Showing papers in "Journal of Materials Science: Materials in Electronics in 2013"

A review on fabrication, sensing mechanisms and performance of metal oxide gas sensors

Abstract: Processes for developing layers onto a substrate as the active component of metal oxide gas sensors are presented and other promising alternatives as thermal spraying are also proposed. In order to understand the electrochemical mechanisms involved, the relationship between surface reactions and the electrical signal is presented as determined by the influence of three main factors: the receptor function, the transducer function and the approachability. Distinct aspects for each key-step are discussed with the aim of achieving a better comprehension of the overall system. Performances of the most operated metal oxides and target-gases in distinct application markets are also reviewed.

Role of annealing temperature on microstructural and electro-optical properties of ITO films produced by sputtering

Abstract: This study probes the effect of annealing temperature on electrical, optical and microstructural properties of indium tin oxide (ITO) films deposited onto soda lime glass substrates by conventional direct current (DC) magnetron reactive sputtering technique at 100 watt using an ITO ceramic target (In2O3:SnO2, 90:10 wt%) in argon atmosphere at room temperature. The films obtained are exposed to the calcination process at different temperature up to 700 °C. X–ray diffractometer (XRD), ultra violet-visible spectrometer (UV–vis) and atomic force microscopy (AFM) measurements are performed to characterize the samples. Moreover, phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. The results obtained show that all the properties depend strongly on the annealing temperature. XRD results indicate that all the samples produced contain the In2O3 phase only and exhibit the polycrystalline and cubic bixbite structure with more intensity of diffraction lines with increasing the annealing temperature until 400 °C; in fact the strongest intensity of (222) peak is obtained for the sample annealed at 400 °C, meaning that the sample has the greatest ratio I222/I400 and the maximum grain size (54 nm). As for the AFM results, the sample prepared at 400 °C has the best microstructure with the lower surface roughness. Additionally, the transmittance measurements illustrate that the amplitude of interference oscillation is in the range from 78 (for the film annealed at 400 °C) to 93 % (for the film annealed at 100 °C). The refractive index, packing density, porosity and optical band gap of the ITO thin films are also evaluated from the transmittance spectra. According to the results, the film annealed at 400 °C obtains the better optical properties due to the high refractive index while the film produced at 100 °C exhibits much better photoactivity than the other films as a result of the large optical energy band gap.

Structural and optical properties of Cu 2 SnS 3 and Cu 3 SnS 4 thin films by successive ionic layer adsorption and reaction

Abstract: Thin films of Cu2SnS3 and Cu3SnS4 were obtained by sulfurizing (Cu, Sn)S structured precursors prepared by successive ionic layer absorption and reaction method. The results of energy dispersive spectroscopy (EDS) indicate that some loss in Sn with increasing sulfurization temperature. For the sulfurization temperatures of 380, 400 and 500 °C, tetragonal (I-42m) Cu2SnS3, cubic (F-43m) Cu2SnS3 and tetragonal (I-42m) Cu3SnS4 were formed, respectively. The combination of X-ray diffraction (XRD) results and Raman spectroscopy reveals that there are small Cu2−x S phase existing in the CTS thin films (400 and 500 °C). Scanning electron microscopy was used to study the morphology of the layers. The ternary compounds present a high optical absorption coefficient (>104 cm−1). The band gap energy (E g ) of the CTS thin films is estimated by reflection spectroscopy. The ternary compounds present a high optical absorption coefficient (>104 cm−1). The estimated band gap energy (E g ) is 1.05 eV for tetragonal (I-42m) Cu2SnS3, 1.19 eV for cubic (F-43m) Cu2SnS3, and 1.22 eV for tetragonal (I-42m) Cu3SnS4.

