Editing Electron (section)

=== Confinement of individual electrons ===
Individual electrons can now be easily confined in ultra small ({{nowrap|1=''L'' = 20 nm}}, {{nowrap|1=''W'' = 20 nm}}) CMOS transistors operated at cryogenic temperature over a range of about 4&nbsp;[[kelvin|K]] (−269&nbsp;°C) to 15&nbsp;[[kelvin|K]] (−258&nbsp;°C).<ref>
{{cite journal
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 | journal = Nanotechnology
 | volume = 23 | issue = 21 | pages = 215204
 | year = 2012
 | doi = 10.1088/0957-4484/23/21/215204
 | pmid =  22552118 |arxiv = 1203.4811
 | bibcode = 2012Nanot..23u5204P | citeseerx = 10.1.1.756.4383 | s2cid = 206063658
}}</ref> The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in the single particle formalism, by replacing its mass with the [[effective mass (solid-state physics)|effective-mass tensor]].