Search

Polarization dependence of water adsorption and desorption on LiNbO surfaces was demonstrated using X-ray photoelectron spectroscopy (XPS) carried out in situ under near-ambient conditions. Positive and negative (0001) faces (z-cut) of the same crystal were compared for the same temperature and pressure conditions. Our results indicate a preferential adsorption on the positive face of the crystal with increasing water pressure and also higher desorption temperature of the adsorbed molecular water at the positive face. Adsorption measurements on the (1100) face (y-cut) showed also strong affinity to water, as observed for the z-cut positive surface. We found a direct relation between the capacity of the surface to discharge and/or to screen surface charges and the affinity for water of each face. XPS spectra indicate the presence of OH groups at the surface for all the conditions and surfaces measured., This work has been partially funded by the 2014 SGR 1216 project from the Generalitat de Catalunya, the MAT2012-38319-C02-01, the FIS2013-48668-C2-1-P, and FIS2015- 73932-JIN from the Spanish Ministerio de Economia y Competitividad (MINECO). K.C-E.’s work was funded by an ERC Starting Grant from the EU (Project No. 308023). N.D. is also grateful to MINECO for the “Ramon y Cajal” contract RYC-2010-06365. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

The kinetics of anodic reactions occurring on copper in thiocarbamide-citrate solutions was studied. Thiocarbamide forms stable copper (I) complexes of the cationic type with a coordination number equal to unity. Citric acid ensures acid pH value of electrolyte and causes active dissolution of copper under conditions of anode polarization. The joint presence of CS(NH₂)₂ and C₆H₈O₇ in the solution contributes to the copper electrode activation under conditions of anodic polarization. Increasing the concentration of thiocarbamide leads to a drastic shift of copper dissolution potentials towards the region of negative values. Study of the kinetics of anodic behavior of copper by acquiring the voltammograms revealed the nature of the limiting stage of reaction. It is shown that the process of dissolution in a thiocarbamide-citrate electrolyte is controlled by the diffusion phase. This is confirmed by the results of graphical processing of polarization dependences in coordinates η–lg(1–ja/jd). An increase in υр within 5‒100 mV·s⁻¹ causes an increase in jd from 2.2 to 12.0 mА·cm⁻², which indicates diffusion control over the process. The process of copper dissolution proceeds under stationary mode with uniform etching of intragrain boundaries and volume of the metal's grain. Досліджено кінетику анодних реакцій на міді у тіокарбамідно-цитратних розчинах. Встановлено, що анодне розчинення металу приводить до появи комплексних сполук одновалентної міді. Тіокарбамід утворює з міддю комплекс катіонного типу. Лимонна кислота забезпечує кисле значення рН та сприяє активному розчиненню міді. Результати проведених досліджень показують, що анодне розчинення міді відповідає закономірностям дифузійної кінетики.

Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an iodoethynyl-containing azobenzene comes out on top of the supramolecular hierarchy to provide unprecedented photoinduced surface patterning efficiency. Specifically, the iodoethynyl motif seems highly promising in future development of polymeric optical and photoactive materials driven by halogen bonding. publishedVersion

The impact of the chloride ions concentration and the temperature of the circulating water on the process of corrosion destruction of carbon steel and cast iron has been investigated. It has been shown that an increase in the concentration of chloride ions causes a shift in the values of the stationary potentials of steel and cast iron to the region of negative values and reduces the passive state of these alloys. This leads to an increase in the corrosion rate of St.3 steel and CI 18-36 cast iron. The results of electrochemical studies have shown that the more reliable protective films are formed on steel than on cast iron. The limiting concentration of NaCl, at which reliable operation of equipment made from these alloys is possible, depends on the pH of the solution. At pH=7, it is about 1.2 g l⁻¹, which is about an order of magnitude less than at pH=12. When the circulating water temperature rises, the corrosion rate of steel and cast iron increases. The stationary potentials of steel and cast iron are shifted to the negative range, and the polarization of the anode process decreases. Corrosion process is limited by the rate of oxygen supply to the cathode areas. Досліджений вплив концентрації іонів хлору і температури оборотної води на процес корозійного руйнування вуглецевої сталі і сірого чавуну. Встановлено, що збільшення концентрації хлорид-іонів обумовлює зміщення величин стаціонарних потенціалів сталі і чавуну в область негативних значень і зменшує область пасивного стану зазначених сплавів. В результаті проведених досліджень встановлено, що обладнання, виготовлене з сталі Ст. 3 і чавуну СЧ 18-36, можна використовувати в оборотній воді з рН=12, що містить до 10 г∙л⁻¹∙NaCl при температурі не більше 40 °C.

