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To research further into different
areas of advanced materials,
including the possibility of
invisibility cloaks, £2.5 million is
being invested by the UK’s
Engineering and Physical
Sciences Research Council.
Concepts in fields such as acoustic
metamaterials and thermal
cloaking will be applied in order to
engineer designer metamaterials
with specific properties. Leading
UK scientists based at Imperial
College London, the University of
Liverpool, and Liverpool John
Moores University will work on
the five-year study.
.
The University of Chicago’s
Institute for Molecular
Engineering will build a major
new facility for nanoscale
fabrication within the William
Eckhardt Research Center,
supported by a $15 million gift
from the Pritzker Foundation. In
recognition of the gift, the 12,000-
sq-ft building will be named the
Pritzker Nanofabrication Facility.
With advanced tools and enough
room for a wide range of projects,
the space will support work on
new applications in computing,
health care, communications,
smart materials, and more.
.
Illustration of high-speed optical
networks that could enable
quantum information processing
and communication. Courtesy of
Peter Allen.
Electron beam builds teeny tiny nanowires
Junhao Lin, a Vanderbilt University Ph.D. student
and visiting scientist at Oak Ridge National Laboratory
(ORNL), Tenn., discovered how to use a finely focused
beam of electrons to create some of the tiniest wires ever
made. The flexible metallic wires are only three atoms
wide—one-thousandth the width of microscopic wires
used to connect the transistors in today’s integrated cir-
cuits. According to collaborators, the technique is an ex-
citing way to manipulate matter at the nanoscale and
should boost efforts to create electronic circuits out of
atomic monolayers, the thinnest possible form factor for
solid objects.
The tiny wires are made of a special family of semiconducting materials that naturally
formmonolayers, called transition-metal dichalcogenides (TMDCs). TMDCs are made by
combining molybdenum or tungsten with either sulfur or selenium. Atomic monolayers
have exceptional strength, flexibility, transparency, and high electron mobility. Interest in
them was sparked in 2004 by the discovery of an easy way to create graphene. Yet despite
graphene’s promising properties, converting it into useful devices is problematic, which is
why scientists have turned to other monolayer materials like the TMDCs. Other research
groups have already created functioning transistors and flash memory gates made of
TMDC materials. Now, the discovery of how to make wires provides the means for inter-
connecting these basic elements. .
Strain engineering enables new areas of materials research
In the ongoing search for new materials for fuel cells, batteries, photovoltaics, separa-
tion membranes, and electronic devices, one newer approach involves applying and man-
aging stresses within known materials to give them dramatically different properties.
Known as elastic strain engineering, the discipline was long envisioned by theorists, but
only arose formally about 20 years ago. It initially focused on pure silicon, whose tensile
stress improves the speed of charges in integrated circuits, and on metal catalysts, where
tensile stress improves surface reactivity.
“Traditionally, materials are made by changing compositions and structures, but we
now recognize that strain is an additional parameter that can be changed, instead of look-
ing for new compositions,” says Bilge Yildiz, associate professor of nuclear science and en-
gineering at Massachusetts Institute of Technology (Cambridge), one of the pioneers of
this approach. “Even though we are dealing with small amounts of strain—displacing atoms
within a structure by only a few percent—the effects can be exponential.”
Putting these theoretical improvements into practice in a device, however, is a major
challenge. Yildiz focuses on improving diffusion and reaction rates in metal oxides, which
could affect how fast an energy storage or conversion device, such as a battery, works. Ox-
ides are more complex than pure silicon or metal catalysts, says Yildiz, but offer a much
larger array of potential material properties.
For example, oxides including cobaltites and
manganites, used as fuel-cell electrodes, show
performance gains through stretching and
straining. For more information: Bilge Yildiz,
617.324.4009, , .
Illustration background shows a perovskite oxide
structure. By straining this material, the energy
barrier to surface reactions is reduced. Energy
barriers are shown by 3D graphs in foreground
images. Courtesy of Mostafa Youssef, Lixin Sun,
and Bilge Yildiz.
ADVANCED MATERIALS & PROCESSES • JUNE 2014 12
E MERGING T ECHNOLOGY
Molecular model of nanowires
made of TMDCs.