29 research outputs found
X-ray diffraction from dislocation half-loops in epitaxial films
X-ray diffraction from dislocation half-loops consisting of a misfit segment
and two threading arms extending from it to the surface is calculated by the
Monte Carlo method. The diffraction profiles and reciprocal space maps are
controlled by the ratio of the total lengths of the misfit and the threading
segments of the half-loops. A continuous transformation from the diffraction
characteristic of misfit dislocations to that of threading dislocations with
increasing thickness of an epitaxial film is studied. Diffraction from
dislocations with edge and screw threading arms is considered and the
contributions of both types of dislocations are compared
Small-angle X-ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness and Porod's law
Small-angle X-ray scattering from GaN nanowires grown on Si(111) is measured in the grazing-incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q-4. The intensity depends on the orientation of the side facets with respect to the incident X-ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root-mean-square roughness of 0.9 nm, which is the height of just 3-4 atomic steps per micrometre-long facet, already gives rise to a strong intensity reduction. open access
Crystal truncation rods in kinematical and dynamical x-ray diffraction theories
Crystal truncation rods calculated in the kinematical approximation are shown
to quantitatively agree with the sum of the diffracted waves obtained in the
two-beam dynamical calculations for different reflections along the rod. The
choice and the number of these reflections are specified. The agreement extends
down to at least of the peak intensity. For lower intensities,
the accuracy of dynamical calculations is limited by truncation of the electron
density at a mathematically planar surface, arising from the Fourier series
expansion of the crystal polarizability
Small-angle X-ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness and Porod's law
Small-angle X-ray scattering from GaN nanowires grown on Si(111) is measured in the grazing-incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q-4. The intensity depends on the orientation of the side facets with respect to the incident X-ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root-mean-square roughness of 0.9 nm, which is the height of just 3-4 atomic steps per micrometre-long facet, already gives rise to a strong intensity reduction. open acces
X-ray scattering study of GaN nanowires grown on Ti/AlO by molecular beam epitaxy
GaN nanowires (NWs) grown by molecular beam epitaxy on Ti films sputtered on
AlO are studied by X-ray diffraction (XRD) and grazing incidence
small-angle X-ray scattering (GISAXS). XRD, performed both in symmetric Bragg
reflection and at grazing incidence, reveals Ti, TiO, TiAl, and
TiON crystallites with in-plane and out-of-plane lattice parameters
intermediate between those of AlO and GaN. These topotaxial
crystallites in Ti film, formed due to interfacial reactions and N exposure,
possess fairly little misorientation with respect to AlO. As a
result, GaN NWs grow on the top TiN layer possessing a high degree of epitaxial
orientation with respect to the substrate. The measured GISAXS intensity
distributions are modeled by the Monte Carlo method taking into account the
orientational distributions of NWs, a variety of their cross-sectional shapes
and sizes, and roughness of their side facets. The cross-sectional size
distributions of the NWs and the relative fractions of and
side facets are determined