Carbon nanotube metrology for

science and manufacturing

John Hart

and manufacturing

John HartUniversity of Michigan

aj @ ohnh umich.edu

www.mechanosynthesis.comFebruary 28, 2011

Order = quality, purity, alignmen

Quantity = #/volume

Configurations

highforest (aligned) individual yh

1 m

Order network (tangled) 

Stanford, ETH dispers

lowFlorida

Quantity [#/vol] few 
Applications

highTransistors Filtration/desalination Lightweigh

Enabled by longer, more 

h

E itt

Interconnects

g g

Organized 

/

3D energy devices

Thermal interfaces

Transparent

Emitters, memory

Now co

Order

conductors

Batteries(powder electro

Higher precision of CNT

diameter (chirality) needed

lowE

few (<< 1g) 

Quantity [#/vol]
http://www.nist.gov/mml/polymers/complex_fluids/4th‐carbon‐nanotube‐workshop.cfm 

RM 8281 is a set of dispersed nanotube populations with different average lengths; t

long, medium and short fraction fraction, as well as a 1 % (mass/volume) (mass/volume) surfactant surfactant blank. A 

sealed, sterilized, ampule (~2.6 mL) of each component. These sets were produced u

centrifugation based separation of a common parent dispersion produced from SRM 

Applications of these materials include fundamental research, instrument calibration

applications

http://www.nist.gov/mml/polymers/complex_fluids/nanotube‐reference‐materials.cfm

http://www.nist.gov/mml/polymers/complex_fluids/4th‐carbon‐nanotube‐workshop.cfm

applications.
CNT material measurements

 Structure Structure

 Diameter and chirality

 Length

 Quality (= defect density)

TEM, AFM, Raman, PhotoluminescencTEM, SEM

 Quality (= defect density) Raman TEM TGA

 Morphology

Raman, TEM, TGA

Morphology

 Bundling Alignment Connectivity/ends

SEM, TEMOptical polarization,

Connectivity/ends X‐ray scattering

 Chemistry

X ray scattering

 Purity; residual catalyst

 Functionalization Interaction with surroundings (e g in

TGAIR spectroscopy

Interaction with surroundings (e.g., in

composites)
ensembles

mm

2 (films, fibers,

forests)

sizeSample

m

2

S

<m

individual CNTs

Measurement resolution low 
Typical CNT film Raman spectrum

RBM

ight

=

SWNT 

G/D Rati

o Si peak heiG/D Rati

CNT q

D‐band = 

normalizedtoD band 

CNTs and 

carbon o

nsity [a.u.],n Inten

la

after Jorio et al., New Journ. Phys., 5:139.1–139.17, 2003 
  220 / d 10

d  220

 10

Raman shift

 [cm‐1]

A. Swan, chapter 4 in “Measurement Issues in Single Wall Carbon Nanotubes”, NIST 960‐19 
The Kataura plot: visibility vs. laser energy

A. Swan, chapter 4 in “Measurement Issues in Single Wall Carbon Nanotubes”, NIST 960‐19 
MWNT spectra – effect of collection time

1 sec0 5. sec0.2 sec

 Improvements in detectors, control o

courtesy of Victor Sapirstein, Lambda Solutions Inc. 
G/D ratio as a measure of quality

Example:Annealing of aDWNT powder

reduces G‐ban

peak intensityand width

 High quality samples: G/D = 10 100 High‐quality samples: G/D = 10‐100

A. Swan, chapter 4 in “Measurement Issues in Single Wall Carbon Nanotubes”, NIST 960‐19
Measuring purity by thermogravimetric

analysis ( ) TGA

S. Arepalli, chapter 2 in “Measurement Issues in Single Wall Carbon Nanotubes”, NIST 960‐19 
Identification of defects in TEM

Suenaga et al., Nature Nanotechnology, 2:358, 2007. 
Growth/processing advances help metrolo

 P i rec se cont l ro of catl t a ys size and composition

 Growth of narrow chirality distributions

 CNT separations by diameter, chirality, and length

 Ultracentrifugation Gel electrophoresis DNA wrapping/functionalization

 Directed placement of CNTs on substrates

 Aligned (vertical, horizontal) growth Hersam gro Dielectrophoresis

 Understanding of how dispersion methods modify CNT Understanding of how dispersion methods modify CNT

quality, bundling, length
Challenges in overcoming CNT growth limit

 How is carbon incorporated incorporated into growing growing CNTs? What determines CNT chirality?

 When is it established?

 What causes chirality changes?

 What limits CNT growth rate and length? How do interactions among CNTs affect collective growt

assembly?

Can CNTs be grown to indefinite length?What are the limits of alignment and density?What are the limits of alignment and density?
CNT process metrology

 Catalyst

 Size (and distribution)

 Chemical state

 Composition

 Gas chemistry

 Hd b y rocarbons

 Hydrogen Oxygen and water

 Temperatures and flows How the CNTs evolve in situ
Watching SWNT nucleation in TEM

Hofmann, Sharma, et al. Nano Letters 7:602‐608, 2007. 
Watching SWNT nucleation in TEM

Hofmann, Sharma, et al. Nano Letters 7:602‐608, 2007. 
Problem: CNT growth is a “black bo

1 millimeter

Meshot, Plata, Tawfick, Zhang, Verploegen, Hart. ACS Nano 3(9):2477‐2486, 2009.

Hart and Slocum, J. Phys. Chem. B 110:8250‐7, 2006.

