An
international team led by UCL (University College
London) scientists at the London Centre for Nanotechnology
has unravelled the properties of a novel ceramic
material that could help pave the way for new designs
of electronic devices and applications.
Working with researchers from the Swiss Federal
Institute of Technology (ETH), Zurich, the University
of Tokyo and Lucent Technologies, USA, they reveal
in a Letter to Nature that the complex material,
which is an oxide of manganese, functions as a self-assembled
or 'natural' layered integrated circuit. By conducting
electricity only in certain directions, it opens
up the possibility of constructing thin metal layers,
or racetracks, insulated from other layers only a
few atoms away.
Currently, the race for increasingly small and more
powerful devices has relied on two-dimensional integrated
circuits, where functional elements such as transistors
are engineered via planar patterning of the electrical
properties of a semiconductor. Packing more functionalities
into tiny electronic devices has until now been achieved
by reducing the lateral size of each component, but
a new realm of opportunity opens with the ability
of building three-dimensional structures.
Professor Gabriel Aeppli, Director of the London
Centre for Nanotechnology and co-author of the study,
explains: "There is an issue of how you deal with
leakage between layers when you pack circuits into
three dimensions. Our work with the Tokyo-Lucent
groups shows that you can have many layers with little
or no leakage between them. This is because we're
not dealing with ordinary electrons, but with larger
objects, consisting of electrons bound to magnetic
and other disturbances of the atomic fabric of the
material, which can't travel across the barriers
between layers."
The flow of electricity in modern electronic devices
relies on the fact that electrons move readily in
certain solids, such as metals like copper, and are
blocked from moving in insulators such as quartz.
In ordinary solids, electrons move similarly in all
three dimensions, therefore if a material is metallic
along one direction, it will be metallic in all directions.
The ceramic – a manganese oxide alloy with the chemical
formula La1.6Sr1.4Mn2O7 – has fascinated scientists
for a decade due to the extraordinary sensitivity
of its electrical properties to magnets placed near
it. Most interesting was the discovery by the University
of Tokyo group that even quite small magnets can
switch electrical currents in the same way in this
ceramic as in much more expensive, individually fabricated
electronic devices of the type being tested for advanced
magnetic data storage.
Using one of the classic tools of nanotechnology,
the scanning tunnelling microscope, Dr Henrik Rønnow
(ETH) and Dr Christoph Renner (LCN and UCL) swept
a tiny metallic tip with sub-atomic accuracy over
the surface of the ceramic to sense its topographic
and electronic properties at spatial resolution of
less than the diameter of a single atom. The data
showed that this ceramic behaves like a perfect metal
along the planes parallel to the surface and like
an insulator along the direction perpendicular to
the surface.
The results also revealed the first snap-shot of
a possible culprit for this unusual electronic behaviour.
In conventional solids, charge is carried by simple
electrons, but in such ceramics, it is shuttled around
by more complex objects, known as polarons, which
consist of electrons bound to a magnetic disturbance
as well as local displacements of atoms away from
their ordinary positions. Notes to editors
Title: 'Polarons and confinement of electronic motion
to two dimensions in a layered manganite'
Journal: Nature (20/04/06)
Authors: H. M. Rønnow (1), Ch. Renner (2),
G. Aeppli (2), T. Kimura (3) and Y. Tokura (4)
(1) Laboratory for Neutron Scattering, ETH-Zürich
and Paul Scherrer Institut, 5232 Villigen, Switzerland.
(2) London Centre for Nanotechnology and the UCL
Department of Physics & Astronomy, University
College London, Gower Street, London WC1E 6BT, UK.
(3) Bell Laboratories, Lucent Technologies, 600
Mountain Avenue, Murray Hill, New Jersey 07974, USA.
(4) Department of Applied Physics, University of
Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan, and Spin
Superstructure Project (SSS), ERATO, Japan Science
and Technology Agency (JST), Tsukuba 305-0046, Japan.
For further information, please contact:
Judith H Moore
UCL Media Relations
Tel: +44 (0) 20 7679 7678
Mobile: +44 (0)77333 075 96
Out-of-hours: +44 (0)7917 271 364
Email: judith.moore@ucl.ac.uk
Professor Gabriel Aeppli
Director of the London Centre for Nanotechnology
Tel: +44 20 7679 3448
Email: gabriel.aeppli@ucl.ac.uk
About the London Centre for Nanotechnology
The London Centre for Nanotechnology (LCN) is a new UK based multidisciplinary
enterprise operating at the forefront of science and technology. Structured
to form a bridge between the physical and biomedical sciences, it brings
together two of the world's leading institutions in nanotechnology, UCL and
Imperial College London. In pulling together world-class research, infrastructure
and commercial best practices, the LCN ranks with leading facilities worldwide,
promising excellent exploitation prospects across the pharmaceutical, biotech,
engineering and computing markets.
About UCL
Founded in 1826, UCL was the first English university established after Oxford
and Cambridge, the first to admit students regardless of race, class, religion
or gender, and the first to provide systematic teaching of law, architecture
and medicine. In the government's most recent Research Assessment Exercise,
59 UCL departments achieved top ratings of 5* and 5, indicating research
quality of international excellence.
UCL is the fourth-ranked UK university in the 2005
league table of the top 500 world universities produced
by the Shanghai Jiao Tong University. UCL alumni
include Mahatma Gandhi (Laws 1889, Indian political
and spiritual leader); Jonathan Dimbleby (Philosophy
1969, writer and television presenter); Junichiro
Koizumi (Economics 1969, Prime Minister of Japan);
Lord Woolf (Laws 1954, former Lord Chief Justice
of England & Wales); Alexander Graham Bell (Phonetics
1860s, inventor of the telephone); and members of
the band Coldplay.
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