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Molecular beam epitaxy of PbTe on BaF 2 ͑111͒ is studied using UHV-scanning tunneling microscopy and atomic force microscopy. It is shown that PbTe growth is totally dominated by growth spirals formed around threading dislocations ͑TD͒ that originate from the growth on the 4.2% lattice-mismatched substrate. Due to dislocation annihilation, the TD density rapidly decreases with layer thickness, which results in a dramatic increase of the electron mobilities in the layers.

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We report magnetotransport measurements performed on a 10 nm n-type PbTe/ Pb 0.9 Eu 0.1 Te quantum well grown on a BaF 2 substrate. In contrast to previous work, both the Hall and longitudinal resistances show a clearly defined signature of the integer quantum Hall effect with no sign of parallel conduction. Due to the large carrier density, the occupation of two longitudinal subbands and one oblique valley subband leads to an unusual sequence of filling factors.

The structure of porous silicon layers was accurately investigated by diverse x-ray methods. A series of samples with etching times varying from 1 to 10 min was produced by chemical etch using a HF/ HNO 3 -based solution assisted with NaNO 2 . The porosity determined from low-angle x-ray reflectivity spectra was found to fluctuate from 35% to 55% as the etch proceeds. Reciprocal space mapping around the ͑004͒ Si lattice point revealed that the Si crystallites are deformed due to a distribution of in-plane compressive strain caused by the neighboring pores, which leads to an expansion of the perpendicular lattice parameter. No signature of mosaicity was found. The perpendicular strain could be precisely determined by fitting the x-ray-diffraction spectra, measured in the triple-axis configuration, to a set of Voigt and Gaussian distributions. These strain distributions are certainly associated with the different population of crystallite sizes formed during the stain etching process. We were able here to determine the temporal evolution of the strain inside the nanostructured porous silicon.