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Extensive high resolution transmission and scanning transmission electron microscopy observations were performed in In(Ga)N/GaN multi-quantum well short period superlattices comprising two-dimensional quantum wells (QWs) of nominal thicknesses 1, 2, and 4 monolayers (MLs) in order to obtain a correlation between their average composition, geometry, and strain. The high angle annular dark field Z-contrast observations were quantified for such layers, regarding the indium content of the QWs, and were correlated to their strain state using peak finding and geometrical phase analysis. Image simulations taking into thorough account the experimental imaging conditions were employed in order to associate the observed Z-contrast to the indium content. Energetically relaxed supercells calculated with a Tersoff empirical interatomic potential were used as the input for such simulations. We found a deviation from the tetragonal distortion prescribed by continuum elasticity for thin films, i.e., the strain in the relaxed cells was lower than expected for the case of 1 ML QWs. In all samples, the QW thickness and strain were confined in up to 2 ML with possible indium enrichment of the immediately abutting MLs. The average composition of the QWs was quantified in the form of alloy content. [ABSTRACT FROM AUTHOR]

Experiments were conducted to obtain the synthesis of 'side chain' functionalized MCM-41 inorganic-organic hybrids through the exchange method of the template with the cationic organosiloxanes. The results show that the derivative obtained retained the hexagonal symmetry of the original MCM-41 material and the final solids exhibit rather small BET surface areas and microporosity.

Low-field giant magnetoresistance in (111)-textured cobalt/gold multilayers that were prepared using the magnetron sputtering technique was investigated. A series of magnetron-sputtered cobalt-gold multilayers was deposited on silicon(100) substrates covered with a SiNx buffer layer. Experimental results showed that the multilayers with (111) texturing have a low-field giant magnetoresistance effect. Deposition of the multilayers on SiNx buffer layers appears to induce the development of a considerable fraction of faults in the stacking of cobalt along the growth direction.

We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults and threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults. [ABSTRACT FROM AUTHOR]

Antiphase boundaries (APBs) from demisteps on the Si substrate at intersection shifts the misfit dislocation families by half of their periodicity. Transmission electron microscopy is used to study the interfacial misfit dislocations which are the dominant interfacial defects in GaAs and Si interface. The APBs do not interrupt the continuity of the network of dislocations, and the discontinuity of dislocation lines is due to dynamical contrast conditions.

In the present study, the effects of various types of strain and indium concentration on the total energy and optoelectronic properties of GaN nanowires (NWs) with embedded InxGa1-xN nanodisks (NDs) are examined. In particular, the bi-axial, hydrostatic, and uniaxial strain states of the embedded InxGa1-xN NDs are investigated for multiple In concentrations. Density functional theory is employed to calculate the band structure of the NWs. The theoretical analysis finds that the supercell-size-dependent characteristics calculated for our 972-atom NW models are very close to the infinite supercell-size limit. It is established that the embedded InxGa1-xN NDs do not induce deep states in the band gap of the NWs. A bowing parameter of 1.82?eV is derived from our analysis in the quadratic Vegard's formula for the band gaps at the various In concentrations of the investigated InxGa1-xN NDs in GaN NW structures. It is concluded that up to ~10% of In, the hydrostatic strain state is competitive with the bi-axial due to the radial absorption of the strain on the surfaces. Above this value, the dominant strain state is the bi-axial one. Thus, hydrostatic and bi-axial strain components coexist in the embedded NDs, and they are of different physical origin. The bi-axial strain comes from growth on lattice mismatched substrates, while the hydrostatic strain originates from the lateral relaxation of the surfaces. [ABSTRACT FROM AUTHOR]