Showing papers in "Electronic Materials Letters in 2014"

SnO2nanoparticles-modified polyaniline films as highly selective, sensitive, reproducible and stable ammonia sensors

Abstract: Nanocomposites of polyaniline (PANi) and tin oxide (SnO2) were prepared by adding SnO2 nanoparticles (NPs) in different weight ratios (0%–50%) into the PANi matrix. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to form the polyaniline-SnO2 nanocomposites (PANi-SnO2) — a polymer-composite. PANi films modified with SnO2NPs were prepared by the spin coating method. The gas sensing properties of PANi, SnO2 and PANi-SnO2 polymercomposite films were observed and it was found that: The response of PANi film to 100 ppm NH3 at room temperature was 30% (stability 58%). The response of SnO2 film to 100 ppm NO2 was 19% (stability 79%) at operating temperature 200°C, which is higher than the room temperature. However, SnO2 exhibited no response to NO2 and NH3 at room temperature. The properties of the polymer-composite as a gas sensor were studied for various reducing (CH3OH, C2H5OH, NH3, H2S) as well as oxidising (NO2 and Cl2) gases. We demonstrated that the PANi-SnO2 (50%) polymer-composite film offers high stability and reproducibility and is a superior sensor to toxic gases operating at room temperature. (Results showed that they are highly selective to NH3 along with maximum response − 72% to 100 ppm, fast-response time of 167 s and better stability − 86% at room temperature. The unique nanostructure of this polymer composite with its high surface area offers these advantages.

Influence of Mn on crystal structure and thermoelectric properties of GeTe compounds

Abstract: The thermoelectric properties of the Ge1−xMnxTe compounds were investigated in the temperature range from 300 K to 773 K. The crystal structure of the compound was gradually changed with Mn, changing from a rhombohedral to a cubic-like cell. The Seebeck coefficient and the electrical resistivity were increased with Mn. From the Hall coefficient measurement, the reduction of the carrier concentration was confirmed and was responsible for the change of the electrical properties. The thermal conductivity was also reduced with Mn. The maximum dimensionless figure of merit, ZT, was obtained for x = 0.05 composition, where the value was ZT = 1.3 at 773 K. The evolution of the crystal structure with Mn attributed to the change of the thermoelectric properties. The Mn-doped compound which has a more cubic phase than a rhombohedral exhibited superior thermoelectric properties to the pure rhombohedral phase. Open image in new window

Multifractal characterization of water soluble copper phthalocyanine based films surfaces

Abstract: This paper presents a multifractal approach to characterize the structural complexity of 3D surface roughness of CuTsPc films on the glass and quartz substrate, obtained with atomic force microscopy (AFM) analysis. CuTsPc films prepared by drop cast method were investigated. CuTsPc films surface roughness was studied by AFM in tapping-mode™, in an aqueous environment, on square areas of 100 μm2 and 2500 μm2. A detailed methodology for CuTsPc films surface multifractal characterization, which may be applied for AFM data, was also presented. Analysis of surface roughness revealed that CuTsPc films have a multifractal geometry at various magnifications. The generalized dimension D q and the singularity spectrum f(α) provided quantitative values that characterize the local scale properties of CuTsPc films surface morphology at nanometer scale. Multifractal analysis provides different yet complementary information to that offered by traditional surface statistical parameters.

Study on the formation of zinc peroxide on zinc oxide with hydrogen peroxide treatment using x-ray photoelectron spectroscopy (XPS)

Abstract: In a previous study, we found that zinc oxide (ZnO) samples under different hydrogen peroxide (H2O2) treatment durations show the ability to dramatically rectify a diode’s behavior. In this study, the H2O2 mechanism is examined by grazing incidence x-ray diffraction (GIXRD) and x-ray photoelectron spectroscopy (XPS) analyses. In GIXRD, a diffraction peak (111) from the zinc peroxide (ZnO2) was observed for the films grown at low temperatures. The XPS depth profiles of the core O1s clearly indicated oxidation, and an interfacial ZnO2 layer covered the ZnO surface via the H2O2 treatment. The Schottky barrier heights of the treated and untreated samples were illustrated using energy band diagrams.

