Studies on electrical switching behavior and optical band gap of amorphous Ge-Te-Sn thin films

Amorphous thin film Ge15Te85-xSnx (1 <= x <= 5) and Ge17Te83-xSnx (1 <= x <= 4) switching devices have been deposited in sandwich geometry using a flash evaporation technique, with aluminum as the top and bottom electrodes. Electrical switching studies indicate that these films exhibit memory type electrical switching behavior. The switching fields for both the series of samples have been found to decrease with increase in Sn concentration, which confirms that the metallicity effect on switching fields/voltages, commonly seen in bulk glassy chalcogenides, is valid in amorphous chalcogenide thin films also. In addition, there is no manifestation of rigidity percolation in the composition dependence of switching fields of Ge15Te85-xSnx and Ge17Te83-xSnx amorphous thin film samples. The observed composition dependence of switching fields of amorphous Ge15Te85-xSnx and Ge17Te83-xSnx thin films has been understood on the basis of Chemically Ordered Network model. The optical band gap for these samples, calculated from the absorption spectra, has been found to exhibit a decreasing trend with increasing Sn concentration, which is consistent with the composition dependence of switching fields.

Compositional dependence optical properties study of As40Se60-xSbx thin films

Thin films were thermally evaporated from the bulk glasses of As40Se60-xSbx (with x = 0, 5, 10, 15 at.%) under high vacuum. We have characterized the deposited films by Fourier Transform Infrared spectroscopy. The relationship between the structural and optical properties and the compositional variation has been investigated. Increasing Sb content was found to affect the thermal and optical properties of these films. Non-direct electronic transition was found to be responsible for the photon absorption inside the investigated films. It was found that, the optical band gap E-o decreases while the width of localized states (Urbach energy) E-e increases. (C) 2011 Elsevier B.V. All rights reserved.

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al2O3) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 degrees C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al2O3-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance. AC conductivity and activation energy were determined and the results are discussed. (C) 2011 Elsevier B.V. All rights reserved.

Studies on Field Dependent Domain Structures in Multi-Grained 0.85PbMg(1/3)Nb(2/3)O3-0.15PbTiO(3) Thin Films by Scanning Force Microscopy

0.85PbMg(1/3)Nb(2/3)O(3)-0.15PbTiO(3) (0.85PMN-0.15PT) ferroelectric relaxor thin films have been deposited on La0.5Sr0.5CoO3/(111) Pt/TiO2/SiO2/Si by pulsed laser ablation by varying the oxygen partial pressures from 50 mTorr to 400 mTorr. The X-ray diffraction pattern reveals a pyrochlore free polycrystalline film. The grain morphology of the deposited films was studied using scanning electron microscopy and was found to be affected by oxygen pressure. By employing dynamic contact-electrostatic force microscopy we found that the distribution of polar nanoregions is majorly affected by oxygen pressure. Finally, the electric field induced switching in these films is discussed in terms of domain wall pinning.

Role of electrolyte additives on in-vitro electrochemical behavior of micro arc oxidized titania films on Cp Ti

The present work is aimed at studying the influence of electrolyte chemistry on the voltage-time (V-T) response characteristics, phase structure, surface morphology, film growth rate and corrosion properties of titania films fabricated by micro arc oxidation (MAO) on Cp Ti. The titania films were developed with a sodium phosphate based reference electrolyte comprising the additives such as sodium carbonate (Na2CO3), sodium nitrite (NaNO2) and urea (CO(NH2)(2)). The phase composition, surface morphology, elemental composition and thickness of the films were assessed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. The corrosion characteristics of the fabricated films were studied under Kokubo simulated body fluid (SBF) condition by potentiodynamic polarization, long term potential and linear polarization resistance (LPR) measurements and electrochemical impedance spectroscopy (EIS) methods. In addition, the corrosion characteristics of the grown films were analyzed by EIS curve fitting and equivalent circuit modeling. Salt spray test (SST) as per ASTM B 117 standard was also conducted to verify the corrosion resistance of the grown films. The XRD results showed that the titania films were composed of both anatase and rutile phases at different proportions. Besides, the films grown in carbonate and nitrite containing electrolyte systems showed an enhanced growth of their rutile phase in the 1 0 1] direction which could be attributed to the modifications introduced in the growth process by the abundant oxygen available during the process. The SEM-EDX and elemental mapping results showed that the respective electrolyte borne elements were incorporated and distributed uniformly in all the films. Among all the grown films under study, the film developed in carbonate containing electrolyte system exhibited considerably improved corrosion resistance due to suitable modifications in its structural and morphological characteristics. The rate of anatase to rutile phase transformation and the rutile growth direction were strongly influenced by the abundant oxidizing species available during the film growth process. (C) 2012 Elsevier B. V. All rights reserved.

