Development of X-ray Emission Spectroscopy Analyzer with Low Voltage SEM and STJ Array X-ray Detector

1. Development of X-ray emission spectroscopy analyzer with low voltage SEM and STJ array X-ray detector for nanometer-scale chemical state imaging 1 : National Institute of Advanced Industrial Science and Technology (AIST) 2 : Mitsubishi Heavy Industries, Ltd. Go Fujii1, Masahiro Ukibe1, Shigetomo Shiki1, kiyoka Takagi2 and Masataka Ohkubo1 The STJs were fabricated in the clean room for analog-digital superconductivity (CRAVITY) at AIST. A part of this work was supported by Innovative Science and Technology Initiative for Security, ATLA, Japan, Cross-ministerial Strategic Innovation Promotion Program D66 operated by the cabinet office, Japan, and JSPS KAKENHI Grant Number 17K14141.

2. Outline • Motivation • X-ray emission spectroscopy analyzer with STJ array • Chemical state analysis of CFRP • Summary

3. Motivation CFRP(Carbon Fiber Reinforced Plastic) -Strength-to-weight ratio is very high Other 5 % Steels 10 % Applications : - Wing spars and fuselage components of the aircraft, Bodyofthecar, etc. CFRP >50 % Titanium alloys 15 % Boeing 787 Aluminum alloys 20 % Bolting No bolting However, large CFRP composite structure should be fabricated by bonding the CFRP parts with an adhesive and bolting because the reliability of the adhesive strength between the CFRP parts hasn’t been established yet. Optical microscope image CFRP/ Adhesive/ CFRP Chemical state analysisof the boundary is important Nano-scaled chemical bonding state imaging

4. Chemical state analysis at nanoscale 700 V Nanoscale chemical bonding state analysis ●Low acceleration voltage SEMs (LVSEM) 　→　Nanometer-scaled spatial resolution Ex.) <10 nm @700 V + ●X-raydetectorwithhighenergyresolution　→　Chemicalstateanalysis with X-ray emission spectroscopy 10 nm Epoxy Inorderto demonstrate theanalysis, we have developed a LVSEM-EDX system employing a superconducting-tunnel-junction array X-ray detector.

5. Required performances of X-ray detectors Highenergy resolution @ <1 keV: < a few eV - To perform X-ray emission spectroscopy High throughput @1 keV : >10 mSr - Low dose analysis is necessary because the damage threshold of the epoxies is several MGy High timing resolution: <1 ms-High speed e-beam scanning is essential to prevent charge up and damage

6. Comparison of soft X-ray spectrometers@ soft X-ray( < 1 keV) Energy-dispersive type Wave-dispersive type Oxford instruments High Target Silicon drift detector(SDD)(10-1sr, 50 eV) 100 pixel Superconducting- tunnel-junction(STJ)(10-2sr, 4 eV) Low speed Throughput JEOLLtd. Diffracting crystal (WDS)(10-5sr, <a few eV) SXES(10-3sr, 0.3 eV) TES(10-3sr, ~ a few eV) Low Energy resolution Good Bad Grating + CCD

7. Superconducting-tunnel-junction(STJ) Nb/Al-STJ Advantage • Small energy gap (2.6 meV) ⇒　High energy resolution (Theoretical limit: 2 eV @ O-Ka) • Short life time of quasi-particles (a few ms) ⇒ High count rate (> kcps/pixel)⇒ High timing resolution (< 1 ms) • Large capacitance (~0.1pF/1 mm squire)⇒　Smalldetection area (100 mm□)⇒　Array of large pixel (> 100): Detection area >1 mm2 1 pixel 4096 pixels Disadvantage 100 mm Detection area: 40 mm2 100 pixels

8. X-ray emission spectroscopy analyzer with low voltage SEM and STJ array X-ray detector

9. LVSEM-EDX system with our STJ spectrometer STJ spectrometer system LVSEM (JSM 7200F, JEOL) Cryogen-free He3 cryostat

10. LVSEM-EDX system with our STJ spectrometer LVSEM X-ray windows @50K and 4 K 100-pixel STJ array chip E-beam X-ray X-ray lens sample

11. Our STJ array X-ray spectrometer for LVSEMs X-ray windows @50K and 4K 100-pixel STJ array Polycapillary focusing lens X-ray spot 300 K Spot size: ~1 mm 50 K Detection area: ~1.2 mm squire 4 K 0.3 K • Throughput of the X-ray lens: 20 mSr • Total transmittance of the X-ray windows: 75 % • Detection efficiency of the STJs ~ 100 % • Filling factor of the STJ array: ~ 70 % Total throughput : ~10 mSr(=20*0.75*1*0.7)

12. LVSEM-EDX system with our STJ spectrometer 96 charge amplifiers 80 coaxial cables 100 twisted pair cables LVSEM Oscilloscope 100-pixel STJs 80 ch Pulse height processers SEM’ssynchronized signal 12

13. Energy resolution X-ray for Diamond Monoenergetic X-ray 277 eV 260 eV 12 eV FWHM 4 eV FWHM Energy resolution: ~4 eV

14. Counting rate of STJ detector The same energy resolution up to ~100 kcps

15. Spatialresolution Sample: Gold particles SEMconditionVacc: 5 kV WD：　15 mm Ip: ~1 nA Gap~5nm Spatialresolution：<10nm

16. Chemical state imaging of CFRP

17. Comparison of performances for soft X-ray STJ array with low FF SDD Detection area size: 30 mm2 X-ray window: SiN Sample： PPS 2.4 mm squire FF:~ 17 % x20 Vacc: 5 kV X-raybeam Improve ~10 times by STJ array with high FF FWHM ~12 eV The STJ X-ray spectrometer can achieve high energy resolution,high throughput, and high timming resolution. 17

18. Chemical state analysis with STJs ~ Emission spectroscopy ~ SEM images of a CFRPcomposite O-K Carbon fibers ~5 mm Adhesive ~ 12 eV Satellite peaks CFRP Adhesive Boundary • It can be observed that the peak shape of O-K line of the resin and the adhesive are different. • The satellite peaks were observed at about 40 eV lower than O-K line peak in the resin. Epoxy resin

19. Summary • We have developed the LVSEM utilizing 100-pixel STJ array- Throughput: ~10 mSr- Energy resolution: ~4 eV- Max. counting rate: >100 kcps- Spatial resolution：　<10 nm • We have performed chemical state analysis of the CFRP composite sample. It can be observed that the spectral shape of O-K line of the epoxy resin and the adhesive are different.

20. Thank you for your attention