Effect of Sm-substitution on structural, electrical and magnetic properties of BiFeO3

Abstract: Samarium-modified bismuth ferrites (i.e., Bi1−x Sm x FeO3 (BSFO; x = 0, 0.05, 0.15, 0.25) were synthesized in a single-phase by a solid-state reaction method. Preliminary x-ray structural analysis suggested that crystal structure of the material is rhombohedral for x = 0.0, 0.05, 0.15 and orthorhombic for x = 0.25 composition. The surface morphology and textures of the pellet samples, recorded by scanning electron microscope at room temperature, show uniform distribution of the different size of plate- and rod-shaped grains on the surface of the samples. The grain size generally decreases with increase of Sm-content in BSFO. Detailed studies of permittivity and impedance parameters of the samples in a wide frequency range (1 kHz — 1 MHz) at different temperatures (30°C–450°C) provide many new and interesting results about relaxation processes. Room temperature magnetic hysteresis loops revealed that the spontaneous magnetization increases due to structural distortion and partial destruction of spiral spin structure caused by the substitution of Sm in BiFeO3. Enhancement in magneto-electric coupling coefficient of BFO was observed with increase of Sm in BSFO.

Effect of antimony on the optical and physical properties of Sb-V 2 O 5 -TeO 2 glasses

Abstract: Ternary glass systems of the form xSb-(60-x) V2O5-40TeO2 (Sx glasses) with 0 ≤ x ≤ 15 (in mol. %) have been prepared by using the normal melt quenching technique. The optical absorption spectra of these glasses have been recorded within wavelength range of 190 — 1100 nm. The absorption spectrum fitting method was employed to obtain the energy band gap. In this method, only the measurement of absorbance spectrum of the glass is needed. The position of the absorption edge and therefore the optical band gap values were found to be depend on glass composition. Results show that the optical band gap is in the range 1.57 — 2.14 eV. For each sample, the width of the band tail was determined. The densities of present glasses were measured and the molar volumes were calculated. Also, some thermal properties such as glass transition temperature (T g ) and crystallization temperature (TCr) were obtained by using differential scanning calorimetry (DSC) technique, and from which the glass thermal stability S and glass forming tendency K gl were calculated. Results show that these glasses (specially for x ≥ 10 mol. %) have good stability and therefore good resistance against thermal shocks for technological applications in fiber devices. Also, T g values indicate the rigidity and packing of the samples increase with increasing the Sb concentration as a network modifier.

Effect of Te on linear and non-linear optical properties of new quaternary Ge-Se-Sb-Te chalcogenide glasses

Abstract: We report linear and non-linear optical properties of a new quaternary chalcogenide glass series Ge19-ySe63.8Sb17.2Tey (y = 0, 2, 4, 6, 8, 10). In linear optical properties; refractive index, extinction coefficient and the Tauc gap are reported and their variation with Te content has been discussed. In non-linear properties; third order nonlinear susceptibility and non-linear refractive index has been discussed. The variation of non-linear refractive index has also been reported with normalized photon energy. A correlation between the Tauc gap and nonlinear refractive index has been discussed. Results indicate that these materials may find applications in modern optical devices.

Spray-deposited nanocrystalline WO 3 thin films prepared using tungsten hexachloride dissolved in N-N dimethylformamide and influence of in doping on their structural, optical and electrical properties

Abstract: Undoped and In-doped nanocrystalline tungsten oxide (WO3) thin films were prepared by chemical spray pyrolysis using tungsten hexachloride (WCl6) dissolved in N-N dimethylformamide as the host precursor solution and indium chloride (InCl3) as the source of dopant. XRD analyses confirm the monoclinic phase of the prepared films with the predominance of triplet (002), (020) and (200) in the spectra. On indium doping, the crystallinity of the films decreases and becomes minimum at 1.5 at. % doping. EDX analyses confirm the incorporation of In dopants into the WO3 lattice network. SEM micrographs show nonspherical grains over the surface and the average grain size decreases with higher In doping. AFM images of the films exhibit large nicely separated conical columnar grains (except in 1 at. %) throughout the surface with coalescence of some columnar grains at few places. UV-visible measurements reveal that the optical transmittance of the 1 at. % In-doped film increases significantly throughout the wavelength range 300–800 nm relative to that of the undoped film. Room temperature photoluminescence spectra show pronounced enhancement in the peak intensity of NBE emission on In doping. Electrical conductivity has been found to increase on In doping.

