The microanalysis of fluorine-containing organic compounds

Summary The method previously described for the micro-determination of fluorine in organic compounds by fusion with alkali metal in a nickel bomb followed by a thorium nitrate titration using a back-titration procedure, has been modified to meet the interferences caused by the presence of phosphorus and arsenic in the organic compound. The method ofOverman andGarrett for the removal of phosphate and arsenate ions by the addition of solid zinc carbonate was adapted for the quantitative removal of those ions. Difficulties in the determinations of carbon and hydrogen in fluoro-phosphorus compounds were overcome by mixing the samples with tungstic oxide.

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Zusammenfassung Die früher beschriebene Methode zur Mikrobestimmung von Fluor in organischen Verbindungen durch Schmelzen mit Alkalimetall in einer Nickelbombe und nachfolgende Titration mit Thoriumnitrat unter Verwendung eines Rücktitrationsverfahrens wurde weiter ausgearbeitet, um Störungen durch allenfalls anwesenden Phosphor oder Arsen zu vermeiden. Die vonOverman undGarrett angegebene Bindung von Phosphat und Arsenat durch Zusatz von festem Zinkcarbonat wurde zu einer quantitativen Entfernung dieser Ionen entwickelt. Schwierigkeiten bei der C-H-Bestimmung in fluor- und phosphorhältigen Verbindungen können durch Mischen der Probe mit Wolframoxyd umgangen werden.

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Résumé Les perturbations apportées par la présence du phosphore et de l'arsenic ont conduit à modifier la méthode antérieurement décrite pour le microdosage du fluor dans les composés organiques et qui comportait une fusion en présence d'un métal alcalin dans une bombe de nickel suivie par un titrage par le nitrate de thorium d'après une technique de dosage en retour. La méthode deOverman etGarrett pour l'élimination des ions phosphate et arseniate par addition de carbonate de zinc solide a été adaptée à l'élimination quantitative de ces ions. Les difficultés rencontrées lors du dosage du carbone et de l'hydrogène dans les composés simultanément fluorés et phosphorés ont été surmontées par le mélange des prises d'essais avec de l'oxyde tungstique.

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We wish to express our thanks to Dr.K. Sellars for the provision of samples and to Dr.J. C. Tatlow for his interest in this project.     

Numerical simulations of confocal Raman spectroscopic depth profiles of materials: a photon scattering approach

We present a simple model that uses a novel photon scattering approach to predict the depth profile response obtained when confocal Raman spectroscopy is applied both to silicon and to a number of related polymeric materials of varying optical clarity. This paper first provides an overview of the models proposed to date to demonstrate the evolution in understanding of the confocal Raman response of semi‐transparent materials, based upon geometrical optics. A new model is then described that is based upon the twin notions of a permanent extended Raman illuminated volume and the degree of extinction of the incident and Raman scattered photons from the whole of the illuminated volume as it is gradually moved further into, or defocused above, the sample. The model's predictions are compared with empirical data from previous studies of a range of semi‐crystalline polymers with different scattering properties and, by means of contrast, with that of a silicon sample. We show that, despite its inherent simplicity, the physics this model utilizes is able successfully to predict the form of the depth profile for each material, something that has not been achieved by any model previously proposed, and that the parameters used in the model scale with independent physical measurements. Finally the model is used to account for the fact that useful Raman spectra can be obtained when the laser is focused as much as 40 µm above the sample surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Room Temperature Synthesis of Phosphine-Capped Lead Bromide Perovskite Nanocrystals without Coordinating Solvents

