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Journal Details
Format
Journal
eISSN
2083-134X
ISSN
2083-1331
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

Volume 31 (2013): Issue 3 (August 2013)

Journal Details
Format
Journal
eISSN
2083-134X
ISSN
2083-1331
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

25 Articles
access type Open Access

Gas sensing performance of nanocrystalline ZnO prepared by a simple route

Published Online: 29 Aug 2013
Page range: 298 - 305

Abstract

Abstract

The nanocrystalline powders of pure and Al3+-doped ZnO with hexagonal structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and the microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution between Al2O3 and ZnO. DC electrical properties of the prepared nanoparticles were studied by DC conductivity measurements. The indirect heating structure sensors based on pure and doped ZnO as sensitive materials were fabricated on an alumna tube with Au electrodes. Gas-sensing properties of the sensor elements were measured as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure ZnO exhibited high response to NH3 gas at an operating temperature of 200 °C. Doping of ZnO with Al3+ increased its response towards NH3 and the Al3+-doped ZnO (3.0 wt% Al2O3) showed the maximum response at 175 °C. The selectivity of the sensor elements for NH3 against different reducing gases like LPG, H2S and H2 was studied. The results on response and recovery time were also discussed.

Keywords

  • nanocrystalline zinc oxide
  • H2S
  • gas sensor
  • selectivity
  • recovery time
access type Open Access

UV-induced photodecomposition of 2, 2′, 4, 4′, 6, 6′-hexanitrostillbene (HNS)

Published Online: 29 Aug 2013
Page range: 306 - 311

Abstract

Abstract

HNS (2, 2′, 4, 4′, 6, 6′-hexanitrostillbene) is a heat-resistant photosensitive explosive widely used in the booster charge. Investigation of the photodecomposition mechanism may provide important information for controlling and enhancing the detonation performance, also for the lifetime prediction. The UV-induced photodecomposition of HNS has been subjected to experimental studies. The UV-Vis spectra, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) demonstrate the formation of NO2 free radicals and nitroso derivatives of HNS upon UV irradiation, which proves well known facts that C-NO2 breaking and removal of oxygen from the nitro group take part in the photodecomposition of HNS.

Keywords

  • HNS
  • photodecomposition
  • C-NO2 breaking
  • removal of oxygen
access type Open Access

Stability of ZnO nanofibers in processing liquid agents

Published Online: 29 Aug 2013
Page range: 312 - 317

Abstract

Abstract

The aim of the research was to determine the impact of developers, removers and solvents on the stability of ZnO nanofibers. Surface imaging of nanofiber morphology was studied using Scanning Electron Microscope. From the obtained results a set of factors which have the least influence on the etching of ZnO nanofibers during device processing was selected. The dependence of the grains size on the fibers robustness in the liquid solutions was investigated. It was found that the nanofibers calcinated at higher temperatures were more stable. This was due to the grain size of the fiber as the fibers calcinated at higher temperatures revealed larger grain size. The studies have shown that smaller grains were dissolved much faster, leaving the porous core of the ZnO nanofiber.

Keywords

  • nanofibers
  • zinc oxide
  • etching
access type Open Access

The influence of the deposition time on morphological and optical properties of CuxS films deposited on polypropylene substrate

Published Online: 29 Aug 2013
Page range: 318 - 324

Abstract

Abstract

Copper sulfide (CuxS) films deposited on polypropylene substrate were obtained by chemical bath deposition (CBD) method. The influence of the deposition time on the morphology of CuxS films was studied by means of scanning electron microscopy. We have found that the average particles dimension increased from 37 to 49 nm with the increase of deposition time from 20 to 30 minutes. The study of optical properties of the copper sulfide films was carried out based on optical transmission spectra recorded in the 400–1000 nm wavelength range. The optical constants, such as refractive index, extinction coefficient and dielectric constant as well as electrical and optical conductivity of CuxS films were calculated. The obtained values are in accordance with the ones reported in the literature:We have shown that both, morphological and optical properties of CuxS films are strongly affected by the deposition time.

Keywords

  • CuxS
  • polypropylene
  • CBD
  • surface morphology
access type Open Access

Comparative study on different annealing methods and choice of solvent in organic field effect transistors based on Poly(3-hexylthiophene)

Published Online: 29 Aug 2013
Page range: 325 - 330

Abstract

Abstract

A simple approach to study the effect of processing on the charge carrier mobility in an organic field effect transistor (OFET) based on regioregular poly(3-hexylthiophene) (RR P3HT) is investigated in this paper. It is found that different processing conditions can induce different degrees of hysteresis, which is well correlated with the charge mobility where lower hysteresis represents higher stability and hence higher charge mobility. Solvent annealing tends to create large nano-scale pinholes in P3HT which degrade the mobility.

Keywords

  • organic field effect transistor
  • regioregular poly(3-hexylthiophene)
  • solvent annealing
  • thermal annealing
access type Open Access

Irregular shaping of polystyrene nanosphere array by plasma etching

Published Online: 29 Aug 2013
Page range: 331 - 337

Abstract

Abstract

The morphology of nanospheres is crucial for designing the nanofabrication in the nanosphere lithography. Here, by plasma etching, the controllable tailoring of the nanosphere is realized and its morphology dependence on the initial shape, microscopic roughness, and the etching conditions is investigated quantitatively. The results show that the shape evolution strongly depends on the etching gas, power, and process duration. Particularly, the aspect ratio (diameter/height) significantly increases with violent etching, turning the spherical shape into tiny ellipsoidal nanoparticles. The findings are practical to the protocol of non-uniform etching of nanoobjects and provide the useful design tool for the device fabrication at nanoscale.

Keywords

  • polystyrene
  • nanosphere array
  • self-assembly
access type Open Access

One dimensionality and spectroscopy in carbon nanotubes

Published Online: 29 Aug 2013
Page range: 338 - 342

Abstract

Abstract

Unlike regular three-dimensional solids two of a nanotube dimensions are confined and quantized. Bulk samples consist of irregular networks of merging and splitting bundles of parallel tubes. On a local scale, nanotubes are at the same time one-dimensional crystals and two-dimensional quantum rings. They have attracted extensive studies on individual aspects in their electronic and optical properties [1]. The current contribution aims at bridging the fundamental physical concepts behind carbon nanotubes to their unique spectroscopic signatures in optical absorption, luminescence, Raman and electron energy loss spectroscopy. The aim is not to compete with the local depth of a focused review, but to briefly convey the physical concept and related spectroscopic signatures of one-dimensionality. Indirect signatures are the manifold appearances of van Hove singularities in their optical transitions. Direct probes of one-dimensionality unveil the confined momentum space, which manifests in the distinction of localized and propagating excitations.

