# Germanene

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{{Short description|Bi-dimensional crystalline structure of germanium}}
{{Use dmy dates|date=March 2017}}
[[File:Germanene microscopy.jpg|thumb|upright=1.5|(a) [STM](/source/Scanning_tunneling_microscope) image of germanene. (b) Profile (black line in (a)) showing step heights of ~3.2  Å. (c) High-resolution STM image (distorted by sample drift). (d) Profiles along the white continuous and dashed lines in (c) showing a ~9–10  Å separation between protrusions having heights of ~0.2  Å. (e) [Electron diffraction](/source/Electron_diffraction) pattern. (f) Model of germanene on Au(111).<ref>{{cite journal|doi=10.1038/srep20714|pmid=26860590|pmc=4748270|title=Few layer epitaxial germanene: A novel two-dimensional Dirac material|journal=Scientific Reports|volume=6|article-number=20714|year=2016|last1=Dávila|first1=María Eugenia|last2=Le Lay|first2=Guy|bibcode=2016NatSR...620714D}}</ref>]]
'''Germanene''' is a material made up of a single layer of [germanium](/source/germanium) atoms.<ref name=phys2014>{{cite news|title=Graphene gets a 'cousin' in the shape of germanene|url=http://phys.org/news/2014-09-graphene-cousin-germanene.html|date=10 September 2014|work=Phys.org|publisher=Institute of Physics}}</ref> The material is created in a process similar to that of [silicene](/source/silicene) and [graphene](/source/graphene), in which high vacuum and high temperature are used to deposit a layer of germanium atoms on a substrate.<ref name=phys2014 /><ref>{{cite journal | title=Continuous germanene layer on Al (111) | author=Derivaz, Mickael and Dentel, Didier and Stephan, Regis and Hanf, Marie-Christine and Mehdaoui, Ahmed and Sonnet, Philippe and Pirri, Carmelo | journal=Nano Letters | volume=15 | number=4 | pages=2510–2516
 | year=2015 | publisher=ACS Publications | doi=10.1021/acs.nanolett.5b00085 | pmid=25802988 | bibcode=2015NanoL..15.2510D }}</ref><ref>{{Cite journal
| doi = 10.1002/adma.201400909 | pmid = 24841358 
| volume = 26 | issue = 28 | pages = 4820–4824
| last = Li | first = Linfei
| author2 = Shuang-zan Lu
| author3 = Jinbo Pan
| author4 = Zhihui Qin
| author5 = Yu-qi Wang
| author6 = Yeliang Wang
| author7 = Geng-yu Cao
| author8 = Shixuan Du
| author9 = Hong-Jun Gao
| title = Buckled Germanene Formation on Pt(111)
| journal = Advanced Materials
| date = 2014| bibcode = 2014AdM....26.4820L 
| s2cid = 1951633 
}}</ref> High-quality thin films of germanene have revealed unusual two-dimensional structures with novel electronic properties suitable for semiconductor device applications and [materials science](/source/materials_science) research.

==Preparation and structure==
In September 2014, G. Le Lay and others reported the deposition of a single atom thickness, ordered and two-dimensional multi-phase film by [molecular beam epitaxy](/source/molecular_beam_epitaxy) upon a [gold](/source/gold) surface in a [crystal lattice](/source/crystal_lattice) with [Miller indices](/source/Miller_indices) (111). The structure was confirmed with [scanning tunneling microscopy](/source/scanning_tunneling_microscopy) (STM) revealing a nearly flat honeycomb structure.<ref name=Lay2014>{{Cite journal
| doi = 10.1088/1367-2630/16/9/095002 
| volume = 16 | issue = 9 | article-number = 095002
| last = Dávila | first = M. E.
| title = Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene
| journal = New Journal of Physics
| date = 2014
| bibcode = 2014NJPh...16i5002D | arxiv = 1406.2488| s2cid = 53453703 }}</ref> 
{{quote|We have provided compelling evidence of the birth of nearly flat germanene—a novel, synthetic germanium allotrope which does not exist in nature. It is a new cousin of graphene.|Guy Le Lay from [Aix-Marseille University](/source/Aix-Marseille_University)| New Journal of Physics}}

