The Story of Graphene and One of the Key Researchers Behind It

The situation is not entirely unproblematic for an accomplished basic researcher like Sergey Kubatkin. Suddenly the world has begun to form great expectations about something that, to his mind, is only one of many attractive paths in the research field.

Recently, Chalmers has famously taken on the role of coordinator for the large EU-funded "research flagship”. And Sergey Kubatkin is recognized as the researcher responsible for putting Chalmers on the graphene research map in the most tangible of ways.
He, however, is reluctant to define himself exclusively as a graphene researcher.
"There are many other areas of research that I work with and am interested in, in addition to the graphene," he emphasizes.

Nor does he hide his slight skepticism of some of the future areas of application envisioned by various enthusiasts. "There's no doubt there is hype surrounding the graphene. There is a strong pressure to find applications," he says, adding with a laugh:
"That's why I'm glad that I am involved in basic research, it gives me more freedom. Because, as a material, graphene presents us physicists with some very interesting questions."
 
His own path to graphene research began, as is so often the case, somewhere else:
"Originally, my group and I studied the ability to exploit quantum phenomena in individual molecules. The idea behind the research is that such molecules can be used in the electronics of the future, instead of silicon as is the custom today," he says.
Attempts to get the molecule to behave like it should were promising, but there was one big problem: The electrical contacts. Even the thinnest metal wire is gigantic in scale compared to a single molecule. This affects function. The challenge is similar to linking two mountains with a grain of sand.
 
"That's when I got the idea that we should try contacts made of graphene instead of metal," he says.
Graphene, only one atom layer thick and an excellent electrical conductor, should in theory be ideal for the purpose. At the time, however, five years ago, it was difficult to get hold of graphene of sufficiently high quality.

It turned out that materials scientists at Linköping University, led by Professor Rositza Yakimova, had come far in their attempts to produce graphene in a new way. The material was grown on a silicon carbide surface by exposing this material to extreme heat of 2000 degrees Celsius. A partnership was initiated: Linköping manufactured, Chalmers tested.
 
"In the beginning it was not real graphene but graphite, because the samples we received consisted of several carbon atom layers. But by 2009 the technology had been refined to the point where virtually flawless graphene could be produced in pieces of about 7 times 7 millimeters.”

But how do you know that it is truly two-dimensional graphene you are dealing with? A material less than one nanometer thick? Well, you can tell by its properties, says Sergey Kubatkin.
"The main feature is that graphene very clearly demonstrates what is known as a quantized Hall effect. This means that the electrical resistance of the material increases by leaps and bounds when you expose it to a strong magnetic field.”
 
This peculiar behavior is in fact something that occurs in all two-dimensional materials.
So what is the practical use of this phenomenon? This is not something that basic researchers usually ponder. But Sergey Kubatkin, in this area for the first time, is in the midst of an applied research project. Something that may indeed result in a product.

The project is about metrology, or the science of measurement; more specifically, the calibration of measuring instruments. For a long time in metrology, there has been an attempt to get away from physical norms, such as the well-known Swedish national meter and Swedish national kilo. It would be better if calibration could be based on an immutable, natural constant. The national meter, for example, has now been replaced by a laser, while a kilo remains the same physical clump of matter as before.

When it comes to defining electrical resistance, the authorities responsible for measurement in different countries have traditionally relied on "national coils" with a very high and well-defined resistance.
"But the material ages, and resistance in the coils changes slightly with time. In practice, different countries end up with differing standards for resistance, which must be compensated for. It gets complicated in the long run," says Sergey Kubatkin ,.

"In the end of 80’s 'the national coils' were replaced by Quantum Hall Effect resistance standards based on artificially created two dimensional electron gas in semiconductors. Klaus von Klitzing got a Nobel Prize for that. However those semiconducting standards require extremely demanding conditions, so they could not be used outside metrology labs - in industry in academia. Graphene, truly two-dimensional material is special, because the quantized Hall effect occurs even at room temperature. "

His research has now opened the possibility of exploiting the quantum resistance of graphene for reference.
"Our group, along with a few other European research groups, has shown that graphene actually has the potential to be fundamentally a much better yardstick. That's why we are now involved in a joint project with the European measurement authorities. The advantage of graphene is not only greater accuracy, but also the portability of calibration equipment."
 
