Carbon nanomaterials Gavin Lawes Wayne State University glawes@wayne.edu
Outline 1. Carbon structures 2. Carbon nanostructures 3. Potential applications for Carbon nanostructures
Periodic table from bpc.edu
Carbon atom Electron (-) Proton (+) Neutron
Carbon-based molecules are somewhat important for life on Earth amino group Amino acids from msu.edu/gallego carboxylic acid group
Lecithin from indiana.edu/oso Phospholipids
and are also important for all industrial activity Pentane from wikimedia.org
Electron orbitals s orbital p orbital from britannica.com
Hybridization from ASDN.net
sp 3 hybridized C crystals from diamonds.net from cnx.org
sp 2 hybridized C crystals from cochise.edu/wellerr
Graphite consists of layers of hexagonal Carbon sheets. from chem.wisc.edu
Diamond Graphite Electrical insulator Electrical conductor* Very hard Very soft* Transparent Opaque Expensive Cheap
Nanoscale carbon structures
Buckminsterfullerene Molecule consisting of 60 C atoms sp 2 hybridized bonds Has 20 hexagons, 12 pentagons Other related structures have 70 or 84 C atoms from sciencedaily.com
C 60 is named for Buckminster Fuller who designed geodesic domes. from unusualife.com
Original report of C 60
1996 Nobel Prize in Chemistry Robert Curl, Sir Harold Kroto, Richard Smalley for their discovery of fullerenes. from Nobelprize.org
Carbon nanotubes Rolled up sheet of sp 2 bonded carbon atoms from informaworld.com
Carbon nanotubes can be formed from a single sheet of C atoms or several sheets Single walled carbon nanotube (single sheet of carbon atoms) Multiwalled carbon nanotube (several sheets of carbon atoms) from rice.edu
Carbon sheets can also be rolled up in different directions to give different types of nanotubes.
The properties of nanotubes depend on how they are rolled up Electrical conductor Electrical insulator from phycomp.technion.ac.il
Nanotube sizes also depend on how they are rolled up
Graphene (single sp 2 bonded carbon sheet)
C atoms in hexagonal array from cnx.org
From ncem.lbl.gov Scale bar 0.2 nm
Nobel Prize in Physics 2010 Andre Geim and Konstantin Novoselov for groundbreaking experiments regarding the two-dimensional material graphene. from Nobelprize.org
Carbon nanostructures
Why are carbon nanostructures interesting?
They are strong Multiwall carbon nanotube breaking
Multiwall carbon nanotube composite Silica fibres +MWCNT Mechanical properties can improve by 50% or more by adding carbon nanotubes.
Damascus sabre steel contains nanotubes Multiwalled carbon nanotubes found in 17 th century sword. 10 nm These are formed during the synthesis and may have produced the very good mechanical properties.
They have good electrical properties from bpc.edu
Carbon nanostructures may be used in new electronic devices from nanotechweb.org
Devices made with carbon nanotubes
Carbon nanotubes can be used for making electronic devices Carbon Nanotubes. Advanced Topics in the Synthesis, Structure, Properties and Applications, 455-93, 2008
Properties of graphene depend on the subtrate from als.lbl.gov
Geometry of graphene may also affect the properties From nanotechweb.org
Graphene may be used as a transparent electrode
Carbon nanotube mechanical oscillator Force sensitivity of 1 fn Hz -1/2
Graphene mechanical oscillator
Carbon nanotubes may have biomedical applications Carbon nanotubes can be functionalized with different biologically relevant molecules.
Cells incubated with functionalized carbon nanotubes
Electronic bandgap Energy Momentum Metal Semiconductor
The electronic bandgap for graphene looks like a pair of cones touching at their tips for certain positions (in momentum space). This leads to interesting electronic properties. from wikipedia.com
Schrodinger Equation i t ψ = 2 2m 2 ψ + Vψ (for massive particles) E~p 2 Dirac Equation i t Ψ = ( iσ a e µ ( a µ ia ) µ + βm)ψ E~p (for relativistic particles) Appropriate for electrons in graphene
How do you make carbon nanotubes? 1. Carbon arc discharge. Hold two carbon (graphite) electrodes at some potential difference in a Helium atmosphere and bring the electrodes together. At some separation and arc will be produced, and carbon nanotubes will grow on the cathode. These will normally be multiwalled nanotubes, but single walled nanotubes can be grown by adding Ni, Fe, or Co to the cathode.
2. Laser ablation. Heat up a lump of graphite to ~1200 C in an Ar atmosphere, and then blast it with a laser. This can make single walled nanotubes if the graphite has a catalyst like Co or Ni included. 3. Catalytic growth. Heat up hydrocarbons (e.g. acetylene) to high temperatures and then let them settle on a substrate coated with a catalyst (Fe, Co, Ni). This will form either multiwalled nanotubes or single walled nanotubes depending on the growth conditions. How do you make graphene? Graphite and scotch tape.
Open problems 1. To be useful for devices, these carbon nanomaterials need to be prepared on and/or connected reliably to electrodes. 2. Since the properties of these nanomaterials depend strongly on structure (e.g. armchair vs zig-zag nanotubes), we need to have good control over these structural details. 3. Many unanswered physics questions remain, including the magnetism, superconductivity, and optical properties of these materials.
Summary 1. A number of carbon allotropes naturally form interesting nanostructures 2. These nanostructures have enormous potential in developing new electronic, optical, and nano-mechanical devices.
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