Transcript Microscopy of the chemical state rather than just elemental

Towards X-ray excited optical microscopy (XEOM)
for
cultural heritage, spectroelectrochemistry, and
wider applications
Mark Dowsett1, Annemie Adriaens2, Gareth Jones1 and Alice Elia2
1Analytical
Science Projects Group, University of Warwick
2Electrochemistry and Surface Analysis Group, Ghent University
Thanks to : Paul Thompson, Simon Brown (XMaS, ESRF)
Sergey Nikitenko (DUBBLE, ESRF), Nigel Poolton (Formerly SRS, Daresbury)
Analytical Science Projects
Goal:
Develop XEOL microscope coupled to an
environmental cell for synchrotron applications
Real time process monitoring in controlled electrochemical and
gaseous ambients – corrosion and protection studies
Ultimate goal:
Develop a portable version for direct chemical
imaging in museums etc.
Microscopy of the chemical state rather than just elemental
composition (i.e. A step beyond portable XRF)
Why XEOL?
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Based on transoptical emission (200-1000 nm) caused by keV X-ray irradiation
- phosphorescence, fluorescence
Electronic processes responsible for XANES and EXAFS impose similar
structure on the light emission
Extra band specific-features due to excitation of chromophores by LE
electron scattering
Spectra are (at least) two dimensional – X-ray energy and emitted optical
wavelength
Technique has a high surface specificity – sees thin layers on surfaces
invisible to conventional XAS
Basis of a chemically specific optical microscopy
- image formation using broadband light optics
A surface or transmission microscopy tool
e-
Shutter
Web cam (1 of 2)
Stepper 1
Filter housing
X-ray port 1
Ref. electrode
Broadband PM
Optical bench
Illumination
Optics
Proof of concept - ODXAS 1
Stepper 2
X-ray port 2
X-ray detector
eCell
Filter
sample
Silica
condenser
Silica objective
window
piston
Copper – XAS and XEOL-XAS
Fluorescence/Arb units
1.0
XAS
XAS
(DUBBLE)
(DUBBLE)
XEOL
XEOL
(XMaS)
(XMaS)
0.8
0.6
0.4
Parallel XAS
(XMaS)
0.2
0.0
8.95
9.00
9.05
9.10
Energy/keV
9.15
Nantokite on copper – XEOL surface specificity
5
1.4
CuCl on Cu (ODXAS)
(XEOL)
CuCl on Cu (XAS)
Normalized 
1.2
Cu(XAS)
CuCl ref (XAS)
1.0
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
8.96
0.0
8.9
9.0
9.1
8.97
8.98
9.2
Energy / keV
8.99
9.3
9.00
9.01
9.4
9.02
9.5
Cuprite (Cu20) – XAS and XEOL-XAS Comparison
Cuprite comparison
106
Log(Raw count)
XEOL, XMaS+ODXAS 1
105
XEOL, stn 9.2 SRS
104
Behind fluid window,
XEOL, stn 9.2 SRS
XAS, DUBBLE
103
102
8.7
8.8
8.9
9.0
9.1
Energy / keV
Dowsett, Adriaens, Jones, Fiddy, Nikitenko,
Anal. Chem. 80 (2008) 8717-8724
9.2
Materials of construction
Copper broadband XEOL - Raw I/<I0>
... and
e.g. The
the rest
eCell...window
broadband
visible
keVcase,
X-rays)
Note - a Relative
single mean
value of
I0 hasfluorescence
been used in(13
each
rather than a point by point normalization.
220
1
0.9
0.8
0.7
200
eCell body
6 m Ultralene
Same mean as "No window"
0.5
160
0.4
I/ I0
140
No window
0.6
180
Normalized intensity
PCTFE
X-ray shielding
10 m "Clingfilm"
0.3
15 m PCTFE
Al
120
Optical column
Acetal
Copolymer
0.2
100
6 m Ultralene
BDD
Substrate (for
Powders etc.)
80
60
8900
0.1
8950
0
100
9000
200
9050
300 9100 400
Time / s
Energy / eV
(13 keV X-rays)
9150
9200
Other edges (so far)
1.1
1.1
1.2
Zn
Pb (K)
(LIII)
1.8 eV
Fluorescence/Arb units
1.0
1.0
1.0
0.8
0.9
0.9
Clean metal
0.6
0.8
0.8
Lead
decanoate
0.4
0.7
0.7
0.2
0.6
0.0
0.6
13.00
12.95
9.60
13.01
13.00
9.65
13.02
13.05
9.70
13.03
13.10
9.75
Energy/keV
13.04
13.15
9.80
13.05
13.20
9.85
13.06
Colour filters
Atacamite: XMaS June 2009 EX10 XEOL with Filters
1.2
1.1
1.0
1.0
Normalized Intensity
Atacamite
Nantokite
(CuCl)
(Cu
2(OH)3Cl)
on copper
0.8
0.9
0.6
0.8
0.4
0.7
0.2
0.6
8.95
8.95
9.00
9.00
9.05
9.05
9.109.10
Energy / keV
9.15 9.15
9.20
Identifying mixtures with filters
Paratacamite/Atatcamite 2009 06 EX08S4 EX14S7
1.8
Optical emission - arb. units
1.6
Thick layer on copper
1.4
1.2
1.0
0.8
“Fine dusting” on acetal
0.6
Through green filter
0.4
0.2
8.90
8.95
9.00
9.05
Energy/keV
9.10
9.15
Potential imaging modes
Time to a mean 3% precision per pixel in broadband image
< 1000 s for 2048 x 2048 pixels
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Filtered images
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Dispersed images
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Near edge image spectra
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Edge correlated images (form image on correlation with specific oxidation state etc.
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EXAFS image spectra – given time
Next steps
Image
Broadband CCD 2,
2048 x 2048
Filtered
(imaging) or
broadband
(spectroscopy)
Filters
(imaging
mode)
Focusing
condenser
Objective
optics
X-rays
Broadband
optical
emission
Sample
Schematic diagram of XEOM 1 - Imaging
Next steps
Projection
optics
Grating
Spectrum/Image
spectrum
Broadband CCD 1,
500 x 2048
Focusing
condenser
Objective
optics
X-rays
Broadband
optical
emission
Sample
Schematic diagram of XEOM 1 - Spectroscopy
Summary and Conclusions
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Silica lens – based microscope –> mid to end 2010
Mirror-based device -> 2011-2012
Portable device ?
XEOL provides multispectral information including XANES and EXAFS from heritage
metals and corrosion products
Optical devices with constructed with broadband optics will provide
microscopy with (light) wavelength limited resolution
Suitable for beam lines with large (millimetres ) footprint
XEOM has potential applications in
Measurements in controlled environments
Metal corrosion research
Geosciences
Semiconductor research
Organo-metallics
...