Additional confirmation was obtained by spectroscopic measurement and [density functional theory](/source/density_functional_theory) calculations. The development of high quality and nearly flat single atom films created speculation that germanene may replace [graphene](/source/graphene) if not merely add an alternative to the novel properties of related nanomaterials.<ref name=phys2014 /><ref name=Lay2014 /><ref>{{Cite web
| title = Aix-Marseille University Researchers Produce Germanium Allotrope Germanene
| date = 10 September 2014
| author = Clifford, Jonathan
| url = http://uncovercalifornia.com/content/21548-aix-marseille-university-researchers-produce-germanium-allotrope-germanene
| publisher = Uncover California Online Media
| access-date = 11 September 2014
| archive-date = 17 February 2020
| archive-url = https://web.archive.org/web/20200217161618/http://uncovercalifornia.com/content/21548-aix-marseille-university-researchers-produce-germanium-allotrope-germanene
}}</ref><ref>{{Cite web
| title = Gold Substrate Used To Synthesize Graphene's Cousin Germanene
| access-date = 11 September 2014
| url = http://www.capitalotc.com/gold-substrate-used-to-synthesize-graphenes-cousin-germanene/22073/
| publisher = Capital OTC
| date = 2014-09-10
| archive-date = 11 September 2014
| archive-url = https://web.archive.org/web/20140911182409/http://www.capitalotc.com/gold-substrate-used-to-synthesize-graphenes-cousin-germanene/22073/
| url-status = usurped
}}</ref><ref>{{Cite news
| title = Germanene: Have scientists just created the new graphene?
| date = 10 September 2014|author=Spickernell, Sarah 
| url = http://www.cityam.com/1410362513/germanene-europes-answer-super-material-graphene
| newspaper= City A.M.
}}</ref><ref>{{Cite web | title = New Member In The Family 'Germanene' | date = 10 September 2014 | author = Leathers, Jason | url = http://www.capitalwired.com/new-member-in-the-family-germanene/22038/ | work = Capital Wired | access-date = 11 September 2014 | archive-date = 3 June 2016 | archive-url = https://web.archive.org/web/20160603105117/http://www.capitalwired.com/new-member-in-the-family-germanene/22038/ }}</ref>

Bampoulis and others<ref name=Bampoulis2014>{{Cite journal
| doi = 10.1088/0953-8984/26/44/442001
| volume = 26| issue = 44| article-number = 442001 
| last = Bampoulis| first = P. | author2 = Zhang, L.| author3 =Safaei, A.| author4 =van Gastel, R.| author5 =Poelsema, B.| author6 = Zandvliet, H. J. W.
| title = Germanene termination of Ge<sub>2</sub>Pt crystals on Ge(110)
| journal = Journal of Physics: Condensed Matter
| date = 2014| pmid=25210978
| bibcode = 2014JPCM...26R2001B| arxiv = 1706.00697| s2cid = 36478002}}</ref> have reported the formation of germanene on the outermost layer of Ge<sub>2</sub>Pt nanocrystals. Atomically resolved STM images of germanene on Ge<sub>2</sub>Pt nanocrystals reveal a buckled honeycomb structure. This honeycomb lattice is composed of two hexagonal sublattices displaced by 0.2 Å in the vertical direction with respect to each other. The nearest-neighbor distance was found to be 2.5±0.1 Å, in close agreement with the Ge-Ge distance in germanene.

Based on STM observations and density functional theory calculations, formation of an apparently more distorted form of germanene has been reported on [platinum](/source/platinum).<ref name=Lay2014 /><ref>{{Cite journal
| doi = 10.1002/adma.201400909 | pmid = 24841358 
| volume = 26 | issue = 28 | pages = 4820–4824
| last = Li | first = Linfei
| author2 = Shuang-zan Lu
| author3 = Jinbo Pan
| author4 = Zhihui Qin
| author5 = Yu-qi Wang
| author6 = Yeliang Wang
| author7 = Geng-yu Cao
| author8 = Shixuan Du
| author9 = Hong-Jun Gao
| title = Buckled Germanene Formation on Pt(111)
| journal = Advanced Materials
| date = 2014| bibcode = 2014AdM....26.4820L 
| s2cid = 1951633 
}}</ref> Epitaxial growth of germanene crystals on [GaAs](/source/Gallium_arsenide)(0001) has also been demonstrated, and calculations suggest that the minimal interactions should allow germanene to be readily removed from this substrate.<ref>{{Cite journal | doi = 10.1063/1.4830016| title = Weak interaction between germanene and GaAs(0001) by H intercalation: A route to exfoliation| journal = Journal of Applied Physics| volume = 114| issue = 18| pages = 184307–184307–4| date = 13 November 2013| last1 = Kaloni | first1 = T. P.| last2 = Schwingenschlögl | first2 = U.| url = https://www.scienceopen.com/document/vid/9b823c3f-05fe-4d0d-a6d6-7ffb519a82ca| bibcode = 2013JAP...114r4307K| arxiv = 1310.7688}}</ref>

