 | Acta Crystallographica Section A Acta Crystallographica Section A FOUNDATIONS AND ADVANCES |
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![[Figure 5]](ae5046fig5mag.jpg)
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Figure 5
(a) Several 2θ scans for fixed Ω settings with the interpretation in (b) based on the modified 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 at a and b, which is the same for both conventional and new theories. The two peaks, c and d, correspond to the d111 plane spacing for both the Cu Kα and Cu Kβ wavelengths, i.e. 2θα and 2θβ; in the conventional description these should not exist. The peaks at c and d can only be described with the new theory, i.e. the persistent intensity at 2θα and 2θβ. The 2θα peak can be observed up to |Ω − θB| ∼ 6°. 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 regions on the sample and dominate). The features at the base of the specular peaks are tube focus artefacts. |
![[Figure 5]](ae5046fig5.jpg)
| FOUNDATIONS ADVANCES |
ISSN: 2053-2733
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