Prof.
Ushioda says, "It may be hard to imagine putting labels
on individual nano-structures." But he has realized
such labeling with STM light emission spectroscopy. "You
can see atoms of nano-structure surfaces with a conventional
scanning tunneling microscope. But you see only the exterior
shapes of these atoms. With STM light emission spectroscopy,
you can understand the characteristics of each atom."
In
STM light emission spectroscopy, it is necessary first to
check the shape of the surface of a sample material through
measurements with STM to decide which area of the nano-structure
should be investigated.
The next step is fixing the STM tip on the nano-structure,
and injecting electrons into the structure through the tip.
Then, light with energy characteristic to the structure
is emitted. Through spectral analysis of the emitted light,
the electronic properties of the structure can be understood
and, as a result, one can identify what materials the structure
is composed of. A research group led by Prof. Ushioda has
recently identified single hydrogen atoms whose image cannot
be observed through conventional STM measurements. The diameter
of a hydrogen atom adsorbed on the surface of nickel is
0.1 nm -- that is, a picometer-scale object.
Light
emitted by nano-structures is faint, and only several photons
come out from such structure per second. Prof. Ushioda's
group has been devising various ideas to catch this feeble
light. The group believed the properties of the STM tip
to be the key to improving the luminous efficiency of nano-structures.
It developed STM tips of various shapes and materials. As
a result, the group has developed silver tips with STM luminous
efficiency several dozen times higher than that of probes
used in conventional STM measurements. It has also found
that a sharp tip with an apex angle of some 90 degrees can
generate the strongest STM light emission. The group has
also developed a unique method to fix the probe on a specific
point of a sample material accurately for collecting light
strong enough for spectral analyses. This method allows
the probe to return to its original position by making an
STM image identical to the image at its original position,
if its position changes.
Prof.
Ushioda says he specializes in characterizing nano-structures.
He says, "Even if you develop a new nano-structure,
you cannot understand what it is nor what applications it
could be used for, unless you can characterize it."
He says there are only four or five groups worldwide that
can characterize the electronic properties of individual
nano-structures by analyzing the faint light from them.
He is sometimes asked by other researchers to characterize
their nano- structures. He says, "I usually provide
characterization data to researchers who ask me to do so,
without showing strenuous effort.
But, much of my characterization data were actually obtained
through a year's worth of hard work." Data obtained
through such work tends to contain a lot of new information.
His efforts to analyze the faint light are leading to major
research projects in the nanotechnology field for characterizing
and searching for new nano-structures and nano-devices.
To
promote intellectual curiosity among students, Prof. Ushioda
stresses the need for education that provides students with
a broad outlook. He is also the research supervisor for
"Creation of Innovative Technology by Integration of
Nanotechnology with Information, Biological and Environmental
Technologies," the Nano Virtual Lab (Virtual Laboratory
in Nanotechnology Areas) of the Japan Science and Technology
Agency. He is helping to create an environment in which
young researchers from various fields can stimulate their
intellectual curiosity by collaborating together. He expects
new unique technologies to be developed via interaction
among young researchers.
(Interviewer: Yu Tatsukawa, Cosmopia, Inc.)
For more information,
http://www.nanonet.go.jp/english/mailmag/2005/035a.html
