Transmission electron-microscopy

An electron gun delivers the electron beam, as in SEM, and the microscope column is under high vacuum also. 

The computer controls the scanning coils and also manipulates the data received by the detectors. 

It is now possible to obtain scanning transmission electron microscopes (STEMs). With a STEM, the electrons pass through the specimen but, as in SEM, the electron optics focus the beam into a narrow spot that is scanned over the sample in a raster. This makes these microscopes suitable for analysis techniques such as mapping by energy dispersive X-ray (EDX) spectroscopy among others. Also, the resolution on the latest STEM instruments is less than one Angstrom. 

A technique called cryogenic temperature transmission electron microscopy (cryo-TEM) has been used by biologists for some years but is now also being used by chemists to examine a wide range of samples. CryoTEM involves the fast cooling of a thin film of liquid sample and transferring the sample into the TEM where it is maintained at 

Scanning electron microscope Topological structure 40X-300KX 15 

Notes TSEM is a mode of the transmission electron miorosorope. Approximate value, see references In text. 

Fljring-spot instruments permit point-by-point analysis of surface properties. At first, it would appear that transmission electron microscopes, which illuminate an entire sample, would not be suitable for such an application, and in general, this is so. However, a new transmission electron microscope named EMMA 4 has been developed with combined transmission electron microscope and probe capability by introducing a minilens into the illumination system (Cook etal, 1969 Jacobs, 1971). The EMMA 4 has demonstrated eonsiderable power in a number of applications and could easily be applied to surfaees, but it will not be further considered here because our primary emphasis is on the topography of paint. 

This subject is too broad to permit detailed description of any kind of microscope or of the theory by which it is employed. Since many excellent books have been written on the microscope itself (Klemperer, 1953 Thomas, 1962 Haine eta/., 1961 Heidenreich, 1964 Grivet, 1965 Hirsh e/a/. 1965 Amelinckx, 1964, 1970 Hall, 1966 Wyckofi 1949) on methods of preparing specimens (Wyckofi 1949 Kay, 1961 Thomas, 1971), and on the theory of contrast (Heidenreich, 1964 Hirsh eta/., 1965 Amelinckx, 1964, 1970), only a very brief description is provided of contrast principles, specimen preparation methods and applications where replication and sectioning techniques have been successfidly employed to study surfaces. 

Although this method of obtaining contrast is quite general, the scattering processes involved vary widely for different materials thus, it is convenient to 

The identification of the electron by J.J. Thomson in 1897 [1] was one of the most important scientific discoveries of aU time, and changed human life completely. In 1924, the theory of the wave motion of the electron was established by Louis de Broglie [2]. From the wave motion of the electron comes one of the most fascinating and powerful applications of the electron, namely the electron microscope. The first electron diffraction experiments were performed by G.P. Thomson in 1927 [3], proving Louis de Broglie s theory. The first electron microscope was constructed by Ruska and Knoll in 1931. 

Although the theory of electron optics was established many years ago, technical developments of TEM continue. It is well known that a crystal structure can be 

Metal Oxide Catalysis. Edited by S. David Jackson and Justin S. J. Hargreaves Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31815-5 

Transmission electron microscopy (TEM) is a powerful technique that is used to determine the microstructure of materials at very high resolution (2-10 nm size). Because the technique requires a very thin specimen, special sample preparation methods have been developed such as ultramicrotomy and ion milling. 

Thus the end user is required to apply significant amount of energy to redisperse the agglomerates in order to realize the full potential of the pigment. 

In order to use electron microscopy to visualise the microemulsion structure, the problem of the fixation of the liquid mixtures has to be solved. The method of choice is to solidify the microemulsion structure via cryofixation. However, given that the phase behaviour as well as the curvature of the amphiphilic film (see Fig. 1.18) and with it the microstructure of most micro emulsions show a strong temperature-dependence it has to be ensured that the cooling rate should be as high ( 104 K/s) and the reorganisation kinetics of the microstructure as slow as possible. 

