Microscopic techniques optical microscopy

Visual examination, digital photography, and microscopic techniques (optic, electronic, and atomic force microscopies) are powerful tools for collecting valuable information on the mechanisms responsible of the ultimate failure of the specimens under analysis. 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

Williams PM, Cheema MS, Davies MC, Jackson DE, Tedler SJB. Methods in Molecular Biology, Vol. 22, Microscopy, Optical Spectroscopy and Microscopic Techniques (Jones C, Mulloy B, Thomas AH, eds.), Humana Press, Totowa, NJ,... 

Seeing the surface of a catalyst, preferably in atomic detail, is the ideal of every catalytic chemist. Unfortunately, optical microscopy is of no use for achieving this, simply because the rather long wavelength of visible light (a few hundred nanometers) does not enable features smaller than about one micrometer to be detected. Electron beams offer better opportunities. Development over the past 40 years has resulted in electron microscopes which routinely achieve magnifications on the order of one million times and reveal details with a resolution of about 0.1 nm [1], The technique has become very popular in catalysis, and several reviews offer a good overview of what electron microscopy and related techniques tell us about a catalyst 12-6],... 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

Microscopic techniques, 70 428 Microscopists, role of, 76 467 Microscopy, 76 464-509, See also Atomic force microscopy (AFM) Electron microscopy Light microscopy Microscopes Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) acronyms related to, 76 506-507 atomic force, 76 499-501 atom probe, 76 503 cathodoluminescence, 76 484 confocal, 76 483-484 electron, 76 487-495 in examining trace evidence, 72 99 field emission, 76 503 field ion, 76 503 fluorescence, 76 483 near-held scanning optical,... 

Other more advanced microscopic techniques have been developed, including near-held scanning optical microscopy [166] and scanning probe microscopy techniques, such as atomic force microscopy and scanning tunnelling microscopy [166, 167],... 

Confocal microscopy (CM) is another microscope technique for apparent optical sectioning, achieved by exclusion of out-of-focus emitted light with a set of image plane pinholes. CM has the clear advantage in versatility its method of optical sectioning works at any plane of the sample, not just at an interface between substances having dissimilar refractive indices. However, other differences exist which, in some special applications, can favor the use of TIRF ... 

Confocal laser scanning microscopy (CLSM) in conjunction with specific staining techniques is best suited to elucidate intracellular trafficking and localization. CLSM is a specific epifluorescence microscopical technique capable of optical cross-sectioning with a spatial resolution of 1 /urn and below [41, 42],... 

The Sccmning Electron Microscope (SEM) is a standard imaging technique based on electron back-scattering from the sample surface. It analyses the surfaces of solid objects, producing images with the resolution which is about order of magnitude better than that of optical microscopy (typically 10 nm). The SEM avoids the problem of thin samples (TEM) but the SEM observation requires the deposition of a thin conductive metal film on the sample surface to prevent sample charging. 

The fiber fragment length can be measured using a conventional optical microscope for transparent matrix composites, notably those containing thermoset polymer matrices. The photoelastic technique along with polarized optical microscopy allows the spatial distribution of stresses to be evaluated in the matrix around the fiber and near its broken ends. 

In this paper, we first briefly recall the main features of the collagen molecule, then we describe the structure of the gels, using different experimental techniques (optical rotation (O.R.), electron microscopy, proton nuclear magnetic resonance (N.M.R.)) for different thermal treatments. A phenomenological and a microscopic interpretation of the mechanisms of gel formation is suggested. 

Powerful methods that have been developed more recently, and are currently used to observe surface micro topographs of crystal faces, include scanning tunnel microscopy (STM), atomic force microscopy (AFM), and phase shifting microscopy (PSM). Both STM and AFM use microscopes that (i) are able to detect and measure the differences in levels of nanometer order (ii) can increase two-dimensional magnification, and (iii) will increase the detection of the horizontal limit beyond that achievable with phase contrast or differential interference contrast microscopy. The presence of two-dimensional nuclei on terraced surfaces between steps, which were not observable under optical microscopes, has been successfully detected by these methods [8], [9]. In situ observation of the movement of steps of nanometer order in height is also made possible by these techniques. However, it is possible to observe step movement in situ, and to measure the surface driving force using optical microscopy. The latter measurement is not possible by STM and AFM. 

Because of the particle sizes involved, classically the optical microscope has been the instrument of choice especially for lyophobic colloids. Excellent books and manuals are available (Bradbury 1991 Cherry 1991 Schaeffer 1953) on the numerous variations of optical microscopy, and we do not go into all the details. Our purpose here is merely to point out some very elementary principles that make this method ideally suited for direct examination of colloids. We also use this introduction as a first step in pointing out modern techniques that fall under the class of microscopy but use principles (e.g., electron tunneling see Vignette 1.8) and radiation (e.g., electron or x-ray) other than those used in optical microscopy. 

We shall first examine the microscopic techniques which allowed us to study these transformations and to show the striking analogy between the images obtained by optical microscopy in polarized light and by electron microscopy with ultrathin sections, despite the difference of the absorption mechanisms of light and electrons. Once this analogy was established, we sought to use electron microscopy and electron microdiffraction to learn more about the texture and structure of the anisotropic areas. 

Techniques of optical microscopy (OM) are well known and often used for the examination of fibers and yams from archaeological textiles. Many texts provide the fundamentals of the technique (e.g. 40-43). Some manuscripts describe the methods that may be employed in the study of archaeological materials in particular (44, 45), while others report the results of optical microscopic examination in identification and characterization of archaeological fibers (e.g., 12, 46). 

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