Analyzing the kinetic response of tin oxide-carbon and tin oxide-CNT composites gas sensors for alcohols detection

Tin oxide nanoparticles are synthesized using solution combustion technique and tin oxide - carbon composite thick films are fabricated with amorphous carbon as well as carbon nanotubes (CNTs). The x-ray diffraction, Raman spectroscopy and porosity measurements show that the as-synthesized nanoparticles are having rutile phase with average crystallite size similar to 7 nm and similar to 95 m(2)/g surface area. The difference between morphologies of the carbon doped and CNT doped SnO2 thick films, are characterized using scanning electron microscopy and transmission electron microscopy. The adsorption-desorption kinetics and transient response curves are analyzed using Langmuir isotherm curve fittings and modeled using power law of semiconductor gas sensors. (C) 2015 Author(s).

Incorporation of Cr3+ ions in tuning the magnetic and transport properties of nano zinc ferrite

Cost effective and low temperature synthesis methods namely solution combustion and hydrothermal methods were used to prepare chromium incorporated nanocrystalline zinc ferrites. The effect of incorporation of low concentration Cr3+ ions on the structural, morphological, magnetic and transport properties of the zinc ferrite compounds were investigated. The crystalline nature and size variation with chromium content were valid from powder x-ray diffraction. Particles size and crystallite size variation were valid from scanning electron microscopy and transmission electron microscopy respectively. With the increase in chromium incorporation, the crystallite and particles sizes were decreased. Fourier transform infrared spectroscopy (FTIR) studies confirmed the presence of strong metal-oxygen bonds. The elastic properties of the materials in both the methods were estimated by FTIR studies. Magnetic properties namely saturation magentization, remanent magnetization and coercivity values were decreased with increase in Cr3+ ions concentration. The dielectric properties of the samples decreased with increase in the Cr3+ ions. The dielectric constant was observed to be of the order of 10(6) at low frequency and almost 1 at higher frequency range. The activation energy estimated using Arrhenius plots was of the order of 0.182 eV and 0.368 eV respectively for the compounds prepared by solution combustion and hydrothermal methods. The emission spectra of the samples excited at 344 nm were reported using photoluminescence (PL) spectroscopy. Further, the approximate energy band gap(E-g) was estimated from PL studies. The E-g of the materials were lie in the range of 2.11-1.98 eV. (C) 2015 Elsevier B.V. All rights reserved.

CuIn1-xAlxSe2 Thin Films Grown by Co-Sputtering and Modified Selenization: Application in Flexible Solar Cells

Thin films of CuIn1-xAlxSe2 (CIAS) were grown on the flexible 10 micrometer thin stainless steel substrates, by dc co-sputtering from the elemental cathodes, followed by annealing with modified selenization. CuInAl alloyed precursor films were selenized both by noble gas assisted Se vapor transport in a tubular furnace and vacuum evaporation of Se in an evaporation chamber. CIAS thin films were optimized for better adhesion. X-ray diffraction, scanning electron microscopy, and UV-visible absorption spectroscopy were used to characterize the selenized films. The composition of CIAS films was varied by substituting In with Al in CuInSe2 (CIS) from 0 <= x <= 0.65 (x = Al/Al+In). Lattice parameters, average crystallite sizes, and compact density of the films, decreased when compared to CIS and (112) peak shifted to higher Bragg's angle, upon Al incorporation. The dislocation density and strain were found to increase with Al doping. Solar cells with SS/Mo/CIAS/CdS/iZnO: AZnO/Al configuration were fabricated and were tested for current-voltage characteristics for various `x' values, under Air Mass 1.5 Global one sun illumination. The best CIAS solar cell showed the efficiency of 6.8%, with x = 0.13, Eg = 1.17 eV, fill factor 45.04, and short circuit current density J(sc) 30 mA/cm(2).