Reliability behavior of lead-free solder joints in electronic components

Abstract: With more consumer products moving towards environmentally friendly packaging, making solder Pb-free has become an urgent task for electronics assemblies. Solder joints are responsible for both electrical and mechanical connections. Solder joint does not have adequate ductility to ensure the repeated relative displacements due to the mismatch between expansion coefficients of the chip carrier and the circuit board. Materials behavior of solder joints involves a creep–fatigue interaction, making it a poor material for mechanical connections. The reliability of solder joints of electronics components has been found playing a more important role in service for microelectronics components and micro-electro-mechanical systems. So many researchers in the world investigated reliability of solder joints based on finite element simulation and experiments about the electronics devices, such as CR, QFP, QFN, PLCC, BGA, CSP, FCBGA and CCGA, which were reviewed systematically and extensively. Synchronously the investigation on reliability of solder joints was improved further with the high-speed development of lead-free electronic packaging, especially the constitutive equations and the fatigue life prediction equations. In this paper, the application and research status of constitutive equations and fatigue life prediction equations were reviewed, which provide theoretic guide for the reliability of lead-free solder joints.

Broadband electromagnetic shielding and dielectric properties of polyaniline-stannous oxide composites

Abstract: Conducting polyaniline-stannous oxide (PAni-SnO) composites were synthesized by the in situ polymerization of aniline in the presence of SnO The composites formed were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) As there is a greater need for materials with electromagnetic interference (EMI) shielding properties over a large operating frequency band, the present study highlights the dielectric and EMI shielding response of PAni-SnO composites in the microwave frequency range from 8 to 18 GHz (X and Ku bands) All the computations were based on microwave scattering parameters measured by transmission line waveguide technique The EMI shielding effectiveness (EMI SE), return loss, microwave absorption and dielectric properties of the PAni-SnO composites were evaluated for various wt% of SnO (10, 20, 30, 40 and 50 wt%) in PAni In X-band, the composites exhibits EMI SE in the range −18 to −23 dB, with microwave absorbance of 70–83 % and in the Ku-band, the composites exhibits EMI SE values of −175 to −225 dB with 67–85 % absorbance Our investigations reveal that the PAni-SnO composites are potential candidates for EMI shielding applications for both the X and Ku bands

Polyaniline–CuO hybrid nanocomposites: synthesis, structural, morphological, optical and electrical transport studies

Abstract: Thin films of semiconducting polyaniline (PANi) nanofibers reinforced with copper oxide (CuO) nanoparticles (NPs) were prepared on glass substrate using spin coating technique. Polyaniline (PANi) have been synthesized by chemical oxidative polymerization method with monomer aniline in presence of (NH4)2S2O8 as an oxidant at 0 °C. The copper oxide (CuO) nanoparticles were synthesized by sol–gel method. Physical properties of nanocomposite (NCs) films were characterized and analyzed by X-ray diffraction, Scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy, Two probe resistivity measurement technique and Thermo-emf measurement. Structural analysis showed that the crystal structure of CuO is not disturbed in the PANi–CuO hybrid nanocomposite. Surface morphology study shows the uniform distribution of CuO nanoparticles in PANi matrix. FTIR and UV–Visible studies confirm the presence of polyaniline in emeraldine base form in the composites and suggest incorporation of CuO in polymer. Two probe electrical resistivity measurements of nanocomposites (NCs) film revealed that the resistivity of PANi increases with increasing content of CuO NPs.

Optical and magnetic properties of Cu-doped ZnO nanoparticles

Abstract: Cu-doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Cu:Zn atomic ratio from 0 to 5 % The synthesis process was based on the hydrolysis of zinc acetate dehydrate and copper acetate tetrahydrate heated under reflux to 65 °C using methanol as a solvent X-ray diffraction (XRD) analysis reveals that the Cu-doped ZnO crystallize in a wurtzite structure with a change of crystal size from 12 nm for undoped ZnO to 5 nm for Cu-doped ZnO These nano size crystallites of Cu doped ZnO self-organized into microspheres The XRD patterns, Scanning electron microscopy and transmission electron microscopy micrographs of doping of Cu in ZnO confirmed the formation of microspheres and indicated that the Cu2+ is successfully substituted into the ZnO host structure of the Zn2+ site Cu doping shifts the absorption onset to blue from 373 to 350 nm, indicating an increase in the band gap from 333 to 355 eV A relative increase in the intensity of the deep trap emission of Cu-doped ZnO is observed when increasing the concentration of Cu Magnetic measurements indicate that Cu-doped ZnO samples are ferromagnetic at room temperature except pure ZnO

