7. Carbon Nanostructures
Repetition from the Last Lecture
• Name the 3 basic steps of micromachining.
• List at least 3 techniques of NEMS fabrication.
• What forces are used by the NEMS gyroscope?
• Where is the MEMS component located in a DLP projector?
• List 3 basic fluid pumping options in microfluidic applications.
Carbon – Orbital Hybridisation
• sp3
• 4 sp orbitals pointing to the corners of
a regular tetrahedron
• Tetrahedral diamond structure
https://socratic.org/questions/how-does-sp2-hybridized-carbon-differ-from-sp3https://www.projectorreviews.com/terms/dlp/
http://www.dianerdiamonds.com/diamond_info/diamond_world_data
Carbon – Orbital Hybridisation
• sp2
• 3 sp orbitals pointing to the corners of an
equilateral triangle, 1 p orbital perpendicular
to the plane of the triangle
• Graphite structure
https://socratic.org/questions/how-does-sp2-hybridized-carbon-differ-from-sp3https://www.projectorreviews.com/terms/dlp/
http://www.dianerdiamonds.com/diamond_info/diamond_world_data
Diamond and Graphite Properties
Diamond
• Insulator
• Hardest material (10 on the
Mohs scale)
Graphite
• Excellent electrical conductor
• Soft material (1.5 on the Mohs
scale) due to p bonding
mediated by 2 pz orbitals
https://sustainable-nano.com/2014/02/18/the-atomic-difference-between-diamonds-and-graphite/
Graphene
• Single layer of sp2 graphite
• 2D material – electrons can only
move in the plane of the material
and not perpendicular to it
• 2004 prepared, 2010 Nobel Prize
• The base material for other carbon
allotropes – carbon nanotubes and
fullerenes
• Yet discovered last – transformed
into another energetically more
favorable allotropes during
production
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Graphene production
• Micromechanical exfoliation
• Preparation from graphite using adhesive
tape (first preparation method)
• Chemical vapour deposition (CVD)
• Deposition from hydrocarbon gas on a
suitable metal substrate (Ni, Cu)
• Thermal decomposition of carbides
• High temperature annealing of carbides
(> 1000°C) and graphitisation of their
surface
• Chemical exfoliation in solvent
• Production of either pure graphene but
only in very small pieces or graphene
oxide
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Graphene Properties
• Mechanical properties measurements have
shown a Young's modulus of ~1 TPa, extremely
high material stiffness and also high intrinsic
strength – the strongest ever measured
• The motion of electrons can be described by the
Dirac relativistic equation (Schrödinger equation
for 3D materials). Confirmation of quantum
electrodynamics – the interaction of electrons
and periodic structure - electrons described as
massless particles (Dirac fermions) moving at a
constant velocity of approximately 106 m/s.
Klein paradox – they can tunnel through an
energy barrier of any height and thickness with
probability of 1 – electrons can propagate long
distances (microns) in graphene even in the
presence of defects or other potentials.
• Light absorption in the visible region is only
2.3% – transparent conductive material
• Chemical activity is entirely surface dependent
(every carbon atom that forms graphene is on
the surface) – extreme sensitivity.
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Graphene Applications
• Structural and electrical composites
• Improving the mechanical properties
of materials while increasing their
conductivity. Often in the form of thin
films (organic photovoltaics,
photocatalysis, electrochemical
catalysis...)
• Transparent conductive coatings
• Replacement of current ITO (indiumtin-oxide)
coatings
• Retain their properties even when
mechanically stretched by up to several
percent – flexible electronics
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Graphene Applications 2
• Chemical sensors
• High chemical sensitivity due to large
surface area, low electrical noise due to
high electron mobility
• Detection limit in ppb (parts per billion) –
detection of warfare chemicals and
explosives.
• Electronic components
• Conductive graphene can be made into a
semiconductor – e.g. by limiting the
movement of electrons in one direction
of the surface (graphene nanoribbons) –
forbidden band dependent on the
thickness of the ribbon; possibly by an
external electric field. Use for FET.
• Production of graphene quantum dots for
SET – Coulomb blockade.
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Graphene Applications 3
• Photonics and optoelectronics
• Graphene has a much larger range
of absorbed wavelengths
compared to conventional
semiconductors. At too large
wavelengths (typically > 1 micron),
semiconductors are transparent
(photons have lower energy than
the forbidden band width energy).