A natural constant in a portfolio, then?
"Something like that," says Sergey Kubatkin, adding: "It's actually a really great feeling that something that started as curiosity already seems to be of practical use - even within such a small niche as metrology."

Within the large flagship initiative, Sergey Kubatkin is responsible for a sub-project intended to investigate the smallest-sized working graphene device that can physically be produced.
"This of course relates to my research into individual molecules. That's probably why I got the job," he says with a laugh.
 
Sergey Kubatkin became interested in "the physics of small things" as a doctoral student at the Institute for Physical Problems in Moscow, a distinguished research institution that is also called the Kapitsa Institute, after its founder. Pyotr Kapitsa won the Nobel Prize in Physics in 1978 for his discovery of superfluidity of helium.
“When I was a student this was one of the best places in the world for those who wanted to learn physics. Moreover, the scientific community at the institute was something of a haven for someone like me, who did not want to become embroiled in communist party controlled politics," says Sergey Kubatkin. "Research became a way of life - and survival."

But a gradual decrease in funding forced Sergey to conclude that the agency lacked the resources to acquire equipment for the type of experiment he wanted to conduct.
And so, after the Soviet Union collapsed in the early 1990s, he began to look for a position abroad. He had been in contact with Chalmers researchers during his doctoral studies and realized that it was a "good place".
"So I was very happy in 1993, when an invitation turned up to visit for a few months."
There would be more visits to Gothenburg over the next few years, and in 1998 he took the opportunity to move here permanently.
 
During the fifteen years that have passed since then, Sergey has helped to establish the three key factors which according to him are necessary to a good quantum physics experiment: a good fabrication lab (MC2's high-class clean room), a good measurement lab and a good research team.
"It takes time to get it all in place, but now I have just the right conditions here at Chalmers," he says.

That's why he has been all but immune to the siren calls from other universities that have reached out to him in recent years: from Denmark, Great Britain and Russia, among others.
"Here at MC2 we have a large group of researchers with interests close to my own, I appreciate that very much. We are a real quantum community."
Part of the community has grown particularly close: Sergey Kubatkin is married to one of his research colleagues at MC2, professor Floriana Lombardi.
"But we don't work in the same group. That's probably what protects our working life and private life from too much collision," says Sergey. He does not deny, however, that a certain amount of conversation about quantum mechanics goes on at the dinner table.
"It is inevitable, and we quickly realized that it would be so.”

One consequence of the growing body of graphene research in recent years is the labs at MC2 beginning to become crowded.  For Sergey Kubatkin, that means stopping his own experimental work.
"It's sad, because I really enjoy working with my own hands. Making your own experiments was what attracted me to research. Now, my group has grown in size and my time is spent following my students' work, devising experiments, discussing and writing."
 
Two of his students are directly involved in graphene-related research, while the rest of the group is engaged in other forms of quantum physics engineering.
Much of this research focuses on the future of electronics, since the traditional silicon-based semiconductor technology is now approaching the limit of what is physically possible in terms of size reduction and speed.
Many hope that graphene, perhaps in combination with other two-dimensional materials, will one day take the place currently held by silicon.
 
According to Sergey Kubatkin, this represents a major challenge.
"Graphene is not a semiconductor, but rather a very good electrical conductor. There is no energy gap. That's why many researchers are now attempting to create such a gap artificially, for example by making the graphene component very small. For my part, I doubt this is a good idea. It feels as if we are trying to weigh down a new material with the baggage of an old way of thinking The solution likely lies elsewhere."

But to know for sure, you have to try. And that's what Sergey Kubatkin intends to do:
"After all, the idea exists and we have to reflect on it. Even though I might not truly believe in graphene as a transistor, there are interesting insights in this way of thinking. We will be experimenting with the concept."
The result, according to Sergey Kubatkin, may very well be something that no one expected.
"That's often how the scientific process works: There is a problem you are trying to solve, and while engaged with it, you find the solution to a different problem entirely." -- by Björn Forsman, © Chalmers