同步辐射技术及应用同学-以前课件xafscourse8a

NSRLinHefei,China

SynchrotronRadiationinMaterialScience

ShiqiangWei

NationalSynchrotronRadiationLaboratoryUniversityofScience&TechnologyofChinaHefei,230029,P.R.China

XAFS方法的优点

(1)EXAFS现象来源于吸收原子周围最近邻的几个配位壳层原子的短程作用，不依赖于晶体结构，可用于非晶态物质的研究。结果为吸收原子近邻配位原子的种类、距离、配位数及无序度因子。

(2)X射线吸收边具有原子特征，可调节X射线的能量对不同元素的原子周围环境分别进行研究。

(3)

利用高强射线光源或荧光探测技术可以测量几个ppm浓度的样品。

(4)EXAFS可用于测量固体、液体、气体样品，一般不需要高真空，不损坏样品。

Principles,experimentanddataanalysisofXAFStechnique

同步辐射XAFS实验站及其应用物理,31,40(2002)

韦世强，谢亚宁，徐法强，胡天斗，刘文汉，刘涛

hEXAFS的基本原理

EXAFS的产生

当X光照射物质，在某能量位置处，X光能量正好对应于物质中元素A内壳层电子的束缚能，吸收系数突增，即吸收边位置。中心原子A吸收X后，内层电子由n态激发出来向外出射光电子波，此波在向外传播过程中，受到邻近几个壳层原子的作用而被散射，散射波与出射波的相互干涉改变了原子A的电子终态，导致原子A对X射线的吸收在高能侧出现振荡现象。c(k)=jFj(k,p)S02(k)g(R)/kRj2

exp(-2Rj/l(k))

sin[2kRj+fj(k)]dR

单散射理论和多重散射理论

XAFS的数据分析处理方法NSRLXAFS3.0软件包homepage:

EXAFS函数的普通表达式

c(k)=jNjF(k,p)S02(k)/kRj2exp(-2sj2k2)

exp(-2Rj/l(k))sin[2kRj+fj(k)]k：为光电子波矢，Nj：j壳层原子数，Rj：j壳层原子与中心原子距离，f(k,):振幅函数，(k)非弹性散射的平均自由程，j：热无序因子，fj(k)：相移函数。XAFS数据分析的步骤(1)求-E曲线(2)背景扣除(3)0拟合

(4)E→k转换(5)求(k)及加权和加窗(6)快速Fourier变换(7)Fourier滤波(8)曲线拟合Pre-EdgeBackgroundRemovalFitμ0kweightk/Å-1χ(k)k/Å-1χ(k)k3Fouriertransform(FFT)Distance/ÅInverseTransformsk/Å-1χ(k)k3FittingParametersk/Å-1χ(k)k3拟合结果

参数名称实验值拟合结果键长(nm)0.2550.253配位数12.011.81结构无序度（nm）0.00.0011热无序度（nm）0.00860.0086E0（eV）0.0-4.38拟合相对误差：5％

XAFSin

MaterialScience

(1)AnnealedcrystallizationofNi-BandNi-P

nano-amorphousalloys

Phys.Rev.B63,224201(2001)

SignificationsTM-Mtypenano-amorphousalloy(TM=Ni,Co,Fe;M=B,P)havethehighratioofsurfaceatomsandamorphousstructure.Applicationsinferrofluid,catalystsandmagneticrecordingmaterials.

Preparation

Chemicalmethod:KBH4,2mol/LNi(CH3COO)24H2O,0.25mol/Lice-waterbathandvigorouslyagitatedbyamagneticstirrer.

Catalyticactivitiesofnano-amorphousNi-BandNi-PforBenzeneHydrogenation

DTA

profilesofNiBandNiPXRDresultsofNiBwithdifferentannealedtemperaturesXRDspectraofNiPatdifferenttemperature

XAFSresults

k3(k)-kfunctionofNiBandNiPRDFsofultrafinealloyNiBandNiP

FittingresultsofNiBandNiPSampleAnnealingPairRj(nm)R0(nm)NT(10-2nm)S(10-2nm)E0(eV)

Temp

Ni-B25oCNi-Ni0.2740.2410.00111.01.00.693.3-0.2Ni-B0.2180.2150.0012.70.20.460.34-4.7Ni-P25oCNi-Ni0.2710.2430.00110.01.00.602.8-2.9Ni-P0.2230.2150.0011.60.20.400.805.3Ni-B300oCNi-Ni0.2550.2430.0019.91.00.601.1-0.9Ni-B0.2180.2150.0012.60.20.600.345.0Ni-P300oCNi-Ni0.2580.2420.00110.11.00.631.6-1.3Ni-P0.2220.2150.0010.80.20.490.658.7Ni-B500oCNi-Ni0.2490.2450.00110.81.00.700.391.6Ni-B0.2170.2150.0010.30.20.560.23-5.0Ni-P500oCNi-Ni0.2550.2430.00110.41.00.601.25-2.8Ni-P0.2250.2190.0010.60.20.400.567.6NifoilNi-Ni0.24912.00.74AveragedistanceRj=R0+σsR’serror=0.001nm，T’serror=0.0510-2nm，S’serror=0.110-2nm。ThestructureparametersofNiBandNiPatdifferentannealingtemperatureConclusionTheXAFSresultsdemonstratethatafcc-likenanocrystallineNiphasewithamedium-rangeorderisformedat573

Kwherethefirstexothermicprocessisobserved.Themetastableintermediatestatesconsistofthetwophases,i.e.,nanocrystallineNiandcrystallineNi3Balloy.

