Carbon Nanostructures (I)

Carbon Nanostructures (I)

Ming-Show Wong

May, 2013

(All the contents in this file are solely for educational purpose)

Name: carbon

Symbol: C

Atomic number: 6

Atomic weight: 12.0107 (8) g r

Group in periodic table: 14

Period in periodic table: 2

Block in periodic table: p-block

CAS registry ID: 7440-44-0

Standard state: solid at 298 K

Colour: graphite is black, diamond is colourless

http://www.webelements.com/webelements/elements/text/C/key.html

Carbon Nanostructures In 1980 we knew of only three forms of carbon, namely diamond, graphite and amorphous.

If diamond sheets could be made cheaply all objects that

need to be hard and indestructible would be made from

diamond.

Until 1964 it was generally believed that no other carbon bond angles were possible

in hydrocarbons. But two more carbon bond were synthesized successfully.

1964

Phil Eaton

University of Chicago

1983

L. Paquette

Ohio State University

Cubane C8H8 Dodecahedron C20H20

New Carbon Structure

Types of Hybridization Digonal sp Trigonal sp2 Tetrahedral sp3

Orbitals used for bond s, px s, px, py s, px, py, pz

Example Acetylene C2H2 Ethylene C2H4 Methane CH4

Value of l 1 21/2 31/2

Bond angle 180o 120o 109o 28’

SP Hybridization

ps lWavefunction

Diamond lattice Graphite lattice

http://www.bris.ac.uk/Depts/Chemistry/MOTM/diamond/diamond.htm

http://www.seed.slb.com/en/watch/fullerenes/begin.htm

C C

C C C

C

C

C

C C C C C C

C C C C C C C

CC

C

C C

C

C C C C C C C C C

C

C

C

C C

C

CC

C

C

C

CC

CC

CC

C

C

Small Carbon Clusters

For small clusters of N < 30, they are

linear structure when N is odd, and

closed structure when N is even.

Discovery of C60

1. There is optical extinction at 220 nm (5.6 eV) of light coming from stars.

2. Donald Huffman (U. of Arizona) and Wolfgang Kratschmer (Max Planck

Institute of Nuclear Physics in Heidelberg) simulate the “graphite” production

in the laboratory by striking an arc between two graphite electrodes in helium

environment. They found the spectral lines in IR (Raman) absorption spectrum

that does not originate from graphite. Using isotope methods the IR lines shift

follows what was postulated as C60 molecule.

3. Harlod Kroto (U. of Sussex in England) found the presence of carbon

chains in “red giant” in outer space and would like to reproduce them in the

laboratory. So he contacted Professor Smalley.

Richard Smalley (Rice Univ. in Houston) use high-powered pulsed laser to

produce carbon vapor. One kind of the clusters from condensation of vapor by

helium swept has mass corresponding to C60 measured by mass spectrometer.

Mass Spectrum of Carbon Clusters By laser ablation and mass spectrometer

The Nobel Prize in Chemistry 1996

"for their discovery of fullerenes"

Robert F. Curl Jr.

Sir Harold W. Kroto

Richard E. Smalley

1/3 of the prize 1/3 of the prize 1/3 of the prize

USA United Kingdom USA

Rice University Houston, TX, USA

University of Sussex Brighton, United Kingdom

Rice University Houston, TX, USA

b. 1933 b. 1939 b. 1943

http://www.cochem2.tutkie.tut.ac.jp/Fuller/fsl/higher.html

12 pentagonal (5 sided) and 20 hexagonal (6 sided)

R. Buckminister Fuller, architect and inventer who designed the geodesic

dome resemble this structure at the 1965 New York World's Fair .

C60 - Buckministerfullerene

http://sbchem.sunysb.edu/msl/fullerene.html

Unit cell of C60 Crystal – An FCC

Single crystal is prepared by slow evaporation of solution of C60 in benzene.

Van der Waals force.

1 nm 1 nm

Endohedral and Exahedral

N @ C60

http://www.organik.uni-erlangen.de/hirsch/endo_chem.html

Superconductivity of C60

F. Hebard at Bell Labs doped C60 with potassium (K3C60) in 1991.

• Placed C60 and potassium in evacuated tubes and heated to 400oC.

• A reduction of the magnetic susceptibility c of the sample to c = -1

(MKS system) at 18K and below.

