同步輻射技術(shù)及應(yīng)用同學(xué)-以前課件xafscourse8a

NSRLinHefei,China

SynchrotronRadiationinMaterialScience

ShiqiangWei

NationalSynchrotronRadiationLaboratoryUniversityofScience&TechnologyofChinaHefei,230029,P.R.China

XAFS方法的優(yōu)點(diǎn)

(1)EXAFS現(xiàn)象來源于吸收原子周圍最近鄰的幾個(gè)配位殼層原子的短程作用，不依賴于晶體結(jié)構(gòu)，可用于非晶態(tài)物質(zhì)的研究。結(jié)果為吸收原子近鄰配位原子的種類、距離、配位數(shù)及無序度因子。

(2)X射線吸收邊具有原子特征，可調(diào)節(jié)X射線的能量對(duì)不同元素的原子周圍環(huán)境分別進(jìn)行研究。

(3)

利用高強(qiáng)射線光源或熒光探測(cè)技術(shù)可以測(cè)量幾個(gè)ppm濃度的樣品。

(4)EXAFS可用于測(cè)量固體、液體、氣體樣品，一般不需要高真空，不損壞樣品。

Principles,experimentanddataanalysisofXAFStechnique

同步輻射XAFS實(shí)驗(yàn)站及其應(yīng)用物理,31,40(2002)

韋世強(qiáng)，謝亞寧，徐法強(qiáng)，胡天斗，劉文漢，劉濤

hEXAFS的基本原理

EXAFS的產(chǎn)生

當(dāng)X光照射物質(zhì)，在某能量位置處，X光能量正好對(duì)應(yīng)于物質(zhì)中元素A內(nèi)殼層電子的束縛能，吸收系數(shù)突增，即吸收邊位置。中心原子A吸收X后，內(nèi)層電子由n態(tài)激發(fā)出來向外出射光電子波，此波在向外傳播過程中，受到鄰近幾個(gè)殼層原子的作用而被散射，散射波與出射波的相互干涉改變了原子A的電子終態(tài)，導(dǎo)致原子A對(duì)X射線的吸收在高能側(cè)出現(xiàn)振蕩現(xiàn)象。c(k)=jFj(k,p)S02(k)g(R)/kRj2

exp(-2Rj/l(k))

sin[2kRj+fj(k)]dR

單散射理論和多重散射理論

XAFS的數(shù)據(jù)分析處理方法NSRLXAFS3.0軟件包homepage:

EXAFS函數(shù)的普通表達(dá)式

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

exp(-2Rj/l(k))sin[2kRj+fj(k)]k：為光電子波矢，Nj：j殼層原子數(shù)，Rj：j殼層原子與中心原子距離，f(k,):振幅函數(shù)，(k)非彈性散射的平均自由程，j：熱無序因子，fj(k)：相移函數(shù)。XAFS數(shù)據(jù)分析的步驟(1)求-E曲線(2)背景扣除(3)0擬合

(4)E→k轉(zhuǎn)換(5)求(k)及加權(quán)和加窗(6)快速Fourier變換(7)Fourier濾波(8)曲線擬合Pre-EdgeBackgroundRemovalFitμ0kweightk/?-1χ(k)k/?-1χ(k)k3Fouriertransform(FFT)Distance/?InverseTransformsk/?-1χ(k)k3FittingParametersk/?-1χ(k)k3擬合結(jié)果

參數(shù)名稱實(shí)驗(yàn)值擬合結(jié)果鍵長(nm)0.2550.253配位數(shù)12.011.81結(jié)構(gòu)無序度（nm）0.00.0011熱無序度（nm）0.00860.0086E0（eV）0.0-4.38擬合相對(duì)誤差：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(?)R(?)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(?)R(?)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).Calculatedpenetrationdepthofevanescentwaveabout90?Monochromatorslew-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:ImmediatePbenvironmentsuggestscarboxylbindingFeaturesbetween3and4?suggestthepresenceofPb-Pbinteractions.Morecarefulfitting:EachPbhas0.90.2carboxylgroupsand2.80.9PbneighborsconsistentwiththeadsorptionofeitheraPb3trianglebyitself,orofthePb3trianglethatisonefaceofthePb4tetrahedroninthePb4(OH)4hydrolysiscomplexWhatdoesthismean?PbatomsdonotbindassimplePb2+ions,butmostlylikelyastetrahedralcomplexesResultsconsistentwithtriangularbaseofcomplexbindingtothreedifferentchainmolecules,actingastemplatefor

solidificationExplainsthelarge

changesinphase

diagram,other

properties2022/12/2864