• Volume 30, Issue 6

December 2007,   pages  541-636

• Diamond like carbon coatings deposited by microwave plasma CVD: XPS and ellipsometric studies

Diamond-like carbon (DLC) films were deposited by microwave assisted chemical vapour deposition system using d.c. bias voltage ranging from –100 V to –300 V. These films were characterized by X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry techniques for estimating 𝑠𝑝3/𝑠𝑝2 ratio. The 𝑠𝑝3/𝑠𝑝2 ratio obtained by XPS is found to have an opposite trend to that obtained by spectroscopic ellipsometry. These results are explained using sub-plantation picture of DLC growth. Our results clearly indicate that the film is composed of two different layers, having entirely different properties in terms of void percentage and 𝑠𝑝3/𝑠𝑝2 ratio. The upper layer is relatively thinner as compared to the bottom layer.

• Structural and optical properties of electron beam evaporated CdSe thin films

Thin films of cadmium selenide (CdSe) as a semiconductor is well suited for opto-electronic applications such as photo detection or solar energy conversion, due to its optical and electrical properties, as well as its good chemical and mechanical stability. In order to explore the possibility of using this in optoelectronics, a preliminary and thorough study of optical and structural properties of the host material is an important step. Based on the above view, the structural and optical properties of CdSe films have been studied thoroughly in the present work. The host material, CdSe film, has been prepared by the physical vapour deposition method of electron beam evaporation (PVD: EBE) technique under a pressure of 5 × 10-5 mbar. The structural properties have been studied by XRD technique. The hexagonal structure with a preferred orientation along the (0 0 2) direction of films has been confirmed by the X-ray diffraction analysis. The films have been analysed for optical band gap and absorbed a direct intrinsic band gap of 1.92 eV.

• Ethanol gas sensing properties of Al2O3-doped ZnO thick film resistors

The characterization and ethanol gas sensing properties of pure and doped ZnO thick films were investigated. Thick films of pure zinc oxide were prepared by the screen printing technique. Pure zinc oxide was almost insensitive to ethanol. Thick films of Al2O3 (1 wt%) doped ZnO were observed to be highly sensitive to ethanol vapours at 300°C. Aluminium oxide grains dispersed around ZnO grains would result into the barrier height among the grains. Upon exposure of ethanol vapours, the barrier height would decrease greatly leading to drastic increase in conductance. It is reported that the surface misfits, calcination temperature and operating temperature can affect the microstructure and gas sensing performance of the sensor. The efforts are, therefore, made to create surface misfits by doping Al2O3 into zinc oxide and to study the sensing performance. The quick response and fast recovery are the main features of this sensor. The effects of microstructure and additive concentration on the gas response, selectivity, response time and recovery time of the sensor in the presence of ethanol vapours were studied and discussed.

• Etching of GaAs substrates to create As-rich surface

Several different cleaning procedures for GaAs (100) substrates are compared using X-ray photoelectron spectroscopy and optical microscopy. This work emphasizes the effect of the last etching step: using either HCl, HF–ethanol (5%) or static deionized water after HCl cleaning. All the procedures except HCl solution (1 : 1) produce an As-rich surface. Also, none of the etchants except HF–ethanol solution produce Ga or As-rich (oxide free) surfaces. Optical microscopic study shows different etch pits produced due to etching in different solutions.

• Microwave synthesis and sintering characteristics of CaCu3Ti4O12

CaCu3Ti4O12 (CCTO) was synthesized and sintered by microwave processing at 2.45 GHz, 1.1 kW. The optimum calcination temperature using microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size to be in the range 1–7 𝜇m. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary from 11000–7700 in the 100 Hz–100 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered by conventional sintering routes and decreases with increase in frequency.

• Facile synthesis of ZnO hollow fibres

In this paper, cotton fibres were used as bio-template to successfully synthesize new ceramic materials, ZnO hollow fibres and in an effort to explore the synthesis condition, and simplify the synthesis procedure. In this synthesis, a direct thermal decomposition of zinc acetate dihydrate coated on the surface of cotton fibres was explored. The wall porosity of the ZnO hollow fibres was controlled by changing the concentration of zinc acetate aqueous solution.

• Dielectric properties and relaxation of Bi0.5Na0.5TiO3–BaNb2O6 lead-free ceramics

A new member of lead-free piezoelectric ceramics of the BNT-based group, (1 – 𝑥)Bi0.5Na0.5TiO$_{3}–x$ BaNb2O6, was prepared by conventional solid state reaction and its dielectric properties and relaxation was investigated. X-ray diffraction showed that BaNb2O6 diffused into the lattice of Bi0.5Na0.5TiO3 to form a solid solution with perovskite-type structure. A diffuse character was proved by the linear fitting of the modified Curie–Weiss law. The temperature dependence of dielectric constant at different frequencies revealed that the solid solution exhibited relaxor characteristics different from classic relaxor ferroelectrics. The samples with 𝑥 = 0.002 and 0.006 exhibited obvious relaxor characteristics near the low temperature dielectric abnormal peak, 𝑇f, and the samples with 𝑥 = 0.010 and 0.014 exhibited obvious relaxor characteristics between room temperature and 𝑇f. The mechanism of relaxor behaviour was also discussed according to the macro-domain to micro-domain transition theory.

