Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO2) nanowires have been synthesized at a low substrate temperature of 450 degrees C via vapor-liquid-solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2-4 mu m and diameter of 20-60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO2 nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO2 nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 x 10(-4) mbar suggested that a temperature equal to or greater than 450 degrees C was the best condition for phase pure SnO2 nanowires growth. The SnO2 nanowires grown on a SiO2 substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO2 NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 mu W/cm(2) UV lamp (330 nm) intensity on the photo detector.

Insight into morphology changes of nanoparticle laden droplets in acoustic field

Hollow structures with unique morphologies form due to particle agglomeration in acoustically levitated nanofluid functional droplets when subjected to external heating. The final diameter of the structure depends only on the ratio of agglomeration to evaporation time scales for various nanoparticle laden droplets, and not on the type of the suspended particles. These time scales depend only on nanoparticle concentration. This valuable information may be exploited to form microstructures with desired properties from ceramic compounds. Phase diagrams for alumina and silica droplets indicate the transition from a bowl to ring structure depending on concentration.

Characterization and magnetic response of multiwall carbon nanotubes filled with iron nanoparticles of different aspect ratios

Three samples of multiwall carbon nanotubes (MWCNT) TF200, TF150 and TF100, where T and F stand for toluene and ferrocene respectively, and numeral denotes the amount (mg) of ferrocene] filled with iron-nanoparticles (Fe-NPs) of different aspect ratios are grown by chemical vapor deposition of toluene-ferrocene mixture. Energy dispersive X-ray analysis shows a systematic variation in the intensities of peak corresponding to Fe, indicating that Fe is present in different amounts in the three MWCNT samples. The lengths of Fe-NPs lie in the range of 200-250; 80-120; and 30-40 nm for TF200, TF150 and TF100, respectively, as estimated statistically from transmission electron microscopy micrographs. However, the diameter of the encapsulated Fe-NPs does not vary significantly for different samples and is 20-30 nm for all samples. Hysteresis loop measurements on these MWCNT samples were done at 10, 150 and 300 K up to an applied field of 1.5 T. At 10 K, values of coercivity are 2584, 2315, and 2251 Oe for TF200, TF150 and TF100 respectively. This is attributed to the strong shape anisotropy of the Fe-NPs and significant dipolar interactions between them. Further, M-H loops reveal that saturation magnetization of TF200 is almost four times that of TF100 at all temperatures.

The effect of base roughness on the development of a dense granular flow down an inclined plane

The development of the flow of a granular material down an inclined plane starting from rest is studied as a function of the base roughness. In the simulations, the particles are rough frictional spheres interacting via the Hertz contact law. The rough base is made of a random configuration of fixed spheres with diameter different from the flowing particles, and the base roughness is decreased by decreasing the diameter of the base particles. The transition from an ordered to a disordered flowing state at a critical value of the base particle diameter, first reported by Kumaran and Maheshwari Phys. Fluids 24, 053302 (2012)] for particles with the linear contact model, is observed for the Hertzian contact model as well. The flow development for the ordered and disordered flows is very different. During the development of the disordered flow for the rougher base, there is shearing throughout the height. During the development of the ordered flow for the smoother base, there is a shear layer at the bottom and a plug region with no internal shearing above. In the shear layer, the particles are layered and hexagonally ordered in the plane parallel to the base, and the velocity profile is well approximated by Bagnold law. The flow develops in two phases. In the first phase, the thickness of the shear layer and the maximum velocity increase linearly in time till the shear front reaches the top. In the second phase, after the shear layer encompasses the entire flow, there is a much slower increase in the maximum velocity until the steady state is reached. (C) 2013 AIP Publishing LLC.

Stability of a long unsupported circular tunnel in soils with seismic forces

By using the lower-bound finite element limit analysis, the stability of a long unsupported circular tunnel has been examined with an inclusion of seismic body forces. The numerical results have been presented in terms of a non-dimensional stability number (gamma H/c) which is plotted as a function of horizontal seismic earth pressure coefficient (k (h)) for different combinations of H/D and I center dot; where (1) H is the depth of the crest of the tunnel from ground surface, (2) D is the diameter of the tunnel, (3) k (h) is the earthquake acceleration coefficient and (4) gamma, c and I center dot define unit weight, cohesion and internal friction angle of soil mass, respectively. The stability numbers have been found to decrease continuously with an increase in k (h). With an inclusion of k (h), the plastic zone around the periphery of the tunnel becomes asymmetric. As compared to the results reported in the literature, the present analysis provides a little lower estimate of the stability numbers. The numerical results obtained would be useful for examining the stability of unsupported tunnel under seismic forces.

