Download presentation
Presentation is loading. Please wait.
Published byKelly James Modified over 9 years ago
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
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.