1. Full-field PIXE imaging
:40
Full-field PIXE imaging
Multi-frame super-resolution
to overcome
optics pattern and imaging-based
resolution limitations
Josef Buchriegler
N. Klingner, D. Hanf, F. Munnik, S.H. Nowak, J. von Borany, R. Ziegenrücker
15th International Conference on PIXE
2nd – 7th April 2017, Split, Croatia

2. Imaging enhancements:
Outline
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Full-field HZDR
Imaging challenges:
optics’ pattern & unevenness
pixel resolution
Imaging enhancements:
Image stacking
Super resolution
Sub-pixel correction
Bright-field correction
Examples
Summary & Outlook

3. Motivation → classical µ-beam PIXE set-up: scanning point by point
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→ classical µ-beam PIXE set-up: scanning point by point
object
50x50 μm2
aperture
1x1 mm2
lens
sample surface
MeV
proton beam
(3 µA)
proton current
on sample: 0.5 nA
detector
elemental distribution has to be mapped offline
→ full-field approach: simultaneous detection of a large area (full-field)
MeV
proton beam
(<1 µA)
sample surface
X-ray guidance
elemental mapping in real-time
pixel
detector
screening of large samples for resource technology
mapping of minor and trace elemental distributions

4. Full-field detector Specifications: 12 cm number of pixel
Name
Value
number of pixel
264 × 264 =
pixels size
48 × 48 µm²
imaging area
12 × 12 mm²
frame rate Hz
sensitive energy range
2 – 20 keV
active sensor thickness
450 µm
energy resolution
152 Mn Kα
quantum efficiency
keV
20 keV
X-ray optics
parallel (78 mm, 1:1)
conical (82 mm, 6:1)

5. Full-field PIXE imaging @ HZDR
Super-SIMS
Sources
AMS sources
6 MV Tandem-
accelerator
PIXE cam
10 m
2 – 4 MeV protons
up to 1 µA current
~90 m beam path from ion source to sample surface
Proton beam
Poly-capillary optics
Color X-ray camera
Samples
3-axis stage
D. Hanf et al. 2016, NIM B 377, 17-24, DOI: /j.nimb

6. Imaging challenges Imaging principle – poly-capillary optics (1:1)
1.0 mm
Sample
pnCCD-chip
Proton beam
capillaries
(20 µm diameter)

7. Imaging challenges Poly-capillary optics – transmission properties
[× median]
Eventmap of Cu-plate:
measurement time: 60 min
~220 nA total current
6 GB data (EVT-format)
35 x 106 events in total
550 evts/px (median)
hexagonal pattern
radial unevenness
[× median]

8. position information is thrown away
Imaging challenges
Charge collection – pixel resolution
X-ray photon
electron
cloud
pixel
shift register
photon can affect up to 4 pixels
larger/implausible pattern are discarded
■ electron cloud
■ considered charge
■ involved pixels
× assigned pixel
position information is thrown away
O. Scharf et al. 2011, Anal. Chem. 83, , DOI: /ac102811p

9. lateral resolution: (76±23) µm
Imaging challenges
Limits of pixel resolution
Cr pattern on Si
170x170 µm²
1x1 mm²
lateral resolution: (76±23) µm

10. Imaging enhancements A) ImageStacking original image single image
optics pattern

11. Imaging enhancements A) ImageStacking image 2 image 1 + 2 image 1
single image
image

12. Imaging enhancements A) ImageStacking
first image
original image
sum of 2 images
sum of 10 images
sum of 9 images
sum of 8 images
sum of 7 images
sum of 6 images
sum of 5 images
sum of 3 images
influence of pattern is “diluted”
features are added up
same total measurement time
sum of 4 images
caution: Moiré-pattern possible

13. Imaging enhancements B) SuperResolution
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B) SuperResolution
original image
series of LR-images shifted in sub-pixel-range
6x6 pixel (LR)
stack of 9 images
sub-pixel information emerges due to “lateral oversampling”
intrinsic feature of image stacking
stack of 9 up-scaled images
18x18 pixel (3x up-scaled)
stack of 5 up-scaled images

