Multilayers of InGaAs Nanostructures Grown on GaAs(210) Substrates

Multilayers of InGaAs nanostructures are grown on GaAs(210) by molecular beam epitaxy. With reducing the thickness of GaAs interlayer spacer, a transition from InGaAs quantum dashes to arrow-like nanostructures is observed by atomic force microscopy. Photoluminescence measurements reveal all the samples of different spacers with good optical properties. By adjusting the InGaAs coverage, both one-dimensional and two-dimensional lateral ordering of InGaAs/GaAs(210) nanostructures are achieved.     

The use of noncovalently modified carbon nanotubes for preparation of hybrid polymeric composite materials with electrically conductive and lightning resistant properties

In this work, approach to use of noncovalently modified carbon nanotubes is given for preparation of functional hybrid polymeric composite materials (HPCM) based on epoxy resin. Conductive glass‐fiber plastics with resistivity in transverse and lengthwise direction 9.0·× 10² and 30–50 Ohm cm, respectively, were obtained. The tetrafluoroethylene telomer and fluorocontaining organosilicon copolymer with amino groups were used as modifiers for carbon nanotubes. Thermal, electrical, and mechanical properties of the obtained materials were studied. The mechanism of the effect of noncovalent modification of carbon nanotubes on functional properties of HPCM was discussed. It was found, that type of modifier significantly affects the level of functional properties. The use of fluorocontaining organosilicon copolymer is more optimal in comparison with tetrafluoroethylene telomer. Thus, HPCM with carbon‐fiber filler and this modifier has higher electrical conductivity and lightning strike resistance in comparison with nonmodified HPCM. This approach is promising to impart antistatic properties for glass‐fiber plastics and increase lightning resistance of carbon‐fiber plastics. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46108.     

The influence of different irradiation sources on the treatment of nitrobenzene

This work describes the influence of light on the treatment of nitrobenzene (NB) in aqueous solutions. Three different experimental devices were used to perform a detailed study: a photoreactor with four low-pressure mercury lamps (λ=253.7 nm), a tubular photoreactor with a polychromatic Xe lamp (290<λ<1200 nm), and finally a solar reactor (sunlight). TOC analyses were performed in order to monitor and compare the extent of these processes, each of them being performed with one of the three different sources of light. The influence of Fe(II), Fe(III), H₂O₂, and light on the mineralization of NB in aqueous solutions was also studied. The successful use of sunlight as a source of energy and its effectiveness regarding Fenton processes as well as direct photolysis in the treatment of NB are presented.     

Comparative analysis of the physicochemical characteristics of SiO<Subscript>2</Subscript> aerogels prepared by drying under subcritical and supercritical conditions

SiO₂-based aerogels have been produced be removing a solvent (ethanol or hexafluoroisopropanol) from lyogels both above and below the critical temperature of the alcohols (in the range 210–260 and 160–220°C, respectively). The resultant materials have been characterized by low-temperature nitrogen adsorption measurements, X-ray diffraction, thermal analysis, scanning electron microscopy, X-ray microanalysis, and small-angle and ultrasmall-angle neutron scattering. The results demonstrate that removing the solvent 20–30°C below the critical temperature of the solvent yields silica that is characterized by higher specific porosity and has the same or a larger specific surface area in comparison with the aerogels produced by drying under supercritical conditions. The nature of the solvent used and the solvent removal temperature influence the size and aggregation behavior of primary clusters and the cluster aggregate size in the aerogels.     

Gold Nanoparticle‐Based Sensors Activated by External Radio Frequency Fields

A novel molecular beacon (a nanomachine) is constructed that can be actuated by a radio frequency (RF) field. The nanomachine consists of the following elements arranged in molecular beacon configuration: a gold nanoparticle that acts both as quencher for fluorescence and a localized heat source; one reporter fluorochrome, and; a piece of DNA as a hinge and recognition sequence. When the nanomachines are irradiated with a 3 GHz RF field the fluorescence signal increases due to melting of the stem of the molecular beacon. A control experiment, performed using molecular beacons synthesized by substituting the gold nanoparticle by an organic quencher, shows no increase in fluorescence signal when exposed to the RF field. It may therefore be concluded that the increased fluorescence for the gold nanoparticle‐conjugated nanomachines is not due to bulk heating of the solution, but is caused by the presence of the gold nanoparticles and their interaction with the RF field; however, existing models for heating of gold nanoparticles in a RF field are unable to explain the experimental results. Due to the biocompatibility of the construct and RF treatment, the nanomachines may possibly be used inside living cells. In a separate experiment a substantial increase in the dielectric losses can be detected in a RF waveguide setup coupled to a microfluidic channel when gold nanoparticles are added to a low RF loss liquid. This work sheds some light on RF heating of gold nanoparticles, which is a subject of significant controversy in the literature.     

