PhD Theses (Nanotechnology)


Recent Submissions

Now showing 1 - 20 of 43
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    Interaction of Surface Acoustic Waves with Organic Semiconductor and its Applications
    (2023) Bhattacharjee, Paromita
    With the introduction of the concept of surface acoustic wave (SAW) by Lord Rayleigh in 1885 and after the advent of the interdigital transducer (IDT) in 1965, the propagation of SAW has been widely studied in piezoelectric based devices. A SAW device provides multitude of signal processing and frequency response related attributes, depending on the geometry of the IDTs deposited and on the properties of the piezoelectric substrate. SAW based signal processing units such as filters, oscillators, convolvers, correlators, matched filters etc. find their applications in radar systems, TV receivers, digital radio, spread-spectrum communications, electronic counter-measures, air traffic control and data-handling systems. SAW devices have also been used for sensing pressure, humidity, temperature, as well as bio and chemical analytes by analyzing the respective change in the SAW propagation parameters.
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    Studies on high power pulsed magnetron and dielectric window for S-band linear accelerator
    (2023) Anilkumar, Patibandla
    Magnetron is a member of the vacuum tube family, a high-power microwave (HPM) electromagnetic source. It offers numerous advantages and finds application in diverse fields. This thesis primarily focuses on its application in medical fields, specifically in the linear accelerator (linac) for treating cancer cells. It concentrates on optimizing the output power, efficiency of the magnetron by emphasizing the design of the magnetron and pillbox dielectric window.
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    Engineering Solution Processable Organic Field Effect Transistor for Opto-electronic Applications
    (2022) Choudhury, Anwesha
    Electronic devices have made people’s life easier, and in today’s modern lifestyle electronic devices have become one of the basic requirements of human beings. Inorganic material are used extensively in electronic devices but the requirement of energy efficient, low-cost and flexible devices can be easily fulfilled by the organic solution processable materials. Organic field effect transistors (OFET) will enable easy implementation of large scale and flexible applications. Organic materials also have the advantage of easy tunability of the optoelectronic properties. OFETs have numerous applications like various sensors, smart card, e-skin etc. Some of the organic electronic devices like OLED, solar cell is already available in market, but low mobility and stability is a road block for organic transistors to be commercialized in high end applications.
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    SiO2 Trench Embedded Field Effect Transistor for Biosensing Applications
    (2022) Naorem, Monica
    Bio-FETs couple a transistor device with a bio-sensitive layer that can specifically detect bio-molecules. There are many challenges involved in a Bio-FET such as the selection of a suitable substrate and channel material, provision of a sensing film layer on the active site of FET, setting up a receptor on the sensing film layer to enable ion detection, the inclusion of liquid holding facility, etc. Moreover, rapid response and higher sensitivity are required for the sensor. The proposed structure has a SiO2 trench along with a reservoir that removes the need for any extra mold for containing the analyte liquid. The inbuilt trench structure brings additional benefits such as ease in the analyte pouring during the sensing, helps in the storage of liquid, minimizes the overflow of the analyte liquid and improves gate control by an increment in effective oxide capacitance. The device was fabricated using photolithography followed by etching steps. A basic trench embedded FET device was electrically characterized with KCl as an ionic liquid channel. Using the fabricated device, H2O2 was sensed using GO/PPy nanocomposites as the channel, and glucose & LDH were sensed using GO/Ag NPs. This FET device can detect the occurrence of a chemical reaction in real-time.
