Dinesh Amalnerkar

Firing and processing effects on microstructure of fritted silver thick film electrode materials for solar cells

Thick film materials (viz. conductor, resistor, dielectric and solder pastes) have been proved to possesses economical processing and functional advantages over other technologies in high volume and quick turn-around production of hybrid microelectronic circuits. Silver thick films are widely used for the front electrode metallization of silicon solar cells. This paper reports the microstructural, physico-chemical and electrical properties of the fritted silver thick film electrode materials (for silicon solar cells) formulated using different processing conditions, which also included treatment with surfactants.

A Facile Template-Free Approach for the Large-Scale Solid-Phase Synthesis of CdS Nanostructures and Their Excellent Photocatalytic Performance

The simple, template-free, low-temperature, large-scale synthesis of nanostructured CdS with the hexagonal wurtzite phase from bulk cadmium oxide under solid-phase conditions is demonstrated for the first time. The novel approach involves the homogenization of cadmium oxide (CdO) and thiourea in various stoichiometric ratios at moderate temperature. Among the different molar ratios of CdO and thiourea studied, the CdO/NH(2) CSNH(2) molar ratio of 1:2 is found to be the best to obtain highly pure CdS. The obtained CdS nanostructures exhibit excellent cubic morphology and high specific surface area with a particle size in the range of 5-7 nm. The bandgap of the nanostructured CdS is in the range of 2.42 to 2.46 eV due to its nanocrystalline nature. In photoluminescence studies, emission is observed at 520.34 and 536.42 nm, which is characteristic of the greenish-yellow region of the visible spectrum. Considering the bandgap of the CdS is within the visible region, the photocatalytic activity for H(2) generation and organic dye degradation are performed under visible-light irradiation. The maximum H(2) evolution of 2945 μmol h(-1) is obtained using nanostructured CdS prepared in the 1:2 ratio, which is three times higher than that of bulk CdS (1010 μmol h(-1) ). CdS synthesized using the 1:2 molar ratio shows maximum methylene blue degradation (87.5%) over a period of 60 min, which is approximately four times higher than that of bulk CdS (22%). This amazing performance of the material is due to its nanocrystalline nature and the high surface area of the CdS. The proposed simple methodology is believed to be a significant breakthrough in the field of nanotechnology, and the method can be further generalized as a rational preparation scheme for the large-scale synthesis of various other nanostructured metal sulfides.

A study on sintering and microstructure development of fritless silver thick film conductors

Thick film materials have proved to possess economic processing and functional advantages over other technologies in high-volume production of miniaturized circuits. The development of a low-cost fritless silver paste with different binder composition is described in the present work. The effect of composition and firing temperature (700–900 °C) on the microstructure is also reported. The sheet resistivity and surface morphology of all the indigenously formulated Ag thick film pastes are compared with the imported (ESL) paste. The results suggest that the thick films can be fired at 700 °C instead of the conventional 900 °C firing temperature.

A novel template free, one pot large scale synthesis of cubic zinc sulfide nanotriangles and its functionality as an efficient photocatalyst for hydrogen production and dye degradation

Herein, we have demonstrated a novel, facile, template free method for the synthesis of nanostructured zinc sulfide from bulk zinc oxide. This synthesis method may provide an easy, inexpensive and pollution free way to synthesize nanostructured zinc sulfide on a large scale. Zinc oxide and thiourea in various stoichiometric ratios were homogenized at moderate temperature to obtain zinc sulfide. The phase pure nanostructured cubic zinc sulfide was obtained using a 1 : 2 molar ratio of zinc oxide & thiourea and in excess of thiourea as well. Surprisingly, monodispersed nanotriangles of zinc sulfide were obtained using all molar ratios of zinc oxide and thiourea. The nanotriangles of size 5–6 nm were obtained for zinc sulfide of a 1 : 2 molar ratio. The band gap of nanostructured zinc sulfide was observed to be in the range of 3.86 to 3.75 eV, which is higher than that of the reported value. The blue shift was obtained due to the nanocrystalline nature of the zinc sulfide. Considering the significant morphology of zinc sulfide, it has been used as a photocatalyst for water splitting to produce hydrogen and for degradation of methylene blue as well. The hydrogen evolution rate was observed to be 2050 μmol h−1 g−1, which is much more than the bulk zinc sulfide (410 μmol h−1 g−1) as well as reported nanostructured ZnS. Three fold enhancements in the degradation of methylene blue as compared to bulk zinc sulfide have also been observed. The proposed simple methodology is believed to be a significant breakthrough in the field of nanotechnology and the method can be further generalized as a rational preparation scheme for the large-scale synthesis of various other nanostructured metal sulfides.

Synthesis and Characterization of Hydrophobic TMES/TEOS Based Silica Aerogels

The experimental results on the effect of adding trimethylethoxysilane (TMES) as a co-precursor on the hydrophobicity and physical properties of tetraethoxysilane (TEOS) based silica aerogels, are reported. The molar ratio of TEOS, ethanol (EtOH), water (0.001 M oxalic acid catalyst) was kept constant at 1:5:7 respectively, while the molar ratio of TMES/TEOS (A) was varied from 0 to 0.6. It has been observed that as the A value increases, the gelation time increases. The hydrophobicity was tested by measuring the contact angle, and the surface chemical modification was confirmed by the FTIR spectroscopy studies. The thermal stability of the hydrophobic aerogels was studied in the temperature range from 25 to 800°C. The hydrophobic nature of the aerogel could be maintained up to a temperature of 287°C and above this temperature the aerogels become hydrophilic. The bulk density and the optical transmittance of the aerogels have been found to decrease with increase in A value. The aerogels have been characterized by Fourier transform infrared spectroscopy (FTIR), Optical transmittance, Scanning electron microscopy (SEM), Differential thermal analysis (DTA) and Thermogravimetric analysis (TGA), and Contact angle measurements.

