Full-field PIXE imaging 15.06.2018 14:40 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

Imaging enhancements: Outline 15.06.2018 14:40 Full-field PIXE @ HZDR Imaging challenges: optics’ pattern & unevenness pixel resolution Imaging enhancements: Image stacking Super resolution Sub-pixel correction Bright-field correction Examples Summary & Outlook

Motivation → classical µ-beam PIXE set-up: scanning point by point 15.06.2018 14:40 → 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

Full-field detector Specifications: 12 cm number of pixel Name Value number of pixel 264 × 264 = 69 696 pixels size 48 × 48 µm² imaging area 12 × 12 mm² frame rate 200 - 1000 Hz sensitive energy range 2 – 20 keV active sensor thickness 450 µm energy resolution 152 keV @ Mn Kα quantum efficiency >95% @ 3-10 keV >30% @ 20 keV X-ray optics parallel (78 mm, 1:1) conical (82 mm, 6:1)

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: 10.1016/j.nimb.2016.03.032

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

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]

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, 2532-2538, DOI: 10.1021/ac102811p

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

Imaging enhancements A) ImageStacking original image single image optics pattern

Imaging enhancements A) ImageStacking image 2 image 1 + 2 image 1 single image image 1 + 2 + 3

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

Imaging enhancements B) SuperResolution 15.06.2018 14:40 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

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, 1831-2026, DOI: 10.1039/c5ja00028a

Imaging enhancements D) Bright-field Correction 1300 1.4 1.0

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

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)

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

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

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

Summary & Outlook Summary Outlook full-field PIXE set-up at HZDR 15.06.2018 14:40 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

Thank you for your attention ! Acknowledgements 15.06.2018 14:40 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. 317169.