Difficulties in the growth and characterization of non-linear optical materials: A case study of salts of amino acids

In the crystallographic literature, there is an ever-increasing number of publications on crystals that are referred to as ‘new non-linear optical materials’, many of them reporting salts of amino acids. However, the term NLO material is used improperly in most cases. In fact, the establishment of any crystal species as such a material requires several experimental and computational procedures, which are seldom satisfied when characterizing a supposedly new species. Here, some frequent hazards and problems are addressed and observations of papers reporting amino acid compounds as supposedly new NLO materials are made.     

Extended defects in CdZnTe crystals: Effects on device performance

We explored some unique defects in a batch of cadmium zinc telluride (CdZnTe) crystals, along with dislocations and Te-rich decorated features, revealed by chemical etching. We extensively investigated these distinctive imperfections in the crystals to identify their origin, dimensions, and distribution in the bulk material. We estimated that these features ranged from 50 to 500 μm in diameter, and their depth was about ∼300 μm. The density of these features ranged between 2×10² and 1×10³ per cm³. We elaborated a model of them and projected their effect on charge collection and spectral response. In addition, we fabricated detectors with these defective crystals and acquired fine details of charge-transport phenomena over the detectors’ volume using a high-spatial resolution (25 μm) X-ray response mapping technique. We related the results to better understand the defects and their influence on the charge-transport properties of the devices. The role of the defects was identified by correlating their signatures with the findings from our theoretical model and our experimental data.     

Elaboration of nanometric amorphous silica from quartz-based minerals using the fluorination method

A method of elaboration of nanometric amorphous silica is proposed using a rational processing of quartz-based ores with the help of a fluorination method. The different steps of the process are described, including the kinetics of the interaction mechanism of ammonium bifluoride with the initial raw materials, the sublimation of ammonium fluorosilicate and the formation of nanometric amorphous silica. Rate constants and activation energy of the chemical reactions are calculated.     

On the redox reactions of radicals with AlIII(phthalocyaninate) pendants covalently bonded to poly(ethyleneamide). Mechanistic alterations when radicals are formed inside pockets of micelle‐like polymer aggregates

The mechanisms of the redox reactions between a polymer containing Al(III) sulfonated phthalocyanine pendants, (Al^III(^?NHS(O₂)trspc)^2?)₂, and radicals have been investigated in this work. Pulse radiolysis and photochemical methods were used for these studies. Oxidizing radicals, OH^?, HCO₃^?, (CH₃)₂COHCH₂^?, and N₃^?, as well as reducing radicals, e_aq^?, CO₂^??, and (CH₃)₂C^?OH, respectively accept or donate one electron forming pendent phthalocyanine radicals, Al^III(^?NHS(O₂)trspc ^?)^{? or 3?}. The kinetics of the redox processes is consistent with a mechanism where the pendants react with radicals formed inside aggregates of five to six polymer strands. Electron donating radicals, that is, CO₂^?? and (CH₃)₂C^?OH, produce one‐electron reduced phthalocyanine pendants that, even though they were stable under anaerobic conditions, donated charge to a Pt catalyst. While the polymer was regenerated in the Pt catalyzed processes, 2‐propanol and CO₂ were respectively reduced to propane and CO. The reaction of SO₃^?? radicals with the polymer stood in contrast with the reactions of the radicals mentioned above. A first step of the mechanism, the coordination of the SO₃^?? radical to the Al(III), was subsequently followed by the formation of a SO₃^?? ‐ phthalocyanine ligand adduct. The decay of the SO₃^?? ‐ phthalocyanine ligand adduct in a ～10² ms time domain regenerates the polymer, and it was attributed to the dimerization/disproportionation of SO₃^?? radicals escaping from the aggregates of polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Double-stranded helical lanthanide(III) supramolecular networks with rigid diimine ligands: Synthesis, structure, and physical properties

Two lanthanide coordination complexes [Nd(NO₃)₃(CH₃OH)₂(4,4′-bipy)₂] (1) (4,4′-bipy=4,4′-bipyridine) and [4,4′-Hbipy][La(NO₃)₄(H₂O)₂(4,4′-bipy)] (2), with a salt of cationic diprotonated 4,4′-bipy, [2(4,4′-H₂bipy)][4(NO₃)] (3), have been identified and isolated from a methanol solution of Ln(NO₃)₃·6H₂O, 4,4′-bipyridine and pyrazine in 1:2:1 ratio. Their structures have been determined by single-crystal X-ray diffraction analyses, which reveal that 1 has an interesting three-dimensional supramolecular architecture containing 2₁ double-stranded helical chains through hydrogen bonding and π–π interactions, while 2 and 3 have well defined infinite chiral 3D open networks that undergo self-interpenetration. The electrospray ionization mass spectra (ESI-MS) indicate that the covalent complex has higher stability than the electrostatic bonding one. ESI-MS/MS of these ions reveal that the Ln–O bond forms a stronger coordinated bonding than that of Ln–N system and the nitrate anion remains bound to the lanthanide centers after complete dissociation in methanol solution.     

Análise da confiabilidade de estruturas de concreto armado com uma metodologia para inclusão de efeitos estocásticos de propriedades dos materiais

In this paper, special emphasis is given to the inclusion of uncertainties in the evaluation of structural behaviour aiming at a better representation of the system characteristics and the quantification of the importance of these uncertainties in the project. It deals with the structural reliability analysis problem accounting the effect of spatial variability of material properties. To this end it is proposed a finite element model to represent the behaviour of reinforced concrete for short and long-term loads, which includes the main features observed in this material. It was developed a model for the generation of multidimensional non-Gaussian stochastic fields for the material properties that is independent of the finite element mesh. First, an example of a two-dimensional non-Gaussian stochastic field generation in a square steel plate is presented. Latter, the reliability analysis is performed to a limit state function based on prescribed values of mid-span displacements on a simply-supported reinforced beam. Finally, the influence of long-term effects on the reliability of a reinforced concrete beam is studied considering the effect of steel reinforcement corrosion.     

Ab initio calculations of magnetic structure and lattice dynamics of Fe/Pt multilayers

The magnetization distribution, its energetic characterization by the interlayer coupling constants and lattice dynamics of (001)-oriented Fe/Pt multilayers are investigated using density functional theory combined with the direct method to determine phonon frequencies. It is found that ferromagnetic order between consecutive Fe layers is favoured, with the enhanced magnetic moments at the interface. The bilinear and biquadratic coupling coefficients between Fe layers are shown to saturate fast with increasing thickness of nonmagnetic Pt layers which separate them. The phonon calculations demonstrate a rather strong dependence of partial iron phonon densities of states on the actual position of Fe monolayer in the multilayer structure.