Synthesis and structural characterization of a turbostratically disordered polymorph of (PbSe)1.18(TiSe2)2 is reported. The structure of this compound consists of an intergrowth between one distorted rock salt structured PbSe bilayer and two transition metal dichalcogenide structured Se–Ti–Se trilayers. In addition to the lattice mismatch, there is extensive rotational disorder between these constituents. The electrical resistivity of (PbSe)1.18(TiSe2)2 is a factor of 9 lower at room temperature, and the Seebeck coefficient is almost double that reported for the crystalline misfit layered compound analogue.

International audienceA semi-automatic technique for the mapping of nanocrystal phases and orientations in a transmission electron microscope (TEM) is described. It is based primarily on the projected reciprocal lattice geometry, but also utilizes the intensity of reflections that are extracted from precession-enhanced electron diffraction spot patterns of polycrystalline materials and multi-material composites. At the core of the method, experimental (precession-enhanced) electron diffraction spot patterns are cross correlated with pre-calculated templates for a set of model structures. The required hardware facilitates a scanning-precession movement of the primary electron beam on the polycrystalline and/or multi-material sample and can be interfaced to any newer or older mid-voltage TEM. The software that goes with this hardware is so flexible in its intake of experimental data that it can also create crystallite orientation and phase maps of nanocrystals from the amplitude part of Fourier transforms of high resolution TEM images. Experimentally obtained crystallite orientation and phase maps are shown for a clausthalite nanocrystal powder sample, polycrystalline aluminum and copper films, fine-grained palladium films, as well as MnAs crystallites that are partly embedded in a GaAs wafer. Comprehensive open-access and commercial crystallographic databases that may provide reference data in support of the nanocrystal phase identification process of the software are briefly mentioned. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Incorporating anisotropic surface charges on atomically precise gold nanoclusters led to a intense shortwave infrared photoluminescence exceeding 1100 nm with QY up to 6.1%.

The structural properties and the strain state of InGaN/GaN superlattices embedded in GaN nanowires were analyzed as a function of superlattice growth temperature, using complementary transmission electron microscopy techniques supplemented by optical analysis using photoluminescence and spatially resolved microphotoluminescence spectroscopy. A truncated pyramidal shape was observed for the 4 nm thick InGaN inclusions, where their (0001¯) central facet was delimited by six-fold {101¯l} facets towards the m-plane sidewalls of the nanowires. The defect content of the nanowires comprised multiple basal stacking faults localized at the GaN base/superlattice interface, causing the formation of zinc-blende cubic regions, and often single stacking faults at the GaN/InGaN bilayer interfaces. No misfit dislocations or cracks were detected in the heterostructure, implying a fully strained configuration. Geometrical phase analysis showed a rather uniform radial distribution of elastic strain in the (0001¯) facet of the InGaN inclusions. Depending on the superlattice growth temperature, the elastic strain energy is partitioned among the successive InGaN/GaN layers in the case of low-temperature growth, while at higher superlattice growth temperature the in-plane tensile misfit strain of the GaN barriers is accommodated through restrained diffusion of indium from the preceding InGaN layers. The corresponding In contents of the central facet were estimated at 0.42 and 0.25, respectively. However, in the latter case, successful reproduction of the experimental electron microscopy images by image simulations was only feasible, allowing for a much higher occupancy of indium adatoms at lattice sites of the semipolar facets, compared to the invariable 25% assigned to the polar facet. Thus, a high complexity in indium incorporation and strain allocation between the different crystallographic facets of the InGaN inclusions is anticipated and supported by the results of photoluminescence and spatially resolved microphotoluminescence spectroscopy.

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