 | Acta Crystallographica Section A Acta Crystallographica Section A FOUNDATIONS AND ADVANCES |
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![[Figure 3]](vk5022fig3mag.jpg)
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Figure 3
(a) Several 2θ scans for fixed Ω settings with the interpretation in (c) based on the Ewald sphere construction. The spheres have different radii: 1/λα and 1/λβ, centred on p and o, respectively. Consider the 2θ scan for Ω = 12.5° in (a) (the crystal is orientated 1.7° from the Bragg angle θBα for the Cu Kα wavelength). There is a single specular peak (the intersection of the 2θ scan and the truncation rod) that is described in (b), where the specular contributions occur at the same 2θ but capture different positions on the truncation rod a and b, which is the same for both conventional and new theories. The two peaks corresponding to the d111 plane spacing for both the Cu Kα and Cu Kβ wavelengths, i.e. at 2θα and 2θβ, should not exist according to the conventional description. The peaks at c and d can only be described with the new theory. These enhancement peaks can be observed up to |Ω − θB| ≃ 6°, which are given in (b) where a baseline for the intensity level from either side of each peak reveals more intensity above the line than below. This is very close to the observational limit for this experiment. The specular peaks are sharp (they are dominated by the proportion of the incident-beam divergence that satisfies this condition, i.e. a small region on the sample), and the enhancement peaks are broad (because all the incident-beam divergence directions will form intensity at 2θB and these exist over the full footprint of the beam on the sample. As the Bragg condition is approached the peak will sharpen because the strongest contributions come from a smaller range of divergence and smaller positions on the sample, and dominate). |
![[Figure 3]](vk5022fig3.jpg)
| FOUNDATIONS ADVANCES |
ISSN: 2053-2733
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