Germanene's structure is described as "a group-IV graphene-like two-dimensional buckled [nanosheet](/source/nanosheet)".<ref name=Ye2014>{{Cite journal
| doi = 10.1039/C4RA01802H
| volume = 4 | issue = 41 | pages = 21216–21220
| last = Ye | first = Xue-Sheng | author2 = Zhi-Gang Shao | author3 = Hongbo Zhao | author4 = Lei Yang | author5 = Cang-Long Wang
| title = Intrinsic carrier mobility of germanene is larger than graphene's: first-principle calculations
| journal = RSC Advances
| date = 2014
| bibcode = 2014RSCAd...421216Y }}</ref> Adsorption of additional germanium onto the graphene-like sheet leads to formation of "[dumbbell](/source/dumbbell)" units, each with two out-of-plane atoms of germanium, one on either side of the plane. Dumbbells attract each other. Periodically repeating arrangements of dumbbell structures may lead to additional stable phases of germanene, with altered electronic and magnetic properties.<ref name=Ciraci2014>{{Cite journal
| doi = 10.1021/jz500977v
| pmid = 26277965
| volume = 5
| issue = 15
| pages = 2694–2699
| last = Özçelik
| first = V. Ongun
| author2 = E. Durgun
| author3 = Salim Ciraci
| title = New Phases of Germanene
| journal = The Journal of Physical Chemistry Letters
| date = 2014
| arxiv = 1407.4170
| s2cid = 40693268
}}</ref>

In October 2018, Junji Yuhara and others reported that germanene is easily prepared by a segregation method, using a bare Ag [thin film](/source/thin_film) on a Ge substrate and achieved in situ its epitaxial growth.<ref name="Postgraphene">{{Cite journal|last=Yuhara|first=Junji|author2=Hiroki Shimazu|author3=Kouichi Ito|author4=Akio Ohta|author5=Masaaki Araidai|author6=Masashi Kurosawa|author7=Masashi Nakatake|author8=Guy Le Lay|date=2018|title=Germanene Epitaxial Growth by Segregation through Ag(111) Thin Films on Ge(111)|journal=ACS Nano|volume=12|issue=11|pages=11632–11637|doi=10.1021/acsnano.8b07006|pmid=30371060|bibcode=2018ACSNa..1211632Y |s2cid=53102735 }}</ref> The growth of germanene, akin to graphene and silicene, by a segregation method, is considered to be technically very important for the easy synthesis and transfer of this highly promising 2D electronic material.

