Backscattered electrons, SEM

Figure 6. Backscatter electron SEM photograph of same transistor 15,000X.

Fig. 11. AI2O2—Al TiO typical microstructure showiag grain bridging, B (SEM backscattered electron image).

The SEM can also be used to provide crystallographic information. Surfaces that to exhibit grain structure (fracture surfaces, etched, or decorated surfaces) can obviously be characterized as to grain size and shape. Electrons also can be channeled through a crystal lattice and when channeling occurs, fewer backscattered electrons can exit the surface. The channeling patterns so generated can be used to determine lattice parameters and strain. 

Because X-ray counting rates are relatively low, it typically requires 100 seconds or more to accumulate adequate counting statistics for a quantitative analysis. As a result, the usual strategy in applying electron probe microanalysis is to make quantitative measurements at a limited collection of points. Specific analysis locations are selected with the aid of a rapid imaging technique, such as an SEM image prepared with backscattered electrons, which are sensitive to compositional variations, or with the associated optical microscope. 

Figure 3 The SEM pictures of Pd/C type 2 catalyst a)secondary mode, b) backscattered electron.

The interaction of the electron beam with the sample is generally onion-shaped and results in a number of different processes, as shown in Fig. 8. The formation of secondary electrons and backscattered electrons is the basis for the imaging capabilities of the SEM. 

Fig. 2. SEM backscattered electron image of a Type II vein containing euhedral to cataclastically brecciated arsenopyrite (asp), pyrite (py), quartz, and calcite. A thin Type 1 quartz vein showed a SEM-EDAX analysis of a very fine-grained mineral mass rich in Hg-Au-As vein (arrow).

Fig. 1. SEM backscattered electron image, Si X-ray map, Ca X-ray map, and Na X-ray map of alteration in pyrochlore from Vishnevogorskii, Russia. Note the loss of Na and Ca and incorporation of Si along cracks and the dark area near the middle of the backseaUered image.

Fig. 3. SEM backscattered electron image of alteration in zirconolite from the Afrikanda alkaline complex, Kola Peninsula, Russia. This crystal exhibits complex magmatic zoning, late-stage replacement by an unknown Ba-Zr-Ti-silicate phase, and preferential alteration along cracks and Th-U-rich zones.

Fig. 4. SEM backscattered electron images of alteration in natural brannerite (a) Part of a large brannerite specimen showing minor alteration around the rim of the crystal and along fractures extending into the interior (b) Brannerite crystals showing extensive alteration along their rims, together with the presence of U-rich phases along cracks in the host rock.

Figure 2. (a) Backscattered electron image and (b) SEM micrograph of Lao 2Sr0 8Fe0 55Ti045O3 8 sintered at 1400°C/10 h. 

A conventional SEM (backscattered electrons) micrograph of a Ni-Al203 nanocomposite demonstrating problematic use of the BSE signal for microstructure characterization. 

Particle analysis is the most informative method to date for the identification of FDR particles. It does, however, suffer from several major disadvantages including high cost of instrumentation and lengthy and tedious procedures requiring specialized staff Since its introduction serious attempts have been made to solve the time problem. These include the use of backscattered electron images, automation of the search procedure, and sample manipulation to pre-concentrate the sample prior to SEM examination.145151... 

Scanning electron micrographs (SEM) were obtained using a JSM 5500 LV (Jeol, Japan) electron microscope. The observations were performed in a secondary electron (SE) and in a backscattering electron (BSE) mode at a low vacuum pressure of 12 kPa. 

Electron backscatter diffraction (EBSD) — The focused electron beam of Scanning Electron Microscopes (SEM) can be used to detect the crystallographic orientation of the top layers of a sample. The backscattered electrons (information depth 40-70 nm at 25 kV accelerating potential, lateral resolution around 200 nm) provide characteristic diffraction patterns (Kikuchi lines) on a phosphor screen. The patterns are recorded by a CCD-camera and interpreted by software. The position of the unit cell of the sample is determined by the corresponding Euler angles. In scanning mode, the software produces a surface orientation mapping that consists of... 

The main drawbacks of this approach are the low availability of such instruments in laboratories, and the fact that many samples are sensitive to ion beam damage, require specific preparation (95), and can induce low contrast. Moreover, the imaging between two milling periods is typically performed in the backscattered electrons mode, which is not always favorable this is the case for carbon nanotubes in a polymer matrix as the atomic number contrast is low. This is probably the reason why, even if the FIB/SEM approach is used on polymer nanocomposites, it not used in the literature for carbon nanotubes in polymer matrix. In this last application, the tomo-STEM technique is a good alternative to obtain images of relatively thick samples with high contrast and resolution (91). 

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