Taking the temperature of nanoscale objects

Scientists at the University of California, Irvine have discovered a one-dimensional nanoscale material whose colour changes with the temperature, enabling them to make very small and sensitive thermometers. The team’s results have been published in the journal Advanced Materials.

UC Irvine Professor Maxx Arguilla, whose research group led the study, likened the thermometers to “nanoscale mood rings”, referring to the jewellery that changes colour depending on the wearer’s body temperature. But instead of simply taking a qualitative temperature reading, the changes in the colour of these materials “can be calibrated and used to optically take temperature readings at the nanoscale”, Arguilla said.

The breakthrough happened when the group grew crystals in their lab that, at nanometre-length scales, resemble helical ‘slinkies’. They grew the crystals at first so they could subject them to heat stress to see at what temperatures the crystals disintegrate.

Postdoctoral scholar Dmitri Cordova and undergraduate researcher Leo Cheng noticed that the colours of the crystals systematically shifted from yellow to orange, depending on the temperature. The team then took precise measurements of the temperature range the colours corresponded with, and they found that light yellow colours corresponded to temperatures around -190°C, while red-orange colours corresponded to temperatures around 200°C.

To retrieve nanoscale samples of the material, the researchers stuck a piece of adhesive tape to bulk-scale crystals, peeled it back and transferred nanoscale samples stuck to the tape onto transparent substrates. Arguilla explained, “We can peel off these structures, and we can use them as nanoscale thermometers that can be transferred, reconfigured and coupled with other materials or surfaces.”

Arguilla said the discovery is the first step toward discovering new classes of materials to take temperature readings at nanometre scales. The need to measure temperature at these scales is important, he said, because a lot of biological and industrial processes depend on tracking minute changes in temperature. “We may now have thermometers that we could try poking into the cells,” he added.

Cordova said the optical thermometers can also potentially measure the temperatures and assess the efficiencies of micro- and nano-electronics, including circuits and data storage devices. Industries already have optical thermometers they use when fabricating computer components, but the team’s new material is “at least an order of magnitude more sensitive”, according to Cordova.

Next, the lab plans to test other nanoscale materials to see if they can develop thermometers that can measure a wider range of temperatures. According to Arguilla, “We’re now trying to hack the materials design rules to make even more sensitive materials. We’re trying to open the toolbox for optical thermometry from the bulk scale down to the nanoscale.”

Image caption: With the help of a microscope, Dmitri Cordova inspects a sample of the crystal that the lab of Professor Maxx Arguilla used to discover the new nanoscale thermometers. Image credit: Lucas Van Wyk Joel.