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 Warwick2Electrochemistry 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?

• 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-

Proof of concept - ODXAS 1

Broadband PM

Shutter

Optical bench

Filter housing

Web cam (1 of 2)

X-ray port 1

eCell

Ref. electrode

Stepper 1

Stepper 2

X-ray port 2

X-ray detector

Illumination

Optics

sample

pistonwindow

Silica objective

Filter

Silica condenser

Energy/keV

8.95 9.00 9.05 9.10 9.15

Flu

ore

sce

nce

/Arb

uni

ts

0.0

0.2

0.4

0.6

0.8

1.0XAS (DUBBLE)

Energy/keV

8.95 9.00 9.05 9.10 9.15

Flu

ore

sce

nce

/Arb

uni

ts

0.0

0.2

0.4

0.6

0.8

1.0XAS (DUBBLE)

XEOL (XMaS)

Copper – XAS and XEOL-XAS

Energy/keV

8.95 9.00 9.05 9.10 9.15

Flu

ore

sce

nce

/Arb

uni

ts

0.0

0.2

0.4

0.6

0.8

1.0XAS (DUBBLE)

XEOL (XMaS)

Parallel XAS (XMaS)

Nantokite on copper – XEOL surface specificity5

Energy / keV

8.9 9.0 9.1 9.2 9.3 9.4 9.5

No

rma

lize

d

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

8.96 8.97 8.98 8.99 9.00 9.01 9.020.0

0.2

0.4

0.6

0.8

1.0

CuCl on Cu (XAS)

CuCl on Cu (ODXAS)

Cu(XAS)

CuCl ref (XAS)

(XEOL)

Cuprite (Cu20) – XAS and XEOL-XAS Comparison

Cuprite comparison

Energy / keV

8.7 8.8 8.9 9.0 9.1 9.2

Log(

Ra

w c

ount

)

102

103

104

105

106

XAS, DUBBLE

XEOL, stn 9.2 SRS

Behind fluid window, XEOL, stn 9.2 SRS

Dowsett, Adriaens, Jones, Fiddy, Nikitenko,Anal. Chem. 80 (2008) 8717-8724

Cuprite comparison

Energy / keV

8.7 8.8 8.9 9.0 9.1 9.2

Log(

Ra

w c

ount

)

102

103

104

105

106

XAS, DUBBLE

XEOL, stn 9.2 SRS

Behind fluid window, XEOL, stn 9.2 SRS

XEOL, XMaS+ODXAS 1

Copper broadband XEOL - Raw I/<I0>

Energy / eV

8900 8950 9000 9050 9100 9150 9200

No

rma

lized

inte

nsi

ty

60

80

100

120

140

160

180

200

220

No window

15 m PCTFE10 m "Clingfilm"

6 m Ultralene

Note - a single mean value of I0 has been used in each case,

rather than a point by point normalization.

6 m Ultralene Same mean as "No window"

Relative broadband visible fluorescence (13 keV X-rays)

Time / s

0 100 200 300 400

I /

I 0

0.2

0.3

0.4

0.5

0.6

0.7

0.80.9

0.1

1

Al

BDD

PCTFE

Acetal Copolymer

Materials of construction

... e.g. The eCell window... and the rest ...

eCell body

X-ray shielding

Optical column

Substrate (for Powders etc.)

(13 keV X-rays)

Other edges (so far)

Energy/keV

9.60 9.65 9.70 9.75 9.80 9.85

Flu

ore

sce

nce

/Arb

uni

ts

0.0

0.2

0.4

0.6

0.8

1.0

1.2 Zn (K)

Energy/keV

12.95 13.00 13.05 13.10 13.15 13.20

Flu

ore

sce

nce

/Arb

uni

ts

0.6

0.7

0.8

0.9

1.0

1.1

Pb (LIII)

Energy/keV

13.00 13.01 13.02 13.03 13.04 13.05 13.06

Flu

ore

sce

nce

/Arb

uni

ts

0.6

0.7

0.8

0.9

1.0

1.1

Clean metal

Lead decanoate

1.8 eVPb (LIII)

Atacamite: XMaS June 2009 EX10 XEOL with Filters

Energy / keV

8.95 9.00 9.05 9.10 9.15 9.20

No

rma

lize

d I

nte

nsi

ty

0.2

0.4

0.6

0.8

1.0

1.2

Atacamite: XMaS June 2009 EX10 XEOL with Filters

Energy / keV

8.95 9.00 9.05 9.10 9.15

No

rma

lize

d I

nte

nsi

ty

0.6

0.7

0.8

0.9

1.0

1.1

Colour filters

Nantokite (CuCl) on copper

Atacamite (Cu2(OH)3Cl) on copper

Paratacamite/Atatcamite 2009 06 EX08S4 EX14S7

Energy/keV

8.90 8.95 9.00 9.05 9.10 9.15

Op

tica

l em

issi

on

- a

rb.

un

its

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Thick layer on copper

“Fine dusting” on acetal

Through green filter

Identifying mixtures with filters

Potential imaging modes

Time to a mean 3% precision per pixel in broadband image < 1000 s for 2048 x 2048 pixels

• Filtered images

• Near edge image spectra

• Dispersed images

• Edge correlated images (form image on correlation with specific oxidation state etc.

• EXAFS image spectra – given time

Next steps

Filters (imaging mode)

Filtered (imaging) or broadband (spectroscopy)

Schematic diagram of XEOM 1 - Imaging

Broadband CCD 2, 2048 x 2048

Sample

X-rays

Objectiveoptics

Broadband optical emission

Image

Focusing condenser

Next steps

Schematic diagram of XEOM 1 - Spectroscopy

Sample

X-rays

Objectiveoptics

Broadband optical emission

Grating

Projection optics

Broadband CCD 1, 500 x 2048

Spectrum/Image spectrum

Focusing condenser

Summary and Conclusions

• 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 ...

• Silica lens – based microscope –> mid to end 2010 Mirror-based device -> 2011-2012 Portable device ?