Search

In many respects it is valuable to know the distribution of elements in many kinds of materials. One of the goal has been, for the past thirty years about, to improve the spatial resolution as far as it can be possible and to extend the number of elements which can be localized. Since the pioneering work by Castaing (Castaing, 1951), many techniques have been developed. They use all kinds of signals obtained from an excited sample by use of different incident particles or also by increasing the temperature. The collected signals concern transmitted, secondary, backscattered or Auger electrons, electromagnetic radiations (from infrared to X rays) and deflected or secondary ions...

By using a Castaing-Henry filtering device adapted on a Siemens Elmiskop I electron microscope, we have directly observed plasmon and inner shell excitations by 60 keV electrons on electron energy loss spectra. Inner shell excitation edges have been detected up to 1900 eV.By comparing L and K inner shell excitation profiles in the case of Magnesium, Aluminium and Silicon, it is concluded that the optical selection rules, △1 = ±1, explain the shape of the spectrum after the edge in a first approximation.

Crystalline as well as amorphous forms of silicon carbide are materials which have important uses in many areas of materials science including structural ceramics, coatings, and semiconductors. The characterization of SiC by the use of the EXELFS technique yields radial distribution functions (RDF) which are sensitive to the structure and composition within near neighbor distances of either C or Si atoms. In this way a quantitative analysis of possible variations in “structure” can be made. EXELFS analyses of crystalline SiC are especially important in order to evaluate the method when comparison with results from the amorphous state are to be made. The EXELFS technique has previously been applied to study both crystalline as well as amorphous materials.Crystalline as well as amorphous SiC was evaluated. One specimen was a commercially available SiC single crystal. Two other specimens utilized a similar SiC starting material which had been made amorphous either by ion implantation with chromium or by irradiation from 300 kV electrons.

As was proposed in several recent review papers (for instance 1-3) it is interesting to use electron energy losses corresponding to inner shell excitations by incident electrons to perform chemical analysis. One of the main advantages of the inner shell excitation spectroscopy (ISES) is that it is essentially available for light elements, contrary to characteristic X ray emission spectroscopy.Two methods can be used :- energy analysis : energy loss spectra are obtained from selected projected area of the sample and elemental characteristic energy losses are detected;- image energy filtering : images are formed by selecting electrons in an energy loss range which contains a characteristic energy loss. They show a map of the distribution of a given element in the object with a high spatial resolution.Combining these two methods is quite essential to perform chemical analysis. Such studies can be achieved in CTEM by means of an energy filtering system preserving the imaging properties of the microscope.

Amorphous phases have been shown to influence properties of many metallic, semiconducting, and ceramic materials. However, analysis of these phases presents a difficult challenge since most conventional characterization techniques provide only limited qualitative information. Extended Energy Loss Fine Structure (EXELFS) analysis is a technique which is sensitive to both structure and composition within near neighbor distances of specific types of atoms in both crystalline and amorphous materials. The fine structure, which is present in the form of modulations on the core loss edges of electron energy loss spectra, results from diffraction of ejected core electrons by neighboring atoms. The ability to obtain EXELFS measurements with an analytical electron microscope allows direct observation of changes in composition, microstructure, and local atomic environment at a spatial resolution (Recently an investigation of the effects of ion implantation on the microstructure and properties of A12O3has revealed differences in the response of various forms of amorphous A12O3to post-implantation annealing.