soft x-ray spectroscopy (and microscopy) for resolving ... · high resolution in soft x-ray...

Soft X-ray Spectroscopy (and Microscopy) for Resolving Corrosion-Related Challenges

Joachim Schnadt MAX IV Laboratory &

Division of Synchrotron Radiation Research, Lund University

Outline

● What are soft x-rays and what are they good for?

● X-ray photoelectron spectroscopy, x-ray

absorption spectrocopy, x-ray emission

spectroscopy/inelastic x-ray scattering

● Soft x-ray beamlines at MAX IV

● Ambient pressure x-ray photoelectron

spectroscopy in corrosion research: an example

● X-ray emission spectroscopy in corrosion

research: an example

● Soft x-ray microscopy @ MAX IV

What are soft x-rays? And what are they good for?


Soft x-ray regime (including the vacuum ultraviolet (VUV) regime): approximately 10 eV – 2000 eV

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All but outermost electron levels have characteristic energies

All elements have electron levels with energies that correspond to soft x-ray energies

Absorption of soft x-ray photons can promote such electrons to the vacuum (photoemission) or into unoccupied states (absorption); alternatively, scattering can be used

Particularly high probability for such excitations for the • 1s electrons of light elements (Li, Be, B, C, N, O, F), • 2p electrons of first row transition elements (Sc, Ti, V,

Cr, M, Fe, Co, Ni, Cu), • 3d electrons of late second row transition elements

(e.g. Ru, Rh, Pd, Ag), • 4f electron of late third row transition elements (e.g.

Ir, Pt, Au) • …

Image: https://nuclear-energy.net/definitions/atom.html


Small (”chemical”) shifts in energies of electron levels depend on chemical environment of atom

High resolution in soft x-ray spectroscopy allows these chemical shifts to be resolved, irrespective of whether photons or electrons are detected

High flux at MAX IV will allow not only static characterisation, but also montoring of dynamics



Most of the soft x-ray techniques at MAX IV are based on

Photoinduced emission of an electron (”photoemission”,

photoelectric effect) Photoelectron spectroscopy

and microscopy

Photon absorption X-ray absorption

spectroscopy

Photon scattering Resonant inelastic x-ray

scattering


1. FemtoMAX (2015) Ultra-fast processes in materials

2. NanoMAX (2016) Imaging, spectroscopic & scattering with nanometer resolution

3. BALDER (2016) X-ray absorption spectroscopy in-situ and time resolved

4. BioMAX (2016) Highly automated macromolecular crystallography

5. VERITAS (2016) RIXS with unique resolving power and momentum resolution

6. HIPPIE (2016) High-pressure photoelectron spectroscopy

7. ARPES (2017) Angle resolved photoelectron spectroscopy

8. FinEstBeaMS (2017) Estonian-Finnish Beamline for Materials Science

9. SPECIES (Transfer) (2017) VUV High-pressure photoelectron spectroscopy and RIXS

10. FlexPES (Transfer) (2017) Photoelectron Spectroscopy and NEXAFS

11. MAXPeem (Transfer) (2017) Photoelectron microscopy

12. CoSAXS (2018) Small angle scattering

13. SoftiMAX (2018) Coherent Soft X-Ray Scattering, Holography…

14. DanMAX (2019)

The MAX IV Laboratory





and microscopy


spectroscopy

Photon scattering X-ray emission spectroscopy;

Resonant inelastic x-ray scattering





and microscopy

Binding energy of electron in sample: EB = hν – Ekin (- φ)





and microscopy

Binding energy of electron in sample: EB = hν – Ekin (- φ)

At the kinetic energies of a soft x-ray experiment, the electrons are attenuated very strongly in (solid) matter: the electrons come from the top layers of material only; the experiment is very surface-sensitive.


Ambient pressure x-ray photoelectron spectroscopy at MAX IV: the HIPPIE and

SPECIES beamlines














14. DanMAX (2019)


High pressure x-ray photoelectron spectroscopy

Near-ambient pressure x-ray photoelectron spectroscopy

Ambient pressure x-ray photoelectron spectroscopy





Conventional XPS





Conventional XPS APXPS


Ambient water pressure: ~20 mbar

Pressures in typical soft x-ray spectroscopy experiments:

10-10 to 10-6 mbar

Pressures in thin film growth:

10-2 mbar and upwards

Pressures in typical catalytic reactors in the chemical industry:

10-2 mbar to hundreds of bar

Pressure in a car catalyst: ~atm


UHV 10-8 Torr CO

1 Torr CO 1 Torr CO

Pt(557)

Tao et al., Science 327 (2010) 850

Structure!

Structural dynamics!

Chemical reactions!


V. A. Saveleva, L. Wang, W. Luo, S. Zafeiratos, C. Ulhaq-Bouillet, A. S. Gago, K. A. Friedrich, E. R. Savinova, Uncovering the Stabilization Mechanism in Bimetallic Ruthenium−Iridium Anodes for Proton Exchange Membrane Electrolyzers, J. Phys. Chem. Lett. 7 (2016) 3240

Ambient pressure x-ray photoelectron spectroscopy in corrosion research

Oxygen evolution reaction (OER) in proton exchange membrane (PEM) electrolyser

Active electrode materials: RuO2, IrO2

RuO2 cheap, but affected by electrochemical corrosion before OER onset

Corrosion attributed to formation of volatile RuO4



Bimetallic Ru/Ir oxides active and more stable than RuO2

RuO2 Ir0.7Ru0.3O2

Stabilisation previously thought to be due to Ir preventing RuO4 formation.

