Multi-Stage Phase-Segregation of Mixed Halide Perovskites under Illumination: A Quantitative Comparison of Experimental Observations and Thermodynamic Models

Photo- and charge-carrier-induced ion migration is a major challenge when utilizing metal halide perovskite semiconductors for optoelectronic applications. For mixed iodide/bromide perovskites, the compositional instability due to light- or electrical bias induced phase-segregation restricts the exploitation of the entire bandgap range. Previous experimental and theoretical work suggests that excited states or charge carriers trigger the process, but the exact mechanism is still under debate. To identify the mechanism and cause of light-induced phase-segregation phenomena, the full compositional range of methylammonium lead bromide/iodide samples are investigated, MAPb(Br_xI_1-x)₃ with x = 0…1, by simultaneous in situ X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy during illumination. The quantitative comparison of composition-dependent in situ XRD and PL shows that at excitation densities of 1 sun, only the initial stage of photo-segregation is rationalized with the previously established thermodynamic models. However, a progression of the phase segregation is observed that is rationalized by considering long-lived accumulative photo-induced material alterations. It is suggested that (additional) photo-induced defects, possibly halide vacancies and interstitials, need to be considered to fully rationalize light-induced phase segregation and anticipate the findings to provide crucial insight for the development of more sophisticated models.     

Using I2P (Invisible Internet Protocol) Encrypted Virtual Tunnels for a Secure and Anonymous Communication in VANets: I2P Vehicular Protocol (IVP)

Wireless Personal Communications - The Invisible Internet Project (I2P) as a secure protocol uses robust mechanisms and strong algorithms to reinforce the security and the anonymity of the...     

Joint Estimation of Location and Scatter in Complex Elliptically Symmetric Distributions

The joint estimation of the location vector and the shape matrix of a set of independent and identically Complex Elliptically Symmetric (CES) distributed observations is investigated from both the theoretical and computational viewpoints. This joint estimation problem is framed in the original context of semiparametric models allowing us to handle the (generally unknown) density generator as an infinite-dimensional nuisance parameter. In the first part of the paper, a computationally efficient and memory saving implementation of the robust and semiparmaetric efficient R-estimator for shape matrices is derived. Building upon this result, in the second part, a joint estimator, relying on the Tyler’s M-estimator of location and on the R-estimator of shape matrix, is proposed and its Mean Squared Error (MSE) performance compared with the Semiparametric Cramér-Rao Bound (SCRB).

     

Identification by Electron Probe Microbeam Analysis of Submicron Borides in Joints of Nickel Base Superalloys

The phases formed at the interface between an intermetallic (NiAl) and a nickel base superalloy joined by combustion synthesis were investigated, particularly the eutectic phases. Owing to their small size, the characterisation of these phases using a Castaings electron microprobe encounters difficulties. The analysis volume size is generally too large to differentiate the phases from their surrounding matrix, even by using low accelerating voltage. Moreover, the eutectic phases contain boron, which is difficult to characterise by EPMA. Independently of the phases shape, the characterisation can be solved by viewing this complex system as a surrounding matrix and a multi layer system. The results of these simulations revealed the presence of two categories of borides: the eutectic boride MM₂B₂ (M=Mo and M=Co, Cr) and the solid solution boride [Cr_1–x (Mo, W)_x]B.     

Receding contact angle in the situation of complete wetting: Experimental check of a model used for evaporating droplets

This paper provides experimental checks of assumptions needed in a model describing the moving contact line of a wetting droplet evaporating in an inert atmosphere. Special interest is given to the maximum extension of the droplet, when the contact line starts receding. The predicted power law dependence between the values of the radius R₀ and the contact angle Θ₀ at the maximum extension is checked against experiments. We find fairly good agreement with theory for very small droplets. However, discrepancies show up rapidly when the droplet size increases.     

Multiresidue method for simultaneous determination of ten quinolone antibacterial residues in multimatrix/multispecies animal tissues by liquid chromatography with fluorescence detection: single laboratory validation study

Quinolone antibacterials are veterinary drugs authorized for use in food animal production. The analysis of residual amounts of drugs in food from animal origin is important for quality control of products for consumers. For this purpose, Maximum Residue Limits (MRLs) have been set up by a European Union Council Regulation on Veterinary Drug Residues (No. 90/2377/EEC and subsequent), and 8 quinolones received MRLs at concentration levels depending on both the matrix and the animal species of interest. A method was developed for screening and confirming 10 quinolone residues (ciprofloxacin, danofloxacin, difloxacin, enrofloxacin, flumequine, marbofloxacin, nalidixic acid, norfloxacin, oxolinic acid, sarafloxacin) in a wide variety of matrixes of different animal species. It involves extraction of the residues from the biological tissues/fluids by acidic aqueous solution, centrifugation and filtration prior to injection on a C18 narrow-bore column, and detection through a 3-step-mode fluorescence detector. The method was validated during a 2-week study for a set of 8 species-matrixes (i.e., bovine raw milk, bovine muscle, porcine muscle, porcine kidney, porcine liver, fish flesh and skin, poultry muscle, whole egg). Residues were quantified down to 15 microg/kg with limits of detection and quantitation ranging from 4 to 11 and 13 to 36 microg/kg, respectively, which are sufficient compared to the wide range of MRLs set for these substances (from 30 microg/kg for danofloxacin in milk to 1900 microg/kg for difloxacin in poultry liver). The limit of performance of the method in terms of CCalpha and CCbeta, the critical concentrations stated in the Decision No. 2002/657/EC and the ISO Standard No. 11843, has been calculated for the authorized (MRL) substances but only estimated in the case of the nonauthorized (non-MRL) substances.     

Electroorganic synthesis. Reductive alkylation of functionalized 1,2-dithiole-3-thiones

Two-electron reduction of some substituted 1,2-dithiole-3-thiones 1 followed by alkylation of the dianionic intermediates leads through electrosynthesis to mixture of Z and E isomers of the corresponding substituted alkyl-(3-thioalkyl)-2-propenedithioates 2, 3 in satisfactory yield. The structure of those products was established by ¹³C and ¹H nmr and mass spectroscopy. The isomers ratios were determined by nmr spectroscopy.     

Ostwald ripening of oil-in-water emulsions stabilized by phenoxy-substituted dextrans

The stability of oil-in-water emulsions prepared using dextran, a natural polysaccharide, hydrophobically substituted with phenoxy groups, was studied. The evolution of the emulsion droplet size was investigated as a function of polymer concentration (Cp=0.2 to 1% w/w in a water phase) and the degree of phenoxy substitution (tau=4.2 to 15.7%). For the highest tau values, emulsions, which presented submicrometer droplets, were stable over more than 4 months at room temperature. The most substituted polymers clearly showed a better efficiency to lower the surface tension at the oil/water interface. DexP did not induce real viscosification of the continuous phase. The linearity of the particle volume variation with time, and the invariability of the volume distribution function, proved that Ostwald ripening was the main destabilization mechanism of the phenoxy dextran emulsions. The nature of the oil dispersed phase drastically affected the behavior of emulsions. While the emulsions prepared with n-dodecane presented a particle growth with time, only few size variations occurred when n-hexadecane was used. Furthermore, small ratios of n-hexadecane in n-dodecane phase reduced the particle growth due to the lower solubility and lower diffusion coefficient in water of n-hexadecane, which acted as a ripening inhibitor.