Keywords

  • carbon nanotube
  • spectroscopy
  • one-dimensionality
access type Open Access

Synthesis of nanocrystalline Ni/Ce-YSZ powder via a polymerization route

Published Online: 29 Aug 2013
Page range: 343 - 349

Abstract

Abstract

Pechini process was used for preparation of three kinds of nanocrystalline powders of yttria-stabilized zirconia (YSZ): doped with 1.5 mol% nickel oxide, doped with 15 mol% ceria, and doped with 1.5 mol% nickel oxide plus 15 mol% ceria. Zirconium chloride, yttrium nitrate, cerium nitrate, nickel nitrate, citric acid and ethylene glycol were polymerized at 80 °C to produce a gel. XRD, SEM and TEM analyses were used to investigate the crystalline phases and microstructures of obtained compounds. The results of XRD revealed the formation of nanocrystalline powder at 900 °C. Morphology of the powder calcined at 900 °C, examined with a scanning electron microscope, showed that the presence of nickel and cerium inhibited the grain growth in the system. The average crystallite size of the material doped with nickel oxide (9.33 nm) was bigger than the one doped with cerium oxide (9.29 nm), while the YSZ doping with the two oxides simultaneously promoted the grain growth with crystallite size of 11.37 nm. Yttria-stabilized zirconia powder with a mean crystallite size of 9.997 nm was prepared successfully by this method.

Keywords

  • yttria-stabilized zirconia
  • Pechini method
  • nanocrystalline Ni/Ce-YSZ powder
  • dopant
access type Open Access

Formation of silicon oxide nanowires in nanomaterial synthesis experiments based on the usage of tube furnace

Published Online: 29 Aug 2013
Page range: 350 - 356

Abstract

Abstract

In an effort to synthesize doped ZnO nanowires, SiOx nanowires were obtained accidently. In the experiment, mixed powders containing chemicals such as ZnO, graphite, Ga2O3, and In2O3 were placed in the center of a tube furnace, where the temperature was set to 1200 °C and the vacuum was approximately 27 Pa. Silicon wafers were placed around the vicinity of the furnace exit to collect the expected nanomaterials. After prolonged heating, grey layers were found on top of one wafer located inside the furnace. The layer showed no adhesion to the substrate. Characterization by using Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Energy Dispersive X-ray Spectroscopy (EDS) revealed that this layer consisted of SiOx nanowires. Formation of Si-containing liquid drop and the subsequent growth of SiOx nanowires out of it are suggested as the growth mechanism.

Keywords

  • silicon
  • oxide
  • nanowires
access type Open Access

Quantum chemical computational studies on bis-thiourea zinc acetate

Published Online: 29 Aug 2013
Page range: 357 - 371

Abstract

Abstract

In this study, quantum chemical calculations of vibrational spectra, Raman spectra, electronic properties (total energy, dipole moment, electronegativity, chemical hardness and softness), Mulliken atomic charges and thermodynamic parameters of bis-thiourea zinc acetate (BTZA) have been performed using Gaussian 09 program. Additionally, nonlinear optical (NLO), conformational, natural bond orbital (NBO) analyses of BTZA have been carried out using the same program. The structural and spectroscopic data of the molecule in the ground state have been calculated using Hartree-Fock (HF) and density functional method (DFT/B3LYP) with the 6-311++G(d,p) basis set. In addition, the molecular frontier orbital energies (HOMO, HOMO-1, LUMO and LUMO+1) of the title compound have been calculated at the HF and B3LYP levels. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Finally, the calculated results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the experimental ones.

Keywords

  • bis-thiourea zinc acetate (BTZA)
  • IR and NMR spectra
  • DFT and HF calculations
  • NLO and NBO analyses, conformational analysis
access type Open Access

Preparation of TiO2/Al-MCM-41 mesoporous materials from coal-series kaolin and photodegradation of methyl orange

Published Online: 29 Aug 2013
Page range: 372 - 377

Abstract

Abstract

TiO2/Al-MCM-41 mesoporous materials were prepared via sol-gel method by loading titania onto Al-MCM-41 mesoporous molecular sieve by hydrothermal treatment from coal-series kaolin as raw material. The TiO2/Al-MCM-41 mesoporous materials were characterized by XRD, FT-IR, HRTEM, N2 adsorption-desorption and the photocatalytic degradation of methyl orange solution under visible light irradiation. The results showed that the TiO2/Al-MCM-41 mesoporous materials possessed a high surface area of 369.9–751.3 m2/g and a homogeneous pore diameters of 2.3–2.8 nm. The titania crystalline phase was anatase, and the particles size of TiO2 increased with TiO2 content. The Al-MCM-41 mesoporous materials exhibited excellent photodegradation activity under visible-light irradiation for methyl orange.

Keywords

  • coal-series kaolin
  • Al-MCM-41
  • TiO2
  • photocatalytic degradation
access type Open Access

Performance of dye-sensitized solar cell fabricated using titania nanoparticles calcined at different temperatures

Published Online: 29 Aug 2013
Page range: 378 - 385

Abstract

Abstract

Synthesis of titania (TiO2) nanoparticles by sol-gel method and their calcination at different temperatures, viz 450 °C, 550 °C and 650 °C (defined as T450, T550 and T650) has been done. Structural analysis indicates that the T450 sample possesses anatase phase. The phase transformation to rutile starts occurring at T550, and, on increasing the calcination temperature, the crystallization and percentage of rutile phase increases. As the temperature increases from 450 to 650 °C, the crystallite size increases by about a factor of two from 11.5 to 20.2 nm. From SEM micrographs, T550 electrode has been found to have appropriate aggregation, which led to enhanced dye desorption, as compared to T450 and T650 based electrodes. TEM images of the synthesized nanoparticles reveal that the particle size increases from 7 to 28 nm on increasing the calcination temperature from 450 to 650 °C. From the photoluminescence and Fourier transform infrared studies, it has been concluded that the surface OH− groups are reduced on calcination, which affects the electron injection efficiency. The dye sensitized solar cell, fabricated using T550 sample, having a ratio of anatase/rutile 89:11, has been found to achieve the highest conversion efficiency.

Keywords

  • DSSC
  • TiO2 nanoparticles
  • calcination
  • anatase/rutile mixture
access type Open Access

Glycerol-assisted solution combustion synthesis of improved LiMn2O4

Published Online: 29 Aug 2013
Page range: 386 - 390

Abstract

Abstract

Spinel LiMn2O4 has been synthesized by a glycerol-assisted combustion synthesis method. The phase composition and morphologies of the compound were ascertained by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical characterization was performed by using CR2032 coin-type cell. XRD analysis indicates that single phase spinel LiMn2O4 with good crystallinity has been obtained as a result of 5 h treatment at 600 °C. SEM investigation indicates that the average particle size of the sample is 200 nm. The initial discharge specific capacity of the LiMn2O4 is 123 mAh/g at a current density of 30 mA/g. When the current density increased to 300 mA/g, the LiMn2O4 offered a discharge specific capacity of 86 mAh/g. Compared with the LiMn2O4 prepared by a conventional solution combustion synthesis method at the same temperature, the prepared LiMn2O4 possesses higher purity, better crystallinity and more uniformly dispersed particles. Moreover, the initial discharge specific capacity, rate capability and cycling performance of the prepared LiMn2O4 are significantly improved.

