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OCR for page 15
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TOPIC 4: MANUFACTURING AND MATERIAL HANDLING
CONSIDERATIONS
Two presentations were made in this session, by Terry Lowe of Los Alamos National Laboratory
and Kevin Hemker of Johns Hopkins University. Their papers are summarized below.
CHALLENGES FOR NANOSCALE MANUFACTURING
Terry Lowe stressed that manufacturing is likely to be the biggest challenge in commercializing
nanodevices and must be embraced, along with R&D, in a comprehensive systems approach. The
semiconductor industry is already facing nanoscale issues as complementary metal oxide silicon (CMOS)
feature sizes continue to be reduced, although new nano methods of making transistors (e.g., using silicon
or carbon nanotubes) are thought to be 10 years in the future. Lowe said that 198 companies worldwide
are producing nanoparticles for various applications. One of the major advantages is the huge increase in
surface area possible. For example, a 100-gram golf ball has a surface area equivalent to a Post-It note,
whereas 100 grams of 40-nm particles have a surface area greater than a soccer field. Nanoscale optical
properties also differ significantly from micrometer-scale optical properties; for example, 30-,um Al
particles are silver in color, whereas 30-nm Al particles are black.
Companies making nanoparticles have found it necessary to perform nanoscale characterization
of their products at various stages of the production process in order to obtain adequate process control.
The best processes today have a variation in particle size of about 4 nm (for an average diameter of 28
hi Tl) over a week of production. Today's plants can produce between 1 and 3 pounds per day; they need
to get to hundreds of pounds to be economically viable. Building such a plant is estimated to require an
investment of $2.5 million for every 100 pounds produced and about 4 years to fully understan(l and
control the process.
Removal of barriers to commercialization will require nano-savvy product and process engineers.
In addition, potential regulatory, environmental, health, and safety issues need immediate attention.
(Debra Rolison, a committee member, said that a book would soon be published on these topics.)
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Summary of the Power Systems Workshop
RESILIENCE OF MICRO - ANO MATERIALS—EFFECTS OF VIBRATION, STRESS,
TEMPERATURE, TIME, ETC.
Kevin Hemker noted that the mechanical, electrical, optical, magnetic, and chemical properties of
materials change at the nanoscale; one exception may be tensile modulus, which appears to be
independent of length scale. Smaller is stronger, up to a point. For example, the fact that flaws are much
smaller in MEMS materials makes it possible to use silicon as a structural material. A 300-fold increase
in strength can be attained by changing the current density during deposition, which results in the
formation of nanocrystals. IIowever, the grain boundaries of nanostructures will increase with extended
exposure to elevated temperatures, increasing flaw sizes and thereby reducing strength The increased
surface area of nanomaterials means increased reactivity and susceptibility to environmental conditions.
Electrodes in Li-ion batteries can swell 300 percent with Li+ ion intercalation, raising all sorts of issues
having to do with stress, fatigue, and so on. Porous battery materials may best be modeled as cellular
solids.
TOPIC 4 DISCUSSION
The panel discussion started with a question about the feasibility of using live organisms—
including engineered organisms to make the desired small particles. One response was that biosynthesis
is slow and one then has to separate the product from the organisms, with attendant concerns about purity,
etc.
There was a question about how long one would have to wait for biomaterials to evolve to a point
that they could} be used reliably in applications. It was pointed out that structural materials used today in
aerospace needed 20+ years to move from laboratory to production. (Note, however, that DARPA has the
Accelerated Insertion of Materials program, which tries to accelerate the transition of advanced materials
into applications.) Nanomaterials are perceived as evolving more rapidly. However, it was pointed out
that as nanomanufacturing processes evolve, the properties of the product change and it is important to
continue to characterize them carefully. Many current microstructure devices—e.g., MEMS are
overdesigned; there is much room to reduce thicknesses and the like without affecting performance. We
will not have that luxury as we move to smaller length scales. We also do not know how atoms jumping
around as a result of thermal fluctuations—caused, for example, by changes in current will affect the
lifetime of nanostructures.
It was noted that for some purposes, e.g., dense crystal microstructures, it is desirable to have a
wide dispersion of starting particle sizes rather than the narrow dispersions discussed by Lowe. There has
been some research on nanoscale composites, but the difficulty is that these particles have a tendency to
agglomerate. Some superalloy composites have been fabricated successfully on the micrometer scale.
One person wanted to know whether there are any catalogs of currently available nanomaterials
for use by designers. The answer was that, in general, there are not, although some companies put out
brochures listing their products. There is an organization for MEMS that puts foundries in contact with
potential users. It was pointer! out that after 40 years of polymer composite material development, we
still clo not have a composites design manual for aerospace engineers, so we are far from having one for
nanomaterials. There has been some progress in compiling the mechanical properties (though not strain
measurements) of materials for micrometer-scale devices; however, in microdevices, the test of material
performance is, in effect, the performance of the device.
Representative terms from entire chapter:
terry lowe
