Probing the properties of individual nanoscale objects

Carbon nanotubes, quantum dots and other nanoscale objects are so small that it has previously been impossible to study them individually with terahertz radiation.

Instead, researchers have had to study the nanoscale objects in bulk, according to Prof John Cunningham of Leeds University, who led the research.

But if we are to continue to produce smaller and smaller electronic systems, we will need to understand exactly how they work at the nanoscale, where devices can exhibit different properties from largescale devices.

Now the team, with funding from the EPSRC and Leeds University, have developed a technique in which a nanostructure is used to filter the terahertz waves. By passing the terahertz radiation through a tiny region of semiconductor, with gates on its surface, the researchers are able to control the spectrum of the radiation passing through it.

The device consists of a nanostructure embedded within a microscopic waveguide, where it is split into three cavities.

A voltage is applied to the device, which controls how electrons inside the cavities oscillate. This in turn determines the frequency of electromagnetic radiation that each cavity can transmit.

“We can control the properties of the terahertz radiation moving through the object using the gate,” said Cunningham.

Tuning the radiation in this way allows the waves to be shaped or modified, meaning information can be encoded in the signal, he said. “When the terahertz radiation is passed down the waveguide, it interacts with the nanoscale object.”

This allows the researchers to study even single nanoscale objects. “The technique in principle allows you to measure almost any nanoscale electronic object,” said Cunningham.

It could be used to measure the properties of graphene, for example, or ultrafast transistors built from nanostructures, and experiments on both of these objects are already underway.

The research has been published in the journal Scientific Reports.