Keywords

  • lithium ion batteries
  • cathode
  • spinel
  • solution combustion synthesis
access type Open Access

Optical and surface morphological studies on CuPcOC8 thin films prepared by physical vapour deposition

Published Online: 29 Aug 2013
Page range: 391 - 396

Abstract

Abstract

2,3,9,10,16,17,23,24-copper octakis (octyloxy) phthalocyanine (CuPcOC8) thin films deposited at room temperature have exhibited a change in their surface morphology with the post deposition annealing temperature under normal atmosphere.These films have been characterised by optical absorption also. SEM images have shown densely packed nano particles and nano-rod like structures on the substrates annealed at different temperatures. The optical transition was found to be direct allowed and the direct energy gap changed with the annealing temperature. The results of optical and surface morphological studies on CuPcOC8 have been discussed.

Keywords

  • copper octakis (octyloxy) phthalocyanine
  • absorption spectra
  • annealing temperature
  • optical band gap
  • Davydov splitting
  • surface morphology
access type Open Access

Bulk ZnO nanorod assemblies fabricated by spin coating of organo-precursor gels on CuO nanowires

Published Online: 29 Aug 2013
Page range: 397 - 403

Abstract

Abstract

Bulk ZnO nanorod assemblies have been successfully fabricated on CuO nanowires through spin coating of organoprecursor gels. A thin film of CuO nanowires was first generated by direct heating of a metallic Cu-foil at 500 °C in an air atmosphere. A stable colloidal organo-precursor sol synthesized by dissolving equimolar zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol was subsequently repeatedly deposited onto the CuO nanowires by spin coating. The formation of ZnO nanorod assemblies was controlled by varying the number of coatings. The average diameter of the ZnO rods was determined to be ∼600 nm.

Keywords

  • ZnO
  • CuO
  • sol-gel
  • Raman spectrum
  • SEM
access type Open Access

Preparation and properties of low temperature sintered CaO-B2O3-SiO2 microwave dielectric ceramics using the solid-state reaction

Published Online: 29 Aug 2013
Page range: 404 - 409

Abstract

Abstract

The LTCC CaO-B2O3-SiO2 (CBS) ceramics were synthesized via solid-state reaction process without any sintering aid. The effects of different sintering temperatures and B2O3 content on the microwave and mechanical properties were investigated. The results show that the best sintering temperature is around 950 °C and increasing amount of B2O3 promotes the crystallization of CaB2O4 enhancing the flexure strength of the CBS ceramics. However, the dielectric and mechanical properties deteriorated rapidly while the amount of B2O3 exceeded 25 wt.%. The sample with 20.5 wt.% B2O3 sintered at 950 °C had the best properties with ɛ r = 6.06; tanδ = 0.0015 (1 MHz) and a high flexure strength σ f > 180 MPa.

Keywords

  • solid state reaction
  • LTCC
  • CaO-B2O3-SiO2
  • flexural strength
  • microwave properties
access type Open Access

Phase, microstructure and dielectric properties of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics prepared by sol-gel technique

Published Online: 29 Aug 2013
Page range: 410 - 414

Abstract

Abstract

0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics were fabricated by sol-gel technique. The XRD results revealed the formation of a single phase perovskite structured Bi0.5Na0.5TiO3-BaTiO3 at 600 °C. The SEM images showed dense microstructure and the optimum density of the ceramics sintered at 1100 °C was 5.2 g/cm3. The saturation polarization (Ps) was found to be increased with increasing temperature while the remnant polarization (Pr) was found to be increased gradually and then decreased abruptly near 85 °C, which could be attributed to the phase transformation. The coercive electric field (Ec) was found to be decreased gradually with increasing temperature. The maximum value of dielectric constant (ɛ r) at room temperature was 800 and dielectric loss at 1 MHz was 0.07.

Keywords

  • lead free
  • perovskite
  • sol-gel
  • FT-IR
  • ferroelectrics
access type Open Access

Mechanical and tribological properties of gradient a-C:H/Ti coatings

Published Online: 29 Aug 2013
Page range: 415 - 423

Abstract

Abstract

The unusual combination of high hardness and very low friction coefficient are the most attractive tribological parameters of DLC (diamond-like carbon) layers. However, their usability is strongly restricted by the limited thickness due to high residual stress. The main goal of the presented work was to obtain thick, wear resistant and well adherent DLC layers while keeping their perfect friction parameters. As a proposed solution a Ti-TixCy gradient layer was manufactured as the adhesion improving interlayer followed by a thick diamond-like carbon film. This kind of combination seems to be very promising for many applications, where dry friction conditions for highly loaded elements can be observed. Both layers were obtained in one process using a hybrid deposition system combining PVD and CVD techniques in one reaction chamber. The investigation was performed on nitrided samples made from X53CrMnNiN21-9 valve steel. Structural features, surface topography, tribological and mechanical properties of manufactured layers were evaluated. The results of the investigation confirmed that the presented deposition technique makes it possible to manufacture thick and well adherent carbon layers with high hardness and very good tribological parameters. Preliminary investigation results prove the possibility of application of presented technology in automotive industry.

Keywords

  • carbon layers
  • friction
  • adhesion
  • wear resistance
access type Open Access

Optimization of sol-gel technique for coating of metallic substrates by hydroxyapatite using the Taguchi method

Published Online: 29 Aug 2013
Page range: 424 - 433

Abstract

Abstract

In this study, the Taguchi method of design of experiment (DOE) was used to optimize the hydroxyapatite (HA) coatings on various metallic substrates deposited by sol-gel dip-coating technique. The experimental design consisted of five factors including substrate material (A), surface preparation of substrate (B), dipping/withdrawal speed (C), number of layers (D), and calcination temperature (E) with three levels of each factor. An orthogonal array of L18 type with mixed levels of the control factors was utilized. The image processing of the micrographs of the coatings was conducted to determine the percentage of coated area (PCA). Chemical and phase composition of HA coatings were studied by XRD, FT-IR, SEM, and EDS techniques. The analysis of variance (ANOVA) indicated that the PCA of HA coatings was significantly affected by the calcination temperature. The optimum conditions from signal-to-noise (S/N) ratio analysis were A: pure Ti, B: polishing and etching for 24 h, C: 50 cm min−1, D: 1, and E: 300 °C. In the confirmation experiment using the optimum conditions, the HA coating with high PCA of 98.5 % was obtained.

