Microanalysis Instrument

The major STEM analysis modes are the imaging, diffraction, and microanalysis modes described above. Indeed, this instrument may be considered a miniature analytical chemistry laboratory inside an electron microscope. Specimens of unknown crystal structure and composition usually require a combination of two or more analysis modes for complete identification. 

In addition to cleanliness (contamination effects), surface morpholt and the alteration of composition during specimen preparation can cause serious artifacts in microanalysis. In some older instruments, the microscope itself produces undesirable high-energy X rays that excite the entire specimen, making difficult the accurate quantitation of locally changing composition. Artifacts also are observed in the EDS X-ray spectrum itself (see the article on EDS). 

Future developments of this instrumentation include field emission electron sources at 200-300 kV that will allow better elemental detectability and better spatial resolution. Multiple X-ray detectors having large collection angles will also improve elemental detectability in X-ray microanalysis. The higher accelerating... 

Electron Probe X-Ray Microanalysis (EPMA) is a spatially resolved, quantitative elemental analysis technique based on the generation of characteristic X rays by a focused beam of energetic electrons. EPMA is used to measure the concentrations of elements (beryllium to the actinides) at levels as low as 100 parts per million (ppm) and to determine lateral distributions by mapping. The modern EPMA instrument consists of several key components ... 

Figure 5.27. A summary of the relationship between the spatial resolution and the MMF for X-ray microanalysis in several electron-probe instruments (references given). The two shaded areas represent the ranges of future EPMA microanalysis predicted by Newbury et al. (1999) and the future AEM microanalysis estimated by Williams et al. (2002). (Reproduced by permission of Williams et al., 2002.)...

Figures 8.27 and 8.28(a) and (b) from Allmand and Jagger, Electron Beam X-ray Microanalysis Systems, by permission of Cambridge Instruments Ltd., U.K.

Oxford Instruments, 2006. INCAEnergy EDS X-ray Microanalysis System. Oxford Instruments Analytical Limited, Oxfordshire,... 

LA-ICP-MS and LIBS instruments can be used for fast and sensitive analysis of a wide variety of samples of interest to the geochemical and mining industries. Localized microanalysis with lateral and depth profiling is easily realized. Either traditional one-element calibration or... 

To a limited extent, the type of results reported here could be obtained with a TEM instrument fitted with a STEM adapter, especially if a field-emission gun is used (10). We will refer here, however, only to the use of dedicated STEM instruments such as the HB5 or HB501 made by VG Microscopes Ltd. having a cold field emission gun. Most of the instruments of this type are specialized for microanalysis using EDS or ELS and some have been applied very effectively for compositional analysis and associated studies on catalyst particles, as reported elsewhere in this volume. 

Electron microscopy is an efficient microscopy technique that has been extensively used for the material characterization of artistic and archaeological objects, especially in combination with x-ray microanalysis [54], The use of electrons instead of light in these instruments is the basis of the higher resolution ( 9-0.2 nm) and has greater depth of held than LM. Thus, characterization of the finest topography of the surface objects is possible, and additional analytical information can be obtained. Different electron microscopes are currently used in art and art conservation studies scanning electron microscopes (SEM), Cryo-SEM... 

Instrumentation. UV/Visible spectra were collected on a Perkin-Elmer Lambda 4 spectrophotometer. IR spectra were collected on a Perkin-Elmer 1640 spectrophotometer. NMR spectra were taken on a Nicolet NT-200 spectrometer. Differential scanning calorimetry was run on a Perkin-Elmer DSC-4 unit, equipped with a system 4 microprocessor controller and a 3600 data station. Elemental analyses were run by the Purdue microanalysis laboratory in the Department of Chemistry at Purdue University and by Huffman Labs (Golden, CO). Lignin group analysis techniques are described in references 19-21. 

This technique encompasses a large scope of instruments ranging from mobile spectrometers to high resolution spectrometers. On-line analysers and probes that can be fitted to scanning electron microscopes (SEMs) allow instant analyses to be performed (i.e. microanalysis by X-ray emission). 

There are many books and articles available regarding microanalysis, so it will not be extensively reviewed here. Usually, it is necessary to trap the peak then perform whatever specific microanalysis techniques necessary to confirm the peak s identity. Several commercial instruments are available for elemental analysis (usually carbon, hydrogen, nitrogen, and halogens). These instruments usually require between 0.1 and 3 mg of sample and often employ trapping systems for quantitative analysis. 

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