Shou-En Zhu [ TEDxDelft ] Nano materials and nanostructures exist everywhere in our natural world. Take a look at the wing of a dragonfly. If we zoom in 100,000 times and look at the transparent membrane, we can see the nanostructures which are invisible to the naked eye.
Graphene is transparent.
This is a molecular model of graphene. To make it visible, it has been magnified over 280 million times. Graphene consists of only one single element: carbon. It’s so simple. However, graphene has lots of special properties. It’s the thinnest of all materials, only one atom thick.
It’s the strongest material ever measured.
The in-plane carbon bond is stronger than the tetrahedral carbon bond in a diamond. At the same time, it is flexible and stretchable. We can fully bend graphene and stretch it up to 20%. It has the highest thermal conductivity of all materials, including copper. It can withstand the highest current density at room temperature, it has the highest intrinsic mobility, which is 100 times more than that in silicon, it is the most impermeable material, even the smallest helium atoms cannot squeeze through.
Graphene will change the world.
There will be, for sure, a completely different intelligent society in 10 to 20 years. Let’s spend some time thinking about the future.
Imagine if all the transparent glass windows could constantly generate electricity under sunlight and supply the energy for all the buildings.
Imagine if all the electrical vehicles and electronic devices could be charged within 10 minutes and last for a few days.
Imagine if the sea water could be desalinated with a pocket device so it turns into drinking water everywhere.
Imagine if smart electronic devices could be integrated into our clothes, and some of them even implanted under our skins.
Imagine if light weight composite materials could be stronger than ever so it turns into the main structural material for the body of ships, vehicles, and airplanes.
Imagine if electronic chips could do computations a thousand time faster with plasmons instead of electrons.
All these dreams will one day become real and revolutionize our society, and I believe it will happen in our lifetime, thanks to the exploration of this new nanomaterial.
But how to produce graphene is a serious problem. Although graphene was known to exist in graphite, most scientists believed that it would be impossible to isolate a stable graphene. In the 1930s, Landau and Peierls predicted that 2D crystals would be thermodynamically unstable and thus could not exist. 30 years later, Mermin further presented the analytical results to fuller validate this hypothesis.
Until 2004, when two scientists, Andre Geim and Kostya Novoselov, used scotch tape to produce graphene.
By putting tape on graphite flakes multiple times, each time peeling off a layer, the graphite will become thinner and thinner. Although most of the area consists of thin graphite flakes, a few small pieces of a single layer graphene were finally isolated. Since then, thousands of scientists started to do research based on this tiny piece of single layer graphene using the scotch tape method. Can you believe that the Nobel Physics Prize in 2010 was awarded to these two scientists based on their groundbreaking scotch tape experiment?
Obviously, it is not a practical way to mass produce graphene and make useful products.
Nowadays, tons of small flakes of multilayer graphene, strictly speaking, thin graphite flakes, can be produced using the chemical exfoliation method. It can be mixed into tennis racquets or bicycle tires to enhance the strength and lower the composite weight. However, the material produced is black, which is inconsistent with the transparent property of graphene. If the color is black, it means the flakes are too thick.
At the same time, the flakes are too small to do the cool things with that I was talking about.
As an experimental researcher working on graphene, I need lots of large area single layer graphene for my experiments. However, I couldn’t find any research group which could supply me with high quality graphene in the Netherlands at that moment. I traveled between Leiden University and Delft University every day, and tried to figure out how I could grow large size graphene samples. With the existing facilities available, I couldn’t isolate high quality graphene, either because the equipment had very rough control of the gas flow, or because the heating area was too small to grow larger size samples of graphene.
Even the power of the heater was not sufficient to reach 1,000 degree Celsius.
Day after day, I woke up at 6 am, and returned home at midnight. I tried all the possibilities that I could think of. However, what I got, was only frustration and reiteration of the problems. I thought: “If I continue in this way, I will never finish my PhD research.”
