Peashell-like Nanostructure — A New Kind of One-dimensional

http://www.77cn.com.cn/chemcomm|ChemComm

Peashell-likenanostructure—anewkindofone-dimensionalnanostructure:thecaseofmagnesiumoxidew

JunLiu,abWenjunWang,aZaipingGuo,bRongZeng,bShixueDoubandXiaolongChen*a

Received1stMarch2010,Accepted12thApril2010

FirstpublishedasanAdvanceArticleontheweb6thMay2010DOI:10.1039/c0cc00167h

Anoveltypeof1Dnanostructurewithcharacteristicsbetweenthoseofasolidnanowireandahollownanotube,i.e.apeashell-likenanostructurecomprisinga1Dwirewithperiodicallyembeddedhollownanobubbles,ispresentedforthe rsttime;asanexample,MgOpeashell-likenanostructuresexhibitextraordinarydielectricandmagnetizationproperties.Sincecarbonnanotubeswerediscovered,1alargenumberoftraditionalbulkmaterialshavebeenfoundtoformone-dimensional(1D)nanostructures(suchassolidnanowiresandhollownanotubes),andtoexhibitinteresting1D-nanostructure-inducedpropertieswhichhaveledto1Dnanostructureswithawiderangeofapplicationsinnanoelectronics,optoelectronics,plasmonics,medicaldiagnostics,catalysis,drugdelivery,therapeutics,separation,andchemicalsensing.2–5However,mostofthese1Dnanostructuresaresolidnanowiresorhollownano-tubes.Therefore,itisstillnecessarytoseeknewkindsof1Dnanostructuresandexplorenewuniquepropertiesandapplications.Herein,wepresentanoveltypeof1Dnanostructurethatisdi erentfromsolidnanowiresandhollownanotubes,i.e.apeashell-likenanostructure,whichisa1Dwirewithperiodicallyembeddedhollownanobubbles.Thecombinationofsuchultra- nehollownanobubblesandthe1Dnanowiremayimpartsomenovelpropertiestothepeashell-likenanostructure.

Inthiscommunication,animportantdielectricmaterial,magnesiumoxide(MgO),6hasbeenselectedasanexampletosynthesizeapeashell-likenanostructureandshowsomeintriguingpropertiesofsuchanovelnanostructure.Thesynthesisstrategyinvolvesaself-catalysisvapor–liquid–solid(VLS)processinconjunctionwiththeKirkendallprocess.Duetotheirultra- nediametersandperiodicallyembeddedhollownanobubbles,thelargelysynthesized1Dpeashell-likeMgOnanostructuresshowgreatlyenhanceddielectricfunction,30timeshigherthanthatofMgOmicropowdersinthelow-frequencyrange.Moreover,suchultra- ne,embedded,hollownanobubblesalsogivethepeashell-likeMgOnanostructuresa9timesstrongersaturationmagnetizationthanthatofMgOnanoparticles(22nm).Therefore,webelievethatthisnewtypeof1Dpeashell-likenanostructurenotonlyconfersthe

BeijingNationalLaboratoryforCondensedMatterPhysics,InstituteofPhysics,ChineseAcademyofSciences,Beijing100190,China.E-mail:chenx29@http://www.77cn.com.cn;Fax:+86-010-82649646;Tel:+86-010-82649036b

InstituteforSuperconductingandElectronicMaterials,UniversityofWollongong,NSW2522,Australia

wElectronicsupplementaryinformation(ESI)available:XRDpattern,TEMimagesofthetipmorphology,bright eldanddark eldTEMimagesofultra- ne1Dpeashell-likeMgOnanostructures,and eld-cooledandzero- eld-cooledhysteresisloopsof1Dpeashell-likeMgOnanostructures.SeeDOI:10.1039/c0cc00167h

capabilitiesofamulti-functionalnanomaterialonMgO,butcanalsoa ecttheproperties(andmayintroducenovelproperties)ofothermaterials,suchastransitionmetaloxides.TheX-raydi raction(XRD)patternofas-synthesizedproductscanbewellindexedtoaface-centeredcubiccellwith

