The instruments used to measure temperature in the macroscopic world, such as mercury thermometers and metallic thermocouples, do not work at the nanoscale, which is why researchers have made thermometers in which gallium rises and falls inside carbon nanotubes. However, these devices are complex because they rely on transmission electron microscopy (TEM) to calibrate how the volume of the gallium changes with temperature.

Now Zongwen Liu and colleagues1 at the University of Sydney in Australia and the National Institute for Materials Science in Japan have developed a much simpler variant of this device that can be used to make precise measurements of temperature up to 250 °C.

The nanothermometers were heated in air and maintained at the appropriate temperature for long enough to allow oxidation of the gallium near the tip of the nanotube. On cooling, a ring remained on the inside of the nanotube where the gallium had oxidized, and this was used as a reference for measuring temperature. Liu and colleagues report that the nanothermometer is accurate to 5%, compared with accuracies of between 5 and 10% for the TEM-based devices. Nanotube-based thermometers could have applications in microelectronics and fuel-cell research.