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Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

Volume 34 (2016): Issue 2 (June 2016)

Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

33 Articles

Research Article

Open Access

Modification in surface properties of poly-allyl-diglycol-carbonate (CR-39) implanted by Au+ ions at different fluences

Published Online: 27 Jun 2016
Page range: 468 - 478

Abstract

Abstract

Ion implantation has a potential to modify the surface properties and to produce thin conductive layers in insulating polymers. For this purpose, poly-allyl-diglycol-carbonate (CR-39) was implanted by 400 keV Au+ ions with ion fluences ranging from 5 × 1013 ions/cm2 to 5 × 1015 ions/cm2. The chemical, morphological and optical properties of implanted CR-39 were analyzed using Raman, Fourier transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM) and UV-Vis spectroscopy. The electrical conductivity of implanted samples was determined through four-point probe technique. Raman spectroscopy revealed the formation of carbonaceous structures in the implanted layer of CR-39. From FT-IR spectroscopy analysis, changes in functional groups of CR-39 after ion implantation were observed. AFM studies revealed that morphology and surface roughness of implanted samples depend on the fluence of Au ions. The optical band gap of implanted samples decreased from 3.15 eV (for pristine) to 1.05 eV (for sample implanted at 5 × 1015 ions/cm2). The electrical conductivity was observed to increase with the ion fluence. It is suggested that due to an increase in ion fluence, the carbonaceous structures formed in the implanted region are responsible for the increase in electrical conductivity.

Key words

  • CR-39
  • ion implantation
  • chemical modification
  • optical band gap
  • electrical conductivity
Open Access

Optical and electrical characterization of BixSe1−x thin films

Published Online: 27 Jun 2016
Page range: 460 - 467

Abstract

Abstract

Bulk samples of the BixSe1-x system with (x = 0, 5, and 10) were prepared using conventional melt quenching technique. Thin films were then deposited by thermal evaporation technique under high vacuum conditions from the prepared bulk samples. Effect of Bi substitution on surface morphology, electrical and optical properties of BixSe1-x thin films was studied. X-ray diffraction studies showed the formation of nanocrystalline clusters at Bi concentration x = 10. Formation of these clusters resulted in a rough surface which was confirmed by AFM measurements. The film surface was smooth, with RMS roughness of 0.0124 nm for Bi5Se95. For Bi10Se90, the RMS roughness increased to 3.93 nm indicating the formation of Bi2Se3 clusters. A simple hot probe technique showed a transition from p-type to n-type due to Bi incorporation. Charge transport mechanisms were investigated by temperature dependent DC electrical conductivity measurements in the temperature range of 209 K to 313 K. Electrical activation energy (ΔE) of the films with different Bi concentrations was found to exhibit a notable change at the p to n transition. At low temperature, the conduction was in reasonable agreement with Mott’s condition of variable range hopping. Mott parameters and the density of localized states near Fermi level were evaluated and correlated with the structural changes resulting from Bi addition. In addition, a red shift of the optical absorption edge of the films under study caused by Bi-Se substitution was observed. Slight changes in the optical parameters were observed with the γ-irradiation. Addition of Bi atoms could be used to tailor the structural, electrical and optical properties of chalcogenide materials such as junctionless photovoltaic devices.

Keywords

  • chalcogenides
  • electrical conductivity
  • optical properties
  • γ-radiation
Open Access

Effect of calcination temperature on the structural, optical and magnetic properties of pure and Fe-doped ZnO nanoparticles

Published Online: 18 Jun 2016
Page range: 451 - 459

Abstract

Abstract

In the present study, pure ZnO and Fe-doped ZnO (Zn0.97Fe0.03O) nanoparticles were synthesized by simple coprecipitation method with zinc acetate, ferric nitrate and sodium hydroxide precursors. Pure ZnO and Fe-doped ZnO were further calcined at 450 °C, 600 °C and 750 °C for 2 h. The structural, morphological and optical properties of the samples were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and UV-Vis absorption spectroscopy. The X-ray diffraction studies revealed that the as-synthesized pure and doped ZnO nanoparticles have hexagonal wurtzite structure. The average crystallite size was calculated using Debye-Scherrer’s formula. The particle size was found to be in nano range and increased with an increase in calcination temperature. SEM micrographs confirmed the formation of spherical nanoparticles. Elemental compositions of various elements in pure and doped ZnO nanoparticles were determined by EDX spectroscopy. UV-Vis absorption spectra showed red shift (decrease in band gap) with increasing calcination temperature. Effect of calcination on the magnetic properties of Fe-doped ZnO sample was also studied using vibrating sample magnetometer (VSM). M-H curves at room temperature revealed that coercivity and remanent polarization increase with an increase in calcination temperature from 450 °C to 750 °C, whereas reverse effect was observed for magnetization saturation.

Key words

  • ZnO nanoparticles
  • co-precipitation
  • X-ray diffractometer
  • optical properties
  • UV-Vis absorption spectroscopy
Open Access

Ultrasound mediated synthesis of CuS nanocrystallites

Published Online: 27 Jun 2016
Page range: 446 - 450

Abstract

Abstract

We present a unique ultrasonication based method for the preparation of copper sulphide nanoparticles in ambient air using a single precursor complex, which acts as a source of both metal and sulphur. The nanoparticles of 3.31 nm have been prepared successfully by the method and characterized using powder X-ray diffractogram (PXRD), dynamic light scattering (DLS) analysis UV-Vis spectroscopy and fluorescence spectroscopy. The results proved that copper sulphide nanoparticles of hexagonal structure (covellite phase) can be prepared by sonochemical method within a very short reaction time of ~5 min. The band gap of the nanomaterial has also been calculated from absorption spectrum and was found to be 2.36 eV.

Key words

  • copper sulphide nanoparticles
  • X-ray diffraction
  • ultrasonication
  • characterization
  • band gap
Open Access

Dielectric and Raman studies of Ba0.06(Na1/2Bi1/2)0.94TiO3–NaNbO3 ceramics

Published Online: 18 Jun 2016
Page range: 437 - 445

Abstract

Abstract

In this work the X-ray diffraction, scanning electron microscopy, Raman and dielectric studies of lead free perovskite (1 – x)Ba0.06(Na1/2Bi1/2)0.94TiO3–xNaNbO3 (0 ⩽ x ⩽ 1.0) ceramics, prepared using a standard solid state reaction method, were investigated. X-ray diffraction studies of all the ceramics suggested the formation of single phase with crystal structure transforming from rhombohedral-tetragonal to orthorhombic symmetry with the increase in NaNbO3 content. Raman spectra also confirmed the formation of solid solution without any new phase. Dielectric studies showed that the phase transition is of diffusive character and diffusivity parameter decreases with increasing NaNbO3 content. The compositional fluctuation was considered to be the main cause of diffusivity.

Key words

  • lead-free
  • structure
  • dielectric constant
  • Raman spectroscopy
Open Access

Experimental investigation on heat transfer rate of Co–Mn ferrofluids in external magnetic field

Published Online: 24 May 2016
Page range: 427 - 436

Abstract

Abstract

Manganese substituted cobalt ferrite (Co1–xMnxFe2O4 with x = 0, 0.3, 0.5, 0.7 and 1) nanopowders were synthesized by chemical coprecipitation method. The synthesized magnetic nanoparticles were investigated by various characterization techniques, such as X-ray diffraction (XRD), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and thermogravimetric and differential thermal analysis (TG/DTA). The XRD results confirmed the presence of cubic spinel structure of the prepared powders and the average crystallite size of magnetic particles ranging from 23 to 45 nm. The VSM results showed that the magnetic properties varied with an increase in substituted manganese while SEM analysis showed the change in the morphology of obtained magnetic nanoparticles. The TG/DTA analysis indicated the formation of crystalline structure of the synthesized samples. The heat transfer rate was measured in specially prepared magnetic nanofluids (nanoparticles dispersed in carrier fluid transformer oil) as a function of time and temperature in presence of external magnetic fields. The experimental analysis indicated enhanced heat transfer rate of the magnetic nanofluids which depended upon the strength of external magnetic field and chemical composition.

Keywords

  • magnetic nanoparticles
  • coprecipitation
  • magnetic fluids
  • rate of heat transfer
  • carrier fluid
Open Access

Influence of plasma treatment on wettability and scratch resistance of Ag-coated polymer substrates

Published Online: 27 Jun 2016
Page range: 418 - 426

Abstract

Abstract

Rapid progress in thin-film coatings based on metals, which can be deposited on polymers, has been recently observed. In this work discussion on the properties of modified polymers and silver thin films deposited on polytetrafluoroethylene (PTFE) and polycarbonate (PC) substrates has been presented. Surface of these polymer substrates were exposed to argon plasma discharge. Additionally, silver thin films were deposited on their surface by electron beam evaporation method. The surfaces of the modified polymers were studied by different methods, i.e. topography, wettability and scratch resistance measurements were performed. The ageing effect of treated substrates was also discussed. It was shown that plasma modification of PTFE and PC substrates increased wettability of their surfaces. The value of water contact angle decreased of about 40 % and 25 % for PTFE and PC surface, respectively. The change of hydrophobic to hydrophilic properties was observed. Plasma modification of substrates improved adhesion between silver coating and polymer substrates. However, it did not influence wettability of Ag coating.