Superconducting transition temperature increases with lattice parameter of

A3C60 for various alkali dopants A.

http://buckminster.physics.sunysb.edu/images/compo_large.jpg

K3C60: 2 tetrahedral and 1 octahedral per C60

C60 C70 C76 C78

http://www.susx.ac.uk/Users/kroto/FullereneCentre/gallery/main.html

The different fullerenes obey to the Euler theorem for polyhedra: f + v = e + 2

where: f is the number of faces, v the number of vertices and e the number of edges

http://www.cm.utexas.edu/academic/courses/Fall1998/CH380L/bp.html

Other Fullerenes

Synthesis of other Fullerenes

C20 by gas-phase dissociation of C20HBr13.

C36H4 by pulsed laser ablation of graphite.

Dodecahedron

V = 20

E = 30

F = 12

20 - 30 + 12 = 2

• Pure C60 are only semi-conducting. Resistivity = 108 W-cm at

25oC.

• Resistivity of MnC60 reduces as n reduce to 3, and increases as n

increase to 6, i.e., M3C60 has the lowest resistivity while M6C60 is

an insulator.

• M3C60 is also an superconductor with transition temperature = -

243oC for M = Rb.

Resistivity of C60

• Polymerization of carbon cages into a rigid framework

• Energy for escaping the carbon cage is 6 eV.

• “Metal-semiconductor” junction may be formed

Metals Semiconductor

Heterojunction Formation by molecule Polymerization

Optimized structures of Si20Cn clusters.

Novel Silicon-Carbon Fullerene-Like Cages

http://arxiv.org/ftp/cond-mat/papers/0309/0309443.pdf

Tungsten Trapped in a Silicon Cage Cluster

Reported by: H. Hiura et al, Physical Review Letters, 26 February 2001

Types of Nanotubes

http://fy.chalmers.se/f3a/Fullerenes/Nanotubes/projects/SWNTTEMimage.html

SWNT (Unaligned)

http://www.chem.ox.ac.uk/icl/catcentre/Ag_swnt.pdf

http://eoeml-web.gtri.gatech.edu/jready/cntubes.shtml

http://www.ifw-dresden.de/forsch/jb2000/23_26highlight5.pdf

SWNT (Bundles of Ropes)

Micrographs of MWNT, from

above: SEM-image of

MWNT with diameter of 10 –

40nm and TEM-image of

MWNT with hollow core and

Fe catalyst.

HRTEM micrograph of MWNT-

tubular; the graphite planes are

exactly arranged parallel to the

tube axis.

MWNT

http://www.ifw-dresden.de/forsch/jb2000/23_26highlight5.pdf

The structure of carbon nanotubes is determined by the Wrapping Vector:

C=na1+ma2, where n and m are integers.

http://www.rpi.edu/dept/materials/COURSES/NANO/ward/page2.html

CNT Chiralty

•n-m is divisible by three, metallic

•n-m not divisible by three, semiconducting, with a gap of ~0.5 eV.

nanotubes could be either metallic or semiconducting, depending on the 1st

Brillouin Zone determined by using a 1-D tight binding energy

approximation.

Two thirds are semiconductor and one-third metallic.

Metallic tubes have armchair structure.

Tube axis

OA is known as the "rollup" vector

or chiral vector

• All armchair chiralities of CNT display metallic properties (green

circles) n - m = 3i

• All other arrangements of (n, m) in CNT display semi-conductor

properties (Blue circles)

Conditivity dependence on chiral vectors

20 nm

Interlayer spacing

Lattice packing parameter

Lattice parameter (nm) Interlayer spacing (nm)

Armchair (10,10) 1.678 0.338

Zigzag (17,0) 1.652 0.341

Chiral (12,6) 1.652 0.339

Packing Behavior of Bundle of SWNT Ropes

• The structure of the nanotube influences its properties,

including conductance, density, and lattice structure.

• The wider the diameter of the nanotube the more it behaves

like graphite.

• The narrower the diameter the more its intrinsic properties

depend on type.

Structure dependence of CNT Properties

Formation of CNTs

Fabrication of CNTs

Arc discharge (Plasma arcing)

• Potential of 20-25 V is applied across carbon electrodes.

• Electrodes of 5-20 m diameter separated by 1 mm at 500 torr of flowing helium.

• Carbon ejected from positive electrode and form nanotubes on negative electrode.

