[jin890]

Why does the graphene always grows in honeycomb structure?

I think it can grow like a charcoal, because that's more irregular so the entropy must be higher.


also, why the graphene always grows less than 10(?) layers?

i know that the single layer is the best, but in CVD deposition, it has more than 2 layers.

but why the graphene doesn't grow thicker like other films do?

help plz

[vex]

The difference between graphene and graphite is only one of thickness; they have the same structure in two dimensions.

Graphene has to have a honeycomb structure because of its sp² hybridization.

http://en.wikipedia.org/wiki/Graphene

[jin890]

how about entropy?

by not making sp2 hybridization, graphene can has more stable state, i think

since it is homogeneous bonding between only carbon atoms, it can build Diamond structure or ...something not sp2

[vex]

It's a long-standing joke that "diamonds are not forever" because the sp² network of graphite is actually more thermodynamically stable, so people like to say that all diamonds are slowly reverting back to graphite. In reality, this reaction is so slow that we can safely shake our heads and feel sorry for those people buying graphite engagement rings for their significant others...

Anyway, even if graphene were less stable, that doesn't mean it can't exist.

[fledarmus]

Yes, the diamond structure is more stable than the graphite structure under conditions of very high pressure because physically the atoms can be closer together. if the pressure is high enough for the diamond structure to be preferred and the temperature is high enough for the bonds to move freely, the carbon atoms will organize into a diamond structure. If this is cooled while the pressure remains high, the diamond structure will be frozen in place.

Under lower pressures, the graphite structure is preferred. However, the temperature required to change the bonding is rather high, so once the diamond structure is reduced to terrestrial temperatures, it is essentially indefinitely stable and will not revert to the graphene structure.

[jin890]

thanks! you mean that the diamond is metastable state
  - thermodynamically not stable but kinetically stable since the transformation rate is too slow... in other words.

graphite means a thick layer of graphene, as you replied above... since the difference between graphite and graphene is only layer #
then, why the Carbon deposited on Cu or some substrate by CVD method, always has less than 3 layers(graphene) instead of graphite?

is it related with spiral growth morphology,,,, or something like that?

[dipesh747]

Graphite is known as many many graphene layers 'stacked' on top of one another. Graphene is different because <10 layers of 'stacks'

The electronic properties of graphene are very different to graphite.

The electronic properties of monolayer graphene and bilayer graphene and tri layer graphene are actually slightly different to each other too.

At around 10 layers that is when it starts behaving like graphite.

With your question about CVD, CVD for formation of graphene is a technique that has been developed so that graphene can be produced on an industrial scale (which couldn't be done via the initial method of graphene discovery - micro mechanical cleavage).

Have a look at this thesis (pg 23 will answer your question about graphene formation in cvd)

http://physastro.pomona.edu/wp-content/uploads/2012/09/thesis_pollard.pdf