Scattered beam

Figure B1.3.A.9. Diagram depicting the angles used in scattermg experiments employing linearly and circularly polarized light. The subscripts i and s refer to the incident and scattered beam respectively.

In contrast to spectrophotometry, hght-scattering experiments are generally conducted at constant wavelength. Mercury vapor lamps are the most widely used light sources, since the strong lines at 436 and 546 nm are readily isolated by filters to allow monochromatic illumination. Polarizing filters are also included for both the incident and scattered beams so that depolarization can... 

Figure 1 Drawing of single-channei Raman spectrometer showing Czerny-Turner type doubie monochromator. Coiiecting optica for scattered beam are not shown.

Maximum information is obtained by making Raman measurements on oriented, transparent single crystals. The essentials of the experiment are sketched in Figure 3. The crystal is aligned with the crystallographic axes parallel to a laboratory coordinate system defined by the directions of the laser beam and the scattered beam. A useful shorthand for describing the orientational relations (the Porto notation) is illustrated in Figure 3 as z(xz) y. The first symbol is the direction of the laser beam the second symbol is the polarization direction of the laser beam the third symbol is the polarization direction of the scattered beam and the fourth symbol is the direction of the scattered beam, all with respect to the laboratory coordinate system. 

Because Raman spectroscopy requires one only to guide a laser beam to the sample and extract a scattered beam, the technique is easily adaptable to measurements as a function of temperature and pressure. High temperatures can be achieved by using a small furnace built into the sample compartment. Low temperatures, easily to 78 K (liquid nitrogen) and with some diflSculty to 4.2 K (liquid helium), can be achieved with various commercially available cryostats. Chambers suitable for Raman spectroscopy to pressures of a few hundred MPa can be constructed using sapphire windows for the laser and scattered beams. However, Raman spectroscopy is the characterizadon tool of choice in diamond-anvil high-pressure cells, which produce pressures well in excess of 100 GPa. ... 

Fig. 3.52. Normalized back-scattering yields of ions from Pb near the melting point, with the incident beam and scattered beam directed along <101 > crystal axes (double alignment) curve a, 295 K curve b, 506 K curve c, 561 K curve d, 600.5 K curve e, 600.8 K. Spectrum d is fitted by a sum of contributions M, from a liquid surface layer, and I, from a partially ordered transition layer [3.133].

Barkla, originally interested mainly in v-ray scattering, discovered characteristic x-rays by an experimental method similar in principle to that described above. His experimental arrangement (Figure 1-7) is reminiscent of that used today in studies of the Raman effect. By using an absorber in the form of sheets (Figure 1-7) to analyze the scattered beam in the manner of Figure 1-4, he obtained results that clarified the earlier experiments described above. 

Figure 1-8 shows log-log curves calculated from Barkla s absorption-coefficient data. (A log-log plot shows most clearly what Barkla discovered.) For carbon, the wavelength distribution is virtually unchanged from that of the incident polychromatic beam, mainly scattered x-rays being detected the situation is reminiscent of Figure 1-5. The curve for calcium, on the other hand, begins with a straight line that shows the presence in the scattered beam of a relatively intense component for which k is large and sensibly constant. The curve for tin shows two such components. Barkla realized that these components are emitted, and he eventually called them K and L spectra.22 He...

Two factors determine the intensity of the scattered beam the scattering cross section for the incident ion-target atom combination and the neutralization probability of the ion in its interaction with the solid. It is the latter quantity that makes LEIS surface sensitive 1 keV He ions have a neutralization probability of about 99 % on passing through one layer of substrate atoms. Hence, the majority of ions that reach the detector must have scattered off the outermost layer. At present, there is no simple theory to adequately describe the scattering cross section and the neutralization probability. However, satisfactory calibration procedures by use of reference samples exist. The fact that LEIS provides quantitative information on the... 

Angle between transmitted and scattered beam (Chap. VII). 

Raman scattering spectroscopy is used to probe the vibrational excitations of a sample, by measuring the wavelength change of a scattered monochromatic light beam. This is usually performed by impinging a monochromatic laser beam to the sample surface, and by recording the scattered beam spectrum. 

The capillary wave frequency is detected by an optical heterodyne technique. The laser beam, quasi-elastically scattered by the capillary wave at the liquid-liquid interface, is accompanied by a Doppler shift. The scattered beam is optically mixed with the diffracted beam from the diffraction grating to generate an optical beat in the mixed light. The beat frequency obtained here is the same as the Doppler shift, i.e., the capillary wave frequency. By selecting the order of the mixed diffracted beam, we can change the wavelength of the observed capillary wave according to Eq. (11). 

Straggling. The essence of RBS is to measure the energy of the scattered beam and to calculate thereby the depth and/or mass from which scattering occurs. Any uncertainty in particle energy leads to a reduction in the precision with which mass and depth analysis can be achieved. 

A substantial number of electrons are elastically scattered, and this gives rise to a strong elastic peak in the spectrum. When an electron of low energy (2-5 eY) approaches a surface, it can be scattered inelastically by two basic mechanisms, and the data obtained are dependent upon the experimental geometry - specifically the angles of the incident and the (analysed) scattered beams with respect to the surface (0 and 02 in Figure 5.47). Within a certain distance of the surface the incident electron can interact with the dipole field associated a particular surface vibration, e.g. either the vibrations of the surface atoms of the substrate itself, or one or other... 

Collimated Single Scattered beam crystal radiation... 

Raman component of scattered beam with angular frequency CQ-CDv... 

Figure 7.5. Relationship between symmetrical (

reflection geometry. Bold bars symbolize the sample in symmetrical (dashed) and asymmetrical (solid) geometry. Incident and scattered beam are shown by dashed-dotted arrows, the incident angle is a = 0 + scattering vector s. For the tilted sample the sample-fixed scattering vector S3 is indicated (after [84])... 

Diffraction is a scattering phenomenon. When x-rays are incident on crystalline solids, they are scattered in all directions. In some of these directions, the scattered beams are completely in phase and reinforce one another to form the diffracted beams [1,2]. Bragg s law describes the conditions under which this would occur. It is assumed that a perfectly parallel and monochromatic x-ray beam, of wavelength A, is incident on a crystalline sample at an angle 0. Diffraction will occur if... 

Fig. 3. Schematic of the arrangement used in elastic recoil detection (ERD) of hydrogen. Note the foil in front of the detector, used to prevent scattered beam ions from interfering with the detection of recoiling hydrogen. 

An alternative to the common device of determining relative intensities is a study of the fine structure of the scattered beam. This entails resolving the spectrum of scattered light into its three peaks, viz. a central peak and two side ones. The need is thus obviated to refer to I0 or, according to the apparatus, the scattering power of a standard calibration material. The method is used mainly for determining diffusion constants and thermodynamic properties of liquids. 

Dark-field electron microscopy (in which the image is formed from the scattered beam), when combined with improved techniques of sample handling and preparation and minimal radiation exposure, can lead to images of sufficiently undamaged DNA at a resolution of 10 A (116). Figure 45 shows such an image in which the two-dimensional projection of the helix is clearly visible on the undamaged part of the molecule. 

Figure 1.2 shows the possible emerging beams after an incoming beam of intensity /o reaches a solid block. These emerging beams occur as a result of the interaction of the incoming light with atoms and/or defects in the solid part of the incident intensity is reflected in a backward direction as a beam of intensity Ir. Emitted beams of intensity f and/or scattered beams of intensity h spread in all directions. The transmitted beam of intensity f is also represented. 

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