Precision 2D patterns could lead to next-generation electronics

Researchers at the Technical University of Denmark (DTU) have taken the art of patterning nanomaterials to the next level. Such precise patterning of two-dimensional (2D) materials offers a novel route to next-generation computation and storage, which can deliver better performance and much lower power consumption than today's technologies. The researchers report their advance in a paper in ACS Applied Materials & Interfaces.

One of the most significant recent discoveries within physics and material technology is 2D materials such as graphene. Graphene is stronger, smoother, lighter, and better at conducting heat and electricity than any other known material. But perhaps the most unique feature of 2D materials is their programmability. The properties of these materials can be dramatically changed by creating delicate patterns in them.

For more than a decade, scientists at DTU have worked on improving the state-of-the-art in patterning 2D materials, using sophisticated lithography machines in the 1500m² cleanroom facility. Their work is based in DTU's Center for Nanostructured Graphene, supported by the Danish National Research Foundation and a part of The Graphene Flagship.

The electron beam lithography system in DTU Nanolab can write features down to 10nm. Computer calculations can predict exactly what shape and size of patterns are required to create new types of electronics in graphene. These electronics exploit the charge of the electron and quantum properties such as spin or valley degrees of freedom, leading to high-speed calculations with far less power consumption. Unfortunately, the calculations ask for a higher resolution than even the best lithography systems can deliver – atomic resolution.

"If we really want to unlock the treasure chest for future quantum electronics, we need to go below 10nm and approach the atomic scale," says Peter Bøggild, professor and group leader at DTU Physics. And that is exactly what Bøggild and his group have now done.

"We showed in 2019 that circular holes placed with just 12nm spacing turn the semimetallic graphene into a semiconductor. Now we know how to create circular holes and other shapes such as triangles with nanometer sharp corners. Such patterns can sort electrons based on their spin and create essential components for spintronics or valleytronics. The technique also works on other 2D materials. With these super-small structures, we may create very compact and electrically tunable metalenses to be used in high-speed communication and biotechnology."

The research was led by postdoc Lene Gammelgaard, who has played a vital role in the experimental exploration of 2D materials at DTU.

"The trick is to place the nanomaterial hexagonal boron nitride on top of the material you want to pattern," explains Gammelgaard. "Then you drill holes with a particular etching recipe.

"The etching process we developed over the past years can downsize patterns below our electron beam lithography systems' otherwise unbreakable limit of approximately 10nm. Suppose we make a circular hole with a diameter of 20nm; the hole in the graphene can then be downsized to 10nm. While if we make a triangular hole, with the round holes coming from the lithography system, the downsizing will make a smaller triangle with self-sharpened corners. Usually, patterns get more imperfect when you make them smaller. This is the opposite, and this allows us to recreate the structures the theoretical predictions tell us are optimal."

The process could be used to produce flat electronic meta-lenses, which are a kind of super-compact optical lens that can be controlled electrically at very high frequencies. According to Gammelgaard, these meta-lenses can become essential components for the communication technology and biotechnology of the future.

However, the mechanism responsible for fabricating the 'super-resolution' structures is still not well understood. "We have several possible explanations for this unexpected etching behavior, but there is still much we don't understand," says Dorte Danielsen, a student in Bøggild's group. "Still, it is an exciting and highly useful technique for us. At the same time, it is good news for the thousands of researchers around the world pushing the limits for 2D nanoelectronics and nanophotonics."

This story is adapted from material from the Technical University of Denmark, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.