Microscopy, electron scanning

Scanning electron microscopes operate under high vacuum, but ice cream at normal processing or storage temperatures would not be stable under these conditions because the ice would sublime and the structure would collapse. However, ice cream is stable below —100 °C at this temperature the vapour pressure of ice is zero so there is no sublimation, and the matrix is glassy so the ice cream is sufficiently robust to survive the pressure change. 

To prepare suitable samples, a small piece (approximately 5x5 mm X 10 mm) is cut from the centre of a block of ice cream with a cold scalpel blade to prevent melting. This is mounted on a sample holder and plunged into liquid nitrogen or nitrogen slush (a mixture of solid and liquid nitrogen at about —200 C). The very rapid cooling fixes the 

Scanning electron microscopy (SEM) uses a focused electron beam to survey a surface of interest. The working principle of SEM is very similar to that of optical microscopy but with an approximately 250 times higher resolution. The electrons 

Polyurethane degradation is a common issue for polyurethane-based medical implants. The degradation mechanisms vary depending on the type of polyurethane used and their environment. For example, polyester polyurethane undergoes hydrolytic 

Scanning electron microscopy (SEM) is currently the most popular of the microscopic techniques because of the user-friendliness of the apparatus, the ease of specimen preparation, and the general simplicity of image interpretation. The obvious limitation is that only surface features are easily accessible. 

The yield of reflected backscattered electrons (BSE) increases with increasing atomic number of the sample material. Elements with a higher atomic number offer a higher probability of backscattered electrons, giving an additional atomic number contrast material contrast) to the surface topograp y contrast. 

3 Scanning electron microscopy. X-ray diffraction and other techniques 

The intensity of the electrons backscattered from a particular region of a specimen depends approximately on the mean atomic number of the material of which that region is composed more precisely, it is represented by the backscattering coefficient, q, which may be calculated from the formulae  

The application of image analysis to SEM is a rapidly developing technique, and further development may be expected. In addition to giving areas of phases, it can provide information on such matters as the distributions of shape, size and surroundings of particles and of phases and pores within them. It is, of course, essential to examine a sufficient number of samples and fields to ensure that the results are representative, but the labour and subjectivity associated with light microscopic studies of a comparable nature are largely eliminated. 

In scanning electron microscopy (SEM), a focused electron beam scans the sample surface. The electron beam-sample interaction includes various processes to produce different types of radiations, which could be collected by suitable detectors and processed further to form an image of the surface under study. Useful information about the surface morphology, chemical composition can be obtained from the SEM analysis. 

9 Atomic force microscopy and scanning tunnelling microscopy 

As demonstrated above, surfaces play a crucial role in determining the polymorphic outcome of a crystallization. Hence, the smdy of the structure of surfaces and their interaction with a crystallizing material can provide detailed information on the nature of the process. That information may be used to design experiments and processes for the study of nucleation and the selective control of the growth of a particular crystal modification (Palmore et al. 1998) (Section 3.7). These AFM and STM techniques (and rapidly developing spin-off modifications of them) provide that information (Frommer 1992 Ward 1997). For instance, tapping mode atomic force microscopy 

Scanning transmission electron microscopy (STEM), coupled with EDX, has been used to determine metal particle sizes. The specimens for STEM are prepared by dispersing the sample ultrasonicaUy in methanol and placing one drop of the suspension onto a Formvar film supported on a copper grid. 

Sample preparation is easy compared to the transmission electron microscope. Specimens of nearly any size can be examined since it is unnecessary to thin specimens to 100 A thickness. For insulators, a thin layer of gold or carbon about 50 A thick is evaporated on the surface to prevent charge accumulation, although even this often proves to be unnecessary. Finally, the ease of operation and the correspondence of the image to normal vision put this instrument into a unique class. 

Connecting a computer directly to the SEM makes it possible to do quantitative petrography on a scale and with a precision not conceived a decade ago. The particle size, shape, and chemical composition can be automatically determined on either a loose powder or aggregate or a surface of a polycrystalline polyphase body at a speed of roughly 100 sec per frame.  

