第三次課件定性定量分析

1、譜圖概況能級(jí)用En l j表示j為內(nèi)量子數(shù)（或總角動(dòng)量量子數(shù)）旋-軌偶合j = lsAl K能量不足以激出第一層電子發(fā)高結(jié)合能處的臺(tái)階是由于光電子的非彈性碰撞所致低結(jié)合能處的背景主要由Bremsstrahg輻射產(chǎn)生元素的特征的強(qiáng)度Ni 2p1/2、2p3/2最強(qiáng)特征峰也稱(chēng)該元素的主峰雙峰由 j = l + s導(dǎo)致，反映了光發(fā)射后留下的未配對(duì)電子的自旋及軌道角動(dòng)量的矢量的“平行”和“反平行”特點(diǎn)雙峰間的強(qiáng)度比取決于各自的簡(jiǎn)并度（2j1）Subs j valuesA rea ratios1/2-1/2, 3/21:2pd3/2, 5/22:3f5/2, 7/23:4峰寬峰寬E一般定義為半峰寬，F(xiàn)W

2、HM um)(fullwidlfE = (En+ Ep+ Ea )222 1/2一般小于2 eVEn：the natural or inherent width of the core levelEp ：the width of the photon sourceEa：theyser resolutionSecondary structure（二級(jí)結(jié)構(gòu)）X-ray salites （峰）Multiplet splitting （多重裂分）Shake-up and shake-off（振激和振離）Energy loss（能量損失峰）XAES（X光激發(fā)的俄歇電子峰）峰的來(lái)源由于X光的非單色性，導(dǎo)致

3、除韌致輻射和K1,2主線外，還可能有其他副線K1,2：2p3/2, 1/2 1s K：價(jià)帶 1sK3,4：transition in a multiply ionized atomX - ray lin eSepa ra tio n fro m K 1,2( e V ) an d( K 1,2rela tiv eM g en sity=100) A lK K 3K 4K 5K 6K 4.5(1.0) 8.4(9.2) 10.0 ( 5 .1 )17.3 ( 0 .8 )20.5 ( 0 .5 )48.0 ( 2 .0 )5.6( 1.0) 9.6( 7.8) 11.5( 3.3) 19.8(

4、0.4) 23.4( 0.3) 70.0( 2.0) 其他雜峰的甑別 雜峰來(lái)源：陽(yáng)極靶上的雜元素發(fā)射所致 采用鎂靶時(shí)，鋁窗上鋁的發(fā)射：判別原則向高動(dòng)能端位移 233.0 eV 的弱峰 Cu L的發(fā)射由于陽(yáng)極靶的基材為銅，一些使用日久的陽(yáng)極靶或者部分露基材的陽(yáng)極靶會(huì)在峰的低動(dòng)能端出現(xiàn)弱的雜峰（對(duì)鎂靶位移為323.9 eV；對(duì)鋁靶位移為 556.9 eV）。多重裂分 譜線的多重裂分發(fā)生在具有自旋的原子，如價(jià)帶上有不成對(duì)的電子。電子從這些原子的芯能級(jí)發(fā)射出去后，能以兩種或多種方式產(chǎn)生空穴，留下的這個(gè)新的不成對(duì)的電子的自旋能以多種方式和其他不成對(duì)的電子產(chǎn)生耦合，使形成的終態(tài)的數(shù)目大于1，相應(yīng)于每個(gè)終態(tài)

5、有一譜線。這就形成了譜線的多重裂分振激和振離 在光電子發(fā)射過(guò)程中，并不是簡(jiǎn)單地產(chǎn)生一個(gè)光電子和一個(gè)處于基態(tài)的離子。由于一個(gè)電子被發(fā)射出來(lái)，原子自洽場(chǎng)突然發(fā)生變化，這時(shí)最外殼層的電子就可能被激發(fā)到更高的空帶中去，使離子處于比基態(tài)高幾個(gè)eV的激發(fā)態(tài)( shake-up)，也可能使電子激發(fā)到連續(xù)能級(jí)上 (shake-off)。實(shí)際上這時(shí)已經(jīng)電離了。在上述情況下，發(fā)射出的光電子動(dòng)能要減少，從而使主峰左邊（低動(dòng)能側(cè)）出現(xiàn)伴峰Cerium 3d signal from CeO2能量損失峰光電子和表面之間有相互作用，有些光電子要損失一定的能量而出現(xiàn)能量損失峰。金屬樣品中由于等離子激元激發(fā)而變得反而突出。Al

