Optical microscopy reflection microscopes

The compensation birefringence measurement is very easily coupled to optical microscopy in the transmission and reflection modes, thus allowing characterizing orientation with a spatial resolution of a few hundreds of nanometers [14]. Polarizing microscopes are widely available and are often used for birefringence studies even if spatial resolution is not required. Objectives specifically designed for cross-polarized microscopy are necessary to avoid artifacts. 

Antiblock additives can be seen on the surface of films using optical microscopy or SEM. Identification can normally be achieved with internal reflection IR spectroscopy (e.g., with a germanium crystal to minimise sampling depth) or using an X-ray attachment with the electron microscope. 

Optical microscopy is another method that has been used to determine the distribution of minerals in coal. This method is based on the detailed microscopic examination of polished or thin sections of coal in transmitted and/or reflected light. In principle, observing several of its optical properties, such as morphology, reflectance, refractive index, and anisotropy, makes identification of a mineral type possible. 

Microspectrometry is an indispensable technique in criminalistic analyses, being a combination of optical microscopy and spectrometry. Microscopy creates, records and interprets magnified images, whereas spectrometry uses emission, absorption and reflection of radiant energy by matter to determine its structure, properties and composition. On the basis of the type of energy applied, microspectrometry can be divided into IR, visual and ultraviolet (UV-vis), and Raman microspectrometry. This group also includes X-ray microspectrometry, in which an electron microscope takes the place of an optical microscope. Infrared and Raman microspectrometry enable determination and comparison of the chemical composition of studied samples UV-vis microspectrometry serves to compare the colour of samples in an objective way that is independent of the observer and X-ray microspectrometry allows determination of the elemental composition. 

Microscopy is a widely used particle sizing technique in which individual particles are observed and measured. Optical microscopy is used for examination of particles from about 150—0.8 microns. For smaller particles an electron microscope is needed. A single particle has an infinite number of linear dimensions and it is only when they are averaged that a meaningful value is yielded. When a linear dimension is measured parallel to some fixed direction, the size distribution of these measurements reflects the size distribution of the projected areas of the particles [3]. ... 

Studies by optical microscopy of the material left after evaporating the benzene show a variety of what appear to be crystals—mainly rods, platelets and star-like flakes. Figure 1 shows a micrograph of such an assemblage. All crystals tend to exhibit six-fold symmetry. In transmitted light they appear red to brown in colour in reflected light the larger crystals have a metallic appearance whereas the platelets show interference colours. The platelets can be rather thin and are thus ideally suited for electron-diffraction studies in an electron microscope (see the inset in Fig. 3). 

On the other hand, optical microscopy, confocal microscopy, ellipsometry, scanning electron microscopy (SEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and total internal reflection fluorescence (TIRF) are the main microscopic methods for imaging the surface structure. There are many good books and reviews on spectroscopic and chemical surface analysis methods and microscopy of surfaces description of the principles and application details of these advanced instrumental methods is beyond the scope of this book. 

Optical microscopy, using polarized reflected light, has been recognized as a very useful tool and has played a major role in studies of carbonization mechanisms and coke quality properties. Examination of a coke polished surface under a microscope reveals the presence of certain parts without optical activity (isotropic coke) and others with optical activity (anisotropic coke). The anisotropic carbon exhibits yellow, blue, and purple areas of various sizes, <1-200 )tm, and shapes (optical texture) with an interchange of color on rotation of the specimen. 

The reflection technique is more limited in resolution and magnification than is transmission. Reflection optical microscopy of adhered surfaces is often revealing, but the very limited depth of field is a severe handicap. Nevertheless, examination of surfaces after testing or failure is a simple, but important, first step in determining locus of failure (see Stress distribution mode of failure). Surface reflectivity of specimens is often improved by deposition of a layer or metal. The reflection microscope is especially useful when operated in dark-field mode, where topographical differences are accentuated. 

The application of a highly reflective gold film (see Section 3.1) by vapor deposition or sputtering can help alleviate this problem in optical microscopy. When used with certain materials, however, this causes the loss of valuable information that would normally be conveyed by gray tones or other colors of the material s phases. Most oxide and non-oxide ceramics can be examined by optical microscopy without requiring color. However, this is not true for the microscopic examination of classic ceramic materials, e.g., stoneware, porcelain, refractory materials, or cement clinker. In these cases, thin sections are used to exploit the material s transparency, which allows it to be examined by transmission microscopy. 

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