Beam penetration

The spatial resolution of the CI SEM mode depends mainly on the electron-probe size, the size of the excitation volume, which is related to the electron-beam penetration range in the material (see the articles on SEM and EPMA), and the minority carrier diffusion. The spatial resolution also may be afiFected by the signal-to-noise ratio, mechanical vibrations, and electromagnetic interference. In practice, the spatial resolution is determined basically by the size of the excitation volume, and will be between about 0.1 and 1 pm ... 

Fig. 1. Electron beam penetration in various materials as a function of electron beam energy.

The dependence of 7 on 2 results in a layer of O3, the upper portion of the layer being controlled by the exponential decrease of Pq with altitude. The lower part of the layer is controlled by the fall-off of intensity of UV light as the solar beam penetrates into the increasingly dense atmosphere. More extensive treatments of this phenomenon can be found, e.g. in Wayne (1985, p. 117 ff.). 

Simply visualised, the infrared beam penetrates (of the order 0.3-3 pm, dependent on its wavelength) just beyond the ATR crystal-specimen boundary before it is reflected back and makes its way through the crystal to the detector. On this short path (of the evanescent wave) into the sample surface layer, light is absorbed, and the reflected beam carries characteristic spectral information of the sample. The decaying amplitude of the evanescent wave and the depth of penetration dp at which it has decreased to a proportion of 1 /e is defined by the Harrick equation (Equation (2)), where X is the wavelength of the incoming... 

This problem can be overcome by using grain morphology to distinguish between quartz, clay and other minerals. A secondary problem occurs as the low density of the coal matrix allows for a beam penetration to a depth of approximately 10 ym. This means that the BSE image represents a surface volume rather than just a plane. 

The major steps involved were first the move from 200-kV x-rays to cobalt-60 and then to modern electron linear accelerators providing x-ray beams of about 20 MV (and electrons when needed for some patients). Improvements in the beam penetration were, in general, combined with improvements in beam delivery systems, e.g., isocentric gantries, variable collimators, later on multileaf collimators, etc. 

The energy of photons with their optimal beam penetration, the reliability of the beam delivery and collimation systems, and the mechanical stability of the new generation of accelerators have achieved a nearly optimum level of performance. Actually, with the modern linear electron accelerators, it is now possible to irradiate at the prescribed dose (nearly) any target volume of any shape with reduced irradiation of the surrounding organs at risk (OAR). 

Internal-reflection spectroscopy is used to obtain IR spectra of hard-to-handle or hard-to-prepare samples such as solids with limited solubility, films, pastes, adhesives, and powders. Reflection occurs when a beam of radiation passes from a denser to a less dense medium. The fraction of incident beam which is reflected increases as the angle of incidence becomes larger. Beyond a certain critical angle, reflection is complete. During the reflection process the beam penetrates a small distance into... 

Variations in fixed-angle PES are increasing in prominence. Low-photon incidence angles increase the surface sensitivity of PES. Although the photon beam penetrates to the same depth, the component normal to the surface is much less at small incidence angles. 

The X-ray beam penetrates the sample perpendicular to the electric field vector... 

Two special electrochemical cells are used for XRD and XAS measurements. In one case a polymer membrane is pressed on the specimen surface after its electrochemical treatment to reduce the water layer on top, but still permitting potential control during the measurements. In an other case the beam penetrates an electrolyte layer in front of the electrode, which corresponds to the specimen s dimensions, but which is thick enough to reduce the danger of ohmic drops and crevices. Beam lines often provide the exact orientation of the samples with the cell by a goniometer. For XAS measurements a special low cost refraction stage has been constructed which permits the orientation of the sample within 0.01 degrees and which has been used for the study of several systems [108]. 

The depth of IR-beam penetration (dp) can be calculated according to the following equation proposed by Harrick (21) ... 

Whether the depth of the IR-beam penetration predicted by this equation is really approached in an actual internal reflection experiment or not is an important factor to consider in quantitative studies. It would depend on the surface characteristics (e.g., roughness) and deformability of the polymer in addition to the surface characteristics of the reflection plate. 

Figure 3. Depth of IR beam penetration as a function of wave number with KRS-5 plate at the incident angle of 60° (dotted lines indicate the thickness of two barrier films, respectively)...

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