their compounds are used in alloys, biological agents (toxicological, nutritional, and medicinal), catalysts, flame retardants, glasses (oxide and metallic), optical storage media and optoelectronics, pyrotechnics, semiconductors, and electronics.{{refn|1=Olmsted and Williams<ref>[[#Olmsted1997|Olmsted & Williams 1997, p.&nbsp;975]]</ref> commented that, "Until quite recently, chemical interest in the metalloids consisted mainly of isolated curiosities, such as the poisonous nature of arsenic and the mildly therapeutic value of borax. With the development of metalloid semiconductors, however, these elements have become among the most intensely studied".|group=n}}

===Alloys===
[[File:Copper germanium.jpg|thumb|right|[[Copper-germanium alloy]] pellets, likely ~84% Cu; 16% Ge.<ref name="Russell2005401"/> When combined with [[silver]] the result is a [[argentium sterling silver|tarnish resistant sterling silver]]. Also shown are two silver pellets.|alt=Several dozen metallic pellets, reddish-brown. They have a highly polished appearance, as if they had a cellophane coating.]]
Writing early in the history of [[intermetallic|intermetallic compounds]], the British metallurgist Cecil Desch observed that "certain non-metallic elements are capable of forming compounds of distinctly metallic character with metals, and these elements may therefore enter into the composition of alloys". He associated silicon, arsenic, and tellurium, in particular, with the alloy-forming elements.<ref>[[#Desch1914|Desch 1914, p.&nbsp;86]]</ref> Phillips and Williams<ref>[[#Phillips1965|Phillips & Williams 1965, p.&nbsp;620]]</ref> suggested that compounds of silicon, germanium, arsenic, and antimony with [[other metal|B metals]], "are probably best classed as alloys".

Among the lighter metalloids, alloys with [[transition metal]]s are well-represented. Boron can form intermetallic compounds and alloys with such metals of the composition M<sub>''n''</sub>B, if ''n'' > 2.<ref>[[#Vanderput1998|Van der Put 1998, p.&nbsp;123]]</ref> Ferroboron (15% boron) is used to introduce boron into [[steel]]; nickel-boron alloys are ingredients in welding alloys and [[case hardening]] compositions for the engineering industry. Alloys of silicon with [[iron]] and with aluminium are widely used by the steel and automotive industries, respectively. Germanium forms many alloys, most importantly with the [[Group 11 element|coinage metals]].<ref>[[#Klug1958|Klug & Brasted 1958, p.&nbsp;199]]</ref>

The heavier metalloids continue the theme. Arsenic can form alloys with metals, including [[platinum]] and [[copper]];<ref>[[#Good1813|Good et al. 1813]]</ref> it is also added to copper and its alloys to improve corrosion resistance<ref>[[#Sequeira|Sequeira 2011, p.&nbsp;776]]</ref> and appears to confer the same benefit when added to magnesium.<ref>[[#Gary|Gary 2013]]</ref> Antimony is well known as an alloy-former, including with the coinage metals. Its alloys include [[pewter]] (a tin alloy with up to 20% antimony) and [[type metal]] (a lead alloy with up to 25% antimony).<ref>[[#Russell2005|Russell & Lee 2005, pp.&nbsp;405–06; 423–34]]</ref> Tellurium readily alloys with iron, as ferrotellurium (50–58% tellurium), and with copper, in the form of [[Tellurium Copper|copper tellurium]] (40–50% tellurium).<ref>[[#Davidson1973|Davidson & Lakin 1973, p.&nbsp;627]]</ref> Ferrotellurium is used as a stabilizer for carbon in steel casting.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;589]]</ref> Of the non-metallic elements less often recognised as metalloids, selenium – in the form of ferroselenium (50–58% selenium) – is used to improve the [[machinability]] of stainless steels.<ref>[[#Greenwood2002|Greenwood & Earnshaw 2002, p.&nbsp;749]]; [[#Schwartz2002|Schwartz 2002, p.&nbsp;679]]</ref>

===Biological agents===
[[File:Arsenic trioxide.jpg|thumb|right|[[Arsenic trioxide]] or ''white arsenic'', one of the most toxic and prevalent forms of [[arsenic]]. The [[antileukemic drug|antileukaemic]] properties of white arsenic were first reported in 1878.<ref>[[#Antman|Antman 2001]]</ref>|alt=A clear glass dish on which is a small mound of a white crystalline powder.]] All six of the elements commonly recognised as metalloids have toxic, dietary or medicinal properties.<ref>[[#Řezanka|Řezanka & Sigler 2008]]; [[#Sekhon|Sekhon 2012]]</ref> Arsenic and antimony compounds are especially toxic; boron, silicon, and possibly arsenic, are essential trace elements. Boron, silicon, arsenic, and antimony have medical applications, and germanium and tellurium are thought to have potential.

