Wurtzite gallium phosphide (WZ GaP) has been predicted to exhibit a direct bandgap in the green spectral range. Optical transitions, however, are only weakly allowed by the symmetry of the bands. While efficient luminescence has been experimentally shown, the nature of the transitions is not yet clear. Here we apply tensile strain up to 6% and investigate the evolution of the photoluminescence (PL) spectrum of WZ GaP nanowires (NWs). The pressure and polarization dependence of the emission together with a theoretical analysis of strain effects is employed to establish the nature and symmetry of the transitions. We identify the emission lines to be related to localized states with significant admixture of Γ7c symmetry and not exclusively related to the Γ8c conduction band minimum (CBM). The results emphasize the importance of strongly bound state-related emission in the pseudodirect semiconductor WZ GaP and contribute significantly to the understanding of the optoelectronic properties of this novel material.

In this work we study the adhesion between various alumina surfaces and precursors of amine-containing epoxies.To accomplish this we have developed a reactive force field (ReaxFF) parameterization for the aluminum-nitrogen interaction and combined this with the aluminum-water and glycine force fields reported in earlier work. Molecular clusters and reaction paths selected to model interfacial phenomena of amine-containing epoxy precursors on alumina were used in the fitting of the ReaxFF parameters. It is shown how this new force field satisfactorily reproduces equilibrium bond lengths and angles as well as binding energies for the proposed structures. Reaction profiles are also fitted in agreement with ab initio calculations performed making use of the nudge elastic band method. To substantiate the parametrization, room temperature molecular dynamics results of ammonia adsorption on alumina are compared using ab initio and ReaxFF methods. Using this new interaction scheme, adsorption energies of dimethylamine and DETA on differently terminated alumina surfaces are determined for ten different molecule-surface approach conditions each. We find that the mean and rms adsorption energy values vary considerably with the particular molecule/surface combination. It is also shown that the adhesion of the studied epoxy precursors decreases linearly with the hydroxyl coverage on alumina surfaces.

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Metal/polymer system joints are widely encountered nowadays in microscopic structures such as displays and microchips. In several critical cases they undergo thermal and mechanical loading, with contact failure due to fracture as a possible consequence. Because of their variety in nature and composition metal/polymer joints have become major challenges for experimental, theoretical, and numerical studies. Here we report on results of molecular dynamics simulations carried out to study the mechanical response of a metal/polymer joint, in this case the Cu/polybutadiene model system. The behavior of Cu and the cross-linked polybutadiene are modeled, respectively, by the Embedded Atom Method (EAM) and the Universal Force Field (UFF). Loading is applied under compression. Different potentials are used to describe the interactions in the metal/polymer interface, which allows us to qualitatively analyze possible mechanisms of failure in these joints, below the metal melting point and above the polymer glass transition temperatures.

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