The extrinsic nature of double broadband photoluminescence from the BaTiO3 perovskite: generation of white light emitters.

The electronic properties of BaTiO3 perovskite oxides are not completely understood, despite their excellent electro-optical performance and potential for light generation. Particularly, when there is multiple peak formation in the photoluminescence spectra, their origins are not discussed. Their luminescence spectra reveal an unexpected thermodynamic relationship between the core excitonic states and the surface of the BaTiO3. These results give a broad insight into the origins of the emission properties of perovskite oxides. The self-trapped excitons contribution to the broadbands highlights their extrinsic origin. Through spectroscopy techniques and parallel factor analysis (PARAFAC) modeling, we demonstrate that additional broadbands are sensitive to extrinsic defects, type ν-CH3, a product of decomposition of 2-propanol. The presence of C-H bonds shows the dependence with the calcination temperature and the increase of the lattice expansion coefficient until 4.7 × 10-6 K-1 resulting in the contribution to the change of band gap with the temperature ((dEg/dT)P). In this work, we correlated the electronic properties of BaTiO3 with intrinsic and extrinsic defects and elucidated the presence of additional broadbands. This approach differentiates the contributions of excitonic states and surfaces, which is necessary to understand the electronic properties of perovskite oxides.

Understanding the electronic properties of BaTiO3 and Er3+ doped BaTiO3 films through confocal scanning microscopy and XPS: the role of oxygen vacancies.

Photonic and electronic properties exist inherently in ferroelectric barium titanate (BaTiO3); severe luminescence quenching also exists due to the insufficient confinement of excitons. In this sense, high optical emission can only be achieved by its chemical and structural modification. Thin BaTiO3 and Er:BaTiO3 films were grown by the spin coating method on a glass substrate at room temperature. Self-trapping of excitons in the thin BaTiO3 film and its structural modification due to the doping with Er3+ ions (Er:BaTiO3) are verified using scanning confocal fluorescence microscopy (SCFM), where self-trapping excitons never occured in its pure state. By thermal treatment and doping (BaTiO3 and Er:BaTiO3) we obtained localization of the excitons, which would further induce lattice strain around the surface defects, to accommodate the self-trapped excitons. With such a self-trapped state, the structure of BaTiO3 generates broadband emission of several overlapping bands between 1.95 and 2.65 eV at room temperature, while the structure Er:BaTiO3 showed defined emission bands at 2.24 and 2.35 eV, with very weak contributions of the emission due to the self-trapping state. The influence of the variation of the excitation wavelength using 1PE and 2PE on the emission bands of BaTiO3 and Er:BaTiO3 is also investigated. The results of enhanced emission bands suggest a clear dependence of the emission intensity on the excitation energy, where a ∼3 fold enhancement in emission has been demonstrated under Er3+ (1.55 eV) excitation, which can be attributed to effective energy transfer between the Er3+ ions. As a result, it is concluded that the developed BaTiO3 and Er:BaTiO3 can pave the way for future photonic devices.

Realization of Rectangular Artificial Spin Ice and Direct Observation of High Energy Topology.

In this work, we have constructed and experimentally investigated frustrated arrays of dipoles forming two-dimensional artificial spin ices with different lattice parameters (rectangular arrays with horizontal and vertical lattice spacings denoted by a and b respectively). Arrays with three different aspect ratios γ = a/b = [Formula: see text], [Formula: see text] and [Formula: see text] are studied. Theoretical calculations of low-energy demagnetized configurations for these same parameters are also presented. Experimental data for demagnetized samples confirm most of the theoretical results. However, the highest energy topology (doubly-charged monopoles) does not emerge in our theoretical model, while they are seen in experiments for large enough γ. Our results also insinuate that the string tension connecting two magnetic monopoles in a pair vanishes in rectangular lattices with a critical ratio γ = γ c = [Formula: see text], supporting previous theoretical predictions.

Investigation of ferromagnetic resonance and magnetoresistance in anti-spin ice structures.

In this work, we report experimental and theoretical investigations performed in anti-spin ice structures, composed by square lattice of elongated antidots, patterned in nickel thin film. The magnetic vortex crystal state was obtained by micromagnetic simulation as the ground state magnetization, which arises due to the magnetic stray field at the antidot edges inducing chirality in the magnetization of platters among antidots. Ferromagnetic resonance (FMR) and magnetoresistance (MR) measurements were utilized to investigate the vortex crystal magnetization dynamics and magnetoelectric response. By using FMR, it was possible to detect the spin wave modes and vortex crystal resonance, in good agreement with dynamic micromagnetic simulation results. The vortex crystal magnetization configuration and its response to the external magnetic field, were used to explain the isotropic MR behaviour observed.

