Nanotech Advance Makes Carbon Nanotubes More Useful
By Rex Graham
researchers exploited the strong alignment of nanotube growth
with the direction of electric field lines to create tailor-made
Researchers at UCSD
have made carbon nanotubes bent in sharp predetermined angles,
a technical advance that could lead to use of the long, thin
cylinders of carbon as tiny springs, tips for atomic force microscopes,
smaller electrical connectors in integrated circuits, and in
many other nanotechnology applications. In a paper published
in the April 7, 2005, issue of the Journal of Physical Chemistry
B, Sungho Jin, a professor of materials science at UCSD’s
Jacobs School of Engineering, reported a technique to create
bent nanotubes by manipulating the electric field during their
growth and adjusting other conditions.
geometry is necessary to realize the many promised applications
of these materials," said Jin, a professor in the Jacobs
School’s Department of Mechanical and Aerospace Engineering.
“Our new results show that we have taken a step toward
understanding how to shape nanotubes to our specifications,
an achievement that could greatly enhance their value to society.”
student Joseph AuBuchon, left, and professor of materials
science Sungho Jin.
Joseph AuBuchon, a
graduate student in Jin’s group, exploited the strong
alignment of nanotube growth with the direction of electric
field lines. After growing an aligned array of straight nanotubes,
AuBuchon switched the orientation of electric field lines 90
degrees to make L-shaped tubes. He then made more orientation
changes to make zigzags. AuBuchon won a Gold Graduate Student
Award and Best Poster Award for presenting details of his nanotube
research at the spring 2005 meeting of the Materials Research
Society, which was held March 28?April 1 in San Francisco.
connectors as thin as 1.2 nanometers are theoretically capable
of supplying sufficiently large electric currents to integrated
Carbon nanotubes hold
great promise because of their exceptionally strong mechanical
properties, their ability to efficiently carry high densities
of electric current, and other unique electrical and chemical
properties. AuBuchon used a plasma enhanced chemical vapor deposition
technique to grow about 2 billion nanotubes per square centimeter
on silicon wafers seeded with nickel catalyst nanoparticles.
Nanotubes, which are
roughly 10,000 times smaller than a human hair, can be made
almost perfectly straight in special chambers of gas plasma.
Successfully shaping nanotubes has been a goal of materials
scientists since a Japanese researcher discovered them in 1991.
However, the creation of sharp bends is difficult because once
a growth phase of nanotubes is interrupted, the catalyst particles
at the tips of the growing nanotubes become encased with carbon,
blocking future growth. A key to Jin and AuBuchon’s successful
growth of bent nanotubes involved the discovery of a technique
to prevent the unwanted carbon from encasing the catalyst between
to imagine all the possible uses for bent nanotubes, but we
think one of them might be to improve the performance of atomic
force microscopy,” said Jin. Atomic force microscopy uses
a mechanical probe to magnify rigid materials at the atomic
scale to produce 3-D images of the surface.
Jin also noted that
nanotubes may be used as replacements for conventional electrical
connectors made of metal wires in ever smaller integrated circuits.
Such wires are roughly 70 nanometers wide, but nanotube connectors
as thin as 1.2 nanometers are theoretically capable of supplying
sufficiently large electric currents to integrated circuits.
In addition, Jin said
the interconnections between microcircuit devices are often
made with metal alloy solders. Unfortunately, these solders
expand and contract at rates different than those of the microcircuit
device, and cycles of heating and cooling cause fatigue cracking
at interconnections. “If these interconnections were made
with electrically conducting nanotube zigzags, which also act
as springs, not only would we need much less space to make these
interconnections, but the thermal-expansion mismatch also wouldn’t
matter because the interconnections are flexible,” says
Jin. “We call it the compliant nano-interconnect.”
Using a modification
of the approach to make zigzag nanotubes, Jin and AuBuchon also
produced parallel arrays of T- and Y-shaped nanotubes that could
be used to make fuel cells more efficient. These arrays of parallel,
branched nanotubes could act as a 3-D scaffolding for platinum
catalyst particles. High densities of platinum catalyst-tipped
nanotubes could enable fuel cells produce electricity more efficiently.
Media Contacts: Rex
Graham, (858) 822-3075