Fe3Si/Al/Fe3Si/GaAs(001) structures were deposited by molecular-beam epitaxy and characterized by transmission and scanning electron microscopy, and x-ray diffraction. The first Fe3Si film on GaAs(001) is growing epitaxially as (001) oriented single
crystal. The subsequent Al film grows almost 111 oriented in a fibre texture although the underlying Fe3Si is exactly (001) oriented. The growth in this orientation is triggered by a thin transition region which is formed at the Fe3Si/Al interface. In the end after the growth of the second Fe3Si layer on top of the Al the final properties of the whole stack depend on the substrate temperature T_S during deposition of the last film. The upper Fe3Si films are mainly 110 oriented although they are poly-crystalline. At lower T_S, around room temperature, all the films retain their original structural properties.
GaAs nanowires and GaAs/Fe3Si core/shell nanowire structures were grown by molecular-beam epitaxy on oxidized Si(111) substrates and characterized by transmission electron microscopy. The surfaces of the original GaAs NWs are completely covered by ma
gnetic Fe3Si exhibiting nanofacets and an enhanced surface roughness compared to the bare GaAs NWs. Shell growth at a substrate temperature of T{S} = 200 {deg}C leads to regular nanofacetted Fe3Si shells. These facets, which lead to thickness inhomogeneities of the shells, consist mainly of well pronounced Fe3Si(111) planes. The crystallographic orientation of core and shell coincide, i.e. they are pseudomorphic. The nanofacetted Fe3Si shells found in the present work are probably the result of the Vollmer-Weber island growth mode of Fe3Si on the {110} side facets of the GaAs NWs.
GaAs nanowires and GaAs-Fe3Si core-shell nanowire structures were grown by molecular-beam epitaxy on oxidized Si(111) substrates and characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Ga droplets were formed on the o
xide surface, and the semiconducting GaAs nanowires grew epitaxially via the vapor-liquid-solid mechanism as single-crystals from holes in the oxide film. We observed two stages of growth of the GaAs nanowires, first the regular growth and second the residual growth after the Ga supply was finished. The magnetic Fe3Si shells were deposited in an As-free chamber. They completely cover the GaAs cores although they consist of small grains. High-resolution TEM micrographs depict the differently oriented grains in the Fe3Si shells. Selected area diffraction of electrons and XRD gave further evidence that the shells are textured and not single crystals. Facetting of the shells was observed, which lead to thickness inhomogeneities of the shells.
The strain state and composition of a 400 nm thick (In,Ga)N layer grown by metal-organic chemical vapor deposition on a GaN template are investigated by spatially integrated x-ray diffraction and cathodoluminescence (CL) spectroscopy as well as by sp
atially resolved CL and energy dispersive x-ray analysis. The CL investigations confirm a process of strain relaxation accompanied by an increasing indium content toward the surface of the (In,Ga)N layer, which is known as the compositional pulling effect. Moreover, we identify the strained bottom, unstrained top, and gradually relaxed intermediate region of the (In,Ga)N layer. In addition to an increase of the indium content along the growth direction, the strain relaxation leads to an enhancement of the lateral variations of the indium distribution toward the surface.
We analyze the strain state of GaN nanowire ensembles by x-ray diffraction. The nanowires are grown by molecular beam epitaxy on a Si(111) substrate in a self-organized manner. On a macroscopic scale, the nanowires are found to be free of strain. How
ever, coalescence of the nanowires results in micro-strain with a magnitude from +-0.015% to +-0.03%.This micro-strain contributes to the linewidth observed in low-temperature photoluminescence spectra.
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.
Molecular beam epitaxy of Fe3Si on GaAs(001) is studied in situ by grazing incidence x-ray diffraction. Layer-by-layer growth of Fe3Si films is observed at a low growth rate and substrate temperatures near 200 degrees Celsius. A damping of x-ray inte
nsity oscillations due to a gradual surface roughening during growth is found. The corresponding sequence of coverages of the different terrace levels is obtained. The after-deposition surface recovery is very slow. Annealing at 310 degrees Celsius combined with the deposition of one monolayer of Fe3Si restores the surface to high perfection and minimal roughness. Our stoichiometric films possess long-range order and a high quality heteroepitaxial interface.