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    Cancer Theranostics With Nano-Enabled Bacterial Bots
    (2023) Debasmita, Debashree
    The contemporary cancer therapeutics are being strategically designed to obtain improved outcomes as compared to the conventional methods. The primary challenges faced by the conventional mode of therapies such as surgeries, radiation therapies, and later chemotherapy are difficulty in tumor accessibility, undesirable impact on normal cells, ineffectiveness towards cancer stem cells, missing the targets, rapid drug release prior to reaching the targets, poor pharmacokinetics of drugs, and resistance development to the therapy. In order to focus on the improvements, target specificity through small molecules, aptamers, antibodies, nucleic acid, stimuli sensitive polymers have been developed. Coating of the drug with polymers and loading the drugs on nano-carriers for enhanced bioavailability, slower release and safety from immune attacks have also been introduced. Developing methods for immunotherapy are also being practiced. Gradually the newer methods such as gene therapy, immunotherapy, and combined therapies have overtaken the conventional methods. Although these methods have shown improved results in comparison to the previous methods but the threat imposed by the cancer stem cells and drug resistance are still continuing. The advent of bacteria-mediated therapy has shown some light towards a path of developing a resistance – free cancer therapy. Since, the anaerobic bacteria preferably colonize in the hypoxic areas of the tumor and act on the core of the tumor, hence, there is a better opportunity for the bacteria to eradicate the stem cells and prevent relapse of cancer. The attenuated strains achieved through genetic engineering and over-expression of endotoxins and therapeutic genes have generated hopes for a better future of cancer therapeutics. The commonly used strains are Salmonella, Bifidobacterium, Clostridium, E. coli and Lactic acid bacteria (LAB). The bacteria-based therapy can have two usages, first as a therapeutic entity and second as a delivery vehicle. The anti-cancer effects of the bacteria can be inherent or can be inculcated through genetic modifications of endotoxin gene, pro-drug activating enzymes, siRNA, shRNA based silencing, and immune system evoking via over-expression of cytokines specifically activating T-cells and macrophages. The anti-biotic susceptibility, suitability for genetic manipulation, and low immunogenicity are required criteria for bacteria to be a therapeutic agent. The risk factor associated with the bacteria-mediated therapy is controlling the growth and number of bacteria after the therapeutic regimen is over. A few studies have been reported on these aspects and a lot more is yet to be explored. In order to avoid the adversities of using a pathogenic strain, the shift can be made towards opting for safer strains that do not require genetic manipulation and have inherent anticancer effects. The safest option is to use human gut friendly bacteria. The gut bacteria play a pivotal role in drug actions, resistance and overall health of an individual. The gut microbes, which have inherent anti-cancer properties are Streptococcus pyrogenes, Mycobacterium bovis, Serratia marcescens, Lactobacillus plantarum, Lactobacillus rhamnosus GG, Lactobacillus acidophilus, Salmonella, Clostritidium, Bifidobacterium and E. coli. Out of this vast range of bacterial strains the, Lactobacillus are among the safest strains as they are non-pathogenic. This could solve the safety issues of using attenuated pathogenic strains. The Lactobacillus strains are anti-tumorigenic naturally and are antibiotic susceptible, making them suitable as an anti-cancer agent and also as a carrier. The current dissertation work was up-taken to explore the potential of wild type Lactobacillus rhamnosus as a living bacbot that could function as a theranostic agent having anti-cancer effects mediated by an anti-cancer drug methotrexate and their inherent abilities in annihilating cancer tumour
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    Nano-Enabled Optoelectronic and Mechatronic Devices
    (2023) Gogoi, Kasturi
    Moore's Law, which predicts the rise in processing performance of semiconductor chips due to downsizing of device dimensions, has primarily driven advances in semiconductor technology during the last few decades. As the physical device scales approach atomic dimensions, further downsizing is limited due to quantum – mechanical effects and inter-atomic interactions. Hence, nanoelectronics emerged as a promising complementary technology, that provided novel methods and architectures in order to bring in atomic scale interactions to macroscopic functionalities. This dissertation work is focused on exploring functional properties of quantum dots and nanoparticles modified through ligand interactions and fabricating semiconducting devices for applications such as thin film transistors, UV-photodetectors and multi-stimuli responsive mechanoreceptors in flexible frameworks. Chapter 1 presents a brief introduction to nanomaterials, their functional properties and different approaches to tailor their physical and chemical properties. A short insight is given on nanomaterial deposition techniques for fabrication of semiconducting devices. Successively, brief description