by Will Soutter
A study at the University of Wisconsin-Milwaukee has uncovered more valuable information about the electrical properties of graphene, and how they change when the "wonder-material" is brought into contact with semiconducting materials.
Graphene is one of the most exciting materials ever discovered - made of a single sheet of carbon atoms, it is immensely strong, and conducts heat and electricity incredibly well.
However, the ultimate use of graphene - to create a transistor that could be used in computer chips - remains out of practical reach.
The most fundamental property of a transistor is its ability to be switched off, and graphene's superb conductivity makes this very difficult to achieve.
Researchers all over the world have been hunting for a scalable method to create a switchable graphene device. This new UWM study adds another possible method to achieve this, and has discovered some important properties of the way electrons behave in graphene as well, which will impact future research.
The UWM team deposited a layer of graphene onto a semiconducting silicon carbide substrate, and found that the interface between the two materials formed a Schottky barrier - a potential energy barrier prevents electrons from being conducted, unless an electrical field is applied to help them overcome it.
The researchers realized that these properties create a promising prospect for creating graphene-based electronic components, by allowing the conductivity of the material to be switched on and off.
UWM doctoral student Shivani Rajput, first author on the paper, shows a reconstructed image of graphene with the ripples clearly visible. Two postdoctoral researchers also worked on the project: Yaoyi Li (left) and Mingxing Chen. Image credit: Troye Fox/University of Wisconsin-Milwaukee
The study also found that the height of the Schottky barrier - and therefore the amount of energy needed to "turn on" the graphene - varies with the separation between the graphene sheet and its semiconductor substrate.
Unfortunately, it is well known that graphene sheets tend to "ripple", rather than lying totally flat. This phenomenon means that the Shottky barrier varies in height across the sheet, rather than remaining uniform, which could prove an impediment to designing graphene-based electronic devices.
Michael Weinert, professor of physics at UWN, commented:
"This is a cautionary tale - if you're going to use graphene for electronics, you will encounter this phenomenon that you will have to engineer around."