• Depolarization temperature and piezoelectric properties of Na1/2Bi1/2TiO3–Na1/2Bi1/2(Zn1/3Nb2/3)O3 ceramics by two-stage calcination method

A new group of NBT-based lead-free piezoelectric ceramics, Na1/2Bi1/2TiO3–Na1/2Bi1/2(Zn1/3Nb2/3)O3, was synthesized using the two-stage calcination method and depolarization temperatures and piezoelectric properties were also investigated. The XRD analysis showed that the ceramics system had a morphotropic phase boundary (MPB) between the rhombohedral and the tetragonal structure. The highest piezoelectric properties of 𝑑33 = 97 pC/N and 𝑘𝑡 = 0.46 were obtained near MPB compositions. Furthermore, the depolarization temperatures near MPB compositions were slightly decreased and the lowest 𝑇d was maintained at 210°C.

• Low voltage varistor ceramics based on SnO2

The nonlinear current (𝐼)–voltage (𝑉) characteristics of tin dioxide doped with either Nb2O5 and CoO or Sb2O3 and CoO show promising values of nonlinear coefficient (𝛼) values (∼11) with low breakdown voltages (𝐸B, ∼40 V mm-1). The pentavalent antimony or niobium acts as donor and increases the electronic conductivity. The crucial parameter for obtaining low breakdown voltage is the grain size, which depends upon sintering duration and temperature of these oxide ceramics.

• Surface characterization of silver and palladium modified glassy carbon

In this work, the influence of silver and palladium on the surface of undoped, boron doped and phosphorus doped glassy carbon has been studied. The silver and palladium concentrations in solution, after metal deposition, were measured by atomic absorption spectrophotometer. The morphology of metal coatings was characterized by scanning electron microscopy. In order to investigate the nature and thermal stability of surface oxygen groups, temperature-programmed desorption method combined with mass spectrometric analyses, was performed. The results obtained have shown that silver and palladium spontaneously deposit from their salt solutions at the surface of glassy carbon samples. Silver deposits have dendrite structure, whilst palladium forms separate clusters. The highest amount of both silver and palladium deposits at the surface of sample containing the highest quantity of surface oxide complexes. It has been concluded that carboxyl groups and structure defects are responsible for metal reduction. Calculated desorption energies have shown that the surface modification by metal deposition leads to the formation of more stable surface of undoped and doped glassy carbon samples.

• Role of Ti3Al/silicides on tensile properties of Timetal 834 at various temperatures

Extremely fine coherent precipitates of ordered Ti3Al and relatively coarse incoherent precipitates of 𝑆2 silicide exist together in the near 𝛼-titanium alloy, Timetal 834, in the dual phase matrix of primary 𝛼 and transformed 𝛽. In order to assess the role of these precipitates, three heat treatments viz. WQ, WQ–A and WQ–OA, were given to have no precipitates, Ti3Al and silicide and only silicide precipitates in the respective conditions. Tensile properties in the above three heat treated conditions were determined at room temperature, 673 K and 873 K. It was observed that largely Ti3Al precipitates were responsible for increase in the yield strength and decrease in ductility in this alloy.

• Pulsed nanocrystalline plasma electrolytic boriding as a novel method for corrosion protection of CP-Ti (Part 1: Different frequency and duty cycle)

Potentiodynamic polarization and electrochemical impedance spectroscopy were employed to test borided CP-Ti, treated by a relatively new method called pulsed plasma electrolytic boriding. The results show excellent corrosion resistance for modified CP-Ti. The effect of frequency and duty cycle of pulsed current was investigated. It was found that pulse frequency and duty cycle affect the size and porosity of nanocrystalline borides and by controlling these effective parameters, surface modification can render the CP-Ti material extremely corrosion resistant as a biomaterial.

• Performance evaluation of reactive direct current unbalanced magnetron sputter deposited nanostructured TiN coated high-speed steel drill bits

The stainless steels, in general, are considered to be difficult-to-machine materials. In order to machine these materials the surface of the tool is generally coated with physical vapour deposition (PVD) hard coatings such as titanium nitride (TiN), titanium aluminum nitride (TiAlN), etc. The adhesion is of vital importance for the performance of tools coated with PVD coatings. Proper surface treatments (in situ and ex situ) are required to achieve highly adherent PVD coatings on tools. We have deposited nanostructured TiN coatings on high-speed steel (HSS) drill bits and mild steel substrates using an indigenously built semi-industrial fourcathode reactive direct current (d.c.) unbalanced magnetron sputtering system. Various treatments have been given to the substrates for improved adhesion of the TiN coatings. The process parameters have been optimized to achieve highly adherent thick good quality TiN coatings. These coatings have been characterized using X-ray diffraction, nanoindentation and atomic force microscopy techniques. The performance of the coated HSS drill bits is evaluated by drilling a 13 mm thick 304 stainless steel plate under wet conditions. The results show significant improvement in the performance of the TiN coated HSS drill bits.

• Synthesis of silica nanosphere from homogeneous and heterogeneous systems

Silica nanosphere was synthesized using homogeneous and heterogeneous systems, respectively. In homogeneous system, silica spheres were synthesized without cetyltrimethylammonium bromide (CTABr), which gave bimodal particle size and lower yield (77%). To improve the yield, CTABr was added and found that the yield was very high (100%). The particle was in nm range, but the particle sizes are bimodal. To avoid it, reaction in heterogeneous system using CTABr was carried out. Nanosized silica sphere with uniform size (yield, 94%) was observed. Homogeneous system contains a mixture of ethanol, water, aqueous ammonia and tetraethylorthosilicate (TEOS). In the case of heterogeneous system, only ethanol was absent.

• Subject index

• Author index

• # Bulletin of Materials Science

Volume 43, 2020
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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019