Development of a roller quenching apparatus for the production of amorphous phases

The details of an apparatus designed to produce amorphous phases by rapid quenching from the melt are described. A drop of molten material is squeezed between two copper rollers rotating against each other at 5000 RPM and a thin foil of the material is produced. The system produces cooling rates of the order of 105 K/sec. Details of the development and construction are mentioned

Behaviour of ultrasonic velocities in amorphous Se<SUB>90</SUB>Ge<SUB>10</SUB> and Se<SUB>85</SUB>Ge<SUB>15</SUB> alloys near their glass transition

Precise measurements of 10 MHz frequency longitudinal and shear wave velocities are reported in amorphous SeGe alloys near their glass transition temperature Tg . There is a sharp decrease of the velocities near Tg , but the reduction in velocities appears smaller than expected

Preparation of Zinc-Sulfide Thin Films in the Presence of Sodium Tartrate as a complexing agent

The article offers information on the experiment done for the electrodeposition of zinc-sulfide (ZnS) thin films on the titanium substrate in the presence of sodium tartrate as a complexing agent. It states that the electrodeposition process has several advantages such as the possibility for large-scale production and minimum waste of components. It mentions that depositions were carried out by varying the deposition potential to determine the optimal conditions of deposition of ZnS thin film

Study of the electronic and optical bonding properties of doped SnO2

Numerous metal oxide semiconductor materials were reported to be usable as semiconductor gas sensor, such as ZnO, SnO2, TiO2 and so on. These materials have non-stoichiometric structure so free electron originating from oxygen vacancies contribute to electrical conductivity. The interaction of different gas compounds with an oxide surface may lead to changes in the lattice oxygen content at the surface in addition to changes in the amount of adsorbed species. The samples of Cu doped SnO2 have been synthesized by solid-state reaction method. Some aspects of crystal structure of the compound at room temperature were studied using X-ray diffraction technique. The XRD study of the compound shows that there is a change in the crystal structure of SnO2 on substitutions of CuO. The patterns of the SnO2 sample are indexed as tetragonal perovskite type with a = 7.3928 angstrom, c = 5.2879 angstrom but on substitution of CuO the structure becomes orthorhombic with lattice constant a = 21.8594 angstrom, b = 5.3200 angstrom, c = 5.1803 angstrom. Several bands due to fundamentals, overtones and combination of OH, Sn-O and Sn-O-Sn entities appear in 4000-800 cm(-1) range

Recent applications of heat capacity measurement in physicochemical investigations

This review discusses the recent experimental heat capacity measurements which have been very useful in physicochemical investigations. Areas reviewed include critical point phenomena in systems such as fluids, magnetic systems, liquid crystals, co-operative Jahn-Teller transitions, etc. The uses of C<SUB>p</SUB> measurements in the study of discrete energy levels in solids, in glasses at very low temperatures, in thin films and at high pressures are discussed. Calorimetric investigations in A-15 and other superconducting materials and applications of C<SUB>p</SUB> measurements for evaluation of thermodynamic parameters in several new classes of materials are then briefly described. Finally, examples of applications of calorimetry in areas of biophysics, biological sciences and clinical medicine are cited. Two hundred and seventy references are cited and 25 figures are used for illustration

Effect of Ni doping on thick film SnO2 gas sensor

Ni- and/or Al-doped and undoped SnO2 thick film gas sensors were prepared using screen printing technique and tested for their LPG gas sensitivity. Tin oxide powder was prepared using a chemical precipitation technique. The sensitivity, optimum working temperature and response time were investigated in relation to dopants as well as preparation route. The results show that the gas sensitivity is affected not only by the additive but the way it is added into the sensor material. The results indicated a reduction in grain size on Al and Ni doping. The results on resistance, response and recovery time were explained in terms of n-p junction formation between SnO2 and NiO, which increases the depletion barrier height

A comparison of the properties of porous silicon formed on polished and textured (100) Si: High resolution XRD and PL studies

Porous silicon (PS) layers formed by anodization on polished and textured substrates of (100) Si at different current densities for a fixed anodization time of 30 min have been characterized by high resolution X-ray diffraction (HRXRD), and photoluminescence (PL) techniques. Porosity and thickness of PS layers were estimated by gravimetric analysis. PS layers and their interfaces have been characterized by recording topographs, diffraction curves, measuring lattice mismatch/strain and the radius of curvature due to induced biaxial stress caused by the lattice expansion of PS film due to pores. The strain in PS films formed on textured substrates varies linearly upto larger current densities without elastic relaxation. Porosity and strain measurements made on both the types of PS films show that stable and highly porous PS films having different strain values corresponding to wide range of band gaps can be formed on textured substrate. PS films formed on textured substrate show higher PL intensity and higher life time values as compared to those formed on polished substrates for the same current density. The present studies indicate that the structural, mechanical and optical properties of thick PS films formed on textured samples are superior to that formed on polished specimens

Study of structural and microstructural properties of SnO2 powder for LPG and CNG gas sensors

Nanosized tin oxide powders were obtained using microwave assisted synthesis procedure for their application on gas sensor technology. XRD results showed the presence of casseterite structure. As found from the XRD line broadening the crystallite size of the powders were in the range of 20-14 nm even after heating to 600 degrees C for 3 h. TEM results showed microwave assisted powders to be less agglomerated as compared to conventional process. Enhancement in LPG and CNG gas sensitivity was realized after microwave irradiation to a hydrosol solution

Role of surface texturization in the formation of highly luminescent, stable and thick porous silicon films

Porous silicon (PS) films were prepared by anodization on polished and textured substrates of (100) Si at different current densities for a fixed anodization time of 30 min. Using scanning electron microscopy (SEM), high-resolution X-ray diffractometry (HRXRD) and photoluminescence (PL) decay measurements, we have demonstrated that the texturization of silicon surface is a simple and effective method for the formation of mechanically stable thick porous silicon films. The PS formed on textured substrates exhibits higher porosity, negligible PL decay, better adherence to the substrate and non-fractured surface morphology compared to that formed on polished silicon substrates under the same preparation conditions. The morphology of the PS film as observed by SEM indicates the formation of highly porous vertical layers separating macroscopic domains of nanoporous silicon. The lattice mismatch or strain measurements from HRXRD revealed that a variety of good quality PS films having different strain values (by varying the current density) corresponding to wide range of band gaps suitable for sensor applications can be formed on textured substrate