Ultrafast core-loss spectroscopy in four-dimensional electron microscopy
We demonstrate ultrafast core-electron energy-loss spectroscopy in four-dimensional electron microscopy as an element-specific probe of nanoscale dynamics. We apply it to the study of photoexcited graphite with femtosecond and nanosecond resolutions. The transient core-loss spectra, in combination with ab initio molecular dynamics simulations, reveal the elongation of the carbon-carbon bonds, even though the overall behavior is a contraction of the crystal lattice. A prompt energy-gap shrinkage is observed on the picosecond time scale, which is caused by local bond length elongation and the direct renormalization of band energies due to temperature-dependent electron–phonon interactions.
Additional Information© 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. Received 20 February 2015; accepted 23 March 2015; published online 28 April 2015. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research in the Gordon and Betty Moore Center for Physical Biology at the California Institute of Technology. We thank S. T. Park for the helpful collaboration in programming the data acquisition script for energy-drift correction and K. Jorissen for assistance with the FEFF calculations. R.M.V. acknowledges financial and institutional support from S. Techert and the Max Planck Institute for Biophysical Chemistry. T.J.P. thanks the Swiss National supercomputing center for computational time.
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