Water repellent ZnO nanowire arrays synthesized by simple solvothermal technique

The authors report on the water repellent properties of quasialigned zinc oxide (ZnO) nanowire arrays grown by low-temperature solvothermal technique. The uniform and dense ZnO nanowires of average diameter ∼ 75 nm have been found to have hexagonal wurtzite type structure. The as synthesized ZnO nanowire surfaces have hydrophilic nature with a water contact angle of 73° ± 3°. The superhydrophobic behavior with a water contact angle of 145° ± 3° of the nanowire arrays has been realized due to the reduction of surface free energy after being coated with an octadecyltrichlorosilane (OTS) monolayer. This work may be of huge importance from the viewpoint of both the understanding of the mechanisms involved and industrial applications.     

Particle Size and Crystal Phase Dependent Photoluminescence of La2Zr2O7:Eu3+ Nanoparticles

Herein, La₂Zr₂O₇:5% Eu³⁺ nanoparticles (NPs) with different sizes have been synthesized for the first time through a modified facile molten salt process using a single‐source complex precursor of La(OH)₃·ZrO(OH)₂:Eu(OH)₃·nH₂O. It was found that the concentration of the added ammonia to co‐precipitate the corresponding metallic ions to form the precursor can influence the final particle size of the fluorite La₂Zr₂O₇:5%Eu³⁺ NPs. Furthermore, the crystal phase of the La₂Zr₂O₇:5%Eu³⁺ NPs was transferred from fluorite to pyrochlore after thermal treatment at 1000°C. The relationship between photoluminescence (PL), quantum yield (QY), particles size and crystal phase has been further investigated through fluorescence decay, site symmetry, and Judd–Ofelt (J–O) analysis. Specifically, PLQY and lifetime increase with increasing particle size of the fluorite La₂Zr₂O₇:5%Eu³⁺ NPs. Additionally, crystal phase transfer from fluorite to pyrochlore resulted in large PLQY decrease and moderate lifetime increase in the La₂Zr₂O₇:5%Eu³⁺ NPs.     

Electrical properties of niobium doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ferroelectrics

Nb-doped Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅ intergrowth ceramics have been prepared by modified oxalate route. XRD phase analysis confirmed the formation of single phase compound. Nb-doping does not affect the basic crystal structure of the intergrowth. SEM micrographs showed that the grain size of the ceramics decreases with Nb-doping. The temperature dependence of dielectric constant and losses was investigated in the temperature range 30–800 °C and frequency range 1 kHz–1 MHz. With Nb-doping, the T_c of the ferroelectrics reduces and peak permittivity increases. Doping also introduces small relaxor behavior in the ferroelectrics. The dc conductivity of the ceramics decreases with doping. The remnant polarization (P_r) of the intergrowth ferroelectrics is increased with Nb doping.     

Control of thermo reversible gelation of methylcellulose using polyethylene glycol and sodium chloride for sustained delivery of ophthalmic drug

The effect of molecular weight of polyethyleneglycol (PEG) and sodium chloride (NaCl) on the gelation temperature of methylcellulose (MC) was studied with the objective to develop a MC based formulation for sustained delivery of ophthalmic drug. The gelation temperature of 1% MC was 60 ± 0.40°C. It was found that the gelation temperature of MC was reduced with the addition of 10% PEG and extent of reduction of gelation temperature was depended on the molecular weight of PEG at same PEG concentration of 10%. The gelation temperature of MC was reduced by 10.4 to 5.9°C with the increasing molecular weight of PEG starting from 400 to 20,000 (M_n ) depending on the method of determination of gelation temperature. To reduce the gelation temperature of MC close to physiological temperature (37°C), 6% NaCl was added in the different MC‐PEG combinations containing different molecular weight of PEG. It was observed that the drug release time increased from 5 to 8 h with the increase in molecular weight of PEG from 400 to 20,000 (M_n ) and this was due to the maximum viscosity and gel strength of MC‐PEG20000‐NaCl ternary combination. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Redox-catalytic correlations in oxidised copper-ceria CO-PROX catalysts

Four nanostructured oxidised copper-cerium catalysts prepared by two different methods (impregnation of ceria and coprecipitation of the two components within reverse microemulsions) with varying copper loadings have been examined with the aim of establishing correlations between redox and catalytic properties for preferential oxidation of CO in H₂-rich streams. The analysis is based on ex situ TPR examination both with H₂ or CO as well as operando spectroscopic exploration by DRIFTS and XANES, additionally complemented by conventional catalytic tests. The results reveal redox promoting effects on copper oxide reduction and allow establishing a model of the catalytic behaviour of this type of catalysts which can provide keys to control their CO-PROX catalytic properties.     