on thin film transistors, photodetectors and self-powered detectors are presented. An insight is presented on different categories of tactile sensors and in addition, recent advancements in this arena are discussed. At the end, we present an overview of the challenges and scopes for developing multifunctional devices targeting different applications. Chapter 2 presents synthesis of Mn2+ -doped ZnS quantum dots and surface complexation of these quantum dots with 8-hydroxyquinoline 5-sulphonic acid ligand. Herein photoluminescence characteristics of surface complexed quantum dot due to the formation of bluish green emitting zinc quinolate (Zn(QS)2) complex are discussed. Thin film transistors were fabricated and device characteristics such as carrier mobilities, carrier densities, trap state densities and carrier hopping characteristics at variable temperatures were studied. Chapter 3 presents fabrication of Mn2+ doped ZnS quantum dot complex photodetectors (QDC-PD) for efficient and ultrasensitive detection of UVA radiations. In the same context, effect of Mn2+ doping in ZnS Qdot and surface modification of doped Qdot in the detector performance were studied. A shift in the detection band from UVC in Qdot to UVA in QDC was observed due to the formation of a luminescent moiety at the Qdot surface. UV- photodetection under self-powered mode was demonstrated. Also, the dual emitting feature of QDC was utilized as an anti-counterfeiting ink for data encryption. In Chapter 4, a highly sensitive tactile sensor developed from a crosslinked gold nanoparticle network and a micro-structured PDMS layer is demonstrated. Herein, the device responses to mechanical deformations and external stimuli were recorded and piezo-resistive nature of gold nanoparticle network was studied under applied mechanical strain. The tactile sensor enabled recognition of physical activities such as jogging, leg movements, standing, tapping action and also to identify weight and vibration. To enhance the multifunctional attributes of the tactile sensor, the piezo-phototronic nature of the assembled nanoparticles was also explored. Chapter 5 summarizes the works carried out in the dissertation and highlights the key objectives achieved. It also presents future prospects of this dissertation work especially the novel application potential in diverse fields.
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    Transport, Sensing, and Mixing of Nanoscale Objects in Microfluidic Reactors
    (2021) Maity, Surjendu
    Miniaturization of the macroscopic technologies has been one of the most attractive areas of research and development in the recent years. For example, the miniaturized processes are now extensively employed for synthesis of materials, health care diagnostics and therapeutics, renewable and non-renewable energy harvesting, environmental remediation, biotechnology, electronic devices, and materials-electrical-morphological characterization. In this regard, although the progress has been very rapid over the past few decades, however, the detailed understanding on the the scientific and technological nitty-gritties associated with the mesoscale systems is perhaps at their initial stages. Moreover, the emerging quantum technologies require a large-scale experimentation employing a wide range of micro to nanoscale devices. Thus, extensive research activities have been observed in exploring the diverse unknown aspects of the mesoscale systems.
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    Luminescent Composites of Hydroxyapatite Nanoparticles for Theranostic Applications
    (2022) Simon, Anitha T
    The current thesis mainly focuses on a bioinspired inorganic source such as hydroxyapatite, whose composition resembles to that of human hard tissues, and its development into drug delivery nanocarriers. Chapter 1 is the introduction section of the thesis, which focuses on the progressive advancement of nanotechnology through the development of various multifunctional nanocarriers in the recent past. The chapter discusses widely on the antibacterial and theranostic characteristics exhibited by various drug delivery nanosystems. Chapter 2 emphasizes on the synthesis and characterisations of hydroxyapatite nanoparticles, doped with copper nanoclusters. They were further loaded with antibacterial drug namely kanamycin for applying towards antibacterial and antibiofilm applications. The nanoformulation loaded with kanamycin were found to be active against Gram negative bacteria and effective in eradication of biofilms formed by Pseudomonas aeruginosa. Chapter 3 presents studies on copper nanocluster doped hydroxyapatite nanoparticles for cancer theranostics. An anticancer flavonoid drug namely quercetin, was loaded into copper nanocluster doped hydroxyapatite nanoparticles and analysed for anti-cell proliferative effects on monolayer culture and tumor spheroids of HeLa cells (cancer cells). The quercetin loaded nanocarrier triggered formation of reactive oxygen species, disrupted the cell cycle pattern with concomitant induction of apoptosis mediated cell death in treated cancer cells. The drug loaded copper nanocluster doped hydroxyapatite nanoparticles were effective in disrupting and inhibiting the proliferation of tumour spheroids, by releasing the loaded anticancer drug towards their interior. Additionally, the luminescence property inherited