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A Detailed TEM Study of Carbon Nano-Onions’ Structure

Chethan K. Gaddam | Randy L. Vander Wal

Introduction SAED

Bright and Dark Field Tomography

Conclusions

Dr. Trevor Clark & Dr. Ke Wang (EM-2010F, EM-2010 LaB6) Dr. Missy Hazen (EM-FEI Tecnai G2) Chung-Hsuan Huang (Lattice Fringe Analysis)

References 1.  D. Ugarte, Nature, 359(1992)707-708

2.  R. L. Vander Wal, Combust. Sci. and Tech., 126(1997)333-357

3.  Y. Gao et al., Carbon, 51(2013)52-58

4.  F. Banhart et al., Nature, 382(1996)433-435

5.  W. A. de Heer et al., Chem. Phys. Letters, 207(1993)480-486

6.  D. Pech et al., Nature, 5(2010)651-654

7.  S. Tomita et al., Chem. Phys. Letters, 305(1999)225-229

8.  S. Iijima, J. Crys. Growth, 50(1980)675-683

9.  K. Yehliu et al., Combust. Flame, 158(2011)1837-1851

John and Willie Leone Family Dept. of Energy and Mineral Engineering & The EMS Energy Institute The Pennsylvania State University, University Park

(a) (b) (c)

Figure 1. Ray diagrams showing how the objective lens and objective aperture are used in combination to produce (a) a Bright Field imaging, (b) off-axis Dark Field, and (c) on-axis Dark Field

Figure 2. Bright and Dark Field TEM images of CNOs at different magnifications (a)–(b) 40,000x, (c)–(d) 60,000x, and (e)–(f) 100,000x. Dark field images were acquired using the (002) diffraction

Figure 3. Illustration of Bragg diffraction from atomic layer planes

Figure 4. SAED pattern of CNOs. the pattern shows diffraction rings corresponding to graphite (002), (100), (004), and (110) layer planes, respectively.

Carbon Nano-Onions (CNOs) •  Polyhedral carbon nanoshells •  Fabrication by graphitization •  Applications include lubrication, catalyst support,

conductive filler Transmission Electron Microscopy (TEM) •  TEM analyses provide crystalline structure and carbon

bonding information •  Techniques include:

•  Bright-field & Dark-field imaging •  Selected area electron diffraction (SAED) •  Electron energy loss spectroscopy (EELS)

•  We expand these using image analysis algorithms to quantify crystallite parameters evident in bright field imaging, and by tomography, for morphology and dimensionality

HRTEM & Fringe Analysis

EELS

X =1.4nm X =1.12 X = 0.34nm

Figure 6. HRTEM images of CNOs acquired at a magnification of 500,000x

(a)

(b) (c) (d)

Figure 7. Lattice fringe analysis (a) schemes for calculating fringe length, tortuosity and separation, (b)–(d) histograms and overlaid lognormal fits and parameterized mean values, respectively

σ*

π*

Figure 5. Images recorded from a specimen at different tilt-angle positions (as labeled)

Figure 8. A schematic of the EELS and EFTEM experimental setup for a Gatan imaging filter (GIF)

Acknowledgements

•  Bright field images show ordered lamella •  SAED "spotty" pattern demonstrates well developed

crystal structure (along with lattice structure) •  Dark field shows that structure is spatially localized •  EELS indicates bonding is predominantly sp2

•  Image analysis algorithms permit quantification of crystallite parameters

•  Tomography confirms 3D nature of this novel carbon morphology

θ θIncident Angle

Reflection Angle

θθλd

dAtomic Layer Planes

nλ#=#2d#sinθ

Optic AxisObjective Aperture

Direct Beam

Direct Beam

Diffracted Beam

2θ

θSpecimen

ReflectingPlane

IncidentBeam

Optic AxisObjective Aperture

Diffracted Beam

Direct Beam

Diffracted Beam

ObjectiveLens

2θ

θSpecimen

ReflectingPlane

Optic Axis

IncidentBeam

Optic AxisObjective Aperture

Diffracted Beam

Diffracted Beam

Direct Beam

ObjectiveLens

θSpecimen

Optic Axis

2θ = Angle of tilt of incident beam

Objective Aperture

Direct Beam

Objective Aperture

Optic Axis

Tilted Incident Beam

DiaphragmDiaphragm

(a) (b)

(c) (d)

(e) (f)

Electron Beam

Specimen

EntranceAperture

Magnetic Prism

Energy SelectingSlit

Lens Array

CCD Camera

Fringe Length

End point distance

Fringe Separation

(002)(100)

(004)

(110)

~2.45Å (100)

~1.41Å (110)

~3.5Å (002)

Crystallite Structure

(600)

(-200) (00)

(200)

(400)

(-600)

(-200)

(-400)