The electron mirror microscope is still a research instrument. It has a rather low resolution (about 800 A), and the electrostatic lens used gives problems. It is particularly suited for examination of electric and magnetic patterns, but is not yet an instrument of general utility. 

The field emission microscope and the field ion microscope are used primarily in the study of surface phenomena. With the field emission microscope, one can determine how the electron work function varies with crystallographic orientation, and how it is affected by the absorption of foreign materials. Magnifications of better than a million make it possible to observe effects on an atomic scale. Individual atoms and adsorbed molecules can be located with the field ion microscope. Very recently Muller has adapted a mass spectrometer to the field ion microscope so that, in principle, single atoms may be imaged, evaporated, and analyzed. Unfortunately, the field methods are severely limited with respect to the materials that can be studied. Only highly conducting metals can be used, and then they must be thinned to a very sharp point. Some work has been done on molecules adsorbed on the points but this is also very limited. 

The electron beam is rastered across the sample via the scanning coils by ramping voltages on the X- and y-deflection plates through which the electron beam passes (the z-axis is the electron-beam direction). 

The sample can be viewed by detecting back-scattered electrons, secondary electrons or even X-rays emitted by the sample. Each type of detection can give different information about the sample. 

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

Scanning electron microscopy gives the following qualitative information topography (the surface features of an object and their texture), morphology (the shape, size and 

A recent innovation in electron microscopy is environmental SEM, which allows samples to be studied at pressures and humidities that approach ambient conditions. To achieve this, several stages of differential pumping between the electron gun and the sample are used, and the sample itself is placed in a vacuum of a few hundred Pascals. Environmental SEM enables many materials to be examined without pretreatment, unlike conventional SEM, in which specimens must be solid, dry and usually electrically conductive. This now makes possible studies of the natural, unadulterated surfaces of specimens such as polymers, biological tissues and cells, food and drugs and forensic materials. 

Acronyms SEM scanning electron microscopy, SEMPA scanning electron microscopy with polarisation analysis, EDX energy dispersive X-ray analysis, EPMA electron probe microanalysis, STkM scanning Auger microscopy. 

When secondary electrons are emitted from a magnetic material they become polarised and so by using a polarisation sensitive detector such as a Mott detector to collect the secondary electrons an image can be obtained that has magnetic contrast, allowing magnetic domain structures to be studied. This technique is known as scanning electron microscopy with polarization analysis (SEMPA). 

Images with elemental contrast can be obtained by detecting the high energy backscattered electrons, whose intensity is a function of the atomic number of the elements in the sample. These electrons also have a greater penetration depth than secondary electrons and so can be used for studying buried structures. 

Quantitative information about the elemental distribution and concentration can be obtained by analysing the energies of the X-rays emitted, which are characteristic of the elements involved. This is known as energy dispersive X-ray analysis (EDX) or electron probe microanalysis (EPMA). It is essentially a bulk technique that reveals composition down to a depth of several microns. 

Principles and Characteristics The scanning electron microscope (SEM) is often the analytical element of choice when the light microscope no longer provides adequate resolution. In 

SEM requires little sample preparation for metallic and inorganic materials as the information required concerns only the surface structure and the material composition of the layer proximate to the surface. Small samples of up to several millimetres and sometimes even larger can be investigated directly in the SEM if the sample material has a sufficiently high electric conductivity to prevent charging produced by electron bombardment. However, 

State-of-the-art analytical capability now provides a chemical and structural analyser for SEM, 

SEM and AEM are complementary techniques for surface investigations. However, the image formation mechanisms are quite dififerenfi resulting in different types of information about the surface structure. By using two techniques which are complementary, one technique will often compensate for imaging artefacts of the other. 

Detailed reviews are available [53,134,141-144], The principles of operation of SEM are well covered in the literature cfr. Bibliography). Quantitative SEM is described in ref. [145]. 

FIGURE 10.12 Illustration of the types of radiation produced following interaction of an electron beam with a specimen. 

Several authors have used scanning electron microscopy (SEM] to observe surface details in chitosan-starch films. Only some studies that coincide with the use of other described techniques are reviewed in this section. 