Keywords

  • hydroxyapatite
  • sol-gel
  • coating
  • Taguchi method
  • image processing
access type Open Access

Investigation of physicochemical and tribological properties of transparent oxide semiconducting thin films based on Ti-V oxides

Published Online: 29 Aug 2013
Page range: 434 - 445

Abstract

Abstract

In this paper investigations of structural and optical properties of nanocrystalline Ti-V oxide thin films are described. The films were deposited onto Corning 7059 glass using a modified reactive magnetron sputtering method. Structural investigations of prepared Ti-V oxides with vanadium addition of 19 at. % revealed amorphous structure, while incorporation of 21 and 23 at. % of vanadium resulted in V2O5 formation with crystallites sizes of 12.7 and 32.4 nm, respectively. All prepared thin films belong to transparent oxide semiconductors due to their high transmission level of ca. 60–75 % in the visible light range, and resistivity in the range of 3.3·102–1.4·105 Ωcm. Additionally, wettability and hardness tests were performed in order to evaluate the usefulness of the films for functional coatings.

Keywords

  • Ti-V oxide thin films
  • transparent oxide semiconductors
  • magnetron sputtering
  • tribological properties
access type Open Access

Analysis of MIS equivalent electrical circuit of Au/Pd/Ti-SiO2-GaAs structure based on DLTS measurements

Published Online: 29 Aug 2013
Page range: 446 - 453

Abstract

Abstract

In this paper MIS equivalent electrical circuit of Au/Pd/Ti-SiO2-GaAs has been analyzed by a comparison of the results obtained from admittance and DLTS spectroscopy. Two groups of peaks with different magnitude and different gate voltage dependence have been observed in DLTS and admittance spectra. Based on the analysis of the peaks behavior, it has been concluded that they are associated with the response of bulk traps and interface states, respectively. In order to characterize bulk traps and interface states responsible for the occurrence of two groups of peaks in normalized conductance spectra we have used the equivalent circuit with two CPE-R branches. The time constant values estimated for both peaks from admittance analysis have been compared with the time constant determined from DLTS analysis. Some discrepancies have been noted between the time constants obtained for interface states whereas the time constants for bulk traps were compatible. It has been also demonstrated that when conductance peaks overlap, the admittance experimental data can be fitted by the equivalent electrical model with only one CPE-R branch. However, in this case incomplete information about the analyzed process has been obtained despite the fact that all model validity criteria can be fulfilled and the model seems to be correct.

Keywords

  • MIS structure
  • deep levels
  • interface states
  • admittance spectroscopy
  • DLTS
access type Open Access

Effect of working pressure on the structural, optical and electrical properties of titanium-gallium co-doped zinc oxide thin films

Published Online: 29 Aug 2013
Page range: 454 - 461

Abstract

Abstract

The transparent conducting titanium-gallium co-doped zinc oxide (TGZO) thin films were grown on glass substrates by radio-frequency magnetron sputtering technique. The effects of working pressure on the structural, optical and electrical properties of the films were investigated. The results show that the deposited films are polycrystalline with a hexagonal wurtzite structure and highly textured along the c-axis perpendicular to the substrate. The TGZO film prepared at the working pressure of 0.4 Pa exhibits the best crystallinity, the maximal grain size, the highest transmittance, the lowest resistivity and the highest figure of merit. The optical constants of the films were calculated using the method of optical spectrum fitting. The dispersion behavior of the films was studied by the single-electronic oscillator dispersion model. The oscillator parameters and optical bandgaps were determined. The results demonstrate that the microstructure and optoelectrical properties of the TGZO films are dependent on the working pressure.

Keywords

  • transparent conducting oxide
  • ZnO thin films
  • sputtering
  • optoelectrical properties
access type Open Access

Controlled mechanochemical synthesis and properties of a selected perovskite-type electroceramics

Published Online: 29 Aug 2013
Page range: 462 - 470

Abstract

Abstract

This paper presents mechanochemical synthesis as an alternative to the traditional high-temperature synthesis of advanced electrotechnical ceramic materials with a perovskite-type structure. The reaction conditions for high-energy ball milling, e.g. reaction environment, energy of milling and additives to BaTiO3 such as metallic iron or zirconia from the exfoliation of the milling vessel and grinding media are discussed.

Keywords

  • mechanochemistry
  • high-energy ball milling
  • perovskites
  • ferroelectric ceramics
  • barium titanate
access type Open Access

Investigation on multiferroic properties of BiFeO3 ceramics

Published Online: 29 Aug 2013
Page range: 471 - 475

Abstract

Abstract

BiFeO3 polycrystalline ceramics was prepared by solid-state reaction method and its structural, optical and magnetic properties were investigated. BiFeO3 was synthesized in a wide range of temperature (825–880 °C) and a well crystalline phase was obtained at a sintering temperature of 870 °C. X-ray diffraction patterns of the samples were recorded and analyzed for the confirmation of crystal structure and the determination of the lattice parameters. The average grain size of the samples was found to be between 1–2 μm. The determined value of direct bandgap of BiFeO3 ceramics was found to be 2.72 eV. The linear behavior of M-H curve at room temperature confirmed antiferromagetic properties of the BiFeO3 (BFO). S shaped M-H curve was obtained at a temperature of 5 K. In the whole temperature measurement range (5–300 K) of M-T, no anomalies were observed due to high Curie temperature and Neel temperature of the BiFeO3.

Keywords

  • BiFeO3 ceramics
  • multiferroics
  • SQUID
access type Open Access

Silicon carbonitride layers deposited on titanium and polyurethane by PACVD method

Published Online: 29 Aug 2013
Page range: 476 - 483

Abstract

Abstract

This work reports the results concerning formation and tribological properties of SiCxNy(H) layers deposited on Ti Grade 2 and polyurethane foil. Depending on the substrate, two variants of PACVD were used. The SiCxNy(H) layers on titanium were deposited with application of MWCVD (2.45 GHz, 2 kW). The layers on polyurethane were deposited using RFCVD (13.56 MHz, 400 W). Good adhesion between the SiCxNy(H) layers and polymeric foil was achieved by formation of a transitional C:N:H layer and incorporating Si gradient into the structure of the SiCxNy(H) layer. The chemical composition of the layers was tailored by precise control of the gaseous precursors ratios: [SiH4]/[NH3], [SIH4]/[NH3]/[CH4], [SiH4]/[CH4] or [SiH4]/[N2]/[CH4]. The structure and chemical composition of the obtained layers were subjected to further studies (FTIR, SEM/EDS). The roughness, friction coefficient and wear resistance were also measured. The results show that SiCxNy(H) layers offer attractive tribological properties which make them good candidates for various applications, including biomedical devices.

