Composite imaging modes

SSIMS has been used in the TOP SSIMS imaging mode to study very thin layers of organic materials [3.32-3.36], polymeric insulating materials [3.37], and carbon fiber and composite fracture surfaces [3.38]. In these studies a spatial resolution of ca. 80 nm in mass-resolved images was achieved. 

Imaging modes other than secondary electron, such as cathododlumniscence, are available on the SEM instrument, but the only technique other than secondary electron that is likely to be of very much interest in solving adhesion problems is the use of backscattered primary electrons, which give a topographical image with some compositional contrast. 

Fig. 5.6 Fiber surfaces are shown here taken in normal SEM and BEI modes. A BEI compositional image (A) reveals bright particles that are higher atomic number than the fiber itself. A BEI topographical image (B) shows that some particles are present on top of the fiber surface. The normal (SEI) image (C) does not exhibit as much detail. Higher magnification micrographs, taken in the BEI mode (D), and in SEI (E), show this difference in more detail. The cracked background (D) is the metal coating.

During sample preparation, it should be home in mind that etching of the sample surface is not obligatory for SEM and/or AFM investigations. Composite materials can be conveniently studied by SEM using the back-scattered electrons (BSE) imaging mode if the secondary electron (SE) mode does not provide sufficient phase information. In the case of AFM, the most important requirement is the flat surface is free from contamination and that there are sufficient differences in local mechanical properties (e.g., stiffness) between the components. 

Electron Probe Microanalysis, EPMA, as performed in an electron microprobe combines EDS and WDX to give quantitative compositional analysis in the reflection mode from solid surfaces together with the morphological imaging of SEM. The spatial resolution is restricted by the interaction volume below the surface, varying from about 0.2 pm to 5 pm. Flat samples are needed for the best quantitative accuracy. Compositional mapping over a 100 x 100 micron area can be done in 15 minutes for major components Z> 11), several hours for minor components, and about 10 hours for trace elements. 

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. 

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