Novel co-evaporation approach for the growth of Sb doped SnO2 nanowires

Antimony doped tin oxide (Sb:SnO2) nanowires were grown by thermal and e-beam assisted co-evaporation of Sb and Sn in the presence of oxygen at a low substrate temperature of 450 degrees C. The field emission scanning electron microscopy study revealed that the nanowires had a length and diameter of 2-4 mu m and 20-60 nm respectively. Transmission electron microscopy study revealed the single crystalline nature of the nanowires; energy dispersive X-ray spectroscopy (EDS) and EDS mapping on the nanowires confirmed the presence of Sb doping in the nanowires. UV light detection study on the doped SnO2 nanowire films exhibited fast response and recovery time compared to undoped SnO2 nanowire films. This is an innovative and simple method to grow doped SnO2 nanowires.

Role of substrate temperature on the properties of Na-doped ZnO thin film nanorods and performance of ammonia gas sensors using nebulizer spray pyrolysis technique

Sodium doped zinc oxide (Na:ZnO) thin films were deposited on glass substrates at substrate temperatures 300,400 and 500 degrees C by a novel nebulizer spray method. X-ray diffraction shows that all the films are polycrystalline in nature having hexagonal structure with high preferential orientation along (0 0 2) plane. High resolution SEM studies reveal the formation of Na-doped ZnO films having uniformly distributed nano-rods over the entire surface of the substrates at 400 degrees C. The complex impedance of the ZnO nano-rods shows two distinguished semicircles and the diameter of the arcs got decreased in diameter as the temperature increases from 170 to 270 degrees C and thereafter slightly increased. (c) 2013 Elsevier B.V. All rights reserved.

Stability of long unsupported twin circular tunnels in soils

The stability of two long unsupported circular parallel tunnels aligned horizontally in fully cohesive and cohesive-frictional soils has been determined. An upper bound limit analysis in combination with finite elements and linear programming is employed to perform the analysis. For different clear spacing (S) between the tunnels, the stability of tunnels is expressed in terms of a non-dimensional stability number (gamma H-max/c); where H is tunnel cover, c refers to soil cohesion, and gamma(max) is maximum unit weight of soil mass which the tunnels can bear without any collapse. The variation of the stability number with tunnels' spacing has been established for different combinations of H/D, m and phi; where D refers to diameter of each tunnel, phi is the internal friction angle of soil and m accounts for the rate at which the cohesion increases linearly with depth. The stability number reduces continuously with a decrease in the spacing between the tunnels. The optimum spacing (S-opt) between the two tunnels required to eliminate the interference effect increases with (i) an increase in H/D and (ii) a decrease in the values of both m and phi. The value of S-opt lies approximately in a range of 1.5D-3.5D with H/D = 1 and 7D-12D with H/D = 7. The results from the analysis compare reasonably well with the different solutions reported in literature. (C) 2013 Elsevier Ltd. All rights reserved.

CFD Analysis of two phase flow with a prediction of torque demand of a Bi-lobe rotor of a mixing chamber

An attempt to study the fluid dynamic behavior of two phase flow comprising of solid and liquid with nearly equal density in a geometrical case that has an industrial significance in theareas like processing of polymers, food, pharma ceutical, paints. In this work,crystalline silica is considered as the dispersed medium in glycerin. In the CFD analysis carried out,the two phase components are considered to be premixed homogeneously at the initial state. The flow in a cylinder that has an axially driven bi-lobe rotor, a typical blender used in polymer industry for mixing or kneading to render the multi-component mixture to homogeneous condition is considered. A viscous, incompressible, isothermal flow is considered with an assumption that the components do not undergo any physical change and the solids are rigid and mix in fully wetting conditions. Silica with a particle diameter of 0.4 mm is considered and flow is analyzed for different mixing fractions. An industry standard CFD code is used for solving 3D-RANS equations. As the outcome of the study the torque demand by the bi-lobe rotor for different mixture fractions which are estimated show a behavioral consistency to the expected physical phenomena occurring in the domain considered.

Experimental investigation of biofuel drop impact on stainless steel surface

Blends of conventional fuels such as Jet-A1 (aviation kerosene) and diesel with bio-derived components, referred to as biofttels, are gradually replacing the conventional fuels in aircraft and automobile engines. There is a lack of understanding on the interaction of spray drops of such biofuels with solid surfaces. The present study is an experimental investigation on the impact of biofuel drops onto a smooth stainless steel surface. The biofuel is a mixture of 90% commercially available camelina-derived biofuel and 10% aromatics. Biofuel drops were generated using a syringe-hypodermic needle arrangement. On demand, the needle delivers an almost spherical drop with drop diameter in the range 2.05-2.15 mm. Static wetting experiments show that the biofuel drop completely wets the stainless steel surface and exhibits an equilibrium contact angle of 5.6. High speed video camera was used to capture the impact dynamics of biofuel drops with Weber number ranging from 20 to 570. The spreading dynamics and maximum spreading diameter of impacting biofuel drops on the target surface were analyzed. For the impact of high Weber number biofuel drops, the spreading law suggests beta similar to tau(0.5) where beta is the spread factor and tau, the nondimensionalized time. The experimentally observed trend of maximum spread factor, beta(max) of camelina biofuel drop on the target surface with We compares well with the theoretically predicted trend from Ukiwe-Kwok model. After reaching beta(max), the impacting biofuel drop undergoes a prolonged sluggish spreading due to the high wetting nature of the camelina biofuel-stainless steel system. As a result, the final spread factor is found to be a little more than beta(max). (C) 2014 Elsevier Inc. All rights reserved.

