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Seeing into the Liquid-Solid Interface with Standing Wave Ambient Pressure Photoemission (SWAPPS)

Schematic illustration of standing-wave ambient pressure experiment, for thin aqueous film containing Na OH and CsOH deposited on Fe2O3. At right are the concentration profiles of Na+ and Cs+, illustrating the way in which Cs+ is excluded from the region just next to the Fe2O3 surface.

Scientific Achievement
Demonstrated that the use of standing-wave x-rays in ambient pressure photoemission (SWAPPS) permits sub-nanometer depth resolution of all species in a liquid/solid interface

Significance and Impact
The SWAPPS technique will permit study of liquid/solid and gas/solid interfaces with unprecedented resolution in depth, element, chemical state, and electrostatic potential; with wide applications in energy, environmental, and catalysis research.

Research Details

  • Standing-wave and ambient pressure photoemission were developed independently
  • Combining special expertise in these two methods provides powerful new technique
  • A strong standing wave is generated and a phase of the waves is tailored through the interface of interest by rocking the sample around the Bragg angle
  • The photoemission signal from different species is analyzed to determine their spatial arrangement and depth profile with sub-nm accuracy
  • Pros and cons of using harder x-ray excitation focus on photoemission signal strength and standing wave effects amplitude

S Nemšák, H Bluhm, C Fadley, & C Schneider, Nature Communications 5, 5441 (2014), and Faraday Society Discussion, 2015, doi: 10.1039/C5FD00003C