25-05-2012, 03:49 PM
Graphene
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Background - Theory
• The successful isolation of a single sheet of graphene contradicts the
theory of Landau, Peierles and Mermin who argued that 2D crystals
were thermodynamically unstable.
• They formulated a model in which the thermal fluctuations were
calculated to have a divergent contribution in the lower dimensional
system. The resulting displacement would approach interactomic
distances at finite temperature and thus push the system to change its
state (to 0D, 1D or 3D structure).
Background - Experimental
• Chemical Exfoliation
It consists in inserting molecules to graphite
by chemical treatment to modify the van der
Waals forces that hold the single monolayers
of carbon together.
NOT VERY SUCCESSFUL: only restacked
and scrolled graphene sheets are obtained.
Fabrication
The obstacles encountered for carbon nanotubes were a
good learning to identify the upcoming challenges that
graphene will face.
1- mechanical cleavage is a research grade procedure, need
for a large scale production (high throughput)
2- identify to what extend the structure can be controlled
(ex: edge effects, number of layers, sizes…)
3- applications
Possible routes
• Chemical exfoliation of graphite through oxidation and then dispersion in water
down to single graphene sheets
• Thermal exfoliation of graphite oxide.
- chemical vapor deposition (CVD) of hydrocarbons deposited on a metal substrate
- thermal decomposition method : semiconducting SiC substrate heated to over
1200°C until the silicon begins to evaporate, at which point the remaining carbon on top of
the substrate nucleates into graphitic film
• Liquid-phase exfoliation of graphite
• Expandable graphite powders