Seeing is believing

Diamond quantum sensor reveals how current flows in 2D materials

Researchers at the University of Melbourne are the first in the world to image how electrons move in two-dimensional graphene, a boost to the development of next-generation electronics.

Capable of imaging the behaviour of moving electrons in structures only one atom in thickness, the new technique overcomes significant limitations with existing methods for understanding electric currents in devices based on ultra-thin materials.

Next-generation biosensors and electronic devices based on ultra-thin materials will be especially vulnerable to minute cracks and defects that disrupt current flow, said Professor Lloyd Hollenberg, Deputy Director of the Centre for Quantum Computation and Communication Technology (CQC2T) and Thomas Baker Chair at the University of Melbourne.

A team led by ARC Laureate Fellow Hollenberg involving researchers from CQC2T and the Centre for Neural Engineering used a special quantum probe based on an atomic-sized ‘colour centre’ found only in diamonds to image the flow of electric currents in graphene. The technique could be used to understand electron behaviour in a variety of new technologies.

The ability to see how electric currents are affected by these imperfections will allow researchers to improve the reliability and performance of existing and emerging technologies. We are very excited by this result, which enables us to reveal the microscopic behaviour of current in graphene and other 2D materials, he said.

Artist’s impression of a diamond quantum sensor. The blue threads represent the path of the electrons through graphene (a single layer of carbon atoms). Image credit: David Broadway

In addition to understanding and improving nanoelectronics devices the technique could be used with 2D materials to develop next generation bio-chemical sensors electronics, energy storage (batteries) and flexible displays.

The technique is powerful yet relatively simple to implement, which means it could be adopted by researchers and engineers from a wide range of disciplines, said lead author and ARC DECRA Fellow Dr Jean-Philippe Tetienne from the University of Melbourne.

Our method is to shine a green laser on the diamond, and see red light arising from the colour centre’s response to a magnetic field, by analysing the intensity of the red light, we determine the magnetic field created by the electric current and are able to image it, and literally see the effect of material imperfections he said.

The work was a collaboration between diamond-based quantum sensing and graphene researchers. Their complementary expertise was crucial to overcoming technical issues with combining diamond and graphene.

No one has been able to see what is happening with electric currents in graphene before, said Nikolai Dontschuk, a graphene researcher at the University of Melbourne School of Physics.

The ability to image current in this way is game changing for graphene based bio-sensors, explains Dr David Simpson laboratory co-head of the Sensors and Imaging theme of Centre for Neural Engineering. 2D materials such as graphene are showing enormous promise for label free biomolecular detection due to their high sensitivity and specificity. To date, electrical transport measurements are used to readout bulk changes in the current flow. Being able to image the current flow may allow for high resolution site specific biomolecular sensing, adding a new dimension to these types of sensors. he said.

The current-imaging results were recently published in the prestigious Science Advances journal1 and are the culmination of a year’s work. The research is supported with funding from the Australian Research Council through the Centre of Excellence and Laureate Fellowship programs and through the support of the Centre for Neural Engineering.

References

  1. Tetienne, J.-P.; Dontschuk, N.; Broadway, D. A.; Stacey, A.; Simpson, D. A.; Hollenberg, L. C. L., Quantum imaging of current flow in graphene. Science Advances 2017, 3 (4).