Three different techniques, namely FFEM [20, 22], Cryo-Direct Imaging (Cryo-DI) [104] and freeze-fracture direct imaging (FFDI) [105], can be used to visualise the structure of micro emulsions. In FFEM the samples are prepared in a protected fashion in a sandwich. They are then rapidly frozen, fractured, shadowed with metal, and replicated with a thin carbon film. The replica of the fractured surface, the morphology of which is controlled by the sample s microstructure, is then studied by a TEM. In contrast to FFEM, in Cryo-DI thin films of the sample are rapidly frozen but immediately, without replication, trans- 

In conclusion, the transmission electron microscopy images show that for mixtures of water, oil and long-chain non-ionic surfactants the structure gradually changes with 

Since the introduction of transmission electron microscopy in the 1930s, it has become an immensely valuable and versatile technique for the characterization of materials. TEM s high magnification and resolving power allow 

Compared to SEM, where reflecting electrons are utilized to examine a bulk material surface, TEM does not discern any topographic information because it examines thin films with transmitted electrons. The thin-film sample preparation is more complicated, and the TEM operation requires more training as well. The interpretation of a TEM image requires a good understanding of electron microscopy and the structure of the material. 

An elemental composition analysis is also feasible in an analytical TEM based on the physics of chromatic aberration of electrons when they pass through the thin sample. The interactions between the passing electrons and the constituent elements result in various levels of energy loss. An electron energy loss spectroscopy then forms an image showing a characteristic elemental map of the sample based on the atomic absorption of these interactions. 

When the structure cannot be characterized by optical microscopy, transmission electron microscopy comes to the fore, although scanning electron microscopy and or replica techniques are also often helpful. Most of the work to date utilizes osmium tetroxide as a stain. Samples that cannot be stained by osmium tetroxide or another similar agent often cannot be studied by electron microscopy, because the phases cannot be distinguished. Sometimes, a double bond is deliberately added in small quantities during the synthesis to facilitate staining with osmium tetroxide. This is easy to do in acrylic or styrene based systems with an addition of a trace of butadiene or isoprene. 

The Transmission Electron Microscope (TEM) was the first type of electron microscope to be developed and is patterned exactly on the Light Transmission Microscope, except that a focused beam of electrons is used instead of light to see through the specimen. It was developed by Max Knoll and Ernst Ruska in Germany in 1932, 35 years after J. J. Thompson s discovery of the electron. The technique quickly surpassed the resolution of optical microscopy, and in 1938 the first commercial instruments began to be produced by the Siemens-Halske Company in Berlin [85]. 

Using an electron microscope offers the advantages of increased magnification and resolution. The TEM passes an accelerated electron beam flirough a thin sample (50-300 A). Some of the electrons are scattered by the atoms in the sample. 

A phase distortion is created, resulting in a phase contrast that is used to create the image. The TEM enables the operator to see the inside of the sample rather than 

The main use of the Transmission Electron Microscope is to examine the structure, composition, or properties of a specimen in submicroscopic detail. One can see objects to the order of a few Angstroms (10 m). For example, it is possible to study small details in a cell or within inorganic materials down to near-atomic levels. The possibility for high magnifications has made the TEM a valuable tool in numerous fields such as biological, medical, and materials research. 

SEM instruments have resolutions better than 5 nm and are useful for the characte-ization of surfaces and the determination of surface topography. Contrary to transmission electron microscopy (TEM), little sample preparation is required. For polymCTs, which are poor conductors, problems associated with chaige buildup ueed to be ovCTcome. 

In addition to detecting backscattered and secondary electrons, SEM instruments offer information on the sample elemental composition when using x-ray detectors. It has been pointed out earher that the ejection of electrons from an atom is accompanied by emission of x-rays. The x-ray spectrum that is produced is a characteristic feature of any given element, and by measming the energy or the wavelength of the x-rays that are produced, its ideutihcation is possible. 

