Nano Technology - Theses

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    Phenomenological and physical modelling of high homologous temperature deformation
    (University of Hyderabad, 2016-04-01) Sriharsha, Sripathi ; Dibakar Das
    The main focus of this study is to critically assess the relevance or otherwise of a mesoscopic grain boundary sliding controlled flow model, which has been proposed as the common basis for explaining superplastic deformation in different classes of materials. The rationale behind this approach is that, as superplasticity is observed to be a near-ubiquitous phenomenon, there could be an underlying physical phenomenon responsible for this. If this were the case, the phenomenology of the superplastic flow process should also be similar for different classes of materials, i.e. there should be a universal curve for superplastic flow in all systems if the experimental variables like stress, strain-rate, strain-rate sensitivity and temperature of deformation are correctly normalized. Starting from these premises, it has been shown that under isothermal conditions the    log logσ ε plots of superplastic materials of different classes and the variation of the strain-rate sensitivity with  log ε for materials of different classes have near-identical features. The viscosity and the free energy of activation of all the alloy systems at (nearly) the same homologous temperature also vary quite similarly. Thus, the universality in the mechanical response of superplastic alloys is demonstrated. Further, the mesoscopic-grain boundary sliding controlled flow model for superplastic deformation, initially proposed for micron-grained metallic materials, but later extended to include dispersion strengthened alloys, intermetallics, metals with a quasi-crystalline phase, ceramics and ceramic-composites was taken up for consideration. An algorithm was developed to analyze the experimental data in terms of this model, so that many systems could be analyzed successfully. It has been shown that the mesoscopic-grain boundary sliding model satisfactorily describes superplastic deformation in metals and alloys, dispersion strengthened alloysceramics, composites, intermetallics, nanostructured materials and a material containing a quasi-crystalline precipitates and of grain sizes ranging from a few micrometers to a few nanometers. Also, the same approach has been used to satisfactorily explain superplasticity in geological materials and ice. In the present state of its development, in the mesoscopic-grain boundary sliding controlled model, even though theoretical expressions exist, the values of the free energy of activation and the threshold stress needed for the onset of mesoscopic- grain boundary sliding are treated as fitting constants. By way of applying the ideas to an allied, relevant situation, the mesoscopic-grain boundary sliding controlled model was also used to satisfactorily account for the inverse/ reverse Hall- Petch effect observed in materials when the grain size is in the lower ranges of the nanometer scale. Future efforts could be towards a theoretical framework at a mesoscopic level, by estimating the threshold stress necessary for the onset of mesoscopic-grain boundary sliding a priori
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    Study on uniquely modified diamond, diamond / B-SiC nanocomposite and graphene nitride (g-C3 N4) surfaces
    (University of Hyderabad, 2017-08) Vara Lakshmi, Bommidi
    Diamond and diamond/β-SiC composite films are being widely studied for their wear resistant, structural and electronic properties. Of the various methods researchers use to modify the structure of these films, using irrradiation techniques in particular are of interest due to their versatility. This thesis work was carried out to: (i) understand the indentation damage and electrical properties of diamond/β-SiC nanocomposite thin films, (ii) modify (i.e., phase, structural and/or morphological) the diamond films by using ion beam implantation/irradiation technique, (iii) modify the surface morphology of g-C3N4 by using ion implantation/irradiation, (iv)Fabricate the metal-insulator-semiconductor active structures in diamond films. The forms of diamond and diamond/β-SiC nanocomposite films resulting from such modifications are investigated using Raman spectroscopy in conjunction with scanning electron microscopy and x-ray diffraction were carried out to understand the microstructure and phase information. Also as-grown diamond/β-SiC nanocomposite films are investigated with mechanical and electrical testing. The impact of these characterizations will provide the valuable perspective to researchers in materials science. Understanding the changes to the structure and properties of this class of thin films which can be induced through various mechanisms will allow future researchers to refine these films towards technological applications in areas of hard coatings, electronics and biosensing. Raman scattering experiments in conjunction with scanning electron microscopy and x-ray diffraction were carried out to extract microstructure and phase information of the gamma and nitrogen ion irradiated diamond thin film surfaces. The γ-irradiation of diamond films showed no phase, surface and structural changes. The nitrogen ion implantation with 100 keV results increase in sp2-C network in diamond films which leads to improve the surface conductivity of these films. This nitrogen ion implantation of diamond films fabricate the metal-insulator-semiconductor (MIS) active surfaces which are used in electronic device applications. The graphene nitride (g-C3N4) materials are used in energy applications. The silicon implanted/irradiated g-C3N4 showed sheet like morphology with stable phase and structure of graphene nitride which are used in lithium ion batteries applications.