Thick film NTC thermistor for wide range of temperature sensing

Purpose – Aims to focus on temperature sensors.Design/methodology/approach – Negative temperature co‐efficient thermistor powders of ternary Mn, Co, Ni oxide along with RuO2 synthesized at relatively moderates temperature (1,000°C). Thick film thermistor paste compositions were formulated by mixing the semiconducting oxide powder, glass frit and organic vehicle. The physico‐chemical analysis, viz. X‐ray diffraction, scanning electron microscopy and thermogravimetry and IR spectroscopy were carried out for the synthesized powder and the resultant thick films. The X‐ray analysis of the powders showed the cubic spinel structure. The electrical properties like thermistor constant, sensitivity index and activation energy of the thick film NTC thermistor were determined.Findings – The room temperature resistance is observed to range from 490 KΩ to 4.13 MΩ with thermistor constant ranging from 3,275 to 3,980 K, in the temperature range of 25‐300°C.Originality/value – Describes research work on temperature sensor...

One dimensional CdS/ZnO nanocomposites: an efficient photocatalyst for hydrogen generation

One-dimensional ZnO nanostructures were synthesized using solvothermal reaction method, and in situ CdS nanoparticles were grown on 1D ZnO having different CdS compositions such as 0.1, 0.5, 1 and 5 mol% using microwave reaction system. The prepared CdS/ZnO coupled semiconductor catalysts were characterized using various spectroscopic techniques. XRD analysis indicated the presence of a wurtzite structure for all the prepared CdS/ZnO compositions. DRS spectrum showed red shift in the absorbance edge of CdS/ZnO nanocomposites with increasing CdS mol% and absorbance increases in 400 to 500 nm range. Photoluminescence spectra illustrated two emission peaks, with the first one at 390 nm due to the band edge emission of ZnO and the second broad peak centered around 480 nm possibly due to CdS band edge emission or oxygen vacancies in ZnO. FESEM image showed the formation of pencil shaped one-dimensional ZnO nanorods containing spherical CdS nanoparticles on the surface of ZnO. TEM analysis confirms the rod-like morphology of ZnO and the presence of CdS nanoparticles. The activity of the prepared CdS/ZnO catalysts was evaluated by measuring the amount of H2 generated during photocatalytic H2 evolution from water. The photocatalytic activity of prepared coupled CdS/ZnO shows an increase in hydrogen generation compared to that of individual ones. CdS loading enhances the rate of H2 generation and is the highest for 5 mol% CdS/ZnO composition.

Electrical and humidity characterization of m-NA doped Au/PVA nanocomposites

The Meta-Nitroaniline (m-NA) doped (by varying weight percentage (wt. %)) gold/polyvinyl alcohol (Au/PVA) nanocomposites were synthesized using gold salt and hydrazine hydrate (HH) by in situ process. The composite was coated on ceramic rods having two end electrodes by drop casting method for studying their electrical behavior at different relative humidity (RH) levels, ranging from 4 to 95% RH at room temperature. The optimized wt. % was used to prepare coatings of various thicknesses (20-40 microm) of the films. As the humidity decreases, the resistance increases. The low humidity sensing characteristic can be tailored by varying wt. % of m-NA and thicknesses of the nanocomposite films. The resistive-humidity sensor shows two regions of sensitivity having highest sensitivity for lower RH. The sensor response and recovery time is about 6-10s and 52 s respectively. The dynamic range of variation of the resistance allows a promising use of the films as a humidity sensor. The material was characterized by X-ray diffraction (XRD) and impedance spectroscopy at 60% RH.

Innovative biofilm inhibition and anti-microbial behavior of molybdenum sulfide nanostructures generated by microwave-assisted solvothermal route

The incessant use of antibiotics against infectious diseases has translated into a vicious circle of developing new antibiotic drug and its resistant strains in short period of time due to inherent nature of micro-organisms to alter their genes. Many researchers have been trying to formulate inorganic nanoparticles-based antiseptics that may be linked to broad-spectrum activity and far lower propensity to induce microbial resistance than antibiotics. The way-out approaches in this direction are nanomaterials based (1) bactericidal and (2) bacteriostatic activities. We, herein, present hitherto unreported observations on microbial abatement using non-cytotoxic molybdenum disulfide nanostructures (MSNs) which are synthesized using microwave assisted solvothermal route. Inhibition of biofilm formation using MSNs is a unique feature of our study. Furthermore, this study evinces antimicrobial mechanism of MSNs by reactive oxygen species (ROS) dependent generation of superoxide anion radical via disruption of cellular functions.

Removal of OH impurities from GeS2 by reactive atmosphere and its glass preparation

Abstract The transparency of the chalcogenide glasses depends upon the purity of the raw materials used for the glass preparation. Especially, the glasses used for optical fiber systems are generally prepared using high purity raw materials. In optical fiber glasses, the OH radicals are critical since they quench the fluorescence. In the present investigation, we have prepared germanium sulfide-based chalcogenide glasses. The sulfide usually contains significantly large amount of hydroxyl impurities which act as high energy phonons in the glass structure. These high energy phonons are known to quench fluorescence. Hence OH impurity removal is essential for optical fiber systems. Considering the criticality of OH impurity in optical fiber system, the efforts have been made to purify raw materials of germanium sulfide glasses. The present investigation focuses research on decreasing impurities content in the raw materials used for glass preparation. The GeS2, Ga2S3 powders were purified by reactive atmosphere of HCl and hydrogen. The glasses using these powders were melted and thermal and spectroscopic studies have been made.