Electron backscattering

Increases with the atomic number of the detector material 

Increases as the incident angle of the beam deviates from the normal 

An electron energy spectrum measured with a plastic scintillator is shown in Fig. 13.8. It is represented extremely well by the following analytic function, which was developed by Tsoulfanidis et al. ° and is shown in Fig. 13.9. 

Similar results have been obtained with a Si(Li) detector. More references on the subject are given by Bertolini and Coche (see their Sec. 4.3.3). Semiempirical formulas giving the value of b as a function of Z and T have been developed by many authors, but such equations are of limited general value because the response function and the backscattering depend on the geometry of the system for this reason, response function and backscattering should be measured for the actual experimental setup of the individual observer. 

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Fig. 1. Electron backscatter image of a Ca-S04-rich grain showing a secondary precipitate ring (centre) and individual backscatter images for As, Fe, Ni, and Ca of the same grain.

In this type of Microscopy a fine beam of electrons is scanned across the surface of an opaque specimen to which a light conducting film has been applied by evaporation. Secondary electrons, backscattered elections, or (in the electron microprobe)... 

In transmission electron microscopy (TEM), a beam of highly focused and highly energetic electrons is directed toward a thin sample (< 200 nm) which might be prepared from solution as thin film (often cast on water) or by cryocutting of a solid sample. The incident electrons interact with the atoms in the sample, producing characteristic radiation. Information is obtained from both deflected and nondeflected transmitted electrons, backscattered and secondary electrons, and emitted photons. 

A perturbation expansion version of this matrix inversion method in angular momentum space has been introduced with the Reverse Scattering Perturbation (RSP) method, in which the ideas of the RFS method are used the matrix inversion is replaced by an iterative, convergent expansion that exploits the weakness of the electron backscattering by any atom and sums over significant multiple scattering paths only. 

SEM electron backscatter image of lunar soil particles, showing minute beads of metallic iron (white) in silicate glass coatings. The iron beads modify the spectra, accounting for the phenomenon of space weathering. 

Scanning electron microscopes can be equipped with a CL detector. Cathodolumines-cence provides information on the mineralogy of a sample. An electron backscatter... 

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... 

Other names instead of EBSD are Backscatter Kikuchi Diffraction (BKD), Electron Backscatter Pattern Technique (EBSP), Orientation Imaging Microscopy (OIM ), or Automated Crystal Orientation Mapping (ACOM). In combination with electrochemical studies only ex situ applications are possible. 

Ref [i] Schwartz A, Kumar M, Adams BL (2000) Electron backscatter diffraction in material science. Kluwer Plenum, New York... 

The intensity of the electrons backscattered from a particular region of a specimen depends approximately on the mean atomic number of the material of which that region is composed more precisely, it is represented by the backscattering coefficient, q, which may be calculated from the formulae ... 

In a typical direct write e-beam lithographic system, the resolution of a dense line-space array is often limited by the effect of electrons backscattered from the substrate. In these arrays, the backscattered electrons from one exposed line increase the net exposure density in an adjacent line. While this problem of non-uniform exposure can be corrected by varying the exposure dose within the pattern, this form of proximity correction requires sophisticated algorithms and extensive computer facilities. 

This group of techniques is based upon the analysis of electrons backscattered or emitted from metal surfaces. The shallow escape depths of these particles make their use most suitable for interfacial studies since the information they bear are characteristic only of the near-surface layers on the other hand, the short mean-free paths necessitate a high-vacuum enviromnent. The major limitation has always been the possibility of stractural and compositional changes upon emersion (removal from solution under potential control) and transfer of the electrode into the UHV environment. However, numerous studies have established that the compact layer remains largely unperturbed upon emersion, " unless the emersed layer contains feebly bound non-condensed species. 

X-ray absorption spectroscopy is a powerful tool for nanoparticle analysis due to its selectivity and independence of sample physical state. It is limited in range to the region within about 0.5-0.7 nm of a particular (chosen) absorber atom in the structure, but can be applied to amorphous or even liquid samples. The basic theory behind the origins and analysis of the extended X-ray absorption fine structure (EXAFS) has been well described by Sayers et al. (1970, 1971) and Lee et al. (1981). with mineralogical applications detailed by Brown et al. (1988). The crucial aspect of the EXAFS spectrum is that it is formed by an electron backscattering process in the vicinity of the absorber... 

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