(2)MetastablestructuresofimmisicibleFeXCu100-Xsysteminducedbymechanicalalloying

SignificationsThemethodofmechanicalalloyingcanlargelyincreasethesolidsolubilityofimmiscibleFe100-xCuxalloy.UniqueelectronicandmagneticpropertiesforFe-Cusystem.ThemechanismenhancedsolubilityofFe-Cualloyisnotclear.

StructuraltransitionsofmechanicallyalloyedFe100-xCux

systemstudiedbyX-rayabsorptionfinestructurePhysicaB,305,135(2001)ShiqiangWei,WenshengYan,YuzhiLi,WenhanLiu,JiangweiFan,andXinyiZhangMetastablestructuresofimmiscibleFeXCu100-Xsysteminducedbymechanicalalloying.J.Phys.CM,9,11077(1997).ShiqiangWei,HiroyukiOyanagi,CuieWen,YuanzhengYang,andWenhanLiu.PreparationsAlloyompositionFe100-xCux

x=0,10,20,40,60,80,100.WCballstothemixedFe-Cupowder10to1.MAmillingrate:about210r/min.

k3(k)-kfunctionofFe100-xCux

RDFsofFe100-xCuxalloys

FittingresultsoftheFe100-xCuxsamples

ThestructureparametersofFe100-xCuxbyfittingtheFeK-edgeEXAFSspectra3.457.10.50.0980.0052.580.02Fe-Cu4.955.00.50.0980.0052.580.02Fe-FeFe20Cu802.946.40.50.0980.0052.580.02Fe-Cu4.965.70.50.0980.0052.580.02Fe-FeFe30Cu702.635.60.50.0990.0052.580.02Fe-Cu4.996.90.50.0990.0052.580.02Fe-FeFe40Cu60-4.993.50.30.0990.0052.560.02Fe-Cu0.648.70.50.0990.0052.570.02Fe-FeFe60Cu404.311.20.30.0810.0052.480.02Fe-Cu-2.017.20.50.0810.0052.480.02Fe-FeFe80Cu20-1.590.70.30.0800.0052.480.02Fe-Cu-4.017.60.50.0780.0052.480.02Fe-FeFe90Cu102.978.00.50.0700.0052.480.02Fe-FeFepowderE0N(Å)R(Å)BondtypeSampleThestructureparametersofFe100-xCuxbyfittingtheCuK-edgeEXAFSspectra0.412.00.50.0890.0052.550.02Cu-CuCupowder-4.61.50.30.0880.0052.540.02Cu-Fe-2.19.80.50.0890.0052.550.02Cu-CuFe20Cu80-3.82.30.30.0890.0052.540.02Cu-Fe-1.89.70.50.0890.0052.550.02Cu-CuFe30Cu70-4.33.30.30.0890.0052.540.02Cu-Fe-3.98.40.50.0890.0052.560.02Cu-CuFe40Cu600.94.60.50.0870.0052.550.02Cu-Fe2.77.10.50.0890.0052.550.02Cu-CuFe60Cu404.06.20.50.0810.0052.490.02Cu-Fe4.82.10.30.0820.0052.500.02Cu-CuFe80Cu20-5.06.70.50.0730.0052.480.02Cu-Fe-3.11.50.30.0780.0052.480.02Cu-CuFe90Cu10E0N(Å)R(Å)BondtypeSampleConclusions

ThelocalstructuresaroundFeandCuatomsdependontheinitialcomposition.Fe100-xCuxsolidsolutionsx40,fcc-likestructurex20,bcc-likestructure

ThefittingresultsindicatethattheMAFexCu100-xalloyswithx40areinhomogeneoussupersaturatedsolidsolutions,andthereareafccFe-richandafccCu-richregionsinsolidsolutions.ForlowerCuconcentrationswithx20.TheevolutionoftheFTintensitiesandstructuralparametersofFeatomsisidenticalwiththoseofCuatoms.ThisresultsuggeststhattheCuatomsbealmosthomogeneouslyincorporatedintothebccFe-Cuphase.(3)InsituXAFSstudiesinhightemperature

