Materials scientists at Rutgers have devised a novel and easy technique to
make thin, crystal-like materials .

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

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.

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