Imaging of Element Distribution

Surface and Thin Film Analysis Principles, Instrumentation, Applications 

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Fig. 4.30. Imaging of element distribution by X-ray mapping (a) cross-section STEM bright-...

The localization of structural features in the electron probe is aided by scanning techniques " that produce electron microprobe images of small sectors of the sample surface. It is also possible to obtain scanning images of element distribution. The most attractive feature of electron probe microanalysis is the fact that a quantitative analysis is possible, with errors of less than 3 % relative in most cases. Data evaluation requires the use of a computer, but the... 

In practice image quality is also reduced by use of high mass resolution and energy offset. Often, therefore, mass interference cannot he avoided. Determination of element distributions is possible by use of image processing tools for classification of mappings of different masses [3.53]. 

LA-ICP-MS enables images to be produced of the distribution of essential elements such as Zn, Cu, Fe, S, P, Se and Mn as well as of toxic and also radioactive metals (e.g., Hg, Pb, Cd, Th and U) in thin tissue sections with a spatial resolution in the (im range. This spatial resolution of element distribution analysis is sufficient to distinguish between several layered structures in human brain tissue from the hippocampus, as described by Zilles et al.162... 

Imaging of elemental and isotopic distributions on surfaces has proved useful for diffusion measurements, corrosion and reactivity studies, contamination identification, and many other applications. SIMS imaging is particularly useful because of its high sensitivity. An example was the application to a problem in which a U-... 

The dedicated scanning transmission electron microscope (STEM) is an integral tool for characterizing catalysts because of its unique ability to image and analyze nano-sized volumes. This information is valuable in optimizing catalyst formulations and determining causes for reduced catalyst performance. For many commercial catalysts direct correlations between structural features of metal crystallites and catalytic performance are not attainable. When these instances occur, determination of elemental distribution may be the only information available. In this paper we will discuss some of the techniques employed and limitations associated with characterizing commercial catalysts. 

Since then, radioactive tracer elements have been incorporated into innumerable metabolically active molecules, which are then injected intravenously and become concentrated in regions of interest. PETracers emit 511-keV photons imaged by a circle of radiation detectors surrounding the patient s head. A computer constructs images of the distribution of tbe tracer within the brain at various times after injection of the tracer. 

X-rays are shone onto a sample to eject photoelectrons. These are collected and focused onto a phosphor screen to produce a magnified, real time, high-resolution image of the distribution of elements and/or magnetic domains over the sample surface. 

This technique generally requires UHY An X-ray beam from an anode or synchrotron source is used to excite photoelectrons from the sample. These pass through a series of electrostatic lens which focus them to form a magnified real time image of photoelectron distribution on a phosphor screen in a maimer that is analogous to optical microscopes but which is element specific. This image can either be viewed directly by eye or with a CCD camera interfaced to image analysis software. 

PEEM provides high-resolution real time images of elemental or magnetic domain distribution with topographic sensitivity. 

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