Influence of terbium on structure and luminescence of nanocrystalline TiO2 thin films

In this work analysis of the structural and optical properties of TiO₂ thin films doped with terbium has been described. Samples were prepared by a high energy reactive magnetron sputtering process under low pressure of oxygen plasma. X-ray diffraction results have shown that different TiO₂ crystal forms have been produced, depending on the amount of Tb dopant. The undoped matrix had rutile structure with crystallites with a size of 8.7 nm, while incorporation of 0.4 at. % of Tb into the film during the sputtering process resulted in anatase structure with bigger crystallites (11.7 nm). Increasing the amount of terbium up to 2 at. % and 2.6 at. % gave rutile structure with crystallites with a size of 6.6 nm for both films. However, Raman spectroscopy has revealed that in the case of TiO₂:(2 at. % Tb), except for the rutile form, the presence of fine-crystalline anatase was observed. Moreover, the lack of Raman peaks shift attests to the lack of stress in the titania lattice of all of the TiO₂:Tb films. This fact indicates localization of Tb3+ ions on the surface of TiO₂ nanocrystals. In the case of optical investigation, results have shown that doping with terbium has a significant influence on the properties of TiO₂, but it does not decrease the high transparency of the matrix. The observed changes of the transmission characteristics were produced only due to modification of the TiO₂:Tb structure. Photoluminescence measurements have shown that emission of light from TiO₂:Tb films occurs when the amount of terbium is 2.6 at. %. Based on the obtained results a scheme of direct energy transfer from titanium dioxide matrix (with rutile structure) to Tb³⁺ ions has been proposed.     

Structural properties of transparent Ti-V oxide semiconductor thin films

Transparent oxide semiconducting thin films based on mixed Ti-V oxides were prepared using a modified reactive magnetron sputtering method. Based on structural investigations performed with the help of x-ray diffraction and transmission electron microscopy analysis, two distinct regions in the prepared thin film have been observed: a nanocrystalline TiO₂-V₂O₃-V₂O₅ mixed composition, and a thin layer consisting of amorphous phase and nanocystalline TiO₂ phase deposited directly at the substrate. Optical measurements show excellent transmission in the visible spectral range of 73%, on average. Resistivity of the thin film was found at the order of 10⁵ Ω cm at room temperature. The preparation of mixed Ti-V oxides provides a combination of high transparency and semiconducting properties.     

How To Play Two-Player Restricted Quantum Games with 10 Cards

We show that it is possible to play ‘restricted’ two-player quantum games proposed originally by Marinatto and Weber (Phys. Lett. A 272:291–303, 2000) by purely macroscopic means, in the simplest case having as the only equipment a pack of 10 cards. Our example shows also that some apparently ‘genuine quantum’ results, even those that emerge as a consequence of dealing with entangled states, can be obtained by suitable application of Kolmogorovian probability calculus and secondary-school mathematics, without application of the ‘Hilbert space machinery’.     

Temperature dependence of electric field noise above gold surfaces

Electric field noise from fluctuating patch potentials is a significant problem for a broad range of precision experiments, including trapped ion quantum computation and single spin detection. Recent results demonstrated strong suppression of this noise by cryogenic cooling, suggesting an underlying thermal process. We present measurements characterizing the temperature and frequency dependence of the noise from 7 to 100 K, using a single Sr+ ion trapped 75 mum above the surface of a gold plated surface electrode ion trap. The noise amplitude is observed to have an approximate 1/f spectrum around 1 MHz, and grows rapidly with temperature as T;{beta} for beta from 2 to 4. The data are consistent with microfabricated cantilever measurements of noncontact friction but do not extrapolate to the dc measurements with neutral atoms or contact potential probes.     

Blocks adjustment—reduction of bias and variance of detrended fluctuation analysis using Monte Carlo simulation

The length of minimal and maximal blocks equally distant on log-log scale versus fluctuation function considerably influences bias and variance of DFA. Through a number of extensive Monte Carlo simulations and different fractional Brownian motion/fractional Gaussian noise generators, we found the pair of minimal and maximal blocks that minimizes the sum of mean-squared error of estimated Hurst exponents for the series of length . Sensitivity of DFA to sort-range correlations was examined using ARFIMA(p,d,q) generator. Due to the bias of the estimator for anti-persistent processes, we narrowed down the range of Hurst exponent to      

Nonadiabatic excited-state dynamics of polar pi-systems and related model compounds of biological relevance

Multireference ab initio dynamics simulations have become available as a tool for the investigation of photochemical processes, mainly for those related to nonadiabatic phenomena taking place in the sub-picosecond time scale. For organic molecules, these phenomena are in many cases deeply dependent on the relaxation of the photoexcited pi-system. We review the latest contributions of our group to this subject and report new results for systems studied previously, grouping them in single pi bonds, chains and aromatic rings. The dynamics of ethylene and substituted ethylenes is discussed mainly in connection to the competition between the two available relaxation paths in the excited states and their relation to the conical intersections in large systems. The trans-cis and the cis-trans dynamics of the pentadieniminium cation is investigated as well. Finally, we discuss the photodynamics of aminopyrimidine starting in the S1 and S2 states and the conclusions, which can be drawn from this for the interpretation of the adenine dynamics.     

