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Experimental investigations on multiferroic materials
Full text linkBy definition, a single phase multiferroic is a material that simultaneously possesses
two or more so-called ferroic order parameters such as ferroelectricity, ferromagnetism
and ferroelasticity. The possibilities of practical applications of ferromagnetic and ferroelectric
orderings coexisting in a single-phase material have prompted considerable
interest in the field of multiferroics. From an applicational standpoint, the real interest
in multiferroic materials lies in the possibility of strong magnetoelectric coupling and to
create new functionalities in materials. Multiferroics have immense applications in data
storage, spintronics, quantum electromagnets, microelectronic devices, etc. However,
in most of the cases spontaneous polarization and magnetization of these materials are
absent at room temperature, which are the main obstacles for its commercial applications. The ultimate goal for device functionality is to discover multiferroic materials
with strong coupling between ferroelectric and ferromagnetic order parameters at room
temperature, which can be simply used for controlling magnetic properties with an
applied electric field. Unfortunately, evidence of ferroelectric order is very rare compared to the magnetic orders, which have been explored extensively since for a long time in the history of science. Out of ferroelectricity, magnetic order driven ferroelectricity termed as improper ferroelectricity attracts the community for the intriguing
magnetoelectric coupling. The general motivation behind the research in this thesis is to better understand the coupling between electric and magnetic order parameters in
multiferroic and magnetoelectric materials. This thesis entitled Experimental investigations on multiferroic materials is mainly to discuss about the origin of electric polarization and magnetoelectric coupling in different kinds of multiferroic bulk oxide materials, chalcogenides and thin films also. This thesis mainly focuses on the origin of multiferroic properties from the structural point of view. High energy synchrotron radiation is used to find out the small changein structural properties, mainly the case of isostructural transition.The research was carried out under the supervision of Prof. Sourav Giri of the Solid State division under SPS [School of Physical Sciences]The research was conducted under CSIR fellowshi
Equilibrium and Rheological Properties of Model Network Formers
Full text linkThis thesis embodies a study of the static and dynamic aspects of network forming
liquids in two-dimensions starting from a very simple model of binary mixture of
Lennard-Jones type particles to patchy colloids with complex inter-particle interactions. In the rst chapter we provide a general overview of simple and complex colloids which is then followed by a discussion on the various anomalous properties shown by network forming liquids and their computer simulation models focusing mainly on the most common and important network-forming liquid i.e. water. Discussion on the dynamic aspects like di usion, response to external shear and glassy dynamics is then presented in the following section. E ect of con nement
on the thermodynamic and dynamic properties of network-formers is discussed in the last section of this chapter.Research was carried out under the supervision of Prof. Surajit Sengupta of CAM under SPS [School of Physical Sciences]Research was conducted under IACS fellowship and DST gran
Fabrication, Characterization and Reactivity of Bio-electrodes
Full text linkThis thesis focuses on understanding of the electrocatalytic reactivity of the bioelectrodes for the O2 reduction reaction or nitric oxide reduction reaction. A number of synthetic methods were attempted to synthesize a modified heme cofactor. The heme cofactors were modified in a way so that they can be covalently attached to the electrode followed by the site specific attachment of the apoprotein onto the electrodes. A variety of spectroscopic tools have been used to probe the spectroscopic features of the active site structure as well as the protein conformations and the reactivity of the heme based bioelectrocatalysts involved in the reduction of O2 or that of nitric oxide.The research was conducted under Dr. Avishek Dey of Inorganic Chemistry division under SCS [School of Chemical Sciences
First Principles Study Of Emergent Phenomena In Strongly Correlated Systems
Full text linkIn the present thesis work, we have employed first principles as well as model Hamiltonian calculations to understand some of the emergent properties of 3d and 5d transition metal oxides (TMOs) belonging to the family of strongly correlated systems. We have studied nature of magnetism in Cu-based TMOs Na2BaCuV2O8 and PbCuTe2O6. The intriguing crystal geometry of these two cuprates give rise to diverse magnetism ranging
from one-dimensional uniform S = 1/2 antiferromagnetic (AFM) chain as observed in Na2BaCuV2O8 to geometrically frustrated magnetism in PbCuTe2O6, where the arrangement of spins on a lattice precludes satisfying all interactions simultaneously leading to
fascinating quantum spin liquid ground state. In addition, we have also studied copper based pyrovanadate Cu2V2O7 where an evolution of magnetic dimensionality is observed in its various polymorphs namely α, β and γ-Cu2V2O7. Unlike the other polymorphs, the α-phase is found to exhibit giant ferroelectric polarization (0.55 μC/cm2), largest among
the Cu-based multiferroics, driven by symmetric exchange striction mechanism. We have also investigated pyroxenes, a family of potential magnetoelectric and multiferroic materials.
