Interaction of ion beams with matter

Transcription

1 Interaction of ion beams with matter Introduction Nuclear and electronic energy loss Radiation damage process Displacements by nuclear stopping Defects by electronic energy loss Defect-free irradiation

2 Interaction of MeV ion with solid Processes: ) electron pick-up 2) desorption 3) secondary electron Hercules-task! ) sputtering 5) shock wave 6) ionization 7) δ-electrons 8) bremsstrahlung 9) Čerenkov radiation 1) bond breaking 11) characteristic x-rays 12) elastic backscattering we will concentrate on: basic energy transfer to electrons and nuclei resulting defect production 13) scintillation, luminescence ) heating 15) Coulomb-explosion 16) nuclear reactions 17) elastic recoil 18) collision cascade 19) displacement sputtering and implantation completely disregarded ) phonon 21) implantation

3 Acceptable simplification: Energy deposition and material modification are mediated by quasielastic scattering of ions with electrons, nuclei or whole atoms. We distinguish between: energy transfer to electrons electronic stopping energy transfer to nuclei or atoms nuclear stopping

4 Ratio of cross-sections nuclear Ø x 1 5 atomic Ø nuclear area x 1 1 atomic area

5 1 st order treatment of elastic scattering very similar for electrons and nuclei. Consequences: similar shape of energy loss curves for electronic and nuclear part "universal" curve for electronic energy loss Energy loss in ev/nm 1 4 electronic nuclear Ga ions in Si Energy loss in ev/(1 15 at cm -2 ) Ions: Be to U Target: C TRIM/SRIM Energy in kev/amu 1 5 Energy in kev Conclusion: energy loss calculation is "under control"

6 Quantitative comparison of energy loss 1 Energy loss in kev/nm Energy loss in ev / nm 8 electronic 6 4 nuclear 2 Ga ions in Si Energy in MeV electronic 2 15 nuclear 1 de/dx in ev / 1 15 at/cm Total energy loss in silicon O 1 He H Energy / kev Ar Strongly increasing with atomic number of ion 5 He ions in Si Energy in MeV

7 Close look at region of interest 14 Ga ions in Si 12 Energy loss in ev/nm nuclear electronic Energy in kev

8 Distribution of energy loss along an ion track energy into ionization energy loss energy into recoils ion ion track 3 MeV Ga into Si 1 μm

9 Radiation Damage Process Primary radiation damage caused by energetic particles interacting with lattice atoms Diffusion of primary defects Creation of radiation-induced microstructural features (voids, dislocation loops, precipitates, etc.) and/or defect annealing Resultant change in physical and chemical properties of the material (hardness, el. resistance, refractive index, corrosion, etc.)

10 ion range 1 μm 1 μm 1 μm 1 nm Ga ion range in Si Simple facts about initial defect distribution vacancies per ion 1 nm 1 nm 1 kev kev 1 kev 1 MeV ion energy 1 MeV 1 MeV 1 total number of vacancies per ion kev kev kev MeV MeV MeV ion energy vacancies per nm per ion kev initial vacancies at surface 1 kev 1 kev 1 MeV ion energy 1 MeV 1 MeV

11 Estimate of defect production by elastic scattering calculation of electronic and nuclear energy loss number and energy spectrum of recoiling target particles - electronic stopping: cannot directly lead to a displaced atom! - nuclear stopping: simple approach to count displaced atoms (Kinchin-Pease): energy of hit target atom > "displacement energy" atom displaced # of hit atoms displaced knock-on energy simple rule of thumb: N D = E 2E nucl number of displacements D E D

12 Monte Carlo simulations (SRIM/TRIM, etc.): SRIM 5 kev 12 C Si Depth / nm Conclusion: initial displacement production is "under control"

13 Where is the big deal? Kinchin Pease & SRIM/TRIM only yield "immediate" displacements in collision cascades. There are no dynamic properties of the material included. immediate displacements electronic excitation, ionization remaining damage heat What is the reaction of the soild?

14 More refined approaches: Molecular Dynamics calculation 2 kev Cu Cu (Brian Wirth, UCB) Vacancies Interstitials In general: Calculation of defect kinetics is not "under control" (mobility, annealing, clustering)

15 Very badly understood: Defect production by electronic energy loss Observed defect phenomena range from no damage at all to completely amorphised Reason: displaced atoms cannot be created directly. There must be energy transfer from the electronic system to whole atoms

16 Possible mechanisms and keywords thermal spike melting Coulomb explosion shock wave pressure pulse extremelyhigh energy density (e.g. 2 kev/nm ~.2 kev/nm 3 ~ 5' K) extremenon-equilibrium state extremely fast energy transport

17 Examples 5 GeV Pb Fe 9 Zr 7 B 3 23 MeV C 6 InP TEM, A. Dunlop, NIMB 26 TEM, A. Dunlop, NIMB 27

18 1 MeV C 6 Y 3 Fe 5 O 12 TEM, A. Dunlop, NIMB 1998

19 Particle tracks in mica nm MeV Iodine.8.6 μm μm.8 1. nm MeV C μm μm.8 1.

20 The practical benefit: how to avoid surface damage 1 Ga ions in Si electronic 8 Energy loss in ev/nm nuclear Energy in kev

21 Low energy FIB irradiation of silicon Normalized defect production Si in Si Energy in kev