• If electrode contains cobalt, nickel, or iron, single-walled CNTs are produced.

• If no catalyst contained in the carbon electrode, multi-walled CNTs form.

• Single-walled CNTs are 1-5 nm with a length of 1 m.

Laser evaporation

• Graphite target with argon in quartz tube been heated to 1200oC

• Graphite contains cobalt or nickel

• 10-20 nm in diameter and 100 m long.

Chemical vapor deposition

• Decomposing a hydrocarbon (CH4) at 550-1100oC.

• Substrate need to contain cobalt, nickel, or iron.

• Produced CNTs with open ends.

The schematic diagram of synthesizing

MWNT(a) and SWNT(b) by arc discharge.

CNT Synthesis by Arc Discharge (MWNT vs SWNT)

cathode Anode

The fullerenes appear in the soot that is formed, while

the nanotubes are deposited on the opposing electrode,

the cathode.

More hydrogen in the coal tend to form more feather-

like amorphous carbon.

Carbon molecule formation

More hydrogen in the coal tend to form polycyclic

hydrocarbons.

Carbon molecule formation in soot

Cathode deposits consist of two phases, feathers and

matrix.

Matrix is composed of nanotubes and nanoparticles

(shortened scale-like nanotubes).

Feathers consists of the same mix but with amorphous

carbon, called pyrolytic carbon.

More hydrogen tend to form more feather-like

amorphous carbon.

Cathode deposit

Arcing using Coal vs Graphite

In the soot

Other than C60 and C70 - fullerenes, polycyclic hydrocarbons are formed due

to hydrogen in the coal.

On the cathode

The ratio of feathers to matrix increases with hydrogen content in the coal.

Microfilament formation rather than nanotubes from coal.

http://www.acdlabs.com/iupac/nomenclature/79/r79_73.htm

Fused Polycyclic Hydrocarbons

naphthalene

Hard outer shell consisting of fused material

Softer fibrous core containing discrete nanotubes

and nanoparticles

T.W. Ebbesen, “Carbon Nanotubes”, Ann. Rev. Mater. Sci., 24, 235 (1994)

Cathode Deposit

Shell

Core

48. Internationales Wissenschaftliches Kolloquium

Technische Universität Ilmenau

22.-25. September 2003

Transmission Electron Micrographs of particles

formed in the presence of 4.11% cobalt.

Nanotubes (labelled point A and snakes

labelled point B), vesicles (point C) or bladders

(point D) are also observed. Single walled

structures in nanotubes can be observed by

higher resolution as described by others

Journet C, Maser WK, Bernier P, Loisea A, Lamy de la, Chapelle M, Lefrant S,

Deniard P, Lee R, Fischer JE. Nature, 1997;388:756.

Order in carbons produced by plasma arcing in the

presence of cobalt

Isotopic Analysis using Graphite Anode

Large isotopic difference

Isotopically heavy (higher 13C/12C)

Isotopically light

Carbon atoms C1

Carbon atoms C1

Isotopic Analysis using Coal Anode

Small isotopic difference

Isotopically heavy (higher 13C/12C)

Isotopically light

Carbon atoms C1

naphthalene

Much of the soot is directly derived from molecular entities in the

anode and not solely from C1 units.

For naphthalene to be incorporated in the cathode deposit, it must

survive the high temperature of the arc. It is most likely that fullerene

synthesis occurs at lower temperatures at the edge of the arc.

The wider tubes appear to be more predominant at the outer diameter

regions of the anode deposit, possibly because naphthalene survives

more readily here and can be incorporated into the structure.

SWCNT by Laser Vaporization

http://aurora.wells.edu/~ccs/theses/chapin.ppt

Single-walled carbon

nanotubes

1000°C with CH4

Multi-walled carbon

nanotubes

700°C with C2H2

CNT Synthesis by CVD

For acetylene over iron particles at 700oC (ref)

For structure are formed

1. Amorphous carbon layers on the surface of the catalyst

2. Filaments of amorphous carbon

3. Graphitic layers covering metal particles

4. MWNT (covered with amorphous carbon on their outer layer

As grown CNTs generally do not look fully formed. However, the structure is

much improved after heat treatment to 2500-3000oC in argon.