Our calculations provide insights on the magnetism in the Cr-based pyroxene
LiCrSi2O6 where spin-orbit coupling (SOC) is found to play an important role. We show exchange striction is the driving mechanism for the ferroelectric polarization present in this system.Research was conducted under the supervision of Prof. Indra Dasgupta of Solid State Physics division under SPS [School of Physical Sciences]Research was carried out under CSIR research gran
MAGNETIC-FIELD ASSISTED LAYER-BY-LAYER ELECTROSTATIC ASSEMBLY: FILM FORMATION AND CHARACTERIZATION
Full text linkLayer-by-layer (LbL) electrostatic assembly has been a unique approach to grow ultrathin films of polyions. The method has later been extended to organic molecules and
inorganic quantum dots. The LbL method relies on surface charge reversal during adsorption
of anionic and cationic layers in sequence. Morphology of such films has been found to depend
on pH of the ionic species in solutions and functional groups attached to the
molecules/polymers. Since LbL layers are being used for a range of thin-film based
applications, morphology of the films has become increasingly important. In many cases, it has
a large impact on the efficiency or output of devices.
Efforts have been made to control morphology of the films or LbL growth process.
Since the materials used here are ionic in nature, electric field has been the natural choice to do
so. LbL deposition process of polyions and suitably-capped quantum dots has been found to be
greatly affected by an electric field. For ferromagnetic quantum dots, magnetic fields could
orient their magnetic dipoles in a monolayer that in turn supplement electrostatic force of
attraction for the subsequent layer and augment LbL deposition process.
It can be intriguing to introduce an additional force that may supplement the
electrostatic adsorption process. An external electric-field has been considered for LbL
deposition of suitable organic molecules or nanoparticles. Magnetic-moments that are
inherently present in magnetic materials can be another direction in this regard. Since the
magnetic domains can be oriented with a suitable magnetic field, our target here is to enhance
electrostatic adsorption process through magnetic force of attraction. We show how oriented magnetic-moments can accelerate adsorption process of subsequent monolayers in the LbL assembly process. Again, in the presence of external magnetic field, orientation of the paramagnetic organic molecules can be immobilized via the electrostatic adsorption of suitable polycations. The magnetic field-assisted LbL formation has been discussed in chapter three. The LbL films with oriented molecular morphology in each monolayer provide a unique system to study anisotropy of optical, dielectric, and electrical characteristics in these planer organic molecules. The alignment of magnetization-vectors in the monolayer of magnetic materials also offers an opportunity to understand the leading mechanism of conductance switching. The degree of electrical bistability (On/Off ratio), transport gap, and density of states of the materials has been found to depend on their alignment magnetization-vectors. Because of the large energy barrier, the carriers are strictly confined to the organic linker coated quantum dots. This quantum confinement effect could be relaxed for a selective type of carriers by reducing their corresponding energy barrier.The band-offset engineering in core/shell nanoparticles provides the type-selective localization of carriers.The research was conducted under the supervision of Prof. A J Pal of the Solid State Physics division under SPS [School of Physical Sciences]The research was carried out under CSIR fellowship and gran
THEORETICAL STUDY OF ENERGETICS AND KINETICS FOR THE REACTIONS OF ENVIRONMENTAL AND TOXICOLOGICAL INTEREST
Full text linkThis Ph. D thesis presents computational energetics and kinetics investigations of
problems related to environmental and toxicological processes. Ab initio & density
functional theory has been used to gain insight into the origin and nature of such
reactions. The softwareutilized are Gaussians 03 & 09 & GAMESS for molecular orbital
calculations, MOLTRAN for thermodynamics property calculation, NBO 3.1 for natural
bond orbital analysis, AIM 2000 & XAIM for topological analysis and CHRMRTAE &
TheRate for kinetics calculation. A number of visualization software e.g. GaussView,
Chemcraft, MacMolPLt, NBOView also used for the result analysis and presentation.
