The intercomparison of Bragg X-ray reflections from a small single crystal – zero-wavelength-dispersion profile measurement

Abstract

In conventional one-dimensional profile measurement procedures, either by diffractometry ('counter' profile) or by photography ('film' profile), intercomparison of Bragg reflections from a small single crystal, c, in a given experiment is rendered difficult, or impossible, by their wide variation in size with θc. Using synthetic I(Δω, Δ2θ) distributions, obtained by convolution of four components, the mosaic spread of the specimen crystal μ, the emissivity distribution of the source, σ, its wavelength distribution, λ, and the detector aperture, δ, analysis shows how the 'counter' and 'film' profiles change with scan mode. In particular, it is shown that the 'film' profile obtained using an ω/2θ (s = 2) scan mode does not involve wavelength dispersion, so that the profile distribution can yield information about μ for each reflection and therefore about small differences in mosaic spread (and hence reflectivity) between reflections. Possible means of obtaining this profile using film or counter procedures are outlined.