A particular ‘sandwich’ of graphene and boron nitride could lead to the next generation of microelectronics
(Nanowerk News) Moiré pattern occurs everywhere. They are made by layering two similar but not identical geometric designs. A common example is the pattern that sometimes appears when looking at a chain link fence through a second chain link fence.
For more than 10 years, scientists have been experimenting with the moiré pattern that occurs when a sheet of graphene is placed between two sheets of boron nitride. The resulting moiré patterns have demonstrated tantalizing effects that can greatly enhance the semiconductor chips used to power everything from computers to cars.
A new study led by University at Buffalo researchers, and published in Nature Communications (“Heat carrier and hot phonon signatures in the metallic state and re-entrant semiconductors of Moiré slit graphene”), indicating that graphene can fulfill its promise in this context.
“Our recent work shows that this particular sandwich of graphene and boron nitride results in properties suitable for use in new technological applications,” said Jonathan Bird, PhD, professor and chair of the Department of Electrical Engineering at UB. This research was partially funded by the US Department of Energy and a MURI grant from the Air Force Office of Scientific Research.
Graphene is made of carbon, like charcoal and diamond. What sets graphene apart is the way the carbon atoms are held together: they are linked in a hexagonal or honeycomb pattern. The resulting material is the thinnest material ever, so thin that scientists call it two-dimensional.
Left alone, graphene conducts electricity very well – in fact it is too good to be useful in microelectronics technology. But sandwiching graphene between two layers of boron nitride, which also has a hexagonal pattern, results in a moiré pattern. The presence of this pattern is accompanied by a dramatic change in graphene’s properties, essentially transforming what would normally be a conducting material into one with (semiconductor-like) properties that are more usable in advanced microelectronics.
This research establishes how moiré patterns in graphene can be adapted for use in technological applications such as new types of communication devices, lasers and light-emitting diodes. “Our work demonstrates the viability of this approach, demonstrating that the graphene/boron nitride sandwich we studied does have the beneficial properties needed for microelectronics,” said Bird.
The semiconductor chips in question are essential not only in smartphones and medical devices, but also in smart home gadgets such as dishwashers, vacuum cleaners and home security systems. “Modern technologies rely on semiconductor chips that form the heart of their systems and control their operations,” said Bird. “When you speak into your cell phone, it’s a chip that converts your voice into an electronic signal and sends it to the tower.”
The graphene/boron-nitride heterostructure appears to have properties suitable for engineering. Developing future technologies based on these materials may depend on discovering and exploiting properties that enable greater speed and functionality. Bird notes that there’s usually a lag between discovery, excitement about discovery, and realizing the promise of discovery. Graphene – so common that it appears in any note written in pencil – was only discovered in 2004.
Bird earned a PhD in physics, but he was drawn to electrical engineering because it allowed him to explore quantum physics through research on semiconductors. Quantum physics – “a magical kind of physics that occurs at the atomic scale,” he explains – can be observed through experiments using technology that explore matter and processes at the atomic level.
“We can get a system to respond to the actions we take, and that response reflects the details of the atomic and quantum properties of the system,” he says. Graphene caught his attention because it appeared to be a way to study quantum effects by working with semiconductors. At UB, he founded a laboratory called NoMaD, where he, his colleagues, and students studied “quantum phenomena that occur at the nanoscale”. Graduates have gone on to careers at Intel and IBM and other universities.
In this research, Bird and his team explored the properties of graphene to what extent must be achieved to create a new technology. The semiconductor chip industry is a massive industry that is constantly evolving, demanding new materials, new ways of using existing materials, and a new workforce capable of developing both.