The work presented concerns two main topics: Radical-Molecule reactions of
environmental concern and the detoxification mechanism of organophosphorus nerve
agent which are responsible for environmental toxicology. This thesis consists of five articles. In chapter I a comprehensive overview behind the origin and importance of the problems delineate here have been presented. Chapter II gives a brief introduction of the theoretical methods used in the thesis and an explanation of their implementation in Computational Chemistry. Chapter III is divided into two parts, part A and part B. The first part, part A, describes the mechanism and kinetics of the important tropospheric reactions of vinyl acetate with OH radical in presence of 02 and NO. In part B, reaction mechanism, kinetics and product branching ratio are presented reaction of C2H with I-butyne, an important radical molecule reaction of planetary atmosphere. Chapter IV describes the investigations of the reaction energetics and kinetics of isomerization and decomposition of a Model Nerve Agent, Dimethyl Ethylphosphonate. Chapter V is also be divided into two parts. The first part, part A, deals with the detailed reaction mechanism of the reactions involved in the nucleophilic detoxification mechanism, reactivity and the determination of potential attacking sites of the nucleophiles of Fenitrothion insecticide. The second part, part B illustrates the fundamental aminolysis reactions of model nerve agent 0, S - Dimethyl Methylphosphonothiolate in absence or in presence of catalyst. The probabilities for the formation of the products are also analyzed using various modern computational techniques e.g. activation energy, conceptual density functional theory, natural bond orbital (NBO)analysis, and Bader's atoms in molecules (AIM) approach.
Finally a summary of the results in this thesis and an outlook on potential future work is presented.The research was carried out under the supervision of Prof. A K Das of the Spectroscopic division of the SPS [School of Physical Sciences]The research was conducted under CSIR fellowship and research gran
Nanoparticle-Based Advanced Bioimaging Probe with Controlled Number of Conjugated Biomolecule
No full textThe work in this thesis entitled “Nanoparticle-Based Advanced Bioimaging Probe with Controlled Number of Conjugated Biomolecule” was initiated by the author in July 2014 in Centre for advanced Materials and School of Materials Sciences, Indian Association for the Cultivation of Science, Kolkata under the supervision of Prof. Nikhil Ranjan Jana.
Ome of the most important advances in nanomaterial chemistry is the designing of advanced beeimaging probe which can be used as an alternative to molecular probe. Fluorescent nanoparticle offers promises in this area due to their strong photoluminescence and low ghotobleaching property in comparison to the existing organic dyes. Unique properties of nanoparticles like carbon dots, quantum dots, semiconductor nanoparticles, silicon nanoparticles, gold cluster and these nanoparticles are used as superior imaging probes for various bio- Geenostics. For this purpose synthesis and functionalization of nanoparticle is very important. Nanoparticle with tunable surface functionality can target desired subcellular organelle. Sebcellular localization of the nanoparticles is sometimes restricted due to their endosomal shapping which is disadvantage for the gene delivery, drug delivery or bioimaging. It is also own that endocytosis mechanism also plays important role in subcellular localization of the particles. Clathrin-mediated endocytosis leads the particle to the endosomes or lysosomes of the sells whereas caveolae or lipid raft mediated endocytosis bypass the endosomal pathway and tke the particle towards nucleus, Golgi apparatus or endoplasmic reticulum. Interestingly, emdeeytosis mechanism always depends on the size, shape, surface functionalization, ligand density of nanoparticle by which it interacts with the cell membranes.The research was carried out under the supervision of Prof. N R Jana under SMS [School of Materials Science]The research was conducted under CSIR fellowshi
Graphene Based Nanomaterials for Biosensing and Catalytic Application