Keywords

  • PACVD
  • silicon carbonitride layers
  • tribology
25 Articles
access type Open Access

Gas sensing performance of nanocrystalline ZnO prepared by a simple route

Published Online: 29 Aug 2013
Page range: 298 - 305

Abstract

Abstract

The nanocrystalline powders of pure and Al3+-doped ZnO with hexagonal structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and the microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution between Al2O3 and ZnO. DC electrical properties of the prepared nanoparticles were studied by DC conductivity measurements. The indirect heating structure sensors based on pure and doped ZnO as sensitive materials were fabricated on an alumna tube with Au electrodes. Gas-sensing properties of the sensor elements were measured as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure ZnO exhibited high response to NH3 gas at an operating temperature of 200 °C. Doping of ZnO with Al3+ increased its response towards NH3 and the Al3+-doped ZnO (3.0 wt% Al2O3) showed the maximum response at 175 °C. The selectivity of the sensor elements for NH3 against different reducing gases like LPG, H2S and H2 was studied. The results on response and recovery time were also discussed.

Keywords

  • nanocrystalline zinc oxide
  • H2S
  • gas sensor
  • selectivity
  • recovery time
access type Open Access

UV-induced photodecomposition of 2, 2′, 4, 4′, 6, 6′-hexanitrostillbene (HNS)

Published Online: 29 Aug 2013
Page range: 306 - 311

Abstract

Abstract

HNS (2, 2′, 4, 4′, 6, 6′-hexanitrostillbene) is a heat-resistant photosensitive explosive widely used in the booster charge. Investigation of the photodecomposition mechanism may provide important information for controlling and enhancing the detonation performance, also for the lifetime prediction. The UV-induced photodecomposition of HNS has been subjected to experimental studies. The UV-Vis spectra, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) demonstrate the formation of NO2 free radicals and nitroso derivatives of HNS upon UV irradiation, which proves well known facts that C-NO2 breaking and removal of oxygen from the nitro group take part in the photodecomposition of HNS.

Keywords

  • HNS
  • photodecomposition
  • C-NO2 breaking
  • removal of oxygen
access type Open Access

Stability of ZnO nanofibers in processing liquid agents

Published Online: 29 Aug 2013
Page range: 312 - 317

Abstract

Abstract

The aim of the research was to determine the impact of developers, removers and solvents on the stability of ZnO nanofibers. Surface imaging of nanofiber morphology was studied using Scanning Electron Microscope. From the obtained results a set of factors which have the least influence on the etching of ZnO nanofibers during device processing was selected. The dependence of the grains size on the fibers robustness in the liquid solutions was investigated. It was found that the nanofibers calcinated at higher temperatures were more stable. This was due to the grain size of the fiber as the fibers calcinated at higher temperatures revealed larger grain size. The studies have shown that smaller grains were dissolved much faster, leaving the porous core of the ZnO nanofiber.

Keywords

  • nanofibers
  • zinc oxide
  • etching
access type Open Access

The influence of the deposition time on morphological and optical properties of CuxS films deposited on polypropylene substrate

Published Online: 29 Aug 2013
Page range: 318 - 324

Abstract

Abstract

Copper sulfide (CuxS) films deposited on polypropylene substrate were obtained by chemical bath deposition (CBD) method. The influence of the deposition time on the morphology of CuxS films was studied by means of scanning electron microscopy. We have found that the average particles dimension increased from 37 to 49 nm with the increase of deposition time from 20 to 30 minutes. The study of optical properties of the copper sulfide films was carried out based on optical transmission spectra recorded in the 400–1000 nm wavelength range. The optical constants, such as refractive index, extinction coefficient and dielectric constant as well as electrical and optical conductivity of CuxS films were calculated. The obtained values are in accordance with the ones reported in the literature:We have shown that both, morphological and optical properties of CuxS films are strongly affected by the deposition time.

Keywords

  • CuxS
  • polypropylene
  • CBD
  • surface morphology
access type Open Access

Comparative study on different annealing methods and choice of solvent in organic field effect transistors based on Poly(3-hexylthiophene)

Published Online: 29 Aug 2013
Page range: 325 - 330

Abstract

Abstract

A simple approach to study the effect of processing on the charge carrier mobility in an organic field effect transistor (OFET) based on regioregular poly(3-hexylthiophene) (RR P3HT) is investigated in this paper. It is found that different processing conditions can induce different degrees of hysteresis, which is well correlated with the charge mobility where lower hysteresis represents higher stability and hence higher charge mobility. Solvent annealing tends to create large nano-scale pinholes in P3HT which degrade the mobility.

Keywords

  • organic field effect transistor
  • regioregular poly(3-hexylthiophene)
  • solvent annealing
  • thermal annealing
access type Open Access

Irregular shaping of polystyrene nanosphere array by plasma etching

Published Online: 29 Aug 2013
Page range: 331 - 337

Abstract

Abstract

The morphology of nanospheres is crucial for designing the nanofabrication in the nanosphere lithography. Here, by plasma etching, the controllable tailoring of the nanosphere is realized and its morphology dependence on the initial shape, microscopic roughness, and the etching conditions is investigated quantitatively. The results show that the shape evolution strongly depends on the etching gas, power, and process duration. Particularly, the aspect ratio (diameter/height) significantly increases with violent etching, turning the spherical shape into tiny ellipsoidal nanoparticles. The findings are practical to the protocol of non-uniform etching of nanoobjects and provide the useful design tool for the device fabrication at nanoscale.

Keywords

  • polystyrene
  • nanosphere array
  • self-assembly
access type Open Access

One dimensionality and spectroscopy in carbon nanotubes

Published Online: 29 Aug 2013
Page range: 338 - 342

Abstract

Abstract

Unlike regular three-dimensional solids two of a nanotube dimensions are confined and quantized. Bulk samples consist of irregular networks of merging and splitting bundles of parallel tubes. On a local scale, nanotubes are at the same time one-dimensional crystals and two-dimensional quantum rings. They have attracted extensive studies on individual aspects in their electronic and optical properties [1]. The current contribution aims at bridging the fundamental physical concepts behind carbon nanotubes to their unique spectroscopic signatures in optical absorption, luminescence, Raman and electron energy loss spectroscopy. The aim is not to compete with the local depth of a focused review, but to briefly convey the physical concept and related spectroscopic signatures of one-dimensionality. Indirect signatures are the manifold appearances of van Hove singularities in their optical transitions. Direct probes of one-dimensionality unveil the confined momentum space, which manifests in the distinction of localized and propagating excitations.

