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Study of structure and relaxation dynamics of some oxygen ion conductors
Full text linkThis thesis is devoted to the study of the structure and relaxation dynamics in some
oxygen ion conducting materials. Oxide based electrolytes and cathode/anode materials
or fast oxide ion conductors have considerable applications in solid oxide fuel cell, oxygen
gas sensors and solid state based devices. Some crystallographic families have shown
high oxygenion mobility. Recent study on lanthanum molybdenum oxide (LAMOX),
strontium and magnesium doped lanthanum gallate (LSGM) and doped yttria stabilized
zirconia (YSZ) compounds have indicated their high applicability in intermediate
temperature (600 - 800 C) solid oxide fuel cell (IT-SOFC). The structure and ion dynamics of doped La2Mo2O9 ceramic compounds have been studied in detail. The crystalline nature of these materials has been con rmed by X-ray di raction. The formation of doped materials in these samples has also been con rmed using scanning and transmission electron microscopy. The thermal property of these samples has been studied using
thermogravimetry analysis (TGA). The modi cation of lattice structures with addition of di erent dopants has been investigated using Fourier Transform Infrared (FTIR) and Raman Spectroscopy. Electrical measurements of the samples have been performed using a precision RLC meter in a wide temperature range of 300 K - 1200 K and in the frequency range of 10 Hz - 3 GHz. The dc conductivity and the activation energy have been correlated with the structural modi fication of these oxide samples. The electrical measurements have been analyzed in the framework of conductivity, dielectric and electric modulus formalism. The parameters namely, the hopping frequency, concentration
of charge carriers and the frequency exponent have been determined. The dielectric formalism has been used to study the non-Debye relaxation. The electric modulus formalism has been used to study the stretched exponent behavior. Scaling properties of the conductivity and modulus spectra have been investigated to gain insights into the oxygen ion dynamics in these materials.The research was carried out under the supervision of Prof. Aswini Ghosh of Solid State Physics division under SPS [School of Physical Sciences]The research was conducted under DST INSPIRE Fellowshi
Population transfer and dissociation control in diatomic molecules in intense pulse lasers
Full text linkThe study of laser molecular interactions continues to be a highly exciting and significant field of research both for probing the intricacies of molecular dynamics as well as to control the different field induced molecular processes. The control aspects of laser molecular interactions have gained prominence in recent times and with the availability of intense ultrashort laser pulses it has become easier to manipulate the desired outcome of the different field induced molecular processes. The study of multiphoton dissociation and population transfer, in presence of a pulsed laser field within the theoretical framework of wavepacket propagation have been discussed in this thesis. The thesis also includes discussions of results related to generation of wavepackets for molecular ions under intense field and the subsequent probing and control of such wavepackets. Small diatomic molecules have been chosen as the model quantum system for this work and this helps in a simple physical interpretation of the complicated dynamical processes involved. The thesis starts with a brief introduction of the current scenario of the laser molecular interaction studies. It also gives an account of the basic objectives of the works undertaken. The rest of the thesis is divided into two parts. The first part deals with the time dependent studies of laser induced molecular dissociation and wavepacket dynamics- their generation, probing and control. The second part includes studies related to laser induced population transfer to particular quantum states in diatomic molecules.The research was carried out under the supervision of Prof. S S Bhattacharya of the Materials Science division under the SMS [School of Materials Science]The research was conducted under the CSIR research grant and fellowshi
Magnetic Properties of Transition Metal Oxides with Novel Crystal Structure
Full text linkThe family of transition metal oxides (TMOs) are acclaimed for their fascinating,
complex, and diverse thermodynamic properties. This complexity and diversity are
the manifestation of strong interplay between electronic, lattice, orbital and spin degrees of freedom. The magnetic ground states of such oxides depend strongly on the oxygen ions surrounding the metal and also on the interaction pathways between
two adjacent metal ions, which is often mediated through the 2p levels of oxygen.
