Charged particles ranges

The atomic scattering factor for electrons is somewhat more complicated. It is again a Fourier transfonn of a density of scattering matter, but, because the electron is a charged particle, it interacts with the nucleus as well as with the electron cloud. Thus p(r) in equation (B1.8.2h) is replaced by (p(r), the electrostatic potential of an electron situated at radius r from the nucleus. Under a range of conditions the electron scattering factor, y (0, can be represented in temis... 

It should be stressed at this point that, as we shall see, the in and out negaton-positon and electromagnetic fields given by Eqs. (11-56), (11-57), and (11-62) are ill-defined. For the matter field, the reason is that the Coulomb field has an infinite range, and, hence, charged particles, no matter how far apart, still interact with one... 

However, analyses of the interface surrounded by some medium are not easy. When an interface of interest is exposed to a vacuum, electron-based or ion-based methods are available to determine the chemical composition and molecular structure of the top layers. The charged particles with limited penetration range result in a good vertical resolution. Buried interfaces are beyond the range of penetration. Photons, an alternative class of probe particles, have better ability for penetration. When the linear response to the incident electric field is analyzed, the vertical resolution is limited to the order of the wavelength, which is greater than the thickness of the top layers. 

In contrast to PIXE and RBS, where forces are respectively electromagnetic and electrostatic, this kind of microanalysis uses low range nuclear forces. The analysis is based on the detection of the y-rays emitted from nuclei that are in an excited state following a charged particle induced nuclear reaction. 

De Neve et al. (2000) have carried out a feasibility study to investigate the possibilities and limitations of CPAA as a thin layer characterization method (rather than for the determination of elemental concentrations in bulk samples). The required experimental conditions are (a) that the surface layer containing the analyzed element is thinner (1 pm or less) than the range of the charged particles used and (b) that the substrate (i.e. the layer on which the thin layer is deposited) does not contain the element(s) to be analysed. 

CPAA measures the characteristic decay radiation of the radionuclides produced by the incident charged particles. The technique has been widely applied in the determination of trace elements concentrations in bulk samples, but it also has possibilities for surface characterisation, provided the thickness of the layer to be characterised is less than the range of the charged particles employed. 

Vacuum based techniques are capable of producing new materials or new forms of existing materials either in bulk form or as surface layers. There is a wide range of different techniques and applications, only some of which have been covered here. It is clear from the literature that much needs to be done in both the fundamental and applied aspects of such work. For example, relatively little is known about the effects caused by the arrival of clusters or charged particles at a growing film. 

Energy transfer from a charged particle can be considered from two points of view (1) the particle—that is, its charge, range, penetration, etc.—which... 

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