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Application of Field-Emission Transmission Electron Microscopy (HREM and other methods) to Material Analysis at Nanoscale

Epicier Thierry
GEMPPM, umr CNRS 5510, INSA de Lyon, 20 avenue Einstein, 69621 Villeurbanne Cedex, FRANCE

During the last decade, thermally-assisted Field Emission guns have become available on 200 and 300 kV Transmission Electron Microscopes. Compared to cold Field Emission cathodes, such so-called 'Shottky' emitters present the advantage of a very easy and stable use, and similar performances : energy resolution in the range 0.6 - 1 eV, information limit down to 0.1 nm in imaging mode, and smallest probe sizes of 0.2 to 0.4 nm.

The purpose of this contribution is to overview recent studies performed on such a machine, a JEOL 2010F installed at the CLYME (Consortium LYonnais de Microscopie Electronique, Lyon, F). Attention will be focussed on the nano-characterization of various kinds of materials presenting structural heterogeneities at a nano-scale level.
The first kind of materials consists in colloids of a few nanometers in size.

One example concerns Pd-Sn based colloids, used for the metallization of polymers. Those particles present a core-shell structure which is mainly investigated by HREM (High Resolution Electron Microscopy) and EELS (Electron Energy-Loss Spectroscopy) through nano-probe line-scans.

An other example is that of Ni-based solutions used for catalysis applications. A combination of EELS and HREM work has enabled phase transitions to be studied : in particular, the evidence of h.c.p. metallic nickel nanometric particles has been obtained.
A second kind of materials is metallic compounds, illustrated by the case of industrial Al-(Mg,Si,Cu) alloys. Both HREM and EDS (Energy-Dispersive X-Ray Spectroscopy) have been complementarily used in order to ascertain the precipitation sequence occuring during isothermal ageing, i.e. the structure and chemical composition of (Al,Mg,Si,Cu) metastable phases.
The third kind of materials consists in thermo-mechanical ceramics. HREM, EDS and EELS studies are illustrated through the examples of Y-TZP zirconia bio-ceramics and silicon nitride based ceramics, in which the study of non-crystalline grain-boundaries demands a sub-nano-scale investigation.
The last kind of materials of interest in this review is non-crystalline polymer-based hybrids, i.e. nano-composites made of a polymer matrix (e.g. HEMA) reinforced by an inorganic second phase (silica). HREM, electron diffraction and EELS studies have allowed the "bi-continuous" nanostructure of such materials to be quantitatively identified at a nanometric scale.

The author is indebted to numerous colleagues : Dr. G. Thollet (GEMPPM-INSA), Dr. F. Simonet (Institut de Recherches sur la Catalyse - CNRS -, Villeurbanne), Dr. B. Vacher (Ecole Centrale de Lyon, Ecully) for their implication in the CLYME ; O. Holderer, L. Gremillard, Dr. V. Massardier, Dr. J. Chevalier, Dr. V. Dasthizadeh, Prof. C. Esnouf (GEMPPM-INSA), F. Peillon, Dr. F. Thevenot (Ecole Nationale Supérieure des Mines de St-Etienne), and Dr. O. Tillement (Ecole des Mines de Nancy) for their collaboration to the studies presented here.