Light Induced Optical Properties Change in Sb20S40Se40 Thin Films

Thin films of Sb20S40Se40 of thickness 800 nm were prepared by thermal evaporation method. The as-prepared and illuminated thin films were studied by X-ray diffraction, Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy and Raman spectroscopy. The optical band gap was reduced due to photo induced effects along with the increase in disorder. These optical properties changes are due to the change of homopolar bond densities. The core level peak shifting in XPS and Raman spectra supports the optical changes happening in the film due to light exposure.

Sensitivity of polyvinylidene fluoride films to mechanical vibration modes and impact after optimizing stretching conditions

The β-phase of polyvinylidene fluoride (PVDF) is well known for its piezoelectric properties. PVDF films have been developed using solvent cast method. The films thus produced are in α-phase. The α-phase is transformed to piezoelectric β-phase when the film is hot-stretched with various different stretching factors at various different temperatures. The films are then characterized in terms of their mechanical properties and surface morphological changes during the transformation from α- to β-phases by using X-ray diffraction, differential scanning calorimeter, Raman spectra, Infrared spectra, tensile testing, and scanning electron microscopy. The films showed increased crystallinity with stretching at temperature up to 80°C. The optimum conditions to achieve β-phase have been discussed in detail. The fabricated PVDF sensors have been tested for free vibration and impact on plate structure, and its response is compared with conventional piezoelectric wafer type sensor. The resonant and antiresonant peaks in the frequency response of PVDF sensor match well with that of lead zirconate titanate wafer sensors. Effective piezoelectric properties and the variations in the frequency response spectra due to free vibration and impact loading conditions are reported. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers.

Theoretical estimation of electromigration in metallic carbon nanotubes considering self-heating effect

In this paper, we estimate the solution of the electromigration diffusion equation (EMDE) in isotopically pure and impure metallic single-walled carbon nanotubes (CNTs) (SWCNTs) by considering self-heating. The EMDE for SWCNT has been solved not only by invoking the dependence of the electromigration flux on the usual applied static electric field across its two ends but also by considering a temperature-dependent thermal conductivity (κ) which results in a variable temperature distribution (T) along its length due to self-heating. By changing its length and isotopic impurity, we demonstrate that there occurs a significant deviation in the SWCNT electromigration performance. However, if κ is assumed to be temperature independent, the solution may lead to serious errors in performance estimation. We further exhibit a tradeoff between length and impurity effect on the performance toward electromigration. It is suggested that, to reduce the vacancy concentration in longer interconnects of few micrometers, one should opt for an isotopically impure SWCNT at the cost of lower κ, whereas for comparatively short interconnects, pure SWCNT should be used. This tradeoff presented here can be treated as a way for obtaining a fairly well estimation of the vacancy concentration and mean time to failure in the bundles of CNT-based interconnects. © 2012 IEEE.

Increased time-dependent room temperature plasticity in metallic glass nanopillars and its size-dependency

Room temperature, uniaxial compression creep experiments were performed on micro-/nano-sized pillars (having diameters in the range of 250-2000 nm) of a Zr-based bulk metallic glass (BMG) to investigate the influence of sample size on the time-dependent plastic deformation behavior in amorphous alloys. Experimental results reveal that plastic deformation indeed occurs at ambient temperature and at stresses that are well below the nominal quasi-static yield stress. At a given stress, higher total strains accrue in the smaller specimens. In all cases, plastic deformation was found to be devoid of shear bands, i.e., it occurs in homogeneous manner. The stress exponent obtained from the slope of the linear relation between strain rate and applied stress also shows a strong size effect, which is rationalized in terms of the amount of free volume created during deformation and the surface-to-volume ratio of the pillar. (C) 2012 Elsevier Ltd. All rights reserved.

Effect of Thickness on The Optical Properties Change in Bi/As2S3 Bilayer Thin Films

Bilayer thin films of Bi/As2S3 were prepared from Bi and As2S3 by thermal evaporation technique under high vacuum. We have prepared three bilayer films of 905nm, 910nm and 915nm thickness with with As2S3 as bottom layer (900nm) and Bi as top layer (5,10,15 nm). We have compared the optical changes due to the thickness variation of Bi layer on As2S3 film. The changes were characterized by FTIR and XPS techniques.

Effect of Oxygen Pressure on Structural and Magnetic Properties of YIG Thin Films

The effect of oxygen pressure (P-O2) on the Yttrium Iron Garnet (YIG) thin films were grown on silicon substrate by rf sputtering method was studied. The as-deposited films at 300K were amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 800 degrees C/1hr in air. The structural, microstructural and magnetic properties were found to be dependent on P-O2.