Refined model of elastic nanoindentation of a half-space by the blunted Berkovich indenter accounting for tangential displacements on the contact surface

Elastic contact between a non-ideal Berkovich indenter and a half-space is investigated. The derived mathematical model of the contact allows for tangential displacements of the boundary points of the half-space. The tip of the blunted indenter is simulated as a smooth surface. The boundary element method is implemented in the model for numerical simulation of nanoindentation. The relative deviation function is introduced and calculated to quantify the influence of the tangential displacements on the load–displacement curves. A simple expression is derived for the impact of the tangential displacements on the values of the reduced Young’s modulus determined due to nanoindentation studies. The refined model was successfully applied to simulate the experimental load–displacement curves gained by elastic nanoindentations of flat LiF and KCl samples. Such values of the indenter bluntness (the varying parameter) were found that the simulated load–displacement curves coincided with those of the experimental data at displacements higher than 7.5 nm. The model neglecting tangential displacements gives slightly differing values for the parameter of the indenter bluntness.

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Luminescent-plasmonic core–shell microspheres,doped with Nd3+ and modified with gold nanoparticles,exhibiting whispering gallery modes and SERS activity

Multifunctional core/shell type,luminescent-plasmonic material composed of lanthanide doped microspheres(≈50 μm) and gold nanoparticles(Au NPs;≈10-20 nm) deposited onto their surface,were successfully prepared(Nd~(3+):YAS@Au).The material was synthesized to combine the luminescence properties of the Nd~(3+)-doped microspheres,i.e.whispering resonance with plasmonic activity of the surface Au NPs,i.e.surface enhanced Raman scattering(SERS) effect,within a single,micro-sized material.The luminescent-plasmonic microspheres were used as the active SERS substrate for detection of the organic probe,and for generation of Whispering Gallery Modes(WGM),which red-shift together with increasing laser power(temperature elevation).The products obtained were analysed with optical,scanning and transmission electron microscopy(SEM and TEM),as well as by Raman,absorption and photoluminescence spectroscopies.     

Nanofibres of CA/PAN with high amount of carbon nanotubes by core–shell electrospinning

We prepared polyacrylonitrile (PAN) and cellulose acetate (CA) based nanofibres with high amount of carbon nanotubes (CNTs) by core–shell electrospinning. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to evaluate the morphology and structure of the electrospun nanofibres. Raman spectroscopy (Raman) and TEM indicate alignment of CNTs in the polymer fibres. Core–shell electrospinning improved the distribution and uniformity of the fibres. The loading of carbon nanotubes showed better thermal stability.     

Mullite-type EMBO4: synthesis,structural, optical,and vibrational properties of rare tin(II) borates with M = Al and Ga

Metal tin-(II)-borates are rarely studied mainly due to the susceptibility of either oxidation into tin(IV) or disproportionation into elemental tin(0) and tin(IV). We report mullite-type SnAlBO₄ and SnGaBO₄ ceramics produced by conventional solid-state synthesis in sealed quartz tubes at low pressure of 10^–7 MPa. Both compounds are isostructural to PbAlBO₄ as confirmed by Rietveld refinements of powder X-ray data. The crystal structures are highly influenced by the stereochemical activity of the 5s² lone electron pair of the Sn²⁺ cation measured by the Wang–Liebau eccentricity parameter. To further consolidate the structural features ¹¹⁹Sn Mössbauer, solid state NMR, Raman, IR and UV/vis spectroscopic measurements are performed. The ¹¹⁹Sn Mössbauer isomer shifts and the quadrupole splitting values confirm the SnO₄ coordination and Sn(II) valence states. Solid state ¹¹B, ²⁷Al and ¹¹⁹Sn NMR spectra provided insights into the local crystal-chemical environment. The vibrational properties are discussed from group theoretical analysis to mode assignments. SnAlBO₄ and SnGaBO₄, respectively, possess an electronic band gap of 3.73(9) and 3.21(4) eV calculated from the diffuse reflectance UV/Vis spectra.     

Intermittent Flux Penetration at Different Temperatures in?YBa2Cu3O7?x on NdGaO3 Substrates

In type-II superconductors, increasing applied magnetic field penetrates gradually in the form of magnetic vortices. It is of great interest to understand the dynamics of magnetic flux in different superconducting materials, as this phenomenon can severely limit the performance of superconductors in applications. YBa₂Cu₃O_7?x (YBCO) is an important high-temperature superconductor, but until recently, it has been hard to make wires from it due to misalignment of superconducting grains. A solution to this problem is to deposit YBCO on vicinal substrates to better align the grains. Some of these samples show a strongly intermittent flux penetration at low temperatures. In this work, we have studied flux penetration in YBCO deposited on a 14° vicinal substrate of NdGaO₃ (NGO) at different temperatures.