Grenoble-Paris - Microcrystals take the form of tiny grains, so small
that they resemble a powder. How can we determine their structure? Until
today, the technique of X-ray diffraction, normally used to study
crystals, was not an appropriate solution. For the first time,
researchers from the ESRF and the CNRS have used X-ray diffraction to
determine the structure of microcrystal grains of only one cubic
micrometre in size. They gained a factor of a thousand on the size of
the analysable samples thanks to new equipment created at the ESRF. This
breakthrough opens up new possibilities of research to chemists,
physicists and biologists.
A one cubic micrometre sample of a microporous aluminium carboxylate.
Crystalline structure of a microporous aluminium
carboxylate determined at the ESRF by X-ray microdiffraction.
Copyright: T. Loiseau, CNRS 2007
The properties of a crystal are determined by
the arrangement of its atom in space, its crystalline structure.
Scientists use X-ray or neutron diffraction to study crystalline
structure when the size of the crystal is more than 10 cubic
micrometres. Below this limit, the solid material is considered a
powder. Scientists can apply powder diffraction to analyse such a
material but this technique is not easy to exploit. Moreover, powder
diffraction can only be used for materials with grain sizes of less
than three millionths of a cubic micrometre. Due to these limitations,
a determination of the structure of new synthetic solids in powder
form is not always possible because the crystals are too small.
The teams from the ESRF and the Institute Lavoisier (CNRS/Universit�
de Versailles Saint-Quentin) have used new set-up permitting X-ray
diffraction on crystals of a size of one cubic micrometre, a volume a
thousand times smaller than that ever attainable before. This new
set-up consists of a focussing system for the ESRF beam, coupled with
a goniometer, an instrument to position the sample with maximum
precision.
The researchers studied the structure of an organic-inorganic hybrid
compound (a microporous aluminium carboxylate), which could be used
for gas absorption or to encapsulate various organic molecules. This
study confirms that the new set-up allows pushing back the limits in
crystal dimension accessible to X-ray diffraction. �It is a revolution:
what was considered a powder in the past has become a crystal today.
Researchers can now bring forward samples left in their cupboards
because the sizes had previously prevented their study. Now they will
be able to elucidate the structures of these samples, with potentially
great scientific advances on the horizon�, explains Thierry Loiseau,
from the Institut Lavoisier.
