• Volume 25, Issue 6

November 2002,   pages  449-582

• Foreword

• Study of YSZ-based electrochemical sensors with oxide electrodes for high temperature applications

Potentiometric sensors based on yttria stabilized zirconia (YSZ) with WO3 as sensing electrode were fabricated using either Pt or Au electrodes. The sensors were studied in the temperature range 550–700°C in the presence of different concentrations (300–1000 ppm) of NO2 and CO in air. The response to NO2 was very stable with fast response time (20–40 s). The best sensitivity (18.8 mV/decade) using Pt electrodes was observed at 600°C. At the same temperature a cross-sensitivity (– 15 mV/decade) to CO gas was also noticed. The response to CO was decreased (– 4 mV/decade) using Au electrode. The role played by WO3 on the sensing electrode was discussed.

• ZrO2 as a high-𝜅 dielectric for strained SiGe MOS devices

The potential of ZrO2 thin film as a high-𝜅 gate dielectric for scaled MOSFET devices has been studied. ZrO2 has been deposited directly on a Si0.8Ge0.2 substrate by reactive RF magnetron sputtering. An equivalent oxide thickness of &lt; 20 Å with a leakage current of the order of 10–4 A/cm2 at 1 V has been obtained. Well-behaved capacitance–voltage characteristics with an interface state density of 2 × 1011 cm–2eV–1 have been achieved. The deposited dielectric exhibits low charge trapping under constant current stressing.

• Phonons in mixed superionic fluorites (BaF2)1–𝑥(LaF3)𝑥

In recent years, the fluorite-structured solid solutions with the general formula, (MF2)1–𝑥(RF3)𝑥 (M = Ca, Sr, Ba, Pb and R is a rare-earth element or Y), have been the subject of numerous experimental studies focussed on their superionic properties. The overall cubic crystal symmetry (space group 𝐹𝑚3𝑚) is conserved up to 𝑥 ≤ 𝑥max, where 𝑥max 0.4–0.5 depending on M and R. The zone centre phonons and phonon dispersion along three symmetry directions of the mixed superionic compound (BaF2)1–𝑥(LaF3)𝑥 have been investigated by applying de Launey angular force model for 𝑥 ≤ 𝑥max. The calculated results are compared and explained with available experimental results.

• A novel method for sensing rotational speed, linear displacement and current using superconducting BPSCCO magnetic sensor

For many decades, magnetic sensors have been of great assistance to mankind in variety of functions that include simple compass based navigational systems to devices that monitor the invisible biological activities. In industries magnetic sensors are in great demand for control and measurement of linear and rotary position sensing etc, because of its non destructive and contact less way of detection. Consequently, newer, smarter and cheaper materials are continuously being explored to suit the varied needs of technological requirements. In the present communication, the characteristics of a magnetic sensor, based on the non linear electromagnetic response of the weak links present in the polycrystalline BPSCCO superconductor are reported. The second harmonic response of sintered superconducting BPSCCO pellet in an alternating magnetic field at 40 kHz and 77 K being a strong linear function of low d.c. magnetic field has been utilized for the development of highly sensitive magnetic field sensors. The noise limited resolution of the sensor is found to be 3.16 × 10–9 T/√ Hz for $H_{a.c.}$ = 16 Oe and frequency 40 kHz. We further demonstrate that such HTSC based magnetic sensors are capable of sensing the rotational speed, small displacement and direct current with good resolution. The experimental methods and results obtained are discussed.

• Tunneling of electrons through semiconductor superlattices

The purpose of the present paper is to report a study of tunneling of electrons through semiconductor superlattices (SSL); specially, we have analysed diverse features of transmission coefficient of SSL. The SSL we have considered is Ga0.7Al0.3As–GaAs which has been drawing considerable attention during the recent past on account of some typical features of its band structure. We have indicated how our results would help fabrication of ultra high speed devices.

• Investigations of surface characterization of silicone rubber due to tracking phenomena under a.c. and d.c. voltages

In the present work, tracking phenomena has been studied with silicone rubber material under the a.c. and d.c. voltages following IEC-587 standards. The surface condition of the tracked zone was analysed using wide angle X-ray diffraction (WAXD) and thermogravimetric differential thermal analysis (TG–DTA) studies. The tracking time was different for a.c. and d.c. voltages.