• Combined with low noise,
graphene is ideal for
photodetectors.
• Biomedical applications
• Biocompatible material
• Very small < 100 nm flakes with
bound drug can penetrate directly
into the cell
• Photothermal treatment of tumors
• Cell growth
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Fullerenes
• Spherical molecules (clusters)
composed of five- and six-atom
rings of carbon atoms.
• 1985 – mass spectroscopy of the
products of carbon disk laser
sputtering in high vacuum
revealed the molecule C60.
Separation of a single graphene
layer to form a sphere to
minimize energy.
• 1996 Nobel Prize in Chemistry
C60 – soccer ball
C70 – rugby ball
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Fullerene Properties
• Extremely mechanically stable (up to
3000 atm)
• Chemically stable, slightly
electronegative (can accept several
electrons)
• Semiconductors
• Possible modifications:
• External surface modification (exohedral
fullerenes)
• Placing an atom, molecule, cluster inside
(endohedral fullerenes)
• Arrangement into 2D and 3D structures
https://en.wikipedia.org/wiki/Transition_metal_fullerene_complex
https://pubmed.ncbi.nlm.nih.gov/20820560/
https://www.researchgate.net/publication/50843622_Surface_electronic_structure_of_fullerides_effects_of_correlation_electron-phonon_coupling_and_polymerization
Fullerene Applications
• Semiconductors
• Forbidden band gap ~ 1.5 eV. Similar
to standard semiconductors. For
photovoltaics.
• Antioxidants
• Can absorb electrons, meaning they
will bind to free radicals and destroy
them.
• Antiviral activity
• Antioxidant properties and molecular
structure lead to antiviral activity –
research on HIV treatment
• Photosensitization activity
• The binding of fullerenes to tumors
and their good absorption of EM
radiation leads to applications in
magnetic resonance imaging of
tumors or EM heating therapy.
• Direct drug delivery to targeted
sites
• Use of endohedral fullerenes
Carbon Nanotubes
• Discovered in 1991 during observations of carbon black prepared in
a low-pressure arc discharge in argon
• There are single wall SWNT (single wall nanotubes) and multiple
wall MWNT (multiple walled nanotubes) carbon nanotubes
• Properties depend on the way the graphene layer is rolled
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Chirality of the Nanotubes
The chiral vector determines the rolling
https://ms.copernicus.org/articles/9/349/2018/
https://pubs.rsc.org/en/content/articlehtml/2016/sc/c5sc04218f
Nanotube Production
• Main methods:
• Electrode evaporation (doped
metals)
• Laser evaporation of carbon target
• Chemical vapor deposition (CVD) –
plasma or temperature dissociates
the gaseous carbon precursor, the
atomic carbon then condenses on
the substrate.
https://www.researchgate.net/publication/316988879_Hydrocarbon_Sources_for_the_Carbon_Nanotubes_Production_by_Chemical_Vapour_Deposition_A_Review
B. Bhushan (Ed.), Springer Handbook of Nanotechnology, 2017
Applications of Carbon Nanotubes
• Tips for probe techniques
• Suitable as SPM or AFM probe tips
due to mechanical and electrical
properties
• Electron emitters
• Highly stable and high yield
• For displays, X-ray sources or
electron microscopes
https://www.indiamart.com/proddetail/carbon-nanotube-based-afm-probe-14893761048.html
https://electronicsmail.wordpress.com/2012/10/09/52/
Applications of Carbon Nanotubes 2
• Flexible Touch-Screen Displays
• even in small quantities, CNT
significantly improve the conductivity of
polymers – composites
• Voltage-independent (non-volatile)
RAM memories
• Light absorbers
• "Carpet" structure – Ventablack
• Mechanical reinforcement of
composites
• Anodes for Li-ion batteries
• Increased capacity over graphite
anode (~ 50% of Li-ion batteries
for mobile phones and laptops
already contain nanotubes as an
additive)
• Chemical sensors
https://www.nextbigfuture.com/2016/08/carbon-nanotube-nonvolatile-nram-memory.html
Conclusion
• Diamond x graphite – hybridization
• Graphene – 2D structure
• Fullerenes – spherical molecules
• Carbon nanotubes