InSbcrystalandnanocrystalstudiedbyin-situXAFSXAFSabsorptionspectrumforSbandInK-edgeofmoltenIn50Sb50

atdifferenttemperaturesEXAFSfunctionsofmoltenIn50Sb50for

SbandInK-edgesatdifferenttemperaturesF(R)functionofmoltenIn50Sb50for

SbandInK-edgesatdifferenttemperaturesEXAFSfunction

:pairradialdistributionfunction:scatteringamplitude:phaseshiftfunctionofback-scatteringatoms

:phaseshiftfunctionofabsorberatomsReverseMontCarloMethodWhereBackgroundremovalanddouble-electronexcitationX(k)FunctionsforthemoltenInSbAtomiccoordinationdistributionfunctionforInandSbK-edgeofliquidIn50Sb50

semiconductor

Pbadsorptiontofattyacid

Langmuirmonolayers

Combinationofgrazing-incidencedifraction

andreflectionmodeXAFS

M.I.Boyanov,1J.Kmetko,2T.Shibata,1A.Datta,2P.Dutta,2B.A.Bunker1

1DepartmentofPhysics,UniversityofNotreDame2DepartmentofPhysicsandAstronomy,NorthwesternUniversityLangmuirmonolayersofcarboxylicacidsInterestingforfundamentalunderstandingofinteractionsin2Dsystemtechnologicalpromiseoftransferred(Langmuir-Blodgett)films.possibleuseastemplatesfororientedgrowthofcrystalsandasamodelforthenucleationphaseofbiomineralizationManystudieswithavarietyoftechniques,includinggrazing-incidencex-raydiffraction.Detailedphasediagramshavebeendetermined,showing2Dgas,liquid,andvarioussolidphasesTwistonthiswork:LangmuirfilmsoverdilutemetalsolutionsDiffractionexperimentsshowstrikingdifferenceinphasediagram,withnogasphasepresent.AlsoevidencefororderingofmetalionscommensuratewithheadgrouporderingWhatistheroleofmetalionsinordering?Whilediffractionexperimentsextremelyusefulfordeterminationofordering,difficulttodeterminehowmetalionsdirectlyparticipateTodeterminelocalenvironmentofmetalions,usegrazing-incidenceXAFSTotalreflectionofx-raysfromwatersurfaceXAFSdetectedbyx-rayfluorescenceMeasurementsinmodifiedHe-filledLangmuirtroughPossibledifficulties:Liquidsurface!HavetoworkhardtoreduceanyvibrationalexcitationofcapillarywavesWithcurrentfacilities,unfortunatelycannoteasilystudypolarizationdependence:Needtorotatepolarizationofbeam(thenextstep!)HavetobesurethatmetalionsareassociatedwithLangmuirfilmMustbeconcernedaboutradiationdamageExperimentalProcedureAmongthemetalsstudiedinpreviousworks,PbhasexhibitedgreatestinfluenceonthemonolayerHere,studiedheneicosanoicacid(CH3(CH2)19COOH)overanaqueousPbCl2solution(pH6.5,10-5M)Studiedinatotalexternalreflectionconfiguration

Alltheactioninthetop100AfromsurfaceExperimental

SetupX-rayMeasurementsincidenceanglesetat0.065deg,slightlybelowcalculatedcriticalangleofair-waterinterface(0.09degat13.6keVphotonenergy).Calculatedpenetrationdepthofevanescentwaveabout90ÅMonochromatorslew-scannedtominimizeradiationexposureduringasinglescan(~3min/EXAFSscan,1min/XANESscan)BeforeXAFSexperiments,GIDdatacollectedfromthepH6.5Pb-LangmuirsampletoverifythatmonolayerstructuresameasobservedinpreviousexperimentsStabilityoffilmtoradiationdamagedeterminedbyobservingchangesintheGIDpatternwithirradiationtime.Freshsamplespreparedevery35minofirradiationtoavoiddamage.leadperchlorateandleadacetateaqueoussolutionsalsostudiedasstandardsExperimentalDatak2-weightedXAFSoscillationsforAqueousPb2+HydrolysiscomplexPb4(OH)4Pbacetate(fourdifferentacetateconcentrations)Pb-LangmuirmonolayerExperimentalResultsTransformsof(a)Pbacetate(bidentatebinding),(b)PbLangmuirfilm,and(c)PbhydrolysiscomplexPb4(OH)4

Models:Knownstructureof(a)and(c)complexesQualitativeresults:ImmediatePbenvironmentsuggestscarboxylbindingFeaturesbetween3and4ÅsuggestthepresenceofPb-Pbinteractions.Morecarefulfitting:EachPbhas0.90.2carboxylgroupsand2.80.9PbneighborsconsistentwiththeadsorptionofeitheraPb3trianglebyitself,orofthePb3trianglethatisonefaceofthePb4tetrahedroninthePb4(OH)4hydrolysiscomplexWhatdoesthismean?PbatomsdonotbindassimplePb2+ions,butmostlylikelyastetrahedralcomplexesResultsconsistentwithtriangularbaseofcomplexbindingtothreedifferentchainmolecules,actingastemplatefor

solidificationExplainsthelarge

changesinphase

diagram,other

properties2022/12/2864