Microscopes and Chemical Microscopy

The two most useful supplementary techniques for the light microscope are EDS and FTIR microscopy. Energy dispersed x-ray systems (EDS) and Eourier-transform infrared absorption (ETIR) are used by chemical microscopists for elemental analyses (EDS) of inorganic compounds and for organic function group analyses (ETIR) of organic compounds. Insofar as they are able to characterize a tiny sample microscopically by PLM, EDS and ETIR ensure rapid and dependable identification when appHed by a trained chemical microscopist. 

Probably the most extensive use of particle morphology and microscopy has been in the area of chemical microscopy. With this approach, derivatives of the analyte species are prepared, crystallized, and identified through the morphological characteristics of these derivatives [21]. Most of these applications have been superseded by modem methods of analysis, but the microscopic method can still be used by skilled practitioners for the study of trace quantities of analyte. The literature developed during the heyday of chemical microscopy is too large to be reviewed here, but advances in the field are still chronicled in the Annual Reviews issue of Analytical Chemistry [22]. A substantial review of the optical characteristics of organic compounds is available [23]. 

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. 

For inorganic substances, chemical reactions may be carried out on a small scale on microscope slides, the crystallization of reaction products being watched. Tests for particular ions or atom groups have been devised, the criterion of identity being, not solubility or colour, as in macroscopic qualitative chemical analysis, but crystallographic properties. For information on such methods, see Handbook of Chemical Microscopy, by Chamot and Mason (1958). 

The magnification attended in the experiment with the photoelectron microscope was M = 10s, and the spatial resolution was around 30 nm, which proved sufficient for the visualization of individual color centers in a LiF crystal with the concentration of such centers less than 10l7cm 3. The results obtained in Ref. 9 may be considered the first successful implementation of laser resonance photoelectron microscopy possessing both subwavelength spatial resolution and chemical selectivity (spectral resolution). It will be necessary to increase the spatial resolution of the technique by approximately an order of magnitude and substantially improve its spectral resolution by effecting resonance multistep photoionization by means of tunable ultrashort laser pulses. 

KLUG, AARON S. I1926-). A South African-born chemist who won the Nobel prize for chemistry in 1982 for his work with the electron microscope and research into the structure of nucleic and protein complexes. His use of crystallographic electron microscopy to analyze the structures of biologically important complex chemicals was noteworthy. He was cited in particular for his establishment of Fourier microscopy. 

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