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Seminar on Graphene

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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.

Graphene


Graphene, a single atomic layer of carbon connected by sp2 hybridized bonds, has attracted intense scientific interest since its recent discovery1. Much of the research on graphene has been directed towards exploration of its novel electronic properties, but the structural aspects of this model two-dimensional system are also of great interest and importance. In particular, microscopic corrugations have been observed on all suspended2 and supported3, 4, 5, 6, 7, 8 graphene sheets studied so far. This rippling has been invoked to explain the thermodynamic stability of free-standing graphene sheets9. Many distinctive electronic10, 11, 12 and chemical13, 14, 15 properties of graphene have been attributed to the presence of ripples, which are also predicted to give rise to new physical phenomena16, 17,18, 19, 20, 21, 22, 23, 24, 25, 26 that would be absent in a planar two-dimensional material. Direct experimental study of such novel ripple physics has, however, been hindered by the lack of flat graphene layers. Here we demonstrate the fabrication of graphene monolayers that are flat down to the atomic level. These samples are produced by deposition on the atomically flat terraces of cleaved mica surfaces. The apparent height variation in the graphene layers observed by high-resolution atomic force microscopy (AFM) is less than 25 picometres, indicating the suppression of any existing intrinsic ripples in graphene. The availability of such ultraflat samples will permit rigorous testing of the impact of ripples on various physical and chemical properties of graphene.