[en] The bimetallic AgCo nanoparticles synthesized by colloidal chemistry and deposited onto Si(1 0 0) substrate are investigated. Size-selective mechanisms of colloidal crystallization during the self-organization are evidenced. The magnetic behavior is studied and correlated with the nanoparticles structure and morphology

[en] The stacking faults (SFs) in the silicon overlayer, which is formed after the implantation of silicon wafers by high doses (2 x 10¹⁸ cm^-2) of oxygen ions, are studied. During the implantation, a three-dimensional network of SiO₂ precipitates is formed along the <100> directions. Stacking faults appear only after a high-temperature annealing when all the SiO₂ precipitates are dissolved. Due to the very low value of the anomalous absorption coefficients of silicon, α-fringe contrast profile calculations are needed for the characterization of SFs. The results show that these SFs are extrinsic in character, bounded by Frank partial dislocations. (author)

[en] First-principles calculations relating to the atomic structure and electronic properties of {1 0 1-bar 3} GaN surfaces reveal significant differentiations between the two polarity orientations. The (1 0 1-bar 3) surface exhibits a remarkable morphological stability, stabilizing a metallic structure (Ga adlayer) over the entire range of the Ga chemical potential. In contrast, the semiconducting, cleaved surface is favoured on (111-bar 3-bar) under extremely and moderately N-rich conditions, a Ga bilayer is stabilized under corresponding Ga-rich conditions and various transitions between metallic reconstructions take place in intermediate growth stoichiometries. Efficient growth schemes for smooth, two-dimensional GaN layers and the isolation of {1 0 1-bar 3} material from parasitic orientations are identified.

[en] Lead-rich solid industrial wastes were vitrified by the addition of glass formers in various concentrations, to produce non-toxic vitreous stabilized products that can be freely disposed or used as construction materials. Toxicity of both the as-received industrial solid waste and the stabilized products was determined using standard leaching test procedures. The chemically stable vitreous products were subjected to thermal annealing in order to investigate the extent of crystal separation that could occur during cooling of large pieces of glass. Leaching tests were repeated to investigate the relation between annealing process and chemical stability. X-ray, scanning and transmission electron microscopy techniques were employed to identify the microstructure of stabilized products before and after thermal treatment. Relation between synthesis and processing, chemical stability and microstructure was investigated

[en] GaN nanowires (NWs) were grown on sapphire by molecular beam epitaxy. NWs form only in the presence of Ni seed particles and only under N-rich conditions. Their length increases linearly with growth time up to about 7.5 μm while their diameter remains almost constant. In contrast, a switch to Ga-rich conditions after NW formation results in radial growth, i.e., the NW diameter increases while lengthening is negligible. These results corroborate the fact that the growth of III-V NWs is governed by the accumulation of group-III atoms in the seeds, while group-V species are not preferentially incorporated at the seeds

[en] We present theoretical and experimental results on the bonding and structural characteristics of AlN:Ag thin film nanocomposites obtained by means of density functional theory (DFT) computations, high resolution transmission electron microscopy (HRTEM) observations, Auger electron spectroscopy (AES), and x-ray diffraction (XRD) measurements. From the theoretical calculations it was determined that the presence of the Ag substitutional of N or Al atoms affects the electronic density of states (EDOS) of the resulting systems. In particular, occupied energy states are introduced (between others) that lie within the energy gap of the AlN matrix due to Ag-d, Al-p (accompanied with a charge transfer from Al to Ag), Ag-p, and N-p hybridizations, respectively. The effect is predicted to be even more pronounced in the case of Ag nanoparticle inclusions affecting the EDOS of the composite system. These predictions were verified by the HRTEM images that gave unequivocal evidence for the presence and stability of Ag nanoparticles in the AlN matrix. In addition, the AES data suggested a metal-metal (Ag-Al) bonding preference, while the XRD patterns revealed that the atomic Ag dispersions in the AlN thin films results in a small elongation of the Wurtzite lattice, which is in agreement with the DFT predictions. These results may useful in tailoring the electronic response of AlN-based systems and the design of devices for various opto-electronic applications.