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    Design of novel mesoporous nanocapsules and their therapeutic efficiencies as a drug delivery carrier and to enhance the immunological responses
    (University of Hyderabad, 2018-11-01) Pradip Paik
    With passing time medical field has been improving rapidly, because of incessant new inventions by researches in this particular field. Presently, nanotechnology has strengthened its root in all trajectory of the biomedical field with a focused persistence for human healthcare and together it can be termed as nanobiotechnology. Consequently, it has shown potential in drug formation, preventing and curing any disease, cancer therapy, drug delivery system, tissue engineering, MRI contrast agent and many more. Biocompatible and biodegradable nanomaterials play a noteworthy part in this trait. Currently, porous nanomaterials have enlightened the tremendous possibilities in the applied field of biotechnology by offering void space to encapsulate or entrapped particles in it like a nanocargo followed by delivery those encapsulated particles in the site of interest by a sustained controlled release and after unloading that nanocargo in physiological condition without leaving any side effects. Encapsulated particles can be drugs, biomolecules, gene, protein and a range of therapeutics. From a healthcare point of view, these nanomaterials with characteristic porous structures can decrease the doses of drugs thereby reducing toxicity occurred due to the therapeutics and also increase the possibility of bioavailability of therapeutics. Then the challenge occurred with the size of the nanocarrier along with the size of the pores. Therefore, synthesis of nanomaterials with all required characteristics as a carrier has become vital. However, polymer nanostructures are getting additional highlights because of their biocompatible and biodegradable nature but few metal NPs like silica, zinc oxide, quantum dots, titanium dioxide, iron oxide, etc. have also proved their efficiency as nanodrugcarrier with small size, rigid arrangements, long shelf life as well as interact with cellular biomolecules thereby facilitates admittance into the cell. This dissertation comprises a detail synthesis approach of three types of polymeric and inorganic nanomaterials with varying sizes, followed by a complete systematic characterization for the biomedical application. Conventional sole gel techniques, chemical synthesis by using nanotemplates and surfactant free sonochemical technique have been followed for the synthesis of nanomaterials with different characteristics such as core-shell, hollow porous and mesoporous. Three different therapeutic fields have been included in this work for theapplication purpose of synthesized porous structured nanomaterials and the fields are Malaria, Immunology and Cancer Therapy. Malaria is becoming a big threat in human by becoming resistant to almost all available malaria medications and thereby causing about 216 million cases in 91 countries annually with 445000 deaths according to WHO. There instant proper up gradation in the Malaria treatment is becoming a very urgent issue. The first part of this dissertation includes the development of a coreshell nanostructure where different sizes of SiO2 NPs synthesized by sole gel technique have been used as core and PCL polymer formed the outer shell layer. Later the templates SiO2 NPs have been etching out to create a new PCL NC with hollow porous morphological characteristics. This novel amorphous hollow porous PCL NCs are biocompatible biodegradable and have a great encapsulation efficiency while loaded with antimalarial drugs Dihydroartemisinin and Chloroquine and Sulfadoxine. Their antimalarial activities have been studied with Malaria causing P. falciparum parasitic cell culture where these NCs have efficiently inhibit the growth of the parasite-infected RBCs compared to free drugs. These NCs are unique because they can be tuned as a “time temperature clock” module i.e., they can be tuned with predetermined drug dosses obligatory for the Malaria treatment with an increase of body temperature due to the infection. This nanodrugcarrier has the potential to control the release of confined drugs from it as soon as the temperature arises gradually reduces the release of drug with a gradual decrease in the temperature to normal. Therefore, this unique polymer based NCs can be used as nanodrug carrier for eradicating P. falciparum growth efficiently. In the field of nanobiotechnology, nanostructures based on metal have received importance recently for the formation of vaccines. Moreover, nanostructured with porous morphology is an excellent candidate in that regard. The second part of this dissertation included designing of nanostructured ZnO with