Supramolecular Organization of Metal Nanoparticles in Solution and of Phenyleneethynylenes on Surfaces

Most of the procedures reported for the synthesis of metal nanoparticles involve the use of strong reducing agents or elevated temperatures. This limits the possibility of developing metal nanoparticle based sensors for the in situ detection of analytes. One of the objectives of the present investigations is to (i) develop newer methodologies for the synthesis of metal nanoparticles in aqueous medium at ambient conditions and (ii) their use in the detection of metal cations by taking advantage of the unique coordination ability. Ideally, biocompatible molecules which possess both the reducing and stabilizing groups are desirable for such applications. Formation of stable supramolecular assembly, by bringing metal nanoparticles close to each other, results in plasmon coupling and this strategy can be effectively utilized for the development of metal nanoparticle based sensors.Another objective of the present study is to understand the supramolecular organization of molecules on surfaces. Various noncovalent interactions between the molecules and with surface play a decisive role in their organizations. An in-depth understanding of these interactions is essential for device fabrications. Recent photophysical studies have revealed that phenyleneethynylene based molecular systems are ideal for device application. The second objective of the thesis focuses on understanding the (i) organization of phenyleneethynylenes on highly oriented pyrolytic graphite (HOPG) surface with atomic level precision and (ii) weak intermolecular interactions which drive their organization.

Novel Melt Transurethane Process for Cycloaliphatic Polyurethanes and Their Self-Organization for Nano-Materials

In this introduction part, importance has been given to the elastomeric properties of polyurethanes. Emphasis has been laid to this property based on microphase separation and how this could be modified by modifying the segment lengths, as well as the structure of the segments. Implication was also made on the mechanical and thermal properties of these copolymers based on various analytical methods usually used for characterization of polymers. A brief overview of the challenges faced by the polyurethane chemistry was also done, pointing to the fact that though polyurethane industry is more than 75 years old, still a lot of questions remain unanswered, that too mostly in the synthesis of polyurethanes. A major challenge in this industry is the utilization of more environmental friendly “Green Chemistry Routes” for the synthesis of polyurethanes which are devoid of any isocyanates or harsh solvents.The research work in this thesis was focused to develop non-isocyanate green chemical process for polyurethanes and also self-organize the resultant novel polymers into nano-materials. The thesis was focused on the following three major aspects:(i) Design and development of novel melt transurethane process for polyurethanes under non-isocyanate and solvent free melt condition. (ii) Solvent induced self-organization of the novel cycloaliphatic polyurethanes prepared by the melt transurethane process into microporous templates and nano-sized polymeric hexagons and spheres. (iii) Novel polyurethane-oligophenylenevinylene random block copolymer nano-materials and their photoluminescence properties. The second chapter of the thesis gives an elaborate discussion on the “Novel Melt Transurethane Process ” for the synthesis of polyurethanes under non-isocyanate and solvent free melt condition. The polycondensation reaction was carried out between equimolar amounts of a di-urethane monomer and a diol in the presence of a catalyst under melt condition to produce polyurethanes followed by the removal of low boiling alcohol from equilibrium. The polymers synthesized through this green chemical route were found to be soluble (devoid of any cross links), thermally stable and free from any isocyanate entities. The polymerization reaction was confirmed by various analytical techniques with specific references to the extent of reaction which is the main watchful point for any successful polymerization reaction. The mechanistic aspects of the reaction were another point of consideration for the novel polymerization route which was successfully dealt with by performing various model reactions. Since this route was successful enough in synthesizing polyurethanes with novel structures, they were employed for the solvent induced self-organization which is an important area of research in the polymer world in the present scenario. Chapter three mesmerizes the reader with multitudes of morphologies depending upon the chemical backbone structure of the polyurethane as well as on the nature and amount of various solvents employed for the self-organization tactics. The rationale towards these morphologies-“Hydrogen Bonding ” have been systematically probed by various techniques. These polyurethanes were then tagged with luminescent 0ligo(phenylene vinylene) units and the effects of these OPV blocks on the morphology of the polyurethanes were analyzed in chapter four. These blocks have resulted in the formation of novel “Blue Luminescent Balls” which could find various applications in optoelectronic devices as well as delivery vehicles.

