Parallel geometry diffractometers

We will not describe here in detail the diffractometers irrstalled on synchrotron sorrrces, since they almost always consist of prototypes adapted to a particular type of study and measurement. We can point out, however, that since the source directly produces a parallel beam, the diffracted beams will be non-divergent regardless of the sample s shape (capillary, plane, transmissiorr, reflection, etc.). 

7 This crystal makes it possible to select a specific wavelength bandwidth. By analogy with spectroscopic methods, it is referred to as an analyzer crystal. 

Since the middle of the 1990s, some authors [SCH 96, FUG 99, GRO 98a] have suggested creating parallel geometry devices in laboratories designed by using the same idea as diflractometeis installed on synchrotron sources. Naturally, the main problem in this case is the intensity of the incident beam. This is why, in most cases, the multi-reflection, front monochromator is replaced with a parabolic multi-layer 

8 The divergence of a beam originating from a Bartels four-reflection monochromator is typically 12 arcseconds, or 2.7 thousandths of a degree. Note that, in the case of parabolic multi-layer monochromator, the divergence is 10 times that. 

Quite clearly, the Bragg-Brentano diffractometer leads to the best angitlar resolution. The peaks which are split in two, specific to the Kotj and Kot2 emission peaks, are plainly visible in the first pattern. The peaks in the second pattern are not split, but they are clearly wider than those obtained with the Bragg-Brentano diffractometer. 

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Diffractometer in parallel geometry. Hybrid front monochromator and flat analyzer crystal... 

In and out-plane X-ray diffraction pattern were recorded on a X-ray diffractometer equipped with a 4-axes goniometer (Rigaku ATX-G). CuKa radiation from copper rotating anode was used for the experiment. Incident angles (oo) for in plane geometry were between 0.14 and 0.36°, those for out of plane were between 0° and 5°. In-plane diffraction pattern is recorded as a result of the periodic structure of the direction perpendicular to the sample surface, out-plane diffraction pattern by structure of the direction parallel to the sample surface. 

The strain in thin crystalline films can also be detected by X-ray diffraction. A deviation of the lattice parameter from the respective bulk value, o, establishes the strain. The stress is then calculated from the elastic constants of the film and the geometry of the experiment. For example, the usual diffractometer geometry is widely enployed to measure the spacing of planes parallel to the substrate. The stress can be calculated from... 

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