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Co2TiSi films were grown by molecular beam epitaxy on GaAs(001) and analyzed using reflection high-energy electron diffraction, and electron microscopy. In addition, X-ray diffraction was combined with lattice parameter calculations by density functional theory comparing the L21 and B2 structures and considering the influence of non-stoichiometry. Columnar growth is found and attributed to inhomogeneous epitaxial strain from non-random alloying. In films with thicknesses up to 13 nm, these columns may be the origin of perpendicular magnetization with the easy axis perpendicular to the sample surface. We found L21 and B2 ordered regions, however the [Co]/[Ti]-ratio is changing in dependence of the position in the film. The resulting columnar structure is leading to anisotropic B2-ordering with the best order parallel to the axes of the columns. [ABSTRACT FROM AUTHOR]

Density functional theory calculations were performed on undoped AlN screw threading dislocations (TDs) as well as TDs doped by indium and oxygen, prompted by integrated experiments through transmission electron microscopy and spectroscopic techniques demonstrating enhanced In and O concentrations in screw dislocation cores. It is revealed that screw TDs act as conduction pathways to charge carriers, introducing multiple levels in the bandgap due to overstrained, dangling, and 'wrong' bonds formed even in the undoped cores. The presence of impurities and especially metallic In elevates the metal-like electronic structure of the distorted material and promotes the conductivity along the dislocation line. Hence screw dislocations in AlN are established as highly prominent conductive nanowires in semiconducting thin films and prospects for novel, highly functional nano-device materials through exploitation of screw TDs are attested. [ABSTRACT FROM AUTHOR]

GaN quantum dots (QDs) grown in semipolar [formula] AlN by plasma-assisted molecular-beam epitaxy were studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy techniques. The embedded [formula]-grown QDs exhibited pyramidal or truncated-pyramidal morphology consistent with the symmetry of the nucleating plane, and were delimited by nonpolar and semipolar nanofacets. It was also found that, in addition to the [formula] surface, QDs nucleated at depressions comprising [formula] facets. This was justified by ab initio density functional theory calculations showing that such GaN/AlN facets are of lower energy compared to [formula]. Based on quantitative high-resolution TEM strain measurements, the three-dimensional QD strain state was analyzed using finite-element simulations. The internal electrostatic field was then estimated, showing small potential drop along the growth direction, and limited localization at most QD interfaces. [ABSTRACT FROM AUTHOR]

In the present paper we report on structural investigations of fivefold In[sub 0.2]Ga[sub 0.8]As/GaAs superlattices which have been grown by means of metal organic chemical vapor deposition on vicinal GaAs(001) substrates. Cross-sectional transmission electron micrographs exhibit an initially flat and nonfaceted grooved surface, while step bunching occurs during subsequent growth stages with an inclined vertical inheritance approximately 45° off the (001) direction. A reconstructed sample cross section on the base of high resolution x-ray diffraction data qualitatively confirms the local morphology proved by transmission electron microscopy. Moreover, a line shape analysis of diffusely scattered intensity using Gauss profiles indicates a lateral short range ordering of step bunches. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A combination of the transmission electron microscopy and scanning transmission electron microscopy techniques is employed to explain the properties exhibited by the self-assembled semipolar GaN quantum dots (QDs) in (1122)AlN compounds. These QDs are shown to exhibit a pyramidal or truncated-pyramidal morphology.

First order reverse curves are used for examining the Preisach distribution and electron holography in order to observe the spatial variation of the magnetization in [Fe.sub.40][Co.sub.40][Nb.sub.4][B.sub.13][Ge.sub.2][Cu.sub.1] nanocomposite alloys after annealing. The irreversible magnetic process is attributed to pinning sites in the intergranular regions as shown by irregularity of magnetic flux line disclosed by electron holography.

First order reverse curves have been used to investigate the Preisach distribution and electron holography to observe the spatial variation of the magnetization in Fe40Co40Nb4B13Ge2Cu1 nanocomposite alloys after annealing at 500, 550, 610, and 960 °C for 1 h. Grain sizes observed for these annealing temperatures varied from 10 to 200 nm. The Preisach distribution reveals that the magnetization process in the sample annealed at 500 °C for 1 h was dominated by reversible processes, consistent with a small coercivity and mobile domain walls in an external field. At higher annealing temperatures, the irreversible magnetization processes became dominant with increasing grain size. Electron holography observations of the domains show that, for the sample annealed at 500 °C, the magnetic flux distribution was uniform with few pinning barriers to domain wall motion consistent with reversible magnetization. The sample annealed at 610 °C exhibited irregularity in the shape of magnetic flux lines attributed to the inhomogeneous magnetization distribution due to the α-FeCo and (FeCoNb)23B6 phases present after secondary crystallization. [ABSTRACT FROM AUTHOR]