Hacker News Reader

Comment by dm2 | Hacker News Reader

Some graphene facts that I've found after a few minutes of research:

- One million times thinner than paper, one atom thick, it's considered a 2D material. http://www.chemistryviews.org/details/ezine/4976821/Is_Graph...

- Strongest material, stronger than diamond. http://engineering.columbia.edu/even-defects-graphene-strong...

- Scotch tape was used to create a piece of graphene only 10 layers thick (I'm guessing that means ~10 atoms thick? wow)

- Moves electrons ~200 times faster than silicon: http://www.samsungvillage.com/blog/2012/05/18/samsungblog-sa...

- Transparent, only absorbs 2.3% of light. http://arxiv.org/pdf/1201.3071.pdf

- Can't switch flow of electricity off? https://gigaom.com/2013/04/19/you-can-pluck-graphene-from-th...

- Can repair itself if you dump carbon atoms on the hole, they snap into place. http://arxiv.org/abs/1207.1487

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

View on HN

Nice list of facts. I would point out that although 2.3% absorption looks small, it's actually huge for just a single layer of atoms! So it's true that graphene is mostly transparent, but it's actually less transparent than almost any other single layer of atoms. That's why the title of your source is "high optical absorption in graphene." :)

I don't understand how it can be described as '2D'.

If it were 2D you would be able to stack an infinite amount without the stack getting higher.

Loosely, it refers to the degrees of freedom an electron has in the material. For example, if you consider the 'density of states' – a quantity which can be thought of as the number of electrons at a given energy level – it has a different characteristic shape depending on whether the material is '1D', '2D', '3D' or even '0D':

http://britneyspears.ac/physics/dos/images/Image441.gif

[As an aside, britneyspears.ac is a surprisingly good resource for a lot of basic solid state physics. You can find a full derivation of the above graph on there.]

Edit: To illustrate, this next graph is the density of states for three different Carbon-based materials: graphite which is '3D', graphene which is '2D' and a nanotube which is '1D'.

http://me3007.wdfiles.com/local--resized-images/thermal-and-... [Source: Hone, J., Quantized Phonon Spectrum of Single-Wall Carbon Nanotubes, Science, 289, 1730, 2000 via http://me3007.wikidot.com/thermal-and-electronic-properties-...]

You can see how these curves are similar to the theoretically-derived curves in the previous graph.

I think there is a different definition of 2D in the materials science field.

http://www.mri.psu.edu/centers/2dlm/

http://www.chemistryviews.org/details/ezine/4976821/Is_Graph...

http://gigaom.com/2013/07/19/graphene-isnt-the-only-2d-mater...

http://www.mrs.org/s13-cfp-o/

My guess is that the people describing it as 2D are focusing on different properties of 2-dimensional space than you are and would agree with you that stacking it would increase the height.

"2D" describes the freedom of the electrons. They can move in X and Y, but not Z. This restricted freedom causes all sorts of unique electronic behavior never seen in 3D systems. You are certainly correct that graphene has height.

Source: I am getting a PhD in 2D electron physics

I think a combination of Graphene and superconductivity would be even more wonderous than each one of them!

In fact, superconductivity can be induced in graphene by a proximity effect: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111...

Reply on news.ycombinator.com