Low Energy Ion Irradiation and Its Applicability to Mimic Materials Irradiation Damage from High Energy Protons Weilin Jiang, David Senor Pacific Northwest National Laboratory HPT R&D Roadmap Workshop May 31 - June 1, 2017, Fermilab
Driving Force for Microstructural Changes Induced by MeV Ion Irradiation in Solids 1. Nuclear energy deposition: Elastic collision, damage cascades 2. Electronic energy deposition: Electron excitation, ionization 3. Electron-phonon coupling: Heat production, temperature increase 2
Emulation of Microstructural Features Using MeV Ion Irradiation and Thermal Annealing Benefits: Accurate dose for emulation of material age Accurate temperature for emulation of the location inside the material with a temperature gradient Minimum or no radiological activation for immediate release and characterization of irradiated materials. Implantation of impurity species into a pre-existing structure without thermal constraints. Fast emulation of structural features within hours to days Low cost Limitations: High dose rate Possible temperature shift 3
MeV Ion Irradiation to Emulate High Energy Proton Irradiated High Power Target Materials Irradiation damage in HPT materials starts from production of point defects, followed by their accumulation and interactions, leading to formation of defect clusters up to full amorphization. Point defects are produced mainly by irradiation of spallation neutrons and ions, especially at low energies, which may be emulated by low energy ion irradiation. The effects of temperature and its possible gradient in HPT materials may be emulated through post-irradiation thermal annealing at high temperatures, which may lead to formation of fractures and cracks. Gas bubbles and solid state precipitates in HPT materials may be emulated by implanting the species. Each contributor may be emulated separately or in a combined way to some extent. 4
Proposed Procedure to Emulate High Energy Proton Irradiated High Power Target Materials To simplify data interpretation, start with highly oriented pyrolytic graphite (HOPG), pure light metals or model alloys without grain boundaries, pores or high-level impurities, followed by polycrystalline materials with increasing levels of material complexities. Perform in-situ damage accumulation study of HOPG irradiated, for example, with H + ions and self-ions (C + ) as a function of dose and temperature. Perform in-situ and ex-situ thermal annealing study of defect recovery and clustering. Perform in-situ HIM irradiation study of microstructural evolution in polycrystalline graphite. Perform microscopy study of HOPG and polycrystalline graphite implanted with H, He and non-gaseous spallation/transmutation species (e.g., Li) and annealed at high temperatures to emulate microstructures for study of various features, including polycrystallization, amorphization, shrinking/swelling, creep, Mrozowski cracks, gas bubbles, and precipitates. Measure physical properties, including thermal conductivity, electrical conductivity, and mechanical strength. Compare the emulated microstructures and properties with those of high energy proton irradiated graphite and develop a fundamental understanding of the structure-property relationships, which may help assess and predict material performance. 5
Fundamental Processes of Ion-Solid Interactions in the MeV Energy Range Rutherford Backscattering Product of Nuclear Reaction (RBS) (NRA) Damage Peak INCIDENT BEAM Ion Implantation TARGET -Ray Recoil Target Atom X-Ray (PIGE) (ERDA) (PIXE) 6
Ion Channeling and RBS/C From L. C. Feldman, et al., RBS/C and random spectra for 6H-SiC “Materials Analysis by Ion Channeling” 7
