carbon nanostructures: background nano-1 nanoscience i ... · pdf filenano-1. kai nordlund,...

Nano-1
Nanoscience I: Hard nanostructures
Kai Nordlund10.10.2010
Faculty of Science
Department of Physics
Division of Materials Physics
Kai Nordlund, Department of Physics, University of Helsinki
Nano-1 Contents
Carbon nanostructuresBackgroundGraphene FullerenesNanotubes
NanoclustersBackgroundNanoclustersNanocrystalline materials
Thin filmsBackgroundPhysical deposition methodsChemical deposition methods
Nano-1 Carbon nanostructures: background
Carbon has 3 main kinds of chemical bonding
sp: linearE.g. acetylene molecule C2
H2
sp2: 3 bonds in a plane, angles of 120o
E.g. ethylene molecule C2
H4Graphite bulk structure
-
Interaction between layers weak
(no covalent bonding)
Single graphene sheet
sp3: 4 bonds symmetric in 3D E.g. methane molecule CH4Diamond bulk structure
Nano-1 Graphene
Individual graphene
sheets were first isolated as late as in 2004
by Andre Geim
et al. at the University of ManchesterAndre Geim
and Konstantin Novoselov
got the Nobel prize for the discovery in 2010!
Isolation technique in principle very simpleSchotch
tape and peel offEven an ordinary pencil draw will make a number if isolated
graphene
sheetsBut the difficult part was to get
large areas, detect and manipulate them in a controlled manner
Now it can be done routinely
A single graphene
sheet can be
macroscopic and visible to the naked eye!
[A. K. Geim Science 324, 1530-1534 (2009)]

Nano-1 Graphene properties
An ideal 2D conducting system
Very durable mechanically, does not oxidize in air
Graphene
can be grown in various ways
e.g. on Ni and then
transferred on Si (C) or on SiC
(D)
Graphene
paper can be
made out of graphene
oxide
[A. K. Geim Science 324, 1530-1534 (2009)]
Nano-1 Graphene has incredible strength
[http://static.nobelprize.org/nobel_prizes/physics/laureates/2010/sciback_phy_10.pdf]
Nano-1 Relation of carbon nanostructures
All of the carbon sp2 structures can be conceptually thought of to derive from grapheneReal growth is different!
[http://static.nobelprize.org/nobel_prizes/physics/laureates/2010/sciback_phy_10.pdf] Kai Nordlund, Department of Physics, University of Helsinki
Nano-1 Fullerenes
The fullerene molecule C60
was found in 1985 Kroto, Smalley & co.
Round carbon molecules
Each carbon atom has 3 bonds, and the atoms form rings with 5 or 6 atoms (pentagons and hexagons) Just like in a traditional soccer football!
Could be imagined to be formed by strongly bending a graphene sheet to a ball Bond reforming needed to form pentagons,
though
Name got inspiration from the architect Buckminster Fuller who designed similar domes Fullerene, Buckyball, Buckminsterfullerene

Nano-1 Different types of fullerenes
Even though C60
is the most common, many other fullerenes do also existAt least C30
C720
The smallest (Natoms
< 30) are likely not closed shells, i.e.
are not fullerenes
The largest are no longer round They have more energetically
favorable hexagons in flat regions
Nano-1 Production
Fullerenes can be made in many
different ways, but the basic idea of most methods is similar to:
Carbon sourceHigh voltage or temperature
makes the carbon gasify The holder has He gas
in a low pressure (e.g. 100 Torr)
In the gas or plasma fullerenes are formed
-
Also ordinary soot
Fullerenes can be dissolved
in e.g. toluene, the soot not
[http://www.sussex.ac.uk/Users/kroto/workshop.html]
Nano-1 Fullerene properties
Individual fullerenes are very elastically hard: The C-C bond in graphite is one of the strongest in existenceExperimental bulk modulus (capability to resist compression) ~ 1000
GPa
(diamond 442 GPa)
But the bond between fullerenes is very weak (same as the so called van der
Waals/dispersion interaction between graphite
shells The bulk modulus of a crystal formed from fullerenes only 14 GPaMelting/boiling point 300 oC
Interesting new chemistryAlready in 1997 over 9000 fullerene
compounds was known
now nobody
is counting any more
It is possible to put atoms or molecules inside fullerenes Endohedral
fullerenes
Nano-1
Fullerene properties: superconductivity
Maybe the most surprising property of fullerenes is that they can be made electrically superconducting Superconductivity = no electrical resistance
For instance the K3
C60 crystal is superconducting below 18.4 K Rubidium-Thallium-doped fullerenes have a
transition temperature as high as 45 K
Compare this with:Normal metals max. about 20 KCeramic copper oxide superconductors
about 50-100 K
Fullerene superconductors are their own class of superconducting materialsNot understood on a fundamental level!