mesoporous morphology by surfactantfree sonochemical method. This unique stable mesoporous ZnO NCs showed outstanding loading efficiency by encapsulating protein Ova. These protein loaded metal oxide NCs have immunized in mice model to investigate the enrichment of immunological responses. Ova has worked as an antigen in this regard for improvement in CD8+ and CD4+ T-cell effector responses. Antigen-specific IgG levels and IgG2a or IgG2b levels in serum has also increased when lymph node and serum of Ova loaded mZnO immunized mice have studied. The role of mesoporous ZnO NCs in enriching the immune response makes it as a good promoter to design nanovaccines in the field of medicine to prohibit various ailments. Later these mesoporous nanocarriers have been used to encapsulate antimalarial drugs Dihydroartemisinin,Chloroquine and Sulfadoxine and anticancer drugs DOX and paclitaxel and a systematic sustained controlled drug release pattern can be observed in each drug conjugate nanoformulations. The cellular level interaction of drugs loaded mZnO NCs with cancer cell line K562 have been studied where these NCs entirely deformed the malignant cell structures and thereby proved their efficiency as a drug carrier. With the development of biomedical field, the therapeutic field Cancer has also developed. A part of credit can be claimed by the involvement of nanotechnology in this particular medical field with new innovative researches to avoid complications related to the treatment. The third part of this dissertation includes engineering of a core-shell nanostructure with mesoporous ZnO NCs as a template and polymer PCL as coating layer where 2-3 templates were coated by a polymeric shell. Later these temples were etched out by leaving pores in the polymer nanostructures. This amorphous NC is biocompatible and biodegradable in nature with a great drug encapsulation efficiency. Biocompatibility of this NCs with the templates as well as without templates were investigated with two different breast cancer cell lines MCF 7 and MDA-MB-231 respectively. The drug Paclitaxel has been used to load inside the NCs pores and cell inhibition assay have been conducted by using MCF 7 and MDA-MB-231 where drug loaded with NCs performed more malignant cell inhibition property compared to free Paclitaxel drug. Moreover, this nanocarrier showed lower IC50 compared to free drug. Thus these polymer-based nanodrug carriers can decrease the toxic drug doses thereby reducing side effects and also can increase the bioavailability of therapeutics.
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    Integration of solution processed novel graphenaceous materials as functional layers in dye sensitized and polymer solar cells
    (University of Hyderabad, 2019-04-01) Charanadhar, Nagavolu ; Srikanth, V.V.S.S
    Harnessing renewable solar energy through different technologies is greatly dependent on the advancement of solar grade materials’ science and engineering. Worldwide, scientists and engineers are focusing on developing novel solar cell designs which can be easily manufactured at low cost. In this context, 3rd generation (3G) solar energy technologies namely Gratzel cells or Dye Sensitized Solar Cells (DSSCs) and Bulk heterojunction organic photovoltaics (BHJ OPV) are expected to challenge the performance of Si based solar cells and compete for a significant market share in the field of next generation solar cells. These technologies gained prominence due to their low cost, light weight construction and printable nature over large area flexible substrates. This thesis work demonstrates an integration of inexpensive novel Graphenaceous Materials solution, for the above mentioned solar technologies energy harvesting, explore selection of suitable material for their energy efficient utilization and fabrication method. Initially, Graphene oxide (GO) was synthesized using a modified Hummers method and was reduced by using focused sunlight to obtain solar reduced graphene oxide (SRGO). GO and SRGO are then used as Pt free counter electrode materials in dye sensitized solar cells (DSSCs). GO and SRGO counter electrodes were prepared by a simple spray coating method to produce homogeneous electrode layers. The DSSCs with GO and SRGO counter electrodes exhibited an overall power conversion efficiencies of ~3.4 and ~4%, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the DSSC with SRGO counter electrode exhibits higher electro-catalytic activity and lower charge transfer resistance at the electrode/electrolyte interface (in comparison to the DSSC with GO) resulting in higher conversion efficiency. Moreover, the microstructural features of SRGO are found to be suitable for its improved interaction with the liquid electrolyte and the enhanced electro-catalytic activity at its surface.