through copper nanoclusters enabled intracellular tracking of nanocarrier distribution, suggesting potential use of the present nanocarrier in cancer cell imaging. Chapter 4 highlights on the combinatorial therapeutic effect implemented through copper nanocluster doped hydroxyapatite nanoparticles through co-delivery approach. The nanoformulation was encapsulated with norfloxacin (NX) and a photosensitizer methylene blue (MB). The nanocarrier carrying two therapeutic molecules was evaluated for combined therapy, conjugating chemotherapy and photodynamic therapy (PDT) on bacteria and cancer cells. In terms of application, combined therapy effectively reduced the colonies of Gram negative bacteria in comparison to individual treatments and reduced cell viability of HeLa and MCF-7 (cancer cells) significantly at lower doses of drug and photosensitizer. Chapter 5 summarizes the major objectives and essential findings reported in the current dissertation. The promising possibilities of hydroxyapatite based nanoparticles as therapeutic and imaging entity have been discussed. The future prospects of the present drug delivery system include monitoring treatment of implant related infections, active targeting for specified therapy, tissue engineering applications and in vivo studies
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    Trap Assisted Organic Semiconductors for Non-Volatile Resistive Random Access Memory Device: Design, Simulations and Experimental Investigations
    (2021) Narasimhan, Rahul A
    Since the evolution of computational technology, memory devices have become one of the most indivisible part of any on-chip computing devices. The recent boom in the big data market and the progress in the Internet of Things (IoT) have nourished the demand for semiconducting memories. Inorganic memory devices have some technological limitations compared to organic memory devices that are expected to be one of the propitious candidates due to their wide advantages like low cost, easy fabrication, low temperature processing, biocompatibility and flexibility. In spite of the promising features, two terminal memory device fabricated using organic materials contain several challenges and remains to be addressed for commercialization. First of all the mechanism behind the switching characteristics in an organic memory devices are not clearly understood. Secondly, inorganic material were always required along with the organic materials in fabricating the active layers of the organic memory device. Though all-organic active layer containing donor-acceptor (D-A) molecules exhibit switching characteristics, the tunability of the memory parameters are not explored very much. Lastly, unlike its counterpart, organic memory devices are not very much used in neuromorphic applications due to its classic binary switching characteristics. This thesis broadly addresses the above challenges with the help of certain state-of-the-art techniques. This thesis is broadly categorized into three parts based on the materials, switching mechanism and the application of the trap controlled organic memory using doping technology. The first part focuses on developing new materials and strategies towards an all organic memory device. D-A polymer containing polyfluorene (PFO) as donor and naphthalimide (NPN) derivative as acceptor is synthesized and fabricated as single active layer in a two terminal memory device which exhibits remarkably high Ion/Ioff ratio of 108. Moreover the PFONPN molecule assists in tunability, where the memory parameters can be varied by changing the concentration of acceptor moiety with respect to donor unit. Further, with an intention to create an all organic memory device, the classic method of including an inorganic material into an organic semiconductor matrix is revoked by designing an organic nanoparticle by reprecipitation of a naphthalimide derivative that are embedded into a polymer matrix. The all organic active layer exhibits an Ion/Ioff ratio of 103 with very good endurance and repeatability. In the second part of the thesis, the switching characteristics of the trap containing memory device is mechanically investigated using kinetic Monte Carlo (KMC) algorithm to clearly understand the reason for the switching characteristics. The ab initio modelling and simulation reveals that Coulomb blockade effect induced by the dopants plays a substantial role in exhibiting the switching characteristics of the memory device and the physical insights from the results of the simulation provides architectural and material guidelines to achieve a highly efficient memory device. Finally, the organic memory devices are further exploited for advanced applications like artificial intelligence (AI). A ferroelectric polymer doped with lithium salt was utilized as an active layer of the memory device that exhibits an analog type switching characteristics, which are helpful to mimic an artificial synapse. The device successfully emulates various characteristics of a biological synapse like potentiation, depression, short term plasticity to long term plasticity, Learning-forgetting-relearning and paired pulse facilitation. The contribution of this thesis towards the theoretical understanding and the practical implementation of the memory device provides the basis for facilitating the commercialization of the organic memory devices in the near future.
