1. Surface, interface and bulk sensitive X-ray absorption spectroscopy probed by total electron yield in liquid cell
Daniela Schön, Jie Xiao, Ronny Golnak, Marc F. Tesch, Emad F. Aziz
Helmholtz-Zentrum Berlin
Freie Universität Berlin
MRS Fall Meeting 2016
November 29, 2016

2. Introduction Motivation Probe of interfacial and bulk species
Detection schemes:
Partial Fluorescence Yield
Total Electron Yield
Chemical reactions occur at solid-liquid interface
Understanding of processes at the interface
Velasco-Velez Science Vol. 346, Issue 6211, pp (2014)
Winter Nature Chemistry 7,192–194 (2015)

3. TEY_Au only membrane; TEY_BE membrane and electrode
Flow cell structure
Keithley 6514
Distance of electrode to membrane: 1 mm
TEY_Au only membrane; TEY_BE membrane and electrode

4. Surface vs Bulk sensitivity
Features II and III are from the bulk, feature I is not.
Intensity ratio depends on either different relaxation channels or embedded oxygen.
Golnak et al Scientific Reports 6, (2016)
Golnak J. Phys. Chem. A, 2016, 120 (18), pp 2808–2814
 TEY_Au spectrum is surface senstive

5. Analysis of the gold coated Membrane
 Cr is not detectable with TEY_Au in liquid cell

6. Analysis of the gold coated Membrane
 Short mean-free-path makes TEY_Au surface sensitive

7. Interface Sensitivity
 TEY_BE is interface sensitive

8. TEY_Au: Auger electron is seperated due to Au dipole
Mechanism of the current production at the Water/gold Interface Under X-ray exposure
TEY_Au: Auger electron is seperated due to Au dipole

9. TEY_Au generates no current  recombination
Mechanism of the current production at the Water/gold Interface Under X-ray exposure
TEY_Au generates no current  recombination

10. TEY_BE: Auger electron induces potential  current
Mechanism of the current production at the Water/gold Interface Under X-ray exposure
TEY_BE: Auger electron induces potential  current

11. TEY_BE ion migrates to backside electrode  recombination
Mechanism of the current production at the Water/gold Interface Under X-ray exposure
TEY_BE ion migrates to backside electrode  recombination

12. Bulk has no contribution due to short mean-free-path
Mechanism of the current production at the Water/gold Interface Under X-ray exposure
Bulk has no contribution due to short mean-free-path

13. backside electrode connected
Mechanism of the current production at the Water/gold Interface Under X-ray exposure
TEY_BE membrane and
backside electrode connected
TEY_Au only membrane connected
TEY_BE: Interface signal / TEY_Au: Surface signal

14. i-TEY signal  Bulk sensitivity
Mn is not at interface.
Resonant absorption of Mn depletes the production of charge pairs at the water/gold interface  i-TEY signal.
Gotz, J. Phys. Chem. Lett., 2012, 3 (12), pp 1619–1623
i-TEY signal  Bulk sensitivity

15. Summary TEY_Au: surface sensitive.
TEY_BE: interface or bulk sensitive, yielding intensity peaks or dips, respectively, thanks to interfacial dipole layer and short mean-free-path of photoelectrons.
Bulk detection of dissolved ions through i-TEY.
TEY_BE exploits photon penetration depth and electron yield probability, maybe capable of probing low concentration samples.

16. Thank you for your attention Questions?
Helmholtz-Zentrum Berlin
Institute of Methods for Material Development