NPG Asia Mater. 1(1) 17–21 (2009) The electronic properties of graphene and carbon nanotubes.pdf

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1、REVIEWARTICLENPGAsiaMater.1(1)17–21(2009)doi:10.1038/10.1038/asiamat.2009.1TheelectronicpropertiesofgrapheneandcarbonnanotubesTsuneyaAndo*TokyoInstituteofTechnology,JapanAbriefreviewisgivenonthecharacteristicfeaturesofelectronicstatesandtransportingrapheneconsistingofa

2、singlesheetofgraphite,anditscylinderformcalledacarbonnanotube.ElectronmotioningrapheneisequivalenttothatofaneutrinoorarelativisticDiracelectronwithvanishingrestmass.ThiscausestheappearanceofanontrivialBerry’sphaseunder2πrotationinwave-vectorspace,leadingtotheabsenceofb

3、ackscatteringandinthemetalliccarbonnanotuberesultinginperfectconductioneveninthepresenceofscatterers.TheenergybandsincarbonnanotubesaredeterminedbyperiodicboundaryconditionswithafictitiousAharonov-Bohmfluxdetermineduniquelybythecircumferentialchiralvector.Ananotubebeco

4、mesmetallicwhenthefluxvanishesandsemiconductingwhenthefluxisnonzero.TheconductivityofgrapheneisessentiallyindependentoftheFermienergyandtheelectronconcentrationaslongasvariationsineffectivescatteringstrengthareneglected,andthereforegrapheneshouldberegardedasametalrathe

5、rthanazero-gapsemiconductor.Variousschemesarenowbeingproposedandtestedforthepurposeofopeningthebandgapingraphene.hebestknowncarboncrystalisdiamond,whosehardnessandPrimitivetranslationvectorsThighdispersionoflightmakeitusefulforindustrialapplicationsArmchairandjewelry.U

6、nderambientpressuresandatroomtemperature,bhowever,themoststableformofcarbonisgraphite,whichisusedaasanindustriallubricantandasthe‘lead’inpencils.GraphiteisalayeredmaterialinwhicheachlayerconsistsofasheetofcarbonatomsAforminghexagonalstructuressimilartobenzenerings.Amon

7、olayerBLofgraphiteiscalledgraphene,andacarbonnanotubeisacylinderChiralUnitcellmadeofgraphene.vectorCarbonnanotubeswerediscoveredbySumioIijimaduringthesynthesisoffullereneC60in1991.AnanotubeexhibitsextraordinaryChiralmechanicalpropertiesthatmakeitidealforreinforcedcompo

8、sites:itηanglehasahugeYoungmodulus,isasstiffasdiamondandtheestimatedZigzagtensilestrengthismorethantentimesthatofstee