Boron is used in insecticides<ref>[[#Emsley2001|Emsley 2001, p.&nbsp;67]]</ref> and herbicides.<ref>[[#Zhang2008|Zhang et al. 2008, p.&nbsp;360]]</ref> It is an essential trace element.<ref name=SLH>[[#SLH|Science Learning Hub 2009]]</ref> As [[boric acid]], it has antiseptic, antifungal, and antiviral properties.<ref>[[#Skinner|Skinner et al. 1979]]; [[#Tom|Tom, Elden & Marsh 2004, p.&nbsp;135]]</ref>

Silicon is present in [[silatrane]], a highly toxic rodenticide.<ref>[[#Büchel|Büchel 1983, p.&nbsp;226]]</ref> Long-term inhalation of silica dust causes [[silicosis]], a fatal disease of the lungs. Silicon is an essential trace element.<ref name=SLH/> [[Silicone]] gel can be applied to badly burned patients to reduce scarring.<ref>[[#Emsley2001|Emsley 2001, p.&nbsp;391]]</ref>

[[Salt (chemistry)|Salts]] of germanium are potentially harmful to humans and animals if ingested on a prolonged basis.<ref>[[#Schauss1991|Schauss 1991]]; [[#Tao1997|Tao & Bolger 1997]]</ref> There is interest in the pharmacological actions of germanium compounds but no licensed medicine as yet.<ref>[[#Eagleson1994|Eagleson 1994, p.&nbsp;450]]; [[#EVM|EVM 2003, pp.&nbsp;197‒202]]</ref>

Arsenic is notoriously poisonous and may also be an [[essential element]] in ultratrace amounts.<ref name=Neilsen>[[#Nielsen|Nielsen 1998]]</ref> During [[World War I]], both sides used "arsenic-based sneezing and vomiting [[diphenylchloroarsine|agents]]…to force enemy soldiers to remove their [[WWI gas mask|gas mask]]s before firing [[mustard gas|mustard]] or [[phosgene]] at them in a second [[salvo]]."<ref>[[#MacKenzie|MacKenzie 2015, p.&nbsp;36]]</ref> It has been used as a pharmaceutical agent since antiquity, including for the treatment of [[syphilis]] before the development of [[antibiotics]].<ref name=Jaouen>[[#Jaouen|Jaouen & Gibaud 2010]]</ref> Arsenic is also a component of [[melarsoprol]], a medicinal drug used in the treatment of human [[African trypanosomiasis]] or sleeping sickness. In 2003, arsenic trioxide (under the trade name [[Trisenox]]) was re-introduced for the treatment of [[acute promyelocytic leukaemia]], a cancer of the blood and bone marrow.<ref name=Jaouen/> Arsenic in drinking water, which causes lung and bladder cancer, has been associated with a reduction in breast cancer mortality rates.<ref>[[#SmithAH|Smith et al. 2014]]</ref>

Metallic antimony is relatively non-toxic, but most antimony compounds are poisonous.<ref>[[#Stevens1990|Stevens & Klarner, p.&nbsp;205]]</ref>
Two antimony compounds, [[sodium stibogluconate]] and [[stibophen]], are used as [[antiparasitic|antiparasitical drugs]].<ref>[[#Sneader|Sneader 2005, pp.&nbsp;57–59]]</ref>

