Magnesium oxide (MgO) prepared by both pulsed laser deposition and sputtering methods showed constriction of lattice constants. To emphasize the effect of the constriction of lattice constants, MgO prepared at high oxygen atmosphere and high substrate temperature, resulted in the growth of cubic-shaped magnesium oxide (MgO) nanoparticles on a Si substrate. In oxygen atmosphere, the nanocubic MgO was scattered on the substrate without the Si surface being covered by a MgO thin film. Interestingly, the growth of nanocubic MgO was restrained on the samples prepared in nitrogen atmosphere. The formation of nanocubic MgO is related to the deposition pressure as well as the etching effect provided by oxygen atmosphere.
The chemical reaction near the crucible wall during directional solidification of Si crystals for solar cells has been investigated. Fragments of the crucible that were used for the crystal growth of a Si ingot were examined. As results, we found that a chemical reaction took place at the coating/crucible interface and that silicon oxynitride particles precipitated near the crucible wall. The oxynitride precipitates were determined as stoichiometric Si2N2O and were revealed not to be amorphous but of orthorhombic crystal symmetry. We show crucial evidence of the formation of stoichiometric Si2N2O microcrystalline precipitates inside the Si crystal.
The polarization reversal in perovskite ferroelectrics having a tetragonal phase is studied using the Landau-theory-based lattice model, extended to the three-dimensional polarization case. Switching at various electric field levels is analyzed for near and far distances from the theoretical morphotropic phase boundary (MPB), in the presence of the latent nuclei. The calculated time dependence of average polarization during switching is correlated with the changes of polarization profiles in the lattice. For low electric fields, switching can be achieved by polarization vector rotations triggered by infinitesimal tilting at the latent nuclei sites. Polarization vector rotations are most significant close to the MPB, where the free energy is isotropic in the space spanned by the polarization components. For electric fields beyond the longitudinal polarization instability, the transversal polarization components do not play a very significant role. Inferior retention properties near the MPB due to the polarization vector rotations are predicted, though higher reversal speed and lower switching threshold are expected.
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