Modeling of growth and motion of equiaxed dendrites in a convecting melt

A numerical micro-scale model is developed to study the behavior of dendrite growth in presence of melt convection. In this method, an explicit, coupled enthalpy model is used to simulate the growth of an equiaxed dendrite, while a Volume of Fluid (VOF) method is used to track the movement of the dendrite in the convecting melt in a two-dimensional Eulerian framework. Numerical results demonstrate the effectiveness of the enthalpy model in simulating the dendritic growth involving complex shape, and the accuracy of VOF method in conserving mass and preserving the complex dendritic shape during motion. Simulations are performed in presence of uniform melt flow for both fixed and moving dendrites, and the difference in dendrite morphology is shown.

Growth and characterization of SrBi2Nb2O9 thin films by pulsed-laser ablation

Polycrystalline films of SrBi2Nb2O9 were grown using pulsed-laser ablation. The ferroelectric properties were achieved by low-temperature deposition followed by a subsequent annealing process. The lower switching voltage was obtained by lowering the thickness, which did not affect the insulating nature of the films. The hysteresis results showed an excellent square-shaped loop with results (Pr = 6 μC/cm2, Ec = 100 kV/cm) in good agreement with earlier reports. The films also exhibited a dielectric constant of 250 and a dissipation factor of 0.02. The transport studies indicated an ohmic behavior, while higher voltages induced a bulk space charge.

Growth, magnetotransport, and magnetic properties of ferromagnetic (In,Mn)Sb crystals

In1−xMnxSb crystals are grown with different Mn doping concentrations (x = 0.006, 0.01, 0.02, and 0.04) beyond the equilibrium solubility limit by the horizontal Bridgman technique. Structural, magnetic, and magnetotransport properties of the grown crystals are studied in the temperature range 1.4–300 K. Negative magnetoresistance and anomalous Hall effect are observed below 10 K. The anomalous Hall coefficient is found to be negative. The temperature dependence of the magnetization measurement shows a magnetic ordering below 10 K, which could arise from InMnSb alloy formation. Also, the saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic MnSb clusters in the crystals, which has been verified by scanning electron microscopy studies. The carrier concentration increases with Mn doping, and this results in a decrease of resistivity. The carrier concentration and mobility at room temperature for the doped crystals are ∼ 2×1019 cm−3 and ∼ 200 cm2/V s, respectively. The observed anomalous Hall effect suggests the carrier mediated ferromagnetism below 10 K in In1−xMnxSb crystals.

Collision Cones for Quadric Surfaces

The problem of collision prediction in dynamic environments appears in several diverse fields, which include robotics, air vehicles, underwater vehicles, and computer animation. In this paper, collision prediction of objects that move in 3-D environments is considered. Most work on collision prediction assumes objects to be modeled as spheres. However, there are many instances of object shapes where an ellipsoidal or a hyperboloid-like bounding box would be more appropriate. In this paper, a collision cone approach is used to determine collision between objects whose shapes can be modeled by general quadric surfaces. Exact collision conditions for such quadric surfaces are obtained in the form of analytical expressions in the relative velocity space. For objects of arbitrary shapes, exact representations of planar sections of the 3-D collision cone are obtained.

Growth and ferroelectric properties of Bi2VO5.5 thin films with metallic LaNiO3 electrodes

Novel ferroelectric bismuth vanadate, Bi2VO5.5 (BVO), thin films have been grown between lattice matched metallic LaNiO3 (LNO) layers deposited on SrTiO3 (STO) by the pulsed laser deposition technique. LNO/BVO/LNO/STO and Au/BVO/LNO/STO trilayer structures exhibited c‐oriented (001) growth of BVO. LNO has been found to be a good metallic electrode with sheet resistance ∼20 Ω in addition to aiding c‐axis oriented BVO growth. The dielectric constant, ϵr of LNO/BVO/LNO/STO, at 300 K was about 12. However, when an Au electrode was used on top of BVO/LNO/STO film, it showed a significant improvement in the dielectric constant (ϵr=123). The ferroelectric properties of BVO thin films have been confirmed by hysteresis behavior with a remnant polarization, Pr=4.6×10−8 C/cm2 and coercive field, Ec=23 kV/cm at 300 K.

