Honeycomb Carbon A Review of Graphene 石墨烯综述(4)

纳米材料在生物医学中的应用

HoneycombCarbon:AReviewofGrapheneChemicalReviews,2010,Vol.110,No.1

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Figure3.Scanningelectronmicrographsofnaturalgraphitebefore(a)andafter(b)expansionbyacidintercalationandthermalshock.(ReprintedwithpermissionbyTheRoyalSocietyofChemistryfromref60.)

Figure4.Scanningelectronmicroscopeimagesofearlyattemptsatmechanicalexfoliationusinggraphitepillars.(aandb)Ruoff’sgrouppeeledawaylayerswithanAFMtip.(Reprintedwithpermissionfromref1.Copyright1999InstituteofPhysics.)(candd)Kim’sgrouptransferredthepillarstoatiplesscantileveranddepositedthinslabsontoothersubstratesintappingmode.AseriesofscanningelectronmicroscopeimagesshowthinsamplescleavedontotheSi/SiO2substrateandatypicalmesoscopicdevice.(Reprintedwithpermissionfromref68.Copyright2005AmericanInstituteofPhysics.)

sample(seeFigure1).Althoughthe akespresentonthetapearemuchthickerthanonelayer,vanderWaalsattractiontothesubstratecandelaminateasinglesheetwhenthetapeisthenliftedaway.Themethodrequiresagreatdealofpatience,asdepositionsputdownbyinexperiencedscientistsareoftenamessofthickslabsinwhichlocatingasinglelayercanbeextremelydif cult.Withpractice,thetechniqueresultsinhigh-qualitycrystallites,whichcanbemorethan100µm2insize.

Perhapsthemostimportantpartofisolatingsinglelayergrapheneforthe rsttimewastheabilitytospotanatomicallythinspecimeninsomereadilyidenti ablefashion.Opticalabsorbanceofgraphenehassincebeenmeasuredatjust2.3%,rulingoutdirectvisualobservation(seeFigure6).70,71Inordertovisualizesingle akes,theManchestergrouptookadvantageofaninterferenceeffectataspeciallychosenthickness(300nm)ofSiO2onSitoenhancetheopticalcontrastunderwhite-lightillumination.72Althoughseeminglyasimpleidea,thiswasamajorstepforwardandhascontributedagreatdealtowardprogressinthis eld.

Figure5.Mechanicalexfoliationproducedthevery rstsinglelayergraphene akes.(a)Anatomicforcemicroscopyimageshowsthesubstrate-graphenestepheightof<1nmandafoldedstepheightof0.4nm.(Reprintedwithpermissionfromref9.Copyright2005PNAS.)(b)TEMimageofafree-standinggraphene lmafteretchingoftheunderlyingsubstrate.[ReprintedwithpermissionfromNature(),ref6.Copyright2007NaturePublishingGroup.]