Keywords

  • thin film
  • plasma modification
  • polymers
  • wettability
  • electron beam evaporation
  • scratch resistance
Open Access

Investigations of M3Al8O15:Eu3+,Dy3+ (M = Ba, Ca, Mg) phosphors

Published Online: 27 Jun 2016
Page range: 412 - 417

Abstract

Abstract

In this work, aluminate type phosphorescence materials were synthesized via the solid state reaction method and the photoluminescence (PL) properties, including excitation and emission bands, were investigated considering the effect of trace amounts of activator (Eu3+) and co-activator (Dy3+). The estimated thermal behavior of the samples at certain temperatures (> 1000 °C) during heat treatment was characterized by differential thermal analysis (DTA) and thermogravimetry (TG). The possible phase formation was characterized by X-ray diffraction (XRD). The morphological characterization of the samples was performed by scanning electron microscopy (SEM). The PL analysis of three samples showed maximum emission bands at around 610 nm, and additionally near 589 nm, 648 nm and 695 nm. The bands were attributed to typical transitions of the Eu3+ ions.

Keywords

  • aluminate phosphors
  • solid state reaction method
  • Eu
  • photoluminescence
  • phase formation
Open Access

Structural and conductivity studies of LiNi0.5Mn0.5O2 cathode materials for lithium-ion batteries

Published Online: 18 Jun 2016
Page range: 404 - 411

Abstract

Abstract

Layered oxide LiMO2 (Ni, Co, Mn) have been proposed as cathode materials for lithium-ion batteries. Mainly LiNiO2 is accepted as an attractive cathode material because of its various advantages such as low cost, high discharge capacity, good reversibility. The LiNi0.5Mn0.5O2 powders are synthesized by a sol-gel method using citric acid as a chelating agent. The structure of the synthesized material is analyzed by using XRD, FT-IR and the microstructures of the samples are observed by using FESEM. The intensities and positions of the peaks are in a good agreement with the previous results. The morphological changes are clearly observed as a result of manganese substitution. The Fourier transform infrared (FT-IR) spectra obtained with KBr pellet data reveal the structure of the oxide lattice constituted by LiO6 and NiO6 octahedra. The conductivity studies are characterized by (EIS) in the frequency range of 42 Hz to 1 MHz at room temperature to 120 °C. The dielectric properties are analyzed in the framework of complex dielectric permittivity and complex electric modulus formalisms. It indicates that the conductivity increases with increasing temperature. The fitting data of EIS plots replicate the non-Debye relaxation process with negative temperature coefficient of resistance (NTCR) behavior.

Keywords

  • layered structure
  • FESEM
  • impedance
  • electric modulus
Open Access

Influence of ion irradiation on temperature dependent electrical transport behavior of thin graphite flakes

Published Online: 18 Jun 2016
Page range: 399 - 403

Abstract

Abstract

In this article, the influence of ion irradiation on temperature dependent electrical transport characteristics of thin graphite flakes was investigated. Thin graphite flakes were exfoliated by mechanical exfoliation method. Scanning electron microscopy was used to study surface morphology of the graphite flakes. The resistance versus temperature studies revealed that the graphite flake not subjected to Ga+ ion-irradiation showed a perfect metallic behavior, while the graphite flake after ion-irradiation showed a semiconducting behavior. The current-voltage (I-V) characteristics of bare and ion-irradiated graphite flakes were investigated. The bare graphite flake showed an ohmic-type I-V characteristics representing metallic behavior, while the ion-irradiated graphite flake showed a non-linear type diode-like characteristics. The temperature-dependent conductance measurements of ion-irradiated graphite flake were also performed and discussed in detail. The effect of Ga+ ions on the electronic transport behavior of thin graphite flakes has been discussed based on the investigation results.

Keywords

  • ion-irradiation
  • electronic transport
  • thin graphite flake
  • temperature dependency
Open Access

Optimization of S:Sn precursor molar concentration on the physical properties of spray deposited single phase Sn2S3 thin films

Published Online: 10 Jun 2016
Page range: 393 - 398

Abstract

Abstract

Nanoneedle structured Sn2S3 thin films were prepared by spray pyrolysis technique from aqueous solutions of tin (II) chloride and thiourea, keeping the molar concentrations of S:Sn = 0.01:0.01, 0.02:0.02, 0.03:0.03 and 0.04:0.04 in the starting solutions. XRD studies reveal that all the films exhibit orthorhombic crystal structure with a preferential orientation along the [2 1 1] direction. The peak intensity of the (2 1 1) plane is found to be maximum for the film coated with 0.02:0.02 S:Sn molar concentration which confirms the improved crystalline nature of this film. SEM images depict that the film coated with S:Sn molar concentration 0.02:0.02 exhibit needle shaped grains. The optical band gap exhibits red shift from 2.12 eV to 2.02 eV with an increase in S:Sn precursor molar concentration. Electrical studies show that the films having S:Sn molar concentrations 0.01:0.01 and 0.02:0.02 exhibit minimum resistivity values of 0.238 and 0.359Ω ·cm, respectively.

© Wroclaw University of Technology.

Key words

  • XRD
  • scanning electron microscopy
  • optical band gap
  • thin films
Open Access

Analysis of X-ray structure, dielectric properties and AC conductivity of (4E)-2-amino-3-cyanobenzo[b]oxocin-6-one

Published Online: 07 Jun 2016
Page range: 386 - 392

Abstract

Abstract

The crystal structure of (4E)-2-amino-3-cyanobenzo[b]oxocin-6-one, denoted as 4(E)-ACBO, was analyzed using X-ray diffraction technique. The dielectric and AC electrical conductivity measurements of the bulk 4(E)-ACBO in the form of pellet were studied in the range of frequency 42 Hz to 5 MHz and the temperature range of 303 K to 373 K. The temperature and frequency dependence of dielectric constant (∊1), dielectric loss (∊2) and AC electrical conductivity (σAC) were investigated. The relaxation time (τ) for electrons to hop over a barrier of height WH was calculated at different temperatures. The AC activation energy was determined from the temperature dependence of σAC at different frequencies.

Keywords

  • chromone derivative
  • X-ray structure
  • dielectric properties
  • AC conductivity
Open Access

The impact of medium frequency pulsed magnetron discharge power on the single probe Langmuir measurements and resulted plasma parameters

Published Online: 20 Apr 2016
Page range: 374 - 385

Abstract

Abstract

The resonant type power supplies of medium frequency designed for magnetron sputtering processes often use pulse density modulation to regulate the average discharge power level. While the output power level changes then number of pulses in a group changes, but the discharge current pulses are the same from pulse to pulse: their parameters (duration time, amplitude) do not change with the discharge power. The goal of this paper is to present the influence of medium frequency discharge power level on the direct current I-V characteristics of a single Langmuir probe and resulting plasma parameters caused by the pulse density modulation. The sputtering processes of titanium and copper were diagnosed at two spatial positions. The measured Langmuir probe I-V characteristics showed strong dependence on the discharge power. As the discharge powering pulses stay the same with the discharge power level change, such influence was unlikely to occur. Using time-resolved analysis of probe current waveforms the origin of this influence was indicated. The influence of discharge power level on the single probe Langmuir I-V characteristics and resulting plasma parameters was eliminated using a simple method of scaling the results. Finally, the reliable plasma parameters were calculated.

Keywords

  • titanium
  • copper
  • magnetron sputtering
  • pulsed magnetron sputtering
  • medium frequency pulsed magnetron sputtering
  • Langmuir probe measurements
  • Dora Power Systems
Open Access

Stable phase CdS nanoparticles for optoelectronics: a study on surface morphology, structural and optical characterization

Published Online: 07 Jun 2016
Page range: 368 - 373

Abstract

Abstract

This work presents a study on the surface morphology, structure and optical behavior of stable phase cadmium sulphide (CdS) nanoparticles synthesized via co-precipitation technique. Scanning electron microscopy (SEM) analysis has been employed to study a cluster formation in the aggregated nanoparticles. An image analysis approach using ImageJ has been used to measure the size of nanoparticles from the SEM micrographs. Fourier transform infrared spectroscopic (FT-IR) analysis identified absorption peaks of Cd–S stretching along with moisture content. X-ray diffraction (XRD) analysis showed that CdS nanoparticles crystallized in wurtzite structure with a preferential orientation along (0 0 2) plane. The particle size, microstrain and lattice constants have been evaluated using XRD data. The lattice parameters of these nanoparticles were found to be shorter than the bulk value which led to lattice contraction. The optical absorption study showed a blue shift in the fundamental absorption edge indicating a quantum size effect.

Keywords

  • CdS nanoparticles
  • surface morphology
  • structural analysis
  • optical absorption
  • quantum size effect
Open Access

Effect of pH and annealing temperature on the structural and magnetic properties of cerium-substituted yttrium iron garnet powders produced by the sol-gel method

Published Online: 10 Jun 2016
Page range: 362 - 367

Abstract

Abstract

Cerium substituted yttrium iron garnet (Ce0.2Y2.8Fe5O12; Ce-YIG) nanoparticles were produced via the sol-gel method from solutions of Ce-, Y- and Fe-based precursors, a solvent and a chelating agent. The solutions were dried at 200°C and heat treated at temperatures between 800 °C and 1400°C for 3 h in air. The effects of pH and annealing temperature on the structure, phase formation, magnetic properties and crystallite size were investigated. A cubic YIG phase was obtained for the sample annealed at 1400 °C. The presented results showed that the pH value of the starting solution affects the crystal size and consequently, the saturation magnetization.