CNT Synthesis by CVD using Acetylene

over Iron Particles

CNT Synthesis by CVD using Acetylene over Co

and Fe Catalysts on Silicon or Zeolite Substrates

For acetylene over Co and Fe catalysts supported on silica or zeolite

• Carbon deposition activity seems to relate to the coboltcontent of the

catalyst

• Nanotube’s selectivity seems to be a function of the pH in catalyst

preparation

• Fullerenes and SWNT are also found among the MWNTs

CNT Synthesis by CVD using Ethylene

For CNTs synthesized by CVD using ethylene and catalysts

1. Metals (Fe, Co, Ni ) seems to induce the growth of isolated SWNTs or

SWNT bundles.

2. SWNTs and DWNTs are formed on Mo-Fe alloy.

3. Reaction temperatures of 545oC for Ni-catalyzed CVD, and 900oC for

uncatalyzed process within pores of aluminum membrane.

4. Resultant CNTs have no caps.

CNT Synthesis by CVD using Methane

For CNTs synthesized by CVD using methane

1. High yield of SWNTs obtained by catalytic decomposition of H2/CH4

mixture over well-dispersed metal particles on MgO at 1000oC

2. Synthesis of composite powders containing well-dispersed CNTs can be

achieved by selective reduction in H2/CH4 of oxide solid solutions between a

non-reducible oxide such as Al2O3 or MgAl2O4 and one or more transition

metal oxides.

3. The decomposition of CH4 over the freshly formed nanoparticles prevents

their further growth and thus results in a very high proportion of SWNTs and

less MWNTs.

Iron-containing compounds as substrates make good nanotube arrays

1998 Nature 395”878-81

1999 J. Chem. Phys. B. 103: 4223-27

Two general growth modes of nanotube in chemical vapor deposition. Left

diagram: base growth mode. Right

diagram: tip growth mode.

Growth Mechanism of CNTs

Other CNTs Synthesis Methods

1. Ball Milling 150 Hrs + Annealing at 1400oC for 6 Hrs (MWNTs)

2. Diffusion flame synthesis

3. Electrolysis

4. Sloar energy

5. Heat treatment of polymer

6. Low temperature solid pyrolysis

合成鑽石技術的演進

•1955 美國奇異公司Bundy et al.,成功的以高溫高壓法合成鑽石

•1962 Eversole 首次以氣相方法沉積鑽石於鑽石晶種上

•1968 Derjaguin et al.,以甲烷及氫氣混合氣體在低壓下成功地合成鑽石

•1971 Angus 證實以熱鎢絲將解離的氫原子與甲烷分解的碳作用後可以

形成鑽石

•1977 Derjaguin et al.,指出數種方式可加速反應氣體中分子的裂解及鑽

石的成長

•1982 Matsumoto et al.,鑽石氣相沉積法的技術進步。利用熱燈絲、高週

波、微波、直流電弧、火炬法等

0

50

100

150

200

250

300

350

400

0 1000 2000 3000 4000 5000

Temperature ( C)

Pre

ssure

(kB

ar)

Liquid Graphite

Stable Diamond

Stable Graphite

Shock

wave

Direct HTHP

Catalyst HTHP

HFCVD，LPSSS

碳的平衡相圖

Synthesis of diamond today:

diamond CVD

• Carbon: methane (ethane, acetylene...)

• Hydrogen: H2

• Add energy, producing CH3, H, etc.

• Growth of a diamond film.

The right chemistry, but little control over the site of

reactions or exactly what is synthesized.

Microwave Plasma CVD Reactor

If diamond sheets could be made cheaply all objects that need to

be hard and indestructible would be made from diamond.

Hot Filament CVD (HFCVD)

• Flexible

• Limited Power Density

• Growth Rate = 0.2~3 m/h

• Insensitive to minor air leak

• Low cost

• An excellent “first reactor”.

Hot-Filament CVD for Diamond Film Growth

Carbon Nanostructures (II)

Graphene

Ming-Show Wong

May 2012

http://en.wikipedia.org/wiki/Graphene

64

Graphene

Graphene is a flat monolayer of carbon atoms tightly packed into a two-

dimensional (2D) honeycomb lattice, and is a basic building block for graphitic

materials of all other dimensionalities. It can be wrapped up into 0D fullerenes,

rolled into 1D nanotubes or stacked into 3D graphite.

66

•In 2004, the Manchester group obtained graphene by mechanical exfoliation of

graphite.

•They used cohesive tape to repeatedly split graphite crystals into increasingly

thinner pieces.