Syntheses of potassium 1,1‐dioxopyrido[4,3‐e]‐1,4,2‐dithiazine‐3‐thiolate and its application to the synthesis of novel sulfonamides with potential biological activity

Potassium 1,1‐dioxopyrido[4,3‐e]‐1,4,2‐dithiazine‐3‐thiolate 2 has been synthesized and applied to the syntheses of 7H‐1,1‐dioxopyrido[4,3‐e]‐1,4,2‐dithiazolium‐3‐thiolate 3 and 3‐methylthiopyrido[4,3‐e]‐1,4,2‐dithiazine 1,1‐dioxide 4 which provided easy access to a variety of its 3‐amino derivatives 5‐10 . Hydrazinolysis of 7, 8 and 10 afforded the corresponding 3‐amino‐2‐(1,4‐dihydro‐4‐thioxopyrid‐3‐ylsulfonyl)guanidines 11‐13 . Subsequent reaction of 12 with 4‐chlorobenzaldehyde gave condensation product 14 . 1,4‐Dihydro‐2‐thioxopyridine‐3‐sulfonamide 15 was also prepared from the potassium salt 2 upon alkaline hydrolysis, whereas alkylation of 15 gave the appropriate S‐substituted derivatives 16‐19 or S,N‐disubstituted compounds 20‐21 .     

Prototypical triplet alkyl phosphonatocarbenes

The current case study focuses on the generation, identification, and characterization of two representative mono- and disubstituted alkyl phosphonatocarbenes by means of matrix isolation techniques in conjunction with density functional theory [B3LYP/6-311++G(d,p)] and coupled cluster [CCSD(T)/cc-pVXZ, X = D, T] computations. The EPR measurements identify both carbenes as triplet ground-state species with D values of 0.660 and 0.623 cm(-1), respectively, exhibiting persistency toward intramolecular reactions (the EPR signal observable in perfluoromethylcyclohexane up to around 70 K for the disubstituted molecule). While the reaction of the carbene center of the conformationally rich tetramethyl bisphosphonatocarbene with the CH bonds of the methyl groups leads to phosphaoxetane at room temperature, its fragmentation via a Wittig-type reaction during high vacuum flash pyrolysis (HVFP) results in dimethyl vinylphosphonate and methyl metaphosphate. The latter has been observed for the first time as an isolated entity.     

Uncertainties in the oxygen isotopic composition of barium sulfate induced by coprecipitation of nitrate

Coprecipitation of nitrate and sulfate by barium has probably resulted in significant error in numerous studies dealing with the oxygen isotopic composition of natural sulfates using chemical/thermal conversion of BaSO(4) and analysis by isotope ratio mass spectrometry. In solutions where NO(3) (-)/SO(4) (2-) molar ratios are above 2 the amount of nitrate coprecipitated with BaSO(4) reaches a maximum of approximately 7% and decreases roughly linearly as the molar ratio decreases. The fraction of coprecipitated nitrate appears to increase with decreasing pH and is also affected by the nature of the cations in the precipitating solution. The size of the oxygen isotope artifact in sulfate depends both on the amount of coprecipitated nitrate and the delta(18)O and Delta(17)O values of the nitrate, both of which can be highly variable. The oxygen isotopic composition of sulfate extracted from atmospheric aerosols or rain waters are probably severely biased because photochemical nitrate is usually also present and it is highly enriched in (18)O (delta(18)O approximately 50-90 per thousand) and has a large mass-independent isotopic composition (Delta(17)O approximately 20-32 per thousand). The sulfate delta(18)O error can be 2-5 per thousand with Delta(17)O artifacts reaching as high as 4.0 per thousand. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Artificial metalloenzyme for enantioselective sulfoxidation based on vanadyl-loaded streptavidin

Nature's catalysts are specifically evolved to carry out efficient and selective reactions. Recent developments in biotechnology have allowed the rapid optimization of existing enzymes for enantioselective processes. However, the ex nihilo creation of catalytic activity from a noncatalytic protein scaffold remains very challenging. Herein, we describe the creation of an artificial enzyme upon incorporation of a vanadyl ion into the biotin-binding pocket of streptavidin, a protein devoid of catalytic activity. The resulting artificial metalloenzyme catalyzes the enantioselective oxidation of prochiral sulfides with good enantioselectivities both for dialkyl and alkyl-aryl substrates (up to 93% enantiomeric excess). Electron paragmagnetic resonance spectroscopy, chemical modification, and mutagenesis studies suggest that the vanadyl ion is located within the biotin-binding pocket and interacts only via second coordination sphere contacts with streptavidin.