2. Carbon Nanotube Formation Detection of Ni atom and C 2 Gary DeBoer LeTourneau University Longview, TX NASA Johnson Space Center Thermal Branch Structures and Mechanics Division Engineering Directorate Summer, 2000 by Laser Induced Fluorescence

3. What are Carbon Nanotubes?

4. SEM of Nanotube Bundles

5. Why should we care? Strong light-weight materials Thermal and electrical properties Gas (hydrogen) storage

6. What’s the Problem? Nanotubes from Tubes@Rice Price = $1000/gram Minimum order = 250 milligrams Please order in 1/4-gram increments only. Carbon nanotubes, single-walled Sigma-Aldrich Package Sizes US $ 100MG 395.90 500MG 1624.00 Product Comments: CarboLex SE- grade, 12-15 angstrom

7. Increase Production Understand the chemical mechanism (particularly the role of the catalyst) modify current methods or design new methods

8. Nanotube Formation Theories Atomic scooter Metal clusters (nm diameters) Melt (  m sized particles or droplets)

9. Laser Induced Fluorescence (LIF) LaserSample Optics Detector

10. Nanotube diagnostics

11. Laser Ablation target tube

12. Plume Emission Spectrum

13. Physical Principles for C 2 LIF Upper electronic state Intermediate state Detector Long wavelength filter Detector Fluorescence at 513 nm Absorbance at 473 nm Lower electronic state

14. C 2 LIF

15. C 2 Rotational Spectra

16. Rotational Temperature

17. DDG Boxcar Averager Laser 2 IR 1064 nm Laser 3 Dye Pump 355 nm Laser 4 Dye tunable Energy meter ICCD LeCroy or Digital Scope

18. C 2 Experiment and Synthetic

19. C 2 Rot Temperature and Intensity

20. C 2 Rot Temperature and Position

21. Summary of C 2 LIF results Lifetimes of more than 50  s Rotational temperatures 300-700 K Rotational temperature is proportional to intensity Signal can be seen up to 5 mm from the target surface Signal propagates at 50 m/s

22. Physical Principles for Ni LIF filter detector Absorbance 224-226 nm non radiative decay Fluorescence at 301 nm intermediate state Lower electronic state Upper electronic state

23. Nickel Transitions in LIF

24. Laser 1 Gr 532 nm DDG 1 DDG 2 Boxcar Averager 60 Hz - 10 Hz Laser 2 IR 1064 nm Laser 3 Dye Pump 355 nm Laser 4 Dye tunable Energy meter ICCD LeCroy or Digital Scope

26. Nickel LIF Spectra

27. Ni Experiment and Synthetic

28. Nickel Temperature 225.2225.4225.6225.8226.0 Wavelength (nm) A B a. 0 b. 204 c. 879 c b b c a 010203040 50 0500100015002000 Pump-Probe Delay (  s) hot cold hot cold

29. Nickel Propagation

30. Summary of Ni LIF Results Lifetime of several milliseconds with a hot target, 20 microseconds with a room temperature target Electronic temperatures from 200 - 1500 K Electronic temperature is proportional to signal intensity Signal can be seen up to 3 mm from the target Signal propagates at about 10 m/s

31. Co results Laser Induced Luminescence (LIL) Lifetimes: Co atom milliseconds Carbon seconds Geohegan et al. Appl. Phys. Letts., 2000, 76 (3) p 182

32. Other Observations Hot emission and cooler LIF is not unique. Brinkman, Appl. Phys. B, 1996 64 p. 689 Pobst, IEPC, 1995 95 (28) p. 203 Raiche, Appl. Opt. 1993 32 p. 4629 Ablation: small molecules and atoms. Becker, Nanostructured Materials, 1998 10 (5) p. 853 Song, Applied Surface Science, 1998 127-129 p 111 Aguilera, Applied Surface Science, 1998 127-129 p. 309 Dillon, Advances in Laser Ablation of Materials (USA), 1998 p. 403-408

33. Summary of Results ablation produces small molecules and atoms (lifetimes) C 2 - hot emission 50  s C 2 - cooler LIF/LIL 100  s Ni and Co LIF/LIL 3 ms C n LIL 3 s C 2 propagation 50 m/s Ni propagation 10 m/s

34. Conclusions Inconsistent with the melt theory Consistent with atomic catalyst theory Could be consistent with small metal cluster theory Need to know when and where nanotubes are formed

35. Future Work Analysis of three laser ablation experiments Analysis of DC arc spectra Further parametric studies C 2 LIF using two ablation lasers Computational modeling for –nanotube formation mechanisms –nanotube interactions with other materials

36. Acknowledgements Sivaram Arepalli William Holmes Pasha Nikolaev Carl Scott Brad Files SFF NASA-ASEE