Carbon Nanotube Formation Detection of Ni atom and C 2 Gary DeBoer LeTourneau University

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?

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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