Unconfined compressive strength of fly ash reinforced with jute geotextiles

A series of unconfined compressive strength (UCS) tests have been conducted on unreinforced fly ash as well as fly ash reinforced with jute geotextiles. The effects of different governing parameters viz., degree of saturation, size of samples, number of jute geotextile layers and age of sample on UCS have been studied. From the test results it is found that the values of UCS are maximum at degree of saturation of 70–75%. The effect of sample size on the values of UCS for unreinforced fly ash is insignificant, whereas with increase in diameter of sample, values of UCS increase in case of reinforced fly ash. With increase in number of jute geotextile layers for reinforced fly ash samples, values of UCS increase and maximum enhancement is found to be around 525% with 4 layers of reinforcement. A non-linear power model has been developed to estimate unconfined compressive strength (UCS_R) of fly ash reinforced with jute geotextiles in terms of unconfined compressive strength (UCS_UR) of unreinforced fly ash and number of layers of reinforcement (N).     

Performance improvement of flash memory using AlN as charge-trapping Layer

Potential of high-k dielectric films for future scaled charge storage non-volatile memory (NVM) device applications is discussed. To overcome the problems of charge loss encountered in conventional flash memories with silicon-nitride (Si₃N₄) films and polysilicon-oxide-nitride-oxide-silicon (SONOS) and nonuniformity issues in nanocrystal memories (NC), such as Si, Ge and metal, it is shown that the use of high-k dielectrics allows more aggressive scaling of the tunnel dielectric, smaller operating voltage, better endurance, and faster program/erase speeds. Charge-trapping characteristics of high-k AlN films with SiO₂ as a blocking oxide in p-Si/SiO₂/AlN/SiO₂/poly-silicon (SOHOS) memory structures have been investigated in detail. The experimental results of program/erase characteristics obtained as the functions of gate bias voltage and pulse width are presented.     

High performance TaYOx-based MIM capacitors

TaYO_x-based metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated. Ultra-thin TaYO_x films in the thickness range of 15-30 nm (EOT ∼ 2.4-4.7 nm) were deposited on Au/SiO₂ (100 nm)/Si (100) structures by rf-magnetron co-sputtering of Ta₂O₅ and Y₂O₃ targets. TaYO_x layers were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) to examine the composition and crystallinity. An atomic percentage of Ta:Y = 58.32:41.67 was confirmed from the EDX analysis while XRD revealed an amorphous phase (up to 500 °C) during rapid thermal annealing. Besides, a high capacitance density of ∼3.7-5.4 fF/μm² at 10 kHz (ε_r ∼ 21), a low value of VCC (voltage coefficients of capacitance, α and β) have been achieved. Also, a highly stable temperature coefficient of capacitance, TCC has been obtained. Capacitance degradation phenomena in TaYO_x-based MIM capacitors under constant current stressing (CCS at 20 nA) have been studied. It is observed that degradation depends strongly on the dielectric thickness and a dielectric breakdown voltage of 3-5 MV/cm was found for TaYO_x films. The maximum energy storage density was estimated to be ∼5.69 J/cm³. Post deposition annealing (PDA) in O₂ ambient at 400 °C has been performed and further improvement in device reliability and electrical performances has been achieved.     

Double-diffusive mixed convection in a vertical pipe: A thermal non-equilibrium approach

In this article, double-diffusive mixed convection in a vertical pipe under local thermal non-equilibrium state has been investigated. The non-Darcy Brinkman–Forchheimer-extended model has been used and solved numerically by spectral collocation method. Special attention is given to understand the effect of buoyancy ratio (N) and thermal non-equilibrium parameters: inter phase heat transfer coefficient (H) as well as porosity scaled thermal conductivity ratio (γ) on the flow profiles as well as on rates of heat and solute transfer. Judged from the influence of buoyancy ratio on velocity profile, when both the buoyancy forces: thermal as well as solutal are in favor of each other and for given any value of H considered in this study, it has been found that for N equal to 10 as well as 100, the basic velocity profile shows back flow for small subdomain of the domain of the flow. When two buoyancy forces are opposing to each other (Ra_T = ?1000), velocity profile possesses a kind of distortion, in which the number of zeroes increases on increasing N. Corresponding variation of heat transfer rate in the (N,  Nu_f)-plane shows a sinusoidal pattern. The flow separation on the flow profile dies out on increasing H for N = 0. It has been also found that for each N, when N < 0.7, there exists a minimum value of H such that the velocity profile becomes free from flow separation. Influence of H on the profiles of solid temperature as well as solute, in both situations are similar. Overall, the impact of LTNE parameters, specially γ, on heat transfer rate of double-diffusive convection is not straight forward.