Grain boundary defects induced room temperature ferromagnetism in V doped ZnO thin films

Vanadium (V) doped ZnO thin films (Zn_1‐xV_x O, where x = 0, 0.05, 0.10) have been grown on sapphire substrates by RF magnetron sputtering to realize room temperature ferromagnetism (RTFM). The grown films have been subjected to X‐ray diffraction (XRD), resonant Raman scattering, photoluminescence (PL) and vibrating sample magnetometer (VSM) measurements to investigate their structural, optical and magnetic properties, respectively. The full width at half maximum of XRD and Raman scattering peaks increases with V ion concentration indicates that the V ions have been substituted on Zn²⁺ ions in the ZnO matrix. The increase in oxygen vacancies with V concentration is evidenced by PL measurements. Rutherford backscattering spectrometry analysis confirms the presence of the V ions in the films. The room temperature VSM measurements reveal the signature of ferromagnetism in V doped ZnO thin films. It has been observed that the grain boundary defects, i.e., oxygen vacancies play a crucial role in inducing RTFM in V doped ZnO films. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of nano ZnO thin film on Al foil by rf glow discharge plasma and its effect on E. coli and P. aeruginosa

Nano ZnO thin films were deposited on thin Al foils by a rf glow discharge plasma method in which sublimed zinc acetate vapor (precursor) reacted with oxygen plasma inside a low-pressure reactor. The films were microstructurally characterized using XRD, TEM, FESEM, optical reflectance and micro-Raman spectroscopy methods. In view of the good scope of ZnO coating in food packaging, the antibacterial activity in the ZnO thin films was studied by exposing the films to E. coli and P. aeruginosa for up to 8 h. Bacterial cell inhibition of up to 98–99 % was observed in the thin films.     

Microstructural analysis of neutron-irradiation induced changes in polyester fibre studied using EPMA

Electron microscopy is an important characterization technique for the study of textile fibre as it gives more information on fabric wear, nature of fibre fracture, chemical degradation, abrasion, fatigue and many others. Electron Probe Micro Analyzer (EPMA) micrographs of virgin and some neutron-irradiated samples (graphite coated) are discussed. The filament diameter, D, of virgin PET fibre obtained from EPMA study was 12.5 μn. The surface topography of single filament distinctly reveals the core and sheath parts of the filament. The core diameter of the virgin fibre was estimated to be 1.43 μm. The fibre irradiated at fluence 1 × 10¹² n/cm² shows radiation induced sphere like polymer balls or spherulites of diameter 2.27 μm in the expanded core region. Due to irradiation, the sheath area crosslinks with expanded core region, which may be responsible for increase of strength and hardness of the polymer materials. Moreover, the micrograph at 3000 X magnifications clearly shows that there is no preferred orientation of the polymer in any direction confirming the isotropic nature of the sample.      

Particulate assisted growth of ZnO nanorods and microrods by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on the gallium nitride (GaN) and sapphire (Al₂O₃) substrates by pulsed laser deposition (PLD) without using any metal catalyst. The experiment was carried out at three different laser wavelengths of Nd:YAG laser (λ = 1064 nm, λ = 532 nm) and KrF excimer laser (λ = 248 nm). The ZnO films grown at λ = 532 nm revealed the presence of ZnO nanorods and microrods. The diameter of the rods varies from 250 nm to 2 μm and the length varies between 9 and 22 μm. The scanning electron microscopy (SEM) images of the rods revealed the absence of frozen balls at the tip of the ZnO rods. The growth of ZnO rods has been explained by vapor-solid (V-S) mechanism. The origin of growth of ZnO rods has been attributed to the ejection of micrometric and sub-micrometric sized particulates from the ZnO target. The ZnO films grown at λ = 1064 nm and λ = 248 nm do not show the rod like morphology. X-ray photoelectron spectroscopy (XPS) has not shown the presence of any impurity except zinc and oxygen.     

