Users days 20&21 october 2011 In situ TEM investigation of helium bubble evolution in SiC at high-temperature under displacing irradiation

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1 In situ TEM investigation of helium bubble evolution in SiC at high-temperature under displacing irradiation Institut P UPR CNRS 3346 SP2MI Téléport 2 Boulevard Marie et Pierre Curie BP F86962 FUTUROSCOPE CHASSENEUIL D1: Presenting Cedex the research activities 1

2 In situ TEM investigation of helium bubble evolution in SiC at high-temperature under displacing irradiation M.F. Beaufort 1, J.F. Barbot 1, C. J. Pawley 2,3 J. A. Hinks 2, E. Oliviero 4 and S.E. Donnelly 2 1 Institut Pprime, CNRS-Université de Poitiers, France. 2 Electron Microscopy and Materials Analysis Group, University of Huddersfield, UK. 3 Centre for Materials and Physics, University of Salford, UK. 4 CSNSM, CNRS-IN2P3, Orsay, France. Institut P UPR CNRS 3346 SP2MI Téléport 2 Boulevard Marie et Pierre Curie BP F86962 FUTUROSCOPE CHASSENEUIL D1: Presenting Cedex the research activities 2

3 Silicon Carbide SiC is a wide-band gap semiconductor and a ceramic Excellent physical and chemical properties (High temperature stability, chemical inertness, small neutron capture cross section) Promising material for several applications Ceramic Development of nuclear systems Encapsulating material for nuclear fuel (fission) Structural component for the first wall of the reactor (fusion) Extreme conditions High temperature and fast neutron fluxes Neutron irradiation induces damages Atomic displacements Helium production (nuclear transmutation) 3

4 Irradiation/implantation induced defects and swelling of the material are well known phenomena Many studies were devoted to the defects induced by neutron irradiation He implantation He + Swelling of the material He.cm -2, 50keV, Ti:700 C Annealing at 1700 C He n -V m complexes He + - lattice dilation (point defects, strain ) - amorphization (10-15%) - bubbles - extended defects Aim of this project Develop a fundamental understanding of the behaviour of SiC subjected to: High temperature Displacing irradiation The presence of helium With a view to understand its performance under reactor conditions. Intensity (a. u.) kev - 1x10 16 cm -2 - RT (0004) unperturbed bulk d/d) M d/d) S 4

5 Experimental details

6 The first experiment of our project: In situ TEM investigation of the evolution of helium bubbles under displacing irradiation at high-temperature In situ helium implantation UK MIAMI facility Now at the University of Huddersfield formerly at the University of Salford Salford Huddersfield CNRS/RS International joint project grant between the groups in Poitiers and Salford 6

7 MIAMI* Facility *Microscope & Ion Accelerators for Materials Investigations Colutron G-2 ion source E: keV He implantation 3.5keV R p :25nm /cm 2 /s JEOL JEM-2000FX (200kV) Angle between electron and ion beams is 25 For details of MIAMI, see: J. A. Hinks, J. A. van den Berg and S. E. Donnelly, J. Vac. Sci & Technol. A 29 (2011)

8 The first experiment of our project In situ TEM investigation of the evolution of helium bubbles under displacing irradiation at high-temperature in SiC In situ helium implantation UK MIAMI facility In situ displacing irradiation at high temperature at the JANNuS facility in Orsay. Ion irradiation To develop levels of atomic displacements in a few hours Equivalent to damage levels that reactor components will receive in an operating lifetime 8

9 JANNuS* Facility * Joint Accelerators for Nanosciences and Nuclear Simulation 190kV ion implanter IRMA 2MV Tandem ARAMIS TEM FEI 200kV TECNAI TM Irradiation with 4 MeV Au ions flux: 2.5x10 11 /cm 2 /s Rp : 600 nm Rp : 88nm SRIM Simulation Of damage ramp of temperature 700 to 1300 C E. Oliviero Supported by the French Network EMIR 9

10 Material and sample preparation Material Wafers of n-type 4H-SiC (0001) Single crystal «Cree Inc.» 8 off-axis Thickness : 400 µm Sample preparation for in situ TEM Thinned specimens were prepared by tripod polishing and ion beam thinning using a PIPS Gatan model with 4keV Ar + ions incident at 4 to the specimen surface

11 Results In situ He-implantation in 4H-SiC in MIAMI facility Effects of Au irradiation on He bubbles in JANNuS facility 11

