X-Ray Emission Spectroscopy

Transcription

1 X-Ray Emission Spectroscopy Axel Knop-Gericke

2 Core Level Spectroscopy Anders Nilsson. Journal of Electron Spectroscopy and Related Phenomena 126 (2002) 3-42

3 Creation of core holes X-Ray Photoelectron Spectroscopy (XPS) X-ray photoelectron spectroscopy(xps) Anders Nilsson. Journal of Electron Spectroscopy and Related Phenomena 126 (2002) 3-42

4 Creation of core holes X-Ray Absorption Spectroscopy (XAS) Anders Nilsson. Journal of Electron Spectroscopy and Related Phenomena 126 (2002) 3-42

5 Decay of core holes X-Ray Emission Spectroscopy (XES) Anders Nilsson. Journal of Electron Spectroscopy and Related Phenomena 126 (2002) 3-42

6 Decay of core holes Auger Electron Spectroscopy Anders Nilsson. Journal of Electron Spectroscopy and Related Phenomena 126 (2002) 3-42

7 Resonant Excitation Resonant X-ray Emission Spectroscopy(RXES) Resonant Inelastic X-ray Scattering(RIXS) Lange et al. Journal of Electron Spectroscopy and Related Phenomena 188 (2002)

8 X-ray attenuation length B. L. Henke Atom Data Nucl. Data 54, 181 (1993)

9 K fluorescence K shellemissionlinesin MnO P. Glatzelet al.; Coordination Chemistry Reviews 249 (2005) Kβ 1 : 3p 3/2, Kβ 3 :3p 1/2 final states Kβ 2 : transitionfrom4p orbitals, Kβ 5 : from3d orbitals

10 X-ray Emission Techniques High-Energy Resolution Fluorescence Detected(HERFD) XAS Experiment: The emittedenergyωistunedtoa fluorescencelineandthe incident energy Ω is scanned through an absorption edge. The intensity variation of the fluorescence line is recorded as a function of the incident energy. Dispersive solid state detector: energy bandwith of ev at Fe Kα line Non linearity at high count rates(pileup effect) Other option: use an X-ray spectrometer and avalanche photodiode(no background)

11 HERFD setup P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

12 Bragg Equation William Lawrence Bragg and Henry Bragg Noble PrizeofPhysicsin 1914

13 TFY-HERFD Detection Mode Pt L 3 edge XANES of a Pt foil M. Tromp,

14 X-ray Emission Techniques Non-Resonant X-Ray Emission Spectroscopy(XES) Experiment: The incident energy Ω is tuned well above an absorption and the emittedenergyωisscannedovertheenergyrangeofa fluorescenceline XES isa secondorder process. Ifthecorehole isreplacedbyanothercore hole, e.g. 3p to1s (Kβ) transitionin a 3d transitionmetal, thesensitivityto the valence electrons is indirect. The final state core hole interacts with the valenceelectronsandthisinteractionshapestheemissionline. The Kβmainline, forexample, aresensitive tothevalenceshellspinstate.

15 K βlines 55 Fe 2 O 3 (solid line) S=5/2 K 3 55 Fe(CN) 6 (dashedline) S=1/2 K 4 55 Fe(CN) 6 (dottedline) S=0 Prussian Blue (Fe 4 [Fe(CN) 6 ] 3 ) Measured after K capture decay P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

16 KβlinesofMnfluoridesandoxides MnF 2 (solid line) MnF 3 (dashedline) MnF 4 (dottedline) MnO(solid line) Mn 2 O 3 (dashedline) MnO 2 (dottedline) Different correlation of fluorides and oxides due to different degree of covalent bonding! P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

17 Extended X-rayAbsorption Fines Structure -EXAFS RbNO 3 watersolution andrb vapour@ RbK edge

18 Extended X-rayAbsorption Fines Structure -EXAFS Ni K-edge EXAFS spectra (left) and their Fourier transform magnitudes (right) measured on the as deposited Ni/Al multilayer sample and on samples after ion mixing at substrate temperatures -140 C, 130 C, 230 C, 280 C and 330 C. For comparison the spectra of Ni metal and NiAlmonocrystalare added. Solid line - experiment; dashed line - EXAFS model.

19 Site selective EXAFS Kβemissionin PrussianBlue (Fe 4 [Fe(CN) 6 ] 3 ) High spincomponent: Fe(III)Fe 2 O 3 Low spincomponent: K 4 Fe(CN) 6 P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

20 Deduced site selective EXAFS spectra P. Glatzel et al. Inorg. Chem. 41 (2002) 3121

21 Kα lines Spectral changes for Kα lines are less pronounced The 2p and3d orbitalsinteractlesswith eachotherthan3p and3d becauseofthe smalleroverlapofthewavefunction. P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

22 Valence electron perturbation upon 1s photoionisation P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

23 Resonant X-ray Emission Resonant X-Ray Emission Spectroscopy (RXES) and Resonant Inelastic X-Ray Scattering (RIXS) Experiment: The incidentenergyωisscannedacrossan absorptionedge. The emitted energy ω is also scanned either over the fluorescence lines or over energies just below the elastically scattered peak. In the later case, the energytransferω-ωbecomessmall(on theorder ofa fewev) andvalence band excitations are observed. -A fluorescence line can be measured after resonant excitation. This is referred to as resonant X-ray emission - Spectral features may occur at emission energies different to the energies ofthefluorescencelines. These featuresarefrequentlyobservedatan energytransferofa fewev.the techniqueisoftenreferredtoasresonant inelasticx-rayscattering(rixs).

