XRay Emission Spectroscopy Photons in and Photons out

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 and the new PGS Synchrotron radiation: 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)

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

Very little has been done with synchrotron radiation: Notoriously low count rates Conduction Valence Core Intermediate 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 . ’

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

Schulz et al. , PRL 1996 2 l’n’l’’ 1 s + e 1 s 2 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…

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

Carbon Dioxide 1. Vibrations break the symmetry O O 2. But not if the energy is detuned Scattering duration time! P. Skytt, et al. , PRL 77, 5035 (-96)

’The core-hole lifetime width will always be limiting the information you can get out of RIXS spectra. ’ Distinguished Professor Energy Conservation 4 d 4 f resonance in La. F 3 Scattering: Gives narrow peaks. intensity indicates that the 4 f electron escapes during the process: Core hole Clock!

’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. , PRB 56 -97

’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/