The effect of two ferromagnetic metal stripes on valley polarization of electrons in a graphene

As the key factor for designing the valleytronic devices is to well understand the valley-dependent transport mechanism in graphene, we investigate, in this work, the effect of two ferromagnetic (FM) metal stripes on the valley polarization in a graphene nanostructure with a strain. The nearly 100% valley polarization is observed at certain energy windows and it can be easily controlled through changing the width and the position of the FM stripe as well as the strength of the magnetic field induced by the FM stripe. Our interesting findings reveal the valley-dependent transport mechanism of electrons and promote the realization of the new types of valleytronic devices modulated by the FM stripe and the strain.     

Nanocomposites based on cationic polyelectrolytes and silver nanoparticles: Synthesis,characterization, molybdate retention and antimicrobial activity

The objective of this work was to synthesize nanocomposites based on cationic polyelectrolytes and silver nanoparticles using poly(N-vinylbenzyl-N-triethylammonium chloride) as polymer phase. For that, a nanostructured crosslinker was synthesized from silver nanoparticles (AgNPs) and acrylic acid. Molybdate retention properties of nanocomposites were studied in function of pH and ionic strength. In addition, their antimicrobial properties were evaluated against E. coli and S. aureus. It was evidenced that AgNPs can be stabilized using acrylic acid and that this material can be incorporated to the polymer phase during polymerization by free radical of cationic monomers. The effect of pH on retention of molybdate, by the nanostructured polymer, was significant only to low ionic strength (the order seen was pH 5.0 > pH 7.0 > pH 9.0 for 0.0% NaCl). Results suggest that the main interaction influencing the molybdate retention is electrostatic in nature. Finally, antimicrobial activity was enhanced by incorporation of polymerizable nanostructured crosslinker based on AgNPs.     

Operation of low driving voltage cascaded modulator over non-cascaded modulator for 4 dB extinction ratio at 100 giga bit per second (Gbps)

This paper describes improved results when comparing cascaded traveling wave electro absorption modulator (TWEAM) to non-cascaded TWEAM by simulation. Large signal modeling is used for both types of modulators to achieve 4 and 10 dB extinction ratios (ERs) with flat frequency response for applications in short distance as well as long distance optical fiber communication. To obtain 4 and 10 dB ERs with 110 GHz 3 dB bandwidth, a cascaded TWEAM requires 0.4 V peak to peak (V_P-P) and 1 V_P-P input driving voltages respectively. A non-cascaded TWEAM requires about two times the input driving voltage compared to the cascaded modulator to achieve the same values of ER and 3 dB bandwidth. Both modulators have been simulated with the same bias and also use the same circuit parameters except for the total active segment lengths (1 and 0.5 mm for cascaded and non-cascaded modulator respectively) and microstrip lengths to obtain the same ERs and 3 dB bandwidths.     

Potassium surface enrichment in mixed alkali glass irradiated with electrons

Sodium-potassium-silicate glass was irradiated with electrons of energy of 1600 eV. The changes in the surface composition were analyzed by means of the angular-resolved X-ray induced photoelectron spectroscopy (ARXPS). Low electron dose irradiation enriched the uppermost glass surface with alkali ions, considerably more with potassium than with sodium ions.     

Dioxygenation of styrenes with molecular oxygen in water

Employing Triton X-100 as a surfactant, the tert-butyl hydroperoxide-mediated dioxygenation of styrene with molecular oxygen and N-hydroxyphthalimide was achieved in water at room temperature, providing the corresponding dioxygenated products in 9–93% yield. This facile method is eco-friendly, feasible on gram scale, and applicable to a wide range of styrene derivatives with a variety of functional groups.     

Positron annihilation lifetime study of organic-inorganic hybrid materials prepared by irradiation

Silica based hybrid materials, some containing zirconia, prepared by gamma-irradiation, were studied by positron annihilation lifetime (PAL) spectroscopy, in the temperature range of 30-370 K. One long-lived component was observed in group of samples without zirconia. The behavior of this component as a function of temperature resembles that for polymers. This is explained by the elastomer like structure of the samples and the excellent linking between the inorganic and organic networks. The average radius, R, of the free-volume holes was in the range 0.26-0.42 nm depending on the temperature. In the group of samples containing zirconia two long-lived components were observed. A model with three different free-volume holes was suggested to explain the PAL results. Small closed holes (R ∼ 0.26 nm) and large closed holes introduced by Zr (R ∼ 0.5 nm), the sizes of both holes not changing with the temperature, together with intermediate polymer-like free-volume holes - the same behavior as those present in samples not containing zirconia.     