Hypothesis tested by APXPS under operation conditions (3 mbar H2O, applied bias)



RuO2, Ru 3d Ir0.7Ru0.3O2, Ru 3d



RuO2, Ru 3d Ir0.7Ru0.3O2, Ru 3d RuO4 formation below OER onset – and below the standard potential of RuO4 phase formation (1.387 V)

RuO4(s) surface layers/islands formed distinct from bulk RuO4

Decline of RuO4(s) intensity at more positive bias points to electrochemical generation

Ir does not attenuate the amount of RuO4(s), contrary to hypothesis

Resonant inelastic x-ray scattering & soft x-ray emission spectroscopy + soft x-ray

absorption spectroscopy at MAX IV: the VERITAS and SPECIES beamlines





and microscopy


spectroscopy

Photon scattering Resonant inelastic x-ray

scattering















14. DanMAX (2019)


J. Forsberg, L.-C. Duda, A. Olsson, T. Schmitt, J. Andersson, J. Nordgren, J. Hedberg, C. Leygraf, T. Aastrup, D. Wallinder, J.H. Guo, System for in situ studies of atmospheric corrosion of metal films using soft x-ray spectroscopy and quartz microbalance, Rev. Sci. Instrum. 78 (2007) 083110

Soft x-ray scattering & soft x-ray absorption spectroscopy in corrosion research

Atmospheric corrosion cell for synchrotron experiments

Spectroscopy correlated to simultaneous quartz crystal microbalance measurements (mass change)

Measurement of soft x-rays (instead of electrons) allows higher pressures – here up to atmospheric pressure

Iron film exposed to air with adjustable relative humidity at atmospheric pressure

J. Forsberg, L.-C. Duda, A. Olsson, T. Schmitt, J. Andersson, J. Nordgren, J. Hedberg, C. Leygraf, T. Aastrup, D. Wallinder, J.H. Guo, System for in situ studies of atmospheric corrosion of metal films using soft x-ray spectroscopy and quartz microbalance, Rev. Sci. Instrum. 78 (2007) 083110

Soft x-ray scattering & soft x-ray absorption spectroscopy in corrosion research

Comparison of dry iron and iron exposed to corrosive atmosphere in presence of NaCl (relevance to e.g. marine environments)

X-ray emission: much more drastic changes due to changes in iron orbital structure

X-ray absorption: shift to higher energies due to change in oxidation state (comparable to photoemission)

Soft x-ray microscopy at MAX IV: MAXPeem and SoftiMAX














14. DanMAX (2019)


Combining spectroscopy and microscopy: MAXPeem and SoftiMAX

MAXPeem: combination of x-ray photoelectron

spectroscopy and microscopy →

photoemission electron microscopy (PEEM)

SoftiMAX: offers combination of x-ray

absorption spectroscopy and microscopy →

scanning transmission x-ray microscopy (STXM)

Greiner et al., J. Phys. Chem. C 112 (2008) 18991

PEEM/micro-XAS of a corrosion-inhibitor on Fe

Michelin et al., J. Anal. At. Spectrom. 28 (2013) 59

STXM of the corrosion products of a 450 year old nail

Concluding remarks • Soft x-ray spectroscopy & microscopy: excellent probe for elemental &

chemical structure of surfaces and for probing chemical processes such as corrosion (oxidation states, spatially resolved spectral information, …)

• MAX IV offers a range of soft x-ray tools, inluding x-ray photoelectron spectroscopy (vacuum & at ambient pressures), x-ray absorption spectroscopy (vacuum & at ambient pressures), x-ray emission spectroscopy/resonant inelastic x-ray scattering, photoemission electron microscopy, and scanning transmission x-ray microscopy

• Different sample environments beyond standard environments are in progress, e.g. H2S, high temperature & gas exposure, electrochemistry (batteries, fuel cells, …).

• High interest in further sample environments (also from academia), e.g. chlorides – talk to us!

• Static characterisation and monitoring of dyanmics

• User operation at HIPPIE starting now; SPECIES & VERITAS will follow in the end of 2017

Contacts (www.maxiv.lu.se)

● HIPPIE beamline (ambient pressure XPS): Spokesperson: [email protected] Beamline scientist: [email protected] Beamline scientist: [email protected]

● SPECIES beamline (ambient pressure XPS, RIXS): Beamline scientist: [email protected]

● VERITAS beamline (RIXS): Beamline scientist: [email protected] Project manager: [email protected]

● MAXPeem beamline (PEEM): Beamline scientist: [email protected]

● SoftiMAX beamline (STXM): Beamline scientist: [email protected]

soft x-ray spectroscopy (and microscopy) for resolving ... · high resolution in soft x-ray...

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