12 In situ He-implantation in 4H-SiC MIAMI facility

13 In Situ He-irradiation in 4H-SiC H-SiC irradiated with He ions/cm 2 /s at 700 C (E:3.5keV, Rp:25nm) BF TEM images Off-zone Recorded with the objective lens underfocused Bubble distribution as a function of fluence Remain on fixed sites (no diffusive motion) Continue to grow Accumulation of injected He and vacancies from the radiation damage Coalescence (bubble contact) Scale marker applies to all panels

14 Effects of Au irradiation on He bubbles JANNuS facility 14

15 Effects of high temperature on He Bubbles Helium bubbles after implantation of 8x10 16 He.cm -2 at 700 C To 1250 C To 1050 C Helium bubbles after subsequent annealing by means of a slow temperature ramp (10 C/min) Clear bubble growth during the ramp of temperature (Ostwald Ripening?) 15

16 Effects of Au irradiation on He bubbles at high temperature 50nm Specimen subjected to a temperature ramp Recorded at 1045 C Mean bubble size: 1.5nm Specimen subjected both to an irradiation with ions/cm 2 of Au at 4 MeV (2dpa) and a temperature ramp Recorded at 1050 C Mean bubble size : 1.2nm A decrease of the bubble size is observed Under temperature ramp Bubbles grew by 60% Under Au irradiation and temperature ramp Bubbles grew by only 19%

17 Towards a qualitative understanding of the effect of Au irradiation on He bubbles System was simulated using the SRIM code A 3 nm-thick helium layer Located in the middle of 40nm-thick layer of SiC. He recoiled out of bubble Stopping of He ejected from a 3nm-thick helium layer following irradiation with Au ions at 4 MeV. Helium density (8.56 x He.cm -3 ) Corresponds to pressure of an equilibrium bubble with r = 1.5 nm. (Temp 700 C) Calculated from an equation of state R.L. Mills et al. (PRB1980) 34% of He will be removed from layer following irradiation with ions/cm 2 of Au at 4 MeV. 17

18 Towards a qualitative understanding of the effect of Au irradiation on He bubbles 34% He loss from 1.5 nm bubble will result in reduction to 1.3 nm radius For equilibrium bubble using EOS from (Mills et al). For isotropic recoiling of helium out of bubble Number of ejected He atoms can be corrected for spherical geometry by surface area considerations 53% He loss corresponding to an equilibrium bubble of radius 1.15 nm. This is very close to the value of the mean bubble size observed experimentally. 18

19 Summary 4H-SiC TEM specimens were implanted with 3.5keV He ions at 700 C in MIAMI Helped by the in situ nature of experiments, we can conclude that once nucleated, helium bubbles remain on fixed sites and continue to grow by accumulation of He and vacancies from the concomitant radiation damage. These bubble populations were then subjected to a simultaneous temperature ramp and 4 MeV Au irradiation in situ in JANNuS Bubble growth was observed to be inhibited by the displacing irradiation as evidenced by reduced bubble growth compare to the thermal ramp alone. The reduced growth is attributed to the displacement of He out of the bubbles by the collision cascades induced by the incident Au ions. Results are in agreement with a previous study on an In situ TEM evolution of helium bubbles in Al during Xe irradiation by Birtcher et al. (PRB94)

20 Next Experiment SiC containing a well-characterized bubble distribution will be irradiated with 4 MeV Au ions up to fluences equivalent to 5dpa. The bubbles will be created either by implantation in MIAMI facility or at P institute in order to obtain a population of larger bubbles. Experiments will be carried out at 900 C (no additional growth of the bubbles and minimization of the surface effect). We wish to conduct a preliminary experiment on the synergistic effects of helium injection and displacing heavy ion irradiation on bubble development in SiC (IRMA+ARAMIS+TEM)

21 In situ TEM investigation of helium bubble evolution in SiC at high-temperature under displacing irradiation Thanks for your attention Thanks to the JANNuS-Orsay staff 21

22 Effects of displacing irradiation and high temperature on a Virgin SiC Virgin sample Sample at 1000 C following ions/cm 2 of 4 MeV Au ions (~2.7dpa) Change of the surface morphology Probably due to graphitisation 22

23 TEM e-beam Accelerating Voltage Ion Beam Accelerating Voltage Ion Species Ion Flux Angle between Ion and Electron Beams Temperature Image Capture Specifications JEOL JEM-2000FX 80 to 200 kv 1 to 100 kv Most ions from H to Xe at all energies (limited by bending magnet) Fluxes of up to cm - 2 s -1 for 6 kv He (for example) to 380 K or RT to 1270 K Gatan ES500W Wide Angle CCD Gatan Orius SC200 (4 Megapixels) D1: Presenting the research activities 23