27 April 2018 Attoscience delves deeper into solids

Experimental setup of the two layers of graphite and incident attosencond SXR pulse

ICFO researchers develop a technique to obtain the electronic, structural and chemical information of a material with atomic resolution at once. X-ray absorption fine-structure (XAFS) spectroscopy is a powerful technique that provides electronic as well as structural and chemical information with atomic resolution. In XAFS, electronic information is extracted from the near-edge XAFS (XANES or NEXAFS), which arises from transitions from inner-shell orbitals to unoccupied electronic states near the Fermi energy level. High spectral resolution is needed to resolve its features, which occur within only a few electron volts. On the other hand, structural information is mainly obtained from the extended XAFS (EXAFS), which extends over several hundred electron volts above the absorption edge. So far, it has been impossible to measure and link electronic with structural information in real time.

Now, in a recently study published in the journal Optica, ICFO researchers Bárbara Buades, Themistoklis P. H. Sidiropoulos, Iker León, Peter Schmidt, Irina Pi, Nicola Di Palo, Seth L. Cousin, Antonio Picón, led by ICREA Professors Jens Biegert and Frank Koppens, in collaboration with the Max Planck Institute for Chemical Energy Conversion and the University of Salamanca, have been able to carry out a simultaneous measurement of XANES and EXAFS with an isolated attosecond soft x-ray (SXR) pulse. In their study, the team of researchers was able to use the generation of isolated attosecond SXR pulses with coverage over the entire water window (284–534 eV) and successfully apply XANES and EXAFS to simultaneously access electronic and lattice parameters.

The results of the study demonstrate the potential of the XAFS technique, in combination with attosecond pulses, as a powerful investigative tool that is equally applicable to gas, liquid, and condensed phase of matter. For example, it can be used to access the characteristic time scale of electronic motion to resolve charge migration, electron-electron correlation, electron-nuclear scattering, and structural transitions.