X-ray diffraction with a four-reflection monochromator

Abstract

A formula is derived for simulating rocking‐curve measurements made with an X‐ray diffractometer fitted with a four‐reflection monochromator. The derivation is carried out both graphically and algebraically. Results of a simulation using this formula are then compared with experimentally obtained rocking curves. The rocking curves were obtained using a diffractometer with a four‐reflection monochromator that uses 440 reflections from two channel‐cut germanium crystals. The experimental data comprise 200, 400, 600, 511, 711, 622, 422 and 444 reflections from thick single‐crystal indium phosphide grown by the vertical‐gradient freeze technique. The simulated data correlate well with the experimental data, although the simulations consistently show somewhat higher reflectivities and narrower linewidths than the experiment, indicating the existence of broadening mechanisms not included in the simulation that are affecting the experiment.

A high-resolution X-ray diffractometer for the study of imperfect materials

“…2. Taking into account the (+,À,À,+) geometry of the monochromator, the transmittance function of the monochromator is simply R m (Á3) = R(Á3) 2 R(ÀÁ3) 2 (Mo È ller, 1994;Sabine, 1987;Slusky & Macrander, 1987). This transmittance function for the '-polarization state is drawn together with R(Á3) in Fig.…”

The three-dimensional resolution function of the four-reflection monochromator: a route to a higher intensity

“…Interesting also are the numbers for the symmetric monochromator. For the 440 setting, a divergence of 5" and a wavelength spread of 3.5 × 10-5 is generally quoted (Bartels, 1983;Slusky & Macrander, 1987). These figures are derived from the 440 rocking curve and not from consideration of the monochromator as a whole.…”

The Instrumental Broadening Function of the Bartels Five-Crystal X-ray Diffractometer

“…Bartels (1983a,b) subsequently developed a four-crystal monochromator using germanium crystals and a Cu X-ray tube as the source, which has led to the popular use of the instrument. Slusky & Macrander (1987), van der Sluis (1994) and M611er (1994) have described the instrumental function for the Bartels five-crystal diffractometer. The results of their work can be applied to predict the shapes and widths of diffraction profiles measured with the fivecrystal diffractometer if the specimen diffraction profile is known.…”