材料表征教学资料-diffractionppt课件.ppt

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1、Dr.DiWu,NanjingUniversity1衍射Dr.DiWu,NanjingUniversity2衍射是什么衍射技术考察大量散射体对电磁辐射的散射。我们主要考虑晶体材料中原子、原子团和分子对电磁辐射的散射。各种衍射技术最后都会给出一个衍射谱图，所谓的衍射pattern。这些衍射谱记录了晶体对射线衍射的角度和强度。Dr.DiWu,NanjingUniversity3衍射能干什么从衍射谱我们可以得到如下信息：•晶体中原子层的面间距；•确定单晶或者晶粒的取向；•确定未知材料的晶体结构；•测量晶粒的大小、形状和内应力。Dr.D

2、iWu,NanjingUniversity4可见光的衍射Fraunhofer衍射：远场衍射，即平面波和散射体的相互作用；Fresnel衍射：近场衍射，除了Fraunhofer衍射以外的衍射；电子衍射在大多数情况下属于Fraunhofer衍射，但是在某些特殊的场合属于Fresnel衍射。Dr.DiWu,NanjingUniversity5波前Huygens:波前上的每一个点都是一个球面波源，这些球面波相互干射形成新的波前。Everypointonthewavefrontisasourceforsphericalwaves.Thes

3、esphericalwavesinterferencewitheachothertoformthenewwavefront.Dr.DiWu,NanjingUniversity6双缝衍射从两个狭缝出射的波之间有光程差，因而有位相差，在距离r,位相差为。dplanewaveDr.DiWu,NanjingUniversity7DoubleslitdiffractionmaximumintensityatorDr.DiWu,NanjingUniversity8MultislitdiffractiondplanewaveDr.DiWu

4、,NanjingUniversity9Multislitdiffraction,whenDr.DiWu,NanjingUniversity10Multislitdiffractionmandhareintegers.Dr.DiWu,NanjingUniversity11MultislitdiffractionThereareN-1diffractionminimumsbetweentwodiffractionmaximums.m=1,2,3,…,N-1andcorrespondtotwointensityminimumsarou

5、ndadiffractionmaximum.Dr.DiWu,NanjingUniversity12MultislitdiffractionThewidthofthediffractionpeakis.LargerNgeneratessharperpeaks.ToX-raydiffraction,Nisdirectlyassociatedwiththesizeofcrystallitesunderdetection.Dr.DiWu,NanjingUniversity13TotheslitattheoriginO,,whiletot

6、heslitaty,.DiffractionfromslitwithfinitewidthplanewaveOydysupposetheslitofinwidthasacombinationofslitsofdyinwidthDr.DiWu,NanjingUniversity14DiffractionfromslitwithfinitewidthDr.DiWu,NanjingUniversity15Diffractionfromslitwithfinitewidth=0,or=0I=Imaxthediffraction

7、peakwidth~2/.=n,orsin=nI=IminDr.DiWu,NanjingUniversity16Diffractionfromasmallhole(aperture)Thepeakwidthis1.22/D.Anyapertureinanymicroscopewouldputlimitationsontheresolution(R).Disthediameter.RDRDr.DiWu,NanjingUniversity17GeometricofDiffractionThegeometricthe

8、oryofdiffractionisessentiallythesameforX-rays,electronsandneutrons.Followingassumptionshasbeenmade,Theintensityofthescatteredbeamis