Influence of annealing on oxidation, microstructure and mechanical properties of Ni-49Ti films

Thin films of Ni-49 at.% Ti were deposited by DC magnetron sputtering on silicon substrates at 300 degrees C. The as-deposited amorphous films were annealed at a vacuum of 10(-6) mbar at various temperatures between 300 and 650 degrees C to study the effect of annealing on microstructure and mechanical properties. The as-deposited films showed partial crystallization on annealing at 500 degrees C. At 500 degrees C, a distinct oxidation layer, rich in titanium but depleted in Ni, was seen on the film surface. A gradual increase in thickness and number of layers of various oxide stoichiometries as well as growth of triangular shaped reaction zones were seen with increase in annealing temperature up to 650 degrees C. Nanoindentation studies showed that the film hardness values increase with increase in annealing temperature up to 600 degrees C and subsequently decrease at 650 degrees C. The results were explained on the basis of the change in microstructure as a result of oxidation on annealing.

Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles-polymer composite films

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles-polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980 degrees C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of similar to 18.6 dB in 26.5-40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction. (C) 2012 Elsevier Ltd. All rights reserved.

Lead ion sensor with electrodes modified by imidazole-functionalized polyaniline

Glassy carbon electrodes (GCE) and carbon paste electrodes (CPE) were modified with imidazole functionalized polyaniline with the aim to develop a sensor for lead (II) in both acidic and basic aqueous solution. The electrodes were characterized by cyclic voltammetry and differential pulse adsorptive stripping voltammetry. The limit of detections obtained with glassy carbon electrode and carbon paste electrode are 20 ng mL(-1) and 2 ng mL(-1) of lead ion, respectively. An interference study was carried out with Cd(II), As(III), Hg(II) and Co(II) ions. Cd(II) ions interfere significantly (peak overlap) and As(III) has a depressing effect on the lead signal. The influence of pH was investigated indicating that bare and modified GCE and CPE show optimum response at pH 4.0 +/- 0.05.

Effect of Multiwall Carbon Nanotubes on Electrical and Structural Properties of Polyaniline

Polyaniline (PANI) and PANI/CNT (multiwall carbon nanotubes, CNT) composites were prepared using an oxidative chemical polymerization method with ammonium persulfate and dodecyl benzene sulfonic acid as the oxidizing agent and surfactant, respectively. Fourier-transform infrared spectroscopy spectra illustrate the presence of PANI in the composite and show that some interaction exists between PANI and CNT. Embedding of CNT in the PANI matrix is confirmed by scanning electron micrography. Conductivity of the PANI/CNT composites was higher than that of pure PANI, and the maximum conductivity obtained was 4.44 S/cm at 20 wt.% CNT.

Coexistence of fast photodarkening and slow photobleaching in Ge19As21Se60 thin films

We experimentally demonstrate the coexistence of two opposite photo-effects, viz. fast photodarkening (PD) and slow photobleaching (PB) in Ge19As21Se60 thin films, when illuminated with a laser of wavelength 671 nm. PD appears to begin instantaneously upon light illumination and saturates in tens of seconds. By comparison, PB is a slower process that starts only after PD has saturated. Both PD and PB follow stretched exponetial dependence on time. Modeling of overall change as a linear sum of two contributions suggests that the changes in As and Ge parts of glass network respond to light effectively indepndent of each other. (C) 2012 Optical Society of America

The effect of potential on electrodeposited CdSe thin films

Cadmium selenide (CdSe) thin films have been successfully prepared by the electrodeposition technique on indium doped tin oxide (ITO) substrates with aqueous solutions of cadmium sulphate and selenium dioxide. The deposited films were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis by X-rays (EDAX), photoluminescence (PL), UV spectrometry and electrical resistivity measurements. XRD analysis shows that the films are polycrystalline in nature with hexagonal crystalline structure. The various parameters such as crystallite size, micro strain, dislocation density and texture coefficients were evaluated. SEM study shows that the total substrate surface is well covered with uniformly distributed spherical shaped grains. Photoluminescence spectra of films were recorded to understand the emission properties of the films. The presence of direct transition with band gap energy 1.75 eV is established from optical studies. The electrical resistivity of the thin films is found to be 10(6) Omega cm and the results are discussed. (c) 2011 Elsevier Ltd. All rights reserved.