Enhancing beta-phase in PVDF through physicochemical modification of cellulose

Abstract: The piezo-, pyro- and ferroelectric properties of polyvinylidene fluoride (PVDF) are strongly associated with its β-phase having an all-trans conformation that can be enhanced via filler addition. Hypothesizing an interaction between -OH groups of cellulose and PVDF, alkali treatment, ball milling and acid hydrolysis of cellulose were carried out to improve the availability of surface -OH groups. β-phase development in PVDF composites was studied with respect to addition of physicochemically altered variants of cellulose at different concentrations. Our study establishes cellulose nanowhiskers produced via acid hydrolysis as the optimal filler for PVDF.

Ab initio calculations of electronic and optical properties of BeO nanosheet

Abstract: The electronic and the linear optical properties of BeO nanosheet and wurtzite structure are investigated by using the full potential linear augmented plane wave plus local orbital (FPLAPW+ lo) in the frame work of the density functional theory (DFT). The dielectric tensor is derived within the random phase approximation (RPA). Specifically, dielectric function, absorption coefficient, optical conductivity, extinction index, loss function, reflectivity and the refraction index of the BeO nanosheet are calculated for both parallel and perpendicular electric field polarizations. The results show that the optical conductivity in E‖x starts with a gap about 5.89 eV confirms that BeO nanosheet has semiconductor property also the optical spectra are anisotropic along these two polarizations. The static refractive index of nanosheet is smaller than wurtzite structure.

Characteristics of photoconductive UV photodetector based on ZnO nanorods grown on polyethylene naphthalate substrate by chemical bath deposition method

Abstract: Vertically aligned ZnO nanorods were synthesized on a polyethylene naphthalate (PEN) substrate using a chemical bath deposition method at a low temperature. The structural and optical investigations revealed the high quality of the fabricated ZnO nanorods on flexible substrate. A metal-semiconductor-metal UV photodetector based on ZnO nanorods was fabricated on the PEN substrate. The optoelectronic characteristics of fabricated UV photodetector were studied in the dark and under 325 nm UV light illumination at −3 V and 3 V bias voltages. The responsivity and photosensitivity of the ZnO nanorod UV photodetector were 2.856 A/W and 1175% at 3 V bias voltage, respectively. Moreover, the response and the recovery times measured during the turn-on and turnoff of UV illumination were 1.2 s and 1.8 s, respectively.

Enhancement of band gap of ZnO nanocrystalline films at a faster rate using Sr dopant

Abstract: A faster rate of band gap enhancement of ZnO nanocrystalline films using strontium dopant is reported for the first time. Hexagonal wurtzite Zn1− x Sr x O films have been deposited by sol gel spin coating using zinc acetate. The optical band gap increases from 3.150 to 3.275 eV as the Sr concentration increases from x = 0 to x = 0.03 showing an enhancement of 3.96% which is substantially higher than those reported earlier using Mg or Ca dopants indicating the possibility of application in optoelectronics. Strong UV and comparatively weak defect related emission are observed in photoluminescence spectra of the films. The NBE emission at 3.10 eV for undoped ZnO thin film shows a blue shift of 53 meV as Sr dopant concentration increases to 3 at. %. Films are also characterized by FTIR, AFM, SEM and EDX. Distinct characteristic absorption for Zn-O stretching modes are present. Surface of Zn1− x Sr x O polycrystalline thin films are significantly smooth and show pentagonal shaped grains which approach to uniform spherical grains throughout the surface with increase in dopant concentration. The crystallite size along (002) plane is less than 10 nm for all samples.