Growth of silicon nanowires by electron beam evaporation using indium catalyst

For the first time silicon nanowires have been grown on indium (In) coated Si (100) substrates using e-beam evaporation at a low substrate temperature of 300 degrees C. Standard spectroscopic and microscopic techniques have been employed for the structural, morphological and compositional properties of as grown Si nanowires. The as grown Si nanowires have randomly oriented with an average length of 600 nm for a deposition time of 15 min. As grown Si nanowires have shown indium nanoparticle (capped) on top of it confirming the Vapor Liquid Solid (VLS) growth mechanism. Transmission Electron Microscope (TEM) measurements have revealed pure and single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires. (C) 2011 Elsevier B.V. All rights reserved.

Multiple garnet growth in garnet-kyanite-staurolite gneiss, Pangong metamorphic complex, Ladakh Himalaya: New constraints on tectonic setting

Garnet-kyanite-staurolite gneiss in the Pangong complex, Ladakh Himalaya, contains porphyroblastic euhedral garnets, blades of kyanite and resorbed staurolite surrounded by a fine-grained muscovite-biotite matrix associated with a leucogranite layer. Sillimanite is absent. The gneiss contains two generations of garnet in cores and rims that represent two stages of metamorphism. Garnet cores are extremely rich in Mn (X(Sps) = 0.35-038) and poor in Fe (X(Alm) = 0.40-0.45), whereas rims are relatively Mn-poor (X(Sps) =0.07-0.08), and rich in Fe (X(Alm), = 0.75-0.77). We suggest that garnet cores formed during prograde metamorphism in a subduction zone followed by abrupt exhumation, during early collision of the Ladakh arc and Karakoram block. The subsequent India-Asia continental collision subducted the metamorphic rocks to a mid-crustal level, where the garnet rims overgrew the Mn-rich cores at ca. 680 degrees C and ca. 8.5 kbar. PT calculations were estimated from phase diagrams calculated using a calculated bulk chemical composition in the Mn-NCKFMASHT system for the garnet-kyanite-staurolite-bearing assemblage. Muscovites from the metamorphic rocks and associated leucogranites have consistent K-Ar ages (ca. 10 Ma), closely related to activation of the Karakoram fault in the Pangong metamorphic complex. These ages indicate the contemporaneity of the exhumation of the metamorphic rocks and the cooling of the leucogranites. (C) 2011 Elsevier B.V. All rights reserved.

Indium flux, growth temperature and RF power induced effects in InN layers grown on GaN/Si substrate by plasma-assisted MBE

In the present work, we report the growth of wurtzite InN epilayers on GaN/Si (1 1 1) substrate by plasma-assisted molecular beam epitaxy (PAMBE). The growth parameters such as indium flux, substrate temperature and RF power affect the crystallographic and morphological properties of InN layers, which were evaluated using high resolution X-ray diffraction (HRXRD) analysis and atomic force microscopy (AFM). It is found that excess indium (In) concentrations and surface roughness were increased with increase in In flux and growth temperature. The intensity of HRXRD (0 0 0 2) peak, corresponding to c-axis orientation has been increased and full width at half maxima (FWHM) has decreased with increase in RF power. It was found that highly c-axis oriented InN epilayers can be grown at 450 degrees C growth temperature, 450 W RF power and 1.30 x 10(-7) mbar In beam equivalent pressure (BEP). The energy gap of InN layers grown by optimizing growth conditions was determined by photoluminescence and optical absorption measurement. (C) 2011 Elsevier B.V. All rights reserved.

Growth and consumption rates of the phase layers during interdiffusion in a diffusion couple with finite end member

The relations for the growth and consumption rates of a layer with finite thickness as an end member and the product phases in the interdiffusion zone are developed. We have used two different methodologies, the diffusion based and the physico-chemical approach to develop the same relations. We have shown that the diffusion based approach is rather straightforward; however, the physico-chemical approach is much more versatile than the other method. It was found that the position of the marker plane becomes vague in the second stage of the interdiffusion process in pure A thin layer/B couple, where two phases grow simultaneously.

Growth mechanism of the Nb(X)Si-2 and [Nb(X)](5)Si-3 phases by reactive diffusion in Nb (X = Ti, Mo, or Zr)-Si systems

The effects of Mo, Ti, and Zr on the diffusion and growth of the Nb(X)Si-2 and Nb(X)(5)Si-3 phases in an Nb(X)-Si system are analyzed. The integrated diffusion coefficients are determined from diffusion couple experiments and compared with the data previously calculated in a binary Nb-Si system. The growth rates of both phases are affected by the addition of Mo and Zr, whereas the addition of Ti has no effect. The atomic mechanism of diffusion is also discussed based on the crystal structure and the possible changes in the defect concentrations due to alloying. Finally, the growth mechanism of the phases is discussed on the basis of a physico-chemical approach. (C) 2011 Elsevier Ltd. All rights reserved.