Modelling of epitaxial film growth with an Ehrlich-Schwoebel barrier dependent on the step height.

The formation of mounded surfaces in epitaxial growth is attributed to the presence of barriers against interlayer diffusion in the terrace edges, known as Ehrlich-Schwoebel (ES) barriers. We investigate a model for epitaxial growth using an ES barrier explicitly dependent on the step height. Our model has an intrinsic topological step barrier even in the absence of an explicit ES barrier. We show that mounded morphologies can be obtained even for a small barrier while a self-affine growth, consistent with the Villain-Lai-Das Sarma equation, is observed in the absence of an explicit step barrier. The mounded surfaces are described by a super-roughness dynamical scaling characterized by locally smooth (facetted) surfaces and a global roughness exponent α > 1. The thin film limit is featured by surfaces with self-assembled three-dimensional structures having an aspect ratio (height/width) that may increase or decrease with temperature depending on the strength of the step barrier.

The hydrophobicity and roughness of a nasoenteral tube surface influences the adhesion of a multi-drug resistant strain of Staphylococcus Aureus

In this study, we examined the physiochemical properties of nasoenteral feeding tubes made from two different types of polymer: silicone materials and polyurethane. The internal surfaces of the nasoenteral feeding tubes were analyzed for their hydrophobicity, roughness, microtopography, rupture-tension and ability to stretch. We also studied the adhesion of an isolated, multi-drug resistant strain of S. aureus to these polymers. The polyurethane nasoenteral tube, which was classified as hydrophilic, was more resistant to rupture-tension and stretching tests than the silicone tube, which was classified as hydrophobic. Additionally, the polyurethane tube had a rougher surface than the silicone tube. Approximately 1.0 log CFU.cm-2 of S. aureus cells adhered to the tubes and this number was not statistically different between the two types of surfaces (p > 0.05). In future studies, new polymers for nasoenteral feeding tubes should be tested for their ability to support bacterial growth. Bacterial adhesion to these polymers can easily be reduced through modification of the polymer's physicochemical surface characteristics.

The hydrophobicity and roughness of a nasoenteral tube surface influences the adhesion of a multi-drug resistant strain of Staphylococcus Aureus.

IN THIS STUDY, WE EXAMINED THE PHYSIOCHEMICAL PROPERTIES OF NASOENTERAL FEEDING TUBES MADE FROM TWO DIFFERENT TYPES OF POLYMER: silicone materials and polyurethane. The internal surfaces of the nasoenteral feeding tubes were analyzed for their hydrophobicity, roughness, microtopography, rupture-tension and ability to stretch. We also studied the adhesion of an isolated, multi-drug resistant strain of S. aureus to these polymers. The polyurethane nasoenteral tube, which was classified as hydrophilic, was more resistant to rupture-tension and stretching tests than the silicone tube, which was classified as hydrophobic. Additionally, the polyurethane tube had a rougher surface than the silicone tube. Approximately 1.0 log CFU.cm(-2) of S. aureus cells adhered to the tubes and this number was not statistically different between the two types of surfaces (p > 0.05). In future studies, new polymers for nasoenteral feeding tubes should be tested for their ability to support bacterial growth. Bacterial adhesion to these polymers can easily be reduced through modification of the polymer's physicochemical surface characteristics.

Roughness of CdTe thin films grown on glass by hot wall epitaxy.

Cadmium telluride films were grown on glass substrates using the hot wall epitaxy (HWE) technique. The samples were polycrystalline with a preferential (111) orientation. Scanning electron micrographs reveal a grain size between 0.1 and 0.5 µm. The surface morphology of the samples was studied by measuring the roughness profile using a stylus profiler. The roughness as a function of growth time and scale size were investigated to determine the growth and roughness exponents, ß and α, respectively. From the results we can conclude that the growth surface has a self-affine character with a roughness exponent α equal to 0.69 ± 0.03 and almost independent of growth time. The growth exponent ß was equal to 0.38 ± 0.06. These values agree with that determined previously for CdTe(111) films grown on GaAs(100).