Optical microscopic techniques, resolution

The analytical techniques used for various types of clay studies have a long list. Due to the fine grain and opaque nature of clays, usual optical microscopic techniques are not applicable. But the high resolution electron microscopy (e.g. scanning and transmission type) is a very useful tool to... 

Optical and Confocal Microscopy A Brief Overview 1525 Table 16.1 Optical microscopic techniques and their resolution limits. 

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. 

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],... 

For this type of superresolution optical microscope, experiments have shown that it is possible to have spatial resolutions of the order of X/50. It is believed that the technique can be improved so to allow spatial resolutions of over X/100. 

In the recent literature the terms nanoparticles and nanosystems are used, in analogy to colloid and colloidal systems. The prefix nano indicates dimensions in the 1 to 100 nm range. This is above the atomic scale and, unless highly refined methods are used, below the resolution of a light microscope and thus also below the accuracy of optical microstructuring techniques. 

Raman microspectroscopy results from coupling of an optical microscope to a Raman spectrometer. The high spatial resolution of the confocal Raman microspectrometry allows the characterization of the structure of food sample at a micrometer scale. The principle of this imaging technique is based on specific vibration bands as markers of Raman technique, which permit the reconstruction of spectral images by surface scanning on an area. 

Laser microprobe mass analyzers permit mass spectrometric analysis of very small volumes (0.01-1 pm3) of thin Sections. The method is based on laser induced ion production from a microvolume and analysis of the evaporated ions in a time-of-flight mass-spectrometer. The technique allows detection of all elements and isotopes with a sensitivity approaching the ppm range and an extremely low limit of detection 10 15 to 10-20 g. Transmission type instruments such as the LAMMA 500 are designed for the analysis of particles of 3 pm in diam. The lateral resolution is about 0.5-1 pm. Because the area to be analyzed is selected by an optical microscope, distribution of chemical constituents can be precisely correlated with morphologic structures (Hillenkamp et al., 1982 39), Simons, 198440), Kaufmann, 1984)41 >. 

At high concentration, when molecules are no longer isolated in space, a conventional optical microscope is unable to resolve them within the diffraction limit. Efforts have been made to circumvent the diffraction limit by engineering the point spread function using nonlinear optical techniques. Spatial resolution of 20 nm in a cell has been demonstrated without using a proximal probe.67... 

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