View source for Graphane

{{distinguish|Grapheme|Graphene|Graphyne}}
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'''Graphane''' is a two-dimensional [[polymer]] of [[carbon]] and [[hydrogen]] with the [[formula unit]] (CH)<sub>n</sub> where ''n'' is large.<ref name="sofo2007" /> Partial hydrogenation results in hydrogenated graphene, which was reported by Elias et al. in 2009 by a [[Transmission electron microscopy|TEM]] study to be "direct evidence for a new graphene-based derivative". The authors viewed the panorama as "a whole range of new two-dimensional crystals with designed electronic and other properties". With the band gap ranges from 0 to 0.8 eV<ref name=elias09>{{cite journal|title =Control of Graphene's Properties by Reversible Hydrogenation: Evidence for Graphane| journal = Science|year =2009|volume = 323| doi = 10.1126/science.1167130| pmid= 19179524| issue= 5914| bibcode=2009Sci...323..610E| pages= 610–3|arxiv = 0810.4706 |display-authors=etal| last1 = Elias| first1 = D. C.| last2 = Nair| first2 = R. R.| last3 = Mohiuddin| first3 = T. M. G.| last4 = Morozov| first4 = S. V.| last5 = Blake| first5 = P.| last6 = Halsall| first6 = M. P.| last7 = Ferrari| first7 = A. C.| last8 = Boukhvalov| first8 = D. W.| last9 = Katsnelson| first9 = M. I.| last10 = Geim| first10 = A. K.| last11 = Novoselov| first11 = K. S.| s2cid = 3536592}}</ref>
==Synthesis==
Its preparation was reported in 2009.<ref name=elias09/> Graphane can be formed by electrolytic hydrogenation of graphene, few-layer graphene or high-oriented [[pyrolytic graphite]]. In the last case mechanical exfoliation of hydrogenated top layers can be used.<ref name="ilyin11">{{cite journal|last1=Ilyin |first1=A. M. |last2=Guseinov |first2=N. R. |last3=Tsyganov |first3=I. A. |last4=Nemkaeva |first4=R. R. |title =Computer simulation and experimental study of graphane-like structures formed by electrolytic hydrogenation| journal=[[Physica (journal)#Physica E: Low-dimensional Systems and Nanostructures|Physica E]]|year=2011|volume=43|doi=10.1016/j.physe.2011.02.012|issue=6|pages=1262–1265|bibcode=2011PhyE...43.1262I|display-authors=etal}}</ref>
==Structure==
The first theoretical description of graphane was reported in 2003.<ref name=sluiter03>{{cite journal | last1 = Sluiter | first1 = Marcel | last2 = Kawazoe | first2 = Yoshiyuki | title = Cluster expansion method for adsorption: Application to hydrogen chemisorption on graphene | journal = Physical Review B | volume = 68 | page = 085410 | year = 2003 | doi = 10.1103/PhysRevB.68.085410|bibcode = 2003PhRvB..68h5410S | issue = 8 }}</ref> The structure was found, using a cluster expansion method, to be the most stable of all the possible hydrogenation ratios of graphene.<ref name=sluiter03/> In 2007, researchers found that the compound is more stable than other compounds containing carbon and hydrogen, such as [[benzene]], [[cyclohexane]] and [[polyethylene]].<ref name="sofo2007">{{cite journal |last1=Sofo |first1=Jorge O. |last2=Chaudhari |first2=Ajay S. |last3=Barber |first3=Greg D. |year=2007 |title=Graphane: A two-dimensional hydrocarbon |journal=[[Physical Review B]] |volume=75 |issue=15 |pages=153401 |arxiv=cond-mat/0606704 |bibcode=2007PhRvB..75o3401S |doi=10.1103/PhysRevB.75.153401|s2cid=101537520 }}</ref> This group named the predicted compound graphane, because it is the fully saturated version of graphene.
[[File:Boat and chair conformers of graphane.png|thumb|714x714px|Boat and chair conformers of graphane]]
Graphane is effectively made up of cyclohexane units, and, in parallel to cyclohexane, the most stable structural conformation is not planar, but an out-of-plane structure, including the chair and boat conformers, in order to minimize ring strain and allow for the ideal tetrahedral bond angle of 109.5° for sp<sup>3</sup>-bonded atoms. However, in contrast to cyclohexane, graphane cannot interconvert between these different conformers because not only are they topologically different, but they are also different structural isomers with different configurations. The chair conformer has the hydrogens alternating above or below the plane from carbon to neighboring carbon, while the boat conformer has the hydrogen atoms alternating in pairs above and below the plane. There are also other possible conformational isomers, including the twist-boat and twist-boat-chair. As with cyclohexane, the most stable conformer for graphane is the chair, followed by the twist-boat structure.