==Properties==
Germanene's electronic and optical properties have been determined from ''[ab initio](/source/ab_initio)'' calculations,<ref name=Ni2014>{{Cite journal
| doi = 10.1021/nl203065e | pmid = 22050667
| volume = 12 | issue = 1 | pages = 113–118
| last1 = Ni | first1 = Zeyuan | last2= Qihang |first2=Liu
| last3 = Tang | first3 = Kechao | last4 = Zheng | first4 = Jiaxin
| last5 = Zhou | first5 = Jing | last6 = Qin | first6 = Rui
| last7 = Gao | first7 = Zhengxiang | last8 = Yu | first8 = Dapeng
| last9 = Lu | first9 = Jing 
| title = Tunable Bandgap in Silicene and Germanene
| journal = Nano Letters
| date = 2012
| bibcode = 2012NanoL..12..113N
}}</ref> and structural and electronic properties from first principles.<ref name=Scalise2014>{{Cite journal
| doi = 10.1007/s12274-012-0277-3 
| volume = 6 | issue = 1 | pages = 19–28
| last = Scalise | first = Emilio
| author2 = Michel Houssa
| author3 = Geoffrey Pourtois
| author4 = B. van den Broek
| author5 = Valery Afanas'ev
| author6 = André Stesmans
| title = Vibrational properties of silicene and germanene
| journal = Nano Research
| date = 2013
| s2cid = 137641923 }}</ref><ref>{{cite journal|last1=Garcia|first1=J. C.|last2=de Lima|first2=D. B.|last3=Assali|first3=L. V. C.|last4=Justo|first4=J. F.|title=Group IV graphene- and graphane-like nanosheets|journal=J. Phys. Chem. C|date=2011|volume=115|issue=27|pages=13242–13246|doi=10.1021/jp203657w|arxiv=1204.2875|s2cid=98682200}}</ref> These properties make the material suitable for use in the channel of a high-performance [field-effect transistor](/source/field-effect_transistor)<ref name=Kaneko2014>{{Cite journal
| doi = 10.7567/APEX.7.035102 
| volume = 7 | issue = 3 | article-number = 035102
| last1 = Kaneko | first1 = Shiro | first2 = Hideaki |last2=Tsuchiya
| last3 = Kamakura | first3 = Yoshinari | last4 = Mori | first4 = Nobuya | last5 = Ogawa | first5 = Matsuto
| title = Theoretical performance estimation of silicene, germanene, and graphene nanoribbon field-effect transistors under ballistic transport
| journal = Applied Physics Express
| date = 2014
| bibcode = 2014APExp...7c5102K
| s2cid = 95179181 }}</ref> and have generated discussion regarding the use of elemental monolayers in other electronic devices.<ref>{{Cite journal
| doi = 10.1021/am501022x | pmid = 24724967
| volume = 6 | issue = 10 | pages = 7743–7750
| last = Roome | first = Nathanael J. | author2 = J. David Carey
| title = Beyond graphene: stable elemental monolayers of silicene and germanene
| journal = ACS Applied Materials & Interfaces
| date = 2014
| bibcode = 2014AAMI....6.7743R
| url = http://epubs.surrey.ac.uk/805581/1/ACS%20AMI%206%20-%20Beyond%20Graphene%202014%20-%20final.pdf
}}</ref> The electronic properties of germanene are unusual, and provide a rare opportunity to test the properties of [Dirac fermion](/source/Dirac_fermion)s.<ref>{{Cite journal
| doi = 10.1038/nphys2379 
| volume = 8 | issue = 9 | pages = 653–657
| last1 = Wang | first1 = Yang | first2 = Victor W. |last2=Brar
| last3 = Shytov | first3 = Andrey V. | last4 = Wu | first4 = Qiong
| last5 = Regan | first5 = William | last6 = Tsai | first6 = Hsin-Zon
| last7 = Zettl | first7 = Alex |author7-link=Alex Zettl | last8 = Levitov | first8 = Leonid S.
| last9 = Crommie | first9 = Michael F. 
| title = Mapping Dirac quasiparticles near a single Coulomb impurity on graphene
| journal = Nature Physics
| date = 2012
| bibcode = 2012NatPh...8..653W
| arxiv = 1205.3206| s2cid = 18586002 }}</ref><ref name=Matthes2014>{{Cite journal
| doi = 10.1088/0953-8984/25/39/395305 | pmid = 24002054
| bibcode = 2013JPCM...25M5305M
| volume = 25 | issue = 39 | article-number = 395305
| last1 = Matthes | first1 = Lars
| last2 = Pulci | first2=Olivia 
| last3 = Bechstedt | first3 = Friedhelm
| title = Massive Dirac quasiparticles in the optical absorbance of graphene, silicene, germanene, and tinene
| journal = Journal of Physics: Condensed Matter
| date = 2013
| s2cid = 43075284
}}</ref> Germanene has no [band gap](/source/band_gap), but attaching a hydrogen atom to each germanium atom creates one.<ref>{{Cite web|title = Beyond Graphene, a Zoo of New 2-D Materials|url = http://blogs.discovermagazine.com/crux/2015/07/17/beyond-graphene/#.Vane-PlVhBe|publisher = Discover Magazine|first = Andy|last = Berger|date = 17 July 2015|access-date = 19 September 2015|archive-date = 1 November 2019|archive-url = https://web.archive.org/web/20191101062332/http://blogs.discovermagazine.com/crux/2015/07/17/beyond-graphene/#.Vane-PlVhBe}}</ref> These unusual properties are generally shared by [graphene](/source/graphene), [silicene](/source/silicene), germanene, [stanene](/source/stanene), and [plumbene](/source/plumbene).<ref name=Matthes2014 /><ref>{{cite journal | first1 = F. | last1 = Zhu | first2 = J. | last2 = Jia | year = 2015 | title = Epitaxial growth of two-dimensional stanene | journal = Nature Materials | volume = 14 | issue = 10 | pages = 1020–1025 | doi = 10.1038/nmat4384| pmid = 26237127 | arxiv = 1506.01601 | bibcode = 2015NatMa..14.1020Z | s2cid = 18643958 }}</ref><ref>{{cite journal | first1 = J. | last1 = Yuhara | first2 = Y. | last2 = Fujii | first3 = G. | last3 = Le Lay | year = 2018 | title = Large Area Planar Stanene Epitaxially Grown on Ag(111) | journal = 2D Materials | volume = 5 | issue = 2 | page = 025002 | doi = 10.1088/2053-1583/aa9ea0| doi-access = free | bibcode = 2018TDM.....5b5002Y | hdl = 21.11116/0000-0001-A92C-0 | hdl-access = free }}</ref><ref>{{Cite journal | first1=J. | last1=Yuhara | first2=B. | last2=He | first3 = G. | last3 = Le Lay | title= Graphene's Latest Cousin: Plumbene Epitaxial Growth on a "Nano WaterCube"|journal= Advanced Materials |volume = 31|issue = 27|article-number = 1901017|year=2019 | doi=10.1002/adma.201901017 | pmid= 31074927 | bibcode=2019AdM....3101017Y | s2cid=149446617 }}</ref>

