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2D materials for an energy-hungry world

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2D materials for an energy-hungry world

17 April, 2020

The heat coming off your laptop or mobile phone represents a huge loss of electrical energy. A loss an energy-hungry, climate- challenged world can ill afford.

Since the discovery of graphene in 2004, 2D materials have been a new frontier of physics. They are the thinnest materials possible, just a single layer of atoms in the case of graphene. This reduces the number of ways electrons can move around and allows greater control over them. 

Graphene is 2D carbon, arranged in a hexagonal fashion. This regular and hyper- stable crystal is one of the strongest materials known and a million times more electrically conductive than copper. The almost unbelievable promise for an infinite number of electronic applications was immediately apparent.

Huge losses of electrical energy

Moire patternsOne application relates to the device you are likely reading this on. The heat coming off your laptop or mobile phone represents a huge loss of electrical energy. A loss an energy-hungry, climate- challenged world can ill afford.

Imagine if it could be reduced to near zero? Imagine a new generation of computers that did not require the high energy input and environmental cost of modern supercomputers? Thousands of scientists around the world have the bit between their teeth.

University of Canterbury Physics Professor and MacDiarmid Institute Principal Investigator, Simon Brown, has been experimenting with 2D materials for the last 15 years.

He is particularly interested in what happens when you superimpose one sheet of atoms onto another. The sheets may be composed of the same or different elements. He says that at the macro-human scale, this is like superimposing two sheets of chicken wire or garden mesh.

Professor Brown explains, “Think of the interference patterns created as you rotate one sheet of chicken wire relative to the other, or when you look through one fence or grid at another fence. These are called moiré patterns, and have become a very ‘big deal’ in 2D science because they can be used to engineer a whole range of exotic physical effects.”

“At the atomic level, these interference patterns are responsible for new kinds of superconductors and materials with completely new ‘fractal’ electronic properties. By that I mean that these properties are the same on different size scales.”

Professor Brown’s PhD student, Maxime Le Ster, originally from Brittany, France, working with postdoc Tobias Maerkl, from Germany, have come up with a “simple equation” (it’s actually seven interlinked equations(!) but they are implemented in straightforward matlab code) describing and predicting the wavelength of these interference patterns, that is the distance between the interference fringes, and their orientations. 

Says Professor Brown, “This will allow more systematic prediction and analysis of the physical properties of different elements and combinations. As the angle between the layers changes, the physical properties, like conductivity, can change dramatically.”

New electronic properties

“Our team has been experimenting with layers of bismuth and antimony, which are the world’s worst metals in terms of conductivity, but which have electronic properties such as ‘spin-orbit coupling’ that lead to exotic topological effects. We evaporate the elements to coat a super-thin layer of them onto a graphite substrate.

“Techniques have moved on since Andre Geim and Konstantin Novoselov, who won the 2010 Nobel Prize for Physics, produced the first single-atom carbon layer by using a bit of adhesive tape to lift graphene flakes from graphite.”

The results of Professor Brown and Mr Le Ster’s work are not just pretty pictures, but hope for the future.

The paper on their powerful new equation, including new experimental observations, has just been published in the journal “2D Materials.”1

1*M. Le Ster, T. Maerkl, and S. A. Brown, 'Simple Analytical Model for Moire Patterns', 2D Materials 7, 011005 (2019).