Nano-1 Carbon nanotubes
Carbon nanotubes are hollow cylindrical tubes of carbon that have a diameter of only a few nanometers, but may have lengths of micronsRecord is 4 cm length for a single tube [Zheng
et al, Nature Materials 2004]
Like a graphene shell rolled to a tube, all atoms in hexagons
The end of the tube can be open or fullerene-like
[C. Dekker, Delft Univ.]
Nano-1 Chirality of carbon nanotubes
A nanotube can conceptually be formed by rolling up a sheet of graphene so that the bonds at the edges match perfectlyA sheet can be rolled up in any wayBut a graphene sheet has bonding directions, so all directions are not
equivalent The types of possible
cuts can be defined by a single vector OA
This vector can be determined from the bonding directions in graphene, vectors a1 , a2 .
These can be used to
form the vector OA as
shown to the right I.e. 4 and 2 vectors: (4,2)
Nano-1 Chirality of carbon nanotubes: notation
The chirality is given by two numbers in the form (A,B), A>B E.g. the cut shown above was (4,2) and the resulting tube becomes:
The tube clearly has a helix-shaped twisted
form, i.e. is chiral
Tubes with indices of the form (A,0) and (A,A) are not chiral They are thus called achiral
Tubes of the form (A,A) are called armchair tubes
Tubes of the form (A,0) are called zigzag tubes
All other types are called chiral
Nano-1 Nanotube chirality, examples
(5,5) armchair
(9,0) zigzag
(10,5) chiral

Nano-1 Armchair ??
Whence the name armchair??
If you look at the tube from the side, you can imagine seeing the shape of an armchair on it
Nano-1 Single vs. multiwalled nanotubes
Nanotubes may have many tubes inside each otherSingle-walled nanotubes SWNT, multi-walled nanotubes MWNT
-
Special cases of MWNTs: double-walled: DWNT, triple-walled: TWNT
Nano-1 Production of the tubes
The basic idea of making carbon nanotubes is the same as that of fullerenesHot gas or plasma of carbon, possibly carrier gases
Single-walled tubes require metal nanoclusters to grow!Otherwise the end closes quickly and one only gets a fullerene
Multi-walled tubes can grow spontaneously The different walls interact with each other and prevent closure
Nano-1 Nanotube structures
The nanotubes can form a bundle
And a rope can be formed from the bundlesNote the scale!
[Zhu et al, Science 296 (2002) 884]

Nano-1 Nanotube forest and -paper
By growing nanotubes from a surface one can form a forest
out of them
Paper can be made from the bundles Paper
in the generalized meaning of a fiber network
[K. Arstila. Accelerator Laboratory]Kai Nordlund, Department of Physics, University of Helsinki
Nano-1 Properties of a single nanotube
A single nanotube has incredibly good properties
Strength:Youngs modulus: 1250 GPa
-
Cf. Fe 211 GPa
Tensile strength: in theory 300 GPa, measured 63 GPa-
Cf. steels 0.5
1.5 GPa
Electrical conductance The tubes are either metallic or semiconducting depending on
chirality:-
Armchair tubes (A,A) are metals-
If A-B is divisible by three: small band-gap semiconductor-
Otherwise: large band gap semiconductor
Very large current-carrying capacity:Estimated at 1000 MA/c

carbon nanostructures: background nano-1 nanoscience i ... · pdf filenano-1. kai nordlund,...

Documents