Therefore, the magnetism of TMOs is closely connected to the crystal structure of the material concerned. The thesis entitled “Magnetic Properties of Transition Metal Oxides with Novel Crystal Structures” is devoted to the experimental investigations focusing the magnetic properties of some exotic transition metal oxides with unusual crystal structures. Where necessary, the electronic properties (dc and ac conductivity, dielectric permittivity, impedance and electric modulus analysis etc.) have also been studied to have a comprehensive understanding of the systems. All the results and analyses based on the investigations performed during this tenure have been included in this thesis along with the theoretical background and experimental methodologies.The research was carried out under the supervision of Prof. Subham Majumdar of the Solid State Physics division under SPS [School of Physical Sciences]The research was conducted under CSIR fellowshi
Functionalised nanoparticle and quantum dot as cellular imaging probe
Full text linkPreface
One of the fundamental goals in biology is to understand the complex
spatiotemporal interplay of biomolecules from the molecular to the integrative level. To
study these interactions, researchers commonly use imaging tool both in in-vitro and invivo
under different imaging modalities. Conventionally used fluorescent based
molecular probes have several potential limitations, such as lower brightness, photo
bleaching problem and broad absorption/emission spectra. In contrast nanoparticles based
imaging probes have advantages as they have high molar extinction coefficients, high
resistance to photo degradation and size/shape dependent tunable optical property. In
addition, nanoparticle or quantum dots (QDs) have narrow and tunable emission but with
a wider excitation window. This feature allows a single excitation source to excite QDs
of different emission colours. Similarly there are advantages to use noble metals (gold
and silver) based plasmonic nanoparticles as dark field imaging and magnetic
nanoparticles as magnetic resonance imaging (MRI) contrast agent in addition to magnetic separation. The basic function of the cell membrane is to protect the cell from its surroundings. It consists of the lipid bilayer with embedded proteins and carbohydrate. The major lipids are phospholipid and glycolipid that are amphipathic in nature. There are also membrane integral proteins called cell membrane receptor. So, the cell membrane is generally negatively charged. So any positively charged nanoparticle is easily welcomed by the cell but a nanoparticle with negative charge is repelled by the membrane. Due to the presence of lipid molecule in the cell membrane the hydrophobic nanoparticle is also taken easily. The nanoparticle engineered by receptor affinity ligand is also welcomed by the cell membrane. For this reason the successful delivery of nanoparticle is very challenging. An ideal cellular delivery nanoprobe should have the following properties (i) bright and detectable with conventional optical methods (e.g. fluorescence/dark field microscope), (ii) soluble in aqueous medium, buffer solution, cell culture media and in body fluid, (iii) functional groups on their surface for site-specific labeling, (iv) low nonspecific binding, (v) smaller size (typically 1–100 nm), (vi) low cytotoxicity and (vii)
option to target organs, cell surface or sub-cellular organelles.The research was carried out under the supervision of Prof. N R Jana of CAM under SMS [School of Materials Sciences]The research was conducted under DST research grant and fellowshi
New Organic-Inorganic Hybrid Nanoporous Phosphates And Silicates: Synthesis, Characterization And Their Adsorption, Optical And Catalytic Applications
Full text linkMicroporous and mesoporous oxides, phosphates, borates, aluminates, silicates, organicinorganic
hybrids, organic polymers etc. remain in the centre of research interest due to their versatile applications in many frontier areas of chemical and physical sciences like symmetric/asymmetric catalysis, gas storage and optoelectronics. Often the structure directing agents (SDA) used in the synthesis of non-silica based mesostructured materials keeping the mesoporous framework intact is a very challenging task. So my aim was to synthesis organicinorganic
hybrid microporous and mesoporous phosphonates and silicates materials from the tailor made organic precursor molecules. These precursor molecules were designed in such a way that the final nanoporous materials had ion-exchange, adsorption, emission, sensing, or catalytic properties etc. Moreover, depending on the nature of the functional groups grafted at the surface of the designed microporous and self-assembled mesoporous organic-inorganic hybrid materials their applications in gas and metal-ion adsorption, optical and catalytic properties were explored. This thesis gives a comprehensive report on the results of the synthesis of porous hybrid tin phosphonates, sulphonated zinc phosphonate, self-assembled titanium phosphonate, iron phosphonate and phosphonic acid functionalized periodic mesoporous organosilica materials together with their catalytic and optoelectronics properties.The research was carried out under the supervision of Prof. Asim Bhaumik of the Materials Science division under the SMS [School of Materials Science]The research was conducted under CSIR fellowshi
Designing The Functional Building Blocks For Syntheses Of Organic And Organic-Inorganic Hybrid Porous Materials
Full text linkThe research embodied in the present thesis entitled “Designing The Functional Building Blocks For Syntheses Of Organic And Organic-Inorganic Hybrid Porous Materials” deals with synthesis and characterization of several novel nanoporous organic and hybrid organicinorganic materials and their applications in the field of gas adsorption and storage,
heterogeneous catalysis, ion-exchange, chromatography and so on. Template directed synthesis of phloroglucinol diimine functionalized pore wall has been developed and showed as outstanding catalytic support for metal mediated catalysis. Further surfactant templating
approach for allylic polymerization of Triazine based monomer for the formation of pure organic polymer with hexagonal arrangement of mesopores has been shown to have excellent scaffold for metal mediated catalysis. On the other hand porphyrin functionalized pure organic polymers are synthesized which act as good sorbent for adsorption and storage of CO2; thereby largely contributes to curb global pollution.The research was carried out under the supervision of Prof. Asim Bhaumik of the Materials Science division under SMS [School of Materials Sciences]The research was conducted under CSIR fellowship and research gran
SYNTHESIS, PHOTO-PHYSICAL STUDIES AND APPLICATIONS OF DIFFERENT DOPED AND UNDOPED SEMICONDUCTOR NANOCRYSTALS
Full text linkHigh quality semiconductor nanocrystals (quantum dots, QDs) are small crystal consisting of hundreds to a few thousand atoms each with typical dimension ranging from 1-100 nm which are great interest for fundamental studies and different technological applications such as light emitting devices, lasers, solar cells and biomedical labeing. The quantum mechanical coupling of over hundreds to thousands atoms develops the band structure in semiconductors. In this regime, the spatial confinement of the electronic charge carriers in the nanocrystal leads to a phenomenon known as Quantum Confinement Effect (QCE).
