R&D
limit to the useful thickness of ferroelectric layers (Nature, April 3,
2003). The researchers modelled a BaTiO3 thin film between two electrodes
(SrRuO3). The electrodes in short circuit lost their ferroelectric
properties below a critical thickness of six unit cells (24Angstroms). The
scientists say that dipoles at the ferroelectric-metal interface create a
depolarising electrostatic field.
Experiments have detected ferroelectricity in 40Angstrom-thick perovskite
layers and in 10Angstrom copolymer films. Previous atomistic simulations
showed a ferroelectric ground state being maintained down to an ultralow
thickness, suggesting that there was no critical thickness. The calculations
did not include the influence of a real perovskite-metal interface. The new
calculation uses density functional theory in a local density approximation.
"Our results suggest the existence of a lower limit for the thickness of
useful ferroelectric layers in electronic devices," comment the scientists.
Manchester Universitys Centre for Mesoscience & Nanotechnology has been
opened on April 7, 2003. A recent GBP1.8mn Science Research Investment Fund
(SRIF) injection by the university has created a multidisciplinary workshop,
allowing researchers to fabricate, visualise and characterise structures and
devices containing individual elements from a few microns down to 10nm in
size. The facility is specially designed for advanced multidisciplinary
research such that researchers with little previous experience in
nanotechnology could use it to join and collaborate with those already
active and experienced in the subject. State-of-the-art facilities include
electron beam lithography, optical and near field optical lithography,
plasma processing, ultra-clean sputter deposition, AFM/MFM/STM and SEM
microscopy.
Professor Steve Furber, Computer Science department head, comments: "Future
electronic technologies involving many thousands of millions of devices per
chip, and information storage technologies capable of extremely high
densities of bits, will all be dependent on the ability to make devices and
study phenomena on a nanoscale. This new centre provides us with the tools
and opportunities to be at the forefront of developments in these areas."
The New Jersey Nanotechnology Consortium (NJNC) claims to be the first US
nanotechnology company in operation to focus on developing and
commercialising products based on nanotechnology with its official opening.
The company includes corporate, academic and government participation. NJNC
will develop cost-effective nanotechnology devices across a variety of
industries, including the pharmaceutical, biomedical, electronic materials,
optical/photonics, defence/aerospace, energy, industrial and semiconductor
markets.
"There are real-world nanotechnology applications and products that can be
brought to market today, specifically in the areas of drug discovery,
disease detection and electronics," says Dr Omkaram Nalamasu, NJNCs chief
technology officer.
The US National Science Foundation predicts that innovations in
nanotechnology will create a $1tr industry within 10 to 15 years, as
companies learn to apply molecular-level engineering to medical treatments,
communications, electronic and defence systems. NJNC will offer immediate,
cost-effective access to fabrication facilities, design and prototyping
services and volume manufacturing processes. In its FY2003, NJNC has
received $2mn in funding from the state of New Jersey.
NJNC already has more than six projects underway from private companies
working to bring nanotech-based products to market.
NJNC is based at the New Jersey Nanofabrication Laboratory, a former Bell
Labs facility in Murray Hill. Valued at more than $400mn, the submicron
facility is claimed to be the only fully operational 200mm fab dedicated to
nanotechnology development in the USA.
Princeton University scientists have developed stretchable gold conductors
(Applied Physics Letters, April 14, 2003). This should enable flexible
electrical connections that don break. The gold is deposited in a 100nm
thick layer on a poly-dimethyl siloxane (PDMS) substrate. Adhesion is
provided by a 5nm thick chrome layer. Conduction is maintained up to strains
of 23%, while charge flow is usually broken by a 1% stretch in a normal gold
strip.
Prions - the misfolded proteins that are believed to be responsible for
diseases such as bovine spongiform encephalopathy (mad cow disease) - could
be used to make nanocircuits, researchers from the Whitehead Institute for
Biomedical Research and the University of Chicago believe (Proceedings of
the National Academy of Sciences, online edition).
Scientists have used the durable, self-assembling fibres formed by prions as
a template on which to deposit electricity-bearing gold and silver, creating
electrical wire much thinner than it is possible to make by current
mechanical processes.
Most of the people working on nanocircuits are trying to build them using
the op-down fabrication techniques used in conventional electrical
engineering. Whitehead Institute director Susan Lindquist, a co-author of
the study, explains the new approach: "We thought wed try a ottom-up
approach, and let molecular self-assembly do the hard work for us."
Prions have another characteristic that makes them ideal for the
mass-manufacturing jobs the researchers have in mind: They recruit other,
properly folded proteins into misforming along with them, a process
Lindquist calls a "conformational cascade".
In the test tube, a conformational cascade generates strings and strings of
tough, durable and heat-resistant protein fibres of a type known as
"amyloid". Amyloids form the plaque that gunks up neurons in people and
other animals with Alzheimers, mad cow disease, scrapie and so on. However,
the yeast prions used as the source of protein in these experiments are
completely harmless, making them safe to work with in manufacturing.
Lindquist and colleagues used a special genetic variant of yeast modified to
produce fibres capable of bonding with gold particles. They then coated
these fibre strings with enough metal to make a working electrical wire.