Thermal analysis and mechanical properties of Sn–1.0Ag–0.5Cu solder alloy after modification with SiC nano-sized particles

Abstract: The size and morphology of intermetallic compounds (IMCs) of Sn–1.0Ag–0.5Cu (SAC105) solder alloys can have a significant influence on the mechanical strength of solder joints. The aim of the present study is to investigate the influence of SiC nano-particles addition on the microstructure, thermal behavior, and corresponding mechanical properties of SAC(105) solder alloys. Results show that the addition of SiC nanoparticles into the SAC(105) alloy melt prompts the formation of primary β-Sn phase with small sub-grain size in the solidified structure. The SiC nanoparticles can offer an additional nucleation sites for the formation of refined Ag3Sn and Cu6Sn5 IMCs. The hard SiC particles and refined IMCs with small spacing could obstruct the dislocation slipping and thus, lead to a strong dispersion strengthening mechanism in the composite solder. As a result, the composite SAC(105)/SiC solder displayed a higher ultimate tensile strength and 0.2 % yield strength (0.2 %YS) than that of plain SAC(105) solder. The addition of SiC nano-sized particles can also effectively reduce the undercooling and pasty range, while the melting temperature is maintained at the SAC(105) level, indicating that the novel composite solder is fit for existing soldering process.

Microstructural stability of Ag sinter joining in thermal cycling

Abstract: As a heat-resistant die attach technology processed at low temperatures, three Ag filler-based sinter joining materials have been proposed. Among these, Ag flake pastes exhibited the greatest potential. Joining was carried out by sintering Ag nanoparticles/flakes in air at 200 °C for 60 min. All of the joined samples survived up to 1,000 thermal cycles in a temperature range from −40 to 180/250 °C with a 30 min dwell time. In particular, the joining strengths with the Ag micron and, Ag nano-thick flake pastes maintained excellent strength. Neither thermal fatigue cracks nor large voids were observed in the Ag sintered layers. Thus, low-temperature and low-pressure sinter joining with Ag flakes is expected to have an application in high power semiconductor devices for ultra-high temperature operation.

Review on microstructure evolution in Sn–Ag–Cu solders and its effect on mechanical integrity of solder joints

Abstract: The use of Pb-bearing solders in electronic assemblies is avoided in many countries due to the inherent toxicity and environmental risks associated with lead. Although a number of “Pb-free” alloys have been invented, none of them meet all the standards generally satisfied by a conventional Pb–Sn alloy. A large number of reliability problems still exist with lead free solder joints. Solder joint reliability depends on mechanical strength, fatigue resistance, hardness, coefficient of thermal expansion which are influenced by the microstructure, type and morphology of inter metallic compounds (IMC). In recent years, Sn rich solders have been considered as suitable replacement for Pb bearing solders. The objective of this review is to study the evolution of microstructural phases in commonly used lead free xSn–yAg–zCu solders and the various factors such as substrate, minor alloying, mechanical and thermo-mechanical strains which affect the microstructure. A complete understanding of the mechanisms that determine the formation and growth of interfacial IMCs is essential for developing solder joints with high reliability. The data available in the open literature have been reviewed and discussed.

Thermal fatigue of Ag flake sintering die-attachment for Si/SiC power devices

Abstract: Emerging SiC power semiconductor devices are expected to work under the high temperature condition of 250–300 °C while the operation of Si devices is limited up to 180 °C. The die-bonding materials for emerging SiC power devices hence need to have sufficient capability in such extreme operating environments. In this study, we investigated the thermomechanical reliability of the die-attach technology using Ag flake paste, which can be processed by low-temperature and low-pressure sintering. The Ag flakes start to sinter immediately after the organic dispersant layer is removed from the flake surface at 160 °C, and die-bonding consequently becomes possible. The tested Si die-attachments joining with the paste maintained high strength (23 MPa) up to 1,000 thermal cycles from −40 to 180 °C. The stable microstructures without crack and no interfacial debonding assure the reliability of the Ag flake paste die-attach of Si. SiC die-attachments also maintained their high strength (24 MPa) up to 1,000 cycles of −40 and 250 °C, though a slight degradation appeared after 1,000 cycles. The debondings at the sintered Ag flake paste layer/SiC wafer interface were affected to the joining strength with the Ag flake paste. The obtained results indicate that our Ag flake paste die-attach can be applied to both Si and SiC power devices capable of high temperature operations.