Key words

  • sol-gel processes
  • Ce-YIG; nanoparticles
Open Access

Optical and sensing properties of Fe doped ZnO nanocrystalline thin films

Published Online: 07 Jun 2016
Page range: 354 - 361

Abstract

Abstract

Undoped and Fe doped ZnO films of different molarities deposited by spray pyrolysis method using zinc nitrate and ferric chloride as precursors show polycrystalline nature and hexagonal wurtzite structure. Crystallite size decreases with an increase in dopant concentration from 0 at.% to 3 at.%. Doping improves the transmission of the films whereas it reduces the optical band gap of ZnO from 3.28 eV to 3.17 eV. The morphology resembles flake-like structures which collapse when the dopant is introduced. The samples are found to be sensitive to CO2 gas. Undoped ZnO shows maximum sensitivity at 350 °C for higher concentration of CO2. Doped samples show maximum sensitivity at 200 °C for all CO2 concentrations i.e. from 500 ppm to 4000 ppm. Maximum sensitivity is achieved at temperatures 350 °C, 250 °C, 300 °C and 450 °C for the samples prepared using precursor solution of 0.1 M molarity.

Keywords

  • thin films
  • spray pyrolysis
  • ZnO
  • iron
  • band gap
  • gas sensing
Open Access

Synthesis, investigation on structural and electrical properties of cobalt doped Mn–Zn ferrite nanocrystalline powders

Published Online: 18 Jun 2016
Page range: 344 - 353

Abstract

Abstract

Synthesis of CoxMnyZnyFe2O4 (x = 0.1, 0.5, 0.9 and y = 0.45, 0.25, 0.05) nanocrystalline powders was done by chemical co-precipitation method. The crystal structure was determined by using X-ray diffraction (XRD) studies. The crystallite size and lattice parameters were calculated from the XRD data. The XRD results revealed that the crystallite size of the nanocrystalline powder was found to decrease from 37 nm to 28 nm with the substitution of cobalt. The effect of cobalt ions on the crystallization process, the lattice parameters and electrical properties of Mn–Zn ferrites has been also investigated. The AC conductivity increased with an increase in frequency but it decreased with an increase in cobalt content. The complex impedance analysis of the data showed that the resistive and capacitive properties of the Co–Mn–Zn ferrite are predominant due to the fact that the processes are associated with the grains and grain boundaries. The dielectric constant and dielectric loss dependence on doping level and frequency at room temperature were also studied.

Keywords

  • nanoferrites
  • cobalt substituted Mn–Zn ferrite
  • Co-precipitation
  • magnetic nanoparticle
  • dielectric constant
Open Access

Effect of deposition time on surface plasmon resonance and Maxwell-Garnett absorption in RF-magnetron sputtered carbon-nickel films

Published Online: 24 May 2016
Page range: 337 - 343

Abstract

Abstract

In this work, carbon-nickel films were grown during four deposition times (50 s, 90 s, 180 s and 600 s) at room temperature on glass substrates by radio frequency magnetron sputtering. The optical absorption spectra of the films were investigated with a special emphasis on the surface plasmon resonance (SPR) of Ni nanoparticles. The optical absorption peaks caused by the surface plasmon resonance of Ni nanoparticles were observed in the wavelength range of 300 nm to 330 nm. It has been shown that the surface plasmon resonance peaks exhibit a red shift and a blue shift depending on the deposition time. The red and blue shifts of the surface plasmon resonance in the absorption spectra of the films were observed with the increase and decrease of Ni nanoparticle size, respectively. The Ni nanoparticle size, dielectric function of carbon matrix εm and plasma frequency of free electrons ωp for the films deposited at deposition time of 180 s have maximum values of 80 nm, 0.401 and 7.25 × 1015 s–1, respectively. These observations are in a good agreement with the electrical resistivity measurements and Maxwell-Garnett (M-G) effective medium theory (EMT).

Key words

  • surface plasmon resonance (SPR)
  • carbon-nickel films
  • deposition time
  • deposition rate
Open Access

Wrinkled graphene: synthesis and characterization of few layer graphene-like nanocarbons from kerosene

Published Online: 07 Jun 2016
Page range: 330 - 336

Abstract

Abstract

Wrinkled graphene, derived from a facile thermal decomposition and chemical method, was subjected to various analysis techniques and the results have been reported here. Raman studies revealed the presence of highly graphitized amorphous carbon, which was evident by the appearance of five peaks in the deconvoluted first order spectrum. This result was very well corroborated by the XRD analysis. XPS and FT-IR spectra confirmed the incorporation of oxygen functionalities into the carbon backbone. AFM and SEM images of the sample disclosed a cluster of few-layer wrinkled graphene fragments. TEM images displayed a chain of nearly spherical aggregates of graphene, resembling nanohorns. The resistivity and sheet resistance of the sample were found to be low, making the obtained material a promising candidate for various device applications. Hence, kerosene soot proved to be an efficient precursor for facile synthesis of few layer graphene-like nanocarbon.

Keywords

  • hydrocarbon
  • Hummers’
  • method
  • wrinkled graphene
  • nanohorns
Open Access

Colossal dielectric constant of NaNbO3 doped BaTiO3 ceramics

Published Online: 18 Jun 2016
Page range: 322 - 329

Abstract

Abstract

BaTiO3 ceramics doped with 0.40 mol% NaNbO3 were prepared using a traditional approach by sintering at temperature of 1250 °C to 1290 °C. The prepared ceramics was characterized by very good dielectric properties, such as high dielectric constant (1.5 × 105), low dielectric loss (0.1), and good dielectric temperature stability in the −40 °C to 100 °C range for the sample sintered below 1270 °C. The dielectric characteristics obtained with XPS confirmed that Ti4+ ions remain in the state without any change. The huge increase in dielectric constant in NaNbO3 doped BaTiO3 samples occurs when large amount of Ba2+ ions are excited to a high energy bound state of Ba2+ − e or Ba+ to create electron hopping conduction. For samples with the content of NaNbO3 higher than 0.40 mol%, or sintering temperature higher than 1280 °C, compensation effect is dominated by cation vacancies with sharply decreasing dielectric constant and increased dielectric loss. The polaron effect is used to explain the relevant mechanism of giant dielectric constant appearing in the ferroelectric phase.

Keywords

  • BaTiO
  • giant dielectric constant
  • XPS
Open Access

Compositional analysis of silicon oxide/silicon nitride thin films

Published Online: 10 Jun 2016
Page range: 315 - 321

Abstract

Abstract

Hydrogen, amorphous silicon nitride (SiNx:H abbreviated SiNx) films were grown on multicrystalline silicon (mc-Si) substrate by plasma enhanced chemical vapour deposition (PECVD) in parallel configuration using NH3/SiH4 gas mixtures. The mc-Si wafers were taken from the same column of Si cast ingot. After the deposition process, the layers were oxidized (thermal oxidation) in dry oxygen ambient environment at 950 °C to get oxide/nitride (ON) structure. Secondary ion mass spectroscopy (SIMS), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX) were employed for analyzing quantitatively the chemical composition and stoichiometry in the oxide-nitride stacked films. The effect of annealing temperature on the chemical composition of ON structure has been investigated. Some species, O, N, Si were redistributed in this structure during the thermal oxidation of SiNx. Indeed, oxygen diffused to the nitride layer into Si2O2N during dry oxidation.

Key words

  • oxidation
  • PECVD
  • annealing temperature
  • elemental analysis
Open Access

Structural and electrochemical investigation of waste newspaper based electrodes for supercapacitor applications

Published Online: 27 Jun 2016
Page range: 302 - 314

Abstract

Abstract

There is a general consensus to develop renewable energy storage and conversion technologies to replace fossil fuel energy for sustainable development. Currently, the development of high performance energy storage and conversion devices is an important step on the road to alternative energy technologies. With a special focus on the upgradation of waste to valuable energy, this paper presents an effective synthetic method that utilizes waste newspapers as the precursor to prepare the activated carbon electrodes by the pyrolysis and chemical activation processes. The amorphous nature and surface morphology of the carbon samples were confirmed by XRD and SEM analysis, respectively. Activated waste newspaper carbon (AWNP) showed good electrochemical properties at 800 °C and its specific capacitance at a scan rate of 2 mV/s was found to be 380 F/g. It is important to mention that the source of the raw material is cost effective and suitable for green technology.

Key words

  • waste newspaper
  • electrode
  • hierarchical porous carbon
  • supercapacitor
Open Access

Characteristics of TlBr single crystals grown using the vertical Bridgman-Stockbarger method for semiconductor-based radiation detector applications

Published Online: 18 Jun 2016
Page range: 297 - 301

Abstract

Abstract

TlBr single crystals grown using the vertical Bridgman-Stockbarger method were characterized for semiconductor based radiation detector applications. It has been shown that the vertical Bridgman-Stockbarger method is effective to grow high-quality single crystalline ingots of TlBr. The TlBr single crystalline sample, which was located 6 cm from the tip of the ingot, exhibited lower impurity concentration, higher crystalline quality, high enough bandgap (>2.7 eV), and higher resistivity (2.5 × 1011 Ω·cm) which enables using the fabricated samples from the middle part of the TlBr ingot for fabricating high performance semiconductor radiation detectors.

