Electron Microscopy - a Review

As often in the history of science the development started practically. The German engineer Ernst Ruska (1906-88) worked with cathode rays and oscilloscopes and, at the age of 25, built the first electron microscope in 1931. He also managed the manufacture of the first commercial electron microscope at the end of the 1930s. Almost 50 years later he received the Nobel Prize for physics. During his active time he was professor of electron-optics at the University of Technology in Berlin and worked at Siemens AG. He also became director of the Fritz Haber Institute for Electron Microscopy. 

In ordinary electron microscopes, TEM and SEM, the electrons pass through the specimen (TEM) or hit the specimen surface. In the latter case secondary electrons are set free and give information about the surface topography (SEM). 

Some electron microscopes utilize electrons from a needle with a very sharp tip, brought so close to the specimen surface that a quantum mechanical interaction arises between the electron cloud of the surface and the electron cloud of the atoms in the tip. This technique opened a fantastic way to really see individual atoms. This microscope, the field ion microscope, was presented in 1956 by the German Erwin Muller, who could for the first time observe individual atoms in a tungsten tip. A widening of the technique, and in fact a new technique, came with the vacuum-tunnding microscope in 1978, developed by Gerd Binnig in Frankfurt and Heinrich Rohrer in Zurich. They shared the Nobel Prize in 1986 with Ernst Ruska. A further development of the field ion microscope is the 3-D atom probe, exemplified below. 

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Stirling, J. (1990) Immuno- and affinity probes for electron microscopy a review of labeling and preparation techniques. J. Histochem. Cytochem. 38, 145-157. 

The crystallographic data for these phases, including tables of calculated d-spacings and intensities for X-ray powder diffraction patterns, have been collected in Chapter 13. Characterization by electron microscopy, a particularly important technique because of the nature of the materials, is reviewed in Chapters 14 and IS. 

Hgure 2 Typical phase-contrast transfer function of a high-resolution 200 kV TEM for LaBe and field-emission guns. (Reprinted with permission from Coene W, Janssen G, Op de Beeck M, and Van Dyck D (1992) Phase retrieval through focus variation for ultra-resolution in field-emission transmission electron microscopy. Physical Review Letters 69 3743-3746. American Physical Society.) (Courtesy of Dr. W. Coene, Philips Research Laboratory, Eindhoven.)... 

Among the different gene transfer techniques, microinjection is by far the most efficient procedure. Only microinjection allows the transfer of a known number of test molecules either into the cytoplasm or into the nuclei of the recipient cell Up to 100% of the recipient cells support expression of the transferred material, and stable transformed cell lines can be isolated with a frequency of 20-30%. Biochemical studies can be performed with 50-100 injected cells, and the injected material (e.g., DNA, RNA) can be reisolated and further analyzed by standard techniques (e.g., Southern and Northern blots, electron microscopy) (for review, see Graessmann and Graessmann, 1983 Graessmann et al., 1983 Ceiis et al., 1986). 

X-ray diffraction (XRD) is a useful, complementary tool in the structural characterization of porous silicon (pSi), providing information not readily available from direct visualization techniques such as electron microscopies. This review outlines key considerations in the use of diffraction techniques for analyses of this material in both thin film form and freestanding porous Si nano or microparticles. Examples of the range of content in the analysis of pSi are provided, ineluding formation mechanisms, layer thickness, extent of pSi oxidation, and degree of crystallinity. Such properties influence practical properties of pSi such as its biodegradability. We also focus on selected key properties where XRD has been particularly informative (a) strain, (b) the structural analysis of pSi multilayers, and (c) an analysis of pSi loaded with small molecules of fundamental or therapeutic interest. 

Khulbe, K. C., and Matsuura, T. (2000). Characterization of synthetic membranes by Raman spectroscopy, electron spin resonance, and atomic force microscopy a review. Polymer 41, 1917. 

High Resolution Transmission Electron Microscopy and Associated Techniques. (P. R. Buseck, J. M. Cowley, and L. Eyring, eds.) Oxford University Press, New York, 1988. A review covering these techniques in detail (except X-ray microanalysis) including extensive material on high-resolution TEM. 

Particle Formation, Electron microscopy and optical microscopy are the diagnostic tools most often used to study particle formation and growth in precipitation polymerizations (7 8). However, in typical polymerizations of this type, the particle formation is normally completed in a few seconds or tens of seconds after the start of the reaction (9 ), and the physical processes which are involved are difficult to measure in a real time manner. As a result, the actual particle formation mechanism is open to a variety of interpretations and the results could fit more than one theoretical model. Barrett and Thomas (10) have presented an excellent review of the four physical processes involved in the particle formation oligomer growth in the diluent oligomer precipitation to form particle nuclei capture of oligomers by particle nuclei, and coalescence or agglomeration of primary particles. 

In addition, data obtained from infrared, thermal, and fluorescence spectroscopic studies of the outermost layer of skin, stratum corneum (SC), and its components imply enhancer-improved permeation of solutes through the SC is associated with alterations involving the hydrocarbon chains of the SC lipid components. Data obtained from electron microscopy and x-ray diffraction reveals that the disordering of the lamellar packing is also an important mechanism for increased permeation of drugs induced by penetration enhancers (for a recent review, see Ref. 206). 

Transition metal oxides, rare earth oxides and various metal complexes deposited on their surface are typical phases of DeNO catalysts that lead to redox properties. For each of these phases, complementary tools exist for a proper characterization of the metal coordination number, oxidation state or nuclearity. Among all the techniques such as EPR [80], UV-vis [81] and IR, Raman, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and NMR, recently reviewed [82] for their application in the study of supported molecular metal complexes, Raman and IR spectroscopies are the only ones we will focus on. The major advantages offered by these spectroscopic techniques are that (1) they can detect XRD inactive amorphous surface metal oxide phases as well as crystalline nanophases and (2) they are able to collect information under various environmental conditions [83], We will describe their contributions to the study of both the support (oxide) and the deposited phase (metal complex). 

A review of preparative methods for metal sols (colloidal metal particles) suspended in solution is given. The problems involved with the preparation and stabilization of non-aqueous metal colloidal particles are noted. A new method is described for preparing non-aqueous metal sols based on the clustering of solvated metal atoms (from metal vaporization) in cold organic solvents. Gold-acetone colloidal solutions are discussed in detail, especially their preparation, control of particle size (2-9 nm), electrophoresis measurements, electron microscopy, GC-MS, resistivity, and related studies. Particle stabilization involves both electrostatic and steric mechanisms and these are discussed in comparison with aqueous systems. 

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