Editing Nanowire (section)

=== Non-catalytic growth ===
[[File:Nanowire growth.png|thumb|In situ observation of CuO nanowire growth]]

The vast majority of nanowire-formation mechanisms are explained through the use of catalytic nanoparticles, which drive the nanowire growth and are either added intentionally or generated during the growth. However, nanowires can be also grown without the help of catalysts, which gives an advantage of pure nanowires and minimizes the number of technological steps. The mechanisms for catalyst-free growth of nanowires (or whiskers) were known from 1950s.<ref>{{cite journal |last1=Sears |first1=G.W. |year=1955 |title=A Growth Mechanism for Mercury Whiskers |journal=Acta Metall |volume=3 |issue=4 |pages=361–366 |doi=10.1016/0001-6160(55)90041-9}}</ref>

The simplest methods to obtain metal oxide nanowires use ordinary heating of the metals, e.g. metal wire heated with battery, by [[Joule heating]] in air<ref>{{cite journal | last1 = Rackauskas | first1 = S. | last2 = Nasibulin | first2 = A. G. | last3 = Jiang | first3 = H. | last4 = Tian | first4 = Y. | last5 = Kleshch | first5 = V. I. | last6 = Sainio | first6 = J. | last7 = Obraztsova | first7 = E. D. | last8 = Bokova | first8 = S. N. | last9 = Obraztsov | first9 = A. N. | last10 = Kauppinen | first10 = E. I. | s2cid = 3529748 | year = 2010 | title = A Novel Method for Metal Oxide Nanowire Synthesis | doi = 10.1088/0957-4484/20/16/165603 | pmid = 19420573 | journal = Nanotechnology | volume = 20 | issue = 16| page = 165603 | bibcode = 2009Nanot..20p5603R }}</ref> can be easily done at home. Spontaneous nanowire formation by non-catalytic methods were explained by the [[dislocations|dislocation]] present in specific directions<ref>{{cite journal | last1 = Frank | first1 = F. C. | s2cid = 53512926 | year = 1949 | title = The influence of dislocations on crystal growth| doi = 10.1039/df9490500048 | journal = Discussions of the Faraday Society| volume = 5 | page = 48 }}</ref><ref>{{cite journal | last1 = Burton | first1 = W. K. | last2 = Cabrera | first2 = N. | last3 = Frank | first3 = F. C. | s2cid = 119643095 | year = 1951 | title = The Growth of Crystals and the Equilibrium Structure of Their Surfaces | doi = 10.1098/rsta.1951.0006 | journal = Philos. Trans. R. Soc. Lond. A | volume = 243 | issue = 866| pages = 299–358 | bibcode = 1951RSPTA.243..299B }}</ref> or the growth anisotropy of various [[crystal|crystal faces]]. Nanowires can grow by [[screw dislocation]]s<ref>{{cite journal | last1 = Morin | first1 = S. A. | last2 = Bierman | first2 = M. J. | last3 = Tong | first3 = J. | last4 = Jin | first4 = S. | s2cid = 30955349 | year = 2010 | title = Mechanism and Kinetics of Spontaneous Nanotube Growth Driven by Screw Dislocations | doi = 10.1126/science.1182977 | journal = Science | volume = 328 | issue = 5977| pages = 476–480 | pmid=20413496| bibcode = 2010Sci...328..476M }}</ref><ref>{{cite journal | last1 = Bierman | first1 = M. J. | last2 = Lau | first2 = Y. K. A. | last3 = Kvit | first3 = A. V | last4 = Schmitt | first4 = A. L. | last5 = Jin | first5 = S. | s2cid = 20919593 | year = 2008 | title = Dislocation-Driven Nanowire Growth and Eshelby Twist | doi = 10.1126/science.1157131 | pmid = 18451264 | journal = Science | volume = 320 | issue = 5879| pages = 1060–1063 | bibcode = 2008Sci...320.1060B }}</ref> or [[Twin boundary|twin boundaries]]<ref>{{cite journal | last1 = Rackauskas | first1 = S. | last2 = Jiang | first2 = H. | last3 = Wagner | first3 = J. B. | last4 = Shandakov | first4 = S. D. | last5 = Hansen | first5 = T. W. | last6 = Kauppinen | first6 = E. I. | last7 = Nasibulin | first7 = A. G. | year = 2014 | title = In Situ Study of Noncatalytic Metal Oxide Nanowire Growth | doi = 10.1021/nl502687s | pmid = 25233273 | journal = Nano Lett. | volume = 14 | issue = 10| pages = 5810–5813 | bibcode = 2014NanoL..14.5810R }}</ref> were demonstrated. The picture on the right shows a single atomic layer growth on the tip of CuO nanowire, observed by in situ [[Transmission electron microscopy|TEM microscopy]] during the non-catalytic synthesis of nanowire.

Atomic-scale nanowires can also form completely self-organised without need for defects. For example, [[Rare-earth element|rare-earth]] silicide (RESi<sub>2</sub>) nanowires of few nm width and height and several 100&nbsp;nm length form on silicon([[Miller index|001]]) substrates which are covered with a sub-monolayer of a rare earth metal and subsequently annealed.<ref>{{Cite journal |last1=Preinesberger |first1=C. |last2=Becker |first2=S. K. |last3=Vandré |first3=S. |last4=Kalka |first4=T. |last5=Dähne |first5=M. |date=February 2002 |title=Structure of DySi2 nanowires on Si(001) |url=http://aip.scitation.org/doi/10.1063/1.1430540 |journal=Journal of Applied Physics |language=en |volume=91 |issue=3 |pages=1695–1697 |doi=10.1063/1.1430540 |bibcode=2002JAP....91.1695P |issn=0021-8979}}</ref> The lateral dimensions of the nanowires confine the electrons in such a way that the system resembles a (quasi-)one-dimensional metal.<ref>{{Cite journal |last1=Holtgrewe |first1=Kris |last2=Appelfeller |first2=Stephan |last3=Franz |first3=Martin |last4=Dähne |first4=Mario |last5=Sanna |first5=Simone |date=2019-06-10 |title=Structure and one-dimensional metallicity of rare-earth silicide nanowires on Si(001) |url=https://link.aps.org/doi/10.1103/PhysRevB.99.214104 |journal=Physical Review B |language=en |volume=99 |issue=21 |pages=214104 |doi=10.1103/PhysRevB.99.214104 |bibcode=2019PhRvB..99u4104H |s2cid=197525473 |issn=2469-9950}}</ref>  Metallic RESi<sub>2</sub> nanowires form on silicon(''[[Miller index|hhk]]'') as well. This system permits tuning the dimensionality between two-dimensional and one-dimensional by the coverage and the tilt angle of the substrate.<ref>{{Cite journal |last1=Appelfeller |first1=Stephan |last2=Holtgrewe |first2=Kris |last3=Franz |first3=Martin |last4=Freter |first4=Lars |last5=Hassenstein |first5=Christian |last6=Jirschik |first6=Hans-Ferdinand |last7=Sanna |first7=Simone |last8=Dähne |first8=Mario |date=2020-09-24 |title=Continuous crossover from two-dimensional to one-dimensional electronic properties for metallic silicide nanowires |url=https://link.aps.org/doi/10.1103/PhysRevB.102.115433 |journal=Physical Review B |language=en |volume=102 |issue=11 |pages=115433 |doi=10.1103/PhysRevB.102.115433 |bibcode=2020PhRvB.102k5433A |s2cid=224924918 |issn=2469-9950}}</ref>