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

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

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

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

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

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

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

Still going strong…

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

Experiment

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

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

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

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

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…

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)

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)

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!

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

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

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

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

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

Acknowledgements Soft X-ray Group in Uppsala Mjukröntgengruppen http://usxs.fysik.uu.se/