•The tape with attached optically transparent flakes was dissolved in acetone, and,

after a few further steps, the flakes including monolayers were sedimented on a

silicon wafer.

•Individual atomic planes were then hunted in an optical microscope.

•A year later, the researchers simplified the technique and started using dry

deposition, avoiding the stage when graphene floated in a liquid.

•Relatively large crystallites (first, only a few micrometres in size but, eventually,

larger than 1 mm and visible by a naked eye) were obtained by the technique

Scotch tape or drawing method

http://nobelprize.org/nobel_prizes/physics/laureates/2010/

Andre Geim Konstantin Novoselov

The Nobel Prize in Physics 2010

nature photonics | VOL 4 | NOVEMBER 2010

Graphene:2004 2010 C60：1985 1996 核磁共振：1970s 2003 石英光纖：1960s 2009 CCD影像:同上

石墨烯的命名來自英文的graphite(石墨) + -ene(烯類結尾)，也可稱為「單層石墨」

67

可應用於：透明觸控螢幕、光板、軟性電子紙甚至是太陽能電池

Novoselov, K. S., Gaim, A. et al. (2004). "Electric Field Effect in Atomically Thin Carbon Films". Science 306 (5696): 666.

Exfoliated Graphene

Monolayers and Bilayers

Monolayer Bilayer

Reflecting microscope images.

K. S. Novoselov et al., Science 306, 666 (2004).

20 m

69

Home / April 23rd, 2011; Vol.179 #9 / Silicene: It could be the new graphene / File

ONE-ATOM LAYER

Silicon atoms (bright spots) in a honeycomb pattern are a new type of material known as silicene.

Credit: Bernard Aufray / CNRS, Hamid Oughaddou / University of Cergy

•幾乎透明，只吸收2.3%的光

•導熱係數高達5300W/m•K，高於奈米碳管與金剛石

•電子遷移率>15000cm2/V•s，又比奈米碳管或矽晶體高

•電阻率約10-6Ω•cm，比銅或銀更低，目前為世界上電阻最小的材料

•具有高楊氏系數(~1100GPa)、高斷裂強度(125GPa)

Keynote speech by Kostya Novoselov, Nov.2010, Academia Sinica

70

線性光譜 高電子遷移率

獨特光學性質

一個原子厚

堅韌 高延展性

Introduction

3D: Graphite 2D ： Graphene

Graphene is a one-atom-thick planar sheet of sp2-bonded carbon atoms that

are densely packed in a hexagonal crystal lattice.

Graphene is a giant aromatic macromolecule that conducts both electricity

and heat well in two dimensions.

：

0D: Buckyball

1D: Carbon nanotube

Graphene

Graphite

Carbon nanotube Buckyball

Mother of all graphitic forms. Graphene is a 2D building material for carbon materials of all other dimensionalities. It can be wrapped up into 0D buckyballs, rolled into

1D nanotubes or stacked into 3D graphite.

Geim, A. K. and Novoselov, K. S. (2007). "The rise of graphene". Nature Materials 6 (3): 183–191.

Characteristic Young’s modulus(Gpa) Intrinsic strength (GP)

Graphene 1100 125

CNT 1000 150

Carbon fiber 350 2.5

Steel 208 0.4

Fig. Schematic depictions of graphene crystal

structure (lattices), conduction band (blue cones

and curves), valence band (yellow cones and

curves), and Fermi level (dotted lines).

Graphene has a zero bandgap and thus behaves like a metal.

Fig. When a graphene layer is grown on a silicon

carbide substrate), broken symmetry opens a gap (D)

between the valence and conduction bands around the

so-called Dirac energy (ED), as shown in the ARPES

intensity map (lower right), but below the Fermi energy.

Characteristic

• Electron mobility in graphene is extraordinarily high

(200,000 cm2/V.s at room temperature) and ballistic

electron transport at room temperature.

