Search results for "SHELL"

XAFS study of short range order in the heavily disordered MoxW1−wO3 oxides

1995

We have done comparative XAFS analysis on the MoK and WL 3 edges of polycrystalline Mo x W 1-x O 3 solid solutions. It was found that their structures are closely related to corner-shared WO 3 -type for x<0.9 while α-MoO 3 -type structure is present for x≥0.9. The obtained structural parameters for the first shell around metal ions allow to distinguish several structural phase transitions due to the change of composition. A set of subshells within the first shell was found, and they are in good agreement with Raman data

Cylindrical morphologies in asymmetric ABC triblock copolymers

1997

In asymmetric ABC triblock copolymers with C being the matrix-forming majority component, the formation of cylindrical morphologies is governed by the sum of the volume fractions of the components A and B (Φ A + Φ B ) as well as by their ratio (Φ B /Φ A ). The paper describes the morphologies of various polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) and polystyrene-block-poly(ethylene-co-butylene)-block-poly(methyl methacrylate) block copolymers (SEBM) in dependence on these parameters. In addition to previously reported cylinder in cylinder (c i c, core shell) and helical (hel) morphologies, new microphase separated structures as cylinders at cylinder (c a c), undula…

Mechanics of deformation of single- and multi-wall carbon nanotubes

2004

Abstract An effective continuum/finite element (FE) approach for modeling the structure and the deformation of single- and multi-wall carbon nanotubes (CNTs) is presented. Individual tubes are modeled using shell elements, where a specific pairing of elastic properties and mechanical thickness of the tube wall is identified to enable successful modeling with shell theory. The incorporation and role of an initial internal distributed stress through the thickness of the wall, due to the cylindrical nature of the tube, are discussed. The effects of van der Waals forces, crucial in multi-wall nanotubes and in tube/tube or tube/substrate interactions, are simulated by the construction of special…

Fast-Response Single-Nanowire Photodetector Based on ZnO/WS 2 Core/Shell Heterostructures

2018

This work was supported by the Latvian National Research Program IMIS2 and ISSP project for Students and Young Researchers Nr. SJZ/2016/6. S.P. is grateful to the ERA.Net RUS Plus WATERSPLIT project no. 237 for the financial support. S.V. is grateful for partial support by the Estonian Science Foundation grant PUT1689.

The structural properties of GaN/AlN core-shell nanocolumn heterostructures.

2010

International audience; The growth and structural properties of GaN/AlN core-shell nanowire heterostructures have been studied using a combination of resonant x-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy experiments. For a GaN core of 20 nm diameter on average surrounded by a homogeneous AlN shell, the built-in strain in GaN is found to agree with theoretical calculations performed using a valence force field model. It is then concluded that for an AlN thickness up to at least 12 nm both core and shell are in elastic equilibrium. However, in the case of an inhomogeneous growth of the AlN shell caused by the presence of steps on the sides of the …

Resonant Raman scattering of core-shell GaN/AlN nanowires.

2020

Abstract We have analyzed the electron–phonon coupling in GaN/AlN core–shell nanowires by means of Raman scattering excited at various wavelengths in the ultraviolet spectral range (335, 325 and 300 nm) and as a function of the AlN shell thickness. The detailed analysis of the multi-phonon spectra evidences important differences with excitation energy. Under 325 and 300 nm excitation the Raman process is mediated by the allowed A 1(LO) phonon mode, where the atoms vibrate along the NW axis. Considering its selection rules, this mode is easily accessible in backscattering along the wurtzite c axis. Interestingly, for 335 nm excitation the scattering process is instead mediated by the E 1(LO)…

Growth, structural and optical properties of GaN/AlN and GaN/GaInN nanowire heterostructures

2012

Abstract After discussing the GaN NW nucleation issue, we will present the structural properties of axial and radial (i.e. core/shell) GaN/AlN NW heterostructures and adress the issue of critical thickness during the growth of such heterostructures. Next, we will present the growth of InGaN NWs on a GaN NW base. It will be shown that the morphology and structural properties of the InGaN NW sections depend on the In content: for high In content a flat top is observed and plastic relaxation is occuring, with mismatch dislocations formed at the InGaN/GaN interface. By contrast, for In content below 25% InGaN NWs exhibit a pencil-like shape assigned to a purely elastic strain relaxation process…

Ellipsoidal core-shell cylindrical microphases in PS-b -PB-b -PCL triblock copolymers with a crystallizable matrix

1997

Polystyrene-block-polybutadiene-block-poly(e-caprolactone) SBC triblock copolymers with a PCL matrix exhibit microphase separation into three different phases within the spherulitic superstructures. Mixing of the PS-block can occur upon melting of the PCL-block if the molecular weight is low enough. Even though the crystallization takes place well below the PS-glass transition, a deformation of the amorphous microphases into ellipsoidal core-shell cylindrical microdomains is observed by TEM. These copolymers have mechanical properties which are dominated by the PCL (Poly(e-caprolactone)) matrix with an influence of the amorphous blocks.

A convenient approach to amphiphilic hyperbranched polymers with thioether shell for the preparation and stabilization of coinage metal (Cu, Ag, Au) …

2014

Defect Calculations for Yttrium Aluminum Perovskite and Garnet Crystals

2000

Native and impurity point defects in both Yttrium Aluminum Perovskite and Garnet crystals are studied in the framework of the pair-potential and the shell model approximations. The calculated formation energies for native defects suggest that the antisite disorder is preferred over the Frenkel and Schottky-like disorder in both YAP and YAG. In non-stoichiometric compounds, the calculated reaction energies indicate that excess of Y2O3 or Al2O3 is, most likely, to be accommodated by the formation of antisites rather than vacancies or interstitials in the lattice. Enthalpies of the reactions for impurity (Ca2+, Mg2+, Sr2+, Ba2+, Cr3+, Fe3+, Nd3+, Si4+) incorporation into both YAP and YAG latti…