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Graphene has been fascinating scientists since its birth more than ten years ago. This single-atom-thick carbon material has excellent electronic properties, strength, and ultra-light weight, and its use has also been broadened, but how to implant an energy gap (band gap/semiconductor or insulator valence band to conduction band The bottom end of the energy gap, which creates transistors and other electronic devices, has always kept scientists from working out.
Now, researchers at the Massachusetts Institute of Technology (MIT) have made major breakthroughs in this area and are even expected to change some of the theoretical predictions of graphene physics. They introduced another kind of hexagonal boron nitride with single-atom thickness, properties and graphene-like material, and placed a layer of graphene on it. The resulting mixed material had both the conductive properties of graphene. Finally, it also has the energy gap necessary to build a transistor.
Pablo Jarillo-Herrero, assistant professor of MIT Physics, commented: “By combining the two materials, we obtained a hybrid material with properties different from the two. Graphene is an excellent conductor, and hexagonal boron nitride is a good insulator. Block the flow of electrons. Put them together and we get high quality semiconductors."
But the whole process is obviously not as simple as 1+1=2. Researchers must almost perfectly align the atomic frames of the two materials. Both of them have a hexagonal structure, the size (lattice constant) is almost the same, but the hexagonal boron nitride is 1.8% larger, so from the fine point of view, the two atomic frames can be perfectly spliced ​​together, viewed from a large scale There will still be some variability.
There is no perfect solution to this, and researchers say they can only rely on obtaining angular alignment, but there is always a 1/15 chance of making a mistake.
Ray Ashoori, a professor of MIT Physics, said: "The most amazing thing about the semiconductors we get is that by simply adjusting the angle of one layer of material to the other, we can adjust the properties of the final material to obtain materials with various electronic properties."
Prior to this, it was also made into a semiconductor by cutting the graphene layer into thin strips, but this would greatly weaken its electrical properties. The new method will not suffer such losses. However, the current energy gap is still not practical, and further improvement is needed to become a new material for transistor manufacture.
In addition, the MIT team has discovered an interesting physical phenomenon in the new material: When exposed to a magnetic field, it will exhibit fractal qualities, which is the so-called "Hofstadter Butterfly Spectrum." Ten years ago, the theoretical predictions were once thought impossible.
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