Electron spectroscopy Lecture Kai M. Siegbahn ( ) Nobel Price 1981 High resolution Electron Spectroscopy

Transcription

1 Electron spectroscopy Lecture 1-21 Kai M. Siegbahn ( ) Nobel Price 1981 High resolution Electron Spectroscopy

2 653: Electron Spectroscopy urse structure cture 1. Introduction to electron spectroscopies cture 2. Ultraviolet photoelectron spectroscopy: introduction cture 3-4. Electron spectroscopies: experimental methods cture 5-7. Interpretation of UPS, complications, computational methods cture XPS: spectra, interpretation, basic theory of photoelectron spectroscopy

3 Lecture 13-15: Complications of photoemission, many body effects Lecture 16-17: Auger electron spectroscopy Lecture 18-19: Electron spectroscopy case studies: evolution of metallicity, C60, conductivity Lecture 20-21: Electron spectroscopy case studies: surfaces Lecture 22-23: Electron spectroscopy case studies: solids, electronic structure Lecture 24-25: Electron spectroscopy case studies: catalysis

4 Lecture 26-27: Electron spectroscopy case studies: monolayers, LBs Lecture 28-29: Electron energy loss spectroscopy of core levels Lecture 30-31: Electron energy loss spectroscopy of molecules and surfaces Lecture 32-33: Bremstrahlung isochromat spectroscopy Lecture 34: Electron spectroscopy with advanced light sources Lecture 35: Electron spectroscopy: current research

5 ferences Hufner, Photoelectron Spectroscopy, Springer-Verlag, Berlin, C. Smith, Surface Analysis by Electron Spectroscopy, Plenum, New Yor 94. R. Bundle and A. D. Baker (Ed.), Electron Spectroscopy, Vol. 2,, Academi w York, iggs and Seah, Practical Surface Analysis, John Wiley, New York, 1983.

6 J. Berkowitz, Photoabsorption, Photoionization and Photoelectron Spectroscopy, Academic Press, New York T.A. Carlson, Photoelectronand Auger Spectroscopy, Plenum Press, New York, 1975 D. A. Shirley, Ed., Electron Spectroscopy, North-Holland, Amsterdam, K. Siegbahn, C. Nordling, G. Johansson, J. Hedman, P. F. Heden, K. Hamrin, U. Gelius, T. Bergmark, L. O. Werme, R. Manne, and Y. Baer, ESCA Applied to Free Molecules, North-Holland, Amsterdam, Reviews, papers

7 Broad class of spectroscopic techniques, collectively called electron spectroscopy. In general terms, electron spectroscopy can be defined as the energy analysis of electrons ejected or reflected from materials. All of these spectroscopic techniques yield information on the ELECTRONIC STRUCTURE.

8 There are, generally five techniques collectively called electron spectroscopy

9 X-ray photoelectron spectroscopy (XPS) Ultraviolet photoelectron spectroscopy (UPS) Aüger electron spectroscopy (AES) Electron energy loss spectroscopy (EELS) Inverse photoemission spectroscopy (IPS)

10 There are a range of techniques in each of these UPS Photon source variation He I 21.2 ev He II 40.8 ev Ne I Synchrotron radiation

11 UPS Variations of the same basic technique One photon spectroscopy Solids Gases Gas cell Molecular beams

12 Photoelectron-photoion coincidence spectroscopy Zero-kinetic energy photoelectron spectroscopy Multiphoton photoelectron spectroscopy Photodetachment spectroscopy..

13 Structure and Properties of Matter Spectroscopy Scattering Physical Properties Spectroscopy (pre-1965) Absorption Magnetic Mass

14 Spectroscopy using electrons e + M +, M 2+ E e + M + M + Current I 4 I 3 I 2 I 1 Electron KE Ionization efficiency curves Detector

15 hν + M + Detecto M + current I 1 I 2 I 3 I 4 Photon Energy

16 hν + M M + + e hν Constant + (No M 2+, generally) M + + e Photoelectron Spectroscopy Photoelectric effect Early experiments in 1887 Detector KE hν = KE + φ 1905

17 Photoion can be excited M + hν M + (E int ) + e elec vib rot hν -I -E int KE of the electron

18 Conservation of momentum requires that excess energy is partitioned in inverse proportion to the masses. Excited ionic states e I 1 * hν M + I 1 M I 2 E int I p hν

19 Electron and ion separates with equal momenta. mu = MU The relative velocity, V = u + U = U (1+ M/m) = u (1+ m/m) The kinetic energies, ½ MU 2 = 1 m MV 2 m+m 2M ½ mu 2 = 1 m MV 2 2m m+m

20 hν - (I p + E int ) KE hν - KE I p + E int hν -KE 1 IP 1 hν -KE 2 IP 2 hν -KE 3 IP 3.. E int o hν - KE I p Vertical adiabatic E r e

21 Depth of analysis depends on photon energy He I 21.2 ev 2 1 P 1 1 S He II 40.8 ev 2 P 1 S of He + 3 / Al K α1, ev 2 P 2, 1 / 2 1 S Mg K α1, ev Na K α1, ev Si K α1, ev 1000 Core Valence uv Hard X rays Soft X rays

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23 Aüger electron e hν e hν Photoemission X-ray fluorescence Aüger process

24 e e Vac 2, 3 (Z) L 1 (Z) L 2, 3 (z+ z) K(Z) Neutral atom Photo emission Electronic transition Coulomb field redistribution Aügur electron emission Final state

25 E K, L 1, L2, 3 = E k -E L1 - E L 2, 3 E ABC (Z) = E A (Z) - ½ [ E B (Z) + E B (Z+1) ]- ½ [ E C (Z) + E C (Z+1) E s are the binding energies. E ABC K L 1 L 2, 3, K L 1 V, KVV Intense Auger intensities if the valence electron density is high. Fluorescence efficiency increases with transition energy. Fluorescence and Auger are comparable when Ε ~ 10,000 ev.

26 VALENCE SHELL PHOTOELECTRON SPECTROSCOPY

27 Counts / sec ( A ) ( B ) M + Ionization Energy ( 1 ) ( 2 ) ( 3 ) M ( C ) M + ( 3 ) ( 2 ) ( 1 ) I 1 I 2 I 3 M

28 INTERNUCLEAR DISTANCE

29 P σ g non bonding 2345 to 2191 cm -1 Pπ u bonding 2345 to 1850 cm -1 Sσ u weakly antibonding 2345 to 2397 cm -1 E v = E o + ω e (v + ½) - ω e x e (v + ½) 2 D e = ω 2 / 4 ω e x e

30 HeI UPS of H 2 Vibrations and Rotations!

31 ORE LEVEL PHOTOELECTRON SPECTROSCOPY

32 XPS-spectra of the ls core levels of Li, Be, B, C, N, O, F (from S. Hüfner).

33 Counting Rate Binding energy ev

34 Counting Rate Chemical Shift E B =291.2eV

35 INSTRUMENTATION

36 Simplest spectrometer

37 To diffusion pump µ metal shields hν (584 Å) Gas sample Electro countin system

38 Synchrotron Radiation and XPS ELECTRON BEAM Layout of the synchrotron radiation laboratory at DORIS.