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    Synthesis and Surface Modifications of Graphene Oxide and its Derivative Two-dimensional Materials for Various Sensing Applications
    (2022) Singh, Ningthoujam Somorjit
    The present thesis focuses on the synthesis of large lateral-size graphene oxide (GO) and its derivative materials, such as reduced graphene oxide (RGO) and graphene quantum dots (GQDs); further, synthesized materials use various sensing applications. Large lateral-size GO is exfoliated from graphite oxide using a newly proposed technique, mild heating technique. GO sheets are exfoliated up to 106 μm, which is 15 times larger than the general exfoliation technique (ultrasonication). Furthermore, the large lateral size of RGO is synthesized using chemical and thermal treatment by pre-drop cast before reduction treatment. Moreover, Ultra-small GQDs (1.53 nm) are synthesized using the hydrothermal method assisted with the Tip sonication technique. The properties of the GO and its derivative materials are confirmed from the analysis of the XRD, Raman, FESEM, FETEM, XPS, FTIR, PL, and UV absorbance. Structural properties of the GO, RGO, and GQDs are modified using a simple, efficient, and low-cost process, gas plasma treatment. Argon plasma treatment on the GO (Ar-GO) generated structural defects without losing many functional groups, confirmed by the Raman and XPS analysis. The materials are analyzed for the SERS effect of various dyes, such as methyl blue (MB), methyl orange (MO), rhodamine B (RhB), and rose Bengal (RB). RhB has a higher enhancement factor (EF) due to the easy charge transfer between the material and RhB. Further, Ar-GO has improved the EF of RhB by providing more interaction sites for the analyte molecules. GO-based photodetector and CO2 sensor device are made on the 10 μm channel inter-digitated electrode (IDE). Similarly, Ar-GO has exhibited high photo-response compared to the GO and nanohybrid of SnO2 NPs (SO) and GO, possibly due to the increased charge trapping site on the Ar-GO. The electrical conductivity of GO is increased as the annealed temperature increases, which is due to the restoration of sp2 hybridized graphitic structures after the removal of oxygen functional groups. The CO2 sensitivity is 19% for the nanocomposite of the GQDs and SO due to the increased charge transfer to the analyte molecules.
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    Engineering Organic and Perovskite based Solar Cells
    (2022) Gupta, Ritesh Kant
    It has become utmost necessary to address the energy crisis and reduce the carbon emission simultaneously. Therefore, exploration of various renewable energy sources is now the need of the hour. Among all the renewable energy sources, solar energy is considered to be the most sustainable owing to its ample availability on the surface of earth. The first and second generations of solar cell has been already commercialized and is being utilized to reduce the load on the current method of energy production through fossil fuels. However, to further consolidate the efforts, commercial utilization of the third and fourth generations of solution processable solar cells are also important. The organic solar cell (OSC) and perovskite solar cell (PSC) are the front runners among all the solution processed photovoltaic technology owing to its various advantages and PCE reaching beyond 18% and 25% respectively. Further, both these solar cells offers ease of fabrication with low-cost and abundant materials ensuring that they can be significant contributor to commercial photovoltaic technology in the near future. This thesis is broadly organized into two parts. The first part (comprising of one chapter) and second part (comprising of three chapters) focuses on fabrication of OSC and PSC, respectively. Two techniques have been employed in this thesis work for the fabrication of solar cells: (i) hot-casting technique in the first two working chapters, and (ii) room temperature anti-solvent method in the remaining two working chapters. At first, hot-casting technique is used to develop OSC through regulation of morphology and thickness. Highest power conversion efficiency (PCE) of 9.13% was obtained for a thick active layer film. Thereafter, hot-casting technique is again implemented to fabricated mixed-halide PSC by varying the ration of methyl ammonium bromide in the precursor solution. The modified PSC resulted in PCE of 18.08% which also displayed large micrometer sized grain and reduced nanometer sized grain boundaries to minimize the recombination of the photo-generated charges. Further, trifluoro acetic acid is used as additive in perovskite solution to regulate the crystallization, minimize ion migration and charge recombination in PSC. As a result, champion 20.10% PCE was obtained in the modified device. Finally, ptoluene sulphonic acid is utilized to control the crystallization kinetics of the perovskite bulk and also passivate the traps. Simultaneously, polystyrene is used to increase the moisture resistance and reduce the surface defects of the perovskite films. This dual-passivation strategy resulted in champion PCE of 20.62% with superior ambient stability. The efforts made in this thesis highlights the usefulness of various device engineering to develop OSCs and PSCs to regulate the morphology and crystallization of the photo-active layer to achieve highly efficient, stable and repeatable solar cells. The thesis provides the basis for facilitating the commercialization of OSC and PSC in the near future.