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    Development of metal-assisted chemical etching (MACE) based silicon (Si) nano/microstructures and their applications in surface enhanced Raman spectroscopy (SERS) for chemical sensing
    (University of Hyderabad, 2018-04-01) Borgohain, Debabrot ; Dash, Raj Kishora
    Surface-enhanced Raman Scattering (SERS) has emerged as a key research area for its excellent detection capability and fingerprint identification of the various chemicals such as methylene blue (MB), malachite green (MG), melamine etc. Recently, it has drawn tremendous attention for potential application in the food sector, medical sector, security sector etc. Though some progresses have already been achieved in the molecular level detection of chemical species with SERS technique, still more challenges are there such as repeatability, scalability, reproducibility, shelf life. One of the key factors is the development of the SERS substrates for improvements in the SERS signal and detection limit as well. In this regard, significant progress has already been achieved in the fabrication of the SERS-active substrates by using both the top-down and bottom-up approaches. Bottom-up approaches, such chemical synthesis, self-assembly, electrodeposition, dip-coating processes are successfully employed to fabricate SERS-active substrates. On the other hand, the top-down approaches, such as lithography, oblique angle metal film deposition and metal-assisted chemical etching (MACE) and which are mainly used to fabricate various nanostructures, has shown very effective and reproducible SERS-active substrates preparation. However, still preparation of the SERS substrates with enhanced Raman signal and also with higher detection limit have been considered as the main challenges and need to be addressed. Though, several existing approaches such as conventional or unconventional nanofabrication methods are used for the preparation of Si-based SERS substrates by top-down approach, MACE process is emerging as a very simple and cost-effective process for fabrication of the nanostructures and hence, it has gained sufficient attention globally. Thus, the main objective of this present work is to fabricate Si nano/microstructure by using MACE process and then utilizing these Si substrates for detection of the methylene blue (MB).Different nano/microstructures were fabricated on Si by using noble metals catalyst such as gold (Au) and silver (Ag). The effect of different etching parameters such as thermal annealing of the metal catalyst, effect of the concentration of the oxidising agent, those are directly associated with the MACE process were investigated. The experimental results revealed that the thermal annealing process eliminated the pin-holes present in the metal catalyst when 50 nm thick Au acted as metal catalyst and successfully fabricated deeper micro-trenches on Si substrates than the un-annealed counterpart of it. Moreover, it also indicated that higher thickness of the metal catalyst micro-stripes help to fabricate flat bottom type deeper trench than the thinner counterpart. Furthermore, the mechanism for the obtained results are discussed in the thesis. The morphological effect of the metal micro-stripes was also examined and the results indicated that various nano/microstructures could be fabricated by controlling the morphology of the used metal catalyst. As it is very well known fact that the SERS detection limit or enhancement of Raman signal primarily depend on the fabricated nano/microstructures present on the surface of the Si substrate and incorporated with the noble metal (Ag) nanoparticles. The performance of the Si-based SERS substrates was tested for the chemical detection of MB with very low concentrations starting from nM to pM, and the result indicated that nanostructured Si substrate showed better SERS detection than its microstructured counterpart. The probable reasons for such behaviours are also discussed. More studies were also carried out to enhance the detection limit of the MB, since higher the detection limit is better for the usability of these substrates for molecular level detection of different chemical species. Thus, combination of discontinuous Au film and Ag nanoparticles (NPs) were deposited on the nanoporous Si substrates, those were obtained by MACE process and the result suggested that the detection limit of MB can be further improved by depositing discontinuous Au thin film with various thicknesses. It is also noticedfrom the experimental results that up to certain thickness of the Au discontinuous thin films, it helps to improve the limit. On the other hand, higher thickness of the Au discontinuous thin films, degrades the detection limit. Thus, there is a direct correlation between the detection limit and the thickness of the Au discontinuous film on the nanoporous Si substrate. Our experimental findings suggested that the best detection could be achieved when a combination of 30 nm Au discontinuous thin film and Ag NPs were used for preparation of the SERS-active substrates which can detect 10 pM MB. Furthermore, highest enhancement factor of the order of 108 is also achieved with this same combination of Au discontinuous thin film and Ag NPs. Thus, we believe that the prepared SERS-active substrate in this work can have the capability to detect MB at molecular level. We believe that the easy, simple and reusable SERS-active substrates will be more helpful to develop chemical sensors to detect molecular level chemical species other than MB with higher enhancement factor and can be utilized for the food safety, environmental monitoring, security and medical diagnosis in the near future.