Graphene is pure carbon in the form of a very thin, almost transparent sheet, one atom thick. It is has high strength and high efficiency in conducting heat and electricity.
In its current form graphene is not suitable for transistors, which are the foundation of all modern electronics.
For a transistor to be technologically viable, it must be able to ‘switch off’ so that only a small electric current flows through its gate when in standby state. Graphene does not have a band gap so cannot switch off.
The research team, led by Professor Philip Hofmann from Aarhus University in Denmark, used a new material – bilayer graphene – in which two layers of graphene are placed one on top of the other, leaving a small band gap to encourage the transfer of energy between layers.
Using Artemis at STFC’s Central Laser Facility, which is based at the Rutherford Appleton Laboratory in Oxfordshire, the researchers fired ultra-short pump laser pulses at the bilayer graphene sample, boosting electrons into the conduction band.
A second short, extreme ultraviolet, wavelength pulse then ejected electrons from the sample. These were collected and analysed to provide a snapshot of the energies and movement of the electrons.
“We took a series of these measurements, varying the time delay between the infrared laser pump and extreme ultraviolet probe, and sequenced them into a movie,“ said STFC’s Dr Cephise Cacho, one of the research team. “To see how the fast-moving electrons behave, each frame of the movie has to be separated by just a fraction of a billionth of a second.”
There can be imperfections in bilayer graphene as the layers sometimes become misaligned. But the researchers believe that when these imperfections are removed, there is a chance that the switch-off performance of bilayer graphene can be boosted enough to challenge silicon-based devices.
A detailed description of the work is available in the American Physical Society’s Physics Viewpoint.