It
seemed like science-fiction just a few years ago, but
is now common practice for scientists at the Paul Drude
Institute for Solid State Electronics (PDI) in Berlin.
The scientists manipulate single atoms resting on surfaces
and assemble them into wires or tiny clusters. In the
world of nanometric dimensions, fundamental material
properties such as magnetism, electrical conductivity
or chemical reactivity differ from the conventional
behaviour observed in everyday life. If metal clusters
or semiconductor crystals are made just tiny enough, effects often arise which
can be only explained by the laws of quantum physics. Recently, a team of scientists
at the PDI documented the transition of the quantum world characteristics of
atomic structures to the world of macroscopic material properties. They assembled
individual copper atoms on a crystalline copper surface and examined the electronic
properties of these artificial structures. Jérôme Lagoute, Xi Liu
and Stefan Fölsch published their study in the journal Physical Review
Letters *.
The scientists assembled atomic clusters one atom high by manipulating one atom
after another and found that, depending on the number of atoms, characteristic
quantum states are formed which eventually merge into a widely known surface
property, the Shockley surface state. This state can be described as an electron
gas located at the surface. "The two-dimensional surface state is text book physics",
says Stefan Fölsch, "but we found something new.” For the first time, Lagoute
and colleagues revealed the physical linkage between quantum states in atomic-scale
structures and the traditional properties of extended surfaces. The researchers
conclude that their findings apply not only to copper but to other materials
as well.
To manipulate the atoms and to analyze the assembled structures, the scientists
used a home-built low temperature scanning tunneling microscope. “At present,
few research groups world-wide are able to conduct atom manipulation experiments
on this level”, says Fölsch. However, the method will not directly lead
to new products or applications in the near future.“Our experiments are performed
under very well-defined conditions at low temperature and on ultra-clean surfaces." Nevertheless,
studies of suchlike perfect model systems yield fundamental insight which is
essential for future developments in nanoscience and technology. “For instance,
if you assemble a quantum wire atom by atom”, says Fölsch, “you'd like to
know about the detailed electronic characteristics and the electron dynamics
associated with this one-dimensional object." The present experiment by the PDI
scientists provides an instructive approach to exploring how electronic properties
evolve when building artificial structures atom by atom. A detailed understanding
of such a scenario is an essential step towards the ultimate goal of “tailoring” magnetic
and electronic material properties by controlling size, geometry, and composition
at the atomic level.
*
Jérôme Lagoute, Xi Liu, Stefan Fölsch: “The
link between adatom resonances and the Cu(111) Shockley
surface state” , in Physical Review Letters 95 (2005)
136801-1 to 4
For more information contact:
PD Dr. Stefan Fölsch
Paul-Drude-Institut for Solid State Electronics
Hausvogteiplatz 5-7
D-10117 Berlin
Germany
phone +49 30 20377-459 or -321 (laboratory)
fax +49 30 20377 257
http://www.fv-berlin.de
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