How Pencil Lead and Sticky Tape Won a Nobel Prize

 

pencil_lead_and_tape

By Bradley Stockwell

First off, I want to apologize to all of my six followers to this blog. I know I left you in anxious anticipation over my follow-up post to Climate Change Part I on future green technologies. However, after three months of procrastination, I confess I still haven’t written it. I’m sorry, but I’m easily distracted and while attempting to assemble it I came across a story too good not to tell about a fascinating material called graphene. Graphene is the thinnest, strongest and stiffest material on Earth; it conducts electricity and heat better than any other known material; it is transparent and two-dimensional and is the basis for all future technologies and A.I. At the moment, its potential of applications looks limitless. Oh did I mention it was discovered with nothing more than pencil lead and tape? They even gave the guys who discovered it the 2010 Nobel Prize in Physics. Shit, if I knew it was that easy I could’ve scratched Nobel prize in physics off the bucket list a long time ago.

So what is graphene exactly then? In short, it’s a sheet of pencil lead (graphite) an atom thick. But to understand how we arrived at the discovery of graphene, we need to tell another story, the story of carbon. Graphene is an allotrope of carbon which simply means it’s one possible way to structure carbon atoms. The carbon atom has six protons and typically six neutrons in its nucleus. Sometimes the nucleus has eight neutrons, in which case the carbon atom is known as carbon-14. Carbon-14 is unstable, meaning it radioactively decays, but the decay is consistent over long periods of time. Because this form of carbon is found in many materials, measuring its presence gives us a way to age materials—or what is known as carbon dating. Carbon-14 however is not an allotrope of carbon, it is what is known as an isotope, something covered in detail in a previous post, Flight of the Timeless Photon.

Allotrope formation is dependent on the electrons of a carbon atom and the way in which they bond to other carbon electrons. Carbon has six electrons, two of which are buried in its innermost shell near the nucleus, and four in its outermost shell which are called valence electrons. It is these four outermost electrons—and a ton of heat and pressure—that make the difference between a lump of coal and a diamond, another allotrope of carbon. In diamond, a carbon atom’s four valence electrons are bonded with four other carbon valence electrons. This produces an extremely stiff crystalline structure. In fact, a typical diamond is made up of about a million billion billion atoms (1 with 24 zeros after it) all perfectly arranged into a single pyramidal structure, which is key to its extraordinary strength. But diamond is not the strongest and most stable allotrope of carbon. Although DeBeers may want you to think otherwise, a diamond is not forever; every diamond in existence is actually slowly turning into graphite. The process however takes billions of years so no need to worry about your wedding ring just yet.

Graphite is not a crystalline structure like diamond, but planes of carbon atoms connected in a hexagonal pattern, with each plane having an extremely strong and stable structure—stronger and more stable than diamond. Some of you may be asking, is this not the same graphite we write with and grind up into fine powder lubricants? Yes indeed it is, and the conundrum of descriptives can be blamed on electrons. In diamond, a carbon atom shares its four valence electrons with four other carbon atoms, whereas in graphite it shares its electrons with only three (see graphic below). This results in graphite having no electrons left over to form strong bonds between layers, leaving it up to something called van der Waals forces, a weak set of forces generated by fluctuations in a molecular electric field. Basically it’s the universal glue of matter and is something all molecules naturally possess. Because these forces are so weak is why you’re able to write with graphite—a.k.a. pencil lead. As you press your pencil to paper, you’re breaking the van der Waals forces, allowing layers of graphite to slide across one another and deposit themselves on a page. If it weren’t for the weak van der Waals bonds, pencil lead would be stronger than diamond and this is behind the advent of carbon fiber. Carbon fiber is spun graphite, lathered in an epoxy glue to overcome the weak van der Waals forces. Restriction of van der Waals forces is also behind the phenomenality of graphene.

diamond-structure-graphite-structure

Since graphene is a single layer of graphite one atom thick, there is no need to worry about weak van der Waals forces. By default this makes graphene the strongest and thinnest material known to man. Also, because its carbon atoms are not structured in a crystalline lattice like diamond, which leaves no free electrons, it also conducts electricity and heat better than any known material. This means because of its transparency and thinness, we could literally add touch sensitivity to any inanimate object and possibly entire buildings. It also allows for something called Klein tunneling, which is an exotic quantum effect in which electrons can tunnel through something as if it’s not there. Basically it means it has the potential to be an electronic dynamo and may someday replace silicon chips and pave the way for quantum computing. Graphene was purely hypothetical until 2004 when Andre Geim and Konstantin Novoselov discovered it. As stated in the title of this post, they discovered it with nothing more than a lump of graphite and sticky tape. They placed the tape on the graphite and peeled off a layer. They then took another piece of tape and stuck it to the piece of tape with the graphite layer and halved the layer. They continued to do this until they were left with a layer of graphite one atom thick. I’m not exaggerating the simplicity of the procedure in any way. Watch the video below and you can replicate the experiment yourself, the only catch is you need an electron microscope to confirm you indeed created graphene. Until next time my friends, stay curious.

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