2019材料表征教学资料-interaction.ppt

1InteractionofRadiationswithMatterstheprobetomicrostructures2Why?Theinteractionofelectromagneticradiationwithcrystallinesolidsisnowunderstoodinconsiderabledetailsothatitcanbeexploitedtoprovidethenecessaryinformation.Tocharacterizeamicrostructureitisnecessarytoperturbthematerialbyinteractinginsomewaywithit.3ExamplesOneseesamatteronlybecausethematterreflectsvisiblelight.X-rayandhighenergyelectronbeamcould“see”crystallattices.4ThedilemmaInteractionofradiationwithmaterialsunderprobemaycausedamagetoorchangethemicrostructureofthem.Higherresolutionrequiresradiationwithsmallerwavelength,orhigherenergy.Thus,theprobabilityofradiationdamageincreases.5ThecriterionEverycharacterizationshouldacquirethemostinformationontheexpenseoftheleastdamage.Therefore,knowledgeoninteractionofradiationwithmattersisindispensable.6PenetrationdepthPenetrationdepth,ormeanfreedistance,oftheincidentdeterminesthedepthandvolumeinthesamplethatcanbeanalyzed.Inmostcases,thetypeofradiationgeneratedinthesampleisdifferentfromtheincidentradiation.Thesmallermeanfreedistancedeterminestheanalysisvolume.7Penetrationdepth:PhotonsPhotonsarediscretequantaofelectromagneticradiation.Thephotonisidentifiedbythewavelength,,energy,E,andfrequency,,allofwhicharerelatedbytheequationwherehisPlankconstantandcthevelocityoflight./hchE8Penetrationdepth:PhotonsElectromagneticspectrumspansavastrangewithwavelengthvaryingfrom106mto10-14m.Ifwewanttomakeuseofelectromagneticradiationtocharacterizethemicrostructureofmaterials,thewavelengthofphotonsmustbeincomparisonwiththefeatureswewanttoobserve.Therefore,wedonotneedphotonswithwavelengthlargerthan10-4morsmallerthan10-10m.9Penetrationdepth:PhotonsThepenetrationdepthofphotonsdependssensitivelyonmaterialsandphotonenergies.Itisnotpossibleorinstructivetogiveadetailedrelationoverthewholespectrum.However,itispossibletogivearoughdescriptionoversomespecificandimportantwavelength.10Penetrationdepth:PhotonsVisiblelight:~500nm,penetrationdepth~50-300nmInformationfromvisiblelightareaveragedoverafewhundredsofatomiclayers.Ultravioletlight:severeabsorption,onlysuitabletosurfaceanalysisX-ray:generallyafewmicrometers,dependentofabsorptioncoefficientincreaseswithincreasingatomicnumber.)exp(0tII11Penetrationdepth:ElectronsThepenetrationdepthofelectronsvariesdramaticallywithelectronenergyandatomicnumberofmaterials.Thehighertheenergy,thedeeperthepenetration.10keV~0.?m30keV~2m12Penetrationdepth:ElectronsThesmallertheatomicnumber,thedeeperthepenetration.Thisaffectsthecharacterizationmethodsusingelectronbeamsasprobesbecausecommonmaterialsarecomposedofelementswithdifferentatomicnumbers.atomicnumberpenetrationdepth2010m402m13Penetrationdepth:ElectronsThescatteringofelectronsinthematerialslimitsthespaceresolution.14InteractionofelectronswithmattersSecondaryelectronsBackscatteredelectronsAugerelectronsX-raysDiffractedelectrons15SecondaryelectronsSecondaryelectronsareusedtogivescanningelectronmicroscope(SEM)images.Secondaryelectronsarelowenergyelectrons.Thus,onlythosegeneratedbeneaththeincidentbeamorinthevicinityofincidentbeamcanescapeoutofthesurface.Therefore,theresolutionofaSEMisbasicallydeterminedbytheincidentbeamarea.16AugerelectronsTheenergyofAugerelectronsisabout0~2keV,absorbedeasilybythematerials.OnlyAugerelectronsgeneratedwithinafewatomiclayersbeneathsurfacecouldescapeoutofthesurface.LightatomsorlowenergybondsarepronetogenerateAugerelectrons.vacuumEcEFvalencebandL3L2L1K17CharacteristicX-raysX-rayphotonshavestrongabilitytopenetratethroughthesample.Therefore,X-raysgeneratedinarelativelylargevolumecanbedetected.Heavyatomshavelargecross-sectionstogeneratecharacteristicX-rays.CharacteristicX-raysaresuitabletodetectheavyatoms.vacuumEcEFvalencebandL3L2L1KcharacteristicX-rays18Radiationdamage:PhotonsPhotonshavetheleastdamagetomaterials.Generally,thedamagefromphotonscomesfromheatingeffect.Theamplitudeofthedamagedependsonpenetrationdepth,photonenergyandcurrentdensity.Example:Stronglasercancausemeltandevaporationinashorttime,e.g.theinteractionoflaserwithtargetinpulselaserdeposition.19Radiationdamage:ElectronsRadiolysis:inelasticscattering(mainlyionization)breakschemicalbondsinmaterials,especiallypolymersandalkali-halogenchemicals.Knock-ondamage:directknockouttheatomsfromlatticesitestoformpointdefects,effectivetoallkindsofmaterials.Heatingeffect:negligibletometalorothergoodheatconductors.Itcanbesevereproblemsforinsulators.Ceramicmicropowderscanbeheatedto~17000Cintransmissionelectronmicroscope.20Radiationdamage:ElectronsRadiolysisisduetoelectron-electroninteraction.Itcannotbereducedbycoolingthesample.Thehighertheelectronenergy,themoretheknock-ondamage.Thesmallertheelectronenergy,themoretheradiolysisandheatingdamage.Itisnotpossibletowhollyavoidelectrondamage.21TheEnd