6. carbon nanostructures: fullerenes and carbon nanotubes 1
Post on 23-Jan-2016
243 views
TRANSCRIPT
6. Carbon nanostructures: fullerenes and carbon nanotubes
1
C is unique in its versatility
Diamond (sp3 Carbon):-hardest material-perfect insulator or semiconductor when doped
Graphene (sp2 Carbon):-soft material-highly anisotropic
Acetylene (sp1 Carbon):
Fullerenes (C60):Diameter = 0.71 nmSMALLEY 1985
Nanotubes:Metallic or SemiconductingDiameter: 0.5 - 50 nmLength: < 50 µmIIJIMA 1991
2
Carbon materials
•19th century: 1st fibre by T. A. Edison(from bamboo filaments)•1950s introduction of carbon reinforced materials(composites)•PAN (polyacrylonitrile) fibres•C-whiskers•vapor phase grown (CVD)•1985 discovery of fullerenesand conjecture of Smalley of the possible existence of1d fullerenes•discovery by Iijima with TEM breakthrough
3
Graphene
4
⇒
Single perfect sheet of graphite (so called graphene)
5
6
7
8
9
“”
LCAO bandstructure of graphene
10
Reciprocal lattive of graphene and the -point
11
Fullerenes
12
◆
C20+2n
⇒12 pentagonal ringsn hexagonal rings
Coordination number =3, ∼sp2
hybridization
C60
C70 C
78
C78
13
◆
- 12 pentagons and 20 hexagons
- Icosahedral (Ih) point group symmetry (5-fold rotation axis)
- σ and π bonds, two bond lengths 1.40 Å and 1.45 Å
- Found first in astronomic spectra, then obtained in carbon-arc shoot (end of 80´s)
C60
14
C60 , buckminsterfullerene
•Solid C60
, FCC close packing
3 Å
10 Å
15
Solid C60
•Van der Waals bonds between molecules
•FCC lattice
• low T: oriented C60
-molecules
•High T: rotation of C60
-molecules
molecular bonding
16
17
C60 solids
Para ver esta película, debedisponer de QuickTime™ y de
un descompresor TIFF (sin comprimir).Para ver esta película, debedisponer de QuickTime™ y de
un descompresor TIFF (sin comprimir).
C60
doped solid
M3C60 , M=alcaline metal
metal ortype II superconductor, as the lattice parameter is changed
fcc, semiconductor 0.5 eVC60
Molecule
Solid
HOMO
εFsemiconductor
metal
semiconductor
LUMO
band-gap
18
M3C
60 compounds are superconducting (Type II)
- Relatively high Tc (45 K for pure (Tl2Rb)C
60),
higher than other intermetallic as Nb3Ge
- a↑ ⇒ g(εF) ↑ ⇒ Tc↑
(BCS) 19
Para ver esta película, debedisponer de QuickTime™ y de
un descompresor TIFF (sin comprimir).
Atoms encapsulated in C60
20
Carbon nanotubes
21
Produced in DC-arc struck between two carbon electrodes (Iijima, NEC,
Tsukuba 1991)
Single-walled nanotube(usually concentric
multi-walled nanotubes)
22
23
24
25
26
The first experimental electron microscope images published, S. Iijima , Nature (1991), reporting the discovery of carbon nanotubes.
First electron microscope image and diffraction pattern from single-walled carbon nanotubes [S. Iijima & T. Ichihashi Nature 363, 603 (1993).]
The smallest CN
27
28
29
Carbon nanotubes: types and description
30
Nanotube geometry
31
Nanotube = wrapped sheet of graphite
Chiral vector
A A’
32
33
34
(5, 5) armchair nanotube
(9, 0) zigzag nanotube
(10, 5) chiral nanotube
Armchair nanotubes n=m , chiral angle 30°. Zigzag nanotubes , either nor m are zero, chiral angle is 0°. Chiral nanotubeschiral angles intermediate between 0° and 30°
http://physicsweb.org/article/world/11/1/9#world-11-1-9-6
,diameter
35
Carbon nanotubes: band structure
36
1D bands of CN
Bandstructure of a (10; 10) armchair carbon nanotube. The shaded region is the 1: Brillouinzone. Note, each band is doubly degenerate, except for the ones crossing E = 0 and the ones withmaximal and minimal energy. There are in total 40 bands.
37
1D character
38
Metallic and semiconducting nanotubes
Zig-zag-tube Arm-chair-tube
metalsemimetal semiconductor
e--pockets
graphite 1. BZ
39
40
1D model
a)Zig-zag tube
- 1 BZ of graphite: elctron pockets at K ⇒ metallic
- Tubes: periodicity around the axis → allowed -values on lines
- If n=3p, p ∈ integer ⇒ line of allowed -points intersects K
⇒ metallic zig-zag -wire (3p,n)- If n=3p+1, 3p+2 ⇒ semiconductor
b)Arm-chair tube
- Line of allowed -points intersects K⇒ metallic⇒ transistors?
41
42
Carbon nanotubes: properties and applications
43
Single-wall carbon nanotubes are also expected to be very strong and to resist fracture under extension, just as the carbon fibers commonly used in aerospace
applications
Unlike carbon fibres, however, single-wall
nanotubes are remarkably flexible.
Mechanical properties
Ultimate material in strength
44
Ruoff et al. Science 287, 637 (2000)
Mechanics, pulling...
45
46
Viola Barwich & Ernst Meyer, Basel
SFM tips
47
48
Vibrating Carbon Nanotubes
Ebbesen et al, Nature 381, 678 (1996)
49
Raman (radial breathing modes)
50
NanoelectronicsElectronic properties
51
52
Nanotube transistors
Gate (Si)
SiO2
Source (Au) Drain(Au)
Nanotube
FET at
room temperature
SET a 4 K
53
FET (unipolar)
54
5540
1D electronic properties: quantization of conductance
de Heer’s experiment
Optical properties
56
Nanotube lights (different colors).Light emission when an electric field is applied
57
Nanotubes for better TV screens
Aligned carbon nanotubes into different patterns
New flat screens, longer lasting, more energy efficient, thinner and flexible.
58
59
Fullereness (C60) encapsulated in single wall CNs
60
ReferencesScience and Application of Nanotubes, edited by D. Tomanek and R. J. Enbody,(Kluwer Academic/Plenum Publishers, 1999)
M. S. Dresselhaus, G. Dresselhaus and P. C. Eklund, Science of Fullerenes andCarbon Nanotubes; Academic Press: New York, 1996.
Carbon Nanotubes, edited by M.S. Dresselhaus, G. Dresselhaus and Ph. Avouris(Springer, Berlin Heidelberg, New York 2001)
Physics Today, May 1999, p22
Physics World, Vol.13, Issue 6, June 2000
R. Saito, G. Dresselhaus and M. S. Dresselhaus, Physical Properties ofCarbon Nanotubes; Imperial College Press: London, 1998, 1999, 2001.
61