纳米固体的声子硬化和光子软化

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1、http://www.paper.edu.cnSize-inducedacoustichardeningandopticsofteningofphononsinCdS,InP,CeO2,SnO2,andSinanostructuresChangQSunSchlEEE,NTU,Singaporeecqsun@ntu.edu.sg;www.ntu.edu.sg/home/ecqsun/IthasbeenpuzzlingthattheRamanopticalmodesshifttolowerfrequency(ortermedasopticalmodesoftening)associ

2、atedwithcreationofRamanacousticmodesthatshifttohigherenergy(orcalledasacoustichardening)uponnanosolidformationandsizereduction.Understandingsofthemechanismbehindthesize-inducedacoustichardeningandopticsofteninghavebeenquitecontroversial.Onthebasisoftherecentbondorder-length-strength(BOLS)cor

3、relation[Phys.Rev.B69045105(2004)],weshowthattheopticalsofteningarisesfromatomiccohesiveenergyweakeningofsurfaceatomsandtheacousticmodehardeningispredominatedbyintergraininteraction.AgreementbetweenpredictionsandobservationshasbeenreachedforSi,CdS,InP,TiO2,CeO2,andSnO2nanostructureswitheluci

4、dationofvibrationfrequencyofthecorrespondingisolateddimers.Findingsfurtherevidencetheimpactofbondorderlosstolow-dimensionalsystemsandtheessentialityoftheBOLScorrelationindescribingthebehaviorofnanostructures.PACS:61.46.+w;78.30.-j;78.67.-n;63.22.+mKeywords:nanostructures;Ramanshift;BOLScorre

5、lation;surfacebondcontraction;interparticleinteraction-1-http://www.paper.edu.cnIIntroductionAtomicvibrationisofhighinterestbecausethebehaviorofphononsinfluencedirectlyontheelectricalandopticalpropertiesinsolidmaterialsanddevicessuchaselectron-phononcouplinginphotoabsorptionandphotoemission,

6、andphonon1scatteringindevicetransportdynamics.Ithasbeenlongsurprisingthatwithstructuralminiaturizationdowntonanometerscalethetransverseandthelongitudinaloptical(TO/LO)Ramanmodesshifttowardslowerfrequency(orcalledasoptical2modesoftening)accompaniedwithgenerationoflow-frequencyRaman(LFR)-1acou

7、sticmodesatwavenumbersofafeworafewtenscm.TheLFRpeakshiftsup(orcalledasacousticmodehardening)towardshigherfrequencyuponthesolidsize3,4beingreduced.Generally,thesizedependentRamanshiftsfollowascaling2,4relation:κω(Kj)=ω(∞)+AfKjwhereAfandκareadjustabl