CuIn1-xAlxSe2 Thin Films Grown by Co-Sputtering and Modified Selenization: Application in Flexible Solar Cells

Thin films of CuIn1-xAlxSe2 (CIAS) were grown on the flexible 10 micrometer thin stainless steel substrates, by dc co-sputtering from the elemental cathodes, followed by annealing with modified selenization. CuInAl alloyed precursor films were selenized both by noble gas assisted Se vapor transport in a tubular furnace and vacuum evaporation of Se in an evaporation chamber. CIAS thin films were optimized for better adhesion. X-ray diffraction, scanning electron microscopy, and UV-visible absorption spectroscopy were used to characterize the selenized films. The composition of CIAS films was varied by substituting In with Al in CuInSe2 (CIS) from 0 <= x <= 0.65 (x = Al/Al+In). Lattice parameters, average crystallite sizes, and compact density of the films, decreased when compared to CIS and (112) peak shifted to higher Bragg's angle, upon Al incorporation. The dislocation density and strain were found to increase with Al doping. Solar cells with SS/Mo/CIAS/CdS/iZnO: AZnO/Al configuration were fabricated and were tested for current-voltage characteristics for various `x' values, under Air Mass 1.5 Global one sun illumination. The best CIAS solar cell showed the efficiency of 6.8%, with x = 0.13, Eg = 1.17 eV, fill factor 45.04, and short circuit current density J(sc) 30 mA/cm(2).

Friction and Wear Studies of Octadecyltrichlorosilane SAM on Silicon

A self-assembled monolayer of octadecyltrichlorosilane (OTS) was prepared on a single-crystal silicon wafer (111) and its tribological properties were examined with a one-way reciprocating tribometer. The worn surfaces and transfer film on the counterface were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that, due to the wear of the OTS monolayer and the formation of the transfer film on the counterpart ball, the friction coefficient gradually increases from 0.06 to 0.13 with increasing sliding cycles and then keeps stable at a normal load of 0.5N. The transfer film is characterized by deposition, accumulation, and spalling at extended test duration. Though low friction coefficients of the monolayer in sliding against steel or ceramic counterfaces are recorded, poor load-carrying capacity and antiwear ability are also shown. Moreover, the monolayer itself or the corresponding transfer film on the counterface fails to lubricate even at a normal load of 1.0 N. Thus, the self-assembled monolayer of octadecyltrichlorosilane can be a potential boundary lubricant only at very low loads.

Microstructure and mechanical behaviour of a SiC particles reinforced Al-5Cu composite under dynamic loading

The mechanical behaviour of a composite of Al–5Cu matrix reinforced with 15% SiC particles was studied at different strain rates from 1×10−3 to 2.5×103 s−1 using both a conventional universal testing machine (for low strain-rate tests) and a split Hopkinson bar (for tests at dynamic strain rates). Whilst the yield stress of the composite increases as the strain rate increases, the maximum flow stresses, 440 MPa for compression and 450 MPa for tension, are independent of strain rate. The microstructures and defect structures of the deformed composite were studied with both scanning electron microscopy and transmission electron microscopy and were correlated to the observed mechanical behaviour. Fracture surface studies of samples after dynamic tensile testing indicates that failure of the composite is controlled by ductile failure of the aluminium matrix by the nucleation, growth and coalescence of voids.

Phase Evolution and its Effect on Magnetic Properties of Nd60Al10Fe20Co10 Bulk Metallic Glass

The thermal stability of nanocrystalline clusters, the phase evolution, and their effects on magnetic Propertieswere studied for as-cast Nd60Al10Fe20Co10 alloy using differential scanning calorimetry curves, x-ray diffraction patterns, scanning electron microscopy, and high-resolution transition electron microscopy. Thermomagnetic curves and hysteresis loops of the bulk metallic glass were measured during the annealing process. The high thermostability of the hardmagnetic properties of the samples observed is attributed to the stability of the nanocrystalline clusters upon annealing, while the slight enhancement in the magnetization is due to the precipitation of some Nd-rich metastable phases. The mechanism of thermostability of the nanocrystalline clusters and the formation of the metastable phases are discussed.

Growth Mechanism And Joint Structure Of Zno Tetrapods

Regular zinc oxide (ZnO) tetrapods with a flat plane have been obtained on Si(1 0 0) substrate via the chemical vapour deposition approach. The x-ray diffraction result suggests that these tetrapods are all single crystals with a wurtzite structure that grow along the (0 0 0 1) direction and corresponding electron backscatter diffraction analysis reveals the crystal orientation of growth and exposed surface. Furthermore, we find some ZnO tetrapods with some legs off and the angles between every two legs are measured with the aid of scanning electron microscopy and image analysis, which benefit to reveal the structure of ZnO tetrapods joint. The structure model and growth mechanism of ZnO tetrapods are proposed. Besides, the stable model of the interface was obtained through the density-functional theory calculation and the energy needed to break the twin plane junction was calculated as 5.651 J m(-2).

