Downloaded by Hong Kong Baptist University Library on 21 September 2011Published on 19 September 2011 on www.1mpi.com | doi:10.1039/C1CC14103A

Fig.4Structuralanalyses.SAEDpatternsof(a)CdSnanocrystalsand(b)CdS–CdTeoligomers.Scalebarsare2nmÀ1for(a)and(b).STEM-EDSpro lingof(c)sulfur(S)andtellurium(Te),andselenium(Se)andTealongalongaxisofasingleshortCdS–CdTeoligomer,andaCdSe–CdTeoligomer,respectively.InsetimagesshowtheHAADF-STEMimageoftheoligomerscorrespondingto(c)and

(d).

Fig.2BF-TEMimagesof(a)CdSNCs,(b)CdSeNCs,(c)CdS-CdTeoligomers,and(d)CdSe–CdTeoligomers.HAADF-STEMimagesof(e)CdS–CdTeoligomers,and(f)CdSe–CdTeoligomers,respectively.Scalebarsare50nm,50nm,50nm,50nm,10nm,and5nmfor(a–f),

respectively.

withsubnanometreresolution.14AnEDSlinescanforasingleshortwirerevealedclearlythattheoligomerwasformedandcomposedofatleast5distinctdomainsofCdS-andCdTe-basedparts,whichwerealternativelyconnectedinonedimen-sion.Also,thesameprocedurecon rmedphase-separationinaCdSe–CdTeoligomer(Fig.4d).InthecaseofCdSe–CdTeoligomers,wefoundsuperposeddi ractionpatternsofwurtzitestructureofCdSeandCdTe.11

Tofurthergeneralizethismethod,wesynthesizedoligomersfromnanorod-shapedseeds.CdSNRsweresynthesizedfollowingapreviousreport(Fig.5a).15ThesynthesisofCdSNR–CdTeoligomerswasconductedinafashionanalogoustothatofCdSsphere–CdTeoligomers.TEMobservationsrevealedsuccessfulsynthesisofCdSNRsandthecorrespondingCdSNR–CdTeoligomers(Fig.5b).Theirshapeswerestillone-dimensionalandCdTeseemstobepreferentiallydepositedonaspeci cfacetofCdS.Furthermore,two-dimensionalelementalmappingshowedthatTe-richpartsexistedatjunctionsbetweenS-richparts(Fig.5candd),beingindicativeof

CdTe

Fig.3AbsorptionspectraofCdSnanocrystals(solid,black),CdS–CdTeoligomersbefore2401Cannealing(dotted,black)andafterannealing(solid,

gray).

structureofCdSseedsiswurtzite(Fig.4a).AftertheCdTedepositionat1801C,SAEDpatternswithalesscrystallinecubicfeatureappearedinadditiontothewurtziteCdSlattice,andthebriefannealingat2401Chighlightedallpeaks(Fig.4b).GiventheCdS–CdTeheterostructures,thelatticeconstantfortheCdTepartreproducedfromcubic(111)latticespacingwasestimatedtobeB0.639nm,slightlysmallerthanthatofpure,bulkcubicCdTe(a=0.648nm),suggestingpartialalloyingwithCdS12orstrainduetothelatticemis-match.13TheseobservationsareconsistentwiththeUV-VisabsorptionspectralchangeandXRDcharacterization.11FurthercharacterizationusingscanningTEMenergydisper-siveX-rayspectroscopy(STEM-EDS)wasemployedtocon- rmelementalcompositionsofCdS–CdTenanowires(Fig.4c).Thismethodrealizeselementalmappingofcrystals

Chem.Commun.

Fig.5BF-TEMimagesof(a)CdSNRs,and(b)CdSNR–CdTeoligomers.(c)AHAADF-STEMimage,and(d)thecorrespondingelementalmappingofCdSNR–CdTeoligomers.Blue,red,andgreendotsshowCd,S,andTeexistences,respectively.Scalebars:(a,b)50nm,(c,d)10nm.

ThisjournaliscTheRoyalSocietyofChemistry2011