Multistage effect in enhancing the field emission behaviour of ZnO branched nanostructures

We report the synthesis of branched ZnO nanostructures by vapour phase transport and their multistage effect in enhancing the field emission behaviour. First, the ZnO nanowires (first generation) are grown and second generation nanowires are grown on first one and so on to obtain the branched structures. The number of branches increases and the diameter of the branches decreases till the third generation nanowires. Fourth generation onwards, dense branched structures are obtained eventually yielding nanoforest-like morphology. The field emission behaviour is found to improve till the third generation and is assigned to smaller diameter of the branches. (C) 2014 AIP Publishing LLC.

Correlation between Optical Properties and Nanomorphology of Fluoranthene-Based Conjugated Copolymer

Nanoparticles of conjugated polymers are receiving attention due to their interesting optical properties. Here we report nanoparticles of fluoranthene-based conjugated copolymer prepared by the Suzuki coupling reaction. The copolymer forms nanoparticles by the spontaneous self-assembly after evaporation of organic solvent. The mean diameter of the nanoparticles can be manipulated by varying solvent composition. We investigated the parameters that govern the nanostructured morphology of polymer by systematic variation of good and poor solvent. The UV vis and time-resolved fluorescence spectroscopy measurement reveal the use of poor solvent in the organization of nanostructures. Furthermore, transmission electron microscopy highlights the importance of rigidity of the polymer backbone in morphological development.

Electron microscopy of Ag-(Ni-O) core-shell nanowires

This report provides information about an electrodeposition based two-step synthesis methodology for producing core-shell Ag-(Ni-O) nanowires and their detailed structural and compositional characterization using electron microscopy technique. Nanowires were produced by employing anodic alumina templates with a pore diameter of 200 nm. In the first step of the synthesis process, nanocrystalline Ni-O was electrodeposited in a controlled manner such that it heterogeneously nucleated and grew only on the template pore walls without filling the pores from bottom upwards. This alumina template with pore walls coated with Ni-O was then utilized as a template during the electrodeposition of Ag in the second step. Electrodeposited Ag filled the template pores to finally produce Ag-(Ni-O) core-shell nanowires with an overall diameter of 200 nm.

Rapid, microwave-assisted synthesis of Gd2O3 and Eu:Gd2O3 nanocrystals: characterization, magnetic, optical and biological studies

Ultra-small crystals of undoped and Eu-doped gadolinium oxide (Gd2O3) were synthesised by a simple, rapid microwave-assisted route, using benzyl alcohol as the reaction solvent. XRD, XPS and TEM analysis reveal that the as-prepared powder material consists of nearly monodisperse Gd2O3 nanocrystals with an average diameter of 5.2 nm. The nanocrystals show good magnetic behaviour and exhibit a larger reduction in relaxation time of water protons than the standard Gd-DTPA complex currently used in MRI imaging. Cytotoxicity studies (both concentration- and time-dependent) of the Gd2O3 nanocrystals show no adverse effect on cell viability, evidencing their high biological compatibility. Finally, Eu:Gd2O3 nanocrystals were prepared by a similar route and the red luminescence of Eu3+ activator ions was used to study the cell permeability of the nanocrystals. Red fluorescence from Eu3+ ions observed by fluorescence microscopy shows that the nanocrystals (Gd2O3 and Eu:Gd2O3) can permeate not only the cell membrane but can also enter the cell nucleus, rendering them candidate materials not only for MRI imaging but also for drug delivery when tagged or functionalized with specific drug molecules.

Enhancing the photocatalytic efficiency of sprayed ZnO thin films through double doping (Sn plus F) and annealing under different ambiences

Doubly (Sn + F) doped zinc oxide (ZnO:Sn:F) thin films were deposited onto glass substrates using a simplified spray pyrolysis technique. The deposited films were annealed at 400 degrees C under two different ambiences (air and vacuum) for 2 h. The photocatalytic activity of these films was assessed through photocatalytic decolorization kinetics of Methylene Blue (MB) dye and the decolorization efficiency of the annealed films was compared with that of their as-deposited counterpart. The photocatalytic studies reveal that the ZnO:Sn:F films annealed under vacuum environment exhibits better photocatalytic efficiency when compared with both air annealed and as-deposited films. The SEM and TEM images depict that the surface of each of the films has an overlayer comprising of nanobars formed on a bottom layer, having spherical grains. The studies show that the diameter of the nanobars plays crucial role in enhancing the photocatalytic activity of the ZnO:Sn:F films. The structural, optical and electrical studies substantiate the discussions on the photocatalytic ability of the deposited films. (C) 2014 Elsevier B.V. All rights reserved.