材料分析测试技术 chapter 5 透射电镜的结构

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1、第五章透射电镜的结构光学显微镜的发明为人类认识微观世界提供了重要的工具。随着科学技术的发展，光学显微镜因其有限的分辨本领而难以满足许多微观分析的需求。上世纪30年代后，电子显微镜的发明将分辨本领提高到纳米量级，同时也将显微镜的功能由单一的形貌观察扩展到集形貌观察、晶体结构、成分分析等于一体。人类认识微观世界的能力从此有了长足的发展。DefinitionsMicroscope-Adevicewithalensorseriesoflensesthatenlarge(magnify)theappearanceofanobject.Doesno

2、tapplytoSEM.Lens-Alensisanopticalcomponentwhichisusedtofocusbeamsofradiation.Lensesforlightareusuallymadeofaglassymaterial,whereasnon-uniformelectromagneticfieldsareusedaslensforelectrons.Image-Perceptionofanobjectusingyoureyes(vision).Onecansenseanobjectwithoutvision(to

3、uch,etc..).Requiresvisiblelight.LensesCurvedglassormirrorforVisiblelightConcavesurfaceofmetal(e.g.satellitedish)RadiowavesConcavemirrororFresnellensHeatSolenoid(electromagneticfieldsthatcanbevaried)Subatomicparticles(electrons,protons,positrons)concaveconvexResolution-Th

4、epointatwhichtwoormoreobjectscanbedistinguishedasseparate.Magnification-Theratiobetweenimagesizetotheobjectsize.Canbevariedbychangingthedistancebetweentheobjectandthefinallens(oftheeye)orbyinsertingasecondlensbetweenthetwo.History:Firstrecordofusingglasslensformagnificat

5、ionwasbyanArabianfromwhatisnowknownasIran,Alhazen,inthe10and11thcentury.HecontradictedPtolemy'sandEuclid'stheoryofvisionthatobjectsareseenbyraysoflightemanatingfromtheeyes;accordingtohimtheraysoriginateintheobjectofvisionandnotintheeye.Becauseofhisextensiveresearchonvisi

6、on,hehasbeenconsideredbymanyasthefatherofmodernoptics.15thcenturyon-Studiesdonewithglassmagnifierstostudyobjectsindetailmostlyasacuriositybynon-scientists-AntonievanLeeuwenhoek(linendraper)describedthreeshapesofbacterialcellsusinghissimple,singlelensmicroscope(glassbeadi

7、nmetalholder).Bymid-19thcentury,becameevidentthattheoreticallimitsoflightwerereached.Abovemagnificationof1500,resolutionlost.Imagewaslarger,butblurred(emptymagnification).In1870,ErnstAbbederivedmathematicalexpressionforresolutionofmicroscope:Resolutionislimitedtoapprox.1

8、/2thewavelengthofilluminatingsource.Wavelength-distancebetweenpeaksofthewaveformBluelighthasawavelength