Effect of aluminium additions on wettability and intermetallic compound (IMC) growth of lead free Sn (2 wt. % Ag, 5 wt. % Bi) soldered joints

Abstract: The effect of a trace Al addition (0, 0.01, 0.05 and 0.1 wt. %) in the Sn-2Ag-5Bi solder alloy on wettability and intermetallic compound (IMC) formation of the alloy was investigated. The interface between the solder and a Cu(17 μm)/Ni(4 μm)/Au (0.02 μm) under bump metallized (UBM) substrate was studied. The microstructure of the bulk solder and the interface of the soldered joints was observed in a scanning electron microscope (SEM), and the thickness of the interface reaction layers was estimated. Various IMC phases were identified by energy dispersive spectroscopy (EDS) and by the electron probe micro analyzer (EPMA). The experimental results indicated that the addition of 0.01 wt. % Al in the Sn-2Ag-5Bi solder alloy significantly improved the wettability of the solder more than the other Al additions did. The IMC layer between the bulk Sn-2Ag5Bi-0.01Al solder and the Cu/Ni/Au UBM substrate was almost uniform and thinner than those between the solders containing 0, 0.05, and 0.1 wt. % Al and their respective Cu/Ni/Au UBM substrates. Furthermore, the growth rate of the IMC layer between the Sn-2Ag-5Bi-0.01Al solder and Cu/Ni/Au UBM after 1 to 10 reflow times was lower than that of the IMC layer between the Sn-2Ag-5Bi solder and Cu/Ni/Au UBM. The IMCs in the solder joint interface (e.g., Ni3Sn4) of the Sn-2Ag-5Bi-0.01Al solder were well distributed near the Bi and fine Ag3Sn. The addition of 0.01 wt. % Al in the Sn-2Ag-5Bi solder yielded the best wetting properties for the solder and the minimum growth rate of the IMCs because it increased the nucleation rate of Ag3Sn and uniformly segregated the Bi phase.

Electrical characteristics of TMAH-surface treated Ni/Au/Al2O3/GaN MIS Schottky structures

Abstract: The electrical characteristics and reverse leakage mechanisms of tetramethylammonium hydroxide (TMAH) surface-treated Ni/Au/Al2O3/GaN metal-insulator-semiconductor (MIS) diodes were investigated by using the current-voltage (I–V) and capacitance-voltage (C–V) characteristics. The MIS diode was formed on n-GaN after etching the AlGaN in the AlGaN/GaN heterostructures. The TMAH-treated MIS diode showed better Schottky characteristics with a lower ideality factor, higher barrier height and lower reverse leakage current compared to the TMAH-free MIS diode. In addition, the TMAH-free MIS diodes exhibited a transition from Poole-Frenkel emission at low voltages to Schottky emission at high voltages, whereas the TMAH-treated MIS diodes showed Schottky emission over the entire voltage range. Reasonable mechanisms for the improved device-performance characteristics in the TMAH-treated MIS diode are discussed in terms of the decreased interface state density or traps associated with an oxide material and the reduced tunneling probability.

Current trends in studies on reverse-mode polymer dispersed liquid-crystal films — A review

Abstract: Reverse-mode polymer dispersed liquid crystals (PDLCs) comprise an important new class of materials for optical device applications. Generally reverse-mode PDLCs are transparent and opaque in the absence and presence of an external field, respectively. Display devices based on reverse-mode PDLC technology are useful for large-area displays; because their fabrication for manufacturing shutters is considered to be easier and faster, they are also employed for automotive technology and smart windows. These devices can be operated at a low voltage, which conserves energy in intelligent-device applications. This work presents a comprehensive review of past research regarding reverse-mode PDLCs and includes the advantageous features, applications, and various fabrication methods of reverse-mode PDLCs and photo-chromic reverse-mode PDLCs. In addition, some new features of this technology that have recently been reported and future investigations by a variety of research groups are presented.

