Spray pyrolysis of La0.6Sr0.4Co0.2Fe0.8O3-δ thin film cathodes

Spray pyrolysis has been used to prepare La0.6 Sr0.4Co0.2Fe0.8O3-δ thin film cathodes for solid oxide fuel cell (SOFC) applications. The films are polycrystalline with nano-meter sized grains and less than 1 μm in thickness. Deposition parameters for film deposition have been established. The ratio of deposition temperature to solvent boiling point is found to be the most important processing parameter that determines whether a crack free homogeneous and coherent film is obtained. The morphology can be tailored by the deposition parameters. Annealing at 650∘C for four hours in air results in coherent films of the desired perovskite phase. The films are potential cathodes for thin film micro-solid oxide fuel cell

Spray pyrolysis of La0.6Sr0.4Co0.2Fe0.8O3-δ thin film cathodes

Spray pyrolysis has been used to prepare La0.6 Sr0.4Co0.2Fe0.8O3-δ thin film cathodes for solid oxide fuel cell (SOFC) applications. The films are polycrystalline with nano-meter sized grains and less than 1 μm in thickness. Deposition parameters for film deposition have been established. The ratio of deposition temperature to solvent boiling point is found to be the most important processing parameter that determines whether a crack free homogeneous and coherent film is obtained. The morphology can be tailored by the deposition parameters. Annealing at 650∘C for four hours in air results in coherent films of the desired perovskite phase. The films are potential cathodes for thin film micro-solid oxide fuel cell

Electron-phonon interaction in quantum-dot/quantum-well semiconductor heterostructures

Polar optical phonons are studied in the framework of the dielectric continuum approach for a prototypical quantum-dot/quantum-well (QD/QW) heterostructure, including the derivation of the electron-phonon interaction Hamiltonian and a discussion of the effects of this interaction on the electronic energy levels. The particular example of the CdS/HgS QD/QW is addressed and the system is modelled according to the spherical geometry, considering a core sphere of material "1" surrounded by a spherically concentric layer of material "2", while the whole structure is embedded in a host matrix assumed as an infinite dielectric medium. The strength of the electron-LO phonon coupling is discussed in details and the polaronic corrections to both ground state and excited state electron energy levels are calculated. Interesting results concerning the dependence of polaronic corrections with the QD/QW structure size are analyzed.Comment: 8 pages, 5 figure

Facile synthesis of self-healing microcapsules

In nature biological materials self-heal and adapt repeatedly to stresses caused by the environment. So far, major efforts have been made to create engineered microcapsules that can, upon rupturing, release a healing agent. To mimic the dynamic biological function, we create functional microcapsules that release self-healing agents, but may also themselves be healed, allowing for multiple release events. Currently there are many limitations in synthesizing microcapsules with self-healing hydrogel shells. We address these challenges with a facile strategy for synthesizing monodisperse hydrogel microcapsules by the deprotection and aqueous solubilization of an initially water-insoluble polymer shell. We use a microfluidic approach to produce w/o/w emulsions as a template for microcapsules [1], where the monomer is in the oil phase. Using such a technique one can prepare poly(acrylic acid) shell microcapsules by the deprotection of a poly(tert-butyl acrylate) shell microcapsule through hydrolysis [2]. Hydrophobic comonomers and water insoluble interpenetrating polymers may be included with the tert-butyl acrylate monomer in order to form microcapsules with self-healing shell materials such as semi-interpenetrating hydrogels or hydrophobic association hydrogels [3,4]. To stabilize self-healing microcapsules we used particle armoring as self-healing hydrogels posses sticky surfaces and tend to aggregate [5]. With this work we demonstrate an easy approach to produce microcapsules with self-healing shells. These capsules will open up the possibility of repeated release from microcapsules, taking a step closer to reproducing self-healing processes seen in nature. [1] Utada, A. S.; Lorenceau, E.; Link, D. R.; Kaplan, P. D.; Stone, H. A.; Weitz, D. A. Science 2005, 308, 537–541. [2] Heise, A.; Hedrick, J. L.; Trollsås, M.; Miller, R. D. … 1999. [3] Hou, C.; Huang, T.; Wang, H.; Yu, H.; Zhang, Q.; Li, Y. Sci Rep 2013, 3, 3138. [4] Jiang, G.; Liu, C.; Liu, X.; Chen, Q.; Zhang, G.; Yang, M.; Liu, F. Polymer 2010. [5] Chen, R.; Pearce, D. J. G.; Fortuna, S.; Cheung, D. L.; Bon, S. A. F. J. Am. Chem. Soc. 2011, 133, 2151–2153. Please click Additional Files below to see the full abstract

Edge helicons and repulsion of fundamental edge magnetoplasmons in the quantum Hall regime

A quasi-microscopic treatment of edge magnetoplasmons (EMP) is presented for very low temperatures and confining potentials smooth on the scale of the magnetic length $\ell_{0}$ but sufficiently steep at the edges such that Landau level (LL) flattening can be discarded. The profile of the unperturbed electron density is sharp and the dissipation taken into account comes only from electron intra-edge and intra-LL transitions due to scattering by acoustic phonons. For wide channels and filling factors $\nu =1$ and 2, there exist independent EMP modes spatially symmetric and antisymmetric with respect to the edge. Some of these modes, named edge helicons, can propagate nearly undamped even when the dissipation is strong. Their density profile changes qualitatively during propagation and is given by a rotation of a complex vector function. For $\nu >2,$ the Coulomb coupling between the LLs leads to a repulsion of the uncoupled fundamental LL modes: the new modes have very different group velocities and are nearly undamped. The theory accounts well for the experimentally observed plateau structure of the delay times as well as for the EMP's period and decay rates.Comment: 12 pages, 6 figure

Exchange interaction effects in the thermodynamic properties of quantum dots

We study electron-electron interaction effects in the thermodynamic properties of quantum-dot systems. We obtain the direct and exchange contributions to the specific heat C_v in the self-consistent Hartree-Fock approximation at finite temperatures. An exchange-induced phase transition is observed and the transition temperature is shown to be inversely proportional to the size of the system. The exchange contribution to C_v dominates over the direct and kinetic contributions in the intermediate regime of interaction strength (r_s ~ 1). Furthermore, the electron-electron interaction modifies both the amplitude and the period of magnetic field induced oscillations in C_v.Comment: 4 pages, 4 figures; To appear in Phys. Rev.

Drying of complex suspensions

We investigate the 3D structure and drying dynamics of complex mixtures of emulsion droplets and colloidal particles, using confocal microscopy. Air invades and rapidly collapses large emulsion droplets, forcing their contents into the surrounding porous particle pack at a rate proportional to the square of the droplet radius. By contrast, small droplets do not collapse, but remain intact and are merely deformed. A simple model coupling the Laplace pressure to Darcy's law correctly estimates both the threshold radius separating these two behaviors, and the rate of large-droplet evacuation. Finally, we use these systems to make novel hierarchical structures.Comment: 4 pages, 4 figure

Plasma dispersion of multisubband electron systems over liquid helium

Density-density response functions are evaluated for nondegenerate multisubband electron systems in the random-phase approximation for arbitrary wave number and subband index. We consider both quasi-two-dimensional and quasi-one- dimensional systems for electrons confined to the surface of liquid helium. The dispersion relations of longitudinal intrasubband and transverse intersubband modes are calculated at low temperatures and for long wavelengths. We discuss the effects of screening and two-subband occupancy on the plasmon spectrum. The characteristic absorption edge of the intersubband modes is shifted relatively to the single-particle intersubband separation and the depolarization shift correction can be significant at high electron densities