Transmission electron microscopy (TEM) is used to analyze very thin samples (less than 100 nm thick), provided that the specimen has structural features that scatter electrons in difframt amounts. One of the main problems with using TEM for polymers is that these arc made up of low-atomic-number elements, which are low scatterCTs of electrons. Low scattoing and the fact that there is little spatial variation in electron density in a polymer sample leads to poor contrast. One way to overcome this problem is to stain the specimen with a heavy metal, such as uranium or osmium, that preferentially attaches itself to certain regions of the sample. 

Different techniques can be used to enhance the contrast. For example, dark-held images can be produced by blocking the transmitted electrons and using only the scattered electrons. 

4 Atomic Force Microscopy and Scanning Tunneling Microscopy 

Kreshiy-deaved mica or cleaned glass slide 

The typical thickness of amorphous carbon Aims is 2-5 nm, whereas polymer Aims have thicknesses on the order of 30 nm. As you might expect, all plastic Aims are subject to decomposition by the electron beam. Sometimes, this exposure also causes further crosslinking which will cause the Aim to shrink and become more brittle. The 

The most common staining agents are aqueous solutions (co. 2 wt% concentration) 

Due to the high spatial resolution and predictive scattering modes, TEMs are often employed to determine the three-dimensional crystal structure of solid-state 

In order to understand the information contained within the diffraction pattern of a crystal lattice, it is necessary to construct a secondary lattice known as a reciprocal lattice. This lattice is related to the real crystalline array by the following 

Hirsch obtained his Ph.D. and went olT into industry in 195.2 he was aw ardcd a fellowship which allowed him to return to Cambridge, and here he set out, 

The key here was the theory. The pioneers familiarity with both the kinematic and the dynamic theory of diffraction and with the real structure of real crystals (the subject-matter of Lai s review cited in Section 4.2.4) enabled them to work out, by degrees, how to get good contrast for dislocations of various kinds and, later, other defects such as stacking-faults. Several other physicists who have since become well known, such as A. Kelly and J. Menter, were also involved Hirsch goes to considerable pains in his 1986 paper to attribute credit to all those who played a major part. 

To form an idea of the highly sophisticated nature of the analysis of image formation, it suffices to refer to some of the classics of this field - notably the early book by Hirsch et al. (1965), a recent study in depth by Amelinckx (1992) and a book from Australia devoted to the theory of image formation and its simulation in the study of interfaces (Forwood and Clarebrough 1991). 

Transmission electron microscopes (TEM) with their variants (scanning transmission microscopes, analytical microscopes, high-resolution microscopes, high-voltage microscopes) are now crucial tools in the study of materials crystal defects of all kinds, radiation damage, ofif-stoichiometric compounds, features of atomic order, polyphase microstructures, stages in phase transformations, orientation relationships between phases, recrystallisation, local textures, compositions of phases... there is no end to the features that are today studied by TEM. Newbury and Williams (2000) have surveyed the place of the electron microscope as the materials characterisation tool of the millennium . 

A special mention is in order of high-resolution electron microscopy (HREM), a variant that permits columns of atoms normal to the specimen surface to be imaged the resolution is better than an atomic diameter, but the nature of the image is not safely interpretable without the use of computer simulation of images to check whether the assumed interpretation matches what is actually seen. Solid-state chemists studying complex, non-stoichiometric oxides found this image simulation approach essential for their work. The technique has proved immensely powerful, especially with respect to the many types of defect that are found in microstructures. 

Department of Earth and Planetary Science Graduate School of Science, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-0033 Japan 

An early study of mica by HRTEM was reported by Buseck and lijima (1974). They clearly observed three dark lines representing a mica layer (the lines correspond to the two tetrahedral sheets and one octahedral sheet) and that cleavage was formed at the interlayer. During a quarter century after this pioneering work, many HRTEM studies for mica and related phyllosilicates have been reported (for instance, see the references in Baronnet 1992). These included many studies of mica, e.g., polytypism, transformations, defects and interface research. In the following section, recent HRTEM and related techniques are briefly reviewed. Next, two topics of HRTEM investigation, polytype and defect analyses are presented based on studies, mainly by the author and his colleagues. 