A study of structural, ferroelectric, ferromagnetic, dielectric properties of NiFe2O4–BaTiO3 multiferroic composites

Abstract: The mixed spinel-perovskite multiferroic composites of xNiFe2O4-(1 − x)BaTiO3 (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) have been prepared by sol–gel method. The structure and morphology of the composites were examined by means of X-ray diffraction and transmission electron microscope. High-resolution transmission electron microscope image indicates a clear view of ferrite and ferroelectric phase. Moreover, we observed a fine interface between the two phases, where the coupling effect of ferrite and ferroelectric phase happened. The composites show excellent ferromagnetic and ferroelectric properties. The saturation magnetization (Ms) reaches to 24.139 emu/g for x = 0.6 at room temperature, the magnetization is about 2.37 emu/g for x = 0.6 when the temperature decreases to 90 k, and the polarization reaches to 3.75 μC/cm2 for x = 0.1. Frequency dependent variations of dielectric constant and loss tangent for xNiFe2O4-(1 − x)BaTiO3 were studied in detail.

Phase transformation and grain orientation of Cu–Sn intermetallic compounds during low temperature bonding process

Abstract: The interconnection lengths between the stacked chips in three-dimensional (3D) package are a few of microns, hence the solder joints for the stacked chips joining are mainly composed by intermetallic compounds (IMCs) after reflow processes. To evaluate the phase transformation of Cu–Sn IMCs in the small interconnection joints, the Cu/Sn/Cu structures were bonded with different bonding times at various temperatures in argon gas atmosphere in this study. Scanning electron microscope and energy-dispersive X-ray were used to observe the joint interfacial microstructures and electron back scattering diffraction was used to identify the grain orientations in the joints. Scalloped Cu6Sn5 grains were found to be initially formed on the Cu substrates at the early stage. A lot of small Cu6Sn5 grains formed on the surfaces of the big scallop Cu6Sn5 grains. Those small grains gradually grew up to merge into the big Cu6Sn5 grains. With longer reflow time, the Cu6Sn5 grains initiated at both side of Cu substrate continued to grow up and started to contact with each other. Meantime, the different Cu6Sn5 grains with different grain orientations have merged into some bigger grains. The Cu3Sn grains formed between Cu6Sn5 layers and Cu substrates have further developed at the expense of the depletion of Cu6Sn5. Most of columnar Cu3Sn grains were vertical to Cu substrate surface and their grain sizes were 1–5 μm. With 960 min at 300 °C, the pure Cu3Sn IMC joint has formed. The Cu3Sn grains in IMC joint had different grain orientations and a contact line was observed in the middle of the Cu3Sn IMC joint.

Effects of annealing on thermoelectric properties of Sb2Te3 thin films prepared by radio frequency magnetron sputtering

Abstract: Antimony telluride (Sb2Te3) thin films were deposited on silicon substrates at room temperature (300 K) by radio frequency magnetron sputtering method. The effects of annealing in N2 atmosphere on their thermoelectric properties were investigated. The microstructure and composition of these films were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. Both of the Seebeck coefficient and Hall coefficient measurement showed that the prepared Sb2Te3 thin films were p-type semiconductor materials. By optimizing the annealing temperature, the power factor achieved a maximum value of 18.02 μW cm−1 K−2 when the annealing temperature was increased to 523 K for 6 h with a maximum electrical conductivity (1.17 × 103 S/cm) and moderate Seebeck coefficient (123.9 μV/K).

