Monday, September 14, 2009
Atoms have the habit of jumping through solids—a practice
that physicists have recently been able to follow for the first time using a
brand new method. This scientific advance was made possible thanks to the
utilization of cutting-edge X-ray sources, known as electron synchrotrons. The
detailed findings of the project, backed by the Austrian Science Fund FWF, were
recently published in the journal Nature
Materials. The work unlocks new potential for the study of material aging
processes at the atomic level.
Now and then, things can get pretty "wild" in
solids. For example, billions of atoms in a gold ring can shift position every
second. However, it is not just ordinary people who cannot see the atoms
jumping around—physicists too have long been unable to witness this process for
themselves. However, there is one very good reason in particular why scientists
should want to change all that. The restlessness of atoms is responsible for aging,
and therefore the loss of specific material properties.
To the naked eye, a wedding ring shows no traces of its "internal unrest". At the atomic level, however, it's a stormy affair, with billions of atoms changing position every second.
Scientific understanding of atomic movement has now been
significantly enhanced. A team of researchers from the Faculty of Physics at
the University of
Vienna have pioneered a
method to directly track atoms as they jump through solids. To achieve this
breakthrough, the team applied state-of-the-art technology in the form of the
European Synchrotron Radiation Facility in Grenoble, France,
which creates special X-rays of exceptional intensity and quality. These X-rays—which
can at present only be generated at three research facilities worldwide—allowed
the researchers to observe the movement of atoms in a copper/gold alloy.
Twice the jump rate
The scientists discovered how far and in what directions
atoms jump, and how this movement is affected by temperature. Team member Mag.
Michael Leitner
explains: "Our investigations have shown that, at a
temperature of 270 degrees Celsius, atoms change position in the crystal
lattice about once per hour. But that's not all. If we increase the temperature
by just 10 degrees Celsius, the jump rate of the atoms doubles. And, of course,
the same happens in reverse—if the temperature drops by 10 degrees, the atoms
only jump half as often."
In the future, the recently accomplished experiment will
serve as a basis for the measurement of atomic movement in numerous,
technically important metallic systems. This is an important first step in
understanding the aging processes of materials, which is due to the internal
unrest of atoms.
For example, to ensure that a car engine does not wear and
that a computer can function properly, foreign atoms need to be allocated to
specific positions under controlled production conditions, usually at high
temperatures. Unfortunately, these atoms also tend to leave their
"allocated" positions quickly when exposed to high temperatures and,
as a result, the materials lose their desired properties.
The means are the end
Quite apart from the findings on atomic movement yielded by
the experiment, the very implementation of the project itself is a major
achievement.
Indeed, it was only the ingenious use of various filters
that enabled the scientists to extract special "coherent" X-rays from
the synchrotron. This alone constitutes an enormous advance in the Vienna-based
physics team's field of research. Mag. Leitner: "Work is currently
underway to enhance the quality of X-rays even further. For example, the
European X-ray Free-Electron-Laser is being built in Hamburg, Germany.
This laser will open up a whole range of new and exciting possibilities."
The European X-ray Laser is to be used for applications well
beyond the investigation of materials. It will also be a unique tool in the
study of structures in vital substances such as proteins. Although the use of
"coherent" X-rays is still in its infancy, the FWF-supported project
has already taken an important step towards their universal application -
placing Austrian scientists at the forefront of scientific progress.
Original
article
"Atomic
diffusion studied with coherent X-rays"