TEMS AND RELATED TECHNIQUES FOR THE INVESTIGATION OF MICA Transmission electron microscopy 

Muscovite-2Mi viewed along [100], (b) Annite-2Mi viewed along [100]. (c) Annite-2Mi viewed along [010]. The parameters for the simulation are defocus = -42 nm (Scherzer focus) and specimen thickness = 2.5 nm. 

Probably, 200 kV TEMs with a point resolution of 0.15 nm will be available in the near future. FE is necessary for such next generation TEMs because such a low point resolution defined by the above equation cannot be attained with TE owing to its limited coherency of the electron wave. 

The alignment of CNTs can be quantified by evaluation of the correlation function. In contrast to other techniques, an orientation factor O,. for low filled composites and 

In membrane application studies, imaging by TEM showed the presence of an irreversible biofilm on the fouled membrane used to filter surface water in reverse osmosis [22]. Then, quantitative analysis on the spatial arrangements and cellular ultrastructures of biofilm layer growth on a supporting surface was also clearly 

Sample preparations Dried and coated with gold or carbon Lightly coated with platinum Not required Thinly sliced and stained 

Sample conditions Dried Dried Dried or wet Dried 

The differences of the electron microscope techniques (SEM, FESEM, ESEM, TEM) in terms of sample preparations, sample conditions, resolutions and acceleration voltage are listed in Table 14.2. 

AFM analysis can provide an insight of sample morphology, giving important information on single colloid/cell interaction on a substrate [53]. The interaction forces between surface and probe can be measured and plotted as a function of its distance, giving an indication of the strength of adhesive forces [56]. The adhesion 

The characterization of the interfacial chemical reactions and the reaction kinetics are very challenging topics in this area. In fact the quantitative analysis of the interfacial chemical reactions and reaction kinetics has still to be performed for most of the melt reactions despite their crucial importance for the understanding of the relationship between melt reactions, blend phase morphology and ultimate properties. The copolymer generated as a result of the interfacial reactions is difficult to separate and to characterize. Several investigations are still being made to identify and characterize the in situ formed copolymer. 

It is also important to mention that further in-depth studies have to be undertaken for the quantitative analysis of the phase morphology development, phase co-continuity, phase stability, and the crystallization behavior of several reactive blend systems. 

Finally since reactive blending often gives rise to thicker interfaces, the characterization of the interfacial layer thickness is very important. Several sophisticated techniques such as neutron reflectometry, ellipsometry, and TEM are being used for this purpose. 

The authors are indebted to the Research Council of the KU Leuven for fellowships to two of them (S.T. and C.H.) and to the Fund for Scientific Research-Flanders (Belgium) for the financial support given to the MSC laboratory. 

Heikens, N. Hoen, W. Barentsen, P. Piet and H. Ladan, J. Polym. Sci. Polym. Symp., 62, 309 (1978). D.R. Paul and S. Newman (Eds) Polymer Blends , Chap. 12, Academic Press, New York (1978). 

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Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

Thomas G and Goringe M J 1981 Transmission Electron Microscopy of Materials (New York Wiiey)... 

The history of EM (for an overview see table Bl.17,1) can be interpreted as the development of two concepts the electron beam either illuminates a large area of tire sample ( flood-beam illumination , as in the typical transmission electron microscope (TEM) imaging using a spread-out beam) or just one point, i.e. focused to the smallest spot possible, which is then scaimed across the sample (scaiming transmission electron microscopy (STEM) or scaiming electron microscopy (SEM)). In both situations the electron beam is considered as a matter wave interacting with the sample and microscopy simply studies the interaction of the scattered electrons. 

Williams D B and Carter C B 1996 Transmission Electron Microscopy, A Textbook for Material Science (New York Plenum)... 

Reimer L 1993 Transmission Electron Microscopy (Berlin Springer)... 