Keywords

  • semiconductor single crystal
  • TlBr
  • radiation detection
  • crystalline quality
  • impurity
  • resistivity
  • optical bandgap
Open Access

Magnetic studies of 0.7(Fe2O3)/0.3(ZnO) nanocomposites in nanopowder form and dispersed in polymer matrix

Published Online: 24 May 2016
Page range: 286 - 296

Abstract

Abstract

Magnetic properties of 0.7(Fe2O3)/0.3(ZnO) nanocomposite synthesized by traditional wet chemistry method and containing only two phases: ZnO (nonmagnetic) and ZnFe2O4 (magnetic, with nanocrystallites of average size 12 nm, but forming large agglomerates, up to 100 nm in size) were studied by DC magnetization and ferromagnetic resonance (FMR). The investigated nanocomposite was either in a form of nanopowder or dispersed at concentration of 0.1 wt.% in poly(ethylene naphthalate-block-tetramethylene oxide) PTMO-b-PEN polymer matrix. Similarities and differences in magnetic behavior of these two samples revealed by the study of static magnetization and FMR spectra have been discussed relative to different morphologies and the associated variation of interparticle interactions. Moreover, thermal and thermo-oxidative stability of the nanocomposite and the neat polymer have been studied by thermogravimetric method.

Key words

  • ferromagnetic resonance
  • magnetization
  • thermogravimetry
  • zinc ferrite nanoparticles
  • polymer nanocomposite
Open Access

Electronic structure, first and second order physical properties of MPS4: a theoretical study

Published Online: 10 Jun 2016
Page range: 275 - 285

Abstract

Abstract

We have calculated the electronic structure and physical properties of metal thiophosphate compounds InPS4 and AlPS 4by means of pseudopotential density functional theory (DFT) coupled with the modern theory of polarization. The targeted physical properties are first and second order optical properties as well as elastic, piezoelectric and electro-optic coefficients. Furthermore, population analysis is presented in order to evaluate the covalent-ionic character of the constituent bonds. The calculated elastic constants, refractive indices and second order optical coefficients of InPS4 are in good agreement with experimental values. With the absence of any theoretical or experimental physical properties of AlPS4, we predict that this compound has high piezoelectric coefficients with d14 = − 73.82 pm/V, d25 = − 10.96 pm/V and d36 = 28.19 pm/V.

Key words

  • metal thiophosphate
  • DFT
  • optical
  • elastic
  • piezoelectric
  • electro-optic properties
Open Access

Characterization of NiO–Al2O3 composite and its conductivity in biogas for solid oxide fuel cell

Published Online: 09 May 2016
Page range: 266 - 274

Abstract

Abstract

NiO–Al2O3 nanocomposite has been synthesized by mixing combustion synthesized powders. The nanocomposite is an effective anode/anode functional layer for intermediate temperature solid oxide fuel cells. The TEM of NiO and Al2O3 revealed spherical particles of 30 nm and platelets of 70 nm, respectively. The XRD analysis of NiO–Al2O3 composite sintered at 900 °C showed presence of cubic NiO and rhombohedral α-Al2O3 which were chemically stable. However, above 1200 °C NiAl2O4 started to appear. The conductivity of NiO–Al2O3 was the highest in hydrogen (4.3 × 10–3 S/cm at 600 °C). In biogas, the conductivity was 3.2 × 10–3 S/cm with the activation energy of 0.67 eV. The stability of the composite in biogas was also examined.

Keywords

  • oxides
  • chemical synthesis
  • X-ray diffraction
  • electrical conductivity
  • microstructure
Open Access

Kinetics of oxygen adsorption on ZnS nanoparticles synthesized by precipitation process

Published Online: 24 May 2016
Page range: 260 - 265

Abstract

Abstract

ZnS nanoparticles were synthesized through a one-step precipitation process. Effect of time and temperature on the formation reaction was investigated. The synthesized samples were characterized by X-ray diffraction (XRD), ultraviolet (UV) visible absorption and photoluminescence (PL) spectrophotometry. Based on XRD and UV-Vis data, the particles produced at 70 °C had a mean particle size of about 5 nm. Increasing time and temperature of the synthesis reaction resulted in photoluminescence intensification. PL spectroscopy helped understanding the adsorption kinetics of oxygen on ZnS nanoparticles during the precipitation synthesis process. Fabrication of ZnS structures with appropriate oxygen adsorption capacity was suggested as a means of PL emission intensity control.

Key words

  • ZnS nanoparticles
  • UV-Vis spectrophotometry
  • Avrami model
Open Access

Site preference and electronic structure of Mn2RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb): a theoretical study

Published Online: 09 May 2016
Page range: 251 - 259

Abstract

Abstract

The electronic structure and magnetism of Mn2RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) Heusler alloys have been studied by using first-principles calculations. Three half-metallic ferromagnets, namely, Mn2RhAl, Mn2RhGe and Mn2RhSb have been considered. The calculated equilibrium lattice constant increases with increasing atomic number of Z atoms lying in same column of periodic table. The calculated total magnetic moments Mtot are 2 µB/f.u. for Mn2RhAl and Mn2RhGa, 3 µB/f.u. for Mn2RhSi, Mn2RhGe and Mn2RhSn, and 4 µB/f.u. for Mn2RhSb, which agrees with the Slater-Pauling curve quite well. In all these compounds, except for Mn2RhSb, the moments of Mn (A) and Mn (B) are antiparallel to each other. The total magnetic moments of the three considered half-metals assume integral values in a wide range of equilibrium lattice parameters.

Keywords

  • Heusler alloy
  • electronic structure
  • h-metal
  • site preference
Open Access

Temperature study of magnetic resonance spectra of co-modified (Co,N)-TiO2 nanocomposites

Published Online: 27 Jun 2016
Page range: 242 - 250

Abstract

Abstract

The (nCo,N)-TiO2 (n = 1, 5 and 10 wt.% of Co) nanocomposites were investigated by magnetic resonance spectroscopy in 4 K to 290 K range. Analyses of ferromagnetic/electron paramagnetic resonance (FMR/EPR) spectra in terms of four Callen lineshape components revealed the existence of two types of magnetic centers, one derived from metallic cobalt nanoparticles in superparamagnetic (SPM) phase and the other from cobalt clusters in the TiO2 lattice. Additionally, at low temperature the EPR spectrum arising from Ti3+ ions was also registered. Both relaxations of the Landau-Lifshitz type and the Bloch-Bloembergen type played an important role at high temperature in determining the linewidths and the latter relaxation was prevailing at low temperature. Analysis of the integrated intensity showed that the SPM signal is due to small size FM cobalt nanoparticles while the paramagnetic signal from Co clusters originates from those nanoparticles in which the concentration of magnetic polarons is below the percolation threshold.

Key words

  • nano titanium dioxide
  • electron paramagnetic resonance
  • photocatalyst
Open Access

Deciphering lead and cadmium stripping peaks for porous antimony deposited electrodes

Published Online: 07 Jun 2016
Page range: 233 - 241

Abstract

Abstract

Cadmium and lead are generally taken as model heavy metal ions in water to scale the detection limit of various electrode sensors, using electrochemical sensing techniques. These ions interact with the electrochemically deposited antimony electrodes depending on the diffusion limitations. The phenomenon acts differently for the in-situ and ex-situ deposition as well as for porous and non-porous electrodes. A method has been adopted in this study to discourage the stripping and deposition of the working ions (antimony) to understand the principle of heavy metal ion detection. X-ray photoelectron spectroscopy (XPS) technique was used to establish the interaction between the working and dissolved ions. In addition to the distinct peaks for each analyte, researchers also observed a shoulder peak. A possible reason for the presence of this peak was provided. Different electrochemical tests were performed to ascertain the theory on the basis of the experimental observations.

Keywords

  • anodic stripping voltammetry
  • activated carbon
  • sensor electrodes
Open Access

Electrospinning synthesis of 3D porous NiO nanorods as anode material for lithium-ion batteries

Published Online: 24 May 2016
Page range: 227 - 232

Abstract

Abstract

Three-dimensional NiO nanorods were synthesized as anode material by electrospinning method. X-ray diffraction results revealed that the product sintered at 400 °C had impure metallic nickel phase which, however, became pure NiO phase as the sintering temperature rose. Nevertheless, the nanorods sintered at 400, 500 and 600 °C had similar diameters (∼200 nm).The NiO nanorod material sintered at 500 °C was chip-shaped with a diameter of 200 nm and it exhibited a porous 3D structure. The nanorod sintered at 500 °C had the optimal electrochemical performance. Its discharge specific capacity was 1127 mAh·g−1 initially and remained as high as 400 mAh·g−1 at a current density of 55 mA·g−1 after 50 cycles.