Enhancement in the electrical and antibacterial properties of sprayed ZnO films by simultaneous doping of Mg and F

Abstract: Undoped and Doubly (Magnesium + Fluorine) doped zinc oxide (ZnO:Mg:F) thin films with different Mg doping levels (4, 8, 12 and 16 at.%) and constant F doping level (20 at.%) were fabricated by employing a simplified spray pyrolysis technique. The antibacterial and certain physical properties of the films were studied as a function of Mg doping level. All the films exhibited hexagonal wurtzite structure with preferential orientation along the (002) plane. A lesser electrical resistivity was achieved in the present study than earlier reports of ZnO:Mg films thanks to the simultaneous doping of F with Mg in ZnO films. From the optical studies, it was observed that, all the films showed good transparency (≈85 %) with significant enhancement in the optical band gap with Mg doping level. The obtained PL spectra were well corroborated with the structural and optical studies. Further, it was also found that the antibacterial activity of doubly doped ZnO films was enhanced remarkably by the increasing incorporation of Mg concentration.

Chemical mechanical polishing (CMP) of on-axis Si-face 6H-SiC wafer for obtaining atomically flat defect-free surface

Abstract: Due to its high mechanical hardness and excellent chemical inertness, SiC single-crystal wafer is extremely difficult to realize effectively removed total planarization. Owing to crystalline polarity and anisotropy, material removal rate (MRR) on Si-face (0001) of SiC wafer is significantly lower than C-face (000 $$ \bar{1} $$ ) for a defect-free surface. In the paper, the slurry containing hydrogen peroxide (H2O2), potassium hydroxide and abrasive colloidal silica, is introduced to chemical mechanical polishing (CMP) of on-axis Si-face 6H-SiC wafer, resulting in acquiring high MRR with 105 nm/h, and atomically flat defect-free surface with atomic step-terrace structure and roughness of 0.0667 nm by atomic force microscope (AFM), in order to satisfy further demands of electronic device fabrication towards substrate wafer performance. The effects of the three ingredients in the slurry towards MRR of SiC wafer, polished surface quality and coefficient of friction in polishing process are studied. Optical microscope, optical interferometry profiler and AFM are used to observe the polished surface. In addition, the CMP removal mechanism of SiC wafer and the formation of ultra-smooth surface are discussed.

Formation of Cu2SnS3 thin film by the heat treatment of electrodeposited SnS-Cu layers

Abstract: Thin films of copper tin sulfide (Cu2SnS3) were obtained by sulfurizing a stack of thin layers of Cu and SnS in nitrogen atmosphere. The film stack was obtained by the sequential electrodeposition of SnS and Cu. The Cu2SnS3 film was characterized for structural, morphological, composition, optical, spectroscopic, and electrical properties. The optimum condition for the formation of Cu2SnS3 was developed after testing different sulfurization temperatures. The films were polycrystalline with monoclinic structure which was confirmed by Raman and transmission electron microscopy analysis. The interplanar spacings estimated from the high resolution transmission electron microscopy images are 2.74, 2.19, and 2.06 A. The average crystallite size is 13 nm, and the band gap of the film is in the range of 1 eV. The surface chemical composition determined by X-ray photoelectron spectroscopy showed the Cu:Sn:S ratio as 1.9:1:2.85 which is close to the stoichiometric Cu2SnS3. The films are p-type, photosensitive, and the conductivity measured in dark was in the range of 4 × 10−3 Ω−1 cm−1. The comprehensive characterization presented in this paper will update the knowledge on this material.

Ferroelectric and piezoelectric properties of (1 − x) (Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

Abstract: Lead-free ceramics based on bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT)–barium titanate (BaTiO3,BT) have been prepared by solid state reaction process. The (1−x)BNT–(x)BT (x = 0.01,0.03,0.05,0.07) ceramics were sintered at 1,150 °C for 4 h in air, show a pure perovskite structure. X-ray diffraction analysis indicates that a solid solution is formed in (1−x)BNT–(x)BT ceramics with presence of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at x = 0.07. Raman spectroscopy shows the splitting of (TO3) mode at x = 0.07 confirming the presence of MPB region. The temperature dependence dielectric study shows a diffuse phase transition with gradual decrease in phase transition temperature (Tm). The dielectric constant and diffusivity increases with increase in BT content and is maximum at the MPB region. With the increase in BT content the maximum breakdown field increases, accordingly the coercive field (Ec) and remnant polarization (Pr) increases. The piezoelectric constant of (1 − x)BNT–(x)BT ceramics increases with increase in BT content and maximum at x = 0.07, which is the MPB region. The BNT–BT system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric material.

