twins are forced to share, it can put a significant strain on their
relationship. While this observation is perhaps unsurprising in the behavior of
children, it is less obvious when it comes to nanoparticles.
spending close to a decade examining the structure of nanowires made of pure
silver, scientists at the U.S. Department of Energy’s (DOE) Argonne National
Laboratory have discovered a set of unusual behaviors in nanocrystals with a
strained, five-fold symmetry formed by “twinning” in the crystal structure. The
twinned crystals’ unusual pentagonal symmetry and complicated structures
distinguish them from the cubic crystalline lattices typical of many silver
The “twinned” structures occur when adjacent domains within the nanoparticle
arrange themselves by sharing the same planes, says Argonne nanoscientist Yugang
Sun. Since the five-fold twinned structures do not perfectly fill the volume
that the atoms would normally occupy in silver, there is a lot of strain in the
atomic structure or lattice. Typically, nanoparticles made from precious metals
have formed highly symmetric lattices in a configuration called
“face-centered cubic”; but the strains in five-fold twinned nanowires
distort the lattices into a body-centered tetragonal symmetry.
difference between the atom arrangements in nanoparticles could determine both
the strength of the material as well as its efficiency as a catalyst, Sun says. “This is a fundamental study that looks in depth into the nature of metals at
the most basic level,” he says. “However, it’s essential that scientists
understand such properties in order to exploit any advantages that these very
small structures might provide us down the road.”
and his colleagues also discovered that the lattice stresses are absorbed
unequally by different regions of the nanowires. The center, he says, exhibits
signs of high strain, while the outer layer is not strained as much. This
behavior suggests each nanowire is actually composed of two distinct regions—something
that is very important to determine the stability of the highly strained
unusual structure of the silver nanowires also allows materials scientists to
establish how strain distributes itself along one extended dimension. “This can
answer a lot of questions that remain in materials science, particularly for
this kind of common structure,” Sun says.
paper was published online in Nature Communications.
Source: Argonne National Laboratory