In situ x-ray diffraction study of epitaxial growth of ordered Fe3Si films

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 intensity 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.Comment: 8 pages, 3 figure

Chirality effects on 2D phase transitions

Monolayers of the racemate and pure enantiomers of 1-hexadecyl-glycerol were investigated by grazing incidence X-ray diffraction (GID) at 5 and 20 °C on compression from 0 mN m−1 to pressures greater than 30 mN m−1. The racemate lattice is centred-rectangular for both temperatures at all investigated pressures. However, at both temperatures, there is a sharp phase transition from a low-pressure phase, in which the molecules are tilted towards nearest neighbours (NN) and the distortion azimuth also points towards NN, to a high-pressure phase, in which the molecules are tilted towards next-nearest neighbours (NNN) and an NNN-distorted lattice is observed. At 5 °C, the transition pressure is 15 mN m−1, whereas at 20 °C it is 18 mN m−1. Chirality destroys this transition: the pure enantiomer always exhibits an oblique lattice with tilted molecules, and the azimuths of tilt and distortion continuously vary from a direction close to NN to a direction close to NNN. The nature of the phase transition and the influence of chirality on it are discussed within the framework of Landau's theory of phase transitions

Strain nonuniformity in GaAs heteroepitaxial films on Si(001) studied by x-ray diffraction

High-resolution x-ray diffraction measurements are used to fully characterize the strain state of relaxed highly mismatched GaAs films, grown on vicinal Si (001) substrates by molecular beam epitaxy. The nonuniformity of the misfit dislocation network at the GaAsSi (001) interface is studied by analyzing the profiles of x-ray diffraction peaks and the reciprocal space maps for different reflections. The detailed analysis of the peak positions shows a dependence of the relaxation on the crystallographic direction, with the relaxation being larger in the direction perpendicular to the α -dislocation lines. Based on analytical expressions for the full width at half maximum in the longitudinal and transverse sections, an advanced version of the Williamson-Hall plot [Acta Metall. 1, 22 (1953)] is proposed that takes into account the geometry of dislocation distribution and the scattering geometry. We show that this type of analysis can reveal both the type and density of misfit dislocations. The measured peak widths are attributed to random uncorrelated 60°-type misfit dislocations with density much smaller than the total dislocation density required for lattice-mismatch relaxation. The major part of the GaAsSi lattice mismatch is accommodated by periodic arrays of edge-type perfect dislocations that do not cause nonuniform strain in the film. The applied theoretical and experimental analysis is easily applicable on other zinc blende highly lattice-mismatched systems. © 2007 American Institute of Physics

Structural properties of InN films grown on O-face ZnO(000(1)over-bar) by plasma-assisted molecular beam epitaxy

We study the impact of substrate temperature and layer thickness on the morphological and structural properties of InN films directly grown on O-face ZnO(000 (1) over bar) substrates by plasma-assisted molecular beam epitaxy. With increasing substrate temperature, an interfacial reaction between InN and ZnO takes place that eventually results in the formation of cubic In2O3 and voids. The properties of the InN films, however, are found to be unaffected by this reaction for substrate temperatures less than 550 degrees C. In fact, both the morphological and the structural quality of InN improve with increasing substrate temperature in the range from 350 to 500 degrees C. High quality films with low threading dislocation densities are demonstrated. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3702572

Structural and magnetic phase transition in MnAs 0001 GaAs 111 epitaxial films

The ferromagnetic phase transition in a MnAs film on GaAs 111 , where the MnAs unit cell is epitaxially fixed in its hexagonal plane, proceeds under conditions qualitatively different from the transition in bulk MnAs crystals or in MnAs films on GaAs 001 . We present experimental evidence for the coexistence between ferromagnetic and paramagnetic phases in a temperature interval of 10degreesC. Temperature dependencies of the phase fractions and the in plane lattice parameters obtained by grazing incidence x ray diffraction are compared with magnetization measurement