Elemental tellurium is not considered particularly toxic; two grams of sodium tellurate, if administered, can be lethal.<ref>[[#Keall1946|Keall, Martin and Tunbridge 1946]]</ref> People exposed to small amounts of airborne tellurium exude a foul and persistent garlic-like odour.<ref>[[#Emsley2001|Emsley 2001, p.&nbsp;426]]</ref> Tellurium dioxide has been used to treat [[seborrhoeic dermatitis]]; other tellurium compounds were used as [[antimicrobial]] agents before the development of antibiotics.<ref>[[#Oldfield1974|Oldfield et al. 1974, p.&nbsp;65]]; [[#Turner2011|Turner 2011]]</ref> In the future, such compounds may need to be substituted for antibiotics that have become ineffective due to bacterial resistance.<ref>[[#Ba|Ba et al. 2010]]; [[#Daniel-Hoffmann|Daniel-Hoffmann, Sredni & Nitzan 2012]]; [[#Molina-Quiroz|Molina-Quiroz et al. 2012]]</ref>

Of the elements less often recognised as metalloids, beryllium and lead are noted for their toxicity; [[lead arsenate]] has been extensively used as an [[insecticide]].<ref>[[#Peryea|Peryea 1998]]</ref> Sulfur is one of the oldest of the fungicides and pesticides. Phosphorus, sulfur, zinc, selenium, and iodine are essential nutrients, and aluminium, tin, and lead may be.<ref name=Neilsen/> Sulfur, gallium, selenium, iodine, and bismuth have medicinal applications. Sulfur is a constituent of [[Sulfonamide (medicine)|sulfonamide drugs]], still widely used for conditions such as acne and urinary tract infections.<ref>[[#Hager|Hager 2006, p.&nbsp;299]]</ref> [[Gallium nitrate]] is used to treat the side effects of cancer;<ref>[[#Apseloff|Apseloff 1999]]</ref> gallium citrate, a [[radiopharmaceutical]], facilitates imaging of inflamed body areas.<ref>[[#Trivedi|Trivedi, Yung & Katz 2013, p.&nbsp;209]]</ref> [[Selenium sulfide]] is used in medicinal shampoos and to treat skin infections such as [[tinea versicolor]].<ref>[[#Emsley2001|Emsley 2001, p.&nbsp;382]]; [[#Burkhart|Burkhart, Burkhart & Morrell 2011]]</ref> Iodine is used as a disinfectant in various forms. Bismuth is an ingredient in some [[antibacterial]]s.<ref>[[#Thomas|Thomas, Bialek & Hensel 2013, p.&nbsp;1]]</ref>

===Catalysts===
[[Boron trifluoride]] and [[boron trichloride|trichloride]] are used as homogeneous [[catalyst]]s in organic synthesis and electronics; the [[boron tribromide|tribromide]] is used in the manufacture of [[diborane]].<ref>[[#Perry|Perry 2011, p.&nbsp;74]]</ref> Non-toxic boron [[ligand]]s could replace toxic phosphorus ligands in some transition metal catalysts.<ref>[[#UCR|UCR Today 2011]]; [[#Wang|Wang & Robinson 2011]]; [[#Kinjo|Kinjo et al. 2011]]</ref> [[Silica sulfuric acid]] (SiO<sub>2</sub>OSO<sub>3</sub>H) is used in organic reactions.<ref>[[#Kauthale|Kauthale et al. 2015]]</ref> Germanium dioxide is sometimes used as a catalyst in the production of [[Polyethylene terephthalate|PET]] plastic for containers;<ref>[[#Gunn|Gunn 2014, pp.&nbsp;188, 191]]</ref> cheaper antimony compounds, such as the trioxide or [[antimony triacetate|triacetate]], are more commonly employed for the same purpose<ref>[[#Gupta|Gupta, Mukherjee & Cameotra 1997, p.&nbsp;280]]; [[#Thomas2012|Thomas & Visakh 2012, p.&nbsp;99]]</ref> despite concerns about antimony contamination of food and drinks.<ref>[[#Muncke|Muncke 2013]]</ref> Arsenic trioxide has been used in the production of [[natural gas]], to boost the removal of [[carbon dioxide]], as have [[selenous acid]] and [[tellurous acid]].<ref>[[#Mokhatab|Mokhatab & Poe 2012, p.&nbsp;271]]</ref> Selenium acts as a catalyst in some microorganisms.<ref>[[#Craig|Craig, Eng & Jenkins 2003, p.&nbsp;25]]</ref> Tellurium, its dioxide, and its [[tellurium tetrachloride|tetrachloride]] are strong catalysts for air oxidation of carbon above 500&nbsp;°C.<ref>[[#McKee|McKee 1984]]</ref> [[Graphite oxide]] can be used as a catalyst in the synthesis of [[imine]]s and their derivatives.<ref>[[#Hai|Hai et al. 2012]]</ref> [[Activated carbon]] and [[alumina]] have been used as catalysts for the removal of sulfur contaminants from natural gas.<ref>[[#Kohl|Kohl & Nielsen 1997, pp.&nbsp;699–700]]</ref> [[Titanium]] doped aluminium has been suggested as a substitute for [[noble metal]] catalysts used in the production of industrial chemicals.<ref>[[#Chopra|Chopra et al. 2011]]</ref>