High resolution patterning of silica aerogels

Three-dimensional metallic structures are fabricated with high spatial resolution in silica aerogels. In our method, silica hydrogels are prepared with a standard base-catalyzed route, and exchanged with an aqueous solution typically containing Ag⁺ ions (1 M) and 2-propanol (0.2 M). The metal ions are reduced photolytically with a table-top ultraviolet lamp, or radiolytically, with a focused X-ray beam. We fabricated dots and lines as small as 30 × 70 μm, protruding for several mm into the bulk of the materials. The hydrogels are eventually supercritically dried to yield aerogels, without any measurable change in the shape and spatial resolution of the lithographed structures. Transmission electron microscopy shows that illuminated regions are composed by Ag clusters with a size of several μm, separated by thin layers of silica.     

Insulator-like electrical transport in structurally ordered Al65Cu20+xRu15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5) icosahedral quasicrystals

Low-temperature resistivities, in zero-field and 8 T field, and magnetoresistance have been measured down to 1.4-300 K for stable icosahedral quasicrystals Al₆₅Cu_20+xRu_15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5). The analysis of the magnetoresistance data shows an overwhelming presence of anti weak-localization effect (τ_so ∼ 10⁻¹² s). But the sample with x = −0.5 shows anomalous magnetoresistance and the anti weak-localization effect breaks down (τ_so to be 10⁻¹⁵ s). The in-field σ-T between 5 K and 20 K, for x = 1.0, 0.5, 0.0 and −0.5 samples, and between 1.4 K and 40 K for x = 1.5 sample, follow a power-law behavior with an exponent of 0.5 and above ∼30 K the exponent ranges from 1.17 to 1.58. The observed power-laws basically characterize the presence of critical regime of the metal-insulator (MI) transition, dominated by electron-electron and electron-phonon inelastic scattering events respectively. In samples with x = 1.0, 0.5, 0.0 and −0.5 the in field σ-T has been found to follow ln σ-vs-T^1/4 below 5 K, which indicates the presence of variable range hopping. The observed transport features indicate the occurrence of proximity of metal-insulator transition in these Al-Cu-Ru quasicrystal samples.     

Structural implications of water and boron dissolution in albite glass

A combined nuclear magnetic resonance, infrared and Raman spectroscopic study on the effect of water dissolution on the structure of B-bearing aluminosilicate glasses is presented. The base composition was albite (NaAlSi₃O₈) to which different amounts of B₂O₃ (4.8, 9.1, 16.7 wt%) were added. Hydrous glasses containing 4.4 ± 0.1 wt% water were synthesized at pressures of 2000 bar. The results show that B dissolves in both dry and hydrous glasses by forming predominantly trigonal BO₃ groups although some tetrahedral BO₄ is also present. In anhydrous glasses prepared at high pressures (above 10 kbar) the fraction of BO₄ increased. The hydrous glasses contain more BO₄ groups compared to the dry counterparts, suggesting that this species is stabilized by water. The Raman and NMR (¹⁷O, ²⁷Al, ²⁹Si) spectra show that B interacts with the aluminosilicate network by formation of Si-O-B and probably Al-O-B units. In the hydrous glasses the water speciation changes significantly towards higher hydroxyl concentrations with increasing B-content. The NIR peaks, which are related to OH groups and molecular H₂O, develop additional shoulders, suggesting that possibly B-OH complexes are formed.     

Atomic layer deposition of ZrO2 thin films using a new alkoxide precursor

Zirconium oxide thin films were grown by atomic layer deposition using a new type of Zr alkoxide: [Zr(O^tBu)₂(dmae)₂]₂ (dmae is dimethylaminoethoxide). Water was used as the oxygen source. The films grown at 190-240 °C were amorphous, and the films grown at 290-340 °C were nanocrystalline. The highest refractive index of the films was 2.08 at a wavelength of 580 nm. The permittivity of a film grown at 240 °C was 25.