• Flocculation of chromite ore fines suspension using polysaccharide based graft copolymers

Graft copolymers are being experimented at the laboratory scale as flocculants. All the four graft copolymers, viz. starch-𝑔-polyacrylamide, amylopectin-𝑔-polyacrylamide, sodium alginate-𝑔-polyacylamide and carboxymethyl cellulose-𝑔-polyacrylamide performed well as flocculants on chromite ore fines suspension. Amylopectin-𝑔-polyacrylamide, in particular, performed superior to the rest of the series from the point of view of settling velocity of flocs which is the most important aspect in solid–liquid separation.

• Purification of cadmium up to 5N+ by vacuum distillation

Cadmium was refined by vacuum distillation, a technique suitable for low boiling and melting point materials, to remove the heavy and low vapour pressure impurities at ppm level. The detailed analysis of the purified Cd as well as raw Cd was done by ICP–OES techniques for 27 impurity elements. Purification was carried out in an efficient high-yield vacuum distillation system designed and fabricated for purifying 3N+ purity indigenous cadmium to 5N+ (99.999%). Analysis confirmed the reduction of total impurity content from 134 ppm (3N7) for raw Cd to 3 ppm (5N7) upon vacuum distilled Cd. The present study shows that the analysis of impurities such as Fe, Mg and Ca are contributed from environmental effect, whereas impurities such as Pb, Bi, Ag, Ni, Cu, Zn and Tl require adaptation of elemental analysing technique to counter dilution effect. The Hg trace analysis can however be carried out by hydride generation techniques.

• Characteristics of HgCdTe epilayer grown by LPE using horizontal slider

The characteristics of HgCdTe epilayers grown in a modified horizontal slider system, are reported here. The surface morphology of the grown layers, their IR transmission characteristics, depth and lateral compositional uniformity, structural and electrical characteristics are discussed.

• Development of diamond coated tool and its performance in machining Al–11%Si alloy

An attempt has been made to deposit CVD diamond coating on conventional carbide tool using hot filament CVD process. ISO grade K10 turning inserts with SPGN 120308 geometry were used to deposit diamond coating. This diamond coating well covering the rake surface, cutting edges and flank surfaces could be successfully deposited. The coatings were characterized by SEM, XRD and Raman spectroscopy for coating quality, morphology etc. Performance of diamond coated tool relative to that of uncoated carbide tool was evaluated in turning Al–11%Si alloy under dry environment. The diamond coated tool outperformed the uncoated carbide tool which severely suffered from sizeable built-up edge formation leading not only to escalation of cutting forces but also poorer surface finish. In contrast, the diamond coated tool, owing to chemical inertness of diamond coating towards the work material, did not show any trace of edge built-up even in dry environment and could maintain low level of cutting forces and remarkably improved surface finish. It has been further revealed that success of the diamond coated tool depends primarily on adhesion of the diamond coating with the carbide substrate and this is strongly influenced by the pre-treatment of the carbide substrate surface before coating.

• A novel technique for fabrication of near-net-shape CMCs

A sol–gel vacuum infiltration technique has been developed for the fabrication of near-net-shape ceramic matrix composites (CMCs) using discontinuous mullite fibre preform with 15 vol.% of fibre content and ZrO2.10 wt.% Y2O3 sol as the infiltrant. Effect of sol viscosity, number of infiltration and calcination temperature on physico-mechanical properties of fabricated CMCs were examined. Characterization of the fibre preform, matrix material (in the form of ceramic specimen without fibre) and the developed CMCs were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD indicated the presence of cubic (𝑐) and tetragonal (𝑡) zirconia in both the CMCs and the ceramic specimens calcined even at 1400°C. Flexural strength of the CMCs and the ceramic specimens (calcined at 1400°C), determined by the three-point bending test, was found to be about 14 mPa and 1.40 mPa, respectively. SEM indicated multiple fracture of the matrix which gave rise to pseudo elasticity. This is also evident from the load-displacement curve of the three-point bend test. SEM studies also indicated fibre pull-out in the fracture surface of the CMCs.