Keywords

  • carbon nanotube
  • spectroscopy
  • one-dimensionality
access type Open Access

Synthesis of nanocrystalline Ni/Ce-YSZ powder via a polymerization route

Published Online: 29 Aug 2013
Page range: 343 - 349

Abstract

Abstract

Pechini process was used for preparation of three kinds of nanocrystalline powders of yttria-stabilized zirconia (YSZ): doped with 1.5 mol% nickel oxide, doped with 15 mol% ceria, and doped with 1.5 mol% nickel oxide plus 15 mol% ceria. Zirconium chloride, yttrium nitrate, cerium nitrate, nickel nitrate, citric acid and ethylene glycol were polymerized at 80 °C to produce a gel. XRD, SEM and TEM analyses were used to investigate the crystalline phases and microstructures of obtained compounds. The results of XRD revealed the formation of nanocrystalline powder at 900 °C. Morphology of the powder calcined at 900 °C, examined with a scanning electron microscope, showed that the presence of nickel and cerium inhibited the grain growth in the system. The average crystallite size of the material doped with nickel oxide (9.33 nm) was bigger than the one doped with cerium oxide (9.29 nm), while the YSZ doping with the two oxides simultaneously promoted the grain growth with crystallite size of 11.37 nm. Yttria-stabilized zirconia powder with a mean crystallite size of 9.997 nm was prepared successfully by this method.

Keywords

  • yttria-stabilized zirconia
  • Pechini method
  • nanocrystalline Ni/Ce-YSZ powder
  • dopant
access type Open Access

Formation of silicon oxide nanowires in nanomaterial synthesis experiments based on the usage of tube furnace

Published Online: 29 Aug 2013
Page range: 350 - 356

Abstract

Abstract

In an effort to synthesize doped ZnO nanowires, SiOx nanowires were obtained accidently. In the experiment, mixed powders containing chemicals such as ZnO, graphite, Ga2O3, and In2O3 were placed in the center of a tube furnace, where the temperature was set to 1200 °C and the vacuum was approximately 27 Pa. Silicon wafers were placed around the vicinity of the furnace exit to collect the expected nanomaterials. After prolonged heating, grey layers were found on top of one wafer located inside the furnace. The layer showed no adhesion to the substrate. Characterization by using Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Energy Dispersive X-ray Spectroscopy (EDS) revealed that this layer consisted of SiOx nanowires. Formation of Si-containing liquid drop and the subsequent growth of SiOx nanowires out of it are suggested as the growth mechanism.

Keywords

  • silicon
  • oxide
  • nanowires
access type Open Access

Quantum chemical computational studies on bis-thiourea zinc acetate

Published Online: 29 Aug 2013
Page range: 357 - 371

Abstract

Abstract

In this study, quantum chemical calculations of vibrational spectra, Raman spectra, electronic properties (total energy, dipole moment, electronegativity, chemical hardness and softness), Mulliken atomic charges and thermodynamic parameters of bis-thiourea zinc acetate (BTZA) have been performed using Gaussian 09 program. Additionally, nonlinear optical (NLO), conformational, natural bond orbital (NBO) analyses of BTZA have been carried out using the same program. The structural and spectroscopic data of the molecule in the ground state have been calculated using Hartree-Fock (HF) and density functional method (DFT/B3LYP) with the 6-311++G(d,p) basis set. In addition, the molecular frontier orbital energies (HOMO, HOMO-1, LUMO and LUMO+1) of the title compound have been calculated at the HF and B3LYP levels. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Finally, the calculated results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the experimental ones.

Keywords

  • bis-thiourea zinc acetate (BTZA)
  • IR and NMR spectra
  • DFT and HF calculations
  • NLO and NBO analyses, conformational analysis
access type Open Access

Preparation of TiO2/Al-MCM-41 mesoporous materials from coal-series kaolin and photodegradation of methyl orange

Published Online: 29 Aug 2013
Page range: 372 - 377

Abstract

Abstract

TiO2/Al-MCM-41 mesoporous materials were prepared via sol-gel method by loading titania onto Al-MCM-41 mesoporous molecular sieve by hydrothermal treatment from coal-series kaolin as raw material. The TiO2/Al-MCM-41 mesoporous materials were characterized by XRD, FT-IR, HRTEM, N2 adsorption-desorption and the photocatalytic degradation of methyl orange solution under visible light irradiation. The results showed that the TiO2/Al-MCM-41 mesoporous materials possessed a high surface area of 369.9–751.3 m2/g and a homogeneous pore diameters of 2.3–2.8 nm. The titania crystalline phase was anatase, and the particles size of TiO2 increased with TiO2 content. The Al-MCM-41 mesoporous materials exhibited excellent photodegradation activity under visible-light irradiation for methyl orange.

Keywords

  • coal-series kaolin
  • Al-MCM-41
  • TiO2
  • photocatalytic degradation
access type Open Access

Performance of dye-sensitized solar cell fabricated using titania nanoparticles calcined at different temperatures

Published Online: 29 Aug 2013
Page range: 378 - 385

Abstract

Abstract

Synthesis of titania (TiO2) nanoparticles by sol-gel method and their calcination at different temperatures, viz 450 °C, 550 °C and 650 °C (defined as T450, T550 and T650) has been done. Structural analysis indicates that the T450 sample possesses anatase phase. The phase transformation to rutile starts occurring at T550, and, on increasing the calcination temperature, the crystallization and percentage of rutile phase increases. As the temperature increases from 450 to 650 °C, the crystallite size increases by about a factor of two from 11.5 to 20.2 nm. From SEM micrographs, T550 electrode has been found to have appropriate aggregation, which led to enhanced dye desorption, as compared to T450 and T650 based electrodes. TEM images of the synthesized nanoparticles reveal that the particle size increases from 7 to 28 nm on increasing the calcination temperature from 450 to 650 °C. From the photoluminescence and Fourier transform infrared studies, it has been concluded that the surface OH− groups are reduced on calcination, which affects the electron injection efficiency. The dye sensitized solar cell, fabricated using T550 sample, having a ratio of anatase/rutile 89:11, has been found to achieve the highest conversion efficiency.

Keywords

  • DSSC
  • TiO2 nanoparticles
  • calcination
  • anatase/rutile mixture
access type Open Access

Glycerol-assisted solution combustion synthesis of improved LiMn2O4

Published Online: 29 Aug 2013
Page range: 386 - 390

Abstract

Abstract

Spinel LiMn2O4 has been synthesized by a glycerol-assisted combustion synthesis method. The phase composition and morphologies of the compound were ascertained by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical characterization was performed by using CR2032 coin-type cell. XRD analysis indicates that single phase spinel LiMn2O4 with good crystallinity has been obtained as a result of 5 h treatment at 600 °C. SEM investigation indicates that the average particle size of the sample is 200 nm. The initial discharge specific capacity of the LiMn2O4 is 123 mAh/g at a current density of 30 mA/g. When the current density increased to 300 mA/g, the LiMn2O4 offered a discharge specific capacity of 86 mAh/g. Compared with the LiMn2O4 prepared by a conventional solution combustion synthesis method at the same temperature, the prepared LiMn2O4 possesses higher purity, better crystallinity and more uniformly dispersed particles. Moreover, the initial discharge specific capacity, rate capability and cycling performance of the prepared LiMn2O4 are significantly improved.