We fabricated a superconducting single-photon detector (SSPD) with bilayer structure. The detector consists of two meanders which are superposed face-to-face using optical adhesive. When the two nanowires are superposed perpendicularly, the degree of linear polarization dependence is reduced from 0.16 to 0.000617. This means that the polarization dependence, which has been a drawback in SSPDs, is suppressed almost completely using the present structure.

The effect of laser pulse width on the efficiency of nonphotochemical laser-induced nucleation (NPLIN) of supersaturated aqueous solutions of KCl has been studied. At equivalent peak-power densities it was observed that the same fractions of samples were nucleated for both short (6 ns) and long (200 ns) near-infrared laser pulses. The results show that the efficiency depends on the peak-power density and not on the duration, or total energy, of the laser pulses. It is concluded that the mechanism is unlikely to be based solely on diffusion of solute to a sub-critical cluster. (C) 2009 Elsevier B.V. All rights reserved.

A micro‐spectroscopic method has been developed to probe the accessibility of zeolite crystals using a series of fluorescent 4‐(4‐diethylaminostyryl)‐1‐methylpyridinium iodide (DAMPI) probes of increasing molecular size. Staining large zeolite crystals with MFI (ZSM‐5) topology and subsequent mapping of the resulting fluorescence using confocal fluorescence microscopy reveal differences in structural integrity: the 90° intergrowth sections of MFI crystals are prone to develop structural imperfections, which act as entrance routes for the probes into the zeolite crystal. Polarization‐dependent measurements provide evidence for the probe molecule's alignment within the MFI zeolite pore system. The developed method was extended to BEA (Beta) crystals, showing that the previously observed hourglass pattern is a general feature of BEA crystals with this morphology. Furthermore, the probes can accurately identify at which crystal faces of BEA straight or sinusoidal pores open to the surface. The results show this method can spatially resolve the architecture‐dependent internal pore structure of microporous materials, which is difficult to assess using other characterization techniques such as X‐ray diffraction.

Effects of the presence of a silicon substrate on the leakage loss and phase variation of silica-based parallel waveguides are investigated using the imaginary-distance beam-propagation method. The leakage loss is evaluated as a function of the distance between the core and the substrate. Calculation shows that the loss of the directional coupler can be estimated using the single waveguide with the same cross section. It is also found that the beat length becomes longer than that without the substrate except the case where the core is extremely close to the substrate. In terms of the loss reduction, the insertion of a SiO2 film with a 1-mum thickness corresponds to an increase in the distance between the core and the substrate without the SiO2 film by about 2 mum

Polarization-dependent X-ray absorption spectroscopy is combined with density functional calculations and atomic multiplet calculations to determine the crystal field parameters 10Dq, Ds, and Dt of transition metal phthalocyanines and octaethylporphyrins (Mn, Fe, Co, Ni). The polarization dependence facilitates the assignment of the multiplets in terms of in-plane and out-of-plane orbitals and avoids ambiguities. Crystal field values from density functional calculations provide starting values close to the optimum fit of the data. The resulting systematics of the crystal field can be used for optimizing electron-hole separation in dye-sensitized solar cells.

Non-photochemical laser-induced nucleation (NPLIN) of glacial acetic acid (GAA) is demonstrated. The fraction of samples nucleated depends linearly on peak laser power density at low powers (< 100 MW cm(-2)) with a threshold of (9.0 +/- 4.2) MW cm(-2); at higher laser powers the fraction reaches a plateau of 0.75 +/- 0.24 (2 sigma uncertainties). A simple model based on polarizability of pre-nucleating clusters gives a value of the solid-liquid interfacial tension gamma(SL) = 15.5 mJ m (2). It is hoped that the results will stimulate new developments in experimental and theoretical studies of cluster structure and nucleation in liquids.

We report the observation of non-photochemical laser-induced nucleation (NPLIN) of sodium chlorate from its melt using nanosecond pulses of light at 1064 nm. The fraction of samples that nucleate is shown to depend linearly on the peak power density of the laser pulses. Remarkably, we observe that most samples are nucleated by the laser back into the enantiomorph (dextrorotatory or levorotatory) of the solid prior to melting. We do not observe a significant dependence on polarization of the light, and we put forward symmetry arguments that rule out an optical Kerr effect mechanism. Our observations of retention of chirality can be explained by decomposition of small amounts of the sodium chlorate to form sodium chloride, which provide cavities for retention of clusters of sodium chlorate even 18 degrees C above the melting point. These clusters remain sub-critical on cooling, but can be activated by NPLIN via an isotropic polarizability mechanism. We have developed a heterogeneous model of NPLIN in cavities, which reproduces the experimental data using simple physical data available for sodium chlorate. (C) 2011 American Institute of Physics. [doi:10.1063/1.3637946]