Breakthrough in the search for graphene-based electronics

(Nanowerk News) A team of researchers from Denmark have solved one of the biggest challenges of making effective nano electronics based on graphene. The new results on nanostructured graphene have just been published in Nature Nanotechnology ("Lithographic band structure engineering of graphene").
For 15 years, scientists have tried to exploit the "miracle material" graphene to produce nano-sized electronics. On paper graphene should be great for just that: It is ultra-thin - in fact, only one atom thick and therefore two-dimensional, it is excellent for conducting electrical current, and should be suited for brand new forms of electronics that are faster and more energy efficient.
In addition, graphene consists of carbon atoms – of which we have an unlimited supply.
In theory, graphene can be altered to perform many different tasks within e.g. electronics, photonics or sensors simply by drawing tiny patterns in it, as this fundamentally alters its quantum properties. One “simple” task which has turned out to be surprisingly difficult, is to induce a band gap - which is crucial for making transistors and many other technologically important functions.
However, since graphene is only an atom thick, all the atoms are exposed to the outside world, and the smallest impurities or irregularities in the pattern destroys its properties.
"Graphene is a fantastic material, which I think will play a crucial role in making new nano-sized electronics. The problem is that it is extremely difficult to engineer the electrical properties,” says Peter Bøggild, professor at the DTU Physics, Technical University of Denmark (DTU).
At the Center for Nanostructured Graphene at DTU and Ålborg University, one of the major tasks since its inception in in 2012 has been to adapt and study the electrical properties of graphene, for instance by making a very fine pattern of holes that subtly changes the quantum nature of the electrons, without preventing them from flow freely between the holes.
The team of researchers from DTU and Ålborg experienced the same as many other researchers worldwide: it doesn’t work.
"When you make patterns in a material like graphene, you do so in order to change its properties in a controlled way - to match your design. However, what we have seen throughout the years is that we can make the holes, but not without enough disorder and contamination that it does no longer behave like graphene. It is a bit similar to making a very fine water pipe, which because of coarse manufacturing processes only let the water seep through. On the outside, it looks fine. For electronics, that is obviously disastrous,” says Peter Bøggild.
Now, the team of scientists from DTU and Ålborg University have solved the problem. Two postdocs from DTU Physics, Bjarke Jessen and Lene Gammelgaard, first encapsulated graphene inside another two-dimensional material - hexagonal boron nitride, a non-conductive material that is well-known for its excellent protection of the electronic properties.
Next, they carefully etched an array of ultrasmall and dense holes using a technique called electron beam lithography, through the protective layer of boron nitride. The holes have a diameter of approx. 20 nanometers, with a passage of just 12 nanometers between the edges of the holes. The key thing was to get the roughness of the edges down to 1 nanometer. (1 nanometer = one billionth of a meter). This allows an electrical current 100-1000 times higher to flow through the nanographene, than what is typically the case.
“We have shown that we can control graphene’s band structure and design how it should behave. When we control the band structure, we have access to all of graphene’s properties - and we found to our surprise that some of the most subtle quantum electronic effects survived the dense patterning - that is extremely encouraging. Our work suggests that we can sit in front of the computer and design components and devices - or dream up something entirely new - and then go to the laboratory and realise them in practice,” says Peter Bøggild.
He continues: "Many scientists had long since abandoned making nanolithography in graphene on this scale, and it is quite a pity, since nanostructuring is a crucial tool for exploiting the most exciting features of graphene electronics and photonics. Now we have figured out how it can be done; one could say that the curse is lifted. There are other challenges, but the fact that we can tailor electronic properties of graphene is a big step towards creating new electronics with extremely small dimensions,”says Peter Bøggild.
Source: DTU
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