===Flame retardants===
Compounds of boron, silicon, arsenic, and antimony have been used as [[flame retardant]]s. Boron, in the form of [[borax]], has been used as a textile flame retardant since at least the 18th century.<ref>[[#LeBras|Le Bras, Wilkie & Bourbigot 2005, p.&nbsp;v]]</ref> Silicon compounds such as silicones, [[silane]]s, [[silsesquioxane]], [[silica]], and [[silicate]]s, some of which were developed as alternatives to more toxic [[halogenation|halogenated]] products, can considerably improve the flame retardancy of plastic materials.<ref>[[#Wilkie|Wilkie & Morgan 2009, p.&nbsp;187]]</ref>
Arsenic compounds such as [[sodium arsenite]] or [[sodium arsenate]] are effective flame retardants for wood but have been less frequently used due to their toxicity.<ref>[[#Locke1956|Locke et al. 1956, p.&nbsp;88]]</ref> Antimony trioxide is a flame retardant.<ref>[[#Carlin|Carlin 2011, p.&nbsp;6.2]]</ref> [[Aluminium hydroxide]] has been used as a wood-fibre, rubber, plastic, and textile flame retardant since the 1890s.<ref>[[#Evans|Evans 1993, pp.&nbsp;257–28]]</ref> Apart from aluminium hydroxide, use of phosphorus based flame-retardants – in the form of, for example, [[organophosphate]]s – now exceeds that of any of the other main retardant types. These employ boron, antimony, or [[halogenated hydrocarbon]] compounds.<ref>[[#Corbridge|Corbridge 2013, p.&nbsp;1149]]</ref>

===Glass formation===
[[File:Fibreoptic4.jpg|thumb|right|[[Optical fibers]], usually made of pure [[silicon dioxide]] glass, with additives such as [[boron trioxide]] or [[germanium dioxide]] for increased sensitivity|alt=A bunch of pale yellow semi-transparent thin strands, with bright points of white light at their tips.]]
The oxides [[boron trioxide|B<sub>2</sub>O<sub>3</sub>]], [[silicon dioxide|SiO<sub>2</sub>]], [[germanium dioxide|GeO<sub>2</sub>]], [[arsenic trioxide|As<sub>2</sub>O<sub>3</sub>]], and [[antimony trioxide|Sb<sub>2</sub>O<sub>3</sub>]] readily form [[glass]]es. [[Tellurium dioxide|TeO<sub>2</sub>]] forms a glass but this requires a "heroic quench rate"<ref name=K2002/> or the addition of an impurity; otherwise the crystalline form results.<ref name=K2002>[[#Kaminow2002|Kaminow & Li 2002, p.&nbsp;118]]</ref> These compounds are used in chemical, domestic, and industrial glassware<ref>[[#Deming1925|Deming 1925]], pp.&nbsp;330 (As<sub>2</sub>O<sub>3</sub>), 418 (B<sub>2</sub>O<sub>3</sub>; SiO<sub>2</sub>; Sb<sub>2</sub>O<sub>3</sub>); [[#Witt1968|Witt & Gatos 1968, p.&nbsp;242]] (GeO<sub>2</sub>)</ref> and optics.<ref>[[#Eagleson1994|Eagleson 1994, p.&nbsp;421]] (GeO<sub>2</sub>); [[#Rothenberg1976|Rothenberg 1976, 56, 118–19]] (TeO<sub>2</sub>)</ref> Boron trioxide is used as a [[glass fibre]] additive,<ref>[[#Geckeler1987|Geckeler 1987, p.&nbsp;20]]</ref> and is also a component of [[borosilicate glass]], widely used for laboratory glassware and domestic ovenware for its low thermal expansion.<ref>[[#Kreith2005|Kreith & Goswami 2005, pp.&nbsp;12–109]]</ref> Most ordinary glassware is made from silicon dioxide.<ref>[[#Russell2005|Russell & Lee 2005, p.&nbsp;397]]</ref> Germanium dioxide is used as a glass fibre additive, as well as in infrared optical systems.<ref>[[#Butterman2005|Butterman & Jorgenson 2005, pp.&nbsp;9–10]]</ref> Arsenic trioxide is used in the glass industry as a [[glass coloring and color marking|decolourizing]] and fining agent (for the removal of bubbles),<ref>[[#Shelby|Shelby 2005, p.&nbsp;43]]</ref> as is antimony trioxide.<ref>[[#Butterman2004|Butterman & Carlin 2004, p.&nbsp;22]]; [[#Russell2005|Russell & Lee 2005, p.&nbsp;422]]</ref> Tellurium dioxide finds application in laser and [[nonlinear optics]].<ref>[[#Träger2007|Träger 2007, pp.&nbsp;438, 958]]; [[#Eranna2011|Eranna 2011, p.&nbsp;98]]</ref>