Viability of variable generalised Chaplygin gas: a thermodynamical approach

The viability of the variable generalised Chaplygin gas (VGCG) model is analysed from the standpoint of its thermodynamical stability criteria with the help of an equation of state, \(P = - \frac{B}{\rho ^{\alpha } }\), where \(B = B_{0}V^{-\frac{n}{3}}\). Here \(B_{0}\) is assumed to be a positive universal constant, n is a constant parameter and V is the volume of the cosmic fluid. We get the interesting result that if the well-known stability conditions of a fluid is adhered to, the values of n are constrained to be negative definite to make \( \left( \frac{\partial P}{\partial V}\right) _{S} <0\) & \( \left( \frac{\partial P}{\partial V}\right) _{T} <0\) throughout the evolution. Moreover the positivity of thermal capacity at constant volume \(c_{V}\) as also the validity of the third law of thermodynamics are ensured in this case. For the particular case \(n = 0\) the effective equation of state reduces to \(\Lambda \)CDM model in the late stage of the universe while for \(n <0\) it mimics a phantom-like cosmology which is in broad agreement with the present SNe Ia constraints like VGCG model. The thermal equation of state is discussed and the EoS parameter is found to be an explicit function of temperature only. Further for large volume the thermal equation of state parameter is identical with the caloric equation of state parameter when \( T \rightarrow 0\). It may also be mentioned that like Santos et al. our model does not admit of any critical points. We also observe that although the earlier model of Lu explains many of the current observational findings of different probes it fails to explain the crucial tests of thermodynamical stability.     

Dielectric and phase transition of BaTi<Subscript>0.6</Subscript>Zr<Subscript>0.4</Subscript>O<Subscript>3</Subscript> ceramics prepared by a soft chemical route

BaTi_0.6Zr_0.4O₃ (BTZ) ceramic was synthesized by a soft chemical route. X-ray diffraction at room temperature shows that the sample has cubic perovskite structure with space group Pm-3m. Temperature dependent dielectric study of the sample has been investigated in the frequency range from 50 Hz to 1 MHz. The density of the sample was determined using Archimedes’ principle and found to be ∼ 97% of the X-ray density. The average grain size in the pallet was found to be ∼ 1 μm. The dielectric constant peaks at temperature T_m which is dependent on the frequency. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy = 0.0185 eV, and freezing temperature = 186 K. All these measurements confirm that BTZ is a relaxor ferroelectric. PACS 77.22.Jp; 77.84.-s; 77.80.Bh; 77.22.Gm     

Electric field gradient in transition metal: Scandium

Corrections to results of electric field gradient (EFG) already published [Pramana — J. Phys.41, 443 (1993)] are reported. The corrected net EFG is:q=−8.01×10¹³ esu/cm³ against the published valueq=16.06×10¹³ esu/cm³. The present result agrees reasonably well with the experimental result, |q _expt|=13×10¹³ esu/cm³. Recently, a computational error is detected, which modifies the results of EFG, we have already published [1]. The error was committed mainly in the part that evaluated thep-p contribution [1] to EFG by the conduction electrons. The corrected results are summarized in table 1 which must replace the table 1 of the published work [1]. In addition, the lattice parameters as well as the temperature were also misquoted in the previous work [1]. The right parameters are:a=6.25311 au andc=9.96509 au. The temperature at which EFG’s are calculated is 293 K instead of 11 K as reported before [1]. The discussions and conclusions made in the published work [1] remain almost unchanged except that they now refer to the corrected numbers. Although the corrected net EFG suffers a sign reversal from the one already published [1], the agreement with experiment is still considered reasonably good because the sign of experimental EFG is not determined. The computational error however does not affect the introduction and theory section of the published work [1].     

Micellar catalysis in the oxidation of acetophenones by Ce(IV)

Rate of oxidation of acetophenones by Ce(IV) in aqueous acetic acid 80:20 (v/v) either slows down or remains constant over a range of cetyltrimethyl ammonium bromide (CTAB) concentration exceeding the cmc value. The rate is then found to increase sharply as the surfactant concentration increases with no sign of reaching a maximum or constant value. From Fluorescence quenching, binding constant for p-nitro acetophenone has been evaluated. The rate data have been rationalized on the basis of a reaction between the acetophenones situated on the micelle surface and active Ce(IV) species in the bulk aqueous phase.     

Oxidation of amino acids by peroxomonophosphoric acid—a kinetic study

Aliphatic amino acids are smoothly oxidized by peroxomonophosphoric acid (PMPA) in the pH region 6–10. Kinetic studies reveal second order dependence in the amino acid not observed hitherto in any of the PMPA oxidations. Dependence in PMPA is unity. Rate-pH profile yields a maximum around pH 8. The reaction path includes oxidation steps due to H₂PO₅^? and HPO₅^2?. Second order dependence in the amino acid has been attributed to participation of two Zwitter-ionic molecules of the amino acid to form a nucleophile.