  Co2FeSi/GaAs(110) and Co2FeSi/GaAs(111)B hybrid structures were grown by
molecular-beam epitaxy and characterized by transmission electron microscopy
(TEM) and X-ray diffraction. The films contained inhomogeneous distributions of
ordered L2_1 and B2 phases. The average stoichiometry was controlled by lattice
parameter measurements, however diffusion processes lead to inhomogeneities of
the atomic concentrations and the degradation of the interface, influencing
long-range order. An average long-range order of 30-60% was measured by
grazing-incidence X-ray diffraction, i.e. the as-grown Co2FeSi films were
highly but not fully ordered. Lateral inhomogeneities of the spatial
distribution of long-range order in Co2FeSi were found using dark-field TEM
images taken with superlattice reflections.
