Atom-resolved imaging and chirality control of carbon nanotubes

Hongwei ZhuTsinghua University

OutlineOutline

Atom-resolved imagingChirality determinationNucleation & growthChirality controlConclusions

ATOM-RESOLVED IMAGING

Atomic configurations of individual single-walled and double-walled carbon nanotubes have been obtained by high-resolution transmission electron microscopy (HRTEM) with atomic sensitivity. A structural reconstruction is carried out by Fourier-filtered analysis of Moire´ patterns, and it is now possible to acquire the carbon honeycomb lattice images through all of the periphery of individual nanotubes.

Electron beam

(α, d, β )

Electron diffraction

3D

HRTEM image

2D

Optical diffraction

Fourier transform

Atomic imaging & chirality assignment

A. Hashimoto et al. Nature 2004, 430, 870.

In situ observations of defect formation in single graphene layers by HRTEM.

A desired contrast transfer function (CTF) enables selective visualization of the graphitic network. Each zigzag chain should turn up as a dark line in TEM images and a bright spot should appear in the middle of each hexagonal carbon ring.

Microscopy: JEM2010FVoltage: 120 kVDefocus: -32 nmCs: 0.45 mmDiv: 1 mradDel: 1.1 nm

Microscopy: JEM2010FVoltage: 120 kVDefocus: -32 nmCs: 0.45 mmDiv: 1 mradDel: 1.1 nm

H. W. Zhu et al. J. Phys. Chem. C 2008, 112, 11098.

H. W. Zhu et al. J. Phys. Chem. C 2008, 112, 11098.

CHIRALITY DETERMINATION

A specially fabricated high-resolution imaging technique is used to obtain atomic-resolution TEM images of SWNTs and DWNTs. A new approach to accurately determinate tube chiralities is proposed here involving relevant analysis based on the information of tube diameters and index angles extracted from their TEM images and their optical diffractions with a help of systematic image simulations.

Index angle (α) and diameter (d)

Chiralh2h1

α(0110)

- (1010)-

Armchair

Zigzag

h2h1

30 o

h2h1

M. Kociak, et al. Euro. Phys. J. B 2003, 32, 457.M. Gao, et al. Appl. Phys. Lett. 2003, 82, 2703.A. Hashimoto et al. Nature 2004, 430, 870.

Chiral tube

h1

h2

(0110)- (1010)

-

Solutions dT /nm α A /o δd / δα(27, 17) 3.051 22.948 0.8%/0.2o

(27, 18) 3.115 23.782 1.3%/0.6o

(28, 17) 3.125 22.415 1.6%/0.8o

Possible solutions

H. W. Zhu et al. Chem. Phys. Lett. 2005, 412, 116.

β =10o

(27, 17)

Inverse FT

Simulation

H. W. Zhu et al. Chem. Phys. Lett. 2005, 412, 116.

Achiral tubes

Armchair Zigzag(17, 17)(34, 0)

h1 h2

h1= h2 , α=30o 2h1= h2 , α=0o

h2

h1

H. W. Zhu et al. Chem. Phys. Lett. 2005, 412, 116.

R (nm-1)-3 -2 -1 0 1 2 3

Inte

nsity

(a.u

.)

Double-walled nanotube

(30, 25) @ (41, 24)

H. W. Zhu et al. Chem. Phys. Lett. 2005, 412, 116.

NUCLEATION & GROWTH

A novel and rational approach to visualize the nucleation points of SWNTs on the atomic scale was proposed. The atomic structure of both the catalysts and tubes growing out were seen by HRTEM. The growth pathway extracted from the TEM image sequence demonstrates a root mechanism in SWNT growth. We believe that this result represents a significant first step towards understanding, and ultimately controlling, the chirality of SWNTs.

Nucleation point of a SWNT

Catalyst

SWNT

Substrate

Atomicstructure

Control the Chirality of SWNT

SWNT: Chirality

Catalyst: Crystal structure

Relationship

Metal nano-particles on SiO2 nano-balls

TEM grid SiO2 nano-balls SiO2 film Metal nano-particles

Metal nano-particle

H. W. Zhu et al. Small 2005, 1, 1180.

H. W. Zhu et al. Small 2005, 1, 1180.

Growth pathway

Small cap Step site

H. W. Zhu et al. Small 2005, 1, 1180.

(31, 14)

H. W. Zhu et al. Small 2005, 1, 1180.

CHIRALITY CONTROL

We present a strategy to control the chirality of SWNTs synthesized by CVD over crystalline catalyst nanoparticles. Atomic-resolution imaging of nucleation points makes it possible to explore the structural correlation between the catalysts and the corresponding nanotubes. The formation of nanotubes with specific chirality could be associated with the angle of the step edge on (111) plane of the particle with respect to the growth direction of nanotubes. The result shows the potential in promoting some experimental advances in synthesis of nanotubes with the desired structure.

Zigzag Chiral Armchair

(111)

[011]-

- - -[111]

H. W. Zhu et al. J. Crystal Growth 2008, 310, 5473.

[011]-

H. W. Zhu et al. J. Crystal Growth 2008, 310, 5473.

(n, m)

Catalyst crystal

(31, 14)

H. W. Zhu et al. J. Crystal Growth 2008, 310, 5473.

(n, m) n>m>030o >α> 0o

(n, n) α= 30o

(n, 0) α= 0o

Growth direction

α

ConclusionsStarting from Fourier transformations of TEM images, we perform an atom-resolved reconstructing operation to get the perfect lattice images of individual tubes to further realize accurate chirality identification. We have succeeded in growing individual SWNTs directly on the SiO2 nanoballs. Their nucleation points and growth pathways have been atomically resolved by HRTEM. We have proposed a rational strategy to achieve structural control on SWNTs based on the assumption that the step edges act as growth centers because of the strong binding between such sites and carbon atoms. It is found that the angle of step edge with respect to growth direction is the key factor in determining the tube chirality.

Thank you!

4/12/2011