1. X-Ray Emission Spectroscopy Photons in and Photons out
Jan-Erik Rubensson
Uppsala University
Summer School, Odengården, May 26- June 2, 2008

2. Outline General Introduction Local Partial Density of States
Site Selectivity
Typical attenuation length: 1000Å
Instrumentation
Soft X-ray spectrometers: Resolution, resolution, resolution and the new PGS
Synchrotron radiation: Brilliance, brilliance, brilliance and MAX-IV
RIXS; Resonant Inelastic Soft X-ray Scattering
Always a one-step process
Energy conservation
Momentum conservation
Symmetry selectivity
Dynamics
Interference and vibronic coupling
Core-hole clock
Applications
Complex Systems

3. X-ray emission: Characteristic radiation?
H. G. J. Moseley, M. A. Phil. Mag. (1913), p. 1024

4. Yes, but also uncharacteristic Valence electronic struture
Phys. Rev. 45, 370 (1935)

5. Local Partial Density of States
Core levels are atomic-like:
Local Properties
Dipole Selection rules are valid:
Symmetry Selectivity
Valence Band
Local
Si (s+d)
Si 2p
Local
C p
C 1s
Local Partial Density of States

6. Very little has been done with synchrotron radiation: Notoriously low count rates
Conduction
Intermediate
Valence
Core
0.1%
Final
Ground

7. Rowland spectrometer Source Detector Grating
Combining the focussing properties of a sphere with the dispersive properties of a grating

8. Still going strong…

9. New Concepts for efficiency and resolution
PGS:
Plane grating spectrometer
Two parabolic mirrors and a plane grating
FTS:
Fourier Transform Spectrometer
Wavefront Beamsplitters and mirrors in grazing incidence

10. Experiment

11. X-ray scattering; always a one-step process
Core Excited
Emission:
Absorption:
Valence Excited
Ground State

12. Linear approximation
M. Blume, J. Appl. Phys. 57, 3615 (-85): This equation ’accounts for
most scattering phenomena to the order of ’

13. Helium Doubly excited states 2l’n’l’’ Singly excited states 1snl
’One can get X-ray emission from everything except hydrogen and helium’
Distinguished Professor
Helium
Doubly excited states
2l’n’l’’
Singly excited states
1snl
Ground
1s2

14. Autoionizing resonances?
Schulz et al., PRL 1996
2l’n’l’’
1s + e
1s2
Autoionizing resonances?

15. Symmetry resolution in RIXS
Strict dipole selection rules:
J. Söderström et al., PRA 2008
Influence of s-o coupling and external fields, two-color experiments, PGS measurements…

16. The oxygen molecule Strict dipole selection rules apply:
’A core hole is localized at one atomic site’
Distinguished Professor
The oxygen molecule O O ’
Right?
Both? O O
Left?
Strict dipole selection rules apply:
GeradeUngeradeGerade
Inversion symmetry is not broken
P. Glans, et al. PRL 76, 2488 (-96)

17. O O O O Carbon Dioxide Scattering duration time!
Vibrations break the symmetry
2. But not if the energy is detuned O O O O
Scattering duration time!
P. Skytt, et al., PRL 77, 5035 (-96)

18. Energy Conservation 4d4f resonance in LaF3 Scattering:
’The core-hole lifetime width will always be limiting the information you can get out of RIXS spectra.’
Distinguished Professor
Energy Conservation
4d4f resonance in LaF3
Scattering:
Gives narrow peaks.
intensity indicates
that the 4f electron escapes during the
process: Core hole Clock!

19. Momentum Conservation
’But you can never do band mapping with X-ray emisson because the core hole destroys the translational symmetry.’
Distinguished Professor
Momentum Conservation
S. Eisebitt et al., 1998

20. Silicon Carbide again
J. Lüning et al., PRB56 -97

21. Site Selectivity in Complex Systems
’This gives me a headache’
Distinguished Professor
Site Selectivity in Complex Systems

22. Looking Through Windows
Several 1000 Ångström
-gases
-liquids
-gas/liquid/solid interfaces

24. Many applications of liquid studies
Biology, Pharmaceutics, Drug solubility
Electrochemistry, battery technology, corrosion
Environmental Science, etc...

25. Acknowledgements Soft X-ray Group in Uppsala
Mjukröntgengruppen