Keywords

  • Li-ion battery
  • anode
  • charging/discharging
  • NiO
  • nanorod

Retraction

Open Access

Retraction

Published Online: 27 Jun 2016
Page range: 1 - 1

Abstract

Open Access

Retraction

Published Online: 27 Jun 2016
Page range: 2 - 2

Abstract

33 Articles

Research Article

Open Access

Modification in surface properties of poly-allyl-diglycol-carbonate (CR-39) implanted by Au+ ions at different fluences

Published Online: 27 Jun 2016
Page range: 468 - 478

Abstract

Abstract

Ion implantation has a potential to modify the surface properties and to produce thin conductive layers in insulating polymers. For this purpose, poly-allyl-diglycol-carbonate (CR-39) was implanted by 400 keV Au+ ions with ion fluences ranging from 5 × 1013 ions/cm2 to 5 × 1015 ions/cm2. The chemical, morphological and optical properties of implanted CR-39 were analyzed using Raman, Fourier transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM) and UV-Vis spectroscopy. The electrical conductivity of implanted samples was determined through four-point probe technique. Raman spectroscopy revealed the formation of carbonaceous structures in the implanted layer of CR-39. From FT-IR spectroscopy analysis, changes in functional groups of CR-39 after ion implantation were observed. AFM studies revealed that morphology and surface roughness of implanted samples depend on the fluence of Au ions. The optical band gap of implanted samples decreased from 3.15 eV (for pristine) to 1.05 eV (for sample implanted at 5 × 1015 ions/cm2). The electrical conductivity was observed to increase with the ion fluence. It is suggested that due to an increase in ion fluence, the carbonaceous structures formed in the implanted region are responsible for the increase in electrical conductivity.

Key words

  • CR-39
  • ion implantation
  • chemical modification
  • optical band gap
  • electrical conductivity
Open Access

Optical and electrical characterization of BixSe1−x thin films

Published Online: 27 Jun 2016
Page range: 460 - 467

Abstract

Abstract

Bulk samples of the BixSe1-x system with (x = 0, 5, and 10) were prepared using conventional melt quenching technique. Thin films were then deposited by thermal evaporation technique under high vacuum conditions from the prepared bulk samples. Effect of Bi substitution on surface morphology, electrical and optical properties of BixSe1-x thin films was studied. X-ray diffraction studies showed the formation of nanocrystalline clusters at Bi concentration x = 10. Formation of these clusters resulted in a rough surface which was confirmed by AFM measurements. The film surface was smooth, with RMS roughness of 0.0124 nm for Bi5Se95. For Bi10Se90, the RMS roughness increased to 3.93 nm indicating the formation of Bi2Se3 clusters. A simple hot probe technique showed a transition from p-type to n-type due to Bi incorporation. Charge transport mechanisms were investigated by temperature dependent DC electrical conductivity measurements in the temperature range of 209 K to 313 K. Electrical activation energy (ΔE) of the films with different Bi concentrations was found to exhibit a notable change at the p to n transition. At low temperature, the conduction was in reasonable agreement with Mott’s condition of variable range hopping. Mott parameters and the density of localized states near Fermi level were evaluated and correlated with the structural changes resulting from Bi addition. In addition, a red shift of the optical absorption edge of the films under study caused by Bi-Se substitution was observed. Slight changes in the optical parameters were observed with the γ-irradiation. Addition of Bi atoms could be used to tailor the structural, electrical and optical properties of chalcogenide materials such as junctionless photovoltaic devices.

Keywords

  • chalcogenides
  • electrical conductivity
  • optical properties
  • γ-radiation
Open Access

Effect of calcination temperature on the structural, optical and magnetic properties of pure and Fe-doped ZnO nanoparticles

Published Online: 18 Jun 2016
Page range: 451 - 459

Abstract

Abstract

In the present study, pure ZnO and Fe-doped ZnO (Zn0.97Fe0.03O) nanoparticles were synthesized by simple coprecipitation method with zinc acetate, ferric nitrate and sodium hydroxide precursors. Pure ZnO and Fe-doped ZnO were further calcined at 450 °C, 600 °C and 750 °C for 2 h. The structural, morphological and optical properties of the samples were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and UV-Vis absorption spectroscopy. The X-ray diffraction studies revealed that the as-synthesized pure and doped ZnO nanoparticles have hexagonal wurtzite structure. The average crystallite size was calculated using Debye-Scherrer’s formula. The particle size was found to be in nano range and increased with an increase in calcination temperature. SEM micrographs confirmed the formation of spherical nanoparticles. Elemental compositions of various elements in pure and doped ZnO nanoparticles were determined by EDX spectroscopy. UV-Vis absorption spectra showed red shift (decrease in band gap) with increasing calcination temperature. Effect of calcination on the magnetic properties of Fe-doped ZnO sample was also studied using vibrating sample magnetometer (VSM). M-H curves at room temperature revealed that coercivity and remanent polarization increase with an increase in calcination temperature from 450 °C to 750 °C, whereas reverse effect was observed for magnetization saturation.

Key words

  • ZnO nanoparticles
  • co-precipitation
  • X-ray diffractometer
  • optical properties
  • UV-Vis absorption spectroscopy
Open Access

Ultrasound mediated synthesis of CuS nanocrystallites

Published Online: 27 Jun 2016
Page range: 446 - 450

Abstract

Abstract

We present a unique ultrasonication based method for the preparation of copper sulphide nanoparticles in ambient air using a single precursor complex, which acts as a source of both metal and sulphur. The nanoparticles of 3.31 nm have been prepared successfully by the method and characterized using powder X-ray diffractogram (PXRD), dynamic light scattering (DLS) analysis UV-Vis spectroscopy and fluorescence spectroscopy. The results proved that copper sulphide nanoparticles of hexagonal structure (covellite phase) can be prepared by sonochemical method within a very short reaction time of ~5 min. The band gap of the nanomaterial has also been calculated from absorption spectrum and was found to be 2.36 eV.

Key words

  • copper sulphide nanoparticles
  • X-ray diffraction
  • ultrasonication
  • characterization
  • band gap
Open Access

Dielectric and Raman studies of Ba0.06(Na1/2Bi1/2)0.94TiO3–NaNbO3 ceramics

Published Online: 18 Jun 2016
Page range: 437 - 445

Abstract

Abstract

In this work the X-ray diffraction, scanning electron microscopy, Raman and dielectric studies of lead free perovskite (1 – x)Ba0.06(Na1/2Bi1/2)0.94TiO3–xNaNbO3 (0 ⩽ x ⩽ 1.0) ceramics, prepared using a standard solid state reaction method, were investigated. X-ray diffraction studies of all the ceramics suggested the formation of single phase with crystal structure transforming from rhombohedral-tetragonal to orthorhombic symmetry with the increase in NaNbO3 content. Raman spectra also confirmed the formation of solid solution without any new phase. Dielectric studies showed that the phase transition is of diffusive character and diffusivity parameter decreases with increasing NaNbO3 content. The compositional fluctuation was considered to be the main cause of diffusivity.

Key words

  • lead-free
  • structure
  • dielectric constant
  • Raman spectroscopy
Open Access

Experimental investigation on heat transfer rate of Co–Mn ferrofluids in external magnetic field

Published Online: 24 May 2016
Page range: 427 - 436

Abstract

Abstract

Manganese substituted cobalt ferrite (Co1–xMnxFe2O4 with x = 0, 0.3, 0.5, 0.7 and 1) nanopowders were synthesized by chemical coprecipitation method. The synthesized magnetic nanoparticles were investigated by various characterization techniques, such as X-ray diffraction (XRD), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and thermogravimetric and differential thermal analysis (TG/DTA). The XRD results confirmed the presence of cubic spinel structure of the prepared powders and the average crystallite size of magnetic particles ranging from 23 to 45 nm. The VSM results showed that the magnetic properties varied with an increase in substituted manganese while SEM analysis showed the change in the morphology of obtained magnetic nanoparticles. The TG/DTA analysis indicated the formation of crystalline structure of the synthesized samples. The heat transfer rate was measured in specially prepared magnetic nanofluids (nanoparticles dispersed in carrier fluid transformer oil) as a function of time and temperature in presence of external magnetic fields. The experimental analysis indicated enhanced heat transfer rate of the magnetic nanofluids which depended upon the strength of external magnetic field and chemical composition.

Keywords

  • magnetic nanoparticles
  • coprecipitation
  • magnetic fluids
  • rate of heat transfer
  • carrier fluid
Open Access

Influence of plasma treatment on wettability and scratch resistance of Ag-coated polymer substrates

Published Online: 27 Jun 2016
Page range: 418 - 426

Abstract

Abstract

Rapid progress in thin-film coatings based on metals, which can be deposited on polymers, has been recently observed. In this work discussion on the properties of modified polymers and silver thin films deposited on polytetrafluoroethylene (PTFE) and polycarbonate (PC) substrates has been presented. Surface of these polymer substrates were exposed to argon plasma discharge. Additionally, silver thin films were deposited on their surface by electron beam evaporation method. The surfaces of the modified polymers were studied by different methods, i.e. topography, wettability and scratch resistance measurements were performed. The ageing effect of treated substrates was also discussed. It was shown that plasma modification of PTFE and PC substrates increased wettability of their surfaces. The value of water contact angle decreased of about 40 % and 25 % for PTFE and PC surface, respectively. The change of hydrophobic to hydrophilic properties was observed. Plasma modification of substrates improved adhesion between silver coating and polymer substrates. However, it did not influence wettability of Ag coating.

