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Researchers at the Centre d'Etudes de Chimie Métallurgique (Metallurgical
Chemistry Research Center, CECM, Vitry-sur-Seine, France), and the Centre
de Recherches sur les Macromolécules Végétales (Plant
Macromolecule Research Center, CERMAV, Grenoble) of the CNRS, in partnership
with the Department of Basic Research on Condensed Matter of the CEA (CEA-G,
Grenoble), have measured the displacement field around a dislocation with
a precision never before achieved (3pm)(1) . These measurements
open new prospects in the area of micro and nanoelectronics. These results
were published in the journal Nature on May 15, 2003.
Dislocations, or defects in crystalline materials, are at the root of
material plasticity and deformation mechanisms. Many theories have been
developed in order to describe the atomic displacements that occur around
these basic defects, elastic theory being the most notable. This theory
is based on macroscopic behavior and does not explicitly take the existence
of atoms into account. It is therefore generally assumed that it is not
valid at the atomic scale.
Researchers wanted to test the limits of this theory by measuring the
displacement field around a dislocation. To do this, they made observations
of dislocations in pure silicon using high-resolution electron microscopy,
a technique that makes it possible to obtain images of atomic networks
in crystalline materials.
The experimental displacement field obtained was compared to the theoretical
displacement field of the elastic theory according to its two variations:
isotropic and anisotropic(2) . In order to perform these
operations, researchers developed a new technique for processing images
known as "phase image analysis".
They demonstrated that it is the anisotropic theory that is verified,
with a precision of 3pm: at a distance of several nanometers from the
center of the dislocation, the crystal deforms differently, depending
on the distinct crystallographic directions.
From the point of view of basic research, these results make it possible
to experimentally confirm the validity of anisotropic theory at the nanometric
scale. The analysis method of phase images could then be used to measure
the anisotropy of crystals. In the future, it will be possible to study
the limits of anisotropic theory that should no longer be valid as we
approach the very center of the defects.
From the technical point of view, this research showed that high-resolution
electron microscopy is an invaluable tool for analyzing and measuring
deformation fields at the atomic level. Among other things, it will make
it possible to test the modeling of deformations in small volumes, particularly
in electronic nanostructures whose performance and reliability are often
limited by constraints.
This research was carried out within the framework of the Groupement de
Recherche Européen (GdRE), "Transmission electron microscopy
measurements and quantification".
(1)A
picometer is one thousandth of a billionth of a meter (1pm=10-12m), or
approximately one hundredth of an interatomic distance.
(2)Isotropic: said of a medium whose physical properties
are the same in all directions.
Researcher
contact:
Martin Hytch
Centre d'études de chimie métallurgique
Tel: +33 1 56 70 30 38
e-mail: martin.hytch@glvt-cnrs.fr
Press contact:
Muriel Ilous
Tel: +33 1 44 96 43 09
e-mail: muriel.ilous@cnrs-dir.fr
Contact – Chemical Sciences Department:
Laurence Mordenti
Tel: +33 1 44 96 41 09
e-mail: laurence.mordenti@cnrs-dir.fr
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