The IBM lab responsible for inventing
the scanning tunneling microscope and the atomic force microscope has
invented another critical tool for helping us understand the nanoworld.
Accurately measuring the temperature of
objects at the nanoscale has been challenging
scientists for decades. Current techniques are not accurate and they typically
generate artifacts, limiting their reliability.
Motivated by this challenge and their
need to precisely characterize the temperature of new transistor designs to meet the demand of future cognitive
computers, scientists in Switzerland from IBM and ETH Zurich have invented
a breakthrough technique to measure the temperature of nano- and macro-sized
objects. The patent-pending invention is being disclosed for the first time
today in the peer-review journal Nature Communications,
"Temperature mapping of operating nanoscale devices by scanning probe
A History of Invention
In the 1980s, IBM scientists Gerd
Binnig and the late Heinrich Rohrer wanted to directly explore a surface’s
electronic structure and imperfections. The instrument they needed to take such
measurements didn’t exist, yet. So they did what any good scientist would do:
they invented one. It became known as the scanning tunneling microscope (STM),
opening the door to nanotechnology. Just a few years later, the invention was
recognized with the highest of honors, the Nobel Prize for Physics in 1986.
More than 30 years later IBM scientists continue to
follow in the footsteps of Binnig and Rohrer and with their latest invention.
Dr. Fabian Menges, an IBM postdoc and co-inventor
of the technique said, “We started back in 2010 and simply never gave up.
Previous research was focused on a nanoscale thermometer, but we should have
been inventing a thermometer for the nanoscale — an important distinction. This
adjustment led us to develop a technique which combines local thermal sensing
with the measuring capability of a microscope — we call it scanning probe thermometry.”
|IBM scientist Fabian Menges with his invention.|
How it Works: A Scanning Probe
The most common technique to measure
temperature on the macroscale is to bring a thermometer into thermal contact
with the sample. This is how a fever thermometer works. Once it’s placed under
our tongue it equilibrates to our body temperature so that we can determine our
temperature at a healthy 37 degrees C. Unfortunately, it gets a little more
challenging when using a thermometer to measure a nanoscopic object.
For example, it would be impossible to
use a typical thermometer to measure the temperature of an individual virus.
The size of the virus is too small and the thermometer cannot equilibrate
without significantly disturbing the virus temperature.
To solve this challenge, IBM scientists
developed a single scan non-equilibrium contact thermometry technique to
measure the temperature of nanoscopic objects using a scanning probe.
As the scanning probe thermometer and
the object cannot thermally equilibrate at the nanoscale, two signals are
measured simultaneously: a small heat flux, and its resistance to heat flow.
Combining these two signal the temperature of nanoscopic objects can then be
quantified for an accurate result.
IBM scientist Dr. Bernd Gotsmann and co-inventor
explains, “The technique is analogous to touching a hot plate and inferring its
temperature from sensing the heat flux between our own body and the heat
source. Essentially, the tip of the probe is our the hand. Our perception to
hot and cold can be very helpful to get an idea of an objects temperature, but
it can also be misleading if the resistance to heat flow is unknown.”
Previously, scientists weren’t
accurately including this resistance dependence; but only measuring the rate of
the thermal energy transfer through the surface, know as heat flux. In the
paper, the authors included the effects of local variations of
thermal resistance to measure the temperature of an indium arsenide (InAs)
nanowire, and a self-heated gold interconnect with a combination of a
few-miliKelvin and few-nanometer spatial resolution.
Menges adds, "Not only is the scanning probe thermometer accurate, it meets the trifecta for tools: it's easy to operate, simple to build, and very versatile, in that it can be
used to measure the temperature of nano- and micro-sized hot spots that can locally effect the physical properties of materials or govern chemical
reactions in devices such as transistors, memory cells, thermoelectric energy converters or plasmonic structures. The applications are endless.”
|From left to right, IBM scientists Nico Mosso, |
Bernd Gotsmann, Fabian Motzfeld and Fabian Menges in
the Noise Free Lab with the scanning probe thermometer.
Noise Free Labs
It’s no coincidence that the team began
to see improvements in the development of the scanning probe thermometer 18
months ago when they moved their research into the new Noise Free Labs -- six
meters underground at the Binnig and Rohrer Nanotechnology Center
on the campus of IBM Research-Zurich.
This unique environment, which shields
the experiments from vibration, acoustic noise, electromagnetic signals and
temperature fluctuations, helped the team achieve sub-milliKelvin precision.
“While we had the benefit of this
unique room, the technique can also produce reliable results in normal
environment,” said Menges.
“We hope the paper will produce both a
lot of excitement and relief for scientists, who like us, have been searching
for such a tool,” said Gotsmann. “Similar to the STM, we hope to license this
technique to tool manufacturers who can then bring it to market as an
additional function to their microscopy product line.”
The scientists would like to thank the
7th Program Framework for its support under the NANOHEAT project and the Swiss
National Science Foundation.
Labels: AFM, IBM Research - Zurich, nanodevices, nanotechnology, scanning probe thermometry