Four months later, I decided to stop wasting time and make a furnace myself.
Thanks to my supervisor, and the faculty, I received extra budget for the equipment. At the same time, I also won the Young Wild Idea Prize, worth 10,000 EUR, which allowed me to spend the money freely on the material. I still remember that moment on Tuesday, April 17, 2012.
After a whole year of working long days, I started the first testing of my own setup.
The vacuum pump I grabbed from somewhere in the lab was over eight years old and had run for over 29,000 hours. Not only that, but the pump will stop running once the temperature reached over 40 degree Celsius. So I bought a small fan costing 30 EUR, which did a perfectly good job of cooling the pump.
This is the furnace I have built.
I will explain the advantages of this homemade setup. The furnace can heat up the 1 inch quartz tube to over 1,000 degree Celsius with a temperature fluctuation of less than one degree Celsius. There is a transparent bullet proof Lexan cover, which can protect against any possible gas explosion and secure the safety of the researcher. There is a small hand wheel which can remotely control the moving of the furnace to the left and to the right, with a gear and a chain, similar to chain gears on a bicycle. With this design, I was able to heat the sample and cool the sample 10 times faster than any commercial equipment.
The cost of this setup is less than 20,000 EUR, which is over seven times cheaper than any commercially available equipment .
All the components can be optimized and well controlled. It delivers a much better performance. I enjoyed conducting the experiment with my own setup. This is the graphene I have grown. The graphene crystals grow like snow crystals.
Methane gas, which accounts for about 80% of natural gas used for cooking, can decompose to carbon atoms on copper substrate at one 1,000 degrees Celsius in an inert gas environment.
The carbon atoms will attach to each other and form carbon rings with honeycomb structures, such as in graphite. I can use the carbon isotope to mark the growth procedure. Can you imagine, the size of an individual graphene crystal reached over a few millimeter, which is over one million times larger than the size of the carbon atom? Can you believe that this sample was made six months ago, and the single layer graphene can still protect the copper against any oxidation?
The graphene crystals will grow larger and larger, and connect with neighboring graphene crystals, to finally form a continuous film.
Once there is no bare copper, the graphene growth will stop. So in the end, we will have a single layer high quality graphene film. My colleague and I proved for the first time that the quality of this synthetic graphene is as good as the one with the scotch tape method, however, the size is considerably larger.
To mass produce graphene, and reduce the cost dramatically, a bigger and better furnace was designed and built. The furnace has a larger quartz tube, and the furnace will always maintain a constant temperature. Once the graphene growth has finished, the only thing I need to do is to move the furnace completely away from the tube and take out the graphene sample.
Immediately, I can start the second graphene growth cycle.
The efficiency of high quality graphene growth can be improved ten to twentyfold and the energy consumption will become much lower. If we build hundreds of bigger furnaces, the mass production of graphene will become possible soon. There is a layer of graphene on a transparent substrate. I can see you all through it.
But there is something special. It is conductive and flexible.
Now you can imagine all kinds of future applications with this graphene. Currently, the price of this small piece of graphene will be around 1,000 EUR. I believe the price of this graphene will go down to less than 1 EUR within a few years , because the material we use to produce graphene, such as natural gas and copper foil, are widely accessible. All of us will have access to graphene in the near future, and realize this dream.
Remember that I told you we are going to have better world.
Now, I cannot show you the transparent glass windows which could generate electricity, and I cannot show you the electronics in my clothes. But I can show you something you have never seen before.
There is a transparent graphene patterned into wired structures on this transparent polymer wing.
The graphene is so special that once we put a tiny amount of energy, it will shrink. And graphene is so strong that it can lift up this polymer wing, which is a thousand times heavier, and mimic the flapping function of a bio robot.
Look at what I have done and achieved in these few years. With all of you involved in my endeavor to mass produce high quality large scale graphene, I believe we can make our dream come true together.
FEATURED IMAGE CREDIT: Natural England