Double-crystal

A much better way would be to use phase contrast, rather than attenuation contrast, since the phase change, due to changes in index of refraction, can be up to 1000 times larger than the change in amplitude. However, phase contrast techniques require the disposal of monochromatic X-ray sources, such as synchrotrons, combined with special optics, such as double crystal monochromatics and interferometers [2]. Recently [3] it has been shown that one can also obtain phase contrast by using a polychromatic X-ray source provided the source size and detector resolution are small enough to maintain sufficient spatial coherence. 

Besides, because this probe is suitable for testing various artificial defects such as FBH, SDH, columned holes and cracks and its testing range is larger than ordinary one-transmitting-and-the-other-receiving double crystal creeping wave probe, we can conclude that this probe has a wide use value and prospect. 

Coherent anti-Stokes Raman scatttering, or CARS as it is usually known, depends on the general phenomenon of wave mixing, as occurs, for example, in a frequency doubling crystal (see Section 9.1.6). In that case three-wave mixing occurs involving two incident waves of wavenumber v and the outgoing wave of wavenumber 2v. 

If nutmeg butter, a commercial fat obtained by the hot pressing of ground nutmegs, is available, the above extraction may be omitted. The only operation necessary is a double crystallization of the crude material from boiling 95 per cent alcohol. Since nutmeg butter is frequently adulterated with foreign fats, the purity of the product should be checked by the saponification number (232 for pure trimyristin). 

Grazing Incidence X-Ray Diffraction Grazing Incidence X-Ray Diffraction Double Crystal Diffractometer... 

The 6 Nd YAG lasers pump the DM0, preamplifier and power amplifier (Fig. 19, Friedman et al., 1998). The YAG lasers are built from commercially available flashlamp/laser rod assemblies, acousto-optic Q-switches and frequency doubling crystals (LBO and KTP). Most of the mirror mounts and crystal holders are commercial. Nd YAGs are frequency doubled to 532 nm using a nonlinear crystal. The Nd YAG rod and nonlinear crystal are both in the pump laser cavity to provide efficient frequency conversion. The 532 nm light is coupled out through a dichroic and fed to multimode fibers which transport the light to the DM0 and amplifier dye cells. 

SI(220) double crystal monochromator was used with entrance slit (1 mm high 20 m from the source point) chosen to give a bandpass of 2 eV at the Pt edge, 11,563.7 eV.( ) The operation of the catalyst... 

The typical experimental setup (here the experiment established at beamline G3/ HASYLAB [12] is shown) is outlined in Figure 5. The white synchrotron radiation is monochromatized by a double crystal monochromator using the Ge (311) reflection... 

The crude product may be recrystallized by dissolving it in a minimum amount of 1 N hydrochloric acid at room temperature and cooling in an ice bath to 0°. Concentrated hydrochloric acid is added slowly, 0.5 ml. at a time, until the initial volume is approximately doubled. Crystals are removed by filtration and washed with ethanol and diethyl ether. In a typical run the crude yield is 10.3 g. or 70%, and the recrystallized yield is 7.7 g. or about 53%. 

Similarly one must be cautious in other third-order experiments. While EFISH of condensed phase materials looks like simple SHG if the sample is totally confined to the region of constant field between the electrodes, there is an important difference between this case and the more frequently performed and described study of frequency doubling crystals (31). In the latter case nonvanishing E2w occurs only in the crystal where x 0. However, in EFISH P2" also occurs in air due to its nonvanishing x Contributions to E2w upstream and downstream from the sample must... 

X-ray Instrumentation. All experiments were performed at the Cornell High Energy Synchrotron Source (CHESS) operated at 5.8 GeV (Stations A-3, B and C-2). Monochromatic radiation was obtained with a Si (220) double crystal monochromator. In order to eliminate higher harmonics, 50% detunning was typically employed. ... 

The simplest conditioner is a perfect crystal of the same type as the specimen, using the same reflecting planes, with the deviation of the diffracted beam in the opposite sense to that at the specimen. This is the classic +, - symmetrical double crystal method , as shown inFigrrre 1.5, which gives excellent and easily interpreted resrrlts. Many variations are, however, possible, for example to maximise the sensitivity to strain, or to emphasise the contribution of near-srrrface layers to the diffraction, and we shall treat these in detail in this book. 

There are many methods of X-ray topography, though the most popitlar are the Lang method with slit-collimated radiation and the double-crystal methods, which may be thought of as high resolution diffractometry with an imaging... 

Figure 1.8 A double-crystal topograph of a GaP crystal, taken with CuK i radiation from a conventional 1 kW X-ray tube. Direct imaging X-ray detector (Bede Scientific), 1 minute exposure. Cracks, sub-grain boundaries and variations in dislocation density are...

The denominator (normalising constant) is the integrated reflectivity of the first crystal. Figure 2.13 shows the plane wave and the double-crystal rocking curve, again for Si 220 with CuK 1. We note the following ... 

The double-crystal rocking curve is symmetric, though the plane wave reflectivity curve is not. This is a consequence of the autocorrelation, since the autocorrelation of any function is an even fimction. 

Another way of looking at the traditional double-crystal method is that it measures the difference in reflectivity between the specimen and a reference perfect crystal. This is the original high resolution method and is still the best choice when good reference crystals are available and the specimens to be... 

Figure 2.13 The plane wave and double-crystal rocking curves for Si 220 with CuK j...

The theory of this aberration was worked out in the 1920s by Schwarzchild. For simphcity we shall discuss the case of a beam conditioner comprising a single crystal and an aperture as in the classic double-crystal arrangement. If the Bragg planes are tilted about an axis contained in the incidence plane and the... 

If a specimen is heavily dislocated it may be impossible to distinguish peaks in double-crystal rocking curves. Figure 7.5 shows a five-layer Si-Ge specimen grown with 0.5 //m thick layers, with the Ge content in each layer respectively 10, 20, 30, 40 and 50% the aim being to produce a moderate amount of relaxation at each layer so that the top layer is fully relaxed 50% Ge but without excessive threading dislocations. This was achieved—the dislocation density was... 

Figure 7.5 (a) Double-crystal rocking curve of the five-layer Si-Ge structure, (b) Tripleaxis -2 longitudinal scan of the same structure, (c) Specimen only (rocking curve) scan with the analyser set on the left-hand peak in the triple-axis curve. 004 reflection with CuK, single-reflection Ge analyser for (b) and (c)... 

Finally, we note that the standard double-crystal or high resoluhon rocking curve, in which we have no control over is in effect a horizontal scan through reciprocal space, integrahng all intensihes along the Ewald sphere. It is thus easy to see how the triple-axis instrament can obtain much more information. 

In this chapter we discuss double-crystal topography, in which we obtain a map of the diffracting power of a crystal compared to that of a reference. We first treat the principles and geometries, the mechanisms of image contrast and resolution and the ttse of laboratory and synchrotron radiation. We then discuss applicatiorrs wafer inspection, strain contour mapping, topography of curved crystals. 

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