Graphene: Synthesis and applications
• Graphene is a one-atom-thick planar sheet of sp
2-bonded carbon atoms that are densely
packed in a honeycomb crystal lattice
• Molecular structure of graphene
• High resolution transmission electron microscope images
• (TEM) of graphene
Graphene Oxide
• Graphene is the basic building block of all
other allotropes of carbon. For instance,
graphene can be either wrapped up to form a
0D fullerene, or rolled to form 1D carbon
nanotube or stacked up to yield 3D graphite.
A. K. Geim & K. S. Novoselov. The rise of graphene. Nature Materials Vol . 6 ,183-191 (2007).
Brief history of graphene
•
The term graphene first appeared in
1887 todescribe single sheets of graphite as one of the
constituents of
graphite intercalation compounds(GICs). Larger graphene molecules or sheets (so
that they can be considered as true isolated 2D
crystals) cannot be grown even in principle. In the
1930s, Landau and Peierls (and Mermin, later)showed thermodynamics prevented 2-d crystals in
free state, an article in Physics Today reads:
• "Fundamental forces place seemingly insurmountable barriers in the way of creating [2D crystals] ... Nascent 2D crystallites try to minimize their surface energy and inevitably morph into one of the rich variety of stable 3D structures that occur in soot. But there is a way around the problem. Interactions with 3D structures stabilize 2D crystals during growth. So one can make 2D crystals sandwiched between or placed on top of the atomic planes of a bulk crystal. In that respect, graphene already exists within graphite ... One can then hope to fool Nature and extract single-atom-thick crystallites at a low enough temperature that they remain in the quenched state prescribed by the original higher-temperature 3D growth.”
• In 2004: Andre Geim and Kostya Novoselov at Manchester University managed to extract single- atom-thick crystallites (graphene) from bulk graphite:
Pulled out graphene layers from graphite and transferred them onto thin silicon dioxide on a silicon wafer in a process sometimes called micromechanical cleavage or, simply, the Scotch tape technique. Since 2004, an explosion in the investigation of graphene in term of synthesis, characterization, properties as well as specifically potential application were reported.
• Graphene has many potential applications due to its excellent mechanical, electrical, thermal, and optical properties and its larger surface to weight ratio.
• 1g of graphene can cover several football
pitches.
Graphene is two dimensional
• The material is a single layer of carbon atoms
arranged in a dense honeycomb lattice
structure, resulting in a very thin but extremely
strong material. As Geim told Nature, “with
one gram of graphene you can cover several
football pitches (in Manchester, you know, we
measure surface area in football pitches).” It is
so dense that not even helium, the smallest gas
atom, can pass through it.
It’s so thin, it’s virtually transparent
• Graphene may have a future in touch screens,
light panels and solar cells. When mixed with
plastic, it creates a super strong, flexible
material that conducts electricity while
simultaneously increasing heat resistance.
It could replace silicon
• Graphene can be either a conductor or a semi-
conductor, depending on its shape. Because
electrons encounter little resistance as they
flow across the lattice structure of graphene,
they move more quickly than through silicon,
opening up the possibility for faster
computing, and smaller electronic
components.
• Not only is graphene strong, it can be made to spin faster than any other object. Scientists at the University of Maryland in College Park developed a spinning graphene disk that rotates more than 60 million times per minute. Because of its super- strength, scientists theorize this is a mere one-thousandth of the speed that graphene can obtain while remaining stable.
• Scientists think graphene can also be used to hold microscopic and nanoscopic objects in place under an electron microscope
— like DNA nanoparticles — the same way glass slides hold specimens under those implements used in, for example, biology class.
It might have surprising health benefits
• Chinese scientists have found that water-
based dispersible graphene derivatives can
inhibit the growth of E. coli. This means the
material could be used to make paper for
food-packaging or bandages, or incorporated
into textiles that are highly resistant to
bacteria. Adding graphene oxide, as Korean
scientists have found, makes it even more
effective.
Extraordinary Properties
•
thinnest imaginable material
•
largest surface area (~2,700 m
2per g)
•
strongest material ‘ever measured’ (theoretical limit) Young’s Modulus ~ 1100 GPa, Fracture strength ~ 125 GPa
•
stiffest known material (stiffer than diamond)
•
most stretchable crystal (up to 20% elastically)
•
record thermal conductivity (outperforming
diamond)~5000 Wm
-1K
-1• highest current density at room T (106 times of copper)
• completely impermeable (even He atoms cannot squeeze through)
• highest intrinsic mobility (100 times more than in Si)
• conducts electricity in the limit of no electrons
• lightest charge carriers (zero rest mass)
• longest mean free path at room T (micron range)
• The electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field.
• When an electric field E is applied across a piece of material, the electrons respond by moving with an average velocity called the drift velocity, v
d. Then the electron mobility μ is defined as
• v
d= µ E
• Typical electron mobility for Si at room temperature (300 K) is 1400 cm
2/ (V·s)
• Very high mobility has been found in carbon
nanotubes (100,000 cm
2/(V·s) at room
temperature) and more recently, graphene
(200,000 cm
2/V·s at low temperature)
• Graphene is the strongest material in the world, according to new experiments done by researchers at Columbia University in the US. The secret to the material’s extraordinary strength, says the team, lies in the robustness of the covalent carbon-carbon bond and the fact that the graphene monolayers tested were defect-free.
• The researchers measured the intrinsic strength of the material
— that is the maximum stress that a pristine (or defect-free) material can withstand just before all the atoms in a given cross- section are pulled apart at the same time. This was found to be 42 Nm–1 and represents the intrinsic strength of a defect-free sheet.
• “The intrinsic strength of graphene can be considered as an ‘upper bound’ for the strength of materials — rather like diamond is for hardness — that could serve as a goal for engineers who design materials.
• “To put things in perspective: if a sheet of cling film (which typically has a thickness of around 100 µm) were to have the same strength as pristine graphene, it would require a force of over 20,000 N to puncture it with a pencil,” he explained. “That is the force exerted by a mass of 2000 kg, or a large car!”