14. Imaging enhancements C) Sub-pixel Correction
detection:
stored data:
sub-pixel algorithm:
electron cloud
charge distribution
centre of gravity
assign sub-pixel(s)
energy information of each X-ray is relocated to smaller region
S.H. Nowak et al. 2015, JAAS 30, , DOI: /c5ja00028a

15. Imaging enhancements
D) Bright-field Correction
1300
1.4
1.0

16.  () Imaging enhancements Overview A) ImageStacking
lateral resolution
hexagonal pattern
radial unevenness
A) ImageStacking 
()
B) SuperResolution
C) Sub-pixel correction
D) Bright-field correction

17. Experimental implementation
Generate list of random positions (x/y-shifts)
Measurement: “take an image” on each position
 real positions are logged by independent position sensor (accuracy better than 1 µm)
 charge distribution of each photon stored into ASCII-file
Parse & merge ASCII-files while applying:
shift-correction for each position  ImageStacking (A) + SuperResolution (B)
remap charge-/energy-distribution on sub-pixel matrix  Sub-pixel Correction (C)
filter for energies/peaks of interest to map elemental distributions (ROIs)
Correct ROI-maps with bright-field measurement  Bright-field Correction (D)

18. Examples Cu-stripes 3 mm 3 mm Standard image (52 Min @ ~450 nA)
Stack of 26 images – without SPC/BFC!
(26x 2 ~450 nA)

19. Examples 1 2 Siemens-star 1 2 3 4 3 4 set of 22 images, Ni-Ka map
1 mm 2
Siemens-star
set of 22 images, Ni-Ka map 1 2 3 4
Standard image:
up-scaled
similar statistics
22 shots:
incl. ImageStacking
incl. SuperResolution
22 shots:
incl. ImageStacking
incl. SuperResolution
incl. Sub-pixel correction
22 shots:
incl. ImageStacking
incl. SuperResolution
incl. Sub-pixel correction
incl. Bright-field correction 3 4

20. Examples Geological sample: Ag-mineral K-Kα Fe-Kα Pb-Kβ
Standard image: 52 minutes
(pixel size: 48 µm)
Fully corrected image: 26x 2 minutes
(4x SR/SPC  sub-pixel size: 12 µm)
K-Kα
Fe-Kα
Pb-Kβ

21. Summary & Outlook Summary Outlook full-field PIXE set-up at HZDR
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Summary
full-field PIXE set-up at HZDR
challenges provoked by this new approach
strategies to overcome such difficulties
promising examples
Outlook
automation of shift-mode measurements
measurements with more images to asses limits
implementation of routines into online-evaluation software
 high-resolution imaging in real-time

22. Thank you for your attention !
Acknowledgements
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Helmholtz-Zentrum Dresden-Rossendorf, IBC
Shavkat Akhmadaliev
Jörg Grenzer
Daniel Hanf
René Heller
Nico Klingner
Holger Lange
Frans Munnik
Johannes von Borany
Helmholtz-Zentrum Dresden-Rossendorf, HIF
Sandra Dreßler
Silke Merchel
Axel D. Renno
René Ziegenrücker
Jožef Stefan Institute, Ljubljana, Slovenia
Marko Petric
Companies
Oliver Scharf (IFG Institute for Scientific Instruments, Berlin)
David Kalok (pnSensor, Munich)
beyond Europe
Stanisław H. Nowak (Stanford University, USA)
Wojciech Przybyłowicz (iThemba Labs, South Africa)
Chris Ryan (CSIRO, Australia)
Thank you for your attention !
This work was supported by Marie Curie Actions - Initial Training Networks (ITN) as an Integrating Activity Supporting Postgraduate Research with Internships in Industry and Training Excellence (SPRITE) under EC contract no