[en] Highlights: ► Identification of misfit dislocations (MD) in-plane configuration in InN/GaN interfaces. ► Energetic mapping designates that MD arrays adopt 〈1 1 −2 0〉 line directions with b = 1/3〈2 −1 −1 0〉. ► Local arrangement of the Moiré fringes depends strongly on the thickness of the TEM foil as revealed by HRTEM image simulations. ► Geometric Phase Analysis on simulated images justifies results obtained by energetic mapping. - Abstract: The enhanced structural mismatch of InN and GaN binary alloys leads in almost spontaneous formation of misfit dislocations (MDs) at the corresponding interfaces, thereby accommodating plastic relaxation. The open issue of the MD array in-plane configuration is addressed through a combination of high resolution transmission electron microscopy (HRTEM) observations with energetic mapping and HRTEM image simulation of InN/GaN interfaces extracted by atomistic modeling. Energetic mapping on the interfacial area of InN/GaN supercells relaxed by the Tersoff interatomic potential, designates that the MD arrays adopt 〈112^¯0〉 line directions and their Burgers vectors are b=1/3〈21^¯1^¯0〉. HRTEM image simulations further reveal that the local arrangement of Moiré fringes observed in these interfaces depends strongly on the thickness of the TEM foil, thus resolving contradictory experimental reports. Geometric Phase Analysis on the simulated images justifies the results obtained by energetic mapping.

[en] Elastic model of continuum material is often used to simulate the relaxation of crystalline heterostructures. There are many reports on the successful application of the theory of elasticity to nano-sized crystalline heterostructures, even if the continuum condition for them is hardly fulfilled. On the other hand, progress in epitaxial growth allows for the preparation of stable ultra-thin layers with thickness of few monolayers. For such ultra-thin layers, results provided by continuum model and molecular statics/dynamics calculations become diverging. The key problem seems to be located at the modelling of the interface between layers, which is problematic in the continuum approach. By applying a step-wise substitutive compositional interfacial function, it is possible to obtain good agreement with molecular dynamics calculations, even for a single monolayer heterostructure. We propose another approach that uses composition as an extra parameter during finite element calculations, along with classical nodal displacements. Such an approach creates a chemo-elastic coupling that allows to interpolate the composition much like in the case of atomistic calculations. (paper)

[en] Raman spectroscopy and transmission electron microscopy were employed to study the vibrational properties and the microstructure of epitaxially grown InN films on GaN/Al₂O₃ templates. The variations of the InN lattice constants, as deduced by electron diffraction analysis, along with the red-shifted E²₂ mode frequency reveal that InN films exhibit residual tensile stress, strongly dependent on the epilayer growth temperature. Threading dislocations are the dominant structural defects in the films, having a density in the order of 10⁹-10¹⁰ cm^-2. Profile analysis of the E²₂ Raman peak by means of the Spatial Correlation Model provides useful information concerning the effective mean length for free phonon propagation (L), which is a measure of the structural quality of the samples. In all the studied samples, L monotonically increases with decreasing threading dislocation density of pure screw and mixed type character. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The properties of scattering phases and density of states in a quantum wire with an attractive scatterer are analyzed. We consider two bound states which couple to a scattering channel and give rise to two Fano resonances. It is shown that varying the parameters of the scatterer (such as its strength and position) produces significantly different effects on the phase behavior and density of states, depending on the subband they occur. These effects stem mainly from the difference between the coupling matrix elements of the two resonant levels with the propagating channel mode. -- Highlights: ► The scattering phases and density of states in quantum wires are examined. ► Two bound states are considered with two Fano resonances in different subbands. ► The phases in one subband exhibit opposite behavior to that in another subband. ► The behavior of scattering phases and density of states depends on the subband.