• Bi-layer functionally gradient thick film semiconducting methane sensors

Gas sensors based on metal oxide semiconductors like tin dioxide are widely used for the detection of toxic and combustible gases like carbon monoxide, methane and LPG. One of the problems of such sensors is their lack of sensitivity, which to some extent, can be circumvented by using different catalysts. However, highly reactive volatile organic compounds (VOC) coming from different industrial and domestic products (e.g. paints, lacquers, varnishes etc) can play havoc on such sensors and can give rise to false alarms. Any attempt to adsorb such VOCs (e.g. by using activated charcoal) results in sorption of the detecting gases (e.g. methane) too. To get round the problem, bi-layer sensors have been developed. Such tin oxide based functionally gradient bi-layer sensors have different compositions at the top and bottom layers. Here, instead of adsorbing the VOCs, they are allowed to interact and are consumed on the top layer of the sensors and a combustible gas like methane being less reactive, penetrates the top layer and interacts with the bottom layer. By modifying the chemical compositions of the top and bottom layers and by designing the electrode-lead wire arrangement properly, the top layer can be kept electrically shunted from the bottom layer and the electrical signal generated at the bottom layer from the combustible gas is collected. Such functionally gradient sensors, being very reliable, can find applications in domestic, industrial and strategic sectors.

• Low temperature preparation of nanocrystalline solid solution of strontium barium niobate by chemical process

Sr𝑥Ba1–𝑥Nb2O6 (with 𝑥 = 0.4, 0.5 and 0.6) powders have been prepared by thermolysis of aqueous precursor solutions consisting of triethanolamine (TEA), niobium tartarate and, EDTA complexes of strontium and barium ions. Complete evaporation of the precursor solution by heating at ∼ 200°C, yields in a fluffy, mesoporous carbon rich precursor material, which on calcination at 750°C/2 h has resulted in the pure SBN powders. The crystallite and average particle sizes are found to be around 15 nm and 20 nm, respectively.

• Development of nano indium tin oxide (ITO) grains by alkaline hydrolysis of In(III) and Sn(IV) salts

Indium tin oxide (ITO) nano powders of different compositions (In : Sn = 90 : 10, 70 : 30 and 50 : 50) were prepared by heat treatment (300–450°C) of mixed hydroxides of In(III) and Sn(IV). The hydroxides were obtained by the reaction of aq. NH3 with mixed aq. solutions of In(NO3)3 and SnCl4. FTIR and TG/DTA studies revealed that powders existed as In(OH)3 H2O−SnO3H2 H2O in the solid state and then they transformed to In2O3–SnO2 via some metastable intermediates after 300°C. Cubic phase of In2O3 was identified by XRD for the oxides up to 30% of Sn. Particle size measurements of the solid dispersed in acetone and SEM study for microstructure showed that the oxides were in the nano range (55–75 nm) whereas the size range determined from Debye–Scherrer equation were 11–24 nm.

• UV-photoactivation technique for size and shape controlled synthesis and annealing of stable gold nanoparticles in micelle

Gold nanoparticles of different sizes and shapes have been prepared by UV-photoactivation technique using the micelle TX-100 (poly(oxyethylene) iso-octylphenyl ether) as reducing agent, stabilizing agent as well as template which has been authenticated from the plasmon absorption band and TEM picture. The heating effect on those gold nanoparticles has also been studied.

• Improved zinc oxide film for gas sensor applications

Zinc oxide (ZnO) is a versatile material for different commercial applications such as transparent electrodes, piezoelectric devices, varistors, SAW devices etc because of its high piezoelectric coupling, greater stability of its hexagonal phase and its pyroelectric property. In fact, ZnO is a potential material for gas sensor applications. Good quality ZnO films were deposited on glass and quartz substrates by a novel CVD technique using zinc acetate as the starting solution. X-ray diffraction confirmed the crystallinity of the zinc oxide film and SEM study revealed uniform deposition of fine grains. Undoped ZnO films were used for detection of dimethylamine (DMA) and H2 at different temperatures by recording the change in resistivity of the film in presence of the test gases. The response was faster and the sensitivity was higher compared to the earlier reported ZnO based sensors developed in our laboratory. The main objective of this work was to study the selectivity of the ZnO film for a particular gas in presence of the others. The operating temperature was found to play a key role in the selectivity of such sensors.

• Structural, dielectric and electrical properties of Sm-modified Pb(SnTi)O3 ferroelectric system

We have synthesized (Pb1–𝑥Sm𝑥)(Sn𝑦Ti1–𝑦)1–𝑥/4O3 (PSmST) polycrystalline ferroelectric ceramics with 𝑥 = 0.05, 0.07, 0.1 and 𝑦 = 0.45 by a solid-state reaction technique and performed preliminary X-ray diffraction (XRD) analysis, detailed temperature and frequency dependence dielectric measurements on them. The a.c. conductivity has been investigated over a wide range of temperature and the activation energy ($E_{a.c.}$) has also been calculated. It is observed that

1. the dielectric permittivity (𝜀) and loss tangent (tan 𝛿) are dependent on frequency,

2. the temperature of dielectric permittivity maximum shifts toward lower temperature side with the increase of samarium ion (Sm+3) concentration at the Pb sites, and

3. observed and calculated 𝑑-values of XRD patterns show that the compounds have been formed in orthorhombic single phase.