White light emitting magnetic ZnO:Sm nanoparticles prepared by inclusive Co-precipitation synthesis

Abstract: Inclusion of rare earth Samarium as dopant in nanoparticles of ZnO has been achieved by co-precipitation in highly alkaline medium near room temperature. Substitutional doping of Sm in Zn position in the ZnO lattice could be inferred through change in lattice parameters in response to Sm doping concentration. Dopant Sm enhances broad visible emission of ZnO thus making it a bright white light emitter under UV (300–380 nm) excitation. Observation of room temperature intrinsic ferromagnetism with optimal Sm doping in ZnO:Sm suggests unpaired spin in Sm3+ at zinc substitutional sites could create spin ordering and long range ferromagnetic coupling. Such white light emitting magnetic nanoparticles of ZnO:Sm can have immense potential as LED phosphor and spin LED semiconductor.

In2O3-based micro gas sensor for detecting NOx gases

Abstract: In this study, NO x micro gas sensors for monitoring the indoor atmosphere of automobile were fabricated using MEMS (microelectromechanical system) technology and a sol-gel process. The sensing electrode and micro heater were designed to have a co-planar typed structure in a Pt thin film layer. The thermal characteristics of a micro heater array were analyzed using a finite element method (FEM). The chip size of the gas sensor was approximately 2 mm × 2 mm. Indium oxide as a sensing material for NO x gas was synthesized by a sol-gel process with indium isopropoxide as a precursor. Field emission Scanning electron microscopy and x-ray diffraction showed that particle size of the synthesized In2O3 was approximately 17–45 nm. The maximum gas sensitivity as the relative resistance (R s = R gas /R air ) was observed at 275°C with a value of 8.0 at 1 ppm NO2 gas. The response (80% saturation) and recovery times were within 1 min. The sensing properties of NO2 gas exhibited linear behavior with increasing gas concentration. The sensing mechanism of the gas sensor was explained by the variations in the electron depletion layers and the adsorption of gas molecules on the In2O3 particle surface. These results suggest that in the future, MEMS-based gas sensors can be used as automotive-exhaust-gas sensors.

Al-doped ZnO as a switching layer for transparent bipolar resistive switching memory

Abstract: In this report, we employ an Al-doped ZnO (AZO) layer as a resistive switching layer for transparent resistive switching random access memory devices. An Indium-Tin-Oxide (ITO)/AZO/ITO/glass device exhibits a transmittance of ∼80% (including a glass substrate) in the visible wavelength region and demonstrates reliable bipolar resistive switching behavior over d.c. 300 sweeping cycles with a low operation voltage and a very low variation in the switching threshold voltage. These results indicate that the AZO film is a promising transparent resistive switching layer.

Development of extremely ductile lead-free Sn-Al solders for futuristic electronic packaging applications

Abstract: In the present study, new lead-free Sn-Al solders are developed incorporating varying amount of Al (0.4 and 0.6% by weight) into pure Sn using disintegrated melt deposition technique. Solder samples were then subsequently extruded at room temperature and characterized. Microstructural characterization studies revealed equiaxed grain morphology, minimal porosity, reasonably uniform distribution of Al particles and good Sn-Al interfacial integrity. Melting temperature of Sn-0.6Al (228°C) was found to be close to the eutectic Sn-0.7Cu (227°C) solders. Microhardness was increased with increasing amount of Al in pure Sn. Room temperature tensile test results revealed that newly developed Sn-0.6Al solders exhibited significant improvement in 0.2% yield strength (∼67%), ultimate tensile strength (∼18%) and ductility (∼123%) when compared to commercial Sn-0.7Cu solder. Ductility was improved about 222%, 263% and 81% when compared to commercially available Sn-3.5Ag-0.7Cu, Sn-3.5Ag and Sn-37Pb solders, respectively without compromising strength.

