Influence of Annealing on Physical Properties of CdO Thin Films Prepared by SILAR Method

Cadmium oxide (CdO) thin films were prepared by successive ionic layer adsorption and reaction (SILAR) method and annealed at 250-450℃ for 2 h. The prepared films were characterized by X-ray diffraction (XRD), optical spectroscopy, scanning electron microscopy (SEM) and Hall effect measurement. The XRD analysis reveals that the films were polycrystalline with cubic structure. Both crystallinity and the grain size were found to increase with increasing annealing temperature. SEM analysis shows the porous nature of the surface with spherical nanoclusters. Energy dispersive spectroscopic analysis (EDS) confirmed the presence of Cd and O elements without any additional impurities. The films exhibited maximum transmittance (82%-86%) in infra-red (IR) region. Transmittance was found to decrease with increasing annealing temperature and the estimated band gap energy (Eg) was in the range of 2.24-2.44 eV. Hall effect measurement shows an increase in carrier concentration and a decrease in resistivity with increasing annealing temperature. The carrier concentration (N) and resistivity (ρ) of about 1.26×1022 cm-3 and 8.71×10-3Ω cm are achieved for the film annealed at 450℃for 2 h.     

On the triggering mechanism for the metal–insulator transition in thin film VO<Subscript>2</Subscript> devices: electric field versus thermal effects

Vanadium dioxide (VO₂) has been shown to undergo an abrupt electronic phase transition near 70 °C from a semiconductor to a metal, with an increase in dc conductivity of over three orders of magnitude, making it an interesting candidate for advanced electronics as well as fundamental research in understanding correlated electron systems. Recent experiments suggest that this transition can be manifested independent of a structural phase transition in the system, and that it can be triggered by the application of an electric field across the VO₂ thin film. Several experiments that have studied this behavior, however, also involve a heating of the VO₂ channel by leakage currents, raising doubts about the underlying mechanism behind the transition. To address the important question of thermal effects due to the applied field, we report the results of electro-thermal simulations on a number of experimentally realized device geometries, showing the extent of heating caused by the leakage current in the “off” state of the VO₂ device. The simulations suggest that in a majority of the cases considered, Joule heating is insufficient to trigger the transition by itself, resulting in a typical temperature rise of less than 10 K. However, the heating following a field-induced transition often also induces the structural transition. Nevertheless, for certain devices, we identify the possibility of maintaining the field-induced high conductivity phase without causing the structural phase transition: an important requirement for the prospect of making high-speed switching devices based on VO₂ thin film structures. Such electronically driven transitions may also lead to novel device functionalities including ultra-fast sensors or gated switches incorporating ferroelectrics.     

Exploration of Physical Properties on Pure and Ce Doped Sr0.6Ba0.4Nb2O6 Thin Films

Silicon - Sr0.6Ba0.4Nb2O6 (SBN 60:40) thin films have been grown on various substrates using Radio Frequency (RF) sputtering technique. Influence of cerium ions as the dopant in (SBN 60:40) matrix...     

Structure and morphology of small diameter electrospun aramid fibers

Very small diameter fibers of poly(p-phenylene terephthalamide) (PPTA) ranging in diameter from 40nm to a few hundreds of nanometers were made by the electrospinning process. The fibers have a circular cross-section, are birefringent and stable at temperatures greater than 400°C. Electron diffraction patterns obtained from both as-spun and annealed fibers show meridional and equatorial reflections demonstrating order in the material. The crystal structure and morphology of the fibers were characterized using bright and dark field electron microscopy, electron diffraction and atomic force microscopy.     

A Comparison of Wear Due to Abrasion of WC–Ni Coatings on Aluminium Alloy Sprayed by HVOF and Detonation Gun

In this investigation, aluminum alloy is coated with WC–Ni layer deposited by detonation spraying and high velocity oxy fuel (HVOF) spraying. The important features of microstructure and hardness of the coating are characterized extensively. The wear rates of the coating due to abrasion are determined for different applied loads. The worn coatings are examined under scanning electron microscopy. A correlation is established between the wear rates of the coatings due to abrasion and hardness. The results show that abrasion action takes place by both particle rolling and particle sliding. Fracture of particles during abrasion increases wear rate. In general, the wear rate due to abrasion is higher for the coating deposited by detonation spraying than that of coating deposited by HVOF spraying.     

Compositional and metal-insulator transition characteristics of sputtered vanadium oxide thin films on yttria-stabilized zirconia

Vanadium dioxide (VO₂) thin films have been shown to undergo a rapid electronic phase transition near 70 °C from a semiconductor to a metal, making it an interesting candidate for exploring potential application in high speed electronic devices such as optical switches, tunable capacitors, and field effect transistors. A critical aspect of lithographic fabrication in devices utilizing electric field effects in VO₂ is the ability to grow VO₂ over thin dielectric films. In this article, we study the properties of VO₂ grown on thin films of Yttria-Stabilized Zirconia (YSZ). Near room temperature, YSZ is a good insulator with a high dielectric constant ($\epsilon _{\rm r} > 25$\epsilon _{\rm r} > 25). We demonstrate the sputter growth of polycrystalline VO₂ on YSZ thin films, showing a three order resistivity transition near 70 °C with transition and hysteresis widths of approximately 7 °C each. We examine the relationship between chemical composition and transition characteristics of mixed phase vanadium oxide films. We investigate changes in composition induced by low temperature post-deposition annealing in oxidizing and reducing atmospheres, and report their effects on electronic properties.     

Crystallization kinetics of Nd-substituted yttrium iron garnet prepared through sol–gel auto-combustion method

Nd substituted Y₃Fe₅O₁₂ (YIG) was synthesized using sol–gel auto-combustion method. The phases present in the samples were identified using XRD. The asprepared dried gel was found to transform to the rare earth iron garnet phase at lower temperature when the Nd concentration is lower. Higher concentration of Nd resulted in the formation of orthoferrite as the major phase. The Curie temperature was recorded using thermomagnetic analysis and it was found to increase with the concentration of Nd. The crystallization kinetics of the Nd-substituted garnet phase was studied using TG–DTA. Two stage crystallization was observed from the DTA analysis for Nd₁Y₂Fe₅O₁₂. The activation energy for the formation of Nd₁Y₂Fe₅O₁₂ was 610 kJ/mol, found by using Johnson–Mehl–Avrami (JMA) equation. Three dimensional growth mechanism dominate at lower heating rates for the Nd-substituted YIG.