[[Amorphous]] [[metallic glass]]es are generally most easily prepared if one of the components is a metalloid or "near metalloid" such as boron, carbon, silicon, phosphorus or germanium.<ref>[[#Rao2002|Rao 2002, p.&nbsp;552]]; [[#Loffler|Löffler, Kündig & Dalla Torre 2007, p.&nbsp;17–11]]</ref>{{refn|1=Research published in 2012 suggests that metal-metalloid glasses can be characterised by an interconnected atomic packing scheme in which metallic and [[covalent]] bonding structures coexist.<ref>[[#Guan|Guan et al. 2012]]; [[#World|WPI-AIM 2012]]</ref>|group=n}} Aside from thin films deposited at very low temperatures, the first known metallic glass was an alloy of composition Au<sub>75</sub>Si<sub>25</sub> reported in 1960.<ref>[[#Klement|Klement, Willens & Duwez 1960]]; [[#Wanga|Wanga, Dongb & Shek 2004, p.&nbsp;45]]</ref> A metallic glass having a strength and toughness not previously seen, of composition Pd<sub>82.5</sub>P<sub>6</sub>Si<sub>9.5</sub>Ge<sub>2</sub>, was reported in 2011.<ref>[[#Demetriou|Demetriou et al. 2011]]; [[#Oliwenstein|Oliwenstein 2011]]</ref>

Phosphorus, selenium, and lead, which are less often recognised as metalloids, are also used in glasses. [[Phosphate glass]] has a substrate of phosphorus pentoxide (P<sub>2</sub>O<sub>5</sub>), rather than the silica (SiO<sub>2</sub>) of conventional silicate glasses. It is used, for example, to make [[sodium lamp]]s.<ref>[[#Karabulut|Karabulut et al. 2001, p.&nbsp;15]]; [[#Haynes|Haynes 2012, pp.&nbsp;4–26]]</ref> Selenium compounds can be used both as decolourising agents and to add a red colour to glass.<ref>[[#Schwartz2002|Schwartz 2002, pp.&nbsp;679–80]]</ref> Decorative glassware made of traditional [[lead glass]] contains at least 30% [[lead(II) oxide]] (PbO); lead glass used for radiation shielding may have up to 65% PbO.<ref>[[#Carter|Carter & Norton 2013, p.&nbsp;403]]</ref> Lead-based glasses have also been extensively used in electronic components, enamelling, sealing and glazing materials, and solar cells. Bismuth based oxide glasses have emerged as a less toxic replacement for lead in many of these applications.<ref>[[#Maeder|Maeder 2013, pp.&nbsp;3, 9–11]]</ref>

===Optical storage and optoelectronics===
Varying compositions of [[GeSbTe]] ("GST alloys") and [[AgInSbTe|Ag- and In- doped Sb<sub>2</sub>Te]] ("AIST alloys"), being examples of [[phase-change material]]s, are widely used in rewritable [[optical disc]]s and [[phase-change memory]] devices. By applying heat, they can be switched between amorphous (glassy) and [[crystalline]] states. The change in optical and electrical properties can be used for information storage purposes.<ref>[[#Tominaga2006|Tominaga 2006, pp.&nbsp;327–28]]; [[#Chung2010|Chung 2010, pp.&nbsp;285–86]]; [[#Kolobov 2012|Kolobov & Tominaga 2012, p.&nbsp;149]]</ref> Future applications for GeSbTe may include, "ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent 'smart' glasses, 'smart' contact lenses, and artificial retina devices."<ref>[[#NS2014|New Scientist 2014]]; [[#Hosseini|Hosseini, Wright & Bhaskaran 2014]]; [[#Farandos|Farandos et al. 2014]]</ref>