Fabrication, structural characterization, dielectric and electrical parameters of the synthesized nano-crystalline erbium oxide

Abstract: Nano crystalline erbium oxide (Er2O3) was synthesized in the laboratory through sol-gel method. The effect of different annealing temperatures on the crystal structure has been studied using x-ray diffraction (XRD). The comparison of the specific surface area (s); calculated using Brunauer, Emmett & Teller theory and (XRD) results, was made and found in agreement with an approximate error of 7%. The morphology of the samples has been studied using scanning electron microscope (SEM) and particles are found having a spherical morphology. Elemental analysis of the erbium oxide was also carried using energy dispersive spectrum (EDS) of the synthesized samples. Fourier transform infrared spectrum (FTIR) of the prepared samples showed the characteristic peaks for Er2O3. The dielectric properties of Er2O3 were also studied in the wide range of frequency (100 Hz - 5MHz). The activation energy for erbium oxide was found to be between 0.5–0.8 eV in the temperature range of 373 K–573 K. Hall effect measurements were done on the synthesized erbium oxide and it was found that erbium oxide can have useful applications in the Hall effect sensors (HES).

Resistive Switching and Current Conduction Mechanism in Full Organic Resistive Switch with the Sandwiched Structure of Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/Poly(4-vinylphenol)/Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)

Abstract: The paper reported the fabrication of full organic resistive switch (FORS) with the sandwich structure of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)/poly(4-vinylphenol)(PVP)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS). The fabricated FORS elucidated reversible bipolar resistive switching behavior at higher operational voltage between −20 V and +30 V. The switching mechanism in the FORS device was attributed to the hole injection through PEDOT:PSS electrode and filling of trap sites in the PVP sandwiched layer by the limited injection. Current conduction mechanisms were concluded and supported by the charge transport governing physical laws. The dominant current conduction mechanism in the fabricated FORS was attributed to the transition from trap-limited space charge limited current (SCLC) conduction to trap-free SCLC conduction mechanism. The robustness of the fabricated FORS was tested over 100 multiple voltage sweeps.

Porous carbon particles derived from natural peanut shells as lithium ion battery anode and its electrochemical properties

Abstract: Abandoned peanut shells, a common farm waste, have caused tremendous environmental pollution and huge waste deposits through burned and buried disposal approaches. In targeting to enhance the potential value of peanut shells and discover a new alternative candidate for lithium ion batteries, we adopted an easy to scale-up and highly repeated method to treat fresh and dry peanut shells via acid-treatment and pyrolysis, making porous structures on carbonized peanut shells. The pyrolysis process transformed the peanut shells to porous carbon (PC) materials in a quartz tube furnace at a series of temperatures from 500°C to 700°C in N2 under the condition of 40°C gradient temperatures with a heating rate of 2°C min−1. Scanning electron microscopy (SEM) images show that the irregular porous structures and hundreds of micropores are distributed on the PC materials. The cyclic voltammogram (CV) test and particle size analysis are employed to investigate their characteristics of voltammetry and particle size distribution. PC material obtained at 620°C (PC-620) exhibited good particle distribution, porous structure and less agglomerated particles. When applied as anode materials in lithium ion batteries, the PC-620 electrode displayed the high reversible capacity of 608 mAh g−1. Moreover, the cycling performance of PC-620 was the most stable, with a high Coulombic efficiency of 98.9% at the 20th cycle, demonstrating a reversible capacity of 418 mAh g−1, which is higher than the theoretical capacity of graphite. Most importantly, the PC materials harvested from the wastes of natural resources are turned into valuable electrode materials for the high demand energy storage devices, which can significantly reduce severe environmental pollution and alleviate an energy shortage. Open image in new window

Numerical simulation of high power LED heat-dissipating system

Abstract: In this paper, thermal analysis of the heat dissipation under different heat sink for high-power white Light Emitting Diode (LED) is presented. Junction temperature of LED is elevated as the power of LED increases, which brings up deterioration of light efficiency and other side effects. Heat dissipation is another design concern other than material and illumination efficiency. The purpose of this paper is to investigate the cooling of high-power LED chips and modules for design of heat sinks. Three types of heat sinks are designed for a tandem 12-chip module and an extensive numerical investigation of the heat sink design performance is conducted by Computational Fluid Dynamics software Fluent. The effects of heat sink geometry and adhesive material are also investigated. Design variables are the thickness of sink base, number, thickness and length of fins. The total wetted area is the dominant factor to the junction temperature. The objective of design regarding the junction temperatures around 50°C is easily achieved. However, its effect is limited at high values of these parameters, furthermore an excessive number of fins incurs reverse consequence due to problem of ventilation also waste of material.