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    Electric Field Induced Patterning of Thin Polymer Film
    (2021) Roy, Pritam
    Considering the present era of miniaturization, the demand for soft patterning in micro/nanoscale is an important and relevant topic for research. In this direction, the thesis of Mr. Pritam Roy titled “Electric Field Induced Patterning of Thin Polymer Film” provides important advancement of the existing know-how and describes a novel approach capable of modulating features, reducing time scale of deformation, and most importantly template-less patterning and e-writing. We reported the development of template-less electrohydrodynamic-contact-line-lithography (ECLL) to generate micropatterns on PDMS-liquid crystal interface. The novelty of this work lies in the use of a thin film of liquid crystals. Previous work mainly focused on the interface between air and polymer or between two polymer films. The unique properties of liquid crystals (high dielectric constants and low interfacial tension) and rheological properties of the polymer film bring new insights in the so-called electrohydrodynamic patterning. New types off patterns (micropillars vs. microwells) were found, and the time scale of pattern formation was shortened by orders of magnitude. This is an extension of the previously developed electric-field induced lithography (EFL) with some novel aspects. In addition, we discovered that the rapid spreading of the 5CB layer on PDMS surface leads to the three-phase contact line movement that triggers the formation of ordered microwell arrays. This discovery is quite exciting and new. In this thesis the fabrication technique of multilength scale hierarchical patterning was also explored in the combination of various soft lithographic techniques such as breath figures, microcontact printing, and modulated electric field-induced lithography. The observations and methodologies reported in the present thesis will be helpful in the future exploration of microfabrication using an electric field with a thin polymer film.
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    Nanomaterial-Enabled Chemiresistive Devices for Sensing Applications
    (2022) Roy, Nirmal Chandra
    The demand for inexpensive, miniaturized, reliable, and portable sensors is ever increasing in the present time. In this regard, nanomaterial enabled sensors are considered promising candidates for numerous sensing applications due to their distinct physical and chemical attributes. The present thesis explores the salient features of nanomaterials by incorporating them in sensor technology for various applications. The thesis aims to develop affordable, compact, and robust nanomaterial enabled chemiresistive sensors for various sensing applications, including healthcare, food processing and agriculture, and environmental monitoring. In this research work, various chemiresistive sensors have been developed by incorporating surface modified multiwall carbon nanotubes (MWCNTs) and metal based nanomaterial composite as the sensing material. In this regard, covalent and noncovalent functionalization techniques have been explored to attach suitable functional groups on the surface of MWCNTs for highly sensitive and selective applications. In one research work, the surface of MWCNTs has been modified with thiol functional groups for urea sensing applications in aqueous solution and raw milk samples. In another work, poly(diallyldimethylammonium chloride) solution (PDDA) has been attached to MWCNTs surface using a noncovalent functionalization approach to form MWCNT-PDDA composites. These MWCNT-PDDA composites have been explored for room temperature carbon monoxide gas sensing applications. A section of research has also demonstrated the synthesis of metal oxide heterojunction composite, where molybdenum disulfide-copper oxide (MoS2-CuO) nanocomposite has been explored for acetone gas sensing application. A section of the research has also demonstrated the development of a paper based enzymatic chemiresistor for point-of-care (POC) detection of ethanol in human breath. The sensor is developed on a biodegradable paper substrate with alcohol dehydrogenase (ADH) modified MWCNT composite as the sensing material. In addition, the sensor is also integrated with an electronic circuit to develop proof-of-concept prototypes for the POC detection of ethanol in human breath.
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    Study on Controlled CVD Growth of Monolayer MoS2 and its Heterostructures for Optoelectronic Applications
    (2020) Mawlong, Larionette P. L.
