take tiny temperatures
Technology Research News
How do you measure the temperature of something
that's smaller than the tip of a thermometer? Researchers in Japan have
designed a thermometer that is not only smaller than the eye can see,
but is also able to measure temperatures hot enough to soften steel.
The researchers found that a carbon nanotube filled with the liquid metal
gallium can act as a thermometer, said Yoshio Bando, a director at the
Advanced Materials Laboratory of the National Institute for Materials
Science (NIMS) in Japan. Carbon nanotubes are rolled-up sheets of carbon
atoms that are a natural component of soot.
The nanotube thermometer is about 75 nanometers in diameter and 8,000
nanometers long, which is about one and a half times as long as a red
blood cell. A nanometer is a millionth of a millimeter. The nanothermometer
works in a way similar to the familiar clinical version that contains
liquid mercury in a glass tube.
The tiny thermometer, however, measures temperatures that run much hotter
-- between 50 and 500 degrees Celsius, said Bando. The wide range is possible
because gallium remains a liquid over a broad range of temperatures. Gallium
stays liquid for the longest range of any metal, from 30 to 2,403 degrees
Celsius, said Bando.
Existing micron-sized cryogenic thermometers already measure the bottom
temperature range from 0 to 80 degrees Kelvin, or -269 to -193 degrees
In the researchers' thermometer, the gallium expands as the temperature
increases, which makes its level rise within the carbon nanotube. The
level can be seen through the carbon nanotube using a scanning electron
microscope (SEM), which magnifies objects as much as 200,000 times. The
microscope bounces a beam of electrons across a specimen; the SEM picture
shows how those electrons are reflected.
"The height change can be read by comparing heights at different temperatures,
and some materials beside the nanothermometer can be taken as references,
such as the support grid mesh" that holds the device, said Bando.
The nanotube also expands slightly during the process. The researchers
take that into account when reading the temperature. "We know the expansion
coefficient of gallium [and] the relation between temperature and height,"
Gallium is particularly appropriate as a measuring liquid because it does
not stick to the nanotube walls; its surface, or meniscus, is neither
concave nor convex, but remains flat, which makes it easier to get accurate
The nanothermometer could be used to to measure temperature shifts within
very small spaces, said Bando. "This thermometer can be used in in-situ
observation of chemical reaction in a micro-region," he said. It can be
used, for example, to measure laser effects, he said.
Another potential use is to estimate the thermal effect of an electron
beam when a material is observed in a transmission electron microscope
(TEM) or a scanning electron microscope, he said.
The researchers plan next to develop a nanothermometer that measures a
wider temperature range -- from 50 to 1,000 or 1,500 degrees Celsius,
The work is interesting for two reasons, said Deepak Srivastava, a senior
scientist at NASA's Ames Research Center. "First... the thermal expansion
behavior of a nanoscale quantity of liquid gallium remains the same as
a macroscopic quantity," he said. This may mean there are more properties
that remain the same for large and microscopic samples.
Second, it increases by an order of magnitude the temperature range that
can be measured over the standard microscopic cryogenic approaches, Srivastava
The problem with using the thermometer would be in reading it, said Srivastava.
"If [the researchers] or anyone else can figure out alternative ways to
measure gallium level within a nanotube, we may have [a] real nanoscale
analytical tool in our hands," he said.
Bando's research colleague was Yihua Gao. They published the research
in the February 6, 2002 issue of Nature. The research was funded by the
TRN Categories: Nanotechnology; Materials Science and Engineering.
Story Type: News
Related Elements: Technical paper, "Carbon Nanothermometer
Containing Gallium," Nature, February 6, 2002.
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