Enhancement of thermoelectric properties of Mg 2 Si compounds with Bi doping through carrier concentration tuning

Abstract: The Bi-doped Mg2Si powder was fabricated with solid state reaction method and consolidated with hot pressing method and then its thermoelectric properties were investigated. The n-type transport properties were measured in all samples and temperature dependence of the electrical properties shows a behavior of degenerate semiconductors for Bi-doped samples. The electrical resistivity and the Seebeck coefficient were greatly reduced with Bi, which was mainly due to the increment of the carrier concentration. The samples have maximum carrier concentration of 8.2 × 1018 cm−3. The largest ZT value of 0.61 was achieve at 873 K for Mg2.04SiBi0.02. The Bi-doping was found to be an effective n-type dopant to adjust carrier concentration.

Shear strength of copper joints prepared by low temperature sintering of silver nanoparticles

Abstract: In this work, mechanical properties of Cu-to-Cu joint samples prepared by low temperature sintering of Ag nanoparticle paste have been investigated. The silver nanopaste was prepared by a controlled thermal decomposition of an organometallic precursor. The as-synthesized Ag particles were spherical, with an average diameter of 8.5 nm. The Cu-to-Cu joint samples were made by placing a small amount of Ag nanopaste between two polished Cu plates and sintering at 150°C, 200°C, 220°C and 350°C in air. A normal load was applied to aid sintering. Mechanical properties were measured by imposing a uniform stress across the sample bond area and measuring the corresponding strain. The application of external load was found to have a positive effect on the material’s mechanical properties. Furthermore, interestingly high values of shear strength were observed.

Surface-treated biocompatible ZnS quantum dots: Synthesis, photo-physical and microstructural properties

Abstract: In the present study, the ZnS semiconductor quantum dots were successfully synthesized via an aqueous method utilizing glutathione (GSH), thioglycolic acid (TGA) and polyvinyl pyrrolidone (PVP) as capping agents. The structural, morphological and photo-physical properties and biocompatibility were investigated using comprehensive characterization techniques such as x-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), dynamic light scattering (DLS), Fourier transform infrared spectrometry (FT-IR), UV-Vis optical absorption, photoluminescence (PL) spectrometer and MTT assay. The XRD patterns showed a cubic zinc blende crystal structure and a crystallite size of about 2–3 nm using Scherrer’s equation confirmed by the electron micrographs and Effective Mass Approximation (EMA). The DLS and zeta-potential results revealed that GSH capped ZnS nanoparticles have the narrowest size distribution with an average size of 27 nm and relatively good colloidal stability. Also, the FT-IR spectrum confirmed the interaction of the capping agent groups with ZnS nanoparticles. According to the UV-Vis absorption results, optical bandgap of the spherical capped nanoparticles is higher compared to the uncapped sample and could be wider than 3.67 eV (corresponding to the bulk ZnS), which is due to the quantum confinement effect. From photoluminescence spectra, it was found that the emission becomes more intensive and shifts towards the shorter wavelengths in the presence of the capping agent. Moreover, the emission mechanism of uncapped and capped ZnS was discussed in detail. Finally, the MTT results revealed the satisfactory (>94%) biocompatibility of GSH capped ZnS quantum dots which would be a promising candidate applicable in fluorescent biological labels.

