Diagramme de diffraction d'électrons lents (LEED) sur un monocristal de Cuivre Cu(001). On remarque la symétrie d'ordre 4 de la surface.

Les techniques de diffraction permettent de sonder l'ordre dans la matière. Pour ceci, on fait interagir une onde dont la longueur d'onde λ est comparable à la taille du motif cristallin élémentaire de l'échantillon. Ce peut être une onde électromagnétique (rayons X, lumière Laser) ou des particules (électrons, neutrons ou des atomes d'hélium).

La présence de pics intenses dans le diagramme de diffraction montre la présence d'ordre. Les pics sont séparés de 2π/a en nombre d'onde (2π/λ) où a est le pas du réseau. La forme des pics de diffraction traduit la qualité de l'ordre : par exemple, la diffraction sur un domaine ordonné de taille L se traduit par un élargissement des pics de diffraction en (2π/L).

Diffraction techniques are used to probe the order in the matter. For this,  a wave with wavelength (λ) comparable with the elementary domain size interact with a sample. It can be an electromagnetic wave (x-rays, Laser light) or particles (electrons, neutrons or helium atoms).

The presence of intense peaks in the diffraction pattern shows the presence of order. The peaks are separated from 2π/a (2π/λ in wave number) where a is the crystal lattice parameter. The shape of the diffraction peaks traduces the quality of the order. Diffraction on an ordered domain of size L results in a broadening of the diffraction peaks in (2π/L).

#116 - Màj : 03/01/2013
News December 2023 The ICONE project and HiCANS in general were presented to the French user community during the Journées de la Neutronique in Erquy. HiCANS High Current Accelerator-driven Neutron Sources - State of the art  (F. Ott) PRESTO: diffraction on ICONE (X. Fabrèges) Spectroscopy : state of the art, and possibilities in HiCANS (Q. Faure) The HERMES - LLB outstation at the JULIC Neutron Platform (M.
Technique (desc. gen.)
X-ray Photoelectron Diffraction is one surface technique used to study the surface structure of sample. The intensity of excited photoelectron as a function of azimuthal or polar angle of sample is recorded by changing the sample position. XPD provides information on surface relaxation and also the local atomic structure down to the monolayer. Quantitative information is given combined with the electron scattering simulation. Besides, XPD is also the basis of the photoelectron holography.
La diffraction d’hélium est une technique encore peu répandue, une dizaine de laboratoires seulement la possède à l'échelle mondiale, mais cette technique a déjà permis des progrès importants dans la compréhension de la structure et de la dynamique des surfaces et des films minces. Son principe consiste à envoyer sur la surface à étudier un faisceau d’atomes d’hélium et d’analyser le faisceau réfléchi et diffracté par celle-ci.
La diffraction d'électrons lents (LEED : Low Energy Electron Diffraction) est une technique qui permet d'étudier la structure et la symétrie des surfaces. Cette technique repose sur la nature ondulatoire des électrons et sur la forte interaction de ceux-ci avec la matière.
Le groupe GOC de l'IRAMIS/SPEC possède un diffractomètre pour poudres D8 Advance (Bruker-axs) équipé d’une chambre en température MRI, permettant de caractériser les matériaux synthétisés (identification des phases cristallines, évaluation de la cristallinité des échantillons et calcul des paramètres cristallins) et étudier leurs structures de l’ambiante à 1100°C.
Voir aussi
TiNi alloy is polymorphic. It exhibits a martensitic transition near room temperature between a cubic CsCl-type (austenite) and a monoclinic TiNi-type (martensite) structure. This transformation is at the origin of its shape memory effect. In addition, TiNi has good hydrogen storage properties under normal conditions of pressure and temperature. In austenic form, TiNi absorbs 1.4 H/f.u. under atmospheric pressure.
Faits marquants scientifiques
23 mai 2024
Influence of Dy3+ environment on magnetic anisotropy and magnetocaloric effect in Dy3⁢B2⁢C3⁢O12 (B=In, Sc, Te ; C=Ga, Al, Li) garnets F. Damay, S. Petit, D. Sheptyakov, C. V. Colin, E. Suard, S. Rols, J. Embs, U. Stuhr, D. Bounoua, O. Demortier, and C. Decorse, Phys. Rev. B 109 (2024) 014419   In the framework of the general phase diagram published recently for a pseudospin S = 1/2 on a hyperkagome network [Kibalin et al., Phys. Rev. Res.
14 janvier 2024
M. Warburton, J.M. Ablett, J.-P. Rueff, P. Baroni, L. Paolasini, L. Noirez We examine the influence at room temperature of the deposit of a water layer on the phonon dynamics of a solid. It is shown that the water wetting at the surface of an Alumina monocrystal has deep effects on acoustic phonons, propagating over several hundred µm distance and taking place on a relatively long time scale.
01 décembre 2023
Anne-Charlotte Le Gulluche, Guylaine Ducouret, Ludovic Olanier, Annie Brûlet, Olivier Sanseau, Paul Sotta, and Alba Marcellan Model hybrid hydrogels reinforced by silica nanoparticles were designed by polymerizing and cross-linking the gels in situ. The polymer–particle interactions were tuned by using either poly(dimethylacrylamide) (PDMA), which adsorbs on silica, or poly(acrylamide) (PAAm), which does not.
14 mars 2023
Michal Swierczewski,  Fabrice Cousin,  Ewa Banach,  Arnulf Rosspeintner,  Latevi Max Lawson Daku,  Abolfazl Ziarati,  Rania Kazan,  Gunnar Jeschke,  Raymond Azoulay,  Lay-Theng Lee,  Thomas Bürgi A bidentate chiral dithiol (diBINAS) is utilised to bridge Au25 nanoclusters to form oligomers. Separation by size allows the isolation of fractions that are stable thanks to the bidentate nature of the linker.
07 novembre 2022
Michal Swierczewski, Alexis Chenneviere, Lay-Theng Lee, Plinio Maroni, Thomas Bürgi Langmuir-Blodgett (LB) technique allows the deposition of gold nanoclusters (atomically precise nanoparticles below 2 nm in diameter) onto solid substrates with an unprecedented degree of control and high transfer ratios. Nanoclusters are expected to follow the crinkle folding mechanism, which promotes the formation of trilayers but kinetically disfavors the formation of the fourth layer.
22 février 2022
J.C.Riedl, M.Sarkar, T.Fiuza, F.Cousin, J.Depeyrot, E.Dubois,G.Mériguet,R.Perzynski and V.Peyre Some of the most promising fields of application of ionic liquid-based colloids imply elevated temperatures. Their careful design and analysis is therefore essential. We assume that tuning the structure of the nanoparticle-ionic liquid interface through its composition can ensure colloidal stability for a wide temperature range, from room temperature up to 200 °C. https://doi.org/10.
02 novembre 2021
Michal Swierczewski, Plinio Maroni, Alexis Chenneviere, Mohammad M. Dadras, Lay-Theng Lee, Thomas Bürgi Nanoscale particles attract much attention due to their size-dependent optical, electrical and chemical properties. Of particular interest are ultrasmall metal nanoclusters which experience strong quantum confinement effect leading to profound changes in the atomic packing structure.


Retour en haut