NEW
BRUNSWICK/PISCATAWAY, N.J. – Materials scientists
at Rutgers, The State University of New Jersey, have
devised a novel and easy technique to make thin,
crystal-like materials for electronic devices. The
technique could supplement today's tedious and exacting
method of growing crystals with an additional benefit
of producing materials in sizes and shapes not now
possible.
In a recent issue of the American Chemical Society
journal Langmuir, Rutgers scientists and collaborators
from Ceramare Corporation and the University of California,
Berkeley, report on a method where they coax thousands
of microscopic grains of individual crystals to assemble
into tightly packed layers. The resulting orderly
array of particles mimics the performance of traditionally
fabricated crystalline wafers, without the time and
expense of growing crystals in a molten mixture or
solution, then slicing them into thin layers.
"The materials we've created in our lab bridge the
gap between single-crystal materials, with their
precisely ordered atomic structures, and ceramics,
which have randomly oriented structures," said Richard
Riman, professor of ceramic and materials engineering. "These
so-called 'single-crystal-like' materials possess
properties approaching those of true single crystal
materials, but since we make them with techniques
drawn from ceramic fabrication, there is potential
to synthesize them economically and in large size
and quantity."
Riman and his colleagues conducted their research
with lead zirconate titanate, or PZT, which is used
in motion sensors, electrical capacitors and even
for vibration damping in high-performance skis and
tennis racquets. PZT has proven almost impossible
to fabricate as a single crystal, which limits practical
applications to the material's polycrystalline form;
that is, a solid mixture of small crystalline particles.
Even the most sophisticated lab techniques have produced
crystals no larger than a quarter-inch across. A
number of new applications in sensing, imaging and
energy storage appear possible if the material can
be fabricated in a variety of sizes and shapes with
the highly ordered atomic structure of crystals.
The
Rutgers-led team created
PZT particles using chemical
processes, forming cubes
of uniform shape and size,
between two and three microns
on a side (almost 50 times
smaller than a grain of
table salt). The team then
made a slurry of PZT cubes
in an alcohol and mineral
oil mixture and placed
droplets of the slurry
on a water surface. Various
forces, including the water's
surface tension, caused
the cubes to "self-assemble" into
a densely packed single layer. The scientists then
picked up the array of cubes onto a glass tube or
microscope slide, resulting in a thin layer of crystal-like
PZT.
Using a sophisticated technique called atomic force
microscopy, the scientists measured piezoelectric
properties, or the ability to generate electricity
by causing vibrations, in the PZT array. They found
it had properties comparable to that of a true single-crystal
structure. While additional work will be needed to
make the fabrication process practical for large-scale
production, the research suggests it will be possible
to make materials with unique shapes and properties.
The work was funded by the Office of Naval Research,
Defense Advanced Research Projects Agency, National
Science Foundation, and the New Jersey Commission
on Science and Technology. In addition to Riman,
the research team members were Xiangyuan Liu, Kate
Mikulka-Bolen, Frederic Cosandey and George Rossetti,
Jr. of Rutgers, Elizabeth McCandlish and Larry McCandlish
of Ceramare Corporation, and Ramomoorthy Ramesh of
the University of California, Berkeley.
|
