P. Sen

Origin of nonmetallicity in PrBa2Cu3O7 from a study of Gd1−xPrxBa2Cu3O7 using soft x-ray absorption at the oxygen K-edge

Abstract We present the x-ray absorption data at the oxygen K-edge using total yield technique for Gd1−xPrxba2Cu3O7 (x= 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0). The data clearly to oxygen that the holes doped in the GdBa2Cu3O7 due to oxygen composition are not removed by Pr doping even for the x = 1.0 sample, suggesting that Pr is predominantly in the formally trivalent state. However, the data also clearly indicate the evidence of hybridization effects between the Pr3+ and the adjacent CuO2 layers. This is suggested to be responsible for the progressive suppression of Tc and the metallicity with Pr doping in these systems.

Polyaniline-CdS Quantum Dots Composite for Mediator Free Biosensing

A novel route has been introduced to fabricate the composite of polyaniline (PANI) and cadmium sulphide quantum dots (CdS-QD) using electrochemical polymerization technique for mediator free biosensing. The synthesis process involves in situ formation of CdS quantum dots that provide template for eletro-polymerization of aniline resulting in nanostructured PANI-(CdS-QD) film deposition on the indium-tin-oxide (ITO) coated glass plate. Transmission electron microscopy and scanning electron microscopy have been used to reveal the formation of CdS-QD and morphological changes involved during incorporation of CdS in PANI matrix and while immobilization of cholesterol oxidase (ChOx). The UV–visible and FT-IR investigations show the formation of PANI-(CdS-QD) composite at the molecular level. This matrix has been utilized for the covalent immobilization of cholesterol oxidase to explore its application for cholesterol sensing. The results of the CV and EIS studies indicate enhanced electrochemical and charge transfer behaviour of the composite. The response studies, carried out using CV technique, reveal this ChOx/ PANI-(CdS-QD)/ITO bioelectrode to detect cholesterol in the concentration range of 50 to 500 mgdL -1 with good detection limit (47.8 mgdL -1 ) and low app m K value (0.82 mM).

Electronic Structure of and the Metal-Insulator Transition in La1-xSrxCoO3-δ: A Soft-X-Ray Absorption Study

We report the soft-X-ray absorption spectra at the oxygen K-edge of La1-xSrxCoO3-δ (x = 0.0, 0.1, 0.2, 0.3 and 0.4) series with experimentally determined δ values. We show that the doping of holes by replacing La3+ with Sr2+ induces states within the band gap of the insulating undoped compound for small x and these doped states have a very substantial oxygen 2p character. This indicates that the insulating compounds belong to the charge transfer insulator regime. With increasing Sr content, the doped states broaden into a band overlapping the top of the primarily oxygen p-derived band, leading to an insulator-metal transition at x ≥ 0.2.

Phase transition in a perovskite superconductor by radiation-induced lattice excitations

We report (2212) → (2223) phase modification in a mixed phase, Bi-based oxide superconductor. In contrast to established procedures, this has been possible employing high-energy ion irradiation at 80 K. A nucleation process, assisted through radiation-induced vacancy creation and their subsequent annihilation by the existing interstitials, is shown to achieve the observed phase transformation.

DISSIPATIVE STRUCTURE FORMATION IN COLD-ROLLED FE AND NI DURING HEAVY ION IRRADIATION

We report 4-probe resistivity measurements of cold-rolled Ni and Fe during 100 MeV oxygen ion irradiation, at 300K. The resistivity shows increase and saturation, marked by jumps. Employing 200 MeV silver ion irradiation of Fe and Si(100) and topographically identifying strain at an artificial interface in the latter, we assign the resistivity behavior to atomic rearrangements arising from dissipation of incident ion energy at internal interfaces of Ni and Fe, with positive feedback.}

Spectroscopic evidence for the removal of mobile holes on Fe doping in YBa2Cu3-xFexO7-δ

Abstract X-ray absorption spectra at the oxygen K edge using the total yield technique are reported for YBa 2 Cu 3 O 6.9 and YBa 2 Cu 2.7 Fe 0.3 O 6.9 . A comparison of the two spectra reveals that the mobile holes in YBa 2 Cu 3 O 7-δ are removed and localized on Fe doping. Fe thus enters the lattice primarily in the formally trivalent oxidation state.

