  Co2FeSi/GaAs(110) and Co2FeSi/GaAs(-1-1-1)B hybrid structures were grown by
molecular-beam epitaxy (MBE) and characterized by transmission electron
microscopy (TEM) and X-ray diffraction (XRD). The films contain inhomogeneous
distributions of ordered L21 and B2 phases. The average stoichiometry could be
determined by XRD for calibration of the MBE sources. Diffusion processes lead
to inhomogeneities, influencing long-range order. An average L21 ordering of up
to 65% was measured by grazing-incidence XRD. Lateral inhomogeneities of the
spatial distribution of long-range order in Co2FeSi were imaged using
dark-field TEM with superlattice reflections and shown to correspond to
variations of the Co/Fe ratio.
