early history of xray and diffractionWord文件下载.docx

early history of xray and diffractionWord文件下载.docx

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Aphysicist,theveryfirstNobelprizewinnerinPhysics?

howdidhediscoverX-rays?

1895,bychance,experimentingwithcathoderays（doingsimilarthingstoJ.JThompson）ononeendofthelaboratory,therewasasheetofpaperthatwascoveredwithaphosphorsittingaroundattheotherendofthelaboratory,experimentinginthedark,henoticedthatphosphorlightsupwhenheswitchesonhiscathoderaytube,draggingoutelectronsandacceleratingthembyapotentialdifference,thecathoderaytubeisexpectedtobeundervacuum,buttherewasjustenoughrestgas（air）thatelectronsgotsloweddownbybeingscatteredbythemolecules,

todayweknow:

whenelectronsaresloweddowntheyradiateofftheirlostinkineticenergy–andthatisX-raysanelectromagneticwave+astreamofhighenergyphotonstravelingatthespeedoflight

atthetimenobodyknowshowtheradiationoriginatesandofwhatkinditwas:

waveorparticles?

Rö

ntgencouldinalongseriesofexperimentsshowed:

-X-rayspenetrateallsubstancestosomeextend,elementsoflowatomicweightareespeciallytransparent,elementsofhighatomicnumbercanbyeusedasshieldsforprotectionagainstX-rays

-X-rayscausemanysubstancestofluoresce,i.e.absorbingthemandradiatingoffelectron-magneticwavesofadifferentwavelength

-X-raysarenotdeflectedinamagneticfield,sotheydonotconsistofchargedparticles

-X-rayscaneffectivelybegeneratedby“cathoderays=acceleratedelectrons”fallonametalanode（andanyothermaterialplacedintheirpath

-X-raysionizethegassesthroughwhichtheypass,causinganincreaseofelectricalconductivity

butnotdiffractionwhichwouldproveX-raysaretobedescribedbywaves!

reason:

then-ofcourse-unknown,thewavelengthofX-raysissosmallthattherewerenomanmadediffractiongratingsavailable

howdoesadiffractionatagratingdifferfromthatofadoubleslitarrangement?

adiffractiongratinghasamuchmuchgreaternumberofslits

forthepositionsofthemaxima

dsinθ=mλ

wherem=0,1,2,…arecalledtheorderofthelineanddiscalledthegratingperiod,i.e.quotientofsomelengthWdividedbythenumberoflines

asthemaximaofthelinesisverywelldefinedandnarrow,onecanmeasurethewavelengthoftheincident（mono-orpolychromaticifitisnottoomany）radiationthatproducedtheinterference/diffractionpattern（foradoubleslitexperimentthebrightfringesarisingfromdifferentwavelengthlightwouldoverlaptoomuchtobedistinguished

by1912,SommerfeldatthePhysicsDepartmentofUniversityofMunich,nominated80timesforNobelprizewithouteverwinningit,diedfromacaraccidenthadcalculatedanorderofmagnitudeforthewavelengthofX-rays:

0.1nm

ifthatweretobetrue,wavelengthwouldbesoshortthatdiffractionof0.1nmX-raysfromastandardopticalgratingofperiod3μmweretogivediffractionangleof0.002°

sopessimism,howissomebodygoingtoproveX-raysarewavesornot

aPhDstudentofSommerfeld,Ewaldworkingonsolidstatetheoryimplicationswhatifcrystalswere,assomeoftheleadingmineralogist（e.g.VictorM.GoldsmithattheMineralogyDepartmentofUofMunich）expectedathree-dimensionalorderedarrangementofatomswithinter-atomicdistancesoftheorderofmagnitude0.1nm–youhavetopausehere,theveryexistenceofatomswasnotwellestablishedatthattimeletalonetheirpossiblearrangementincrystallinesolids,

approachedMaxLaue（anassistantprofessoratSommerfeld’schair）atCafé

“Lutz”,wherestudentsandfacultyusedtohangout,onanquiteunrelatedmatter

Lauewasatthattimeworkingonatreatiseonclassicalopticsandheardforthefirsttimebothhypotheses,thatthewavelengthofX-raysmaybeasshortat0.1nmandthatcrystalsmaypossessapossibleperiodicarrangementoftheatomsin3dimensionswithaspacingoftheorderofmagnitude0.1nm

ontheirwaybacktothePhysicsdepartment,theideaoccurredtoLaue,well,thereshouldbeinterferencesifacrystalisexposedbyabeamof“sufficientlymonochromatic”X-rays

hehimselfbeingatheorist,hetalkedapostdoc,Friedrich,whohadpreviouslyworkedwithRö

ntgen）andapostgraduate,Knipping,intotryingtheexperiment,behindthebackofthebigboss,Sommerfeld,whenSommerfeldheardaboutithewasfuriousespeciallyastheydidn’tgettheresultsLaueexpectedastheydidn’tknowwheretolookfor-sotheprojectcametoanhalt

