A high-temperature nanotube thermometer

has been fabricated. Researchers at the National Institute for Materials Science in Tsukuba, Japan, developed a one-step approach to synthesizing magnesium oxide nanotubes filled with gallium. The several-micron-long tubes have square cross sections, tens of nanometers on a side. Often, the gallium filling has a gap in its midsection, as shown below. The gallium expands linearly as it’s heated; the temperature of the thermometer can be read out by measuring changes in the size of the gap using electron microscopy. And because MgO has excellent high-temperature stability, the thermometer can operate from room temperature up to well over 1000°C. Similar carbon-nanotube thermometers—fabricated by the same group last year—degrade above 700°C. The scientists were also able to fill MgO tubes with indium, and thus suggest that their synthesis technique might be used universally to create metal-filled oxide nanotubes. (Y. B. Li et al., Appl. Phys. Lett. 83 , 999, 2003 http://dx.doi.org/10.1063/1.1597422 .)