FromQuarkstoQuasars

Graphene – Material of the Future?

I’ve been seeing a bunch of articles about this new thing called “graphene” everywhere! Have you looked into this?

Yes! Graphene is an incredible nanomaterial – quite possibly THE material of the future.

What’s so special about it?

[expand title=”For starters, a single layer of graphene is about 100 times stronger than steel yet extremely flexible.”]One of the reasons why graphene is so strong is because its molecules are arranged in a hexagonal honeycomb lattice. Get this – a single layer of graphene is just ONE atom thick, which is flat enough to be considered a 2D material![/expand]

Wait, what? One atom thick? What’s the point in using a material that you can’t even see?

[expand title=”Actually, you CAN see it.”]Graphene absorbs about 2.3% of white light and lets the other 97.7% pass through. This makes graphene very transparent yet a single layer is still visible to the naked eye. Have you ever noticed the tiny flakes of graphite that come off when you are writing with a pencil? Those are essentially flakes of graphene layers.[/expand]

So you can get graphene from graphite?

[expand title=”That’s right.”]Graphene was first isolated in 2004 by some scientists at University of Manchester, England, and the Microelectronics Technology in Chernogolovka, Russia. Basically, they used scotch tape to slowly and carefully strip away thin layers of graphite crystals that they then transferred to a silicon substrate (as a place setter of sorts). They even managed to piece together these minuscule flakes and connect electrodes to it! These brilliant scientists were the first to measure and quantify the baffling properties of graphene.[/expand]

What other properties does graphene have?

Well, its electrical and thermal characteristics are very strange. It is about 200x more electrically conductive than silicon and 10x more thermally conductive than copper. The electrons in graphene move extremely fast and behave very much like photons, which are light particles, with zero effective mass.

How does that work?

An important characteristic of graphene is that it is made up of carbon atoms arranged in a hexagonal honeycomb lattice. So in a single 2D layer of graphene, each carbon atom is connected to 3 other carbon atoms. There are 2 electrons in the inner shell and 4 in the outer shell. Since each carbon atom is connected to three others, 3 of its valence electrons, which are the outer shell ones, are bonded to an electron of the atoms next door. This leaves one last valence electron that is always moving freely, making it super conductive.

Credit: H+ Magazine
Credit: H+ Magazine

So what are the implications of its high conductivity? Would graphene be a good substitute for silicon in transistors then? I’ve heard that one of the problems with silicon is that producers won’t be able to make silicon smaller than a certain size at some point.

Yes and no. Although I agree that the eventual use of graphene in transistors would make an incredible impact on computer and hardware process power, there are a few challenges that researchers have to overcome first. Since you bring up transistors, let’s talk about what makes a transistor a transistor, and why silicon has been the dominant material for so many years.

I only know that transistors are used in computer chips. How do they work?

Transistors are tiny structures that control the flow of electricity in computer circuitry. For transistors to function the material from which it is constructed must have the properties and capacity to manage electric flow. The best material to do this is a semiconductor. In a semiconductor, such as silicon, electrons cannot travel at low energy. So at low energy the material is an insulator and does not conduct electricity. It can become conductive only when enough energy is applied to the electrons, which switches conductivity “on”. The amount of energy that’s needed to do this is called the band gap.

[expand title=”When an electrical signal is applied to one pair of its terminals…”]…a transistor can control the output in proportion to the input signal, acting as a signal amplifier. A transistor can also act as a switch that can turn the electric current on or off. This threshold at which an electron becomes freely moving is called the conduction band.[/expand]

Credit: The Open University
Credit: The Open University

Are you saying that graphene is not capable of doing this? But it’s so conductive!

That’s just it – graphene is TOO conductive. It has no band gap! Those funny little 4 valence electrons are always in a free state, even if there is no energy applied. That means there is no “switch” that can render graphene nonconductive, which is absolutely necessary for transistors.

Is there any way to artificially create this conductivity switch?

Researchers have tried but they haven’t been very successful or consistent. For example they try applying electric fields, doping it with other elemental atoms, stretching, and squeezing the material. There have been a couple of promising techniques though.

Which ones have been successful?

[expand title=”One involves adding another compound to graphene.”]Researchers at University of Manchester and Nottingham separated two layers of graphene with a layer of boron nitride. This technique allows the material to be switched on/off but the trade-off is that the electrons were slowed down significantly.[/expand]

Is there another technique that isolates just pure graphene?

[expand title=”Yes, but it hasn’t been tested experimentally yet, only proven to be possible theoretically.”]Researchers from University of California, Riverside have found that graphene CAN behave like a transistor without needing an artificial band gap. Basically, they are utilizing a phenomenon called negative differential resistance. It occurs when a current entering a material causes the voltage across it to drop. This drop works like an inverted transistor. The researchers hypothesize that graphene logic gates and chips built using this technique can be much smaller, denser together, and more efficient than silicon. They’ll be able to operate at speeds upwards of 400GHz![/expand]

When do you think that those researchers will actually be able to build circuit using this technique?