Surface pressure and heat transfer measurements in the unsteady separated hypersonic flow field over double cones

Reliable bench mark experimental database in the separated hypersonic flow regime is necessary to validate high resolution CFD codes. In this paper we report the surface pressure and heat transfer measurements carried out on double cones (first cone semi-apex angle = 15, 25 deg.; second cone semi-apex angle= 35, 68 deg.) at hypersonic speeds that will be useful for CFD code validation studies. The surface pressure measurements are carried out at nominal Mach number of 8.35 in the IISc hypersonic wind tunnel. On the other hand the surface heat transfer measurements are carried out at a nominal Mach number of 5.75 in the IISc hypersonic shock tunnel. The flow separation point on the first cone, flow reattachment on the second cone and the wild fluctuation of the transmitted shock on the second cone surface (25/68 deg. double cone) in the presence of severe adverse pressure gradient are some of the flow features captured in the measurements. The results from the CFD studies indicate good agreement with experiments in the attached flow regime while considerable differences are noticeable in the separated flow regime.

Atomic layer deposition of ZrO2 thin films: Study of growth kinetics and dielectric behaviour

Thin films of ZrO2 have been deposited by ALD on Si(100) and SIMOX using two different metalorganic complexes of Zr as precursors. These films are characterized by X-ray diffraction, transmission and scanning electron microscopies, infrared spectroscopy, and electrical measurements. These show that amorphous ZrO2 films of high dielectric quality may be grown on Si(100) starting about 400degreesC. As the growth temperature is raised, the films become crystalline, the phase formed and the microstructure depending on precursor molecular structure. The phase of ZrO2 formed depends also on the relative duration of the precursor and oxygen pulses. XPS and IR spectroscopy show that films grown at low temperatures contain chemically unbound carbon, its extent depending on the precursor. C-V measurements show that films grown on Si(100) have low interface state density, low leakage current, a hysteresis width of only 10-250 mV and a dielectric constant of similar to16-25.

Growth of InSb(1-x)Bix crystals by Rotatary Bridgman method and their characterization

The Rotatary Bridgman method was used to grow ternary InSb(1-x)SBix, crystals. In this method the ampoule was subjected to reversible rotation at a rate of 60rpm. High quality crystals of 8mm diameter and 25mm length were grown with 6.5 atomic percentage of Bi. The grown crystals were characterized employing various techniques such as energy dispersive spectroscopy, x-ray diffraction, differential scanning calorimetery, infrared spectroscopy and Hall measurement.

Fatigue crack growth studies on lug joints

Pin loaded lug joints fitted with different types of pins are analysed in the presence of cracks at pin-plate interface. An algorithm for finite element contact stress analysis of joints developed earlier to deal with varying partial contact/separation at the pin-plate interface using a marching solution is used in the present analysis. Stress Intensity Factors (SIF) at the crack tips are evaluated using Modified Crack Closure Integral (MCCI) method within the realm of Linear Elastic Fracture Mechanics (LEFM) assumptions. A comparison of fatigue crack growth lives between interference and push fit pin joints is carried out using these SIF's. Results from a finite element analysis on a push fit pin joint are used to fit experimental fatigue crack growth data.

Synthesis, growth, and characterization of a new NLO material 3-(2,3-dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one

3-(2,3-Dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one (DMPP) a potential second harmonic generating (SHG) has been synthesized and grown as a single crystal by the slow evaporation technique at ambient temperature. The structure determination of the grown crystal was done by single crystal X-ray diffraction study. DMPP crystallizes with orthorhombic system with cell parameters a = 20.3106(8)angstrom, b = 4.9574(2)angstrom, c = 13.4863(5)angstrom, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees and space group Pca2(1). The crystals were characterized by FT-IR, thermal analysis, UV-vis-NIR spectroscopy and SHG measurements. Various functional groups present in DMPP were ascertained by FTIR analysis. DMPP is thermally stable up to 80 degrees C and optically transparent in the visible region. The crystal exhibits SHG efficiency comparable to that of KDP. (C) 2011 Elsevier B.V. All rights reserved.