Studies all transport and magnetic properties of nano particle doped MgB2 superconductor for technological applications

This thesis Entitled Studies on transport and magnetic properties of nano particle doped mgb2 superconductor for technological applications.The thesis ahead focuses on the establishment of enhanced superconducting properties in bulk MgB2 via nano particle doping and its conversion into mono/multifilamentary wires. Further, an attempt has also been made to develop prototypes of MgB2 coil and conduction cooled current lead for technological applications. The thesis is configured into 6 chapters. The opening chapter gives an idea on the phenomenon of superconductivity, the various types of superconductors and its applications in different fields. The second chapter is an introduction on MgB2 superconductor and its relevance which includes crystal and electronic structure, superconducting mechanism, basic superconducting properties along with its present international status. The third chapter provides details on the preparation and characterization techniques followed through out the study on MgB2. Fourth chapter discusses the effect of processing temperature and chemical doping using nano sized dopants on the superconducting properties of MgB2• Fifth chapter deals with the optimization of processing parameters and novel preparation techniques for wire fabrication. Sixth chapter furnishes the preparation of multifilamentary wires with various filament configurations, their electromechanical properties and it also incorporates the development of an MgB2 coil and a general purpose conduction cooled current lead.

Preparation and characterization of micro and nano fiber reinforced natural rubber composites by latex stage processing

Use of short fibers as reinforcing fillers in rubber composites is on an increasing trend. They are popular due to the possibility of obtaining anisotropic properties, ease of processing and economy. In the preparation of these composites short fibers are incorporated on two roll mixing mills or in internal mixers. This is a high energy intensive time consuming process. This calls for developing less energy intensive and less time consuming processes for incorporation and distribution of short fibers in the rubber matrix. One method for this is to incorporate fibers in the latex stage. The present study is primarily to optimize the preparation of short fiber- natural rubber composite by latex stage compounding and to evaluate the resulting composites in terms of mechanical, dynamic mechanical and thermal properties. A synthetic fiber (Nylon) and a natural fiber (Coir) are used to evaluate the advantages of the processing through latex stage. To extract the full reinforcing potential of the coir fibers the macro fibers are converted to micro fibers through chemical and mechanical means. The thesis is presented in 7 chapters

Studies on Catalysis by Nano Titania Modified with Metals and Nonmetals

Semiconductor photocatalysis has received much attention during last three decades as a promising solution for both energy generation and environmental problems. Heterogeneous photocatalytic oxidation allows the degradation of organic compounds into carbon dioxide and water in the presence of a semiconductor catalyst and UV light source. The •OH radicals formed during the photocatalytic processes are powerful oxidizing agents and can mineralise a number of organic contaminants. Titanium dioxide (TiO2), due to its chemical stability, non-toxicity and low cost represents one of the most efficient photocatalyst. However, only the ultraviolet fraction of the solar radiation is active in the photoexcitation processes using pure TiO2 and although, TiO2 can treat a wide range of organic pollutants the effectiveness of the process for pollution abatement is still low. A more effective and efficient catalyst therefore must be formulated. Doping of TiO2 was considered with the aim of improving photocatalytic properties. In this study TiO2 catalyst was prepared using the sol-gel method. Metal and nonmetal doped TiO2 catalysts were prepared. The photoactivity of the catalyst was evaluated by the photodegradation of different dyes and pesticides in aqueous solution. High photocatalytic degradation of all the pollutants was observed with doped TiO2. Structural and optical properties of the catalysts were characterized using XRD, BET surface area, UV-Vis. DRS, CHNS analysis, SEM, EDX, TEM, XPS, FTIR and TG. All the catalysts showed the anatase phase. The presence of dopants shifts the absorption of TiO2 into the visible region indicating the possibility of using visible light for photocatalytic processes.

Investigations on novel polymer nano composites and bio-compatible manganese doped ZnS nanocrystals for photonic and bio-imaging applications

Fluorescence is a powerful tool in biological research, the relevance of which relies greatly on the availability of sensitive and selective fluorescent probes. Nanometer sized fluorescent semiconductor materials have attracted considerable attention in recent years due to the high luminescence intensity, low photobleaching, large Stokes’ shift and high photochemical stability. The optical and spectroscopic features of nanoparticles make them very convincing alternatives to traditional fluorophores in a range of applications. Efficient surface capping agents make these nanocrystals bio-compatible. They can provide a novel platform on which many biomolecules such as DNA, RNA and proteins can be covalently linked. In the second phase of the present work, bio-compatible, fluorescent, manganese doped ZnS (ZnS:Mn) nanocrystals suitable for bioimaging applications have been developed and their cytocompatibility has been assessed. Functionalization of ZnS:Mn nanocrystals by safe materials results in considerable reduction of toxicity and allows conjugation with specific biomolecules. The highly fluorescent, bio-compatible and water- dispersible ZnS:Mn nanocrystals are found to be ideal fluorescent probes for biological labeling

Salmonella cross contamination in retail chicken outlets and the efficacy of spice extracts on salmonella enteritidis growth inhibhition on various surfaces

The source of samonella cross contamination in 15 retail chicken outlets in aresidual area in coimbatore city ,sourthern India was studied. Chopping boards and the butchers hands were predominant followed by knives and the weighing balance tray. Serotyping of the salmonella strains revealed that all strains were salmonella enteritis, except one which was found to be salmonella cerro.The anti bacterial activity of commonly used spices were evaluated.