The room temperature synthesis of perovskite nanocrystals (NCs) is typically achieved by employing a ligand-assisted reprecipitation (LARP) method, which can be handled in air, and its products are comparable to what is obtained using the traditional hot-injection method. However, the LARP method typically requires the use of coordinating polar solvents such as dimethylformamide, which are not appropriate for large-scale production due to toxicity concerns and can also degrade or form defective perovskite NCs. Herein, an amine and oleic-acid-free room temperature synthesis of lead bromide perovskite NCs is reported that uses a combination of trioctylphosphine oxide and diisooctylphosphinic acid ligands. This combination of ligands provides a stable platform for the polar-solvent-free synthesis in air of fully inorganic CsPbBr₃ (fwhm ≈ 14 nm, emission = 519 nm) and hybrid organic-inorganic FAPbBr₃ (fwhm ≈ 19 nm) NCs with photoluminescence emission between 530 and 535 nm, which is in line with the Rec. 2020 color standards. In addition, it is shown that compared to a traditionally used ligand combination, phosphine ligands can be easily removed from the surface of the NCs, which is important for the future development of this technology in optoelectronic devices.     

Imaging of the interstitial iron concentration in crystalline silicon by measuring the dissociation rate of iron–boron pairs

We present a dynamic approach for measuring the interstitial iron concentration in boron‐doped crystalline silicon using photoluminescence (PL) imaging. This camera‐based technique utilizes the characteristic dependence of the dissociation rate of iron–boron pairs on the interstitial iron concentration. We determine the dissociation rate by measuring the time‐dependent PL signal after complete association of iron–boron pairs in the sample. Since we are only interested in the time dependence of the PL signal, we are able to generate images of the interstitial iron concentration in absolute units without any calibration and without knowing the recombination properties of the interstitial iron or iron–boron pairs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A “constrained-chain” network model for viscoelastic fluids

A specific case of the general “constrained-chain” strain-dependent integral viscoelastic model is evaluated with steady simple shear data, stress growth and relaxation data, and steady elongational viscosity data. The model is qualitatively correct and quantitatively reasonable in its predictions and, on balance, compares favourably with strain-dependent, strain-rate-dependent, and stress-dependent models from the current literature. Specific model comparisons are made to demonstrate the effect of the “constrained-chain” or finite extensibility feature of the model.     

Visual Displays that Directly Interface and Provide Read‐Outs of Molecular States via Molecular Graphics Processing Units

The monitoring of molecular systems usually requires sophisticated technologies to interpret nanoscale events into electronic‐decipherable signals. We demonstrate a new method for obtaining read‐outs of molecular states that uses graphics processing units made from molecular circuits. Because they are made from molecules, the units are able to directly interact with molecular systems. We developed deoxyribozyme‐based graphics processing units able to monitor nucleic acids and output alphanumerical read‐outs via a fluorescent display. Using this design we created a molecular 7‐segment display, a molecular calculator able to add and multiply small numbers, and a molecular automaton able to diagnose Ebola and Marburg virus sequences. These molecular graphics processing units provide insight for the construction of autonomous biosensing devices, and are essential components for the development of molecular computing platforms devoid of electronics.     

Note on the parameterization of the constant-phase admittance element

Some background is presented on the constant-phase admittance element, frequently used as part of a circuit for fitting immitance data on solid electrolytes. Several alternate ways of writing an expression for the constant-phase element are discussed and compared, and it is suggested that one particular parameterization seems preferably to the others.     

Layered lattice gas model for the metal-electrolyte interface

Several models of the diffuse double layer in liquid electrolytes are discussed. These models all involve partitioning the space charge region into a number of planar layers parallel to the metal electrode, with ionic liquid lattice gas, as opposed to idea gas, response in each layer. Each layer may contain both ions and solvent molecules. Several difficulties implicit in the earlier work of Liu on such a model are pointed out. These problems seem to have caused the appearance of an initial charge-free region in Liu's results. A layer model involving Liu's original assumptions of point ionic charges and point dipoles is discussed in detail and is shown to be electrostatically inconsistent. It is replaced by a layer model in which ionic charge resides on each basic layer, with each such layer surrounded symmetrically by charge layers representing the effect of finite-extent permanent dipoles. This model leads, as it should, to Gouy-Chapman behavior in the continuum limit. Finally, a method of including ion hydration effects explicitly in such a model is proposed.