Properties of an Au/Pt bilayered counter electrode in dye sensitized solar cells

Abstract: A Ru/Ti bilayer to a flat glass substrate was applied as a counter electrode to improve the energy conversion efficiency of a dye-sensitized solar cell device with the structure of glass/FTO/blocking layer/TiO2/N719(dye)/electrolyte/(50 nm Ru-50 nm Ti)/glass. For comparison, a 100 nm-thick Ru counter electrode on a flat glass substrate was also prepared using the same method. The photovoltaic properties, such as the short circuit current density, open circuit voltage, fill factor, energy conversion efficiency and impedance, were characterized using a solar simulator and potentiostat. The phase of the bilayered films was examined by x-ray diffraction. The measured energy conversion efficiency of the dye-sensitized solar cell device with a Ru/Ti bilayer counter electrode was 2.40%. The efficiency was 1.48 times larger that of the dye-sensitized solar cell with the 100 nm Ru counter electrode. The new phase of RuTi led to a decrease in resistivity and an increase in catalytic activity. The interface resistance at the interface between the counter electrode and electrolyte decreased when Ru/Ti bilayer thin films were applied. This suggests that Ru/Ti bilayer thin films improve the efficiency of dye-sensitized solar cells.

Study on characteristics of CdS quantum dot-sensitized solar cells prepared by successive ionic layer adsorption and reaction with different adsorption times

Abstract: Cadmium sulfide (CdS) quantum dots (QDs) were adsorbed on a titanium dioxide (TiO2) nanoporous film by successive ionic layer adsorption and reaction (SILAR) method with different adsorption times to study the influences of different SILAR adsorption times on CdS quantum dot-sensitized solar cells (QDSCs). The optical properties of CdS sensitized TiO2 films were studied by scanning electron microscopy and UV-Vis absorbance spectroscopy. The particle size of the CdS QDs was approximated using the effective mass approximation theory from the absorbance spectra. The photovoltaic characteristics of the CdS QDSCs were analyzed by I–V characteristics and electrochemical impedance spectroscopy under air mass 1.5 illumination. As a result, the particle size of the CdS QDs became larger and light harvesting was enhanced with increasing SILAR adsorption time. The maximum photovoltaic conversion efficiency of the CdS QDSCs (1.86%) was obtained at the SILAR adsorption time of 30 min with the highest short circuit current density and lowest charge transfer resistance.

Surface enhanced Raman spectroscopy on silver-nanoparticle-coated carbon-nanotube networks fabricated by electrophoretic deposition

Abstract: In this study, the efficiency of silver nanoparticle (AgNP) decorated carbon nanotube (CNT) based porous substrates has been investigated for surface-enhanced Raman spectroscopy (SERS) applications. The fabrication of uniform thin coatings of carbon nanotubes is accomplished by Electrophoretic Deposition (EPD) on organosilane functionalized silicon substrates. The deposition process exemplifies a fast, reproducible and single-step room temperature coating strategy to fabricate horizontally aligned porous CNT network. Surfactant stabilized AgNPs were deposited on the CNT networks by immersion coating. The acquired Raman spectra of Rhodamine6G (R6G) analyte examined on the fabricated Ag-CNT-Si substrates exhibited enhanced signal intensity values when compared to SERS-active planar AgNP-Si substrates. An overall enhancement factor of ∼109 was achieved for the tested analyte which enables pushing the limit of detection to 1 × 10−12 M (1 pM). The enhancement can be attributed to the large surface area offered by the AgNP-CNT porous network, which is expected to increase the number of effective “hot spots” for the SERS effect.

Thermoelectric performance of poly(3-hexylthiophene) films doped by iodine vapor with promising high seebeck coefficient

Abstract: Poly(3-hexylthiophene) (P3HT) films doped with iodine vapor have been prepared by casting a P3HT solution on glass substrates and their thermoelectric (TE) performances has been investigated. The maximum Seebeck coefficient and electrical conductivity of iodine-doped P3HT films were 386 µV·K−1 (at room temperature) and 4.7 × 10−1 S·cm−1, which is about five orders of magnitude higher than that of pristine P3HT films. The power factor of these iodine-doped P3HT films was estimated to be 7.0 µW·m−1·K−2 at room temperature, which is a relative high value for organic TE materials. The UV-vis spectra of iodine-doped P3HT films showed a slight red shift of the iodine-doped P3HT compared to those of pristine P3HT films. Atomic force microscopy images indicated the conformational changes in P3HT chains after treatment with iodine vapor. During this treatment, the P3HT chains self-organized into a more ordered structure, this organization improved the charge carrier transport capability and the TE performance of P3HT the films.