Improved thermoelectric performance of PEDOT:PSS films prepared by polar-solvent vapor annealing method

Abstract: To improve thermoelectric performance, polar-solvent vapor annealing (PSVA) method was introduced into the preparation of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. The solvent vapors included dimethyl sulfoxide, ethylene glycol, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and deionized water (H2O). The PSVA-treated PEDOT:PSS films exhibited significantly enhanced electrical conductivity and the maximum value was up to 496 S cm−1. Especially, utilizing the PSVA method, H2O could also remarkably enhance the electrical conductivity of pristine PEDOT:PSS film from 0.2 to 57 S cm−1. There was no distinct change for the Seebeck coefficient of PSVA-treated films with the significantly enhanced electrical conductivity, thereby a maximum power factor of 9.47 μW m−1 K−2 at room temperature was obtained. The effects of PSVA method on thermoelectric performance of PEDOT:PSS films were also investigated systematically by analyzing the changes in morphology, carrier mobility and carrier concentration. The results confirmed that PSVA-treated PEDOT:PSS films could obtain smoother morphologies and realize the simultaneous increase of carrier mobility and carrier concentration, which results in the improvement of the thermoelectric performance.

Effect of Gd-substitution on phase transition and conduction mechanism of BiFeO3

Abstract: The polycrystalline sample of (Bi0.8Gd0.2)FeO3 was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the sample confirms the formation of the desired compound with rhombohedral phase. The scanning electron micrograph of the sample showed uniform distribution of the plate- and rod-shaped grains. Studies of dielectric and electrical properties of the material were investigated within a wide range of temperature (25–400 °C) and frequency (1 kHz–1 MHz) using complex impedance spectroscopic method. The observation of hysteresis loop of the material confirmed that the material has a ferroelectric property at room temperature. The ac conductivity suggests that the sample obey Jonscher’s universal power law. The dc conductivity follows Arrhenius equation. Detailed studies of ac and dc conductivity show a negative temperature coefficient of resistance (NTCR) behavior of the sample.

Effect of growth temperature on structural, electrical and optical properties of dual ion beam sputtered ZnO thin films

Abstract: ZnO epitaxial thin films were grown on p-type Si(100) substrates by dual ion beam sputtering deposition system. The crystalline quality, surface morphology, optical and electrical properties of as-deposited ZnO thin films at different growth temperatures were studied. Substrate temperature was varied from 100 to 600 °C at constant oxygen percentage O2/(O2 + Ar) % of 66.67 % in a mixed gas of Ar and O2 with constant chamber pressure of 2.75 × 10−4 mBar. X-Ray diffraction analyses revealed that all the films had (002) preferred orientation. The minimum value of stress was reported to be −0.32 × 1010 dyne/cm2 from ZnO film grown at 200 °C. Photoluminescence measurements demonstrated sharp near-band-edge emission (NBE) was observed at ~375 nm along with deep level emission (DLE) in the visible spectral range at room temperature. The DLE Peak was found to have decrement as ZnO growth temperature was increased from 200 to 600 °C. The minimum FWHM of the NBE peak of 16.76 nm was achieved at 600 °C growth temperature. X-Ray photoelectron spectroscopy study revealed presence of oxygen interstitials and vacancies point defects in ZnO film grown at 400 °C. The ZnO thin film was found to be highly resistive when grown at 100 °C. The ZnO films were found to be n-type conducting with decreasing resistivity on increasing substrate temperature from 200 to 500 °C and again increased for film grown at 600 °C. Based on these studies a correlation between native point defects, optical and electrical properties has been established.

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

Abstract: In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co2+ successfully incorporated into the Zn2+ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.