===Pyrotechnics===
[[File:Blue Light.JPG|thumb|right|upright|Archaic [[blue light (pyrotechnic signal)|blue light signal]], fuelled by a mixture of [[sodium nitrate]], [[sulfur]], and (red) [[arsenic trisulfide]]<ref>[[#OO|Ordnance Office 1863, p.&nbsp;293]]</ref>|alt=A man is standing in the dark. He is holding out a short stick at mid-chest level. The end of the stick is alight, burning very brightly, and emitting smoke.]]
The recognised metalloids have either pyrotechnic applications or associated properties. Boron and silicon are commonly encountered;<ref name=Kos>[[#Kosanke|Kosanke 2002, p.&nbsp;110]]</ref> they act somewhat like metal fuels.<ref>[[#Ellern|Ellern 1968, pp.&nbsp;246, 326–27]]</ref> Boron is used in [[pyrotechnic initiator]] compositions (for igniting other hard-to-start compositions), and in [[delay composition]]s that burn at a constant rate.<ref name=Conkling82>[[#Conkling|Conkling & Mocella 2010, p.&nbsp;82]]</ref> [[Boron carbide]] has been identified as a possible replacement for more toxic [[barium]] or [[hexachloroethane]] mixtures in smoke munitions, signal flares, and fireworks.<ref>[[#Crow|Crow 2011]]; [[#Daily|Mainiero 2014]]</ref> Silicon, like boron, is a component of initiator and delay mixtures.<ref name=Conkling82/> Doped germanium can act as a variable speed [[thermite]] fuel.{{refn|1=The reaction involved is Ge + 2 [[MoO3|MoO<sub>3</sub>]] → GeO<sub>2</sub> + 2 [[MoO2|MoO<sub>2</sub>]]. Adding arsenic or antimony ([[extrinsic semiconductor#n-type semiconductors|n-type]] electron donors) increases the rate of reaction; adding gallium or indium ([[intrinsic semiconductor#p-type semiconductors|p-type]] electron acceptors) decreases it.<ref>[[#Schwab|Schwab & Gerlach 1967]]; [[#Yetter|Yetter 2012, p.&nbsp;81]]; [[#Lipscomb|Lipscomb 1972, pp.&nbsp;2–3, 5–6, 15]]</ref>|group=n}} [[Arsenic trisulfide]] As<sub>2</sub>S<sub>3</sub> was used in old [[blue light (pyrotechnic signal)|naval signal lights]]; in fireworks to make white stars;<ref>[[#Ellern|Ellern 1968, p.&nbsp;135]]; [[#Weingart|Weingart 1947, p.&nbsp;9]]</ref> in yellow [[smoke screen]] mixtures; and in initiator compositions.<ref>[[#Conkling|Conkling & Mocella 2010, p.&nbsp;83]]</ref> [[stibnite|Antimony trisulfide]] Sb<sub>2</sub>S<sub>3</sub> is found in white-light fireworks and in [[flash powder|flash and sound]] mixtures.<ref>[[#Conkling|Conkling & Mocella 2010, pp.&nbsp;181, 213]]</ref> Tellurium has been used in delay mixtures and in [[blasting cap]] initiator compositions.<ref name=Ellern>[[#Ellern|Ellern 1968, pp.&nbsp;209–10, 322]]</ref>