The morphological structures of chitosan-starch films were studied by SEM, and revealed rough and irregular surface with bubbles, besides it was found that exist a good interfacial adhesion between the two components (Figs. 15.9 and 15.10] (Mathew et al., 2006 Mathew and Abraham, 2008]. On the other hand, Akter 

Flores-Hernandez et al. (2014) observed that in the fracture surface (Fig. 15.12) streaks caused by a stress rupture were formed. They were able to appreciate that there was a consistency between chitosan and starch, which could be attributed to the microdomains of chitosan that were well dispersed in the starch matrk achieving good interfacial adhesion between these two biopol5miers. 

It was found that no matter which type of starch or chitosan was present, the TS values of the composite films increase with the addition of any of these polysaccharides and the starch-chitosan blend films exhibit significantly higher elongation values compared to films made only with starch or chitosan (Shen et al., 2010 Mathew et al., 2006 Mathew and Abraham, 2008 Akter et al., 2012 Wu et al., 2010 Xu et al., 2005 Baran et al., 2004). 

Pelissari et al. (2012) studied the performance of TS of chitosan-starch films produced by extrusion using glycerol as plasticizer. They reported the systems with highest concentrations of starch and chitosan as the more resistant films with TS values 

2 IMAGING THE BIO-NANO INTERFACE 13.2.1 Scanning Electron Microscopy 

FIGURE 13.1 Schematic showing the aspects of a scanning electron microscope and a representative image of a black widow spider at lOOx magnification. (Unpublished images taken by author KEF.) 

The structural properties of carbon aerogels have been investigated by scanning electron microscopy (SEM), nitrogen adsorption, and X-ray diffraction methods. Specific surface areas are determined by the standard BET (Brunauer-Emmett-Teller) analysis. X-ray diffraction (XRD) of the carbon aerogel is performed in a diffraction with CuKa radiation [54]. 

As was detailed in this section, TEM can bring numerous pieces of information regarding the polymer/nanotube composite microstructure. However, it has to be recalled that nanofillers such as nanotubes easily agglomerates and their dispersion state has to be characterised from the micron to the nanometre scale. This is one reason, among others, why Scanning Electron Microscopy is another widely used to characterise polymer/nanotube composites. 

Oatley and a succession of brilliant students, collaborating with others at the Cavendish Laboratory, by degrees developed an effective instrument a key component was an efficient plastic scintillation counter for the image-forming 

Run-of-the-mill instruments can achieve a resolution of 5-10 nm, while the best reach 1 nm. The remarkable depth of focus derives from the fact that a very small numerical aperture is used, and yet this feature does not spoil the resolution, which is not limited by dilfraction as it is in an optical microscope but rather by various forms of aberration. Scanning electron microscopes can undertake compositional analysis (but with much less accuracy than the instruments treated in the next section) and there is also a way of arranging image formation that allows atomic-number contrast, so that elements of different atomic number show up in various degrees of brightness on the image of a polished surface. 

Another new and much used variant is a procedure called orientation imaging microscopy (Adams ci al. 199.5) patterns created by electrons back-scattered from a grain are automatically interpreted by a computer program, then the grain examined is automatically changed, and finally the orientations so determined are used to create an image of the polycrystal with the grain boundaries colour- or thickness- 

The Stereoscan instruments were a triumphant success and their descendants, mostly made in Britain, France, Japan and the United States, have been sold in thousands over the years. They are indispensable components of modern materials science laboratories. Not only that, but they have uses which were not dreamt of when Oatley developed his first instruments thus, they are used today to image integrated microcircuits and to search for minute defects in them. 

Some instruments can take samples as large as 8 in. square and parts viewed at magnifications varying from 20x to 100,000x at resolutions of 5 to 7 nm. The latest instruments are capable of resolutions down to 0.7 nm. The depth of focus is nearly 300 times that of the optical microscope. Because of its great depth of focus the SEM can give considerable information about the surface texture of particles. 

Le Mont Scientific B-10 system features an energy-dispersive x-ray detector. Particles are loaded and interrogated to find size and shape various software options are available. The Bausch and Lomb system has also been applied to electron beam microscopy [l87,l88].rracor Northern describe an integrated system for the collection and processing of analytical and image data from SEM and STEM [l89,l90].Various sample preparation methods have been described. 

