Home' Technology Review : January 2005 Contents TECHNOLOGY REVIEW
: The Los Alamos team synthesized the
nanotubes by owing ethanol vapors at 900 °C over an iron cat-
alyst spotted onto a silicon wafer. Tubes grew from these cata-
lyst spots; the catalyst was pushed along the wafer surface in the
direction of the gas ow. The longest tubes grew to four centi-
meters as straight lines across the length of the silicon wafer, ter-
minating only at the wafer s edge.
: Bundles of ca rbon na notubes, spun as bers,
havebeenpromotedfor applications wherehighstrengthand
low weight are critical, from sporting equipment like golf
clubs or tennis r ackets to science ction dreams of "elevators"
extending into outer space. Although the shorter tubes have
ma ny promising applic ations in their own right, bundles of
them have failed to perform up to their potential because of
weak links between the tubes. Lengthening the tubes reduces
these problems, bringing resea rchers closer to exploiting the
remarkable strength and conductivity of nanotube bundles.
But the Los Alamos and Duke researchers have done more
than advance a technology; they have done the unthinkable,
building individual molecules as long as a paper clip.
Source: Zheng, L. X. et al. (2004) Ultralong single-wall carbon nanotubes. Nature
A friendlier route to zeolites
: Minerals called zeolites a re essential to industrial
chemistry bec ause they help convert cr ude petroleum into use-
ful chemicals, including the materials used in plastics. By dra-
matic ally reducing the cost of petrochemicals, zeolites make
everything from pills to pocket protectors more a ordable.
Now researcher s at the Univer sity of St. Andrews in Scotla nd
have discovered a way to make these na nostr uctured miner als
that is not only cheaper but also fa ster, safer, a nd less toxic.
: Zeolites are typically made in hot water
at dangerously high pressures. The minerals are riddled with
nanometer-wide pores; molecules tucked inside these pores re-
act quickly and cleanly. Chemists create the zeolites through a
"condensation reaction," during which mineral precursors en-
capsulate molecules added as templates, forming a porous solid.
Instead of making zeolites in water, Emily Cooper, a chemistry
postdoc at St. Andrews, and her colleagues used liquid salts at a
relatively low temperature. These liquids are made of charged
molecules, or ions, so mineral precursors condense around them
directly, eliminating the need for templates. Afterward, the salt
ions are removed, leaving a str ucture with nanometer-sized
holes. The recipe yielded ve new nanoporous materials; two
represented classes that had never been seen before.
: The standard process for making zeolites is
expensive a nd da ngerous, a nd it requires specialized equip-
ment. With the new technique, even a high-school laboratory
should be able to make them. The millions of possible salt
compositions produced through this process could result in
leading to better a nd cheaper everyday products.
Source: Cooper, E. R. et al. (2004) Ionic liquids and eutectic mixtures as solvent and
template in synthesis of zeolite analogues. Nature 430:1012-6.
Gotta Look Sharp
Atomic force microscopy makes
: The r ate of cor rosion in devices like batteries and
semiconductors is often dictated by nanometer-sized imper-
fections. Conducting atomic force microscopes (AFMs) can
image these na no aws, but accur ately measuring their electri-
cal properties requires knowing how much of the microscope s
sharp conductive tip comes in contact with the active surface.
Using a mathematical model, Ryan O Hayre, an assistant pro-
fessor in the Stanford University Department of Mechanical
Engineering, and his colleagues have found a way to indirectly
measure this contact area, overcoming a limit of conductive tip
microscopy a nd improving quality c ontrol.
: Researchers used a platinum-coated
AFM tip to monitor the reaction between hydrogen and oxygen
at the surface of a polymer fuel cell membrane; the fuel cell was
chosen to show that nanoscale measurements can correlate with
macroscale results. The rate of the reaction depends on how
much force the tip applies to the membrane: the force pushes the
materials together, causing them to deform slightly, and thus in-
creases the area of interaction between the two. Crucially, the re-
searchers showed that the area of interaction can be estimated by
determining the hardness of the membrane, accompanied by a
few assumptions and mathematical tricks. The researchers ex-
perimented across three orders of magnitude of force between
tip and sample, and their results were all consistent with conven-
tional experiments, making them more credible.
: Conducting AFM can give nanoscale resolu-
tion to electrical measurements of semiconductors, fuel cells,
batteries, and other devic es. But while it was possible to mea-
sure relative changes in properties like conductivity, capaci-
tance, and impedance across the surface of a single sample of
material, compa ring such measu rements between materials
had been impossible. Conducting A FM, while c apable of nd-
ing aws, c ould not mea sure their absolute severity, since dif-
ferent materials interacted with the AFM tip in di erent ways.
This re nement may conver t c onductive AFM from a resea rch
instrument into a useful tool in a number of industries.
Source: O Hayre, R. et al. (2004) Quantitative impedance measurement using
atomic force microscopy. Journal of Applied Physics 96:3540-9.
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