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Technique sheds light on martensitic transformations
Researchers at SLAC National Accelerator Laboratory,
Menlo Park, Calif., made the first direct measurements of a
small and extremely rapid atomic rearrangement, associated
with a class called martensitic transformations that dramati-
cally change the properties of many important materials, such
as doubling the hardness of steel and causing shape-memory
alloys to revert to a previous shape. Using high-pressure shock
waves and ultrashort x-ray pulses at the Linac Coherent Light
Source (LCLS), researchers observed details of how this trans-
formation changed the internal atomic structure of a model
system, perfect nanocrystals of cadmium sulfide. In the
process, they saw for the first time that the nanocrystals pass
through a theoretically-predicted intermediate state when un-
dergoing this change.
“To design and engineer new materials with desired prop-
erties, we would like to understand the detailed microscopic
pathways they follow as they transform,” says Aaron Linden-
berg, assistant professor at SLAC and Stanford. “The martensitic transformation is espe-
cially important because it occurs in so many important materials. Our technique should
ultimately help us see what’s happening in other atomic transformations as well.” For more
information: Aaron Lindenberg, 650.725.2640, , .
Microcrucible crystal growth mechanism observed
Researchers from University of Bristol, University of
Birmingham, both in the UK, and the National Institute
for Materials Science, Japan, successfully grew nanowires
of a phase of the superconductor yttrium barium copper
oxide that have a constant cross-sectional area. Their
syntheses proceeds via the so-called “microcrucible
mechanism” of crystal growth, which was first proposed
to account for the growth of certain macroscopic metal
oxide whiskers in 1994, but had never been witnessed.
The observation was made using a high-resolution
transmission electron microscope with video capture and
an in-situ furnace. Researchers directly viewed molten
nanoparticles of barium carbonate migrating through a
porous yttriumand copper-richmatrix, catalyzing nanowire
outgrowth from nanosized microcrucibles on reaching the surface. .
Nanowire transistors enable next-generation electronics
A new approach to integrated circuits—combining atoms of semiconductor materials
into nanowires and structures on top of silicon surfaces—shows promise for a new gener-
ation of fast and sturdy electronic and photonic devices. Using this approach, engineers at
the University of California Davis demonstrated 3D nanowire transistors that open fur-
ther opportunities for integrating other semiconductors, such as gallium nitride, on silicon
substrates. “Silicon can’t do everything,” says Saif Islam, professor of electrical and com-
puter engineering. Circuits built on conventionally etched silicon have reached their lower
size limit, which restricts operation speed and integration density. Additionally, conven-
tional silicon circuits cannot function at temperatures above 250°C (~480°F), or handle
high power or voltages, or optical applications. Researchers created silicon wafers with
“nanopillars” of materials such as gallium arsenide, gallium nitride, or indium phosphide
on them, and grew tiny nanowire “bridges” between the nanopillars. For more informa-
tion: Saif Islam, 530.754.6732, , .
ADVANCED MATERIALS & PROCESSES • JULY 2014 14
NANOTECHNOLOGY
briefs
A team led by researchers from the
University of California Los
Angeles developed a process to
control molecular growth within
the “building block” components of
inorganic materials. The method
uses nanoparticles to organize
components during a critical phase
of the manufacturing process and
could lead to innovative new
materials, such as self-lubricating
bearings for engines. It could also
make mass production of such
materials more feasible. For
example, the method could be
used for aluminum-bismuth alloys.
Aluminum and bismuth cannot be
completely mixed, but with the
nanoparticle-controlled process,
researchers created a uniform and
high performance aluminum-
bismuth alloy. .
A Swedish-German research team
successfully tested a new method
of producing ultra-strong cellulose
fibers at Deutsches Elektronen-
Synchrotron’s (DESY) research
light source PETRA III in Germany.
The novel procedure spins
extremely tough filaments from
tiny cellulose fibrils by aligning
them in parallel during the
production process: Nanometer-
sized cellulose fibrils are fed
together with water through a
small channel. Two additional
water jets coming in perpendicular
from left and right accelerate fibril
flow. Following acceleration, all
nanofibrils align themselves more
or less parallel with the flow. Salt is
then added to the outer streams,
which makes the fibrils attach to
each other, thereby locking the
filament structure. Once the
filaments dry, they shrink to form a
strong fiber. .
Artist’s impression of the
production of ultra-strong
cellulose fibers. Courtesy of
DESY/Eberhard Reimann.
The transformation of
cadmium sulfide
nanocrystals from a
hexagonal arrangement
(left) to a cubic one (right).
A slightly compressed
intermediate state is
portrayed in the middle.
Courtesy of Greg Stew-
art/SLAC.
Schematic of molten barium-
rich nanoparticles moving to the
surface of an yttrium- and
copper-rich matrix.