Carbon, aluminium, phosphorus, and selenium continue the theme. Carbon, in [[black powder]], is a constituent of fireworks rocket propellants, bursting charges, and effects mixtures, and military delay fuses and igniters.<ref>[[#RussellF|Russell 2009, pp.&nbsp;15, 17, 41, 79–80]]</ref>{{refn|1=Ellern, writing in ''Military and Civilian Pyrotechnics'' (1968), comments that [[carbon black]] "has been specified for and used in a nuclear air-burst simulator."<ref>[[#Ellern|Ellern 1968, p.&nbsp;324]]</ref>|group=n}} Aluminium is a common pyrotechnic ingredient,<ref name=Kos/> and is widely employed for its capacity to generate light and heat,<ref>[[#Ellern|Ellern 1968, p.&nbsp;328]]</ref> including in thermite mixtures.<ref>[[#Conkling|Conkling & Mocella 2010, p.&nbsp;171]]</ref> Phosphorus can be found in smoke and incendiary munitions, [[Armstrong's mixture|paper caps]] used in [[cap gun|toy guns]], and [[party popper]]s.<ref>[[#Conkling|Conkling & Mocella 2011, pp.&nbsp;83–84]]</ref> Selenium has been used in the same way as tellurium.<ref name=Ellern/>

===Semiconductors and electronics===
[[File:Semiconductor-1.jpg|thumb|left|[[Semiconductor]]-based electronic components. From left to right: a [[transistor]], an [[integrated circuit]], and an [[LED]]. The elements commonly recognised as metalloids find widespread use in such devices, as elemental or [[compound semiconductor]] constituents ([[silicon|Si]], [[germanium|Ge]] or [[GaAs]], for example) or as [[doping (semiconductor)|doping agents]] ([[boron|B]], [[antimony|Sb]], [[tellurium|Te]], for example).|alt=A small square plastic piece with three parallel wire protrusions on one side; a larger rectangular plastic chip with multiple plastic and metal pin-like legs; and a small red light globe with two long wires coming out of its base.]]

All the elements commonly recognised as metalloids (or their compounds) have been used in the semiconductor or solid-state electronic industries.<ref>[[#Berger1997|Berger 1997, p.&nbsp;91]]; [[#Hampel1968|Hampel 1968, passim]]</ref>

Some properties of boron have limited its use as a semiconductor. It has a high melting point, single [[crystal]]s are relatively hard to obtain, and introducing and retaining controlled impurities is difficult.<ref>[[#Rochow1966|Rochow 1966, p.&nbsp;41]]; [[#Berger1997|Berger 1997, pp.&nbsp;42–43]]</ref>

Silicon is the leading commercial semiconductor; it forms the basis of modern electronics (including standard solar cells)<ref name=Bom>[[#Bomgardner|Bomgardner 2013, p.&nbsp;20]]</ref> and information and communication technologies.<ref>[[#Russell2005|Russell & Lee 2005, p.&nbsp;395]]; [[#Brown2009|Brown et al. 2009, p.&nbsp;489]]</ref> This was despite the study of semiconductors, early in the 20th century, having been regarded as the "physics of dirt" and not deserving of close attention.<ref>[[#Haller 2006|Haller 2006, p.&nbsp;4]]: "The study and understanding of the physics of semiconductors progressed slowly in the 19th and early 20th centuries&nbsp;... Impurities and defects&nbsp;... could not be controlled to the degree necessary to obtain reproducible results. This led influential physicists, including [[Wolfgang Pauli|W. Pauli]] and [[Isidor Isaac Rabi|I. Rabi]], to comment derogatorily on the 'Physics of Dirt'."; [[#Hoddeson2007|Hoddeson 2007, pp.&nbsp;25–34 (29)]]</ref>

Germanium has largely been replaced by silicon in semiconducting devices, being cheaper, more resilient at higher operating temperatures, and easier to work during the microelectronic fabrication process.<ref name=Russell2005401>[[#Russell2005|Russell & Lee 2005, p.&nbsp;401]]; [[#Büchel2003|Büchel, Moretto & Woditsch 2003, p.&nbsp;278]]</ref> Germanium is still a constituent of semiconducting [[silicon-germanium]] "alloys" and these have been growing in use, particularly for wireless communication devices; such alloys exploit the higher carrier mobility of germanium.<ref name=Russell2005401/> The synthesis of gram-scale quantities of semiconducting [[germanane]] was reported in 2013. This consists of one-atom thick sheets of hydrogen-terminated germanium atoms, analogous to [[graphane]]. It conducts electrons more than ten times faster than silicon and five times faster than germanium, and is thought to have potential for optoelectronic and sensing applications.<ref>[[#Bianco2013|Bianco et al. 2013]]</ref> The development of a germanium-wire based anode that more than doubles the capacity of [[lithium-ion battery|lithium-ion batteries]] was reported in 2014.<ref>[[#Limerick|University of Limerick 2014]]; [[#Kennedy|Kennedy et al. 2014]]</ref> In the same year, Lee et al. reported that defect-free crystals of [[graphene]] large enough to have electronic uses could be grown on, and removed from, a germanium substrate.<ref>[[#Lee|Lee et al. 2014]]</ref>