24 RIXS energy scheme for 1s(2,3)p RIXS in a transition metal atom P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

25 Resonant inelastic X-ray scattering(rixs) Inelastic scattering of the incident photon at a resonance energy of the metalionandistheoreticallydescribedbythekramers-heisenberg formular: f T2 n n T1 g Γf / 2π F( Ω, ω) = 2 E E + Ω iγ / 2 f n g n n 2 ( ) 2 E E + Ω ω + Γ / 4 g f f n = 1s3d n+1 g f =3d n =(2,3)p 5 3d n+1 E g, E n ande f : Energiesofground, intermediate andfinal state Γ n, Γ f : lifetimebroadeningsoftheintermediate andfinal state T 1, T 2 : transitionoperatorsforabsorptionandemission

26 Resonant inelastic X-ray scattering 1) The absorbingatomisnot ionizedin thecaseofresonant excitation, as the photoexcited electron stays within a bound state. 2) The spectral feature becomes sharper because it is the lifetime of the final state which determines the broadening 3) The final state electronic configuration may formally be equal to other spectroscopies, e.g. the L-edge in 1s3d2p RIXS of 3d transition metals or UV-Visin RIXS thatexhibitsa hole in thevalenceband in thefinal state. investigatethedipolallowed2p-3d transition(below1.1 KeVin ambient pressure) 4) Less radiation damage

27 Howtostudythe3d shellbyk shellspectroscopy? Dipol selectionrulesδl= + 1 Quadrupol transition are by more than two orders of magnitude lower Two approaches: investigate 2p or 3p - 1s fluorescence lines that emitted after 1s hole creation Information on the 3d metal shell will be derived indirectly by analysingtheinteractionofthe2p or3p hole withthe3d electrons (large overlap of wave functions) K fluorescence show a pronounced chemical sensitivity

28 Second approach: Study the weak K absorption pre-edge structure by probing directly the transition1s-3d RIXS enables the separation of pre-edge structures from main K absorption edge

29 HERFD/RIXS setup Photon flux: photons/s (secondgenerationsynchrotronradiationfacility) Photon flux: photons/s (thirdgenarationsynchrotronradiationfacility) ESRF, APS, Spring8, PetraIII, SOLEIL, DIAMOND P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

30 SurfaceplotoftheRIXS plane P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

31 Theoretical RIXS plane with three line plots Γ K = 1.1 ev Γ L = 0.5 ev P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

32 Continuum excitations P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

33 Experimental dataofthe1s 3d resonancein NiF 2 a) K absorption pre-edge b) CEE lineplotwith5 ev emissionanalyser bandwith c) CEE lineplotwith1 ev emissionanalyser bandwith d) CET line plot integrated over 2p3/2 final states P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) 65-95

34 Resonant inelastic X-ray scattering Less resrictive than UPS with respect to the sample environment Element selective Probing the electronic structure around the Fermi level van Bokhoven et al. JACS 132, 2555 (2010)

35 2p 3/2 RIXS planes ofptnanoparticles: metallic andwithco adsorbed Metallic state: elastic peak merge with valance-band excitations Fermi level lies within a partially filled band ρ ' ρ ( ε ) ( ε + Ω ω) d d F( Ω, ω) = E + Γ 2 2 n ( ε ω) 4 ρ :densities of occupied Ptd states ρ : densitiesof unoccupied Pt states Γ n : lifetimebroadeningof the2p 3/2 corehole (5.4 ev) van Bokhoven et al. JACS 132, 2555 (2010)

36 HERFD L 3 XAS RIXS Dashedlines: exp. HERFD XAS Solid lines: RIXS Calculated spectra: HERFD XAS Solid lines: RIXS van Bokhoven et al. JACS 132, 2555 (2010)

37 Literature A. Nilsson; Journal of Electron Spectroscopy and Related Phenomena 126 (2002) 3-42 P. Glatzel, U. Bergmann; Coordination Chemistry Reviews 249 (2005) K. Lange ; Journal of Electron Spectroscopy and Related Phenomena 188 (2013)

38 Literature

39 Creation of Core holes Ionisation Excitation X-ray photoelectron spectroscopy(xps) X-ray absorption spectroscopy XAS X-ray Inelastic scattering (XIS) Anders Nilsson. Journal of Electron Spectroscopy and Related Phenomena 126 (2002) 3-42

40 Core Level Spectroscopy XPS XAS

41 Core Level Spectroscopy XES AES