Effect of sintering temperature on the microstructure and electrical properties of zirconium doped barium titanate ceramics

Abstract: Lead-free Ba(Zr0.15Ti0.85)O3 (BZT15) ceramics were synthesized by adopting the solid-state synthesis method. The effect of increasing sintering temperature (Ts) in the range of 1,350–1,450 °C on the microstructure, dielectric, polarization, and electric field induced strain of the ceramics was studied. Fine grained (~260 nm) BZT15 ceramics displayed single phase perovskite structure with relative densities >94 % of the theoretical density. Both grain size and shape were influenced by the sintering parameters. With increase in Ts, not only the maximum dielectric constant decreased from 11,412 to 8,734 along with an increase in the degree of diffuseness, but also interestingly the Curie temperatures were found to vary within an interval of 61–73 °C. Optimum sintering temperature has been found resulting in high remnant polarisation and strain in these ceramics. The properties observed are attributed to a contribution from all polar vectors present in coexistent phases.

Magnetic, optical and structural studies on Ag doped ZnO nanoparticles

Abstract: The influences of annealing effects have been explored on the crystallinity, morphology, optical and magnetic properties of Ag–ZnO nanostructures prepared by a simple sol–gel method. X-ray powder diffraction, scanning electron microscope, high resolution transmission electron microscope (HRTEM), vibrating sample magnetometer and photoluminescence spectroscopy (PL) have been used to characterize the crystal structures, surface morphology, magnetic and optical properties of the pure ZnO and Ag–ZnO nanostructures respectively. The synthesized Ag–ZnO nanostructures are found to have hexagonal wurtzite crystal structures and their grain size increases while lattice strain decreases on annealing. From HRTEM observation, it is found that the annealed samples show nanorod like structures with Ag nanoparticles (NPs) embedded on the surface. Due to annealing effect, Ag–ZnO shows higher saturation magnetization at room temperature.

Structural, vibrational, optical and magnetic properties of sol–gel derived Nd doped ZnO nanoparticles

Abstract: Nd doped ZnO (Zn1-xNdxO, x = 0.0, 0.03, 0.06 and 0.10) nanoparticles were prepared by sol–gel method. Phase identification and effect of Nd ions substitution in ZnO lattice were confirmed by Rietveld analysis of XRD patterns. UV–Visible absorption spectra of pure and Nd doped ZnO nanoparticles showed the variation of the band gap in the range of 3.31–3.26 eV. The FTIR analysis of pure and Nd doped ZnO nanoparticles exhibited similar patterns in Zn/Nd–O bond length as obtained from the Rietveld refinement. Raman analysis confirmed the formation of a wurtzite structure wherein the local structure of ZnO nanoparticles is distorted due to Nd substitution. Magnetization-magnetic field hysteresis curves for pure and Nd doped ZnO nanoparticles revealed diamagnetic and paramagnetic behaviour, respectively. The paramagnetic behaviour of doped ZnO nanoparticles increased with increasing Nd concentration. However, the weak ferromagnetic behaviour of doped ZnO nanoparticles is observed after subtracting paramagnetic components, whereas the ferromagnetic behavior increased up to x = 0.06 samples, which further declined for x = 0.10 sample due to competition between paramagnetic and ferromagnetic ordering. The reduction in the ferromagnetic behavior for x = 0.10 sample indicates that the solubility limit of Nd atoms in ZnO lattice has been reached and paramagnetically coupled Nd atoms increased due to the increasing secondary phases.

Photoluminescence and photoconductivity studies of ZnO nanoparticles prepared by solid state reaction method

Abstract: In the present work, the effect of annealing temperature on the luminescence and photoconductivity properties of ZnO nanoparticles (NPs) has been investigated. The ZnO NPs have been prepared at low temperature by a simple one step solid state reaction method using ZnSO4·7H2O as a starting precursor. X-ray diffraction results show, the prepared samples have a hexagonal wurtzite structure of ZnO NPs. FE-SEM reveals that the prepared ZnO nanoparticles have perfect spherical shape with little agglomeration. UV–visible absorption spectrum of as-prepared ZnO sample shows an absorbance peak at ~372 nm (~3.32 eV), which is blue shifted as compared to bulk ZnO (~386 nm). The annealed sample exhibits red shift of absorption peak. The photoluminescence spectra of as-prepared sample as well as annealed samples show one emission peak in UV region, and violet, blue, blue-green and green emissions in visible region. The sample annealed at 650 °C results in a significant reduction in luminescence as compared to that of the sample annealed at 450 °C. The photoconductivity properties such as voltage dependence of photocurrent, growth and decay of photocurrent as well as wavelength dependence of photocurrent have been studied in detail.