On the microstructure-tensile property correlations in bulk metallic glass matrix composites with crystalline dendrites

Bulk metallic glass (BMG) matrix composites with crystalline dendrites as reinforcements exhibit a wide variance in their microstructures (and thus mechanical properties), which in turn can be attributed to the processing route employed, which affects the size and distribution of the dendrites. A critical investigation on the microstructure and tensile properties of Zr/Ti-based BMG composites of the same composition, but produced by different routes, was conducted so as to identify ``structure-property'' connections in these materials. This was accomplished by employing four different processing methods-arc melting, suction casting, semi-solid forging and induction melting on a water-cooled copper boat-on composites with two different dendrite volume fractions, V-d. The change in processing parameters only affects microstructural length scales such as the interdendritic spacing, lambda, and dendrite size, delta, whereas compositions of the matrix and dendrite are unaffected. Broadly, the composite's properties are insensitive to the microstructural length scales when V-d is high (similar to 75%), whereas they become process dependent for relatively lower V-d (similar to 55%). Larger delta in arc-melted and forged specimens result in higher ductility (7-9%) and lower hardening rates, whereas smaller dendrites increase the hardening rate. A bimodal distribution of dendrites offers excellent ductility at a marginal cost of yield strength. Finer lambda result in marked improvements in both ductility and yield strength, due to the confinement of shear band nucleation sites in smaller volumes of the glassy phase. Forging in the semi-solid state imparts such a microstructure. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effect of doping concentration on the structural and optical properties of pure and tin doped zinc oxide thin films by nebulizer spray pyrolysis (NSP) technique

Pure and tin doped zinc oxide (Sn:ZnO) thin films were prepared for the first time by NSP technique using aqueous solutions of zinc acetate dehydrate, tin (IV) chloride fendahydrate and methanol. X-ray diffraction patterns confirm that the films are polycrystalline in nature exhibiting hexagonal wurtzite type, with (0 0 2) as preferred orientation. The structural parameters such as lattice constant ('a' and `c'), crystallite size, dislocation density, micro strain, stress and texture coefficient were calculated from X-ray diffraction studies. Surface morphology was found to be modified with increasing Sn doping concentration. The ZnO films have high transmittance 85% in the visible region, and the transmittance is found to be decreased with the increase of Sn doping concentration. The corresponding optical band gap decreases from 3.25 to 3.08 eV. Room temperature photoluminescence reveals the sharp emission of strong UV peak at 400 nm (3.10 eV) and a strong sharp green luminescence at 528 nm (2.34 eV) in the Sn doped ZnO films. The electrical resistivity is found to be 10(6) Omega-cm at higher temperature and 10(5) Omega-cm at lower temperature. (C) 2012 Elsevier Ltd. All rights reserved.

Optical, electrochemical and morphological investigations of poly (3,4-propylenedioxythiophene)-sultone (PProDOT-S) thin films

In this paper, we have carried out thin film characterization of poly(3,4-propylenedioxythiophene)-sultone (PProDOT-S), a derivative of electrochromic poly(3,4-propylenedioxythiophene) (PProDOT). PProDOT-S was deposited onto transparent conducting oxide coated glass substrates by solution casting method. Single wavelength spectrophotometry is used to monitor the switching speed and contrast ratio at maximum wavelength (lambda (max)). The percentage transmittance at the lambda (max) of the neutral polymer is monitored as a function of time when the polymer film is repeatedly switched. This experiment gives a quantitative measure of the speed with which a film is able to switch between the two states i.e. the coloured and the bleached states. PProDOT-S films were switched at a voltage of 1 center dot 9 V with a switching speed of 2 s at lambda (max) of 565 nm and showed a contrast of similar to 37%. Cyclic voltammetry performed at different scan rates have shown the characteristic anodic and cathodic peaks. The structural investigations of PProDOT-S films by IR spectra were in good agreement with previously reported results. Raman spectra of PProDOT-S showed a strong Raman peak at 1509 cm (-aEuro parts per thousand 1) and a weak peak at 1410 cm (-aEuro parts per thousand 1) due to the C = C asymmetric and symmetric stretching vibrations of thiophene rings. The morphological investigations carried out by using scanning electron microscope (SEM) of polymer films have shown that these polymers are found to be arranged in dense packed clusters with non-uniform distribution having an average width and length of 95 nm and 160 nm, respectively.

Completely random nanoporous Cu4O3-CuO-C composite thin films for potential application as multiple channel photonic band gap based filter in the telecommunication wavelengths

In 2003, Babin et al. theoretically predicted (J. Appl. Phys. 94:4244, 2003) that fabrication of organic-inorganic hybrid materials would probably be required to implement structures with multiple photonic band gaps. In tune with their prediction, we report synthesis of such an inorganic-organic nanocomposite, comprising Cu4O3-CuO-C thin films that experimentally exhibit the highest (of any known material) number (as many as eleven) of photonic band gaps in the near infrared. On contrary to the report by Wang et al. (Appl. Phys. Lett. 84:1629, 2004) that photonic crystals with multiple stop gaps require highly correlated structural arrangement such as multilayers of variable thicknesses, we demonstrate experimental realization of multiple stop gaps in completely randomized structures comprising inorganic oxide nanocrystals (Cu4O3 and CuO) randomly embedded in a randomly porous carbonaceous matrix. We report one step synthesis of such nanostructured films through the metalorganic chemical vapor deposition technique using a single source metalorganic precursor, Cu-4(deaH)(dea)(oAc)(5) a <...aEuro parts per thousand(CH3)(2)CO. The films displaying multiple (4/9/11) photonic band gaps with equal transmission losses in the infrared are promising materials to find applications as multiple channel photonic band gap based filter for WDM technology.