• Thermal sensor properties of PANI(EB)–CSA𝑋 (𝑋 = 0.4 ± 0.1 mol) polymer thin films

Films of polyaniline(EB) doped with camphor sulfonic acid (CSA) from 𝑚-cresol on glass substrates exhibit considerable metallic properties. Such polymer metallic films have thermal sensitivity superior to ceramic metal (Cermet) films, prepared by metallo organic deposition (MOD) technique on silicon substrates. These PANI(EB)–CSA𝑋 (𝑋 = 0.5, 0.4, 0.3 mol) polymer films were developed through controlled temperature atmosphere 60 ± 2°C for 60 min, and with the help of temperature dependence of resistivity (ρ) values, high temperature coefficient of resistance (TCR) i.e. 𝛼 values, and figure of merit (ρ 𝛼) values of these films, thermal sensitivity were compared from that we observed. Among the three doping ratios the PANI(EB)–CSA$_{0.3 mol}$ film (4.4 𝜇m thick) on glass substrate resistivity (ρ) values in the range of 838–1699 𝛺.𝜇m with high TCR i.e. 𝛼 = 10,291 ppm/°C and figure of merit (ρ 𝛼) value in range of 8.62–17.48 𝛺m/°C seems to be the best. This paper deals with these superior thermal-sensing properties together with optical studies and surface topography by atomic force microscopy (AFM). These polymer films offer design advantages in developing ‘thin film polymer thermal sensor’.

• Studies of properties of rubber wood with impregnation of polymer

Impregnation of rubber wood has been carried out under different conditions by using styrene as grafting monomer and glycidyl methacrylate (GMA) as crosslinker. Properties such as dimensional stability, water absorption, hardness, tensile strength, flexural strength, etc of the impregnated wood have been checked and found to be improved by incorporation of GMA as the crosslinker with styrene. The polymer-impregnated wood has also been characterized by FTIR spectroscopy and DSC.

• Synthesis and performance of a novel polyurethaneurea as pervaporation membrane for the selective removal of phenol from industrial waste water

Hydroxyterminated polybutadiene (HTPB) was reacted with 2,4-toluene diisocyanate (TDI)followed by the addition of a diamine chain extender (prepared by the condensation reaction of 4,4′-diaminodiphenylsulfone and terepthalaldehyde) to prepare an imine containing polyurethaneurea (PIUU). The prepared polyurethaneurea was caste in order to obtain polymer film. The new polyurethaneurea film showed high phenol selectivity as pervaporation membrane. About 88% phenol was obtained in condensed permeate when pervaporation was performed at 50°C with 7% aqueous phenol solution as feed and permeate side pressure was maintained at 5 mm of Hg.

• Grafted hydroxypropyl guargum: Development, characterization and application as flocculating agent

Synthesis of hydroxypropyl guargum-𝑔-polyacrylamide was carried out by ceric ion induced redox polymerization technique at 28 ± 1°C. The graft copolymer was characterized by IR and thermal analysis. The flocculation performance of graft copolymer was tested in 1 wt% coal suspension.

• New semiconductor materials for magnetoelectronics at room temperature

Most of the semiconductor materials are diamagnetic by nature and therefore cannot take active part in the operation of the magneto electronic devices. In order to enable them to be useful for such devices a recent effort has been made to develop diluted magnetic semiconductors (DMS) in which small quantity of magnetic ion is introduced into normal semiconductors. The first known such DMS are II–VI and III–V semiconductors diluted with magnetic ions like Mn, Fe, Co, Ni, etc. Most of these DMS exhibit very high electron and hole mobility and thus useful for high speed electronic devices. The recent DMS materials reported are (CdMn)Te, (GaMn)As, (GaMn)Sb, ZnMn(or Co)O, TiMn(or Co)O etc. They have been produced as thin films by MBE and other methods. This paper will discuss the details of the growth and properties of the DMS materials and some of their applications.

• Tellurium purification: various techniques and limitations

Limitations and techniques to purify tellurium metal especially using non-chemical techniques such as vacuum distillation and zone refining are discussed. It was found that the clean environments, design, handling and cleaning of quartz ware are equally important in achieving the desired purity levels.