Hart, van Laake, Slocum, Small 3(5):772‐777, 2007.
CNT forest: a model system to understand

p po ulation dynamics during growth

1. Catalyst preparation and

pre‐treatment

‐ deposit thin film

‐ establish chemical state (e.g., Fe2O3Fe)

‐ establish particle size

2. Nucleation

‐ create cap and determine CNT structure‐ maximize yield and uniformity

3. Growth

‐ control carbon “construction”

‐ maintain uniformity (diameter, density)

4. Termination

‐ maximum height = 1‐20 mm ...why?
In situ X‐ray scattering of CNT film growth

G1 beamline at Cornell High Energy Synchrotron Source 
Catalyst particles form rapidly on the subst

As‐deposited

106

2 min. H2

105

nsity [a.u.]

t  1.5 s

20 nm

10 nm

104

Inten

0 nm

0 0.2 0.4 0.6 0.8 1 1.2 1

103

500 nm

q [nm-1]
Fe agglomerates rapidly yet coarsens slowl

As‐deposited

100

s = 20 nm

2 min. H2

10-1

ensity [a.u.]

20 nm

10 nm

10-2

Inte

d = 9 

0 nm 28 min. H2

500 nm

0 0.2 0.4 0.6 0.8 1 1.2 

10-3

q [nm-1]q|| [nm ]

Catalyst migration  Kim et al., J. Phys. Chem. Lett, 2010.
Measuring CNT diameter distribution by SA



/18



±10o I 



 /1



I 

    



2 P R f R dR 1 ቈ ሺln ܴ ߤሻ2቉    

  







0

2

,

( )

P R dR

P R f q R dR

IC q

ܲሺܴሻ ൌ 1 ܴߪ√2ߨ exp ቈെሺln ܴ െ ߤሻ2 2ߪ2቉ 

Log‐normal distribution of

core shell cylinders 0

݂ሺݍ, ܴ, ܿሻ ൌ Δߩܴ 2ሾܬ1ሺܴݍሻ െ ܿܬ1ሺܴܿݍሻሿ ݍܴሺ1 െ ܿ2ሻ

core‐shell cylinders

Wang, Bennett, Verploegen, Hart, Cohen, J. Phys. Chem. C 111(16):5859‐5865, 2007.

Meshot, Plata, Tawfick, Zhang, Verploegen, Hart. ACS Nano, 3(9):2477‐2486, 2009.

ݍܴሺ1 ܿ ሻ

c = r/R
Quantifying CNT alignment

Transmission SAXS

Flightpath (vacuum)

X-ray 

beam

(100 m)

Scattered

CNT forest X-rays 

Monocapillary 

Focused 

X-ray 

beam

3 

1 2 H 

Hermans orientatio

(100 m)

y CCD

z

Motorized 

sample stage

Motorized 

capillary stage

(20 m)

3 cos 

2 2 H   



/ 2

( )sin 



I   







/ 2

0

2 0

( )

cos



 



 I 

H = 1.0: perfecH = 0.0: rando

Hermans, 1948.

Wang, Bennett, Verploegen, Hart, Cohen, J. Phys. Chem. C 111(16):5859‐5865, 2007.

H = ‐0.5: horiz
Time evolution of alignment

Stage II + Stage III

Stage I z

Bedewy, Meshot, Guo, Lu, Hart. J. Phys. Chem. C, 113:20576‐20582 2009. 
Collective growth model

Bedewy et al. J. Phys. Chem. C 113:20576‐20582, 2009. 
Metrology of the reactor environment

Plata, Meshot, et al. ACS Nano 4(10):7185‐7192, 2010. 
1

101

Before pre-heater

Af h

10-310-1 After pre-heater

e (atm)

10-710-5

rtial pressure VOCs PAHs

10-11

10-9

Par

en

ne

ne

ne

ne

ne

ne

ne

ne

ne

ne

ne

PDne hy. nenenenene

H2

hydroge

ethylen

methan

ethan

1,3-butadien

benzen

propen

propyn

pentan

ut-1-en-3-yn

1,2-butadien

1,3-butadiyn

1,3-CP

naphthalen

acenaphth

acenaphthen

fluoren

phenanthren

anthracen

fluoranthen

ethylene CH4

1

bu1ap

Plata, Hart, Reddy, Gschwend. Environmental Science and Technology, 2009. 

naphthalene acenaphthylene 1,3-butadiene benzene 

4
Selective testing reveals alkynes as effectiv

precursors

All Ts = 750 °C, Tp = 25 °C

(+ 0.01 atm of select HC)

Diameter 

pre‐heater ON 

+acetylene 

Plata, Meshot, et al. ACS Nano 4(10):7185‐7192, 2010. 
Benji Maruyama, AFRL
Discussion topics

 Accelerating rapid q y ualit control of CNT production

 Minimum suite of methods?

 What are the key metrics of process health?

 What are the needs/uses needs/uses of in situ techniques? techniques? Ways to close the loop between growth process and material

properties

 Demands for advancement in tools/techniques

 Statistical analysis of CNT populations Characterization across entire SWNT/DWNT diameter range

 Compact instruments and dedicated systems for in situ measure

 Where do the “growth limits” matter?

 Characterization standards/protocols for EHS qualificatio

Mechanosynthesis Group

MostafaBedewy

DavorCopic

Eric Erik Polsen

Meshot

Jinjing Li Sei Jin Park Justin

Beroz

h Mich l ae d

De Volder

Sameh

Tawfick

Megan

Roberts

DanMcNerny

RyanOliver

Anand

Bharath

X‐ray scattering at Cornell: Arthur Woll, Sol Gruner

Precursor chemistry: Desiree Plata (Mt. Holyoke)

YongyiZhang

Jong Ok Aaron

Schmidt

AnneJuggernauth