Soon! At this rate, probably in the next two years or so, and then maybe another 5 years before it is commercially viable. Research on graphene has been exploding.

Yeah the interest in graphene really has been growing substantially. That’s why I think that graphene will be used commercially way sooner than what you said. I mean come on – look at how technological innovation has been growing exponentially over the past few hundred years.

Definitely. If the band gap issue is resolved, graphene could be used in almost any gadget! The possibilities are boundless. Everything from transistors in circuits, optoelectronics, batteries, even armor…

Batteries?

The problem with current batteries and capacitors has to do with energy storage. Batteries can hold a lot of energy but it takes a long time to charge. Capacitors can be charged very quickly but cannot hold much energy. By incorporating graphene, batteries and capacitors could have much higher storage capacities, better longevity, and quicker charge rate than the state-of-the-art ones in the market now. These upgraded batteries can be used in anything from manufacturing machinery and electric vehicles to smartphones, tablets, and appliances.

Credit: Kurzweil AI
Credit: Kurzweil AI

Cool! What else?

Graphene would also be amazing used in optical electronics. Technologies that use displays, touch screens, light panels, and photovoltaic cells require a transparent conductor with low resistance and high transparency. Graphene fits the bill perfectly. It’s also super strong and flexible so something like a graphene-infused smartphone display wouldn’t break nearly as easily as the brittle ones we have.

Credit: Financial Times
Credit: Financial Times

Photovoltaic cells are solar cells, right? Graphene would make solar panels so much more efficient and feasible!

Absolutely! Energy is not the only basic need that graphene can make more accessible to everyone.

[expand title=”Graphene can also be used to make THE best water filter in the world.”]Get this – graphene by itself is hydrophobic, meaning it repels water, but capillaries of graphene oxide actually suck in water! Graphene oxide is a derivative of graphene that’s much easier and cheaper to make. A sheet of graphene oxide is capable of filtering out the finest salts in seawater, gases such as helium, and frankly everything else. Lockheed Martin has actually been building and trying to patent their version of this graphene water filter, which they call Perforene. Apparently it is expected to be available in 2015.[/expand]

 

Credit: Lockheed Martin
Credit: Lockheed Martin

Wow amazing. I can’t wait until graphene is a regular player in the tech market.

Well it’s still to be seen whether graphene is commercially viable. The problem?

[expand title=”Graphene is a non-renewable resource that is incredibly difficult to isolate.”]Mechanically, it can be isolated from graphite using scotch tape and a lot of patience. You can also attach a graphite crystal to the tip of an atomic force microscope and drag it along a surface. In both cases, it is extremely difficult to get flakes of graphene that are less than 10 layers thick. It is also difficult to piece them together uniformly into something you can actually use.

It can be made chemically as well. If you melt silicon from silicon carbide by heating it to 1300 Celsius, you get a thin layer of carbon. Problem is, the resulting carbon layer is very impure and tainted with other atoms. The valuable properties of graphene are dependent on its purity, so you really don’t want to compromise its quality.[/expand]

[expand title=”Another popular method is chemical vapor deposition, CVD for short.”]During CVD, carrier gas molecules are combined in a heated reaction chamber that contains a substrate. When the gases come into contact with the substrate, the reaction deposits a material film on the substrate surface. Although the process is lengthy (the substrate is coated at mere microns of thickness per hour), the resulting film is very high quality and mostly pure. Unfortunately, the gaseous by-products of the process are VERY toxic, which is definitely environmental risk. Scientists have not been able to find a way to process the gases into a benign form. It is also very difficult to separate the graphene from its substrate and actually use it.[/expand]

I’m sure that researchers will find a viable way to extract graphene easily. It’s only a matter of time.

But the other issue is the fact that graphene is a nonrenewable resource. Graphene comes from graphite, which is a rather plentiful resource at the moment, but it won’t be for long. What happens when the demand for graphene is so high that graphite ends up being a scarcity? The price will inevitably spike. By that time, graphene may be used in almost all electronics that we consume. Those who control the production of graphene products will also control the consumption, development, and availability of any technology that utilizes graphene. Of course, with technologies such as 3D printing we may be able to bypass large manufacturers in the future. I sure hope so!

Hmm I see what you mean. You said that graphene is made purely of carbon atoms. Can’t we just synthesize graphene then?

Maybe. That would definitely be one way to ensure the longevity of graphene on Earth. That kind of synthesizing process must take a lot of energy and other resources though. Like with any natural resource on Earth, we should conserve and recycle as much as possible. Modern innovation isn’t about exploiting the Earth’s gifts; it’s about using them in the most efficient way possible with as little waste as possible.

Amen to that.

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