Scanning electron microscopy accessories

Instrumentation, image formation, accessories, and applications of conventional scanning electron microscopy will be discussed. Information about the ESEM will also be presented. 

Scanning electron microscopy with an energy-dispersive x-ray system accessory has been used to identify the composition and nature of minerals in coals and to determine the associations of minerals with each other. Examinations can be made on samples resulting from ashing techniques or whole coal. With this technique it is possible to identify the elemental components and deduce the mineral types present in coal samples. Computerized systems to evaluate scanning electron microscopy images have been developed and are useful in characterizing the minerals in coal mine dusts and in coal. 

The minerals found in United States coals continue to be studied with the availability of improved instrumental procedures such as x-ray diffraction, infrared absorption, and scanning electron microscopy beyond the traditional optical and chemical mineralogical techniques as applied to thin sections, polished pellets, and isolated particles. The minerals may be grouped into the silicates (kaolinite, illite montmorillonite, and chlorite), the oxides (quartz, chalcedony, hematite) the sulfides (pyrite, marcasite, and sphalerite) the sulfates (jarosite, gypsum, barite, and numerous iron sulfate minerals) the carbonates (ankerite, calcite, dolomite, and siderite) and numerous accessory minerals (apatite, phosphorite, zircon, rutile, chlorides, nitrates, and trace minerals). 

LSM, SEKZ and LSCF powders were characterized by XRD using a Shimadzu XDR-7000 diffractometer and scanning electron microscopy (SEM-SSX 550, Shimadzu). Infrared spectra were also recorded with FTIR (IR Prestige-21, Shimadzu) in the 400 - 4600 cm"i spectral range. Specific surface area measurements were performed only for the LSM powders. An infrared reflectance spectrum of a LSM pellet prepared from a powder calcined at 900 °C was recorded with a Fourier-transform spectrometer (Bomem DA 8-02) equipped with a fixed-angle specular reflectance accessory (external incidence angle of 11.5°). 

As compared to TEM, scanning electron microscopy (SEM) can avoid destroying the bulky specimen, because a focused electron beam is scanned during catalyst observation. SE and backscattered electron (BSE) signals can be collected separately or together in any ratios simultaneously. Stereoscopic morphologies can be obtained but with resolution much inferior to that of TEM. Similar to TEM, EDS could be applied as accessory to analyze microdomain composition and element distribution. 

Figure 1. Scanning electron photomicrographs of minerals from coals. The minerals were studied and photographed by a Cambridge Stereoscan microscope with an accessory energy-dispersive x-ray spectrometer at the Center for Electron Microscopy, University of Illinois. A. Pyrite framboids from the low-temperature ash of a sample from the DeKoven Coal Member. B. Pyrite cast of plant cells from the low-temperature ash of a sample from the Colchester (No. 2) Coal Member. C. Kaolinite (left) and sphalerite (right) in minerals from a cleat (vertical fracture), Herrin (No. 6) Coal Member. D. Calcite from a cleat in the Herrin (No. 6) Coal Member. E. Kaolinite books from a cleat in the Herrin (No. 6) Coal Member. F. Galena small crystals in the low-temperature ash of a sample from the DeKoven Coal Member.

Three types of instrumentation exist for dynamic SIMS non-imaging ion probes, direct-imaging ion microanalysers and scanning ion microprobes-micro-scopes. Non-imaging ion probes are often an accessory of Auger electron spectroscopy (AES), electron spectroscopy for chemical applications (ESCA), or electron microscopy systems and allow a point analysis. Imaging equipment allows a point-to-point analysis of the surface with a primary beam of size 10—300 pm (microanalysers) or below 10 pm (microprobes-microscopes). 

---