Scattering Geometries

The vectors k , k/, and Q define the scattering geometry as iiiustrated in Figure i. 

Figure 3 Scattering geometries appropriate to (a) liquids in capillaries or glass fibers ...

Usually, particle size has relatively little effect on Raman line shapes unless the particles are extremely small, less than 100 nm. For this reason, high-quality Raman spectra can be obtained from powders and from polycrystalline bulk specimens like ceramics and rocks by simply reflecting the laser beam from the specimen surface. Solid samples can be measured in the 90° scattering geometry by mounting a slab of the solid sample, or a pressed pellet of a powder sample so that the beam reflects from the surface but not into the entrance slit (Figure 3). 

Figures (a) Scattering geometry for ERS (b) ERS spectrum from 200-A partially deuterated polystyrene on Si, E h 3.0 MeV (adapted from ref. 101 and (cl schematic ERS depth profile spectrum.

Ni(IIO). The top part of the figure shows the scattering geometry. The primary ion energy was 101 keV. 

Figure 5 Si backscattering yiaids (anguiar scans) for normal incidance on the Si (111) (7x7) surface (solid squares) and the Si (111) [Jz x Jz) R30°-Au surface (open circies). The curve is the expected yield from a bulk terminated Si (111) surface. The scattering geometry is shown in the inset.

The depth resolution of ERDA is mainly determined by the energy resolution of the detector system, the scattering geometry, and the type of projectiles and recoils. The depth resolution also depends on the depth analyzed, because of energy straggling and multiple scattering. The relative importance of different contributions to the depth resolution were studied for some specific ERDA arrangements [3.161, 3.163]. 

Obviously, experiments designed to measure cross-sections as a function of energy are needed. At present, tandem experiments are not capable of high precision at low energies because one must assume details of collision mechanics and because it is difficult to estimate collection efficiencies in forward scattering geometry (15). The extension of all known techniques to lower energy (64, 65) and the further development of pulse methods (58) offer the possibility for advances in this area. 

FIGURE 27.7 Grazing incidence X-ray scattering geometry. The X-rays are incident on the sample at an angle (j) and are detected at a combination of two angles 29 and 2c ). ... 

In Raman measurements [57], the 514-nm line of an Ar+ laser, the 325-nm line of a He-Cd laser, and the 244-nm line of an intracavity frequency-doubled Ar+ laser were employed. The incident laser beam was directed onto the sample surface under the back-scattering geometry, and the samples were kept at room temperature. In the 514-nm excitation, the scattered light was collected and dispersed in a SPEX 1403 double monochromator and detected with a photomultiplier. The laser output power was 300 mW. In the 325- and 244-nm excitations, the scattered light was collected with fused silica optics and was analyzed with a UV-enhanced CCD camera, using a Renishaw micro-Raman system 1000 spectrometer modified for use at 325 and 244 nm, respectively. A laser output of 10 mW was used, which resulted in an incident power at the sample of approximately 1.5 mW. The spectral resolution was approximately 2 cm k That no photoalteration of the samples occurred during the UV laser irradiation was ensured by confirming that the visible Raman spectra were unaltered after the UV Raman measurements. 

Conversion electron Mossbauer spectroscopy (CEMS) measurements with back scattering geometry have the merit that spectra can be obtained from a sample with much less isotope content compared with transmission measurements. Another merit is that a sample, deposited on a thick substrate, could be measured, and that because of the limited escape depth of the conversion electrons, depth-selective surface studies are possible. The CEMS technique was found to be best applicable to specimens of 10-100 pg Au cm, i.e., about two orders of magnitudes thinner than required for measurements in transmission mode [443]. This way (1) very thin films of gold alloys, as well as laser- and in beam-modified surfaces in the submicrometers range of depth [443], and (2) metallic gold precipitates in implanted MgO crystals [444] were investigated. 

Figure 9.3. Scattering geometry for the measurement of pole figures in a texture goniometer. The scattering angle 20/,/./ is fixed, (p and (// are scanned...

The total of eight individually pumped chambers separated by small orifices keeps a pressure ratio of 20 orders of magnitude between the He source reservoir and detector. This is done at the expense of the flexibility of the scattering geometry. In the case of the apparatus shown in Fig. 2, the angle between incident and outgoing beam is fixed at 9, -I- 9, = 90°. 

Fig. 15 Raman scattering spectra of a STO 16 and b STO 18-23 observed in x(yy)-x scattering geometry (tetragonal notation). Arrows in a indicate positions of DIRS signal and its higher harmonic component [27]...

Fig. 17 Temperature dependencies of the mode observed in ST016 closed circles), STO 18-23 closed squares), and STO 18-32 closed triangles) observed in the scattering geometry x yy)-x. Crosses indicate the results for STO 16 obtained by the hyper-Raman scattering experiment. The corresponding open symbols denotes the half-width at half maximum of the soft u mode spectrum of each specimen [27]...

Fig. 18 Raman scattering spectra of a ST018-23 and b ST018-32 observed in x(yz)-x scattering geometry in a low-temperature region [27]...

Sun, W. X., and Shen, Z. X. 2003. Apertureless near-field scanning Raman microscopy using reflection scattering geometry. Ultmmicroscopy. 94 237 44. 

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