Comparative effectiveness of solar disinfection using small-scale batch reactors with reflective, absorptive and transmissive rear surfaces

This study investigated the enhancement of solar disinfection using custom-made batch reactors with reflective (foil-backed) or absorptive (black-backed) rear surfaces, under a range of weather conditions in India. Plate counts of Escherichia coli ATCC11775 were made under aerobic conditions and under conditions where reactive oxygen species (ROS) were neutralised, i.e. in growth medium supplemented with 0.05% w/v sodium pyruvate plus incubation under anaerobic conditions. While the addition of either an absorptive or a reflective backing enhanced reactor performance under strong sunlight, the reflective reactor was the only system to show consistent enhancement under low sunlight, where the process was slowest. Counts performed under ROS-neutralised conditions were slightly higher than those in air, indicating that a fraction of the cells become sub-lethally injured during exposure to sunlight to the extent that they were unable to grow aerobically. However, the influence of this phenomenon on the dynamics of inactivation was relatively small

Unusual surface and edge morphologies, sp2 to sp3 hybridized transformation and electronic damage after Ar+ ion irradiation of few-layer graphene surfaces

Roughness and defects induced on few-layer graphene (FLG) irradiated by Ar+ ions at different energies were investigated using X-ray photoemission spectroscopy (XPS) and atomic force microscopy techniques. The results provide direct experimental evidence of ripple formation, sp2 to sp3 hybridized carbon transformation, electronic damage, Ar+ implantation, unusual defects and edge reconstructions in FLG, which depend on the irradiation energy. In addition, shadowing effects similar to those found in oblique-angle growth of thin films were seen. Reliable quantification of the transition from the sp2-bonding to sp3-hybridized state as a result of Ar+ ion irradiation is achieved from the deconvolution of the XPS C (1s) peak. Although the ion irradiation effect is demonstrated through the shape of the derivative of the Auger transition C KVV spectra, we show that the D parameter values obtained from these spectra which are normally used in the literature fail to account for the sp2 to sp3 hybridization transition. In contrast to what is known, it is revealed that using ion irradiation at large FLG sample tilt angles can lead to edge reconstructions. Furthermore, FLG irradiation by low energy of 0.25 keV can be a plausible way of peeling graphene layers without the need of Joule heating reported previously

Cure Characteristics and Mechanical Properties of Rubber Ferrite Composites Based on Nano-Nickel Ferrites

Ultra fine nickel ferrite have been synthesized by the sol-gel method. By heat treating different portions of the prepared powder separately at different temperatures, nano-sized particles of nickel ferrite with varying particle sizes were obtained. These powders were characterised by the X-ray diffraction and then incorporated in the nitrile rubber matrix according to a specific recipe for various loadings. The cure characteristics and the mechanical properties of these rubber ferrite composites (RFCs) were evaluated. The effect of loading and the grain size of the filler on the cure characteristics and tensile properties were also evaluated. It is found that the grain size and porosity of the filler plays a vital role in determining the mechanical properties of the RFCs

Modification of Polypropylene/Polystyrene blend using Nanoclay and Sisal Cellulose nano fiber

Cochin University of Science and Technology

Adsorption kinetic investigations of phthalocyanine derivatives self assembled monolayers (SAMs) on gold: Temperature influence on the SAM formation process and quality

The ordered nano-structured surfaces, like self-assembled monolayers (SAMs) are of a great scientific interest, due to the low cost, simplicity, and versatility of this method. SAMs found numerous of applications in molecular electronics, biochemistry and optical devices. Phthalocyanine (Pc) complexes are of particular interest for the SAM preparation. These molecules exhibit fascinating physical properties and are chemically and thermally stable. Moreover their complex structure is advantageous for the fabrication of switchable surfaces. In this work the adsorption process of Pcs derivatives, namely, subphthalocyanines (SubPcB) and terbium (2TbPc) sandwich complexes on gold has been investigated. The influence of the molecular concentration, chain length of peripheral groups, and temperature on the film formation process has been examined using a number of techniques. The SAMs formation process has been followed in situ and in real time by means of second harmonic generation (SHG) and surface plasmon resonance (SPR) spectroscopy. To investigate the quality of the SAMs prepared at different temperatures atomic force microscopy (AFM) and X-Ray photoelectron spectroscopy (XPS)measurements were performed. Valuable information about SubPcB and 2TbPc adsorbtion process has been obtained in the frame of this work. The kinetic data, obtained with SHG and SPR, shows the best conformance with the first order Langmuir kinetic model. Comparing SHG and SPR results, it has been found, that the film formation occurs faster than the formation of chemical bonds. Such, the maximum amount of molecules on the surface is reached after 6 min for SubPcB and 30 min for 2TbPc. However, at this time the amount of formed chemicals bonds is only 10% and 40% for SubPcB and 2TbPc, respectively. The most intriguing result, among others, was obtained at T = 2 °C, where the formation of the less dense SAMs have been detected with SHG.However, analyzing XPS and AFM data, it has been revealed, that there is the same amount of molecules on the surface at both temperature T = 2 °C, and T = 21 °C, but the amount of formed chemicals bond is different. At T = 2 °C molecules form aggregates, therefore many of available anchor groups stay unattached.