Lauefinallygotpermissiontogoaheadbutthebigbosswasstillconvinceditwasastupidexperimentashecalculated,eveniftherewereX-rayinterferences,thethermalmotionoftheatomsattheirrespectiveplacesinacrystalwouldsmearthemout.

littledidheknow…

andMaxvonLaue,i.e.hegotknighted,gotforthecorrectinterpretationoftheintensitymaximaandthedevelopmentofthesocalledkinematictheoryofX-raydiffractionhis1914Nobelprize.

whatwasfoundinoneexperimentnotonlythatX-raysdoindeedpossesswavespropertiesandthatcrystalsindeedpossessathreedimensionalarrangementofatoms,butalsonothinglessthanthediscoveryofamethodtoprobetheinnerstructureofcrystallinematter,whichweknowtodayisalmostallsolids,betheymetals,ceramics,semiconductors,….（notglass,rubber,andcertainplastics）

adiffractiongratingisreallyaonedimensionalthing,thenaturallyoccurringcrystalsare,however,3dimensional,thereforewegetaslightlydifferentrelationforthedistributiononintensityonascreenofphotograph

Bragg’sequation:

nλ=2dsinθwherenisorderofreflection

allowingcrystalstobeusedaskindofagratingformeasuringwavelengthofcharacteristicX-rayswhicharisefromelectronictransitionsoftheinnermostelectrons

andanalysisofcrystalsstructures,solidsingeneral

asamatteroffactanewsciencewasenabledwhichgoesbythenamematerialsscience/crystallography

newsciencesalwaysstartoutasaparepistemes（R.W.Cahn）

fromtheancientGreek:

episteme–meaningadomainofknowledge

par-meansamongstotherthingssubsidiary

i.e.asubsidiarysubjectwithinascienceissomethingrightatthefringesofattentionandfundingthatdoesnotprimarilyaimforsolvinganypracticalproblem,peopleonlydoitforthefunofit,becausetheyfinditinteresting.Chandescribeditas:

“lookingattheforest,notjustselectingatreeforlogging…”

lateron,electron,andneutrondiffraction,whicharecomplementarytoX-raydiffraction–thesinglemostimportanttoolsofmaterialsscience

ascienceinitsownright?

It’sasciencewhenithasitsownjournals,conferences,societies,institutionalizeddepartments,degrees,graduatestudents,…whenithassomethinguniquethatdistinguishesitfromthesciencethatgavebirthtoit（whichisprobablyalwaysPhysics）

whatisuniqueaboutmaterialsscience/crystallography?

R.WChan:

“…thematerialsscientisthastoworkatseverallevelsoforganization,eachofwhichisunder-pinnedbythenextlevel.Here,again,heisbrotherundertheskinofthebiologist,whodoesjustthesame:

staringwiththecellwall,say,thegoesontostudythemorphologyandeconomyofthecellasawhole,thentheisolatedorgan（madeofcells）,thentheorganismasawhole.…theconceptofmicrostructureisthemostimportantsingledefinitionthemeofMaterialsScienceandEngineering.”

perhapssomethingisasciencewhenithasspunoffanengineeringdiscipline,whatdoyouthink?

perhapssomethingisasciencewhenconsistentlyNobelprizeshavebeenawardedinthatfield,whatdoyouthink?

NobelprizesPhysics:

1914MaxvonLaue,X-raysareanelectromagneticwaveofabout0.1nmwavelength,atomsincrystalsarearrangedinaregular3Dlatticewithspacinginthe0.1nmrange,thereisX-raydiffractionfromcrystals,thepossibilityofanalyzingthearrangementsofmatterincrystals,（Laueequations）,1912

1915SirWilliamHenryBraggandWilliamLawrenceBragg（sonoftheformer）,X-raycrystallography,W.L.Braggequation,X-raycrystalspectrometer,1913

1937ClintonDavidsonandSirGeorgeP.Thompson（J.J.Thompson’ssonwhofirstshowedelectronsareparticles）,electrondiffractionbycrystals,inotherwordselectronsarewaves,1927

1986ErnstRuska,inventingtheelectronmicroscopewhereoneoperationmodeiselectrondiffraction（1931）togetherwithGerdBinningandHeinrichRohrer,scanningtunnelingmicroscope,（completelyunrelated）

1994BertramN.BrockhouseandCliffordG.Schull,pioneeringneutrondiffractionandspectroscopy

NobelPrizesChemistry

1936PeterJ.Debye

X-rayandelectrondiffractionanalysesofmolecules

1962MaxF.Perutz,JohnC.Kendrew

X-raydiffractionanalysisofhaemoglobinundmyoglobin

1964DameDorothyCrowfootHodgkin

X-raydiffractionanalysisofbiochemicalmacromolecules

1976WilliamN.Lipscomb

X-raydiffractionanalysisofborhydrids

1982AaronKlug

X-raydiffractionanalysisofnucleicacidsandproteincomplexes

1985HerbertA.Hauptmann,JeromeKarle

directmethodsofX-raycrystallography

1988JohannDeisenhofer,RobertHuber,HartmutMichel

structureandfunctionofprotein-chromoph