Used properly, the SEM-EDXA allows one to precisely elucidate some of the microstructural and compositional details unseen with other techniques of mi- 

Stutzman (1994) and Stutzman and Odler (1991) illustrated some of the profound implications in application of electron imaging in clinker and concrete analysis, demonstrating the details of microstructures at magnifications having resolutions of approximately 0.2 gm. 

Bonen and Diamond (1991) with image analysis comparisons of roller-milled and ball-milled cements illustrated that two major variants in cement performance are phase abimdance and phase specific surface, particularly in the finer fractions. Roller mill cements differed from ball mill cements in having fewer very small parficles, lower aspect ratios and shape factors, and differences in the content of particles of specific mineralogies. Alite was relatively enriched in the finest fractions of the ball-milled cement. 

In a laboratory study of grinding techniques (ball mill vs. roller mill) Chen and Odler (1992) showed that roller mill cements exhibit inferior quality because of higher water demand, resulting from adverse packing characteristics developed during grinding. Microscopically, clear cut differences were observed with regard to particle size, shape, Blaine, and additionally, dry bulk density and flow rates. 

Sarkar and Samet (1994), utilizing x-ray diffraction and light and electron microscopy, concluded that an abundance of a potassium-calcium sulfate (from excessive insufflation) and unusually large belite crystals (from long residence times) were responsible for low 

When anisotropic specimens such as fibers are rotated on the rotatable stage, they go through four extinction positions of minimum intensity and four positions of maximum intensity. In the extinction positions, the fiber orientation direction is aligned parallel to one polarization direction, at 0° or 90°. Maximum intensity is at the 45° positions (for an example, see Fig. 5.4). Circularly polarized light, obtained and analyzed by the addition of two crossed quarter-wave plates (marked A74) into the light path, one between each polar and the specimen, eliminates these extinction positions. All anisotropic specimens are bright between crossed circular polars regardless of their orientation. 

In principle, birefringence can be measured directly, by measuring the two refractive indices 

In white light, anisotropic structures may appear brightly colored when viewed in crossed (or parallel) polars. These polarization colors or interference colors depend on the retardation (see Section 3.1.7). An estimate of sample retardation can be made from the standard sequence of colors, published as the Michel-Levy chart in many texts [5, 8, 9, 26, 28]. Color can also be used to find the sign of a small retardation when a first-order red plate is inserted as a compensator in white light. Modem devices exist where the polarizing elements are electrically driven and computer controlled. These allow simultaneous measurement of retardation and orientation direction at every point on the image and thus the creation of retardation and orientation maps [29]. 

The scanning electron microscope (SEM) forms an image by scanning a probe, a focused electron beam, across the specimen. The probe 

They appear as though the specimen is viewed from the source of the scanning beam and illuminated by a light at the detector position. 

TEM has played a major role in the characterization of the ordered structures developed by block copolymers and in following the changes in morphology that accrue inhomopolymer/hlock copolymer mixtures such as (styrene-b-isoprene) (SI)/ polystyrene blends [128-130]. 

TEM can also be used to follow the development of structural features during spinodal decomposition [131] and reaction-induced phase separation [1]. 

Additional information can be obtained from energy-filtering transmission electron microscopy (EFTEM), a technique that makes it possible to create elemental distribution images through the analysis of the elemental compositions by electron energy loss spectroscopy. As shown by Horiuchi et al. for the PMMA/SAN immiscible blend, the technique can provide information on the blend composition in the interfacial region of a phase separated blend. 

SEM instruments have a resolution better than 5 nm and are useful for the characterization of surfaces and the determination of surface topography. Unlike TEM, little sample preparation is required. For polymers that are poor conductors problems associated vdth charge build-up need to be overcome. 

In addition to detecting backscattered and secondary electrons, SEM instruments may also offer information on the elemental composition of the sample. Interaction of the primary beam vhth the sample results in the emission of X-rays. Since the energy of the emitted X-rays is a specific feature of an atom, by measuring the energy or the wavelength of the X-rays that are produced it is possible to achieve quantitative analysis of elemental composition (energy dispersive X-ray spectroscopy or EDS). 