Microstructure Observation And Mechanical Behavior Modeling For Limnetic Nacre

In the present research, microstructure of a kind of limnetic shell (Hyriopsis cumingii) is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are carried out by using bending and tensile tests. The dependence of mechanical properties of the shell nacre on its microstructure is analyzed by using a modified shear-lag model, and the overall stress-strain relation is obtained. The experimental results reveal that the mechanical properties of shell nacre strongly depend on the water contents of the limnetic shell. Dry nacre shows a brittle behavior, whereas wetting nacre displays a strong ductility. Compared to the tensile test, the bending test overestimates the strength and underestimates the Young's modulus. The modified shear-lag model can characterize the deformation features of nacre effectively.

Heteroepitaxy of Group IV and Group III-V semiconductor alloys for photovoltaic applications

Photovoltaic energy conversion represents a economically viable technology for realizing collection of the largest energy resource known to the Earth -- the sun. Energy conversion efficiency is the most leveraging factor in the price of energy derived from this process. This thesis focuses on two routes for high efficiency, low cost devices: first, to use Group IV semiconductor alloy wire array bottom cells and epitaxially grown Group III-V compound semiconductor alloy top cells in a tandem configuration, and second, GaP growth on planar Si for heterojunction and tandem cell applications.

Metal catalyzed vapor-liquid-solid grown microwire arrays are an intriguing alternative for wafer-free Si and SiGe materials which can be removed as flexible membranes. Selected area Cu-catalyzed vapor-liquid solid growth of SiGe microwires is achieved using chlorosilane and chlorogermane precursors. The composition can be tuned up to 12% Ge with a simultaneous decrease in the growth rate from 7 to 1 μm/min^-1. Significant changes to the morphology were observed, including tapering and faceting on the sidewalls and along the lengths of the wires. Characterization of axial and radial cross sections with transmission electron microscopy revealed no evidence of defects at facet corners and edges, and the tapering is shown to be due to in-situ removal of catalyst material during growth. X-ray diffraction and transmission electron microscopy reveal a Ge-rich crystal at the tip of the wires, strongly suggesting that the Ge incorporation is limited by the crystallization rate.

Tandem Ga_1-xIn_xP/Si microwire array solar cells are a route towards a high efficiency, low cost, flexible, wafer-free solar technology. Realizing tandem Group III-V compound semiconductor/Si wire array devices requires optimization of materials growth and device performance. GaP and Ga_1-xIn_xP layers were grown heteroepitaxially with metalorganic chemical vapor deposition on Si microwire array substrates. The layer morphology and crystalline quality have been studied with scanning electron microscopy and transmission electron microscopy, and they provide a baseline for the growth and characterization of a full device stack. Ultimately, the complexity of the substrates and the prevalence of defects resulted in material without detectable photoluminescence, unsuitable for optoelectronic applications.

Coupled full-field optical and device physics simulations of a Ga_0.51In_0.49P/Si wire array tandem are used to predict device performance. A 500 nm thick, highly doped "buffer" layer between the bottom cell and tunnel junction is assumed to harbor a high density of lattice mismatch and heteroepitaxial defects. Under simulated AM1.5G illumination, the device structure explored in this work has a simulated efficiency of 23.84% with realistic top cell SRH lifetimes and surface recombination velocities. The relative insensitivity to surface recombination is likely due to optical generation further away from the free surfaces and interfaces of the device structure.

Finally, GaP has been grown free of antiphase domains on Si (112) oriented substrates using metalorganic chemical vapor deposition. Low temperature pulsed nucleation is followed by high temperature continuous growth, yielding smooth, specular thin films. Atomic force microscopy topography mapping showed very smooth surfaces (4-6 Å RMS roughness) with small depressions in the surface. Thin films (~ 50 nm) were pseudomorphic, as confirmed by high resolution x-ray diffraction reciprocal space mapping, and 200 nm thick films showed full relaxation. Transmission electron microscopy showed no evidence of antiphase domain formation, but there is a population of microtwin and stacking fault defects.

