Researchers
at the University of Pennsylvania have announced
that they have bridged a major obstruction in the
creation of nanoscale electronics by developing a
simple, reliable and observable method of creating
tiny, tiny gaps between electrodes.
Such "nanogaps" will make it possible to make electrical
contact to structures on the nanoscale billionths
of a meter. In a recent edition of the journal
Applied Physics Letters, online now, physicists Marija
Drndic and Michael Fischbein describe the creation
of nanogaps, which could have applications ranging
from ultra ast electronics to quantum computing to
high-speed gene reading.
"A number of people have proposed nanoelectronic
devices that use nanogaps, but nobody has been able
to create nanogaps reliably in practice," said Marija
Drndic, an assistant professor in Penn's Department
of Physics and Astronomy in the School of Arts and
Sciences. "For the first time, we were able
to make the world's smallest and cleanest nanometer
gaps that can be imaged directly with atomic resolution. These
nanogaps can be used to electrically connect small
objects, such as an individual molecule."
The ability to hook individual molecules -whether
they are the product of nanotechnology or biotechnology
-to electronic circuits is the goal of many researchers. Such
systems will have applications in medicine, robotics,
materials science and even security. In addition,
electronics on the nanoscale will be used to create
denser, faster storage devices and microprocessor
chips.
To create these gaps, Drndic and graduate student
Michael Fischbein used electron beam lithography,
a common nanotechnology tool that uses electrons
to create patterns on a surface. Their research
succeeded where previous efforts failed because of
the type of surface they used, thin layers of silicon
nitride.
"Electon beam lithography works on small scale,
but it is limited down to about 10 nanometers." Drndic
said. "It is not like drawing a line on a page;
as an electron beam hits a material the electrons
tend to scatter forward and backward, which makes
it difficult to create tiny lines."
While other researchers focused on breaking small
wires to create nanogaps, similar to how a fuse can
be popped open, the Penn researchers went the opposite
route, making the gaps directly.
"Contrary to many expectations, the thin layer of
silicon nitride, which we used instead of the usual
xide on silicon,helped minimize the amount of electron
scattering to the point where we could make clean
gaps," Fischbein said.
Just as important, these nanogaps are compatible
with high-resolution transmission electron microscopy,
or HRTEM. Because nanogaps are created on thin
films, it is easy to study the structure through
HRTEM and assess their quality.
Already, the researchers have used nanogaps to measure
electrical charge through several coupled nanocrystals,
which are also referred to as quantum dots. Previous
researchers have demonstrated that quantum dots can
be manipulated to change their physical properties,
particularly their optical properties. In fact,
the blue laser, which will soon be put into use in
commercial products, was a result of early research
in changing the colors of quantum dots.
"Nanogaps allow us to inject charge directly into
individual nanocrystals, which may enable us to control
their properties on a quantum level," Fischbein said. "It
is a small gap, but across it we can bridge classical
and quantum physics. This research was funded through
grants from the National Science Foundation, the
Office of Naval Research and the American Chemical
Society.
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