La microscopie electronique a transmission (MET), en donnant de l’objet mince une image globale avec une resolution meilleure qu’un dixieme de nanometre, est une des techniques qui permettent l’etude des materiaux a l’echelle nanometrique. Elle est basee sur le fait que les electrons sont des particules chargees dont les trajectoires sont modifiables par l’action de champs magnetiques et electrostatiques. Apres un descriptif de l’appareil, cet article expose les differentes methodes de preparation des echantillons. Sont ensuite exposees les parametres et les choix techniques existants lors de l’utilisation d’un MET, ainsi que les problemes frequemment rencontres. Pour terminer, est introduite la methode de diffraction en faisceau convergent.

The behaviour of clays is not still well understood. Most information concerning clays has been obtained by techniques which give statistical information on the structure and chemistry. However papers have reported results from scanning and high resolution electron microscopy. This work presents a nanoscopic approach, using electron energy loss spectroscopy (EELS), of different puri. fied clays. EELS permitted to detect all the elements found by classical chemistry at a macroscopic level. In particular it made it possible to determine the Si/Al ratio in kaolinite (Si/ Al similar to 1), smectite and illite ( Si/ Al similar to 2). In all the cases, the K edge oxygen energy loss near edge structure ( ELNES) is often similar to that of other clays we studied, but a strong heterogeneity has been observed. It was also possible to highlight an influence of the presence of iron on the profile of the oxygen peak.

Plastic deformation of single crystals of niobium Tensile tests have been performed on high purity niobium single crystals between 2.17 and 300 K. Yield stresses, activation volumes and energies and dislocation structures have been investigated. It seems that three different deformation mechanisms are operating, each of them in a definite temperature range. At the lower temperatures very simple experimental laws have been found. These experimental results have been compared to the existing models for the yield stress of b.c.c. metals.

We present an ab initio calculation of the electron energy loss spectrum of rutile TiO2 in the energy range of 0 to 60 eV, focusing our interest on the excitation from the titanium 3p semicore levels. The results are compared to our measurements. Local field effects turn out to be crucial at those energies, and their inclusion in the calculation yields excellent agreement between theory and experiment. We show how in rutile these effects induce an anisotropy in the otherwise isotropic transitions from quasispherical 3p semicore states to 3d states of almost cubic symmetry.

Scanning and transmission electron microscopy convergent beam electron diffraction x-ray characterization EELS x-ray synchrotron radiation (EXAFS, XANES) SIMS auger microscopy PIXE near field microscopy.

The Inelastic Scattering Cross-Section. There is a clear distinction between energy loss to inner-shell electrons and to valence or conduction electrons. The reason for the different treatment of these two processes is essentially that, in the former case, the initial state has a sharp energy while in the latter, there is a range of energy within the valence or conduction band. Orbitals of inner shell electrons show almost no overlap between neighbouring sites, so the exchange integral is negligibly small, leading to an extremely small bandwidth. The K-band in Na has a width of 2 × 10-19 eV, and a K-electron in Na jumps roughly once a week to a neighbouring site [3.1]. Those electrons — loyal to their atoms — are well described within an atomic model, which means that energy loss to inner-shell electrons can be treated within atomic theory. (Strictly speaking, this is true only for final states far above the Fermi level. When the excited inner shell electron, after interaction with the fast beam electron, occupies states slightly above the Fermi energy, the density of unoccupied states is mirrored as near edge structure, a typical solid state effect.)

In this paper we report the effect of noble gas ions bombardment on the degradation of atomically flat Si(111) surfaces at room and high (400-degrees-C-600-degrees-C) temperatures. Reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) have been used to characterize the topography and structure of the as-implanted and post annealed surface layers. It is shown that the fading of the specularly reflected beam is not directly related to the amorphization of the surface. This experimental study has also evidenced the difficulties one meets to regrow a defect-free material after amorphization by noble gas bombardment. For high temperature for which the amorphization is not possible, the surface loses its stepped structure and turns into a monocrystalline but atomically rough surface. This roughness is a function of substrate temperature.

Journal of Electron Microscopy TechniqueVolume 11, Issue 3 p. 185-185 Preface Electron microscopy in France, part I: Material science B. Jouffrey, B. Jouffrey Lab D'Optique Electr. du Ctr. Nat. de la Recherche Sci. Toulouse, FranceSearch for more papers by this author B. Jouffrey, B. Jouffrey Lab D'Optique Electr. du Ctr. Nat. de la Recherche Sci. Toulouse, FranceSearch for more papers by this author First published: March 1989 https://doi.org/10.1002/jemt.1060110302AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume11, Issue3March 1989Pages 185-185 RelatedInformation