Graphene is a one atom thick superlative material. It is stronger than steel and diamond, more conductive than copper, thinner than one millionth of a paper’s thickness and almost invisible. Graphene is touted to be the next big thing across many industries. For example, with regards to the semiconductor industry it has been called the next silicon. It has many disruptive theorized applications across other verticals like water purification technology, touch-screen displays, thermal management systems, solar cells, inks, paints and coatings etc.
But we have been hearing these claims for quite a while now without really witnessing any commercially viable, real world breakthroughs except for a few sporadic mentions scattered across the internet. Let us go through what it is and then discuss the reasons behind why it hasn’t seen the market penetration that it was expected to.
Graphene’s structure and how it was made?
Carbon is a fairly common element. It has a few allotropes; diamond, graphite, buckminsterfullerene and carbon nanotubes. The structural variation among these allotropes is responsible for the difference in their properties.
Diamond has a single carbon atom connected to four other carbon atoms, resulting in a tetrahedral shape. Hence it is very strong. Also, without the presence of any free electrons it is an electrical insulator.
Graphite has each of its carbons connected to three other carbons. Graphene, our wonder material, is obtained from graphite. It is comparatively easy to obtain graphene in a small quantity than synthesizing large amounts of it. Its structure is just a single layer of graphite. It is basically one atom thick. You can call it a two dimensional element, although technically it is not. But it is as close to 2D as we can get.
In 2004, two scientists at the University of Manchester were trying to get the smallest flake from a graphite block. They noticed that using scotch tape to peel of a layer and then repeating that process on the peeled off layer led to incredibly thin sheets. This playful experiment resulted in the discovery of graphene. Andre Geim and Konstantin Novoselov were awarded the Nobel prize for Physics in 2010.
What makes graphene so awesome?
Graphene is one of the key materials that makes our foray into the field of materials on the nano scale very interesting. It is one of the very few materials that are as close to being two-dimensional as possible. The interesting part is that when we combine two-dimensional materials with other molecules to produce three-dimensional materials, some interesting things begin to happen. Beyond the properties inherent to pure graphene, the new vistas it presents upon further tinkering can result in quite interesting properties.
Let us take a look at some of the most important properties of Graphene and their possible resulting applications.
It is stronger than steel. Columbia University’s mechanical engineering professor James Hone once said it is “so strong it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.”
It is stiffer than diamond because of the perfect crystalline structure and strong internal bonding. It is also the thinnest material in the world – One million times thinner than paper. Better conductor of heat than copper. Also, in spite of being 1 atom thick, graphene is stable even at room temperature. It is also extremely resistant to tearing by stretching. It can be stretched to a quarter of it’s length.
It has a high level of biocompatibility. Add that to its mechanical strength, and it becomes beneficial for composite bio-materials like artificial implants. Add its electrical conductivity to the mix and it can be used for organs that require conductivity, like nerve tissues and spinal elements. Researchers at Michigan Technological University are working on creating 3D printed replacement nerves with graphene as the electrical conductor. Graphene oxide is being looked into as a possible bio-sensing element to detect heart attacks and toxins. It has also been found that graphene oxide could act as an anti-cancer agent that selectively targets cancer stem cells. This could help contain cancer from spreading and also help in tumor shrinkage.
It is a better conductor than silver and copper. It can be used to enhance batteries. It can increase storage capacity of a battery and also decrease the duration of charging. It can be used with other chemicals to enhance the power density of Li-ion batteries and increase charge cycle durability. Graphene can also be used to make super capacitors that store a large amount of energy, charge and discharge quickly and maintain that for more than tens of thousand of charging cycles.
But the most touted application of graphene, which can theoretically alter the world of computing is its ability to be used as a replacement for silicon. Compared to silicon which is the backbone of the semiconductor industry, it is more energy efficient, it can conduct electricity 250 times faster, it is one atom thick and can dissipate heat faster. The only problem currently is that we haven’t been able to find a process turns graphene into a seminconductor.
How can graphene be used in computers and why hasn’t it been, yet?
Graphene has, with its astounding properties, risen as a competitor to silicon. At least in theory. It is theorized that semiconductor manufacturing process with Silicon would reach it’s limit at a transistor size of 5 nm and that would signal the end of Moore’s law, which states that the number of transistors on a single wafer doubles every year. We are currently manufacturing at 12nm.
Companies like Intel, that are working at the cutting edge of semiconductor technology invest a lot of money to reduce the size of transistors and eventually it will come to its limit in the next 10-15 years. When that happens we will be looking at new materials for computing and graphene is a mighty contender to replace silicon. Again, in theory.
The problem right now is that silicon is a semiconductor and pure graphene is a conductor. Meaning that according to the band theory, silicon has a gap between the conduction band and the valence band. Which technically means that it is easy to switch on and off. Which is necessary to produce digital logic.
Graphene, in contrast is a better conductor than metals. So in its crystalline form, graphene can not be used as a semiconductor because it cannot be switched off very easily. But, since it is almost a 2D structure, it is more reactive, and we can dope it to tweak some of its properties.
IBM has made standalone graphene transistors. In 2011, they made a working circuit using graphene transistors on silicon carbide wafers. They have operated this circuit at frequencies up to 100 gigahertz, which is comparable to the highest frequencies attainable with pure silicon transistors. Graphene based components are estimated to reach frequencies of 1000GHz. In 2014, they were able to make a graphene chip with a new manufacturing technique that was compatible with the standard CMOS fabrication method. So we are inching closer to a commercial graphene chip but these are still analog chips. IBM still has not found a way to instill a band gap.
There also exists another form of graphene called bilayered graphene where you can mimic the presence of a band gap, but it’s difficult to fabricate and is slower than silicon.
We will only know with time, if we can successfully figure out a way to use graphene as a commercial substitute for silicon before reaching the 5nm threshold. Also, just last week a team at Berkeley Labs has reportedly made a transistor smaller than 5nm, giving us more time to figure out the band-gap issue with graphene.
Why haven’t we seen graphene in the market yet? In any industry?
Graphene is really hard to synthesize. We have made interesting things out of graphene at the laboratory level but to manufacture something on a large scale, processes that can be automated are required. Also these processes are run on special machinery and we do not have enough data to build those. There are some companies that have started producing niche products based on graphene but it will still take some time and investment for graphene to truly penetrate its possible markets.
Fortunately, a lot of research is still ongoing with major investments from a lot of big players. The Graphene Flagship is Europe’s biggest ever research initiative with a budget of €1 billion. It has been formed with an aim to bring together academic and industrial researchers “to take graphene from the realm of academic laboratories into European society in the space of 10 years” with the purpose of generating economic growth and new jobs.
While the scientific community is still looking for ways to find the right methods to easily synthesize graphene in terms of purity of the final material and economical processing, there has been an improvement over the last few years with regards to what we know and an increment in the number of methods to extract graphene.
Here are some products that are made using graphene and are available for commercial sale.
Despite it’s integration with the commercial market, graphene is still feared to be emerging too late for many of it’s possible applications. We are getting to a point where we can manufacture graphene on a large scale but it is still too expensive for practical applications. For example, activated carbon and graphite are already being used in cars and they are relatively inexpensive. Personally, I believe that graphene will re-capture everyone’s attention once the issue of introducing a band gap is solved. Until then we will be spectators of the slow growth of a massively superlative material.