Keywords

  • lithium ion batteries
  • cathode
  • spinel
  • solution combustion synthesis
access type Open Access

Optical and surface morphological studies on CuPcOC8 thin films prepared by physical vapour deposition

Published Online: 29 Aug 2013
Page range: 391 - 396

Abstract

Abstract

2,3,9,10,16,17,23,24-copper octakis (octyloxy) phthalocyanine (CuPcOC8) thin films deposited at room temperature have exhibited a change in their surface morphology with the post deposition annealing temperature under normal atmosphere.These films have been characterised by optical absorption also. SEM images have shown densely packed nano particles and nano-rod like structures on the substrates annealed at different temperatures. The optical transition was found to be direct allowed and the direct energy gap changed with the annealing temperature. The results of optical and surface morphological studies on CuPcOC8 have been discussed.

Keywords

  • copper octakis (octyloxy) phthalocyanine
  • absorption spectra
  • annealing temperature
  • optical band gap
  • Davydov splitting
  • surface morphology
access type Open Access

Bulk ZnO nanorod assemblies fabricated by spin coating of organo-precursor gels on CuO nanowires

Published Online: 29 Aug 2013
Page range: 397 - 403

Abstract

Abstract

Bulk ZnO nanorod assemblies have been successfully fabricated on CuO nanowires through spin coating of organoprecursor gels. A thin film of CuO nanowires was first generated by direct heating of a metallic Cu-foil at 500 °C in an air atmosphere. A stable colloidal organo-precursor sol synthesized by dissolving equimolar zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol was subsequently repeatedly deposited onto the CuO nanowires by spin coating. The formation of ZnO nanorod assemblies was controlled by varying the number of coatings. The average diameter of the ZnO rods was determined to be ∼600 nm.

Keywords

  • ZnO
  • CuO
  • sol-gel
  • Raman spectrum
  • SEM
access type Open Access

Preparation and properties of low temperature sintered CaO-B2O3-SiO2 microwave dielectric ceramics using the solid-state reaction

Published Online: 29 Aug 2013
Page range: 404 - 409

Abstract

Abstract

The LTCC CaO-B2O3-SiO2 (CBS) ceramics were synthesized via solid-state reaction process without any sintering aid. The effects of different sintering temperatures and B2O3 content on the microwave and mechanical properties were investigated. The results show that the best sintering temperature is around 950 °C and increasing amount of B2O3 promotes the crystallization of CaB2O4 enhancing the flexure strength of the CBS ceramics. However, the dielectric and mechanical properties deteriorated rapidly while the amount of B2O3 exceeded 25 wt.%. The sample with 20.5 wt.% B2O3 sintered at 950 °C had the best properties with ɛ r = 6.06; tanδ = 0.0015 (1 MHz) and a high flexure strength σ f > 180 MPa.

Keywords

  • solid state reaction
  • LTCC
  • CaO-B2O3-SiO2
  • flexural strength
  • microwave properties
access type Open Access

Phase, microstructure and dielectric properties of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics prepared by sol-gel technique

Published Online: 29 Aug 2013
Page range: 410 - 414

Abstract

Abstract

0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics were fabricated by sol-gel technique. The XRD results revealed the formation of a single phase perovskite structured Bi0.5Na0.5TiO3-BaTiO3 at 600 °C. The SEM images showed dense microstructure and the optimum density of the ceramics sintered at 1100 °C was 5.2 g/cm3. The saturation polarization (Ps) was found to be increased with increasing temperature while the remnant polarization (Pr) was found to be increased gradually and then decreased abruptly near 85 °C, which could be attributed to the phase transformation. The coercive electric field (Ec) was found to be decreased gradually with increasing temperature. The maximum value of dielectric constant (ɛ r) at room temperature was 800 and dielectric loss at 1 MHz was 0.07.

Keywords

  • lead free
  • perovskite
  • sol-gel
  • FT-IR
  • ferroelectrics
access type Open Access

Mechanical and tribological properties of gradient a-C:H/Ti coatings

Published Online: 29 Aug 2013
Page range: 415 - 423

Abstract

Abstract

The unusual combination of high hardness and very low friction coefficient are the most attractive tribological parameters of DLC (diamond-like carbon) layers. However, their usability is strongly restricted by the limited thickness due to high residual stress. The main goal of the presented work was to obtain thick, wear resistant and well adherent DLC layers while keeping their perfect friction parameters. As a proposed solution a Ti-TixCy gradient layer was manufactured as the adhesion improving interlayer followed by a thick diamond-like carbon film. This kind of combination seems to be very promising for many applications, where dry friction conditions for highly loaded elements can be observed. Both layers were obtained in one process using a hybrid deposition system combining PVD and CVD techniques in one reaction chamber. The investigation was performed on nitrided samples made from X53CrMnNiN21-9 valve steel. Structural features, surface topography, tribological and mechanical properties of manufactured layers were evaluated. The results of the investigation confirmed that the presented deposition technique makes it possible to manufacture thick and well adherent carbon layers with high hardness and very good tribological parameters. Preliminary investigation results prove the possibility of application of presented technology in automotive industry.

Keywords

  • carbon layers
  • friction
  • adhesion
  • wear resistance
access type Open Access

Optimization of sol-gel technique for coating of metallic substrates by hydroxyapatite using the Taguchi method

Published Online: 29 Aug 2013
Page range: 424 - 433

Abstract

Abstract

In this study, the Taguchi method of design of experiment (DOE) was used to optimize the hydroxyapatite (HA) coatings on various metallic substrates deposited by sol-gel dip-coating technique. The experimental design consisted of five factors including substrate material (A), surface preparation of substrate (B), dipping/withdrawal speed (C), number of layers (D), and calcination temperature (E) with three levels of each factor. An orthogonal array of L18 type with mixed levels of the control factors was utilized. The image processing of the micrographs of the coatings was conducted to determine the percentage of coated area (PCA). Chemical and phase composition of HA coatings were studied by XRD, FT-IR, SEM, and EDS techniques. The analysis of variance (ANOVA) indicated that the PCA of HA coatings was significantly affected by the calcination temperature. The optimum conditions from signal-to-noise (S/N) ratio analysis were A: pure Ti, B: polishing and etching for 24 h, C: 50 cm min−1, D: 1, and E: 300 °C. In the confirmation experiment using the optimum conditions, the HA coating with high PCA of 98.5 % was obtained.

