Kristin Benke ISMS 2017 Ultrafast tabletop XUV spectroscopy 2 3p 6 3d n 3p 5 3d n 1 High harmonic generation HHG Gasfilled cell NIR laser Popmintchev T et al Proc Natl Acad Sci ID: 637264
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Slide1
Liquid phase tabletop XUV spectroscopy for the study of transition metal catalysts
Kristin BenkeISMS 2017Slide2
Ultrafast tabletop XUV spectroscopy
2
3p
6
3d
n 3p53dn+1
High harmonic generation (HHG)
Gas-filled cell
NIR laser
Popmintchev
, T., et. al. Proc. Natl. Acad. Sci. 2009, 106, 10516-10521.Slide3
XUV spectroscopy gives electronic structure of metal-centered complexes.
3
Zhang, K.,
et. al. J
. Phys. Chem. Lett.
2016, 7, 3383-3387.HHG output
Ligand field differentiationSlide4
Ultrafast XUV spectroscopy is well suited to study metal-centered catalysts.
Raugei, S. et. al. ACS Catal
.
,
2015
, 5, 5436-5452.Ni+
Ni0
Ni
2+Ni2+Ni+
Ni2+
Ni0
Ni+
Ni0DuBois’ catalyst
4
Techniques used to study catalysis
EPR
tUV
/Vis
tIR
Synchrotron based
tXAS
and
tXESSlide5
Studying a homogenous catalyst requires liquid phase compatibility.
5
Thin film for XUV spectroscopy
http://cxro.lbl.gov
/
Predicted transmission of XUV light by common solventsSlide6
Liquid phase tabletop XUV spectroscopy
requires a specialized liquid flow cell.
6
1 cm
X-ray transmissive silicon nitride windows
Compatible with high vacuum
Continual sample renewal prevents sample damageSlide7
Transmission of XUV flux is hindered by behavior of the window under vacuum.
7
Window deformation
spacer length
Maximum deflection at center (
) can be controlled by
membrane
thickness (
)
window dimensions (
)
pressure across membrane (
)
P
vacuum
Slide8
Adjacent fields have implemented various methods to mitigate window deformation.
8
Dukes
, M.
J.
Microsc. Microanal. 2013, 19 (
Suppl 2), 406–407.Environmental TEMSlide9
Adjacent fields have implemented various methods to mitigate window deformation.
9
Nagasaka
, M.
J. Electron
Spectros. Relat. Phenomena 2010, 177 (2-3), 130–134.
Soft x-ray XASSlide10
Window deformation can be alleviated by locally increased pressure.
10
Implementation for tabletop XUV spectroscopy requires minimization of losses in flux
gas in
gas outSlide11
Adjusting the gas pressure allows for a tunable pathlength.
11
Transmission at
corresponding
pathlengths
Images of window at
different
pathlengths
gas ingas outSlide12
Ongoing challenges
Ground state spectrum
Overcoming instrument drift during sample switching
Transient spectrum
Maximizing signal to noise ratio
Avoiding photodeposition12
gas in
gas outSlide13
Summary
13
X-ray spectroscopy with high accessibility and high time resolution
Development of liquid phase compatibility
Electronic structure of transition metal catalystsSlide14
Acknowledgements
14
Prof. Josh
Vura
-Weis
Vura
-Weis group
Ryan,
Muffaddal
, Michaela, Sean, Suds, Ming-Fu, Liz,
Yusef
,
Aastha, Kori, Max, Kaili
Funding
AFSOR YIP
UIUC Start-up Fund
NSF CAREER Slide15
M-edge spectroscopy has element, oxidation- and spin-state, and ligand field specificity.
15
Zhang, K.,
et. al. J
. Phys. Chem. Lett.
2016, 7, 3383-3387.
Oxidation state
Ligand field
Spin state
Experiment
SimulationSlide16
What else is known about DuBois’ catalyst?
16
31
P NMR
–examination of
diamagnetic Ni(0)
and
Ni(II) shows
that the complex can get “stuck” in certain conformers (Bullock 2013)EPR –examination of paramagnetic Ni(I) state shows that the hydride adduct does not form for this oxidation state (Van
Gastel 2014)Stop flow kinetics –isolation of the Ni(II)
hydride adduct (Dempsey 2015)tr-XAS –observation of the first
step in the proposed cycle (Mulfort 2016)Bullock, R. M. J. Am. Chem. Soc.
2013,
135,
9700-9712.
van
Gastel
, M.
J. Phys. Chem. C.
2014,
118,
2350-2360
.
Dempsey, J. L.
J. Am. Chem. Soc.
2015
,
137
, 13371-13380.
Mulfort
, K.L.
J. Phys. Chem. C
2016,
120, 20049-20057.
Slide17
Effects of sample inhomogeneity in tabletop XUV spectroscopy
Spatial chirp
17
Sample inhomogeneity on scale of beam size
Lin, M.-F.,
et. al.
J
. Opt. Soc. Am. B
33,
1986-1992 (2016)Slide18
Liquid cell pump probe spectroscopy
18Slide19
19
Valence
K-edge
L-edge
M
-edge
1s
2s, 2p
3
s, 3p
~500-1,000 eV
~1,000-10,000 eV
~30-100 eVSlide20
HHG conditions can be tuned to output an XUV continuum.
20
Mn
Fe
Co
NiSlide21
21
~10-100 nm sample
Silicon nitride substrate
Silicon wafer support
100 µmSlide22
Adjusting the gas pressure allows for a tunable pathlength.
22
A
)
B)
C)
D)
100 µm
100 µm
100 µm
100 µm
Transmission at different
pathlengths
Images of window at corresponding
pathlengths