Electron diffraction techniques

A New Electron Diffraction Technique, Potentially Applicable to Research in Catalysis L. H. Germer... 

The ordered structure and molecule orientation in the monolayers, as suggested by the Hardy model, have been studied by various means. Electron diffraction techniques, for example, including both reflection and transmission, have been employed to examine the molecular orientation of adsorbed monolayers or surface hlms. The observations from these studies can be summarized as follows [3]. 

AOTF w/c RMs bearing the silver, silver iodide and silver sulfide nanoparticles were depressurized slowly and the nanoparticles in the cell were collected and re-dispersed in ethanol. Finally, the sample grids for the TEM (FEl TECNAl G ) measurements were prepared by placing a drop of ethanolic dispersion of nanoparticles on the copper grid. The morphology and size distribution of the silver, silver iodide, and silver sulfide nanoparticles were determined by TEM at an operation voltage of 200kV. The crystallinity of the silver, silver iodide, and silver sulfide nanoparticles was studied by electron diffraction techniques. 

It is noteworthy that the HRTEM cannot distinguish core and shell even by combining X-ray or electron diffraction techniques for some small nanoparticles. If the shell epitaxially grows on the core in the case of two kinds of metals with same crystal type and little difference of lattice constant, the precise structure of the bimetallic nanoparticles cannot be well characterized by the present technique. Hodak et al. [153] investigated Au-core/Ag-shell or Ag-core/Au-shell bimetallic nanoparticles. They confirmed that Au shell forms on Ag core by the epitaxial growth. In the TEM observations, the core/shell structures of Ag/Au nanoparticles are not clear even in the HRTEM images in this case (Figure 7). 

The discussion in this section relates to structural studies carried out by calculation, x-ray diffraction, or electron diffraction techniques and will concentrate on how the molecular structures are influenced... 

L. H. Germer and A. U. MacRae, A new low electron diffraction technique having possible applications to catalysis, The Robert A. Welch Foundation Research Bulletin, 1961, No. 11. 

Cowley, J.M. (Ed.) (1993) Electron Diffraction Techniques, Oxford University Press, Oxford. 

X-ray, neutron, and electron diffraction techniques are used to determine crystal structures and can thus be used for molecular structure determinations. Because of its high resolution and applicability to small and often weakly diffracting samples, x-ray crystallography and powder diffraction are by far the methods of choice for most structure determinations on crystalline compounds,... 

Abstract The main types of electron diffraction techniques are described Selected-Area... 

Convergent-Beam eleetron Diffraction and Microdiffraction) become available on analytical transmission electron microscopes. Most of the electron diffraction techniques use a stationary incident beam, but some specific methods like the precession method take advantage of a moving incident beam. 

Various electron diffraction techniques are available on modem transmission electron microscopes. Selected-Area Electron Diffraction (SAED) and Microdiffraction are performed with a parallel or nearly parallel incident beam and give spot patterns. Convergent-Beam Electron Diffraction (CBED) and Large-Angle Convergent-Beam Electron Diffraction (LACBED) are performed with a focused and defocused convergent beam... 

Vainshtein B.K., Zvyagin B.B., Avilov A.S. (1992) Electron diffraction structure analysis. In Electron diffraction techniques Vol. 1 (Ed. J. Cowley), lUCr Monographs on Crystallography, Oxford Science Publications, pp. 216-312. 

Hargittai, L, Hargittai, M., Eds., Stereochemical Applications of Gas-Phase Electron Diffraction. Part A The Electron Diffraction Technique Part B Stmctural Information for Selected Classes of Compounds. VCH, New York, 1988. 

Boron is a light atom. Compared with other atoms in the crystal, B has a relatively stronger scattering power for electrons than that for X-ray. Thus the electron diffraction technique has been successfully applied to study positions of boron atoms in several other crystals [10, 29]. We study the position of B atoms in the crystal of (Yo eCao 4)(SrBa)(Cu2 5B0 5)07 s by means of the image processing technique. 

BK Vainshtein, BB Zvyagin, AS Avilov. Electron diffraction structure analysis, in Electron Diffraction Techniques, Vol. 1, J.M. Cowley, ed., Oxford Univ. Press, Oxford, 1992, pp. 216-312. 

By the early fifties a technique was developed mainly by J. and I. L. Karle to quantitatively treat the experimental data in order to obtain accurate geometrical and vibrational parameters. The new technique was called the sector-microphotometer method. As the name has been used ever since, today it has a wider meaning than just a reference to the experimental technique, and it usually signifies all the experimental, computational, and theoretical developments of the electron diffraction technique. 

No direct method exists by which monolayer film structures on water can be studied. Therefore, the LB method has been used to study molecular structures in past decades. The most useful method for investigating the detailed LB-deposited film structure is the well-known electron diffraction technique (or the scanning probe microscope [Birdi, 2002a]). The molecular arrangements of deposited mono-and multilayer films of fatty acids and their salts, using this technique, have been reported. The analyses showed that the molecules were almost perpendicular to the solid surface in the first monolayer. It was also reported that Ba-stearate molecules have a more precise normal alignment compared to stearic-acid monolayers. In some investigations, the thermal stability of these films has been found to be remarkably stable up to 90°C. 

Based on structural analyses obtained by the electron diffraction technique, the deposited films are known to be monocrystalline in nature, and thus, can be regarded as a special case of a layer-bilayer mechanical growth forming almost two-dimensional crystals. However, there is evidence that Ba-behenate multilayers do in fact show absence of crystallization, as demonstrated by electron micrographic studies. 

Electron diffraction techniques, Volume 1 J. M. Cowley, editor... 

We shall now show some examples of studies on shear compounds performed using electron microscope (lattice image and structure image) and electron diffraction techniques. Figure 2.13 shows the lattice image of a slightly reduced WO3 ( the bundle of black lines (lattice image)... 

A large effort has been expended in order to determine accurately the structures of the ylides using a variety of techniques. Single-crystal X-ray structures of over 40 ylides have been reported. Three small ylides have been characterized in the gas phase using electron diffraction techniques. While theoretical chemists had restricted their studies to methyl-enephosphorane, recent advances in computational techniques3 and computer hardware have allowed for the geometry optimization of larger ylides. 

---