Suppression of defect level emissions in low temperature fabricated one-dimensional Mn doped ZnO nanorods

One-dimensional Mn doped ZnO nanocrystallites were synthesized through a facile low temperature surfactant free chemical route. The crystallite structure and morphological evolution of the particles were revealed to be of wurtzite phase and rod like structures from the X-ray diffraction and transmission electron microscopic analysis, respectively. Using Raman spectroscopy the role of oxygen related defects and phase purity in the Mn substituted ZnO systems were studied systematically. A significant suppression in the sub-band edge emission was visualized in the room temperature emission spectra of the Mn doped systems. The intensity ratio in between the near-band edge and defect-level emissions was observed to increase, signifying the reduction in oxygen related defects and revealing their influence on the crystallinity on the Mn substituted ZnO species. These variations were correlated with the increasing number of Mn ions in the host lattice, which results with their passivating action on the surface defects.     

Green synthesis of silver nanoparticles using Beta vulgaris: Role of process conditions on size distribution and surface structure

The present work reports the green synthesis of silver nanoparticles, using Beta vulgaris peel extract with a subsequent investigation on the size distribution and surface structure of nanoparticles formed under various process conditions. The green-chemical reduction mechanism of silver ions to nanoparticles by the active organic functional groups present in the extract was characterized, using the respective spectroscopic techniques. The effects of various process parameters, including induced intraparticle ripening, were attributed to the controlled formation of anisotropic silver nanoparticles within the supporting matrix of the extract. The plasmon absorption and resonance scattering properties were expected to be favourable for small and larger size nanoparticles (below 25 nm and above 75 nm) respectively, which was considered to be an indicative aspect for synthesizing nanoparticles of narrow size distribution. The zeta potential and dynamic light scattering (DLS) results suggest the good stability and mono-dispersed size distribution of the silver nanoparticles. The transmission electron microscope, selective area electron diffraction (SAED) and X-ray diffraction studies infer that the nanoparticles formed were spherical/quasi-spherical in shape, which primarily exhibited a face centred cubic crystal (FCC) structure. The green-chemical reduction of organic phases in the extract (especially amine (NH₂) groups) as reflected through shifts observed in the Fourier-transform infra red (FTIR) peaks, reveal the possible interaction of the organic molecules with the silver ions in the effective formation, surface modification and stabilization of the silver nanoparticles.     

Preparation of a functional nanofibrous polymer membrane incorporated with poly(2-aminothio phenol) stabilized gold nanoparticles

Functional nanofibrous polymer membranes were prepared by incorporating poly(2-aminothio phenol) (P2AT) stabilized Au NPs onto electrospun polyvinylidene fluoride (PVdF) nanofibers (designated as P2AT-Au NPs@PVdF-NFM). The preparation of P2AT-Au NPs@PVdF-NFM involves two steps: loading of 2AT (monomer) into electrospun PVdF nanofibrous membrane and polymerization of 2AT by gold chloride. P2AT and Au NPs were simultaneously formed into the electrospun PVdF-NFM. Transmission electron microscope image of P2AT-Au NPs@PVdF-NFM informs the presence of Au NPs (with sizes ~10 nm) onto PVdF-NFM.     

Effect of Y2O3 on Spark Plasma Sintering Kinetics of Nanocrystalline 9Cr-1Mo Ferritic Oxide Dispersion-Strengthened Steels

Nanocrystalline mechanically alloyed powders of 9Cr-1Mo ferritic steels with and without yttria dispersoids were densified using spark plasma sintering (SPS) to near-theoretical density at a temperature of 1073 K (800 °C). Studies on densification behaviour revealed that steels with dispersoids densified faster when compared to Fe-9Cr-1Mo steel. The evaluation of densification mechanisms during SPS reveals that grain boundary and lattice diffusion to be predominant at relative densities ranging from >0.7 to 0.9 in both the alloys.     