Keywords

  • thin film
  • plasma modification
  • polymers
  • wettability
  • electron beam evaporation
  • scratch resistance
Open Access

Investigations of M3Al8O15:Eu3+,Dy3+ (M = Ba, Ca, Mg) phosphors

Published Online: 27 Jun 2016
Page range: 412 - 417

Abstract

Abstract

In this work, aluminate type phosphorescence materials were synthesized via the solid state reaction method and the photoluminescence (PL) properties, including excitation and emission bands, were investigated considering the effect of trace amounts of activator (Eu3+) and co-activator (Dy3+). The estimated thermal behavior of the samples at certain temperatures (> 1000 °C) during heat treatment was characterized by differential thermal analysis (DTA) and thermogravimetry (TG). The possible phase formation was characterized by X-ray diffraction (XRD). The morphological characterization of the samples was performed by scanning electron microscopy (SEM). The PL analysis of three samples showed maximum emission bands at around 610 nm, and additionally near 589 nm, 648 nm and 695 nm. The bands were attributed to typical transitions of the Eu3+ ions.

Keywords

  • aluminate phosphors
  • solid state reaction method
  • Eu
  • photoluminescence
  • phase formation
Open Access

Structural and conductivity studies of LiNi0.5Mn0.5O2 cathode materials for lithium-ion batteries

Published Online: 18 Jun 2016
Page range: 404 - 411

Abstract

Abstract

Layered oxide LiMO2 (Ni, Co, Mn) have been proposed as cathode materials for lithium-ion batteries. Mainly LiNiO2 is accepted as an attractive cathode material because of its various advantages such as low cost, high discharge capacity, good reversibility. The LiNi0.5Mn0.5O2 powders are synthesized by a sol-gel method using citric acid as a chelating agent. The structure of the synthesized material is analyzed by using XRD, FT-IR and the microstructures of the samples are observed by using FESEM. The intensities and positions of the peaks are in a good agreement with the previous results. The morphological changes are clearly observed as a result of manganese substitution. The Fourier transform infrared (FT-IR) spectra obtained with KBr pellet data reveal the structure of the oxide lattice constituted by LiO6 and NiO6 octahedra. The conductivity studies are characterized by (EIS) in the frequency range of 42 Hz to 1 MHz at room temperature to 120 °C. The dielectric properties are analyzed in the framework of complex dielectric permittivity and complex electric modulus formalisms. It indicates that the conductivity increases with increasing temperature. The fitting data of EIS plots replicate the non-Debye relaxation process with negative temperature coefficient of resistance (NTCR) behavior.

Keywords

  • layered structure
  • FESEM
  • impedance
  • electric modulus
Open Access

Influence of ion irradiation on temperature dependent electrical transport behavior of thin graphite flakes

Published Online: 18 Jun 2016
Page range: 399 - 403

Abstract

Abstract

In this article, the influence of ion irradiation on temperature dependent electrical transport characteristics of thin graphite flakes was investigated. Thin graphite flakes were exfoliated by mechanical exfoliation method. Scanning electron microscopy was used to study surface morphology of the graphite flakes. The resistance versus temperature studies revealed that the graphite flake not subjected to Ga+ ion-irradiation showed a perfect metallic behavior, while the graphite flake after ion-irradiation showed a semiconducting behavior. The current-voltage (I-V) characteristics of bare and ion-irradiated graphite flakes were investigated. The bare graphite flake showed an ohmic-type I-V characteristics representing metallic behavior, while the ion-irradiated graphite flake showed a non-linear type diode-like characteristics. The temperature-dependent conductance measurements of ion-irradiated graphite flake were also performed and discussed in detail. The effect of Ga+ ions on the electronic transport behavior of thin graphite flakes has been discussed based on the investigation results.

Keywords

  • ion-irradiation
  • electronic transport
  • thin graphite flake
  • temperature dependency
Open Access

Optimization of S:Sn precursor molar concentration on the physical properties of spray deposited single phase Sn2S3 thin films

Published Online: 10 Jun 2016
Page range: 393 - 398

Abstract

Abstract

Nanoneedle structured Sn2S3 thin films were prepared by spray pyrolysis technique from aqueous solutions of tin (II) chloride and thiourea, keeping the molar concentrations of S:Sn = 0.01:0.01, 0.02:0.02, 0.03:0.03 and 0.04:0.04 in the starting solutions. XRD studies reveal that all the films exhibit orthorhombic crystal structure with a preferential orientation along the [2 1 1] direction. The peak intensity of the (2 1 1) plane is found to be maximum for the film coated with 0.02:0.02 S:Sn molar concentration which confirms the improved crystalline nature of this film. SEM images depict that the film coated with S:Sn molar concentration 0.02:0.02 exhibit needle shaped grains. The optical band gap exhibits red shift from 2.12 eV to 2.02 eV with an increase in S:Sn precursor molar concentration. Electrical studies show that the films having S:Sn molar concentrations 0.01:0.01 and 0.02:0.02 exhibit minimum resistivity values of 0.238 and 0.359Ω ·cm, respectively.

© Wroclaw University of Technology.

Key words

  • XRD
  • scanning electron microscopy
  • optical band gap
  • thin films
Open Access

Analysis of X-ray structure, dielectric properties and AC conductivity of (4E)-2-amino-3-cyanobenzo[b]oxocin-6-one

Published Online: 07 Jun 2016
Page range: 386 - 392

Abstract

Abstract

The crystal structure of (4E)-2-amino-3-cyanobenzo[b]oxocin-6-one, denoted as 4(E)-ACBO, was analyzed using X-ray diffraction technique. The dielectric and AC electrical conductivity measurements of the bulk 4(E)-ACBO in the form of pellet were studied in the range of frequency 42 Hz to 5 MHz and the temperature range of 303 K to 373 K. The temperature and frequency dependence of dielectric constant (∊1), dielectric loss (∊2) and AC electrical conductivity (σAC) were investigated. The relaxation time (τ) for electrons to hop over a barrier of height WH was calculated at different temperatures. The AC activation energy was determined from the temperature dependence of σAC at different frequencies.

Keywords

  • chromone derivative
  • X-ray structure
  • dielectric properties
  • AC conductivity
Open Access

The impact of medium frequency pulsed magnetron discharge power on the single probe Langmuir measurements and resulted plasma parameters

Published Online: 20 Apr 2016
Page range: 374 - 385

Abstract

Abstract

The resonant type power supplies of medium frequency designed for magnetron sputtering processes often use pulse density modulation to regulate the average discharge power level. While the output power level changes then number of pulses in a group changes, but the discharge current pulses are the same from pulse to pulse: their parameters (duration time, amplitude) do not change with the discharge power. The goal of this paper is to present the influence of medium frequency discharge power level on the direct current I-V characteristics of a single Langmuir probe and resulting plasma parameters caused by the pulse density modulation. The sputtering processes of titanium and copper were diagnosed at two spatial positions. The measured Langmuir probe I-V characteristics showed strong dependence on the discharge power. As the discharge powering pulses stay the same with the discharge power level change, such influence was unlikely to occur. Using time-resolved analysis of probe current waveforms the origin of this influence was indicated. The influence of discharge power level on the single probe Langmuir I-V characteristics and resulting plasma parameters was eliminated using a simple method of scaling the results. Finally, the reliable plasma parameters were calculated.

Keywords

  • titanium
  • copper
  • magnetron sputtering
  • pulsed magnetron sputtering
  • medium frequency pulsed magnetron sputtering
  • Langmuir probe measurements
  • Dora Power Systems
Open Access

Stable phase CdS nanoparticles for optoelectronics: a study on surface morphology, structural and optical characterization

Published Online: 07 Jun 2016
Page range: 368 - 373

Abstract

Abstract

This work presents a study on the surface morphology, structure and optical behavior of stable phase cadmium sulphide (CdS) nanoparticles synthesized via co-precipitation technique. Scanning electron microscopy (SEM) analysis has been employed to study a cluster formation in the aggregated nanoparticles. An image analysis approach using ImageJ has been used to measure the size of nanoparticles from the SEM micrographs. Fourier transform infrared spectroscopic (FT-IR) analysis identified absorption peaks of Cd–S stretching along with moisture content. X-ray diffraction (XRD) analysis showed that CdS nanoparticles crystallized in wurtzite structure with a preferential orientation along (0 0 2) plane. The particle size, microstrain and lattice constants have been evaluated using XRD data. The lattice parameters of these nanoparticles were found to be shorter than the bulk value which led to lattice contraction. The optical absorption study showed a blue shift in the fundamental absorption edge indicating a quantum size effect.

Keywords

  • CdS nanoparticles
  • surface morphology
  • structural analysis
  • optical absorption
  • quantum size effect
Open Access

Effect of pH and annealing temperature on the structural and magnetic properties of cerium-substituted yttrium iron garnet powders produced by the sol-gel method

Published Online: 10 Jun 2016
Page range: 362 - 367

Abstract

Abstract

Cerium substituted yttrium iron garnet (Ce0.2Y2.8Fe5O12; Ce-YIG) nanoparticles were produced via the sol-gel method from solutions of Ce-, Y- and Fe-based precursors, a solvent and a chelating agent. The solutions were dried at 200°C and heat treated at temperatures between 800 °C and 1400°C for 3 h in air. The effects of pH and annealing temperature on the structure, phase formation, magnetic properties and crystallite size were investigated. A cubic YIG phase was obtained for the sample annealed at 1400 °C. The presented results showed that the pH value of the starting solution affects the crystal size and consequently, the saturation magnetization.

