ExtremeTech explains: What is graphene?
The word “super-material” gets thrown around a lot these days — ceramic super-materials, aerogel super materials, elastomeric super materials. But one super-material overshadows them all, earning its discoverers a Nobel Prize and defining the upper limit for scientific hype and excitement. It has the potential to revolutionize processing, power storage, even space exploration… but it has yet to actually achieve much of anything. It’s called graphene, and it’s the granddaddy of the modern boom in materials science. Graphene has the potential to be one of the most disruptive single inventions of all time — but what is it, really?
Scientists have been talking about graphene for the better part of a hundred years, though not always by that name. The idea was easy enough to come up with: what if we could take a diamond and slice it into wafers just one atom thick? This would make it a so-called “two-dimensional” substance, made entirely out of carbon, yet flexible in a way that diamond cannot be. It not only has the incredible physical properties you’d expect from a sheet of crystal, widely cited as the strongest material ever created on a per-weight basis, but it also has incredibly high electrical conductivity. Being atomically small, graphene could allow much, much more tight packing of transistors in a processor, for instance, and allow many electronics industries to take huge steps forward.
Research showed that while diamond-slicing would be very hard, atom-thin carbon was actually pretty easy to make, in small fragments — bits of graphene even show up when school kids scratch the pure carbon graphite in their pencils over paper.
Yet despite some valiant early attempts, we had to wait until 2004 for anyone to reliably make graphene fragments large enough and quickly enough to be, hypothetically, useful. Their technique centered around “pulling” strands of graphene out of a sample of pure graphite by using the so-called Scotch Tape method, which involves sticking and unsticking clear sticky tape with powdered carbon in the middle. As the tape unsticks each time, it pulls the threads out a few atoms further. This English team was later awarded the Nobel Prize for figuring out how to economically create a substance that, when they received the award, could do precisely nothing outside of materials research labs.
Yet, the excitement persists. Why? Well, because the potential is so great it’s impossible to ignore.
The incredible physical properties of graphene practically beg to be applied in all sorts of thought experiments. if it could be made in threads at least a meter long, some scientists believe these strands of graphene could be woven together to make a tether both strong enough and flexible enough to be the backbone of a space elevator. This single piece of flexible, woven carbon would stretch all the way from the surface of the Earth to beyond geosynchronous orbit. These are the sorts of sci-fi inventions that will become plausible if graphene manufacturing manages to come into its own.
Graphene could be revolutionary for a wide variety of fields. There’s bioengineering, where scientists hope to use graphene’s incredibly small size to penetrate cell walls, potentially inserting a molecule of the researchers’ choice. Graphene could also be used to create an ultra-fine, anti-biotic water filter for quick, easy filtration of potentially dangerous drinking water. It could simply allow design and construction on a smaller scale than ever before, and it’s not surprising that designers and engineers are letting their imaginations run wild at the thought.
Yet, there are limitations to graphene’s near-perfect usefulness. Despite its high conductivity, graphene lacks the usefully small “bandgap” that is needed for many applications in electronics. The bandgap of a substance is the energy difference between the conducting and non-conducting bands for electrons in that substance, and using an applied current to push electrons around between these states is the basis for all modern computing. Without an ability to easily switch a graphene transistor between “on” and “off” by adjusting the current flowing through it, a graphene processor would have to pioneer an alternative to standard digital computing.
The bandgap issue also restricts graphene from quickly revolutionizing solar power. Graphene’s low electrical resistance could make solar panel technology much more energy efficient, but the energy contained in a photon isn’t enough to activate a graphene transistor. “Doping” of graphene with contaminants to increase its absorptive abilities has been a major source of research, since graphene’s lack of resistance and its ability to be packed so densely could grant enormous increases in energy production very quickly. As with all things graphene, however, we will have to wait and see.
The word “graphene” is sometimes used interchangeably with the term “carbon nanotubes” or CNTs. CNTs are exactly what they sound like: sheets of graphene that have been rolled up into a nano-scale tube. The walls of the tube are a single atom thick, but the tube overall is more stable and less reactive with other substances than regular, linear graphene. Many researchers have found greater success using CNT technology, but since carbon nanotubes are made of graphene, many of their most promising applications are still held back by the basic inefficiency in manufacturing.
It’s a foregone conclusion that graphene will change the world — the only question is whether it will do so directly, or indirectly. Actually making it to market, affecting the world with graphene-based technologies, could certainly be in the cards. But it’s also easy to imagine that a variety of specific, graphene-like materials tailored to each specific graphene-like application could beat graphene itself, on average. Still, even if all the material achieves is inspiring a new generation of two-dimensional materials science, it will have been incredibly important in shaping the face of modern technology.