Toplinska stabilnost W1−xSix/Si višeslojeva za rendgensku optiku

The thermal stability of multilayers (MLs) for X-ray mirrors can be increased by using a pair of materials in thermodynamic equilibrium. This was achieved by doping the W-layer by Si to decrease the driving force of interdiffusion. The W0.66Si0.33/Si, W0.5Si0.5/Si, W0.33Si0.66/Si and, for comparison, W/Si MLs with ten bilayers were fabricated by electron-beam deposition in UHV onto oxidized Si substrates. The nominal thickness was 5.5 nm for Si and 2.5 nm for W or W1-xSix layers. The samples were heat treated by halogen-lamp rapid thermal annealing and by standard annealing in vacuum up to 1000 °C for 30 s and 25 min, respectively. Samples were analyzed by X-ray reflectivity and large angle X-ray diffraction measurements. From the results follows an increased stability of W1-xSix/Si MLs in comparison with the W/Si ones. The temperature which the sample can withstand without a serious damage increased from 500 to 850 °C with x increasing from 0 to 0.66 . As-deposited, MLs were amorphous. The crystalline bcc W or WSi2 phases appeared at 500 °C for x Ł 0.5. For x = 0.66, a well developed WSi2 was obtained only after annealing at 1000 °C. Hence, Si helps to keep W in the amorphous state.Primjenom parova materijala, koji se stavljaju u termodinamičku ravnotežu, može se povećati toplinska stabilnost višeslojeva za zrcala rendgenskog zračenja. Sloj volframa dopunjen je silicijem da bi se smanjila difuzija medu slojevima. Istraženi su višeslojevi W1−x Six sa x = 0.66, 0.5, 0.33 i x = 0.0 radi usporedivanja. W/Si višeslojevi sa deset dvoslojeva pripremljeni su nanošenjem uz pomoć elektronskog snopa na oksidirane Si podloge u ultravakuumu. Nominalna debljina slojeva Si bila je 5.5 nm, a W odnosno W1−xSix 2.5 nm. Višeslojevi su toplinski otpuštani. Uzorci su istraživani mjerenjem refleksivnosti i difrakcijom rendgenskog zračenja. Povećanjem x od 0 na 0.66, povisila se granična temperatura bez većeg oštećenja sa 500 na 800 ◦C

Nanoparticle Langmuir-Blodgett Arrays for Sensing of CO and NO2 Gases

Metal oxide sensors with active Fe2O3 and CoFe2O4 nanoparticle arrays were studied. Sensing nanoparticle films from 1, 2, 4 or 7 monolayers were deposited by Langmuir-Blodgett technique. Sensors are formed on the alumina substrates equipped with heating meander. Langmuir-Blodgett layers were heated or UV irradiated to remove the insulating surfactant. Sensing properties were studied towards CO or NO2 gases in concentrations between 0.5 and 100 ppm in mixture with the dry air. Best response values Igas/Iair were obtained with CoFe2O4 device being 3 for 100 ppm of CO and with Fe2O3 device being (38)-1 for 0.5 ppm of NO2

Polyethylene Glycol-Modified Poly(Styrene-co-Ethylene/Butylene-co-Styrene)/Carbon Nanotubes Composite for Humidity Sensing

Polymeric composites of the linear triblock copolymer poly(styrene-co-ethylene/butylene-co-styrene) grafted with maleic anhydride units (SEBS-MA) or MA modified by hydrophilic polyethylene glycol (PEG) and containing various amounts of multiwall carbon nanotubes (MWCNTs) as conducting filler—were prepared by solvent casting. The MWCNT surface was modified by a non-covalent approach with a pyrene-based surfactant to achieve a homogeneous dispersion of the conducting filler within the polymeric matrix. The dispersion of the unmodified and surfactant-modified MWCNTs within the elastomeric SEBS-MA and SEBS-MA-PEG matrices was characterized by studying the morphology by TEM and SAXS. Dynamical mechanical analysis was used to evaluate the interaction between the MWCNTs and copolymer matrix. The electrical conductivity of the prepared composites was measured by dielectric relaxation spectroscopy, and the percolation threshold was calculated. The prepared elastomeric composites were characterized and studied as humidity sensor. Our results demonstrated that at MWCNTs concentration slightly above the percolation threshold could result in large signal changes. In our system, good results were obtained for MWCNT loading of 2 wt% and an ~0.1 mm thin composite film. The thickness of the tested elastomeric composites and the source current appear to be very important factors that influence the sensing performance

Graphene Langmuir-Schaefer films Decorated by Pd Nanoparticles for NO2 and H2 Gas Sensors