Keywords

  • hydroxyapatite
  • sol-gel
  • coating
  • Taguchi method
  • image processing
access type Open Access

Investigation of physicochemical and tribological properties of transparent oxide semiconducting thin films based on Ti-V oxides

Published Online: 29 Aug 2013
Page range: 434 - 445

Abstract

Abstract

In this paper investigations of structural and optical properties of nanocrystalline Ti-V oxide thin films are described. The films were deposited onto Corning 7059 glass using a modified reactive magnetron sputtering method. Structural investigations of prepared Ti-V oxides with vanadium addition of 19 at. % revealed amorphous structure, while incorporation of 21 and 23 at. % of vanadium resulted in V2O5 formation with crystallites sizes of 12.7 and 32.4 nm, respectively. All prepared thin films belong to transparent oxide semiconductors due to their high transmission level of ca. 60–75 % in the visible light range, and resistivity in the range of 3.3·102–1.4·105 Ωcm. Additionally, wettability and hardness tests were performed in order to evaluate the usefulness of the films for functional coatings.

Keywords

  • Ti-V oxide thin films
  • transparent oxide semiconductors
  • magnetron sputtering
  • tribological properties
access type Open Access

Analysis of MIS equivalent electrical circuit of Au/Pd/Ti-SiO2-GaAs structure based on DLTS measurements

Published Online: 29 Aug 2013
Page range: 446 - 453

Abstract

Abstract

In this paper MIS equivalent electrical circuit of Au/Pd/Ti-SiO2-GaAs has been analyzed by a comparison of the results obtained from admittance and DLTS spectroscopy. Two groups of peaks with different magnitude and different gate voltage dependence have been observed in DLTS and admittance spectra. Based on the analysis of the peaks behavior, it has been concluded that they are associated with the response of bulk traps and interface states, respectively. In order to characterize bulk traps and interface states responsible for the occurrence of two groups of peaks in normalized conductance spectra we have used the equivalent circuit with two CPE-R branches. The time constant values estimated for both peaks from admittance analysis have been compared with the time constant determined from DLTS analysis. Some discrepancies have been noted between the time constants obtained for interface states whereas the time constants for bulk traps were compatible. It has been also demonstrated that when conductance peaks overlap, the admittance experimental data can be fitted by the equivalent electrical model with only one CPE-R branch. However, in this case incomplete information about the analyzed process has been obtained despite the fact that all model validity criteria can be fulfilled and the model seems to be correct.

Keywords

  • MIS structure
  • deep levels
  • interface states
  • admittance spectroscopy
  • DLTS
access type Open Access

Effect of working pressure on the structural, optical and electrical properties of titanium-gallium co-doped zinc oxide thin films

Published Online: 29 Aug 2013
Page range: 454 - 461

Abstract

Abstract

The transparent conducting titanium-gallium co-doped zinc oxide (TGZO) thin films were grown on glass substrates by radio-frequency magnetron sputtering technique. The effects of working pressure on the structural, optical and electrical properties of the films were investigated. The results show that the deposited films are polycrystalline with a hexagonal wurtzite structure and highly textured along the c-axis perpendicular to the substrate. The TGZO film prepared at the working pressure of 0.4 Pa exhibits the best crystallinity, the maximal grain size, the highest transmittance, the lowest resistivity and the highest figure of merit. The optical constants of the films were calculated using the method of optical spectrum fitting. The dispersion behavior of the films was studied by the single-electronic oscillator dispersion model. The oscillator parameters and optical bandgaps were determined. The results demonstrate that the microstructure and optoelectrical properties of the TGZO films are dependent on the working pressure.

Keywords

  • transparent conducting oxide
  • ZnO thin films
  • sputtering
  • optoelectrical properties
access type Open Access

Controlled mechanochemical synthesis and properties of a selected perovskite-type electroceramics

Published Online: 29 Aug 2013
Page range: 462 - 470

Abstract

Abstract

This paper presents mechanochemical synthesis as an alternative to the traditional high-temperature synthesis of advanced electrotechnical ceramic materials with a perovskite-type structure. The reaction conditions for high-energy ball milling, e.g. reaction environment, energy of milling and additives to BaTiO3 such as metallic iron or zirconia from the exfoliation of the milling vessel and grinding media are discussed.

Keywords

  • mechanochemistry
  • high-energy ball milling
  • perovskites
  • ferroelectric ceramics
  • barium titanate
access type Open Access

Investigation on multiferroic properties of BiFeO3 ceramics

Published Online: 29 Aug 2013
Page range: 471 - 475

Abstract

Abstract

BiFeO3 polycrystalline ceramics was prepared by solid-state reaction method and its structural, optical and magnetic properties were investigated. BiFeO3 was synthesized in a wide range of temperature (825–880 °C) and a well crystalline phase was obtained at a sintering temperature of 870 °C. X-ray diffraction patterns of the samples were recorded and analyzed for the confirmation of crystal structure and the determination of the lattice parameters. The average grain size of the samples was found to be between 1–2 μm. The determined value of direct bandgap of BiFeO3 ceramics was found to be 2.72 eV. The linear behavior of M-H curve at room temperature confirmed antiferromagetic properties of the BiFeO3 (BFO). S shaped M-H curve was obtained at a temperature of 5 K. In the whole temperature measurement range (5–300 K) of M-T, no anomalies were observed due to high Curie temperature and Neel temperature of the BiFeO3.

Keywords

  • BiFeO3 ceramics
  • multiferroics
  • SQUID
access type Open Access

Silicon carbonitride layers deposited on titanium and polyurethane by PACVD method

Published Online: 29 Aug 2013
Page range: 476 - 483

Abstract

Abstract

This work reports the results concerning formation and tribological properties of SiCxNy(H) layers deposited on Ti Grade 2 and polyurethane foil. Depending on the substrate, two variants of PACVD were used. The SiCxNy(H) layers on titanium were deposited with application of MWCVD (2.45 GHz, 2 kW). The layers on polyurethane were deposited using RFCVD (13.56 MHz, 400 W). Good adhesion between the SiCxNy(H) layers and polymeric foil was achieved by formation of a transitional C:N:H layer and incorporating Si gradient into the structure of the SiCxNy(H) layer. The chemical composition of the layers was tailored by precise control of the gaseous precursors ratios: [SiH4]/[NH3], [SIH4]/[NH3]/[CH4], [SiH4]/[CH4] or [SiH4]/[N2]/[CH4]. The structure and chemical composition of the obtained layers were subjected to further studies (FTIR, SEM/EDS). The roughness, friction coefficient and wear resistance were also measured. The results show that SiCxNy(H) layers offer attractive tribological properties which make them good candidates for various applications, including biomedical devices.

Keywords

  • PACVD
  • silicon carbonitride layers
  • tribology

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