Key words

  • sol-gel processes
  • Ce-YIG; nanoparticles
Open Access

Optical and sensing properties of Fe doped ZnO nanocrystalline thin films

Published Online: 07 Jun 2016
Page range: 354 - 361

Abstract

Abstract

Undoped and Fe doped ZnO films of different molarities deposited by spray pyrolysis method using zinc nitrate and ferric chloride as precursors show polycrystalline nature and hexagonal wurtzite structure. Crystallite size decreases with an increase in dopant concentration from 0 at.% to 3 at.%. Doping improves the transmission of the films whereas it reduces the optical band gap of ZnO from 3.28 eV to 3.17 eV. The morphology resembles flake-like structures which collapse when the dopant is introduced. The samples are found to be sensitive to CO2 gas. Undoped ZnO shows maximum sensitivity at 350 °C for higher concentration of CO2. Doped samples show maximum sensitivity at 200 °C for all CO2 concentrations i.e. from 500 ppm to 4000 ppm. Maximum sensitivity is achieved at temperatures 350 °C, 250 °C, 300 °C and 450 °C for the samples prepared using precursor solution of 0.1 M molarity.

Keywords

  • thin films
  • spray pyrolysis
  • ZnO
  • iron
  • band gap
  • gas sensing
Open Access

Synthesis, investigation on structural and electrical properties of cobalt doped Mn–Zn ferrite nanocrystalline powders

Published Online: 18 Jun 2016
Page range: 344 - 353

Abstract

Abstract

Synthesis of CoxMnyZnyFe2O4 (x = 0.1, 0.5, 0.9 and y = 0.45, 0.25, 0.05) nanocrystalline powders was done by chemical co-precipitation method. The crystal structure was determined by using X-ray diffraction (XRD) studies. The crystallite size and lattice parameters were calculated from the XRD data. The XRD results revealed that the crystallite size of the nanocrystalline powder was found to decrease from 37 nm to 28 nm with the substitution of cobalt. The effect of cobalt ions on the crystallization process, the lattice parameters and electrical properties of Mn–Zn ferrites has been also investigated. The AC conductivity increased with an increase in frequency but it decreased with an increase in cobalt content. The complex impedance analysis of the data showed that the resistive and capacitive properties of the Co–Mn–Zn ferrite are predominant due to the fact that the processes are associated with the grains and grain boundaries. The dielectric constant and dielectric loss dependence on doping level and frequency at room temperature were also studied.

Keywords

  • nanoferrites
  • cobalt substituted Mn–Zn ferrite
  • Co-precipitation
  • magnetic nanoparticle
  • dielectric constant
Open Access

Effect of deposition time on surface plasmon resonance and Maxwell-Garnett absorption in RF-magnetron sputtered carbon-nickel films

Published Online: 24 May 2016
Page range: 337 - 343

Abstract

Abstract

In this work, carbon-nickel films were grown during four deposition times (50 s, 90 s, 180 s and 600 s) at room temperature on glass substrates by radio frequency magnetron sputtering. The optical absorption spectra of the films were investigated with a special emphasis on the surface plasmon resonance (SPR) of Ni nanoparticles. The optical absorption peaks caused by the surface plasmon resonance of Ni nanoparticles were observed in the wavelength range of 300 nm to 330 nm. It has been shown that the surface plasmon resonance peaks exhibit a red shift and a blue shift depending on the deposition time. The red and blue shifts of the surface plasmon resonance in the absorption spectra of the films were observed with the increase and decrease of Ni nanoparticle size, respectively. The Ni nanoparticle size, dielectric function of carbon matrix εm and plasma frequency of free electrons ωp for the films deposited at deposition time of 180 s have maximum values of 80 nm, 0.401 and 7.25 × 1015 s–1, respectively. These observations are in a good agreement with the electrical resistivity measurements and Maxwell-Garnett (M-G) effective medium theory (EMT).

Key words

  • surface plasmon resonance (SPR)
  • carbon-nickel films
  • deposition time
  • deposition rate
Open Access

Wrinkled graphene: synthesis and characterization of few layer graphene-like nanocarbons from kerosene

Published Online: 07 Jun 2016
Page range: 330 - 336

Abstract

Abstract

Wrinkled graphene, derived from a facile thermal decomposition and chemical method, was subjected to various analysis techniques and the results have been reported here. Raman studies revealed the presence of highly graphitized amorphous carbon, which was evident by the appearance of five peaks in the deconvoluted first order spectrum. This result was very well corroborated by the XRD analysis. XPS and FT-IR spectra confirmed the incorporation of oxygen functionalities into the carbon backbone. AFM and SEM images of the sample disclosed a cluster of few-layer wrinkled graphene fragments. TEM images displayed a chain of nearly spherical aggregates of graphene, resembling nanohorns. The resistivity and sheet resistance of the sample were found to be low, making the obtained material a promising candidate for various device applications. Hence, kerosene soot proved to be an efficient precursor for facile synthesis of few layer graphene-like nanocarbon.

Keywords

  • hydrocarbon
  • Hummers’
  • method
  • wrinkled graphene
  • nanohorns
Open Access

Colossal dielectric constant of NaNbO3 doped BaTiO3 ceramics

Published Online: 18 Jun 2016
Page range: 322 - 329

Abstract

Abstract

BaTiO3 ceramics doped with 0.40 mol% NaNbO3 were prepared using a traditional approach by sintering at temperature of 1250 °C to 1290 °C. The prepared ceramics was characterized by very good dielectric properties, such as high dielectric constant (1.5 × 105), low dielectric loss (0.1), and good dielectric temperature stability in the −40 °C to 100 °C range for the sample sintered below 1270 °C. The dielectric characteristics obtained with XPS confirmed that Ti4+ ions remain in the state without any change. The huge increase in dielectric constant in NaNbO3 doped BaTiO3 samples occurs when large amount of Ba2+ ions are excited to a high energy bound state of Ba2+ − e or Ba+ to create electron hopping conduction. For samples with the content of NaNbO3 higher than 0.40 mol%, or sintering temperature higher than 1280 °C, compensation effect is dominated by cation vacancies with sharply decreasing dielectric constant and increased dielectric loss. The polaron effect is used to explain the relevant mechanism of giant dielectric constant appearing in the ferroelectric phase.

Keywords

  • BaTiO
  • giant dielectric constant
  • XPS
Open Access

Compositional analysis of silicon oxide/silicon nitride thin films

Published Online: 10 Jun 2016
Page range: 315 - 321

Abstract

Abstract

Hydrogen, amorphous silicon nitride (SiNx:H abbreviated SiNx) films were grown on multicrystalline silicon (mc-Si) substrate by plasma enhanced chemical vapour deposition (PECVD) in parallel configuration using NH3/SiH4 gas mixtures. The mc-Si wafers were taken from the same column of Si cast ingot. After the deposition process, the layers were oxidized (thermal oxidation) in dry oxygen ambient environment at 950 °C to get oxide/nitride (ON) structure. Secondary ion mass spectroscopy (SIMS), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX) were employed for analyzing quantitatively the chemical composition and stoichiometry in the oxide-nitride stacked films. The effect of annealing temperature on the chemical composition of ON structure has been investigated. Some species, O, N, Si were redistributed in this structure during the thermal oxidation of SiNx. Indeed, oxygen diffused to the nitride layer into Si2O2N during dry oxidation.

Key words

  • oxidation
  • PECVD
  • annealing temperature
  • elemental analysis
Open Access

Structural and electrochemical investigation of waste newspaper based electrodes for supercapacitor applications

Published Online: 27 Jun 2016
Page range: 302 - 314

Abstract

Abstract

There is a general consensus to develop renewable energy storage and conversion technologies to replace fossil fuel energy for sustainable development. Currently, the development of high performance energy storage and conversion devices is an important step on the road to alternative energy technologies. With a special focus on the upgradation of waste to valuable energy, this paper presents an effective synthetic method that utilizes waste newspapers as the precursor to prepare the activated carbon electrodes by the pyrolysis and chemical activation processes. The amorphous nature and surface morphology of the carbon samples were confirmed by XRD and SEM analysis, respectively. Activated waste newspaper carbon (AWNP) showed good electrochemical properties at 800 °C and its specific capacitance at a scan rate of 2 mV/s was found to be 380 F/g. It is important to mention that the source of the raw material is cost effective and suitable for green technology.

Key words

  • waste newspaper
  • electrode
  • hierarchical porous carbon
  • supercapacitor
Open Access

Characteristics of TlBr single crystals grown using the vertical Bridgman-Stockbarger method for semiconductor-based radiation detector applications

Published Online: 18 Jun 2016
Page range: 297 - 301

Abstract

Abstract

TlBr single crystals grown using the vertical Bridgman-Stockbarger method were characterized for semiconductor based radiation detector applications. It has been shown that the vertical Bridgman-Stockbarger method is effective to grow high-quality single crystalline ingots of TlBr. The TlBr single crystalline sample, which was located 6 cm from the tip of the ingot, exhibited lower impurity concentration, higher crystalline quality, high enough bandgap (>2.7 eV), and higher resistivity (2.5 × 1011 Ω·cm) which enables using the fabricated samples from the middle part of the TlBr ingot for fabricating high performance semiconductor radiation detectors.