Application

FET

利用Graphene所製造的電晶體其組成之

微細電路，可以微電路尺寸大幅度縮小。

Flash

其密度可達到快閃記憶體的兩倍。

Line

具備低電阻，還可提供高電子遷移率以及更佳的熱傳導性、更高的機械強度，

並減少相鄰導線間的電容耦合(capacitive coupling)效應。

Transparent conductive layer

Graphene的光通透性極高，每層吸收率僅2%，遠低於

一般氧化銦錫的15~18%。薄膜電阻值在以化學方法摻雜

(doping)過後可降至50歐姆。

Flexible graphene paper

Field effect transistor based on graphene armchair ribbon constriction

76

2 Occurrence and production

2.1 Drawing method

2.2 Epitaxial growth on silicon carbide

2.3 Epitaxial growth on metal substrates

2.4 Graphite oxide reduction

2.5 Growth from metal-carbon melts

2.6 Pyrolysis of sodium ethoxide

2.7 From nanotubes

2.8 From sugar

How to make graphene

Mechanical exfoliation from highly oriented

pyrolytic graphite (HOPG):

Slicing this strongly layered material with gently rubbing it against another surface.

藉由反覆撕黏，將graphite層層

剝離成grphene sheets，最後移

植到製備元件。

Transparent tape Method

Chemical exfoliation from bulk: • Oxidized graphite (by using strong acids) was cleaved

via rapid thermal expansion or ultrasonic dispersion, and

subsequently the graphene oxide sheets were reduced to

graphene in the deoxygenation via chemical reduction.

How to make graphene

Thermal decomposition of carbon terminated

4H–SiC : 1. The hydrogen is used to clean and etch the SiC to

obtain a pristine surface.

2. The hydrogen is purged from the chamber and a

turbomolecular pump is used to reach a pressure

of 1 × 10−6 Torr.

3. The chamber is warmed up to1100°C and The

pressure in the chamber during growth is a 4 × 10−5 Torr

1. This is an approach to making GNRs by unzipping multiwalled

carbon nanotubes by plasma etching of nanotubes partly

embedded in a polymer film.

2. The GNRs have smooth edges and a narrow width distribution

(10–20 nm).

How to make graphene

Carbon nanotubes can be unzipped

to form graphene nanoribbons

a), A pristine MWCNT

was used as the

starting raw material.

b),The MWCNT was deposited on a Si

substrate and then coated with a PMMA

film. c), The PMMA–MWCNT film was

peeled from the Si substrate, turned

over and then exposed to an Ar plasma

d–g), Several possible products were generated after etching for different times: GNRs with CNT

cores were obtained after etching for a short time t1 (d); tri-, bi- and single-layer GNRs were

produced after etching for times t2, t3and t4, respectively (t4.t3.t2.t1; e–g). h, The PMMA was removed

to release the GNR.

h), The PMMA was removed to release

the GNR

Using Acetone vapour

Fig 1. Schematic of the MPCVD system

for the growth of GSs

Equipment:：Commercial 1.5W ASTex MPCVD

system

Gas:10% methane and 90% hydrogen

Total pressure：30 Torr

Flow rate：200 sccm

Microwave power：1200W

Time：5 hours

The substrate holder was heated to 800 C, while the

temperature of the SS cylinder wall was about 500 C.

How to make graphene

Fig 2. (a)SEM image of GSs dispersed on a Cu grid

Fig 2. (b) TEM

image of GS on a Cu

grid

Fig 2.(c)

corresponding

SAED pattern

of the GS.

The typical sixfold asymmetry

expected for graphite/graphene

indicating the GSs have better

crystallinity.

The preferential etching of carbon-containing species adsorbed in the stacking direction relative to those adsorbed in the plane direction.

Vol 457|5 February 2009| doi:10.1038/nature07719

85

SCIENCE VOL 324 5 JUNE 2009

86

DOI: 10.1021/jz1011466 |J. Phys. Chem. Lett. 2010, 1, 3101–3107

87

C A R B ON 4 8 ( 2 0 1 0 ) 3 5 9 –3 6 4

88

2 5 N O V E M B E R 2 0 1 0 | VO L 4 6 8 | N AT U R E

89

深: SiO2/Si substrate 淺:Graphene

A pronounced smooth

surface of the GS

1580 cm-1

1329 cm-1

2653 cm-1

2653 cm-1

(2D): The GS consists of a single-layer of graphene.

1329 cm-1

(D):The defects or structural disorder exit in GSs.

The intensity ratio of the D-to-G peaks is increased with the degree of

disorder in the sheets.

Tw isting

Corrugation

Folded region

Non-uniformity

Vacancies

Distortions

Nano Res (2008) 1: 273 291

92

Materials Science

and Engineering is

Hi-Tek

Let’s start a new ball

game