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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. What are Carbon Nanotubes?. - PowerPoint PPT Presentation
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Carbon Nanotube FormationDetection of Ni atom and C2
Gary DeBoerLeTourneau University
Longview, TX
NASA Johnson Space CenterThermal Branch
Structures and Mechanics DivisionEngineering Directorate
Summer, 2000
byLaser Induced Fluorescence
What areCarbon Nanotubes?
SEM of Nanotube Bundles
Why should we care?
Strong light-weight materials
Thermal and electrical properties
Gas (hydrogen) storage
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-walledSigma-Aldrich Package Sizes US $ 100MG 395.90 500MG 1624.00Product Comments: CarboLex SE- grade, 12-15 angstrom
Increase Production
Understand the chemical mechanism
(particularly the role of the catalyst)
modify current methods or design new methods
Nanotube Formation Theories• Atomic scooter
• Metal clusters (nm diameters)
• Melt (m sized particles or droplets)
Laser Induced Fluorescence (LIF)
Laser Sample
Optics
Detector
Nanotube diagnostics
Laser Ablation
target
tube
Plume Emission Spectrum
Physical Principles for C2 LIF
Upper electronic state
Intermediate state
DetectorL
ong wavelength filter
Detector
Fluorescence at 513 nm
Absorbance at 473 nm
Lower electronic state
C2 LIF
C2 Rotational Spectra
470.0 470.5 471.0 471.5 472.0 472.5 473.0 473.5 474.0
wavelength (nm)
P Branch
Q Branch
R Branch
All Branches
Rotational Temperature
473.0 473.1 473.2 473.3 473.4 473.5 473.6 473.7 473.8
700600500400300
Wavelength (nm)
DDG
Boxcar Averager
Laser 2IR
1064 nm
Laser 3Dye Pump
355 nm
Laser 4Dye
tunable
Energy meter
ICCD
LeCroy or Digital Scope
C2 Experiment and Synthetic
473.0 473.1 473.2 473.3 473.4 473.5 473.6 473.7 473.8
Wavelength (nm)
C2 Rot Temperature and Intensity
340
350
360
370
380
390
400
410
0 10 20 30 40 50
Pump-Probe Delay ( sec)
Open = Rotational TemperatureFilled = Bandhead Intensity
C2 Rot Temperature and Position
100
200
300
400
500
600
700
800
0 1 2 3 4 5
Imaging Distance from Target (mm)
Summary of C2 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
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
Nickel Transitions in LIF
224.
452
3F2 ________________________ (45419)3F3 ________________________ (45281)3D1 ________________________ (45122)
3G3 ________________________ (44565)3D2 ________________________ (44475)?? ________________________ (44336)5D3 ________________________ (44206)
1D2 _________________________ (36601)
1F3 _________________________ (35639)
3D1 _________________________ (34409)
3D2 _________________________ (33611)3D3 _________________________ (33501)3F3 _________________________ (33112)
1D2 _________________________ (3410
3D1 _________________________ (1713)
3D2 _____________________________________________________________ (879.8)
3D3 _____________________________________________________________ (204.8)3F4 _________________________________________________________________ (0)
Las
er I
nd
uce
d E
xcit
atio
n (
nm
air
)
301.200________________(36601) mair
Collected
Em
ission
225.
149
225.
357
nm22
5.48
0
226.
143
225.
815
225.
956
300.249
303.793________________(36601) mair
305.764
310.156________________(36601) m
air
310.188________________(36601) m
air
313.410________________(36601) m
air
Laser 1Gr
532 nm
DDG 1
DDG 2
Boxcar Averager
60 Hz - 10 Hz
Laser 2IR
1064 nm
Laser 3Dye Pump
355 nm
Laser 4Dye
tunable
Energy meter
ICCD
LeCroy or Digital Scope
Nickel LIF Spectra
225.0 225.2 225.4 225.6 225.8 226.0
wavelength (nm)
Ni Experiment and Synthetic
225.0 225.2 225.4 225.6 225.8 226.0
wavelength (nm)
Nickel Temperature
225.2 225.4 225.6 225.8 226.0
Wavelength (nm)
A
B
a. 0 b. 204c. 879
c
b
b
c
a
0 10 20 30 40 50
0 500 1000 1500 2000
Pump-Probe Delay (s)
hot
cold
hot
cold
Nickel Propagation
0 500 1000 1500 2000
1mm From Target2mm From Target3mm From Target (x10)
Pump-Probe Delay ( s)
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
Co resultsLaser Induced Luminescence(LIL)
Lifetimes:Co atom millisecondsCarbon seconds
Geohegan et al.Appl. Phys. Letts., 2000, 76 (3) p 182
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
Summary of Results• ablation produces small molecules and atoms
(lifetimes)
• C2 - hot emission 50 s C2 - cooler LIF/LIL 100 s
• Ni and Co LIF/LIL 3 ms
• Cn LIL 3 s
• C2 propagation 50 m/s
• Ni propagation 10 m/s
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
Future Work
• Analysis of three laser ablation experiments
• Analysis of DC arc spectra
• Further parametric studies
• C2 LIF using two ablation lasers
• Computational modeling for– nanotube formation mechanisms– nanotube interactions with other materials
Acknowledgements
Sivaram ArepalliWilliam HolmesPasha Nikolaev
Carl ScottBrad Files
SFF NASA-ASEE