Due to this effect, the size and shape of these “artificial atoms” can be used to widely tune the energy of discrete electronic energy states and optical transitions. For this the emission from these particles can be tuned throughout the ultraviolet, visible, near-infrared, and mid-infrared spectral ranges, making them useful for both biological imaging and many types of optoelectronic devices. State-of-the-art semiconductor nanocrystals have been designed to have a quantum efficiency of radiative recombination approaching unity at room temperature, far above what has been achieved from bulk materials. The reason of this high efficiency is also govern by the QCE as the strong overlap between the electron and hole wave functions in the confined structure increases the probability of radiative recombination whereas the exciton in bulk semiconductors is not confined in space and can rapidly dissociate, increasing the probability of non-radiative relaxation process associated with crystalline defects and charge carrier traps on crystal surfaces.
Among semiconductor NCs CdSe as the work horse, have been widely studied for their
fundamental properties and applications. Despite their so many advantages, the intrinsic toxicity of Cadmium has cast a doubtful commercial future for this promising field. Wide band gap semiconductor nanocrystals, such as zinc chalcogenide doped with transition
metal ions, has overcome this concern and yet maintained the advantages of the
nanocrystal emitters. Mn and Cu doped zinc chalcogenide semiconductor NCs can give
bright yellow orange and tunable blue green emission respectively which has been found very stable and having high quantum yield making them useful for different practical
application without having highly toxic Cd metal. Besides their low toxicity by replacing cadmium in CdSe quantum dots with zinc, these doped materials do not also reabsorb the photon which avoids self-quenching, a common phenomenon in quantum dots because of small stokes shift. In contrast, the emission color from a dopant, involving d–states of transition metal ions, to a large extent is fixed and independent of the size of the host. The only way to get substantially different dopant colours is to use different dopant ions. Unfortunately, doping such impurity ions into nanoparticle hosts has proven to be
unexpectedly difficult, and different synthesis methods have to be followed to get different
d–dots.The research was carried out under the supervision of Prof. Narayan Pradhan of the Materials Science division under SMS [School of Materials Science
SYNTHESIS AND STUDY OF DIFFERENT PHOTO-PHYSICAL ASPECTS OF DOPED AND UNDOPED SEMICONDUCTOR NANOCRYSTALS
Full text linkIn recent days, synthesis of high quality semiconductor nanocrystals of groups II-VI, III-V, IV-VI like CdSe, InP, SnS etc. remains one of the prime interest for understanding the fundamental photo-physics of semiconductor nanocrystals and their potential applications in advanced technology for fabricating display devices, solar cell, LEDs etc. These nanocrsyals are also extensively used in the field of biology for drug delivery, cell imaging, DNA, protein structure analysis, in different kinds of photo-induced catalytic reactions etc. The optoelectrical properties of the semiconductor nanocrystals can be monitored by tuning its size and this is the most striking feature for the semiconductor nanocrystals. Depending on the semiconductor materials and their size, emission ranging from UV to visible to near IR spectrum can be achieved. The workhorse CdSe quantum dots emit in the entire visible window with tuning the size from 2 to 6 nm. Apart from quantum dots, insertion of different dopant ions in semiconductor nanocrystals can create new relaxation channel for exciton and includes new photophysical properties in the host semiconductor nanocrystals. Cu+ and Mn2+ doped semiconductor nanocrystals have already been proved as alternate nanocrystal emitters
to provide parallel tunable emission compared to undoped nanocrystals (quantum dots). In
brief, optically active transition metal ion doping in semiconductor nanocrystals opens new optical window with stable, tunable and high excited state lifetime emission. Unlike CdSe, the synthesis and related photophysical studies of ZnS and ZnSe are not widely reported in the literature. In ZnSe, the tunability of the excitonic emission has been achieved within 390 to 440 nm but for ZnS surface trap emission mostly dominates. The high quality doped nanomaterials with high quantum efficiency is also achieved by doping Mn2+ ion in different semiconductor hosts. At first, high quality Mn doped ZnSe nanocrystals were synthesized by Norris group using high temperature injection colloidal synthetic route. Using organometallic Zn and Mn precursors they have achieved 22% quantum efficiency (QY) of the dopant emission. Further, Pradhan et. al. has reported synthesis of Mn2+ doped ZnSe and ZnS with quantum yield more than 50% in different techniques. Again, Pradhan et. al. has also reported the high quality tunable emission from Cu doping in ZnSe and CdZnS hosts. Numerous efforts have been put forward since last two decades for synthesizing high quality doped semiconductor nanomaterials to study different associated photo-physical properties and for their versatile utilities in different advanced technological applications.
