Anomalously Large Burgers Vectors of Screw Dislocations in Gallium Nitride Nanowires

Crystallography Reports - The results of structural studies of GaN nanowires containing screw dislocations are presented. It is found that the length of the Burgers vector of dislocations may reach...     

Structure of Dibenzocrown Ethers and their H-bonded Adducts. 3. Isolation of Oxonium Ions by Biphenyl-20-crown-6 and [1.5]Dibenzo-18-Crown-6 in Complexes with [NbF6]− and [TaF6]−

The reaction of Nb₂O₅ and Ta₂O₅ with an aqueous solution of hydrofluoric acid, HF in the presence of biphenyl-20-crown-6 (BP20C6, L¹) or [1.5]dibenzo-18-crown-6 ([1.5]DB18C6, L²) results in the complexes [L¹·(H₃O)][NbF₆] (1), [L¹ (H₃O)][TaF₆] (2), [2L²·(H₇O₃)][NbF₆] (3) and [2L²·(H₇O₃)][TaF₆] (4). Complexes 1–4 were identified by the elemental and X-ray structural analysis and IR spectroscopy. Complexes 1 and 2 are isostructural, with the H₃O⁺ oxonium ion embedded in one crown molecule via OH···O hydrogen bonds. Complexes 3 and 4 represent the supramolecular isomers distinctive by the crown conformations and crystal packing, with the (H₇O₃)⁺ cation enclosed in the cage of two crown molecules. Being poor H-bond acceptors, NbF₆⁻ and TaF₆⁻ anions do not compete with the crown oxygen atoms for the oxonium hydrogen atoms, but are involved in the numerous C–H···F short contacts responsible for the extended supramolecular architectures in all cases. A change of crown ethers’ conformation in complexes 1–4 and a correlation between the degree of proton hydration and an accessibility of the crown ether oxygen atoms is observed. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Coating zinc oxide submicron crystals on poly(methyl methacrylate) chips and spheres via ultrasound irradiation

Ultrasound irradiation is used for anchoring zinc oxide submicron crystals with a main diameter and length of 280 nm and 470 nm, respectively, onto the surface of poly(methyl methacrylate) PMMA chips (2 mm diameter), and zinc oxide crystals with a mean diameter and length of 150 nm and 230 nm, respectively, onto the surface of the PMMA spheres (1–10 μm). The zinc oxide crystals were obtained by sonochemical irradiation of a mixture containing the PMMA, zinc (II) acetate dihydrate, ethanol, water, and 24 wt.% aqueous ammonia for 2 h, yielding a PMMA–zinc oxide composite. By controlling the atmosphere and reaction conditions, we could achieve well-adhered zinc oxide crystals on the surface of poly(methyl methacrylate). The resulting zinc oxide–PMMA composite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX), high-resolution scanning electron microscopy (HRSEM), and photoluminescence (PL) spectroscopy. The zinc oxide-deposited PMMA chips (loaded with 0.03–1.0 wt.% ZnO) were successfully homogenized in melt by extrusion and then injection molded into small, disc-shaped samples. These samples were analyzed with respect to their directional spectral optical properties in UV, Vis and IR spectroscopy.     

Backscattering of light from a dielectric layer on a reflecting substrate

Scattering of light from rough dielectric films is studied experimentally. It is shown that the interference pattern of the scattered field depends critically on the power spectrum of the roughness, especially on its long-scale component. When the height of roughness is small compared with the wavelength, the backscattering peak (if it exists) is due to the interference of the singly scattered fields; hence the properties of the backscattered peak are rather unusual. In particular, the width of the peak is determined by the thickness of the film and is independent of the parameters of disorder. The intensity of the peak increases with an increase of the rms height of the surface roughness and becomes independent of the rms when the roughness is of the order of the wavelength.     

Asymptotic Characteristics of Compact Sets and Stepanets Classes

We obtain estimates for the -entropy and -capacity of sets of periodic functions with mean value zero that have a (, )-derivative belonging to the space L ²(0, 2).     

Thiazole analogs of chalcones,capable of functionalization at the heterocyclic nucleus

The synthesis of new amino and alkoxy derivatives of thiazole-5-carbaldehyde, on the basis of which α,β-unsaturated ketones of the thiazole series were synthesized, are described in this paper. The possibility of obtaining chalcones and variation of substitution reactions in the thiazole ring has been shown.     

The different behavior of rutile and anatase nanoparticles in forming oxy radicals upon illumination with visible light: an EPR study

Photoexcited TiO(2) has been found to generate reactive oxygen species, yet the precise mechanism and chemical nature of the generated oxy species especially regarding the different crystal phases remain to be elucidated. Visible light-induced reactions of a suspension of titanium dioxide (TiO(2)) in water were investigated using electron paramagnetic resonance (EPR) coupled with the spin-trapping technique. Increased levels of both hydroxyl (˙OH) and superoxide anion (˙O(2)(-)) radicals were detected in TiO(2) rutile and anatase nanoparticles (50 nm). The intensity of signals assigned to the ˙OH and ˙O(2)(-) radicals was larger for the anatase phase than that originating from rutile. Moreover, illumination with visible (nonUV) light enhanced ˙O(2)(-) formation in the rutile phase. Singlet oxygen was not detected in water suspension of TiO(2) neither in rutile nor in anatase nanoparticles, but irradiation of the rutile phase with visible light revealed a signal, which could be attributed to singlet oxygen formation. The blue part of visible spectrum (400-500 nm) was found to be responsible for the light-induced ROS in TiO(2) nanoparticles. The characterization of the mechanism of visible light-induced oxy radicals formation by TiO(2) nanoparticles could contribute to its use as a sterilization agent.     

Dibromo and diiodo derivatives of [4.4]dibenzo-24-crown-8 as novel efficient sorbents of elements from mineral acid solutions

The sorption behavior of novel functionalized endoreceptors, halogen (Br, I) derivatives of [4.4]dibenzo-24-crown-8, with respect to sorption of 34 elements from 1–5 M HNO₃ solurions and 29 elements from 1–5 M HCl solutions were studied. The receptors poorly extract elements from nitric acid solutions but are strong sorbents of some elements from concentrated hydrochloric acid solutions. The highest distribution ratios of elements (D, cm³/g) for sorption from 5 M HCl were observed for 4′,4″,5″[4.4]dibromodibenzo-24-crown-8: Au (D = 880) > Ga (469) > Sb (70) > Fe (55) > Sn (14.3) > Mo (10.3) > Re (2.9) > Cd (1.4) > Ge (0.61) > In (0.33) ≈ Zn (0.32) ≈ Ni (0.31) > Zr (0.29) ≈ Cr (0.28) > Sr, Tl (0.25) > Be (0.24) > Mn (0.22) ≈ La (0.21) ≈ Ba (0.20) > Ca, K, Mg, Si (< 0.1). A new way for increasing the sorption properties of dibenzocrown ethers by introducing bromine substituents into the polyether benzene rings was established. The sorption of elements from concentrated hydrochloric acid solutions follows an anion exchange mechanism by analogy with extraction of these elements.