STUDY OF THE MORPHOLOGY OF NANOPARTICLES
BY GRAZING- INCIDENCE SMALL-ANGLE X-RAY SCATTERING
André NAUDON*,** and David BABONNEAU
* Laboratoire de Métallurgie Physique, Université de Poitiers, UMR 6630 du CNRS, bât
SP2MI; Bd 3, Téléport 2, BP 179, 86960 Futuroscope Cedex, France.
** Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE), CNRS-MENCEA, Université de Paris-Sud, 91405 Orsay Cedex, France
(E-mail : Andre.Naudon@Lmp.univ-poitiers.fr)
When an incoming X-ray beam hits the surface of a thin layer at a grazing angle close to the
critical angle for total external reflection, the refracted beam travels parallel to the surface
where it can encounter aggregates deposited on it or buried in the near surface region. This
refracted beam then acts as a primary beam and consequently gives rise to a SAXS signal,
recorded with a two-dimensional detector placed perpendicular to the incident beam. Full
potentiality of this technique is obtained when using a synchrotron source. From the scattering
pattern it is possible to determine, with a very good statistics, size, shape and arrangement of
the aggregates in two different cases : islands deposited on a surface or aggregates buried
in a matrix . We have first developed the GISAXS technique with gold islands on silicon
substrates covered by a carbon sub-layer in order to made the comparison with transmission
electron microscopy (TEM) and scanning probe microscopy (AFM or STM). We showed that
the morphology of the gold islands (in-plane diameter but also their height) can be determined
from the GISAXS scattering spectra; Moreover, when the system is dense, a mean in-plane
distance between the islands can also be determined with a good accuracy. A large area of the
sample surface is analyzed with this technique, leading to statistics over at least 1010 islands in
most of the cases. The case of metal aggregates buried in a carbon matrix (with a metal
showing no miscibility with carbon in the solid state) was then investigated. We demonstrated
that the GISAXS technique is also well adapted in this case when working with an angle of
incidence slightly higher than the critical one. The most striking feature is that the scattering
takes the shape of half an ellipse which indicates strong correlation between metal aggregates
in the carbon matrix. However this correlation is not the same in the plane of the layer as in
the other directions, in particular the in-depth one. That means that the in-plane mean distance
between metal aggregates and their in-plane diameter are smaller than the in-depth ones, the
aggregate growth being consequently columnar. This leads to a relevant information for
magnetic or non linear optical properties of such granular materials.