6、2s出現(xiàn)一系列因等離子激元激發(fā)而產(chǎn)生的光電子能量損失峰，它們的間距約15.3eV。b點(diǎn)是激面等離子體的能量損失峰。絕緣體中的光電子損失峰比金屬弱。XAES峰X(qián)射線也會(huì)使原子受激而產(chǎn)生空穴，然后出現(xiàn)Auger退激過(guò)程Auger電子hBackground:Photoelectrons with energy lossPeak:Photoelectrons without energy lossRelative binding energies and ionization cross-sectionforUFor p, d and f peaks, two peaks are observed.A

7、uThe separation betspin orbital splitting.n the two peaks are namedThe values of spin orbitalsplitting of a core level of an element in differentcompounds are nearly the same.Thepeakarearatiosofacorelevelofanelement in different compounds are also nearlythe same.Spin orbital splitting and peak area

8、ratios assist in element identifications.Spin-orbital splittingPeak NoionsL-S Coupling ( j = l s )e- 1 2 1 2ssj = l12j = l + 12QualiiveysisGolS wide scan spectrum57AugeaksN67O45O45N5N6N67N4N6N67N5N67VBinding Energies1416134213241247Photoelectron Peaks4s4p1/24p3/24d3/2 4d5/25s4f5/24f7/25f1/25p3/2Bind

9、ing763energies643547353331510888474X-ray Induced Auger ElectronsK.E. is independent of the x-ray photon energy.However,he B.E.scale, Augeakitions depend on the x-ray source.General methods in assisting peak identification(1) Check peakitions and relative peakensities of 2 or morepeaks (photoemisline

10、s and Auger lines) of an element(2) Check spin orbital splitting and area ratios for p, d, f peaksA maridiment sample from Victoria HarborSi 2pSi 2sThe followingelements were found: O, C, Cl, Si, F, N, S,Al, Na, Fe, K, Cu,Mn, Ca, Cr, Ni, Sn, Zn, Ti, Pb, VAl 2sAl 2pXPS Sampling Depthi = inelastic mea

11、n free path of an electron in a solidFor an electron ofThe surface, theensity Io emitted at a depth d belowensity is attenuated according to theBeer-Lambert law. So, theas it reaches the surface isensity Is of the same electrone-d/Wi one Is = Iopath length of63% of allelectrons are scattered Samplin

12、g DepthSampling Depth is defined as the depth from which 95% of all photoelectrons are scattered by the time they reach the surface ( 3 )Most s are radiationhe range of 1 3.5 nm for AlKSo the sampling depth (3) for XPS under these conditions is 3-10 nm“Universal Curve” for IMFPdepends onK.E. of the

13、photoelectron the specific materialnm (nanometers)1 monolayer = 0.3 nmive XPS: Iive measurements are as accurateSome XPSas 10%where: Ii=ensity of photoelectron peak “p” for element “i”Ni = average atomic concentration of element “i”hesurface underysisi= photoelectron cross-section (Scofield factor)f

14、or element “i” as expressed by peak “p”i = inelastic mean free path of a photoelectron from element “i” as expressed by peak “p”K= all other factors related toive detection ofa signal (amed to remain constant during expt)Ii = Ni i i KHow to measure ImeasuredWorstAccuracy betterusing ASFsn 15%Use of

15、standards measuredon same instrument or fullexpresbetterabove accuracyn 5%In both cases, reproducibilityBest(preci) bettern 2%TransmisTransmis energy TransmisFunctionfunctionis thedetectionefficiencyoftheelectronenergies.yzer,whichisafunctionofelectronfunction also depends on the parameters of the e

