Experiment

Inelastic Neutron Scattering.

It is important to know about the dynamics of the system to predict the behavior of the materials along with its structure. Inelastic Neutron Scattering is one of the most sensitive methods to study the dynamics of the condensed matter systems. Liquid Deuterium and liquid Hydrogen were studied using this method. The experiments were performed in ISIS, England and ILL, France .

Nanocomposite Material Synthesis.

Composite nano-phase materials have been prepared using physico-chemical routes. The metal and the semiconductor particles of few nanometre diameter have been prepared in citu in suitably chosen host matrix. Polymer, conventional melt quenched glass and sol gel derived glasses were chosen as the host. A synthetic chemistry laboratory equipped with Chemical and Gas handling facility, High temperature furnace, Hot press, Room temperature press, Ultrasonic agitator, etc. was used for the purpose. Following is the list of prepared materials leading to the significant publications.

(a) Metallic silver (nano) in Poly(acrylamide) matrix.

(b) PbS (nano) in Poly(acrylamide) matrix.

(c) PbS (nano) in melt quenched glass matrix.

(d) Pure PbS (nano) in a wide range of size.

(e) Metallic silver (nano) in melt quenched glass matrix.

(f) Fe₂O₃ (nano) in sol-gel derived SiO₂ glass matrix.

(g) Fe ₂ O₃ (nano) in sol-gel derived TiO₂ glass matrix.

(h) PbS (nano) in sol-gel derived PZT matrix.

Dielectric Spectroscopy.

A sol-gel derived PZT matrix was doped with nanocrystalline PbS particles (sample (h)). The particle size was estimated using TEM and XRD. The modification of the dielectric behavior of the system was studied using dielectric spectroscopy.

EPR, Magnetic and Mössbauer Spectroscopy .

Sol gel glass is a good host for the nano materials. a-Fe₂O₃ was doped in sol-gel derived SiO₂ and TiO₂ matrix at room and high temperature. The sample (f) and (g) were studied using DTA-TGA, TEM, XRD, EPR, Magnetic and Mössbauer Spectroscopy. The modification of the composite solgel system with temperature and the super paramagnetic behaviour of the nano a-Fe₂O₃ were studied.

Positron Annihilation Spectroscopy.

Positron Annihilation Spectroscopy (PAS) is one of the best methods to study the defects in a system. Sample (a) and (e) are studied using TEM, XRD and PAS. at room and low temperature. The nano metals show a metal to semiconductor like transition at very low temperatures. This was the first observation of this kind.

TEM, XRD and Electrical Measurements .

Sample (a), (b), (c) and (d) are studied using Electronic Microscopy (TEM & SEM), X-ray diffraction (XRD) and electrical resistivity measurements in a wide range of temperature. The size and size distribution of the nano particles were estimated using TEM and XRD. A fractal morphology and phonon softening was found for the metal particles. For the PbS nano particles an increase of electronic band gap was measured.

Theorey

Gauge Potential And Berry's Phase In Quantum Mechanics.

Gauge potential plays an important role in the fundamental development of Quantum Mechanics. We have performed some calculations to study the nature of Berry's phase in analytically soluble model problems. In another calculation we have shown how gauge potential automatically comes into the scattering calculations.

Relativistic Charge Transfer Scattering.

Relativistic charge transfer scattering calculations were performed under the first Born approximation. A relativistic hydrogen atom type wave function were used for the ions. This was the first relativistic calculation to estimate the effect of inclusion of the inter nuclear interaction in the potential.

Positron-Hydrogen Molecule Scattering.

The computer code was modified to take into account of the rotational degrees of freedoms for the molecules. This was the first rotational close coupling calculation including the excitation channel.

Positron (Electron)-Hydrogen Atoms Scattering.

Ab initio quantum mechanical calculations were performed to predict the differential and total cross sections for positron and electron hydrogen atom scattering. Positronium formation channel was included for the first time to predict the reliable results. Analytical calculations involving use of various mathematical functions (viz., Angular momentum algebra, Bessel, Spherical harmonics, Legendre functions of different kinds etc.) were performed to reduce the dimensionality of the integrals. A large computer code was developed in Fortran language under UNIX to solve a multy channel coupled integral equation.

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