No full textThe research was carried out under the supervision of Prof. N R Jana of SMS [School of Materials Science]The research was carried under CSIR fellowshi
Study of Stochastic Processes in Confined Geometry
Full text linkIt has been choosen the overdamped dynamics of a Brownian particle in a two-dimensional bilobal confinement
as the fundamental model to carry out desired investigations. This is
an entropic analogue of a bistable energetic potential which is the general
set-up to examine phenomena where barrier crossing is somehow
involved, such as, transformation of reactant to product, phase transition,
stochastic resonance, resonant activation, hysteresis, logical stochastic
resonance, erasure of a bit of memory, and many others. The overdamped
Brownian dynamics perfectly incorporates the fluctuations appearing in
the nonequilibrium situations and portrays the features of the trajectories
away from equilibrium which are responsible for the barrier crossing
to occur.The research was carried out under the supervision of Prof. D S Ray of Physical Chemistry division under SCS [School of Chemical Sciences
Diverse role of nonmuscle myosin IIs in cellular dedifferentiation and blebbing
Full text linkNonmucle myosin IIs (NM-IIs) are the most important actin based motor proteins that are
widely distributed throughout the entire organism and play distinct roles in cell adhesion,
migration, division etc. NM IIs have been shown to be localized into stress fibre, sarcomere
and most likely maintain the cortical tension. In this thesis, we have studied the localization
profile of major NM-IIs (NM-IIA and NM-IIB) isoforms and effect of phosphorylation status
of myosin regulatory light chain (RLC20), which is known to induce NM-IIs activity, in 3-
methylcholanthrene (3MC) treated C2C12 myotubes. We have found that 24h post 50nM
3MC treated myotubes exhibit discrete localization of NM-II isoforms in the sarcomere
and/or stress fiber in cytosol- NM-IIA accumulates at the centre of midbody, whereas NMIIB
is at the cortex of midbody. Immunoblot analysis of phosphorylation status of RLC
shows that there is 5.6 ± 0.5 fold reduction in 3MC treated myotubes in comparison to vehicle treated myotubes during the fragmentation step of myotube dedifferentiation. In contrast, expression level of myogenic factors like MyoD, Myogenin and cell cycle
regulatory proteins like Cyclin D, Cyclin E remain unchanged as assessed by real-time PCR array analysis during the fragmentation step of myotubes. Interestingly, addition of myosin light chain kinase inhibitor, ML-7, enhances the fragmentation about 45 ± 3.5 %, whereas phosphatase inhibitor perturbs the 3MC induced fragmentation of myotubes about 20 ± 3.4 In this thesis, we have also studied the functional role of NM-II isoforms in blebbing. We found that the three isoforms of NM-II have differential role in bleb formation. We have shown that ectopically expressed GFP-tagged NM-II isoforms exhibit different types of membrane protrusions such as multiple blebs, lamellipodia, combination of both or without having any protrusions in a human breast tumor cell line MCF-7 as revealed by time lapse video microscopy. Quantification suggests that 49% of GFP-NM-IIA, 26% of GFP-NM-IIB
and 19% of GFP-NM-IIC1 expressing MCF-7 cells show multiple bleb formation.
Interestingly, expression of phospho-dead mutant of regulatory light chain (RLC), but not the phospho-mimic or wild-type, could reduce the bleb formation to 8% in MCF-7 cells. When we induce the bleb formation by disruption of cortex using 405 nm laser light, we find that all the three GFP-tagged NM-II isoforms can re-appear and form filaments at different degree into the growing bleb. GFP-NM-IIB can form filament into the blebs in 48 % of GFP-NMIIB expressing cells compared with GFP-NM-IIA and -II-C1 which form filament only in 10 % and 3 %, of GFP-NM-IIA and GFP-NM-IIC1 expressing cells, respectively. These studies suggest that myosin IIs have differential role in bleb dynamics.Research was conducted under the supervision of Prof. S S Jana of the Biological Chemistry division under SBS [School of Biological Sciences]Research was carried out under CSIR fellowship and gran