Microstructure and Mechanical Properties of Nanostructured Al-4Cu Alloy Produced by Mechanical Alloying and Vacuum Hot Pressing

Bulk nanostructured Al-4 wt pct Cu alloy with high compression strength (879 MPa) was produced by mechanical alloying followed by vacuum hot pressing (VHP). The hot-pressed compacts were nanostructured with a grain size of 50 nm and were densified to more than 99 pct of the theoretical density. Contributions from different strengthening mechanisms were estimated using simplified models and were compared with the experiment.     

Electron spin resonance and AC susceptibility studies on La0.9Pb0.1MnO3 single crystals

Phase separation has been recognized as important properties of manganite to create colossal magnetoresistance (CMR). Frequency dependence of AC susceptibility and electron spin resonance (ESR) studies confirm the phase separated glassy magnetism in the La_0.9Pb_0.1MnO₃ crystals. ESR spectra exhibit a gradual narrowing of the asymmetric FMR signals upon increasing the temperature and approaching the Curie temperature (T_c). The temperature dependence of line width (ΔH_pp), g-factor, double integrated (I) intensity of the resonance signals and frequency dependence peak temperatures are discussed in this paper to explain inhomogeneity in the La_0.9Pb_0.1MnO₃ single crystals.     

Investigations on nucleation thermodynamical parameters of NdBa2Cu3O7-δ (Nd123) crystallization by high temperature solution growth

Investigations on nucleation thermodynamical parameters are very essential for the successful growth of good quality single crystals from high temperature solution. A theoretical estimation of the nucleation thermodynamical parameters like interfacial energy between the solid Nd123 and its flux BaO-CuO, metastable zone-width, Gibbs free energy, critical energy barrier for nucleation and critical nucleation radius have been calculated from the knowledge of solubility data and by applying the classical nucleation theory. Results are discussed to understand the growth kinetics of Nd123 crystals. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore     

Studies on some trace and minor elements in blood. A survey of the Kalpakkam (India) population. Part I: Standardization of analytical methods using ICP-MS and AAS

Blood is one of the widely used specimens for biological trace element research because of its biological significance and ease of sampling. We have conducted a study of the blood of the Kalpakkam township population for trace and minor elements. For this purpose, analytical methods have been developed and standardized in our laboratory for the elemental analysis of blood plasma and red cells. Inductively coupled plasma-mass spectrometry (ICP-MS), a relatively new technique, has been applied for the analysis of trace elements. Details regarding spectral interference and matrix interference encountered in the analysis of blood and the methods of correcting them have been discussed. Flame atomic absorption spectrometry (AAS)/atomic emission spectrometry (AES) has been applied for the determination of minor elements. Precision and accuracy of these methods have also been discussed.     

Diversity among various forms of catechins and its synthesizing enzyme (phenylalanine ammonia lyase) in relation to quality of black tea (Camellia spp.)

BACKGROUND: Quality of tea depends on the cultivar and climatic conditions. Biochemical pathways within the plant and climatic factors can result in noticeable changes in chemical composition, which determine the quality of tea. Black tea quality attributes are influenced by various forms of catechins, namely gallated, non‐gallated, dihydroxylated and trihydroxylated catechins and their ratios. Hence the variations in grouped catechins and their synthesizing enzyme in relation to quality of south Indian black tea grown in different seasons and different cultivars were studied. RESULTS: Gallated, non‐gallated, dihydroxylated, trihydroxylated catechins and catechin index were significantly higher in crop shoots harvested during summer. A significant and wide diversity in various forms of catechins was noticed among the cultivars tested. Among the cultivars, UPASI‐3 registered the higher amount of various forms of catechins and activity of phenylalanine ammonia lyase (PAL), followed by UPASI‐9 and UPASI‐17 respectively, while the lowest amount was exhibited by ‘Assam’ seedlings and TRI‐2043. CONCLUSION: Overall quality as evaluated by tea tasters was positively correlated to the cultivars and seasons tested. This positive correlation can be attributed to higher levels of grouped catechins and PAL activity. Thus the contents of various forms of catechins could be the most important quality parameter of the south Indian black teas. Copyright © 2010 Society of Chemical Industry