  Unique intensity features arising from dynamical diffraction arise in
coherent x-ray nanobeam diffraction patterns of crystals having thicknesses
larger than the x-ray extinction depth or exhibiting combinations of nanoscale
and mesoscale features. We demonstrate that dynamical scattering effects can be
accurately predicted using an optical model combined with the Darwin theory of
dynamical x-ray diffraction. The model includes the highly divergent coherent
x-ray nanobeams produced by Fresnel zone plate focusing optics and accounts for
primary extinction, multiple scattering, and absorption. The simulation
accurately reproduces the dynamical scattering features of experimental
diffraction patterns acquired from a GaAs/AlGaAs epitaxial heterostructure on a
GaAs (001) substrate.
