According to a study published in Nature Communications, researchers at the University of Illinois at Urbana-Champaign discovered new methodology in creating nanoscale-sized electromechanical devices.
"In the last five years, there has been a huge gold rush where researchers figured out we could make 2D materials that are naturally only one molecule thick but can have many different electronic properties, and by stacking them on top of each other, we could engineer nearly any electronic device at molecular sizes," says professor of mechanical science and engineering-- Arend van der Zande. "The challenge was, though we could make these structures down to a few molecules thick, we couldn't pattern them.”
An electronic device, regardless of scale, has layers etched away in precision to control current flows.
"This concept underlies many technologies, like integrated circuits. However, the smaller you go, the harder this is to do," said van der Zande. "For example, how do you make electrical contact on molecular layer three and five, but not on layer four at the atomic level?"
The researcher's discovery was by accident when a postdoctoral researcher-- Jangyup Son --in van der Zande's lab—ran experiments on single layers of graphene using Xenon difluoride, XeF2 and decided to add another component-- hexagonal Boron Nitride (hBN), an electrical insulator.
"Jangyup shoved both materials into the etching chamber at the same time, and what he saw was that a single layer of graphene was still there, but a thick piece of hBN was completely etched away by the Xenon difluoride."
The addition of the hBN allowed the researchers to see the potential of graphene in withstanding the etching agent. When graphene is exposed to the etching agent—XeF2—it will retain its molecular structure and mask or protect the layer below it—stopping the etching.
“Nanoelectronic devices made from atomically thin materials on a silicon chip,”- Science Daily
Credit: University of Illinois Department of Materials Science and Engineering
"This discovery allowed us to pattern two-dimensional structures by placing layers of graphene between other materials, such as hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDCs), and black phosphorus (BP), to selectively and precisely etch one layer without etching the layer underneath."
To test the strengths of the new methodology, researchers created a graphene transistor which out-performed other transistors--"making them the best graphene transistors so far demonstrated in the literature."
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"Because these molecules are all surface, if you have it sitting on anything with any disorder at all, it messes up the ability for the electrons to move through the material and thus the electronic performance," said van der Zande. "In order to make the best device possible, you need to encapsulate the graphene molecule in another two-dimensional material such as insulating hBN to keep it super flat and clean."
With the new methodology, the graphene can remain encapsulated and handle the etching needed to make material contact.
Researchers are hopeful to perform more studies to see how scalable their new technique is in previously impossible electronic devices.