Modification and Analysis of Group-13-Nitride Semiconductor Surfaces: Influence of Adsorbates on Device Characteristics and Processing

Im Rahmen dieser interdisziplinären Doktorarbeit wird eine (Al)GaN Halbleiteroberflächenmodifikation untersucht, mit dem Ziel eine verbesserte Grenzfläche zwischen dem Material und dem Dielektrikum zu erzeugen. Aufgrund von Oberflächenzuständen zeigen GaN basierte HEMT Strukturen üblicherweise große Einsatzspannungsverschiebungen. Bisher wurden zur Grenzflächenmodifikation besonders die Entfernung von Verunreinigungen wie Sauerstoff oder Kohlenstoff analysiert. Die nasschemischen Oberflächenbehandlungen werden vor der Abscheidung des Dielektrikums durchgeführt, wobei die Kontaminationen jedoch nicht vollständig entfernt werden können. In dieser Arbeit werden Modifikationen der Oberfläche in wässrigen Lösungen, in Gasen sowie in Plasma analysiert. Detaillierte Untersuchungen zeigen, dass die inerte (0001) c-Ebene der Oberfläche kaum reagiert, sondern hauptsächlich die weniger polaren r- und m- Ebenen. Dies kann deutlich beim Defektätzen sowie bei der thermischen Oxidation beobachtet werden. Einen weiteren Ansatz zur Oberflächenmodifikation stellen Plasmabehandlungen dar. Hierbei wird die Oberflächenterminierung durch eine nukleophile Substitution mit Lewis Basen, wie Fluorid, Chlorid oder Oxid verändert, wodurch sich die Elektronegativitätsdifferenz zwischen dem Metall und dem Anion im Vergleich zur Metall-Stickstoff Bindung erhöht. Dies führt gleichzeitig zu einer Erhöhung der Potentialdifferenz des Schottky Kontakts. Sauerstoff oder Fluor besitzen die nötige thermische Stabilität um während einer Silicium-nitridabscheidung an der (Al)GaN Oberfläche zu bleiben. Sauerstoffvariationen an der Oberfläche werden in NH3 bei 700°C, welches die nötigen Bedingungen für die Abscheidung darstellen, immer zu etwa 6-8% reduziert – solche Grenzflächen zeigen deswegen auch keine veränderten Ergebnisse in Einsatzspannungsuntersuchungen. Im Gegensatz dazu zeigt die fluorierte Oberfläche ein völlig neues elektrisches Verhalten: ein neuer dominanter Oberflächendonator mit einem schnellen Trapping und Detrapping Verhalten wird gefunden. Das Energieniveau dieses neuen, stabilen Donators liegt um ca. 0,5 eV tiefer in der Bandlücke als die ursprünglichen Energieniveaus der Oberflächenzustände. Physikalisch-chemische Oberflächen- und Grenzflächenuntersuchung mit XPS, AES oder SIMS erlauben keine eindeutige Schlussfolgerung, ob das Fluor nach der Si3N4 Abscheidung tatsächlich noch an der Grenzfläche vorhanden ist, oder einfach eine stabilere Oberflächenrekonstruktion induziert wurde, bei welcher es selbst nicht beteiligt ist. In beiden Fällen ist der neue Donator in einer Konzentration von 4x1013 at/cm-2 vorhanden. Diese Dichte entspricht einer Oberflächenkonzentration von etwa 1%, was genau an der Nachweisgrenze der spektroskopischen Methoden liegt. Jedoch werden die elektrischen Oberflächeneigenschaften durch die Oberflächenmodifikation deutlich verändert und ermöglichen eine potentiell weiter optimierbare Grenzfläche.

Nano Electronics and Computer Science Research Group

This is the website for the Nano Research group based at the University of Southampton ECS department, and details current research topics and the people connected with these. It shows some of the current research topics undertaken at the center, and gives an outline of what can be done for post graduate courses.

Silicon Chips and Nano Devices

A look at the Southampton Nanfabrication Centre where electro-photonic research is carried out and the AMD company's industrial processes for creating commercial quantities of silicon computing devices.