Electron interaction volume

Fig. 2.5 The electron interaction volume in poly(methyl methacrylate) for 20 kV electrons is shown directly by etching away irradiated material. The incident electron dose is the same in (A-G), but the etching time is increased, so the material irradiated less is removed [31].

Electron Probe Microanalysis, EPMA, as performed in an electron microprobe combines EDS and WDX to give quantitative compositional analysis in the reflection mode from solid surfaces together with the morphological imaging of SEM. The spatial resolution is restricted by the interaction volume below the surface, varying from about 0.2 pm to 5 pm. Flat samples are needed for the best quantitative accuracy. Compositional mapping over a 100 x 100 micron area can be done in 15 minutes for major components Z> 11), several hours for minor components, and about 10 hours for trace elements. 

The volume of analysis, i.e., the diameter and depth of the analyzed region, is limited by a combination of the elastic and inelastic scattering.The maximum depth of the interaction volume is described by the Kanaya-Okayama electron range ... 

Steric repulsions come from two orbital-four electron interactions between two occupied orbitals. Facially selective reactions do occur in sterically unbiased systems, and these facial selectivities can be interpreted in terms of unsymmetrical K faces. Particular emphasis has been placed on the dissymmetrization of the orbital extension, i.e., orbital distortions [1, 2]. The orbital distortions are described in (Chapter Orbital Mixing Rules by Inagaki in this volume). Here, we review the effects of unsymmetrization of the orbitals due to phase environment in the vicinity of the reaction centers [3]. 

The spatial resolution in quantitative analysis is defined by how large a particle must be to obtain the required analytical accuracy, and this depends upon the spatial distribution of X-ray production in the analysed region. The volume under the incident electron beam which emits characteristic X-rays for analysis is known as the interaction volume. The shape of the interaction volume depends on the energy of the incident electrons and the atomic number of the specimen, it is roughly spherical, as shown in Figure 5.7, with the lateral spread of the electron beam increasing with the depth of penetration. 

With a thermionic electron source, and a foil thickness of 100 nm, the volume of specimen excited is of the order 10-5 pm3. With a FEG source in a dedicated STEM, however, with a foil of 1 nm thickness this specimen-beam interaction volume can be as small as 10 8pm3. Very small signal levels are thus to be expected in AEM, hence the importance of employing higher brightness sources and the need to modify the specimen-detector configuration to maximize the collection angle. 

In the NO-SCR by NH3, we note the highest reduction activity and selectivity on catalyst containing both vanadium and molybdenum than catalysts issued containing Mo or V, only. Furthermore, it should be underlined that a higher efficiency is obtained with ZSM-5 as host structure than samples issued from USY and MOR. Where a higher loss of porous volume were observed. On the basis of characterization data it has been suggested that the observed synergism in the SCR reaction is related to the existence of electronic interaction between the V and Mo species. In particular, it has been proposed that the presence of such electronic interactions modifies the catalysts redox properties, which have been claimed an essential property in the NO-SCR by NH3 reaction. 

Fig. 8 Schematic of electron beam interaction with a sample and the electron beam interaction volumes for electron-specimen interactions.

Kameta, K. Kouchi, N. Hatano, Y. In Landolt-Bomstein, New series volume I/17C, Photon and Electron Interactions with Atoms, Molecules and Ions — Photon- and electron-interactions with molecules Ionization and dissociation, Itikawa, Y., Ed. Springer-Verlag Berlin, 2003 4-1-4-61, Chapter 4. 

Electron microprobes can be used in spot mode to measure the chemical compositions of individual minerals. Mineral grains with diameters down to a few microns are routinely measured. The chemical composition of the sample is determined by comparing the measured X-ray intensities with those from standards of known composition. Sample counts must be corrected for matrix effects (absorption and fluorescence). The spatial resolution of the electron microprobe is governed by the interaction volume between the electron beam and the sample (Fig. A.l). An electron probe can also be operated in scanning mode to make X-ray maps of a sample. You will often see false-color images of a sample where three elements are plotted in different colors. Such maps allow rapid identification of specific minerals. EMP analysis has become the standard tool for characterizing the minerals in meteorites and lunar samples. 

The study of electron interaction with a chaotic radiation field is essentially similar to problems in molecular physics. However, because of its significance for cosmology, the papers on this subject have been placed in the next volume (see also Ya.B. s review [12]). 

B. L. Altshuler and A. G. Aronov. Electron-Electron Interaction in Disordered Conductors, volume 10 of Modern Problems in Condensed Matter Science, page 1. North-Holland, Amsterdam, 1985. 

Another important property, the apparent molar volume of the solvated electron, is essentially unaffected by the electron-cation and, indeed, the electron-electron interaction (37). 

Quinones-Torrelo et al. (1999 2001) have demonstrated a correlation of pharmacokinetic properties with results from micellar liquid chromatography. In this method micellar solutions of nonionic surfactants are used as the mobile phase in reverse-phase liquid chromatography. Interactions between the mobile and stationary phases are purported to correspond to the membrane/water interface of biological barriers as hydrophobic, steric, and electronic interactions are important for both. For a series of 18 antihistamines Quinones-Torrelo et al. (2001) showed that both volume of distribution and half-life values were better correlated with retention on these columns than with the classical log K, w descriptor. 

The resolution and depth of field of the image are established by the electron beam intensity, energy, interaction volume, and the final spot size, which are attuned with one or more condenser lenses and... 

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