Processing temperature driven morphological evolution of ZnO nanostructures prepared by electro- exploding wire technique

This article presents an effective approach for the synthesis of ZnO nanoparticles with desired morphology via an environmentally benevolent electro-exploding wire (EEW) technique. In this process, ZnO nanoparticles evolve through the plasma generated from the parent Zn metal. Compared to other typical chemical methods, electro-exploding wire technique is a simple and economical technique that normally operates in water or organic liquids under ambient conditions. The effect of different processing temperatures in the range (5–80 °C), on the morphology of ZnO nanoparticles is clearly demonstrated. At 5 °C, nanoparticles with spherical morphology are observed. However, elliptical morphology is observed at room temperature and multipod nanorods at 50 °C and 80 °C. The evolution of ZnO phase is investigated with the help of time dependent UV-vis absorption and photoluminescence (PL) studies. The mechanism of formation and different morphologies of ZnO nanoparticles formed are also proposed.

UV–Visible spectroscopic study of ZnS nanostructures synthesized by a novel micellar method

In this article, we report a novel micellar method to prepare ZnS nanostructures. UV–Visible absorption spectroscopy was employed extensively to study these ZnS nanostructures. A detailed investigation on optical properties of this nanomaterial was performed to determine alteration in absorption energies with the ultimate goal to decipher the role of various parameters involved in the synthesis process. We elucidate the qualitative effects of reactant concentration and reaction temperature on the formation of ZnS nanostructures. Based on this systematic investigation, we have made an attempt to ascertain favourable conditions for optimal production of ZnS nanostructures through the micellar route.

Water driven stabilization of ZnS nanoparticles prepared by exploding wire technique

ZnS nanoparticles, prepared employing exploding wire technique (EWT), demonstrate water-induced stabilization with time. The structural evolution of ZnS nanoparticles and their interaction with the surrounding aqueous media is systematically studied at the three distinct stages of time. The structural properties of nanoparticles were examined by an assortment of characterization techniques. However, in this article we focus on x-ray diffraction (XRD) and x-ray photoelectron spectroscopic (XPS) investigation of nanoparticles. The XRD results indicate transformation of hexagonal phase of prepared ZnS nanocrystals. The lattice constants and strain in ZnS nanoparticles are estimated at each stage of transition. Alteration in crystal structure of ZnS nanoparticles, transforming in presence of water, is an outcome of gradual variation in lattice constants and strain. Variation in stoichiometry of ZnS nanoparticles, at respective stages of transformation, is found through XPS analysis. Furthermore, in order to determine the alterations in the oxidation state and energies of the nanoparticle constituents, line shape analysis of Zn 2p3/2 peaks at three stages, is also performed. Thus, XPS analysis, accompanied with the XRD interpretations, vividly deciphers the structural evolution of ZnS nanoparticles in aqueous environment.

Dissipation of MeV ion energy in solids, structure formation and phase changes

Abstract Instabilities arise out of dynamic events and can lead to nonequilibrium (self-organization) processes. Ion irradiation is by nature a nonequilibrium process and hence formation of structures, metastable or otherwise is to be expected. Recently, it has been theoretically predicted that metals under ion irradiation can lead to dissipative structure formation arising out of radiation damage and their subsequent annealing. The possibility of direct observation of such structures in metals under irradiation is however reduced due to nonavailability of a large concentration of defects (mainly point defects) at any point of time. In this experimental presentation we show that this can be overcome through the involvement of microstructural imperfections which rearrange during irradiation. Employing microstructurally impure specimens of Fe and Ni, it is shown that heavy ions dissipate their electronic energy to modify atomic arrangements at the microstructure. The increased concentration of defects (atomic rearrangements), amenable to statistical decay is shown to produce effects in the 4-probe resistivity measurements which we assign to dissipative structure formation.