16、lectronenergyyzer, such as pass energy.Pure Au after Ar+ sputteringive Scofield Cross-section Factors (i )ysis: IIe been calculatedfor each element from scattering theory, specifically forAlK and MgK radiationInelastic Mean Free Paths (i ) varies with the kinetic energy of the photoelectron. It can

17、be estimatedfrom a “universal curve” or calculated (better).For a multi-element surface layer consisting of elements i, j, k.NiIi=(i i )Ni+Nj+NkIii i+Ijj j+Ikk k Examples of ion I Examples of io Errors in ionIi = sometimes difficult to separate “rinsic”photoelectrons for the “extrinsic” scatteredpho

18、toelectrons which comprise the background ( 5 - 100%)i = calculated value (unknown magnitude)i = estimated error 50%Ses2Chemical shifts in XPSInitial and final sesKoopmans theoremEquivalent core approximationCalculations for binding energies and chemical shiftsLine widths and resolution Chemical Eff

19、ects in XPSChemical shift: change in binding energy of a coreelectron of an element due to a changehe chemical bonding ofement.Qualiive view: Core binding energies are determined by:electrosiceraction betn it and the nucleus, andreduced by:the electrosic shielding of the nuclear charge from allother

20、 electronshe atom (including valence electrons)removal or addition of electronic charge as a result ofchanges in bonding will alter the shieldingWithdrawal of valence electron charge(oxidation)increase in BEAddition of valence electron chargedecrease in BEChemical Shifts: Oxide Compared to MetalBind

21、ing Energy is lowerdue to increased screening of the nucleus by 2s conduction by 2s electronsBinding Energy is higherbecause Li 2s electron density is lost to oxygenPE spectrumLi-metal1s21s21s2Li2O2s62s2s1s21s21s2 2s2LiLi0Li2OLi-metalLi 1sBinding EnergyEFermi2s DensityPhotoemisas 3 steps:Pros can be

22、 thought of(a) Photon absorption and ionisation (initial seffects)e(b) Response of atom and creation of photoelectron(final se effects)(c) Transport of electron to surface (extrinsic effects)BA + B(one additional+ve charge)BABKoopmans TheoremThe BE of an electron is simply the difference betn the in

23、itial se (atomwith n electrons) and final sphotoelectron)e (atom with n-1electrons (ion) and freeBEEfinal(n-1) Einitial(n)If no relaxation* followed photoemis, BE- orbital energy, which can becalculated from Hartree Fock. *this “relaxation” refers to electronicrearrangement following photoemissurfac

24、e atoms. not to be confused with relaxation ofThe Chemical Shift: Charged Sphere MFor a single atom j:E = qve2qv = no. of valence electronsqvrr= average radius of valenceelectronsvvrvEb = qve2rvAdd change ineratomic potentialEb = qve2 - Vijrvwhere Vij = potential of atom i on jOC (1s)CCH3CH3Peak wid

25、th = 1.1-1.5 eVCH3C=OEb285288C-CF3qve2 - VijC-C-CrvTiC2Eb291281Examples ofChemical Shiftsed Iron 2p Spectrum of High Purity IronFe 2p/12x 10Metallic FeFe2O3712710Binding Energy (eV)708706704702700ed Spectrum of Fe 2p line for Magnetite(partly oxidized)Fe 2pHSS2 3/332x 1035Fe (III)3025Fe (II)20157207

26、18716714712710Binding Energy (eV)708706704702700ed Oxygen 1s SpectrumO 1s/22x 10Metal OxideSurfaceHydration1210864540538536534532Binding Energy (eV)530528526524522BeforesputteringAfter 200eVAr+ sputteringB 1sB 1sCubic-BNCrystalBNoxide206 204 202 200 198 196 194 192 190 188 186Binding Energy (eV)206

27、204 202 200 198 196 194 192 190 188 186Binding Energy (eV)N 1sN 1sBNBNO?412 410 408 406 404 402 400 398 396 394 392Binding Energy (eV)412 410 408 406 404 402 400 398 396 394 392Binding Energy (eV)c/sHigh Resolution SpectraArsenopyriteBE 0.000.560.691.252.724.20BE40.9941.5541.6842.2443.7145.19FWHM0.630.750.630.751.661