• Semiconductor applications of plasma immersion ion implantation technology

Many semiconductor integrated circuit manufacturing processes require high dose of implantation at very low energies. Conventional beam line ion implantation system suffers from low beam current at low energies, therefore, cannot be used economically for high dose applications. Plasma immersion ion implantation (PIII) is emerging as a potential technique for such implantations. This method offers high dose rate irrespective of implantation energy. In the present study nitrogen ions were implanted using PIII in order to modify the properties of silicon and some refractory metal films. Oxidation behaviour of silicon was observed for different implantation doses. Diffusion barrier properties of refractory barrier metals were studied for copper metallization.

• Progress in deep-UV photoresists

Higher resolution can be achieved in lithography by decreasing the wavelength of the exposure source. However, resist material and their processing are also important when we move to a shorter wavelength lithography technology. This paper reviews the recent development and challenges of deep-UV photoresists and their processing technology.

• 3-D mapping with ellipsometrically determined physical thickness/refractive index of spin coated sol–gel silica layer

Precursor sol for sol–gel silica layer was prepared from the starting material, tetraethylorthosilicate (TEOS). The sol was deposited onto borosilicate crown (BSC) glass by the spinning technique (rpm 2500). The gel layer thus formed transformed to oxide layer on heating to 450°C for ∼ 30 min. The physical thicknessand the refractive index of the layer were measured ellipsometrically (Rudolph Auto EL II) at 632.8 nm. About 10 × 10 mm surface area of the silica layer was chosen for evaluation of thickness and refractive index values at different points (121 nos.) with 1 mm gap between two points. Those data were utilized in the Autolisp programme for 3-D mapping. Radial distribution of the evaluated values was also displayed.

• Synthesis of SiC from rice husk in a plasma reactor

A new route for production of SiC from rice husk is reported by employing thermal plasma technique. The formation of 𝛽-SiC is observed in a short time of 5 min. The samples are characterized by XRD and SEM.

• Shape forming of ceramics via gelcasting of aqueous particulate slurries

Gelcasting is a promising technique for shape forming of bulk dense or porous ceramic, metal structures. The process offers a number of advantages over processes such as slip casting, injection molding in forming complex ceramic shapes. It is shown here that the optimization of slurry rheology, choice of mold material, mold design and the drying conditions have a significant role in the overall success of the process. In this process, components of simple or complex shapes can be produced to near net shape by direct casting. If required complex shapes can also be produced by machining the green gelcast bodies. The process of gelcasting also has a lot of potential in forming highly porous ceramic shapes.

• Effect of boric acid sintering aid on densification of barium ferrite

Boric acid has been added in 0.1–0.6% range for studying the densification characteristics of solid state sintered barium hexaferrite. Sintering studies have been carried out at three different temperatures. Physical properties like density and porosity have been studied for all compositions. The phase identification and microstructural investigation on the fractured surface have been carried out to understand the effect of sintering aid on the densification characteristics.

• Influence of quench rates on the properties of rapidly solidified FeNbCuSiB alloy

FeNbCuSiB based materials were produced in the form of ribbons by rapid solidification techniques. The crystallization, magnetic, mechanical and corrosion behaviour were studied for the prepared materials as a function of quenching rate from liquid to the solid state. Higher quench rates produced a more amorphous structure exhibiting superior soft magnetic properties with improved corrosion resistance.

• Silver and gold nanocluster catalyzed reduction of methylene blue by arsine in micellar medium

Arsenic can be determined in parts-per-million (ppm) level by absorbance measurement. This method is based on the quantitative colour bleaching of the dye, methylene blue by arsine catalyzed by nanoparticles in micellar medium. The arsine has been generated in situ from sodium arsenate by NaBH4 reduction. The absorbance measurement was carried out at the 𝜆max of the dye at 660 nm. The calibration graph set-up for three linear dynamic ranges (LDR) are 0–8.63 ppm, 0–1.11 ppm and 0–0.11 ppm and limit of detections (LODs) are 1.3, 0.53 and 0.03 ppm, respectively. This method is simple, sensitive and easy to carry out. It is free from phosphate and silicate interference and applicable to real sample analysis.

• Evolution, dissolution and reversible generation of gold and silver nanoclusters in micelle by UV-activation

Gold and silver nanoparticles were produced separately by UV photoactivation (with variable flux density) in the presence of nonionic micelle, TX-100. Even their cyano complexes break down in TX-100 under UV and hence dissolution and reevolution of almost monodispersed nanoparticles (∼ 3 nm) are possible.

• # Bulletin of Materials Science

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