,ingoodagreementwiththestandarddataa=4.2102A

(ICDD-PDF65-0476),con rmingthatthisproductisMgOwithaface-centeredcubicstructure,asshowninaSupportingInformation(SI)Figure(Fig.SI-1w).Fig.1demonstratesthattheproductcontainsalargeamountofuniformultra- ne1Dnanostructures.Eachnanostructurehasabigwhitetipwitharectangularshape(Fig.SI-2w).Thetransmissionelectronmicroscope(TEM)imageinFig.SI-3(a)windicatesthattheseultra- ne1Dnanostructuresare10–30nmindiameter.Eachnanostructurehasperiodicalbrightspotswhenimagedunderbright eldTEMconditions[Fig.SI-3(b)w].Thebrightspotsinvertcontrastandappeardarkwhenimagedunderdark eldTEMconditions[Fig.SI-3(c)w].TheTEMwascon guredtocollectallofthedi ractedelectronintensityfordark eldimaging,asshownbyalloftheMgOnanowiresappearingwhite.Thedark eldimageshowsthatthebrightspotsfromthebright eldimageappeardark,meaningthattheydonotgenerateanydi ractedelectronsintensity.Thiscon rmsthatthebrightspotsareduetoabsorptioncontrastandanincreaseintransmittedelectronintensity.TheincreaseintransmittedelectronintensitycanbeduetoamaterialimpuritylighterinatomicnumberthanMgO,orreducedthicknessoftheMgOnanowire.ConsideringtheabsenceofimpuritiesintheXRDpattern,itisproposedthatthebrightpointsareduetoreducedthickness.Todeterminewhetherthereducedthicknessisduetosurfacedepressionsorinternalpores(nanobubbles),aTEMimageclearlyshowingthenanowirestructureandahighresolutionTEM(HRTEM)areshowninFig.2(a)and(b),respectively.Itcanbeseenthattheatomarrayinthebrightpointsisthesameastheatomarrayinthedarkersurroundingareas.Nosunkenlayerstepscanbeseenaroundthewhitepoints,whichindicatesthatthesewhitepointsarenotumbilicationsonsurfacesofthenanowiresbutarenanobubblesinthenanowires.Suchnanobubblesincreasethetransmittedelectronintensityandappearasbrightpointsunderbright eldimagingconditions.

Inthepastdecade,theVLStechniquehasbeenwidelyappliedtosynthesize1Dnanowiresandnanotubes,inwhichliquidmetallicnanodropletsactascatalyststoadsorbanddissolvereactantspeciestoinducethenucleationandgrowthofnanostructures.7,8TheVLSmechanismhasanobviousfeature,i.e.eachas-prepared1Dnanostructurehasabigtip.DuetothebigtipsobservedintheTEMimagesoftheas-prepared1Dpeashell-likenanostructuresandtheabsence

Fig.1SEMofpeashell-likeMgO

nanostructures.

ofothermetallicdroplets,itislikelythatMgdropletshavefunctionedasacatalyst,inducingtheformationof1DMgOnanostructuresduringourexperiment.Inthe rststep,MgpowderisheatedtogenerateMgvaporsat9501Cunderargonatmosphere,andsomeMgvaporsarecondensedtoformliquidMgdropletsinthelow-temperatureregion.Then,oxygengasisintroducedtoreactwiththeMgvapors,sothatthereactantMgO,andtheunreactedMgvaporsandO2gascanbeadsorbedanddissolvedintheMgdroplets,asisshowninScheme1(A).UponsupersaturationintheliquidMgdroplets,MgOwillprecipitatefromtheedgeoftheMgdroplets(Scheme1(B)).Duetothefas …… 此处隐藏：12201字，全部文档内容请下载后查看。喜欢就下载吧 ……