Low Temperature ‘Mini-lab’ with Closed Cycle Cryostat
About the Equipment:
“It’s just like a fridge,” says Ben. “you press a button and you can go down to 3.5K (-269.5°C)… The other neat thing is that you can hold the temperature steady anywhere in between.” As Ben explains, there are two types of measurements available. “One is temperature dependent resistivity – that’s fantastic for determining whether samples are metallic or semiconducting and learning about the charge transport through them. The other thing is photoconductivity – that’s measuring electrical conductivity when you shine light on something. You can use photoconductivity to probe things like what the band gap is for a semiconductor and what its defect states are.” The facilities are particularly suited to high resistance measurements so are ideal for semiconducting materials.
The in-house cold laboratory is a perfect complement to the group’s new vacuum deposition system in the basement of the same building. They can now grow up to two samples a day and the cold lab provides a quick, easy tool for analysis. “It certainly helps us to grow better materials,” says Ben. “We feed back the results into the next round of samples. It allows for a fast turnover of information.” The ability to hold the temperature steady anywhere between 3.5 K (-269.5°C) and room temperature is also a great advantage – “In our case some of the materials we study become magnetic at about 7 K (-267°C),” Ben explains “and you see anomalies in the resistance and so forth.” Being able to scan smoothly through this transition temperature really helps them to understand these phenomena.
The cold lab is already being used by researchers at GNS, Callaghan Innovation and Victoria and Ben and his team are very happy to train new users. The facility provides constant new data for their extensive network of international collaborators. Having strong connections with overseas labs gives students the opportunity to travel, work in a more international research environment and often improves their career prospects. Bart Ludbrook, who recently finished his Masters in Ben’s group, has just been offered a PhD position at the University of British Columbia in Canada. During his Masters he spent time working with the group’s collaborators in France. “The trip to France was a lot of fun,” Bart says, “which is most important.” He really enjoyed the collaborative approach, getting to use “a range of experimental techniques and learning from others’ expertise. It was doing my Masters that I really realised how much I enjoyed research so I’d say it solidified my resolve to do a PhD.” In the long run Bart sees himself coming back to New Zealand and being part of the MacDiarmid Institute again.
Many of the materials are magnetic, and I am particularly interested in understanding the origins of the magnetic behaviour and how it affects the ability of the materials to conduct electricity.My present focus is on a class of materials called “rare-earth nitrides”, which we prepare in the form of very thin layers grown on top […]