Science News - August 1, 2009

Matter & Energy

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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.
μ+

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.