Structure and electrical properties of K 0.5 Na 0.5 NbO 3 –SrTiO 3 lead-free piezoelectric ceramics with LiSbO 3 doping

Abstract: Lead-free piezoelectric ceramics (1 − x)K0.5Na0.5NbO3–xSrTiO3 with 6 mol% LiSbO3 doping have been prepared by conventional solid state sintering technique at 1,125 °C for 3 h in air. The effects of the SrTiO3 and LiSbO3 on the phase structure and electrical properties of the ceramics were systematically investigated. All ceramic samples show a single phase perovskite structure with tetragonal symmetry when LiSbO3 content was 6 mol% and SrTiO3 content was 2–10 mol% by X-ray diffraction analysis and highly dense structure by SEM patterns. The ceramic with x = 0.04 exhibits optimum electrical properties at room temperature (d 33 = 267 pC/N, k p = 46 %, e r = 1,168, tanδ = 0.021, P r = 30.3 μC/cm2, E C = 1.98 kV/mm), which suggests that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.

Novel method for fabrication of NiO sensor for NO 2 monitoring

Abstract: Nickel oxide (NiO) sensor films were prepared on glass substrate by a sol–gel spin coating technique. These films were characterized for their structural and morphological properties by means of X-ray diffraction, field emission scanning microscopy and atomic force microscopy. The NiO films are oriented along (200) plane with the cubic crystal structure. These films were utilized in nitrogen dioxide gas (NO2) sensor. The dependence of the NO2 response on operating temperature, NO2 concentration was investigated. The NiO film showed selectivity for NO2 over Cl2 compared to H2S $$ \left( {{\text{S}}_{{{\text{NO}}_{ 2} }} /{\text{S}}_{{{\text{Cl}}_{ 2} }} = 3 7. 5,{\text{ S}}_{{{\text{NO}}_{ 2} }} /{\text{S}}_{{{\text{H}}_{ 2} {\text{S}}}} = 3. 4} \right) $$ . The maximum NO2 response of 23.3 % with 85 % stability at gas concentration of 200 ppm at 200 °C was achieved. The response time of 20 s and recovery time of 498 s was also recorded with same operating parameters.

Effect of holding time on the dielectric properties and non-ohmic behavior of CaCu3Ti4O12 capacitor-varistors

Abstract: Giant dielectric ceramics CaCu3Ti4O12 (CCTO) with non-ohmic electrical properties were prepared by a sol–gel processing method. Crystal structure and microstructure of the ceramics have been characterized using X-ray diffraction and Scanning electron microscopy. The effects of sintering duration and cooling rate on electrical properties of the ceramics were investigated by measuring the properties of permittivity, I–V and grain-boundary barriers. Prolonging holding time led to substantial improvement in permittivity, furthermore, the quenched sample showed larger dielectric permittivity than the furnace-cooling one. The non-ohmic behavior relating current density (J) to the applied electric field (E) at different temperatures was characterized. A low-voltage and giant dielectric permittivity CCTO varistor with breakdown voltages in the range of E b = 0.2–3 kV cm−1, nonlinearity coefficient α = 2–6 and dielectric permittivity e = 4,000–30,000 was obtained. A linear relationship between ln(J) and E 1/2 indicated that a Schottky barrier should exist at the grain boundary.

Quantum confinement effect of CdS nanoparticles dispersed within PVP/PVA nanocomposites

Abstract: Nanocomposite films of CdS nanoparticles within PVP/PVA blend were prepared. The prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The amount of Cd+ used strongly influenced the size of the CdS nanoparticles, which was confirmed by XRD, UV–vis absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher content of cadmium. The results of XRD indicate that CdS nanoparticles were formed with hexagonal phase in the polymeric matrix. PL and UV–vis spectra reveal that nanocomposite films shows quantum confinement effect. Optical band gap and particle size were calculated and is in agreement with the results obtained from TEM data. The direct energy band gap was increased up to 2.86 eV.