NO2 and H2 gas sensing by few-layer graphene (FLG) were studied in dependence on the annealing and decoration of graphene by palladium nanoparticles (NPs). Graphene was deposited onto SiO2 (500 nm)/Si substrates by a modified Langmuir-Schaefer technique. A solution of FLG flakes in 1-methyl-2-pyrrolidone was obtained by a mild sonication of the expanded milled graphite. FLG films were characterized by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and the Brunnauer-Emmett-Teller method. Average FLG flake thickness and lateral dimension were 5 nm and 300 nm, respectively. Drop casting of Pd NP (6–7 nm) solution onto FLG film was applied to decorate graphene by Pd. The room temperature (RT) resistance of the samples was stabilized at 15 kΩ by vacuum annealing. Heating cycles of FLG film revealed its semiconducting character. The gas sensing was tested in the mixtures of dry air with H2 gas (10 to 10 000 ppm) and NO2 gas (2 to 200 ppm) between RT and 200 °C. The response of 26 % to H2 was achieved by FLG with Pd decoration at 70 °C and 10 000 ppm of H2 in the mixture. Pure FLG film did not show any response to H2. The response of FLG with Pd to 6 ppm of NO2 at RT was ≥ 23 %. It is 2 times larger than that of the pure FLG sample. Long term stability of sensors was studied

Synthesis and enhanced photocatalytic activity of nitrogen-doped triphasic TiO2 nanoparticles

TiO2 nanoparticles of the single anatase phase, binary anatase-brookite phases, and ternary anatase-brookite-rutile phases were synthesized using an HNO3-catalyzed hydrothermal process. The types and amounts of phases varied depending on the hydrothermal synthesis conditions. The results revealed that N dissolves in different amounts and chemical states, depending on the phases present and their proportions in the nano particles. Brookite and rutile nanoparticles oriented through one direction were found to be crystallized by the surface transformation from anatase. Photocatalytic activity tests, evaluated by degradation of methylene blue (MB) under ultraviolet (UV) and visible light illumination, revealed that the N-doped TiO2 nanoparticles containing a ternary-phase mixture had the best photocatalytic activity. The MB degradation of the visible light-active nanoparticles was three times better than that of a commercially available well-known TiO2 powder, P25 under UV illumination. The enhanced photoactivity was attributed to the following: i) a high surface area, ii) suppression of the recombination of electron-hole pairs with ternary-phase mixture crystallized in heterojunctions, iii) larger anatase phase content, and iv) narrower band gap and facilitation of charge separation by dissolved N atoms

Kinetics of Polymer–Fullerene Phase Separation during Solvent Annealing Studied by Table-Top X‑ray Scattering

Solvent annealing is an efficient way of phase separation in polymer–fullerene blends to optimize bulk heterojunction morphology of active layer in polymer solar cells. To track the process in real time across all relevant stages of solvent evaporation, laboratory-based in situ small- and wide-angle X-ray scattering measurements were applied simultaneously to a model P3HT:PCBM blend dissolved in dichlorobenzene. The PCBM molecule agglomeration starts at ∼7 wt % concentration of solid content of the blend in solvent. Although PCBM agglomeration is slowed-down at ∼10 wt % of solid content, the rate constant of phase separation is not changed, suggesting agglomeration and reordering of P3HT molecular chains. Having the longest duration, this stage most affects BHJ morphology. Phase separation is accelerated rapidly at concentration of ∼25 wt %, having the same rate constant as the growth of P3HT crystals. P3HT crystallization is driving force for phase separation at final stages before a complete solvent evaporation, having no visible temporal overlap with PCBM agglomeration. For the first time, such a study was done in laboratory demonstrating potential of the latest generation table-top high-brilliance X-ray source as a viable alternative before more sophisticated X-ray scattering experiments at synchrotron facilities are performed

A Non-Equilibrium Transient Phase Revealed by in Situ GISAXS Tracking of the Solvent-Assisted Nanoparticle Self-Assembly

We report on a time-resolved study of the colloidal nanoparticle self-assembly into a high-quality nanoparticle crystal with the face-centered cubic crystallographic symmetry. In particular, the grazing-incidence small-angle X-ray scattering technique was employed to track kinetics of the solvent evaporation driven self-assembly on casting a drop of plasmonic Ag nanoparticles on a silicon substrate. The short-range (cumulative) disorder typical for paracrystal structures before the complete solvent evaporation at 300–350 s from the drop casting was found with the exception of the time window of 125–150 s where a highly regular transient phase with the long-range order was observed. This temporary improvement of the nanoparticle crystal perfection occurring shortly before the complete solvent evaporation is the main message of the paper. It is attributed to interaction between the surfactant shells of the neighboring nanoparticles getting into contact in the presence of solvent residua to the end of the solvent evaporation which results in a larger nanoparticle hydrodynamic diameter with a smaller dispersion and improvement of the crystallization. This process has direct impact on the quality of the resulting nanoparticle crystal and tailoring its properties

Советская Сибирь, № 137

The Fe2O3 and CoFe2O4 nanoparticle-based Langmuir-Blodgett films for sensing of nitrogen dioxide (NO2) and acetone vapours have been explored. Both the sensitivity of the chemiresistors and dynamic properties, such as the response/recovery time, have been probed in dependence of the number of nanoparticle monolayers and working temperatures. The response of 23 at the NO2 concentration of 1 ppm has been monitored suggesting the pertinent sensitivity in the deep sub-ppm range, i.e. approaching the canine detection limit, and likewise implying the supposable detection of nitrate-based explosives