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Helium Ion Microscopy Geologic Applications

Helium Ion Microscopy Geologic Applications . Clifford C. Walters ExxonMobil Research & Engineering Corporate Strategic Research. Helium Ion Microscopy. Similar to SEM but uses helium ions instead of electrons. Breakthrough came in 2006 with the invention of the He + trimer ion source.

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Helium Ion Microscopy Geologic Applications

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  1. Helium Ion MicroscopyGeologic Applications Clifford C. WaltersExxonMobil Research & Engineering Corporate Strategic Research

  2. Helium Ion Microscopy • Similar to SEM but uses helium ions instead of electrons • Breakthrough came in 2006 with the invention of the He+trimer ion source

  3. Ultrahigh resolution imaging Probe Size Small probe size (< 0.5nm) allowing high resolution imaging ~3X better resolution than FESEM Smaller wavelength Ions have lower velocity than electrons of equivalent energy – therefore the wavelength of the ion beam is smaller than electrons Diffraction Helium ions are about 8000 X heavier than electrons. Exhibits very little diffraction when passed through an aperture or across an edge Electromagnetic fields are less likely to limit operation . Advantages of He Ion Microscopy Ultra-thin sputtered Pt film on carbon. Surface resolution of 0.35 nm is obtained on this surface.

  4. Surface Detail Signal produced from the top 2-5nm of the sample surface He+ beam produces both secondary electrons (SE) and backscattered ions SE yield is large (~3-9 per He+) so low beam currents work well Interaction volume of He+ beam near the surface is thought to be considerably smaller than that of an SEM The excited volume is restricted and SE generation is near the surface. Minimal signal contribution from recoil. Advantages of He Ion Microscopy 30 kV Helium ion beam is still collimated well below the SE escape depth. 1 keVelectron beam has a larger interaction volume resulting in SE1 and SE2

  5. Surface Detail Carbon nanotubes Advantages of He Ion Microscopy SEM: Field of view = 630 nm HIM: Field of view = 800 nm From NIST (Ming, et al. 2009)

  6. Advantages of He Ion Microscopy Depth of Field ~5X higher depth of field than high resolution FESEM Flat surfaces are not needed to achieve high resolution Ion milling not required. Depth of Field can match ~ 1 µm Depth of View a HIM of laboratory reacted carbonate ooid HIM SEM

  7. Charge Control Electron flood gun neutralizes positive charge. Non-conductive samples can be analyzed without application of coatings. Advantages of He Ion Microscopy Helium + Neon ET Detector He+ Ions r+ SE SE’s Electron Flood Gun He+ Ions Sample Specimen r- SE’s • The positive charge density accumulating on the surface causes secondary electrons to return to the sample resulting in a dark image. • An electron flood beam is multiplexed with the helium imaging beam to neutralize the positive charge on the sample surface and produce a charge neutral image Specimen No charge control Flood Gun OnNon-conductive low maturity Posidonia Shale

  8. Charge Control Microquartz in sandstonereservoir from Teal Field, North Sea Advantages of He Ion Microscopy

  9. Sample Preparation: Mechanical fracture – preferential exposure along lines/surfaces of weakness Organic-inorganic interfaces parallel to deposition Organic porosity easily found Application to Gas Shales Middle Otter Park Fm. Horn River

  10. What is kerogen and what is solid bitumen? Kerogen: spongy texture, high porosity, narrow pore-sizedistributions (2 to 25 nm) Solid bitumen: ropey texture, larger pores, or non-porous Application to Gas Shales Middle Otter Park Fm. Horn River

  11. Organic porosity easily imaged and found to be abundant What is kerogen and what is solid bitumen? Kerogen: spongy texture, high porosity, narrow pore-sizedistributions (2 to 25 nm) Solid bitumen: ropey texture, larger pores, or non-porous Application to Gas Shales Middle Otter Park Fm. Horn River

  12. Crack-like features, > 10 µm in length, are observed in connected porous organic matter Application to Gas Shales Muskwa Shale

  13. Crack-like features, > 10 µm in length, are observed in connected porous organic matter Application to Gas Shales Muskwa Shale

  14. Crack-like features > 10 µm in length observed in connected porous organic matter Application to Gas Shales 40 nm Muskwa Shale

  15. Crack-like features, > 10 µm in length, are observed in connected porous organic matter Application to Gas Shales 20 nm Muskwa Shale

  16. Crack-like features, > 10 µm in length, are observed in connected porous organic matter Application to Gas Shales 20 nm 20 nm

  17. Helium Ion Microscopy can readily image the organic porosity and pore networks in gas shales Two type of organic porosity is observed Kerogen: Highly porous (~20 to 50%), narrow pore distribution (2 to 20 nm), high connectivity between pores perpendicular to depositional plane Solid Bitumen: Present at kerogen-mineral interfaces. Matrix is largely non-porous, but can contain larger pores. Acknowledgements: Chuong Huynh, Carl Zeiss Applications laboratory ExxonMobil Research & Engineering Conclusions

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