Electrocatalytic oxidation of 1,2-propanediol on electrodeposited Pd-poly(3,4-ethylenedioxythiophene) nanodendrite films in alkaline medium

Electrochemical deposition of Pd on conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) coated carbon paper electrode results in the formation of a stable dendritic film of Pd. In the absence of the PEDOT under-layer, Pd deposition is smooth and non-dendritic. Both Pd-PEDOT/C and Pd/C electrodes are studied for electrooxidation of 1,2-propanediol (PD) in an alkaline electrolyte. Owing to enhanced surface area and surface defects on dendritic Pd, the Pd-PEDOT/C electrode exhibits greater catalytic activity than the Pd/C electrode. Cyclic voltammetry studies suggest that peak current density increases with an increase in concentrations of PD and NaOH in the electrolyte. Repetitive cyclic voltammetry and amperometry studies indicate that Pd-PEDOT/C electrode possesses a high electrochemical stability with greater catalytic activity than Pd/C electrode toward electrooxidation of PD. (C) 2012 Elsevier Ltd. All rights reserved.

Influence of GaN underlayer thickness on structural, electrical and optical properties of InN films grown by PAMBE

We present an extensive study on the structural, electrical and optical properties of InN thin films grown on c-Al2O3, GaN(130 nm)/Al2O3, GaN(200 nm)/Al2O3 and GaN(4 mu m)/Al2O3 by using plasma-assisted molecular beam epitaxy. The high resolution X-ray diffraction study reveals better crystalline quality for the film grown on GaN(4 mu m)/Al2O3 as compared to others. The electronic and optical properties seem to be greatly influenced by the structural quality of the films, as can be evidenced from Hall measurement and optical absorption spectroscopy. Kane's k.p model was used to describe the dependence of optical absorption edge of InN films on carrier concentration by considering the non-parabolic dispersion relation for carrier in the conduction band. Room temperature Raman spectra for the InN films grown on GaN show the signature of residual tensile stress in contrast to the compressive stress observed for the films grown directly on c-Al2O3. (C) 2012 Elsevier B.V. All rights reserved.

Magneto-Transport Study of Pure and Co Doped ZnO Thin Films

A detailed low temperature magneto-transport study is carried out to understand the transport mechanism in pure and Co doped ZnO thin films grown by pulsed laser deposition (PLD) technique. A negative transverse magneto-resistance (MR) (with a value similar to 4% at 4.5 K) which decreases monotonically with the increase in temperature, is observed for the undoped ZnO film. A competition between positive and negative MR is observed for the Co doped ZnO samples. In this case at higher field values negative MR contribution dominates over the positive MR, which gives rise to a slope change in the MR data. Our data for MR shows excellent agreement with the semi-empirical formula given by Khosla et al., which is originally proposed for the degenerate semiconductors. This formula incorporates the third order perturbation expansion of the s-d exchange scattering of the conduction electrons from the localised spins. We have also obtained the Hall mobility, carrier conc. and mean free path as function of temperature for the pure ZnO film.

Large nonlinear refraction and two photon absorption in ferroelectric Bi2VO5.5 thin films

Ferroelectric c-oriented Bi2VO5.5 (BVO) thin films (thickness approximate to 300 nm) were fabricated by pulsed laser deposition on corning glass substrates. Nonlinear refractive index (n(2)) and two photon absorption coefficient (beta) were measured by Z-scan technique at 532 nm wavelength delivering pulses with 10 ns duration. Relatively large values of n(2) = 2.05 +/- 0.2 x 10(-10) cm(2)/W and beta = 9.36 +/- 0.3 cm/MW were obtained for BVO thin films. Origin of the large optical nonlinearities in BVO thin films was discussed based on bond-orbital theory of transition metal oxides. (c) 2012 Elsevier B.V. All rights reserved.

Spin injection into a metal from a topological insulator

We study a junction of a topological insulator with a thin two-dimensional nonmagnetic or partially polarized ferromagnetic metallic film deposited on a three-dimensional insulator. We show, by deriving generic boundary conditions applicable to electrons traversing the junction, that there is a finite spin-current injection into the film whose magnitude can be controlled by tuning a voltage V applied across the junction. For ferromagnetic films, the direction of the component of the spin current along the film magnetization can also be tuned by tuning the barrier potential V-0 at the junction. We point out the role of the chiral spin-momentum locking of the Dirac electrons behind this phenomenon and suggest experiments to test our theory.