14-06-2012, 02:59 PM
Seminar on Graphene
Graphene.ppt (Size: 4 MB / Downloads: 102)
What is graphene?
2-dimensional hexagonal lattice of carbon
sp2 hybridized carbon atoms
Basis for C-60 (bucky balls), nanotubes, and graphite
Among strongest bonds in nature
A Two dimensional crystal
In the 1930s, Landau and Peierls (and Mermin, later)showed thermodynamics prevented 2-d crystals in free state.
Melting temperature of thin films decreases rapidly with temperature -> monolayers generally unstable.
In 2004, experimental discovery of graphene- high quality 2-d crystals
Possibly, 3-d rippling stabilizes crystal
How to make graphene
Strangely cheap and easy.
Either draw with a piece of graphite, or repeatedly peel with Scotch tape
Place samples on specific thickness of Silicon wafer. The wrong thickness of silicon leaves graphene invisible.
Graphene visible through feeble interference effect. Different thicknesses are different colors.
Electrons in graphene :
Electrons in p-orbitals above and below plane
p-orbitals become conjugated across the plane
Electrons free to move across plane in delocalized orbitals
Extremely high tensile strength
Relativistic charge carriers :
Linear dispersion relation- charge carriers behave like massless Dirac fermions with an effective speed of light c*~106. (But cyclotron mass is nonzero.)
Relativistic behavior comes from interaction with lattice potential of graphene, not from carriers moving near speed of light.
Behavior ONLY present in monolayer graphene; disappears with 2 or more layers.
Possible Applications :
High carrier mobility even at highest electric-field-induced concentrations, largely unaffected by doping= ballistic electron transport over < m distances at 300K
May lead to ballistic room-temperature transistors.
GaTech group made proof of concept transistor- leaks electrons, but it’s a start.
Energy gap controlled by width of graphene strip.
Must be only 10s of nm wide for reasonable gap.
Etching still difficult consistently and random edge configuration causes scattering.