Arsenic and antimony are not semiconductors in their [[standard state#Liquids and solids|standard states]]. Both form [[compound semiconductor|type III-V semiconductors]] (such as GaAs, [[AlSb]] or GaInAsSb) in which the average number of valence electrons per atom is the same as that of [[Group 14]] elements, but they have [[direct band gap]]s. These compounds are preferred for optical applications.<ref>[[#Russell2005|Russell & Lee 2005, pp.&nbsp;421–22, 424]]</ref> Antimony nanocrystals may enable [[lithium-ion batteries]] to be replaced by more powerful [[sodium-ion battery|sodium ion batteries]].<ref>[[#He|He et al. 2014]]</ref>

Tellurium, which is a semiconductor in its standard state, is used mainly as a component in [[list of semiconductor materials|type II/VI]] semiconducting-[[chalcogenide]]s; these have applications in electro-optics and electronics.<ref>[[#Berger1997|Berger 1997, p.&nbsp;91]]</ref> [[Cadmium telluride]] (CdTe) is used in solar modules for its high conversion efficiency, low manufacturing costs, and large [[band gap]] of 1.44 eV, letting it absorb a wide range of wavelengths.<ref name=Bom/> [[Bismuth telluride]] (Bi<sub>2</sub>Te<sub>3</sub>), alloyed with selenium and antimony, is a component of [[thermoelectric materials|thermoelectric devices]] used for refrigeration or portable power generation.<ref>[[#ScienceDaily|ScienceDaily 2012]]</ref>

Five metalloids – boron, silicon, germanium, arsenic, and antimony – can be found in cell phones (along with at least 39 other metals and nonmetals).<ref>[[#Reardon2005|Reardon 2005]]; [[#Meskers|Meskers, Hagelüken & Van Damme 2009, p.&nbsp;1131]]</ref> Tellurium is expected to find such use.<ref>[[#The Economist|The Economist 2012]]</ref> Of the less often recognised metalloids, phosphorus, gallium (in particular) and selenium have semiconductor applications. Phosphorus is used in trace amounts as a [[dopant]] for [[n-type semiconductor]]s.<ref>[[#Whitten2007|Whitten 2007, p.&nbsp;488]]</ref> The commercial use of gallium compounds is dominated by semiconductor applications –  in integrated circuits, cell phones, [[laser diode]]s, [[light-emitting diode]]s, [[photodetector]]s, and [[solar cell]]s.<ref>[[#Jaskula|Jaskula 2013]]</ref> Selenium is used in the production of solar cells<ref>[[#GES|German Energy Society 2008, pp.&nbsp;43–44]]</ref> and in high-energy [[surge protector]]s.<ref>[[#Patel|Patel 2012, p.&nbsp;248]]</ref>

Boron, silicon, germanium, antimony, and tellurium,<ref>[[#Moore2014|Moore 2104]]; [[#Utah|University of Utah 2014]]; [[#Xu|Xu et al. 2014]]</ref> as well as heavier metals and metalloids such as Sm, Hg, Tl, Pb, Bi, and Se,<ref>[[#Yang|Yang et al. 2012, p.&nbsp;614]]</ref> can be found in [[topological insulator]]s. These are alloys<ref>[[#Moore2010|Moore 2010, p.&nbsp;195]]</ref> or compounds which, at ultracold temperatures or room temperature (depending on their composition), are metallic conductors on their surfaces but insulators through their interiors.<ref>[[#Moore2011|Moore 2011]]</ref> [[Cadmium arsenide]] Cd<sub>3</sub>As<sub>2</sub>, at about 1 K, is a Dirac-semimetal – a bulk electronic analogue of graphene – in which electrons travel effectively as massless particles.<ref>[[#Liu|Liu 2014]]</ref> These two classes of material are thought to have potential [[topological quantum computing|quantum computing]] applications.<ref>[[#Bradley|Bradley 2014]]; [[#Utah|University of Utah 2014]]</ref>
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