The spatial arrangement of atoms in two-dimensional protein arrays can be detennined using high-resolution transmission electron microscopy [20]. The measurements have to be carried out in high vacuum, but since tire metliod is used above all for investigating membrane proteins, it may be supposed tliat tire presence of tire lipid bilayer ensures tliat tire protein remains essentially in its native configuration. 

In many ways the nanocrystal characterization problem is an ideal one for transmission electron microscopy (TEM). Here, an electron beam is used to image a thin sample in transmission mode [119]. The resolution is a sensitive fimction of the beam voltage and electron optics a low-resolution microscope operating at 100 kV might... 

L. Reimer, Transmission Electron Microscopy, Springer Series in Optical Sciences, Vol. 36, 2nd ed., Springer-Vedag Berlin, 1989. 

The very high powers of magnification afforded by the electron microscope, either scanning electron microscopy (sem) or scanning transmission electron microscopy (stem), are used for identification of items such as wood species, in technological studies of ancient metals or ceramics, and especially in the study of deterioration processes taking place in various types of art objects. 

Fig. 6. Microstmcture of transparent P-quart2 soHd solution glass-ceramic as revealed by transmission electron microscopy (white bat = 0.1 jira).

Nylon-6. Nylon-6—clay nanometer composites using montmorillonite clay intercalated with 12-aminolauric acid have been produced (37,38). When mixed with S-caprolactam and polymerized at 100°C for 30 min, a nylon clay—hybrid (NCH) was produced. Transmission electron microscopy (tern) and x-ray diffraction of the NCH confirm both the intercalation and molecular level of mixing between the two phases. The benefits of such materials over ordinary nylon-6 or nonmolecularly mixed, clay-reinforced nylon-6 include increased heat distortion temperature, elastic modulus, tensile strength, and dynamic elastic modulus throughout the —150 to 250°C temperature range. 

Transmission electron microscopy (tern) is used to analyze the stmcture of crystals, such as distinguishing between amorphous siUcon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain stmctures. Tern requires samples that are very thin (10—50 nm) sections, and is a destmctive as well as time-consuming method of analysis. 

The mechanism for coercivity in the Cr—Co—Fe alloys appears to be pinning of domain walls. The magnetic domains extend through particles of both phases. The evidence from transmission electron microscopy studies and measurement of JT, and anisotropy vs T is that the walls are trapped locally by fluctuations in saturation magnetization. 

Transmission electron microscopy is very widely used by biologists as well as materials scientists. The advantage of being able to resolve 0.2 nm outweighs the disadvantages of TEM. The disadvantages include the inabiUty of the common 100-kV electron beam to penetrate more than a few tenths of a micrometer (a 1000-kV beam, rarely used, penetrates specimens about 10 times thicker). Specimen preparation for the TEM is difficult because of the... 

An excellent historical account of the beginning of transmission electron microscopy in North America is available (22). 

The properties and performance of cemented carbide tools depend not only on the type and amount of carbide but also on carbide grain size and the amount of biader metal. Information on porosity, grain size and distribution of WC, soHd solution cubic carbides, and the metallic biader phase is obtained from metaHographicaHy poHshed samples. Optical microscopy and scanning and transmission electron microscopy are employed for microstmctural evaluation. Typical microstmctures of cemented carbides are shown ia Figure 3. 

A progressive etching technique (39,40), combined with x-ray diffraction analysis, revealed the presence of a number of a polytypes within a single crystal of sihcon carbide. Work using lattice imaging techniques via transmission electron microscopy has shown that a-siUcon carbide formed by transformation from the P-phase (cubic) can consist of a number of the a polytypes in a syntactic array (41). 

Occasionally, especially in the developmental phase of catalyst research, it is necessary to determine the oxidation state, exact location, and dispersion of various elements in the catalyst. Eor these studies, either transmission electron microscopy (TEM) or scanning electron microscopy (SEM) combined with various high vacuum x-ray, electron, and ion spectroscopies are used routinely. 

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