K. Vijaya Sarathy

Study of interaction of ethylene glycol/PVP phase on noble metal powders prepared by polyol process

Noble metal powders (Au, Ag, Pt, Pd and Ru) have been synthesized by the polyol process in both the nanometer and submicron scales (sans Pd, Pt and Ru). They have been characterized by both microscopic (TEM and SEM) as well as spectroscopic techniques (FT-IR and XPS). Infrared spectroscopy was employed to study the colloid particles in the presence of ethylene glycol and PVP and the results show that the interaction between the organic phase and the metal particles vary according to the particle size. The role of the solvent, ethylene glycol, during the reduction process was also investigated and we observe formation of >C=O vibration band after the reduction process implying that the solvent reduces the metal ions thereby getting oxidized. XPS measurements carried out on the colloidal sols have shown the presence of the organic phase adsorbed onto the metal particles.

Superlattices of metal and metal-semiconductor quantum dots obtained by layer-by-layer deposition of nanoparticle arrays

Superlattices formed by arrays of Pt or Au nanoparticles have been obtained by layer-by-layer deposition by using dithiols as cross-linkers. The superlattices have been characterized by X-ray diffraction, photoelectron spectroscopy, and scanning tunneling microscopy. The core-level intensities of the metal and of the dithiol in the X-ray photoelectron spectra show the expected increase with successive depositions. The formation of such structures has been confirmed by depositing Pt and Au layers alternatively. Layers of metal and CdS nanoparticles have been deposited alternatively to obtain heterostructures.

A novel method of preparing thiol-derivatised nanoparticles ofgold, platinum and silver forming superstructures

Thiol-derivatised nanoparticles of Au, Pt and Ag (diameter 1–10 nm) forming superstructures, are prepared by the acid-facilitated transfer of well characterized particles in a hydrosol to a toluene layer containing the thiol.

An electron paramagnetic resonance study of electron?hole asymmetry in charge ordered Pr1?xCaxMnO3 (x = 0.64, 0.36)

We present and compare the results of temperature-dependent electron paramagnetic resonance (EPR) studies on

Hopping conduction in charge-ordered rare-earth manganates Ln1−xCaxMnO3 (Ln=rare earth)

Pr_{1-x}Ca_xMnO_3

The tetragonal–orthorhombic transition and the associated changes in the properties of Pr0.5−xNdxSr0.5MnO3

for x = 0.64, which is electron-doped, with results of studies on the hole-doped, x = 0.36 composition. The temperature dependence of the various parameters obtained from the powder and single crystal spectra showsignificant differences between the two manganites. At room temperature the ‘g’ parameter for the electrondoped system is less than the free electron ‘g’ value ‘ge’, whereas for the hole-doped system it is more than ‘ge’. Further, the linewidth obtained from the powder spectra as well as the single crystal spectra show different functional dependences on temperature in the two systems. Quite strikingly, the peak observed at

A comparative study of thin films of hole-doped Pr0.6Ca0.4MnO3 and electron-doped Pr0.4Ca0.6MnO3

T_{co}

Thiol-Derivatized Nanocrystalline Arrays of Gold, Silver, and Platinum

in the temperature dependence of the asymmetry parameter, \alpha, of the single crystal spectra in the hole-doped system, is absent in the electron-doped system. We understand this contrasting behaviour of the EPR parameters in the two systems in terms of the very different nature of microscopic interactions in them.

Electron-hole asymmetry in the rare-earth manganates: A comparative study of the hole- and the electron-doped materials

Abstract Electrical resistivity behavior of single crystals as well as polycrystalline pellets of rare earth manganates has been investigated below the charge-ordering temperatures to understand the mechanism of conduction. The resistivity of both the single- and polycrystalline samples of Gd0.5Ca0.5MnO3 and Nd0.5Ca0.5MnO3 obey the T−1/4 law, characteristic of variable range hopping. A similar dependence is found in the hole-doped Pr0.6Ca0.4MnO3 as well, but the data of the electron-doped Pr0.4Ca0.6MnO3 do not seem to obey any T−1/n law satisfactorily. AC conductivity measurements also reflect the unusual nature of the electron-doped composition.

Effect of ruthenium doping on the properties of Pr0.5A0.5MnO3 (A=Ca,Sr)

The transition from the tetragonal (I4/mcm) to the orthorhombic (Imma) structure associated with a change in A- to CE-type antiferromagnetism in the Pr0.5−xNdxSr0.5MnO3 has been investigated by X-ray diffraction as well as magnetization and resistivity measurements. The transition is found to occur between x=0.1 and 0.2.