Encapsluation of Co and Pd multi-metal nanowires inside multiwalled carbon nanotubes by microwave plasma chemical vapor deposition

We report the synthesis of multiwalled carbon nanotubes (MWCNTs) encapsulated with Co/Pd magnetic and nonmagnetic multi-metal nanowires using Co and Pd thin-layers deposited on Si substrate by microwave plasma enhanced chemical vapor deposition using a bias-enhanced growth method. Detailed structural and compositional investigations of these metal nanowires inside MWCNTs were carried out by scanning electron microscopy and transmission electron microscopy to elucidate the growth mechanisms. Energy dispersive X-ray spectroscopy revealed that MWCNTs were encapsulated with Co and Pd nanowires, separately, at the tube top and the bottom of Co nanowire, respectively. The face-centered-cubic (fcc) structure of Co nanowires was confirmed by a selected area diffraction pattern. We proposed a fruitful description for the encapsulating mechanisms of both Co and Pd multi-metal nanowires. © 2006 Elsevier B.V. All rights reserved.

The nature and origin of deep ocean clay crust from the Gulf of Guinea

Deep ocean sediments off the west coast of Africa exhibit a peculiar undrained strength profile in the form of a crust, albeit of exceptionally high water content, overlying normally consolidated clay. Hot-oil pipelines are installed into these crustal sediments, so their origins and characteristics are of great interest to pipeline designers. This paper provides evidence for the presence of burrowing invertebrates in crust material, and for the way sediment properties are modified through their creation of burrows, and through the deposition of faecal pellets. A variety of imaging techniques are used to make these connections, including photography, scanning electron microscopy and X-ray computer tomography. However, the essential investigative technology is simply the wet-sieving of natural cores, which reveals that up to 60% by dry mass of the crustal material can consist of smooth, highly regular, sand-sized capsules that have been identified as the faecal pellets of invertebrates such as polychaetes. Mechanical tests reveal that these pellets are quite robust under effective stresses of the order of 10 kPa, acting like sand grains within a matrix of fines. Their abundance correlates closely with the measured strength of the crust. While this can easily be accepted in the context of a pellet fraction as high as 60%, the question arises how a smaller proportion of pellets, such as 20%, is apparently able to enhance significantly the strength of a sediment that otherwise appears to be normally consolidated. A hypothesis is suggested based on the composition of the matrix of fines around the pellets. These appear to consist of agglomerates of clay platelets, which may be the result of the breakdown of pellets by other organisms. Their continued degradation at depths in excess of 1 m is taken to explain the progressive loss of crustal strength thereafter.

Strength and hydration products of reactive MgO-silica pastes

The reaction between MgO and microsilica has been studied by many researchers, who confirmed the formation of magnesium silicate hydrate. The blend was reported to have the potential as a novel material for construction and environment purposes. However, the characteristics of MgO vary significantly, e.g., reactivity and purity, which would have an effect on the hydration process of MgO-silica blend. This paper investigated the strength and hydration products of reactive MgO and silica blend at room temperature up to 90 days. The existence of magnesium silicate hydrate after 7 days' curing was confirmed with the help of infrared spectroscopy, thermogravimetric analysis and X-ray diffraction. The microstructural and elemental analysis of the resulting magnesium silicate hydrate was conducted using scanning electron microscopy and energy dispersive spectroscopy. In addition, the effect of characteristics of MgO on the hydration process was discussed. It was found that the synthesis of magnesium silicate hydrate was highly dependent on the reactivity of the precursors. MgO and silica with higher reactivity resulted in higher formation rate of magnesium silicate hydrate. In addition, the impurity in the MgO affects the pH value of the blends, which in turn determines the solubility of silica and the formation of magnesium silicate hydrate. © 2014 Elsevier Ltd. All rights reserved.

Quantitative strain characterization of SiGe heterostructures by high-resolution transmission electron microscopy

We report the quantitative strain characterization in semiconductor heterostructures of silicon-germaniums (Si(0.76)Geo(0.24)) grown on Si substrate by an ultra-high vacuum chemical vapor deposition system. The relaxed SiGe virtual substrate has been achieved by thermal annealing of the SiGe film with an inserted Ge layer. Strain analysis was performed using a combination of high-resolution transmission electron microscopy and geometric phase analysis.

The effects of LT AlN buffer thickness on the optical properties of AlGaN grown by MOCVD and Al composition inhomogeneity analysis

We have investigated the growth of AlGaN epilayers on a sapphire substrate by metalorganic chemical vapour deposition using various low-temperature ( LT) AlN buffer thicknesses. Combined scanning electron microscopy and cathodoluminescence investigations reveal the correlation between the surface morphology and optical properties of AlGaN films in a microscopic scale. It is found that the suitable thickness of the LT AlN buffer for high quality AlGaN growth is around 20 nm. The Al compositional inhomogeneity of the AlGaN epilayer is attributed to the low lateral mobility of Al adatoms on the growing surface.