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时间:2020-10-21
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1、InteractionofRadiationswithMatterstheprobetomicrostructures1Why?Theinteractionofelectromagneticradiationwithcrystallinesolidsisnowunderstoodinconsiderabledetailsothatitcanbeexploitedtoprovidethenecessaryinformation.Tocharacterizeamicrostructureitisnecessarytoperturbthematerialbyinteractingins
2、omewaywithit.2ExamplesOneseesamatteronlybecausethematterreflectsvisiblelight.X-rayandhighenergyelectronbeamcould“see”crystallattices.3ThedilemmaInteractionofradiationwithmaterialsunderprobemaycausedamagetoorchangethemicrostructureofthem.Higherresolutionrequiresradiationwithsmallerwavelength,o
3、rhigherenergy.Thus,theprobabilityofradiationdamageincreases.4ThecriterionEverycharacterizationshouldacquirethemostinformationontheexpenseoftheleastdamage.Therefore,knowledgeoninteractionofradiationwithmattersisindispensable.5PenetrationdepthPenetrationdepth,ormeanfreedistance,oftheincidentdet
4、erminesthedepthandvolumeinthesamplethatcanbeanalyzed.Inmostcases,thetypeofradiationgeneratedinthesampleisdifferentfromtheincidentradiation.Thesmallermeanfreedistancedeterminestheanalysisvolume.6Penetrationdepth:PhotonsPhotonsarediscretequantaofelectromagneticradiation.Thephotonisidentifiedbyt
5、hewavelength,,energy,E,andfrequency,,allofwhicharerelatedbytheequationwherehisPlankconstantandcthevelocityoflight.7Penetrationdepth:PhotonsElectromagneticspectrumspansavastrangewithwavelengthvaryingfrom106mto10-14m.Ifwewanttomakeuseofelectromagneticradiationtocharacterizethemicrostructureof
6、materials,thewavelengthofphotonsmustbeincomparisonwiththefeatureswewanttoobserve.Therefore,wedonotneedphotonswithwavelengthlargerthan10-4morsmallerthan10-10m.8Penetrationdepth:PhotonsThepenetrationdepthofphotonsdependssensitivelyonmaterialsandphotonenergies.Itisnotpossibleorinstructivetogivea
7、detailedrelationoverthewholespectrum.However,itispossibletogivearoughdescriptionoversomespecificandimportantwavelength.9Penetrationdepth:PhotonsVisiblelight:~500nm,penetrationdepth~50-300nmInformationfromvisiblelightareaveragedoverafewhundre
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