Multiple scattering in grazing-incidence X-ray diffraction: impact on lattice-constant determination in thin films
Sprache des Titels:
Dynamical scattering effects are observed in grazing-incidence X-ray diffraction experiments using an organic thin ?lm of 2,20:60,200-ternaphthalene grown on oxidized silicon as substrate. Here, a splitting of all Bragg peaks in the out-of-plane direction (z-direction) has been observed, the magnitude of which depends both on the incidence angle of the primary beam and the out-of-plane angle of the scattered beam. The incident angle was varied between 0.09?? and 0.25?? for synchrotron radiation of 10.5 keV. This study reveals comparable intensities of the split peaks with a maximum for incidence angles close to the critical angle of total external re?ection of the substrate. This observation is rationalized by two different scattering pathways resulting in diffraction peaks at different positions at the detector. In order to minimize the splitting, the data suggest either using incident angles well below the critical angle of total re?ection or angles well above, which suf?ciently attenuates the contributions from the second scattering path. This study highlights that the refraction of X-rays in (organic) thin ?lms has to be corrected accordingly to allow for the determination of peak positions with suf?cient accuracy. Based thereon, a reliable determination of the lattice constants becomes feasible, which is required for crystallographic structure solutions from thin ?lms.