<ref>{{Cite journal |last1=Pumera |first1=Martin |last2=Wong |first2=Colin Hong An |date=2013 |title=Graphane and hydrogenated graphene |url=http://xlink.rsc.org/?DOI=c3cs60132c |journal=Chemical Society Reviews |language=en |volume=42 |issue=14 |pages=5987–5995 |doi=10.1039/c3cs60132c |pmid=23686139 |issn=0306-0012|url-access=subscription }}</ref><ref name="Samarakoon2009">{{Cite journal |last1=Samarakoon |first1=Duminda K. |last2=Wang |first2=Xiao-Qian |date=2009-12-22 |title=Chair and Twist-Boat Membranes in Hydrogenated Graphene |url=https://pubs.acs.org/doi/10.1021/nn901317d |journal=ACS Nano |language=en |volume=3 |issue=12 |pages=4017–4022 |doi=10.1021/nn901317d |pmid=19947580 |issn=1936-0851}}</ref> While the buckling of the chair conformer would imply lattice shrinkage,<ref name="Samarakoon2009" /> calculations show the lattice actually expands by approximately 30%<ref name="Zhou2014">{{Cite journal |last1=Zhou |first1=Chao |last2=Chen |first2=Sihao |last3=Lou |first3=Jianzhong |last4=Wang |first4=Jihu |last5=Yang |first5=Qiujie |last6=Liu |first6=Chuanrong |last7=Huang |first7=Dapeng |last8=Zhu |first8=Tonghe |date=2014-01-13 |title=Graphene's cousin: the present and future of graphane |journal=Nanoscale Research Letters |volume=9 |issue=1 |pages=26 |doi=10.1186/1556-276X-9-26 |issn=1556-276X |pmc=3896693 |pmid=24417937 |doi-access=free }}</ref> due to the opposing effect on the lattice spacing of the longer carbon-carbon (C-C) bonds, as the sp<sup>3</sup>-bonding of graphane yields longer C-C bonds of 1.52 Å compared to the sp<sup>2</sup>-bonding of graphene which yields shorter C-C bonds of 1.42 Å.<ref name="Zhou2014" /> As just established, theoretically if graphane was perfect and everywhere in its stable chair conformer, the lattice would expand; however, the existence of domains where the locally stable twist-boat conformer dominates “contribute to the experimentally observed lattice contraction.”<ref name="Samarakoon2009" /> When experimentalists have characterized graphane, they have found a distribution of lattice spacings, corresponding to different domains exhibiting different conformers.<ref name="Samarakoon2009" /> Any disorder in hydrogenation conformation tends to contract the lattice constant by about 2.0%.<ref name="Graphane_lattice">{{Cite journal |last1=Feng Huang |first1=Liang |last2=Zeng |first2=Zhi |year=2013 |title=Lattice dynamics and disorder-induced contraction in functionalized graphene |journal=[[Journal of Applied Physics]] |volume=113|issue=8 |page=083524<!-- --> |bibcode=2013JAP...113h3524F |doi=10.1063/1.4793790}}</ref>
Graphane is an insulator. Chemical functionalization of graphene with hydrogen may be a suitable method to open a band gap in graphene.<ref name="sofo2007" /> P-doped graphane is proposed to be a [[high-temperature superconductor|high-temperature]] [[BCS theory]] [[superconductor]] with a T<sub>c</sub> above 90 [[kelvin|K]].<ref name="savini10">{{Cite journal |last1=Savini |first1=G. |last2=Ferrari |first2=A. C. |last3=Giustino |first3=F. |year=2010 |title=First-principles prediction of doped graphane as a high-temperature electron-phonon superconductor |journal=[[Physical Review Letters]] |volume=105 |issue=3 |pages=037002 |arxiv=1002.0653 |bibcode=2010PhRvL.105c7002S |doi=10.1103/PhysRevLett.105.037002 |pmid=20867792 |s2cid=118466816}}</ref>
==Variants==
Partial hydrogenation leads to hydrogenated graphene rather than (fully hydrogenated) graphane.<ref name="elias09" /> Such compounds are usually named as "graphane-like" structures. Graphane and graphane-like structures can be formed by electrolytic hydrogenation of graphene or few-layer graphene or high-oriented [[pyrolytic graphite]]. In the last case mechanical exfoliation of hydrogenated top layers can be used.<ref name="ilyin11" />
Hydrogenation of graphene on substrate affects only one side, preserving hexagonal symmetry. One-sided hydrogenation of graphene is possible due to the existence of ripplings. Because the latter are distributed randomly, the obtained material is disordered in contrast to two-sided graphane.<ref name="elias09" /> Annealing allows the hydrogen to disperse, reverting to graphene.<ref>{{cite journal |last=Novoselov |first=Konstantin Novoselov |year=2009 |title=Beyond the wonder material |journal=[[Physics World]] |volume=22 |issue=8 |pages=27–30 |bibcode=2009PhyW...22h..27N |doi=10.1088/2058-7058/22/08/33}}</ref> Simulations revealed the underlying kinetic mechanism.<ref name="Graphane_kinetics">{{Cite journal |last1=Huang |first1=Liang Feng |last2=Zheng |first2=Xiao Hong |last3=Zhang |first3=Guo Ren |last4=Li |first4=Long Long |last5=Zeng |first5=Zhi |year=2011 |title=Understanding the Band Gap, Magnetism, and Kinetics of Graphene Nanostripes in Graphane |journal=[[Journal of Physical Chemistry C]] |volume=115 |issue=43 |pages=21088–21097 |doi=10.1021/jp208067y}}</ref>
==Potential applications==
p-Doped graphane is postulated to be a [[high-temperature superconductor|high-temperature]] [[BCS theory]] [[superconductor]] with a T<sub>c</sub> above 90 [[kelvin|K]].<ref name=savini10/>
Graphane has been proposed for hydrogen storage.<ref name="sofo2007" /> Hydrogenation decreases the dependence of the [[lattice constant]] on temperature, which indicates a possible application in precision instruments.<ref name="Graphane_lattice"/>
==References==
{{reflist|30em}}
==External links==
* [http://nanotechweb.org/cws/article/lab/43687 Sep 14, 2010 Hydrogen vacancies induce stable ferromagnetism in graphane] {{Webarchive|url=https://web.archive.org/web/20101127062429/http://nanotechweb.org/cws/article/lab/43687 |date=November 27, 2010 }}
* [http://www.nanowerk.com/news/newsid=16427.php May 25, 2010 Graphane yields new potential]
* [http://www.technologyreview.com/blog/arxiv/24769/ May 02 2010 Doped Graphane Should Superconduct at 90K]
[[Category:Two-dimensional nanomaterials]]
[[Category:Polymers]]
[[Category:Superconductors]]
[[Category:Hydrocarbons]]