Our Changing World: Using light to study materials

There's a scene in the 2009 science fiction movie Knowing where Nicolas Cage has a revelation.

He walks purposefully past a mountainous piece of stainless-steel equipment, up some stairs with an impressive overview of a machinery-filled warehouse, and into an office, typing frantically to bring up the data that shows that the end of the world is nigh.

Sometimes it's aliens, sometimes it's an asteroid - this time it's a solar flare from our sun that's going to fry our ozone layer.

It's some good old-fashioned sci fi, and as a backdrop, the Australian Synchrotron in Melbourne is pretty ideal.

Producing light a million times brighter than the sun

The Australian Synchrotron was designed and built with one thing in mind - to produce light for use in science. Electrons whizz around stainless steel vacuum tubes and are manipulated by magnets to produce light.

The resulting light spans from high energy gamma rays through x-ray, ultraviolet, visible, down to infrared light. Different types, or frequencies, of light are collected and focused into what are known as 'beamlines' - areas in the synchrotron where researchers come to shine light on their samples.

The Australian Synchrotron opened in July 2007 with 10 operational beamlines. Now it has 14, with plans in the works to open four more. Aotearoa has been a financial contributor from the very start, buying in to allow New Zealand researchers access to the facility.

Many of these beamlines use x-ray light - for investigating the structure of a sample, figuring out the elements inside it or taking really detailed pictures.

But there's one beamline being used by New Zealand scientists that instead uses part of the infrared light spectrum - the terahertz beamline.

The terahertz 'gap'

Terahertz sits between infrared light and microwaves on the light spectrum.

It's sometimes been referred to as the 'terahertz gap' between electronics and optics. Lower frequency light (microwaves and beyond) is used for wireless telecommunication - 5G for your mobile phone, TV and radio broadcast, satellite dishes, and so on. Higher frequency light (the other end of infrared, and visible light) is used for lasers, fibre-optic data transmission and data storage.

But in the middle is the terahertz technology gap, because until relatively recently it was very difficult to make and detect terahertz light.

Enter light sources such as the synchrotron.

The things that terahertz can do

"Terahertz radiation is all around us," said physics master's student Kane Hill. "Anything that has warmth to it will be emitting terahertz radiation - we emit terahertz radiation all the time."

Kane is completing his master's at the University of Auckland and used terahertz radiation during his research project. He says there's a lot of chatter about the potential of terahertz in the wireless telecommunications space. "If we wanted to move to 6G, we'd have to develop technologies that work in a terahertz space," he said.

However, to do that you need to be able to test how new materials and technologies respond to terahertz light.

"At different frequency ranges, materials can behave differently and so we can have effects we're not use to dealing with at lower frequencies or at higher frequencies," said Kane.

And while terahertz light is all around us, to use it in research you want high-powered, structured beams of light, coupled with super sensitive detectors.

Which is why Kane has travelled to the Australian Synchrotron with his University of Auckland colleague Dr Freddy Lyzwa and Victoria University of Wellington PhD candidate Kiri Van Koughnet.

Advanced materials for advanced computing

Kiri has been making rare earth nitride thin films at the Robinson Research Institute. These materials are exciting to scientists because they combine two helpful properties - ferromagnetism and semi-conductivity.

This combination might lead the way to developing more efficient and powerful computer memory storage to replace RAM (the current temporary computer memory storage system).

Freddy is an expert at using spectroscopy to investigate materials, and along with Kiri's thin films, they have brought two other quantum materials to investigate at the terahertz beamline. These materials have shown effects that they can't yet explain, but they are hoping that shining the terahertz light on them and analysing how much the material absorbs will help their understanding.

In particular, the frequency of the light at this terahertz beamline is often used by researchers to learn more about the different vibrational modes of their samples.

Atoms and molecules are always moving around across three dimensions, and then when you have molecules repeating and linked up in a crystal structure, you can get different vibrations happening across the whole structure.

By investigating these vibrational modes across a big temperature difference (20°C to -270°C), Freddy, Kiri and Kane are hoping to learn more about these materials and their potential usefulness in the next generation of computing technology.

Late nights and MOFs

While at the synchrotron, the visiting researchers, or 'users', stay at the onsite guesthouse. It's about a two-minute walk to the synchrotron building, and as in the tearoom in the synchrotron itself, the coffee is abundant and free.

Handy, says PhD researcher Nicholas (Nick) Page, because his 'beamtime' - that is, the allocated time a researcher has with a specific beamline to get their work done - runs across three full 24-hour days.

Nick studies metal organic frameworks, or MOFs. Made up of metal ions and carbon-containing linker molecules, scientists are interested in them because of their ability to capture and store different gases such as hydrogen, nitrogen and carbon dioxide.

Nick is here to test some MOFs he made at the University of Otago, where he is based. This trip to Australia has a couple of stops for him - one at the terahertz beamline to investigate the vibrational patterns and shifts of some of his MOFs, a trip to a different beamline (x-ray powder diffraction) to look at the structure of some others, and then finally he will head to Sydney to his collaborator's lab, to investigate their gas-absorbing capacities.

Now in his third year, this is an important last trip to the synchrotron before the business of putting it all together. "This is basically my last huzzah for results before knuckling down and sort of getting everything all written up," he said.