Scientists make nanothermometer. (Materials Science).

Reading an old-fashioned mercury thermometer sometimes requires some squinting. But that's nothing compared with what's needed to read the newest temperature-measuring device.

Yihua Gao and Yoshio Bando of the National Institute for Materials Science in Tsukuba, Japan, need a powerful electron microscope to read the new thermometer they've created. It works much like the mercury ones, but it would take 100 of the new devices to span the width of a human hair. At this size, the new thermometer can measure temperatures in microscopic environments, says Bando.

The researchers created their thermometer by accident, says Bando. While trying to make nanoscale wires of gallium nitride, he and Gao discovered that they had instead created tiny, hollow cylinders of carbon known as carbon nanotubes. What's more, the nanotubes were filled with the element gallium, which is a liquid over a large temperature range.

In subsequent experiments, the researchers demonstrated that gallium expands in a nanotube at a rate that correlates directly with changes in temperature, Bando and Gao report in the Feb. 7 Nature.

These thermometers are invisible to the naked eye, so it takes an electron microscope to read gallium's position in the tubes, the researchers report. The thermometer works over a range from 50 [degrees] to 500 [degrees] C, they note. --J. G.