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Salt turns to taffy
at the nanoscale
Find suggests new technique
for making miniature wires
study coauthor Nathan Moore of Sandia
National Laboratories in Albuquerque.
This unusual behavior highlights that
different forces rule in the nanoworld,
says Krzysztof Kempa of Boston College.
“Forget about gravity,” he says. At this
scale, surface tension and electrostatic
forces are much more important.
Moore and colleagues guided a micro-
scope that detects various forces toward
a chunk of salt. When the microscope’s
diamond tip was far away, there
was no measured force, but
within about seven nanome-
ters, a strong attraction devel-
oped between the tip and the
salt. The salt then stretched out
to glom on to the tip.
Using an electron micro-
scope to see what was happen-
ing, the researchers observed
that “nanowires” had formed.
The initial attraction between
the tip and salt might be due
to electrostatic forces, the
researchers speculate. Several mecha-
nisms might lead to the elasticity, includ-
ing the excessive role of surface tension in
the nanoworld. (The same tension allows
a water strider to skim the surface of a
pond in the macroworld.)
The surface tension is so strong that
as the microscope pulls away from the
salt, the salt stretches, Kempa says. “The
inside has no choice but to rearrange the
atoms, rather than break,” he says.
Brittle salt becomes elastic in the nanoworld, stretching when tugged by a microscope.
By Rachel Ehrenberg
Inflexible old salt becomes a softy in the
nanoworld, stretching like taffy to more
than twice its length, researchers report
in the June 10 Nano Letters. The findings
may lead to new approaches for making
nanowires that could end up in solar
cells or electronic circuits. The work
also suggests that these ultra-tiny wires
may already exist in sea spray and large
underground salt deposits.
Metals such as gold or lead, in which
bonding angles are loosey-goosey, can
stretch out at temperatures well below
their melting points. But scientists don’t
expect this superplasticity in a rigid, crystalline material like sodium chloride, says
Mass mismatch leads to mystery
Omega-b-minus is detected again, but it’s lighter this time
By Jenny Lauren Lee
A heavy, strange cousin of the proton has
been seen a second time, but it seems to
have lost a little weight.
Omega-b-minus is a three-quark particle related to protons and neutrons. It
has been observed at CDF, a detector at
the Fermi National Accelerator Laboratory in Batavia, Ill., scientists report
online May 19 at arXiv.org. But CDF’s
measurement of the particle’s mass is
significantly lower than a previous measurement, leaving researchers wondering what caused the discrepancy.
“One or both of the measurements are
missing the mark,” says CDF physicist
Pat Lukens, a coauthor of the paper.
DZero, CDF’s sister detector, had
observed the omega-b-minus in fall
The standard model of particle physics predicts the existence and mass of
this particle, which is a baryon, like protons and neutrons, and is made up of two
strange quarks and a bottom quark.
The elusive particle is rarely seen but
does play a supporting role in a grander
enterprise, says Fermilab’s Andreas
Kronfeld. “If the standard model were a
movie, you wouldn’t get Robert De Niro
to play the omega-b baryon,” Kronfeld
says. But understanding
the properties of such
particles helps scientists
answer larger questions,
such as why the universe
is made mostly of matter
instead of antimatter.
FROM TOP: N. MOORE ET AL./NANO LETTERS; CDF COLLABORATION
2008 using the same accelerator, the
Tevatron, at Fermilab (SN: 9/27/08,
p. 9). Although CDF’s recent mass measurement of 6.054 billion electronvolts
agrees better with the expected mass for
an omega-b-minus particle than DZero’s
measurement of 6.165 billion electronvolts, the mismatch in the
results is disconcerting,
the researchers say.
“We don’t have an
explanation,” says Darien
Wood of Northeastern
University in Boston,
cospokesman for DZero.
“We checked for obvious
errors, and we haven’t found
any.” Such discrepancies occasionally come up, he says, and
are resolved with more data.
The omega-b-minus baryon
decays too quickly to be
detected directly, but its pres-
ence is signaled by a telltale
cascade of particles.
14 | SCIENCE NEWS | August 1, 2009