Disorder Accumulation in -LiAlO 2 at 573 K Al Depth (nm) 1000 500 0 + /cm 2 LiAlO 2 (001) H 17 0.6 LiAlO 2 (001) + 3x10 80 keV H 2 17 + 2x10 80 keV H 2 300 60° off, 573 K Relative Al Disorder 17 1x10 60° off, 573 K 16 8x10 O Scattering Yield 16 0.4 6x10 16 200 4x10 16 2x10 Al Random 0.2 100 <001>-aligned Unimplanted 0.0 0 0.0 0.2 0.4 0.6 0.8 1.0 200 300 400 500 Dose (dpa) Channel Number • Disorder on the Al sublattice saturates at levels of 0.3 and 0.5. • No full amorphization occurs at the highest applied dose of 1 dpa. 8
Effect of Irradiation Temperature on Disordering Rate 6H-SiC 1.0 2 MeV Au 2+ 150 K 0.8 Relative Si Disorder 170 K 250 K 300 K 0.6 370 K 410 K 0.4 450 K 500 K 550 K 0.2 0.0 0.01 0.1 1 10 Dose (dpa) Disordering rate decreases with increasing irradiation temperature due to simultaneous recovery 9
Thermal Recovery of Defects on Both Si and C Sublattices in Irradiated SiC 20-min Isochronal Anneals 6H-SiC, 2 MeV Au 2+ , 170 K 28 Si(d,d) 28 Si 12 C(d,p) 13 C 1.0 1.0 Relative Si Disorder Relative C Disorder 0.8 0.8 Au 2+ /nm 2 0.40 0.20 0.6 0.6 I 0.15 0.10 I II 0.4 0.4 0.06 II III 0.2 III 0.2 0.0 900 0.0 300 600 900 300 600 Annealing Temperature (K) Similar recovery stages (I, II, III) on both Si and C sublattices 10
Li and H Out-diffusion in H + Irradiated -LiAlO 2 During H + Implantation During Thermal Annealing Polycrystalline -LiAlO 2 773 K 6 Polycrystalline -LiAlO 2 + , 300 K 10 80 keV H 2 673 K + 573 K 60° off, 10 17 H + /cm 2 80 keV H 2 Normalized Li Yield Normalized H Yield 473 K 60° off, 10 17 H + /cm 2 300 K 300 K impl 4 Unimpl 573 K ann, 6h 673 K ann, 6h 5 773 K ann, 6h 2 0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 Depth (nm) Depth (nm) • Material decomposition, Li diffusion and loss during irradiation • H diffusion and release during thermal annealing 11
Amorphization and Precipitate Formation -LiAlO 2 implanted to 10 17 H + /cm 2 at 773 K • The precipitate in rectangular shape is identified as cubic LiAl 5 O 8 with zone axis [211] that is parallel to -LiAlO 2 [100]. • Precipitates also show in triangular shape, which has a zone axis [111]. • Amorphization and gas bubbles near the surface are observed. 12
STEM-EELS Mapping of Precipitates in 3C-SiC 3C-SiC implanted to 9.6 × 10 16 25 Mg + /cm 2 at 673 K and annealed at 1573 K for 12 h Formation of cubic Mg 2 Si and tetragonal MgC 2 tetrahedra in Mg + implanted 3C-SiC. 13
Helium Ion Microscope (HIM) at PNNL/EMSL Specifications and Capabilities Source Tip Trimer Small beam size: < 0.1 nm High resolution: ≤ 0.35 nm Magnification: 100 – 1,000,000 Field of view: 1 mm – 100 nm Depth of field: 5-7 times SEM RBS spatial resolution: ~10 nm Variable voltage: 5 – 30 kV Beam current: 1 fA – 25 pA No conductive coatings needed High surface sensitivity The Column High image contrast Low Z imaging Backscattered ion imaging As an advanced instrument, HIM was Examples of Applications developed and commercialized in 2007, Nanostructures in nuclear providing cutting-edge imaging and materials Precipitates, gas bubbles, grain chemical analysis with a sub-nanometer boundaries, cracks, interfaces, probe. One of the unique capabilities is etc. the in-situ study of microstructural Irradiation modification of material evolution in bulk material at a microscopic structures using sub-nanometer site of choice under He + ion irradiation. He + ion probe 14
He Bubble Formation in -LiAlO 2 -LiAlO 2 irradiated with 25 keV He + at RT under HIM (He + ion projected range: 236 nm; max. 62.3 at.% He) 15
He Bubble Formation in a -LiAlO 2 Grain under HIM 16
Microstructural Evolution of Amorphous SiO 2 Nanoparticles and LiAlO 2 at a Void under HIM 17
Mg + and H + Irradiated HOPG 1360 1580 Graphite A A C C Raman Intensity (a.u.) A: Mg + and H + irradiated B: H + irradiated 0.78 MeV H + C: Mg + irradiated 10 µm Al foil B B D D D: Non-irradiated DLC HOPG A D G C B A C D 400 800 1200 1600 Raman Shift (cm -1 ) B D Graphite peak at 1580 cm -1 G: Disorder peak at 1360 cm -1 D: DLC: Broad diamond like carbon peak ranging from 1100 to 1700 cm -1 18
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