==References==
{{Reflist|colwidth=30em}}

==External links==
{{Commons category|Germanene}}
*[http://www.science20.com/news_articles/meet_graphenes_sexy_new_cousin_germanene-144557 Meet Graphene's Sexy New Cousin Germanene]
*[https://web.archive.org/web/20140913022354/http://www.designntrend.com/articles/19324/20140910/scientists-use-gold-substrate-to-grow-graphenes-cousin-germanene.htm Scientists Use Gold Substrate to Grow Graphene's Cousin, Germanene]
*[http://www.newsledge.com/graphene-exciting-germanene-makes-appearance-9428 Graphene Family Tree? Germanene Makes Its Appearance]
*{{Cite journal|title = Quantum Spin Hall Effect in Silicene and Two-Dimensional Germanium|journal = Physical Review Letters|date = 1 January 2011|volume = 107|issue = 7|article-number = 076802|doi = 10.1103/PhysRevLett.107.076802|pmid = 21902414|first = Cheng-Cheng|last = Liu|bibcode = 2011PhRvL.107g6802L|arxiv = 1104.1290|s2cid = 16967564}}
*{{Cite journal|title = Low-energy effective Hamiltonian involving spin-orbit coupling in silicene and two-dimensional germanium and tin|journal = Physical Review B|date = 1 January 2011|volume = 84|issue = 19|article-number = 195430|doi = 10.1103/PhysRevB.84.195430|first = Cheng-Cheng|last = Liu|bibcode = 2011PhRvB..84s5430L|arxiv = 1108.2933|s2cid = 44216872}}
*[https://archives.cnrs.fr/inc/article/193 CNRS Website (2015)] {{Webarchive|url=https://web.archive.org/web/20210414164347/https://archives.cnrs.fr/inc/article/193 |date=14 April 2021 }}
*[https://inc.cnrs.fr/fr/cnrsinfo/un-nouveau-cristal-2d-sur-le-point-detre-isole CNRS Website (2017)]

Category:Germanium
Category:Allotropes
Category:Group IV semiconductors
Category:Two-dimensional nanomaterials
Category:2014 in science
Category:Substances discovered in the 2010s

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Adapted from the Wikipedia article [Germanene](https://en.wikipedia.org/wiki/Germanene) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Germanene?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.