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Hard x-ray PhotoElectron Spectroscopy : Ultrafast dynamics and Electron correlation – HAXPES

Submission summary

1- Scientific background and objective This project aims at acquiring a state-of-the-art high-resolution high-energy electron analyzer working in the hard x-ray region (2 – 12 keV).The analyzer is to be installed on the GALAXIES (inelastic x-ray scattering (IXS) and electron spectroscopy) beamline at SOLEIL, whose specifications are optimized to host such an instrument. The use of this instrument fulfills the needs of the two leading communities of the HAXPES project: atomic and molecular physics and hard condensed matter. Owing to its high performances combined to the high kinetic energy range, the HAXPES analyzer will be the sole of its kind in the world. The scientific objective made possible by its novel conception and the beamline qualities covers both the investigation of sub-femto nuclear motion with vibrational resolution and that of complex materials (primarily strongly correlated systems as well as buried layers and nano-objects). 2- Description of project, methodology The high kinetic energy of the electrons is doubly advantageous: the short-lived transient state of core-levels gives access to sub-femtosecond molecular dynamics; the increased electron mean free path, by one order of magnitude compared to standard photoemission, provides a means to probe the bulk state of materials. The analyzer sample environment will be designed to switch between gas and solid phase experiments in a fast and reliable manner; in addition, each setup will have its own dedicated environment. The analyzer will have a maximal energy resolution of 30 meV at 12 keV. In this high-resolution mode, it will be possible to resolve vibrational levels in the resonant Auger spectra which characterize the nuclear motion, and the low-lying states close to the Fermi energy, known to play and important role for the transport properties and superconductivity. At medium resolution, electronic properties and excitation dynamics will be probed by core-level photoemission. Resonant spectra will be obtained by tuning the incident photon energy to specific absorption edges. Then, the measurements will benefit from the intensity enhancement and the sharpening effects implied by the resonance: in the resonant conditions indeed, lifetime broadening can be overcome and process can be probed at a shorter time scale than the core-hole lifetime (resonant Raman effect). The concretization of the project entirely relies on the advent of novel analyzers whose performances would not have been conceivable in the last three years, and the upcoming of novel x-ray sources. SOLEIL will provide the full beamline infrastructure and guarantee best performances for HAXPES. Part of this project will serve to extend the nominal energy range of the GALAXIES beamline, towards 2 keV. Thus, K edges of elements such as S, P or Cl can be reached. To that extend, it is of prime importance that the project be decided at the time the technical specifications of the beamline will be finalized. The main cost of this project covers the expenses for the full electron analyzer, the gas introduction setup and gas cell, the cryo-cooled sample manipulator with He transfer, the preparation chamber, and the pumping stages. It will also include the salary of a post-doc during the last two years of the project. SOLEIL and the LCP-MR have accepted an exceptional funding of 105 000€ for this project one year-equivalent for an engineer of LCP-MR. The final definition of the project will be carried out in full collaboration with the manufacturer and with the help of the international collaborating teams. The expertise gained by the LCP-MR, SOLEIL and IMPMC groups in spectroscopy in the gas and solid phases is a strong guarantee of success. 3- Expected results Among the possibilities provided by the HAXPES instrument, we envisage to carry out original experiments on sub-femtosecond dynamics of nuclear motion in the gas phase and resonant photoemission in strongly correlated materials. In the latter, first results obtained at high energy already point to an in-depth reassessment of the physics in these materials. The existence on the GALAXIES beamline of an IXS-spectrometer and the high-energy electron analyzer, as proposed in this ANR framework, will constitute a unique combination of instruments, at a world-wide level, dedicated to hard x-ray spectroscopies. The competition between electronic relaxations processes by either radiative or non radiative channels could be investigated concomitantly on both experimental stations. Thanks to this analyser, the scientific and financial participation of the group of the professors Svensson and Piancastelli around the thematic of Van der Waals clusters will allow the direct study of the bulk of the cluster and will furnish a bridge between isolated atoms and solids.

Project coordination

Marc SIMON (Université)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

SYNCHROTRON SOLEIL SYNCHROTRON SOLEIL

Help of the ANR 400,000 euros
Beginning and duration of the scientific project: - 36 Months

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