Keywords

  • semiconductor single crystal
  • TlBr
  • radiation detection
  • crystalline quality
  • impurity
  • resistivity
  • optical bandgap
Open Access

Magnetic studies of 0.7(Fe2O3)/0.3(ZnO) nanocomposites in nanopowder form and dispersed in polymer matrix

Published Online: 24 May 2016
Page range: 286 - 296

Abstract

Abstract

Magnetic properties of 0.7(Fe2O3)/0.3(ZnO) nanocomposite synthesized by traditional wet chemistry method and containing only two phases: ZnO (nonmagnetic) and ZnFe2O4 (magnetic, with nanocrystallites of average size 12 nm, but forming large agglomerates, up to 100 nm in size) were studied by DC magnetization and ferromagnetic resonance (FMR). The investigated nanocomposite was either in a form of nanopowder or dispersed at concentration of 0.1 wt.% in poly(ethylene naphthalate-block-tetramethylene oxide) PTMO-b-PEN polymer matrix. Similarities and differences in magnetic behavior of these two samples revealed by the study of static magnetization and FMR spectra have been discussed relative to different morphologies and the associated variation of interparticle interactions. Moreover, thermal and thermo-oxidative stability of the nanocomposite and the neat polymer have been studied by thermogravimetric method.

Key words

  • ferromagnetic resonance
  • magnetization
  • thermogravimetry
  • zinc ferrite nanoparticles
  • polymer nanocomposite
Open Access

Electronic structure, first and second order physical properties of MPS4: a theoretical study

Published Online: 10 Jun 2016
Page range: 275 - 285

Abstract

Abstract

We have calculated the electronic structure and physical properties of metal thiophosphate compounds InPS4 and AlPS 4by means of pseudopotential density functional theory (DFT) coupled with the modern theory of polarization. The targeted physical properties are first and second order optical properties as well as elastic, piezoelectric and electro-optic coefficients. Furthermore, population analysis is presented in order to evaluate the covalent-ionic character of the constituent bonds. The calculated elastic constants, refractive indices and second order optical coefficients of InPS4 are in good agreement with experimental values. With the absence of any theoretical or experimental physical properties of AlPS4, we predict that this compound has high piezoelectric coefficients with d14 = − 73.82 pm/V, d25 = − 10.96 pm/V and d36 = 28.19 pm/V.

Key words

  • metal thiophosphate
  • DFT
  • optical
  • elastic
  • piezoelectric
  • electro-optic properties
Open Access

Characterization of NiO–Al2O3 composite and its conductivity in biogas for solid oxide fuel cell

Published Online: 09 May 2016
Page range: 266 - 274

Abstract

Abstract

NiO–Al2O3 nanocomposite has been synthesized by mixing combustion synthesized powders. The nanocomposite is an effective anode/anode functional layer for intermediate temperature solid oxide fuel cells. The TEM of NiO and Al2O3 revealed spherical particles of 30 nm and platelets of 70 nm, respectively. The XRD analysis of NiO–Al2O3 composite sintered at 900 °C showed presence of cubic NiO and rhombohedral α-Al2O3 which were chemically stable. However, above 1200 °C NiAl2O4 started to appear. The conductivity of NiO–Al2O3 was the highest in hydrogen (4.3 × 10–3 S/cm at 600 °C). In biogas, the conductivity was 3.2 × 10–3 S/cm with the activation energy of 0.67 eV. The stability of the composite in biogas was also examined.

Keywords

  • oxides
  • chemical synthesis
  • X-ray diffraction
  • electrical conductivity
  • microstructure
Open Access

Kinetics of oxygen adsorption on ZnS nanoparticles synthesized by precipitation process

Published Online: 24 May 2016
Page range: 260 - 265

Abstract

Abstract

ZnS nanoparticles were synthesized through a one-step precipitation process. Effect of time and temperature on the formation reaction was investigated. The synthesized samples were characterized by X-ray diffraction (XRD), ultraviolet (UV) visible absorption and photoluminescence (PL) spectrophotometry. Based on XRD and UV-Vis data, the particles produced at 70 °C had a mean particle size of about 5 nm. Increasing time and temperature of the synthesis reaction resulted in photoluminescence intensification. PL spectroscopy helped understanding the adsorption kinetics of oxygen on ZnS nanoparticles during the precipitation synthesis process. Fabrication of ZnS structures with appropriate oxygen adsorption capacity was suggested as a means of PL emission intensity control.

Key words

  • ZnS nanoparticles
  • UV-Vis spectrophotometry
  • Avrami model
Open Access

Site preference and electronic structure of Mn2RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb): a theoretical study

Published Online: 09 May 2016
Page range: 251 - 259

Abstract

Abstract

The electronic structure and magnetism of Mn2RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) Heusler alloys have been studied by using first-principles calculations. Three half-metallic ferromagnets, namely, Mn2RhAl, Mn2RhGe and Mn2RhSb have been considered. The calculated equilibrium lattice constant increases with increasing atomic number of Z atoms lying in same column of periodic table. The calculated total magnetic moments Mtot are 2 µB/f.u. for Mn2RhAl and Mn2RhGa, 3 µB/f.u. for Mn2RhSi, Mn2RhGe and Mn2RhSn, and 4 µB/f.u. for Mn2RhSb, which agrees with the Slater-Pauling curve quite well. In all these compounds, except for Mn2RhSb, the moments of Mn (A) and Mn (B) are antiparallel to each other. The total magnetic moments of the three considered half-metals assume integral values in a wide range of equilibrium lattice parameters.

Keywords

  • Heusler alloy
  • electronic structure
  • h-metal
  • site preference
Open Access

Temperature study of magnetic resonance spectra of co-modified (Co,N)-TiO2 nanocomposites

Published Online: 27 Jun 2016
Page range: 242 - 250

Abstract

Abstract

The (nCo,N)-TiO2 (n = 1, 5 and 10 wt.% of Co) nanocomposites were investigated by magnetic resonance spectroscopy in 4 K to 290 K range. Analyses of ferromagnetic/electron paramagnetic resonance (FMR/EPR) spectra in terms of four Callen lineshape components revealed the existence of two types of magnetic centers, one derived from metallic cobalt nanoparticles in superparamagnetic (SPM) phase and the other from cobalt clusters in the TiO2 lattice. Additionally, at low temperature the EPR spectrum arising from Ti3+ ions was also registered. Both relaxations of the Landau-Lifshitz type and the Bloch-Bloembergen type played an important role at high temperature in determining the linewidths and the latter relaxation was prevailing at low temperature. Analysis of the integrated intensity showed that the SPM signal is due to small size FM cobalt nanoparticles while the paramagnetic signal from Co clusters originates from those nanoparticles in which the concentration of magnetic polarons is below the percolation threshold.

Key words

  • nano titanium dioxide
  • electron paramagnetic resonance
  • photocatalyst
Open Access

Deciphering lead and cadmium stripping peaks for porous antimony deposited electrodes

Published Online: 07 Jun 2016
Page range: 233 - 241

Abstract

Abstract

Cadmium and lead are generally taken as model heavy metal ions in water to scale the detection limit of various electrode sensors, using electrochemical sensing techniques. These ions interact with the electrochemically deposited antimony electrodes depending on the diffusion limitations. The phenomenon acts differently for the in-situ and ex-situ deposition as well as for porous and non-porous electrodes. A method has been adopted in this study to discourage the stripping and deposition of the working ions (antimony) to understand the principle of heavy metal ion detection. X-ray photoelectron spectroscopy (XPS) technique was used to establish the interaction between the working and dissolved ions. In addition to the distinct peaks for each analyte, researchers also observed a shoulder peak. A possible reason for the presence of this peak was provided. Different electrochemical tests were performed to ascertain the theory on the basis of the experimental observations.

Keywords

  • anodic stripping voltammetry
  • activated carbon
  • sensor electrodes
Open Access

Electrospinning synthesis of 3D porous NiO nanorods as anode material for lithium-ion batteries

Published Online: 24 May 2016
Page range: 227 - 232

Abstract

Abstract

Three-dimensional NiO nanorods were synthesized as anode material by electrospinning method. X-ray diffraction results revealed that the product sintered at 400 °C had impure metallic nickel phase which, however, became pure NiO phase as the sintering temperature rose. Nevertheless, the nanorods sintered at 400, 500 and 600 °C had similar diameters (∼200 nm).The NiO nanorod material sintered at 500 °C was chip-shaped with a diameter of 200 nm and it exhibited a porous 3D structure. The nanorod sintered at 500 °C had the optimal electrochemical performance. Its discharge specific capacity was 1127 mAh·g−1 initially and remained as high as 400 mAh·g−1 at a current density of 55 mA·g−1 after 50 cycles.

Keywords

  • Li-ion battery
  • anode
  • charging/discharging
  • NiO
  • nanorod

Retraction

Open Access

Retraction

Published Online: 27 Jun 2016
Page range: 1 - 1

Abstract

Open Access

Retraction

Published Online: 27 Jun 2016
Page range: 2 - 2

Abstract

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