Although, the understanding of crystal growth kinetics and emission properties has been achieved to a certain extent, many associated science and new properties are still hidden. Here, we have investigated the synthesis of different transition metal ion doped and undoped semiconductor nanocrystals and investigated the related photo-physical properties including their possible applications. We have also critically analyzed the related crystals growth/phase of our designed doped and undoped nanocrystals.The research was conducted under the supervision of Prof. Narayan Pradhan of the Materials Science division under SMS [School of Materials Sciences]The research was carried out under CSIR fellowship and grant, the travel grant was taken care by DS
INVESTIGATION ON SOME MAGNETIC AND MULTIFERROIC NANOCOMPOSITES
Full text linkThe present thesis deals with the nanocomposites of magnetic and multiferroic materials. The synthesis, characterization and the study of different physical properties of the nanocomposites are the principal object of this thesis. Magnetic and multiferroic nanocomposites of different systems have been synthesized using different techniques, e.g., mechanical attrition, soft chemical route etc. Some of the
systems show a core-shell structure. The examples are Fe3O4 (core)- -Fe2O3 (shell).
The materials have been characterized by X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, magnetization measurements under both zero field-cooled and field-cooled conditions. Multiferroic nanocomposites have also been prepared. The examples are BiFeO3 in two dimensions using Na-4 mica nanochannels, Bi2Fe4O9 nanotube arrays have been prepared using anodic aluminium oxide templates. Both ferroelectric and ferromagnetic properties have been delineated and the magnetodielectric and magnetoelectric coupling effects have been investigated. The results will be interpreted using suitable theoretical model. The
characterization and detailed analysis of the observed physical properties have been
described in the different chapters.The research was carried out under the supervision of Prof. Dipankar Chakraborty of MLS and Prof. S K Saha of MS division under SMS [School of Materials Science]The financial support received from Department of Science and Technology
(DST), Govt. of India, New Delhi under Indo-Russian Collaborative program
(DST/INT/AUS/PROJ/T-2/08) and under Nano Mission and also Indo-Australian Project
(INT/PFBR/P-02) on nanocomposites funded by DST, Govt. of India, New Delhi and DIISR, Canberra, Australia
Nano-Crystalline Silicon and Quantum Dots in SiOx Matrix: Synthesis by RF Plasma CVD and Characterization for Device Applications
Full text linkThe aim of this thesis is to deal with one of the important technological issues related to silicon based technology and synthesis of silicon based nanostructures by a new approach feasible for device applications. Use of noble gases like, Ar, He, Xe, etc., are generally utilized to increase the deposition rate of silicon thin films in RF plasma CVD. However, high Ar dilution leads to columnar growth and produces mostly defective network, while Xe
dilution maintains an amorphous nature of the network even at a very high RF power to the plasma. Using He as the diluent to the plasma, the recent achievement of superior quality nC-Si:H films at a reasonably good deposition rate from our laboratory leads me to extend the work to one of the most important new material nC-Si in SiOx matrix and for further extension the work to quantum dots regime. Optical, electrical and structural properties of a-SiOx:H thin films prepared from [SiH4 + CO2 + He] plasma has been described in chapter 4. We observed that the a-SiOx:H films has been shown a large shift in Fermi level due to O incorporation and its gradual movement towards the mid band gap on alloying were associated with the change in dark conductivity following the Mayer-Neldel (M–N) rule. Systematic reduction in CH identified a
dehydrogenation process occurring in the Si network during the gradual inclusion of oxygen,
induced by the presence of He as the diluent to the plasma. The result seems opposite to the conventional H2-diluted plasma and appears significantly favourable for the future
development of nC-SiOx:H materials.The research was conducted under the supervision of Prof. Debojyoti Das of the Energy Research Unit [ERU] under SPS [School of Physical Sciences]The research was carried out under IACS fellowship and DST research gran