SEM has been applied to study on the surface morphology and cross-sectional morphology of the PFSA membranes and their composite membranes. Luan and coworkers carried out SEM study on surface morphology of PESA ionomer film prepared from DMF solution at different temperatures. The film prepared at low temperature is assembled loosely by sphere-like globules of about 20 nm, and some of the globules assembled to form aggregates about 60-150 nm, while the surface of 

SEM equipped with an energy-dispersive spectroscopy (EDS) provides image of the materials as well as chemical analysis. Bi et al. investigated the cross-sectional morphology of the Nafion/Si02-supported sulfated zirconia composite membrane and obtained the silicon and zirconium element distribution in the polymer matrix by SEM-EDS. ° Chalkova et al. carried out surface and cross-sectional morphology study of Nafion/Ti02 composite membranes by SEM-EDS.  

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SEM Scanning electron microscopy [7, 10, 14] A beam of electrons scattered from a surface is focused Surface morphology... 

R. E. Lee, Scanning Electron Microscopy and X-Ray Microanalysis, PTR Prentice Hall, Englewood Cliffs, NJ, 1993. 

P. R. Thornton, Scanning Electron Microscopy, Chapman and Hall, 1968. See also Scanning Electron Microscopy Systems and Applications, The Institute of Physics, London, 1973. 

Reimer L 1998 Scanning Electron Microscopy (Berlin Springer)... 

Otlier fonns of microscopy have been used to evaluate nanocrystals. Scanning electron microscopy (SEM), while having lower resolution tlian TEM, is able to image nanoparticles on bulk surfaces, for direct visualization of... 

Additional information on elastomer and SAN microstmcture is provided by C-nmr analysis (100). Rubber particle composition may be inferred from glass-transition data provided by thermal or mechanochemical analysis. Rubber particle morphology as obtained by transmission or scanning electron microscopy (101) is indicative of the ABS manufacturing process (77). (See Figs. 1 and 2.)... 

Physical testing appHcations and methods for fibrous materials are reviewed in the Hterature (101—103) and are generally appHcable to polyester fibers. Microscopic analyses by optical or scanning electron microscopy are useful for evaluating fiber parameters including size, shape, uniformity, and surface characteristics. Computerized image analysis is often used to quantify and evaluate these parameters for quaUty control. 

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. 

Particle Size. Wet sieve analyses are commonly used in the 20 )J.m (using microsieves) to 150 )J.m size range. Sizes in the 1—10 )J.m range are analyzed by light-transmission Hquid-phase sedimentation, laser beam diffraction, or potentiometric variation methods. Electron microscopy is the only rehable procedure for characterizing submicrometer particles. Scanning electron microscopy is useful for characterizing particle shape, and the relation of particle shape to slurry stabiUty. 

Asbestos fiber identification can also be achieved through transmission or scanning electron microscopy (tern, sem) techniques which are especially usefiil with very short fibers, or with extremely small samples (see Microscopy). With appropriate peripheral instmmentation, these techniques can yield the elemental composition of the fibers using energy dispersive x-ray fluorescence, or the crystal stmcture from electron diffraction, selected area electron diffraction (saed). 

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. 

L. Rcimer. Scanning Electron Microscopy. Springer-Verlag, Berlin, 1985. An advanced text for experts, this is probably the most definitive work in the field. 

E. Lifshin. Scanning Electron Microscopy and X-Ray Analysis. Plenum Press, New York, 1981. Developed from a short course held aimually at Lehigh University. The book is concerned with the use and applications of SEM. In the latter context a lengthy discussion of EDS is given. The discussion... 

A. J. Bevolo. Scanning Electron Microscopy. 1985, vol. 4, p. 1449. (Scanning Electron Microscopy, Inc. Elk Grove Village, IL) Thorough exposition of the principles and applications of reflected electron energy-loss microscopy (REELM) as well as a comparison to other techniques, such as SAM, EDS and SEM. 

Scanning Electron Microscopy Scanning Electron Microprobe Secondary Electron Miscroscopy Secondary Electron Backscatteted Electron... 

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