Morphology dependent electrochemical performance of sputter deposited Sn thin films

This study deals with tailoring of the surface morphology, microstructure, and electrochemical properties of Sn thin films deposited by magnetron sputtering with different deposition rates. Scanning electron microscopy and atomic force microscopy are used to characterize the film surface morphology. Electrochemical properties of Sn thin film are measured and compared by cyclic voltammetry and charge-discharge cycle data at a constant current density. Sn thin film fabricated with a higher deposition rate exhibited an initial discharge capacity of 798 mAh g(-1) but reduced to 94 mAh g(-1) at 30th cycle. Film deposited with lower deposition rate delivered 770 mAh g(-1) during 1st cycle with improved capacity retention of 521 mAh g(-1) on 30th cycle. Comparison of electrochemical performances of these films has revealed important distinctions, which are associated with the surface morphology and hence on rate of deposition. (C) 2012 Elsevier Ltd. All rights reserved.

In Situ Electrochemical Polymerization at Air-Water Interface: Surface-Pressure-Induced, Graphene-Oxide-Assisted Preferential Orientation of Polyaniline

In situ electrochemical polymerization of aniline in a Langmuir trough under applied surface pressure assists in the preferential orientation of polyaniline (PANI) in planar polaronic structure. Exfoliated graphene oxide (EGO) spread on water surface is used to bring anilinium cations present in the subphase to air-water interface through electrostatic interactions. Subsequent electrochemical polymerization of aniline under applied surface pressure in the Schaefer mode results in EGO/PANT composite with PANT in planar polaronic form. The orientation of PANI is confirmed by electrochemical and Raman spectroscopic studies. This technique opens up possibilities of 2-D polymerization at the air-water interface. Electrochemical sensing of hydrogen peroxide is used to differentiate the activity of planar and coiled forms of PANI toward electrocatalytic reactions.

Structure and mechanical properties of Ti-C films deposited using combination of pulsed DC and normal DC magnetron co-sputtering

Titanium-carbon (Ti-C) thin films of different compositions were prepared by a combination of pulsed DC (for Ti target) and normal DC (for graphite target) magnetron co-sputtering on oxidized silicon and fused quartz substrates. At 33.7 at.% of C content, pure hcp Ti transforms into fcc-TiC with a preferential orientation of (2 2 0) along with (1 1 1) and (2 0 0). A clear transformation in the preferential orientation from (2 2 0) to (1 1 1) has been observed when the C content was increased to 56 at.%. At 62.5 at.% of C, TiC precipitates in an amorphous carbon matrix whereas further increase in C leads to X-ray amorphous films. The cross-sectional scanning electron microscope images reveal that the films with low carbon content consists of columnar grains, whereas, randomly oriented grains are in an amorphous carbon matrix at higher carbon content. A dramatic variation was observed in the mechanical properties such as hardness, H, from 30 to 1 GPa and in modulus, E, from 255 to 25 GPa with varying carbon content in the films. Resistance to plastic deformation parameter was observed as 0.417 for films containing 62.5 at.% of C. Nanoscratch test reveals that the films are highly scratch resistant with a coefficient of friction ranging from 0.15 to 0.04. (C) 2012 Elsevier B.V. All rights reserved.

Mechanical properties of ZnS nanowires and thin films: Microscopic origin of the dependence on size and growth direction

Mechanical properties of ZnS nanowires and thin films are studied as a function of size and growth direction using all-atom molecular dynamics simulations. Using the stress-strain relationship we extract Young's moduli of nanowires and thin films at room temperature. Our results show that Young's modulus of 0001] nanowires has strong size dependence. On the other hand, 01 (1) over bar0] nanowires do not exhibit a strong size dependence of Young's modulus in the size range we have investigated. We provide a microscopic understanding of this behavior on the basis of bond stretching and contraction due to the rearrangement of atoms in the surface layers. The ultimate tensile strengths of the nanowires do not show much size dependence. To investigate the mechanical behavior of ZnS in two dimensions, we calculate Young's modulus of thin films under tensile strain along the 0001] direction. Young's modulus of thin films converges to the bulk value more rapidly than that of the 0001] nanowire.