    My PhD thesis focuses on the controlled growth of monolayer MoS2 and MoS2 based heterostructure with other 2D material (WS2), TiO2 nanostructures and plasmonic nanoparticles (Ag, Au). These heterostructures are synthesized by various methods including chemical vapour deposition (CVD), RF sputtering and hydrothermal method. We have studied the controlled large area growth of monolayer MoS2 by CVD technique on a variety of different substrates. We have successfully fabricated large area high quality p-n heterojunction between single layer MoS2 (1L- MoS2) and TiO2 nanorods, grown by in-situ CVD technique showing strong enhancement of PL intensity mediated by the charge transfer due to the p-doping effect in 1L-MoS2 . We have also fabricated TiO2 /Au/MoS2 (TiO2 /Ag/MoS2 ) ternary core-shell heterostructure with an array of Au/Ag nanoparticles (NPs) coated on the hydrothermally grown hierarchical TiO2 nanostructures followed by a direct CVD growth of monolayer MoS2 and studied the effect of the plasmonic NPs on the ternary system, thus, causing a giant enhancement in the PL intensity. We studied the tunability of the photoluminescence (PL) of the monolayer MoS 2 (1L-MoS2) by decorating it with WS2 quantum dots (WS2 QD) by solving the four-energy level model involving coupled carrier dynamics based on the coupled rate equations. We have also developed 1L-MoS2/WS2 QD heterojunction photodetector demonstrating ultrafast and broadband high photodetection.
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    Fabrication of Polyaniline-Based Nano Materials for the Application in Energy Harvesting and Sensing Devices
    (2020) Palsaniya, Shatrudhan
    PANI nanomaterials strongly depend on the distribution of nanofillers for property enhancement. Based upon these nanomaterials, a brief introduction of energy storage and sensing devices have been included in Chapter-1. Chapter-2 describes binary and ternary nanocomposites of PANI, G and MoS2. Among them, PANI-G-MoS2 ternary nanocomposite exhibits excellent electrochemical activity and enhanced cyclic stability. Chapter-3 describes GO, RGO, and α‒MnO2 based PANI functionalized binary and ternary nanocomposites. Herein, PANI-RGO-MnO2 has appeared an excellent candidate for high‒density energy storage material with superior dielectric strength. Chapter-4 presents a comparative study of binary and ternary nanocomposites of PA6, rGO, and PANI components. We have observed that PA6-rGO-PANI 1:2 shows an excellent electrochemical performance with improved cyclic stability, as compared to other composites. Further, fabricated symmetric supercapacitor devices also have demonstrated outstanding performance. Chapter 5 unveils ZnO (transition metal oxide), and RGO based PANI functionalized nanocomposites. In particular, PANI-RGO-ZnO 2:1 composite reveals a superior performance as an electrode material. Chapter-6 describes preparation of PANI-ES and PANI-EB thin film, deposited on glass and n-type Si wafer substrates using a vacuum evaporation technique. We have observed that deposition of PANI-EB is relatively easier than PANI-ES. Contrary to PANI-EB, PANI-ES thin-film shows better electrical conductivity. Hence, fabricated thin-film capacitors also have shown remarkable current density and energy density with the high percolation threshold. Chapter-7 presents a hierarchical mesostructure of PANI nanorods by incorporating SDS and F127 as structure-directing agents (SDAs). The PANI-SDS-F127 1:1 composition has shown higher glucose sensitivity with a lower detection limit, attributed to the synergistic effect of available organic components. Chapter 8 summarizes the thesis work, with an outlook for future study.
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    Multifunctional Microbots for Therapeutics
    (2020) Bhuyan, Tamanna
    Nature has perfected a fantastic inventory of tiny protein machines that inspired the scientists to design artificial small-scale machines. Artificial self-propellers for therapeutic delivery in the diseased body-parts have been considered to be one of the most emerging areas of nanoscale research. Unfortunately, the demanding in vivo therapeutic applications greatly precludes the development of such synthetic motors due to toxicity, immune rejection, low biocompatibility and expensive fabrication techniques. Thus, my research was focused on fabrication of biocompatible micro/nanobots (MNMs) and their potential therapeutic applications. The objectives have been directed to implement - (i) simple, and low-cost fabrication processes (ii) use of plant-based materials in MNM design, (iii) fuel-free navigation of MNMs, and (iv) multi-functionality of MNMs, particularly drug loading and on-demand release before these artificial systems can be promoted for real-world biomedical applications. The objectives of the 5 chapters have been briefly discussed below: 1. Biocompatible and self-propelled micromotors were synthesized from the mesoporous button mushrooms with infused magnetic control on acid-alkali chemotaxis. The experiments show the potential of the iMushbots in retaining and transporting drugs in an alkaline medium such as human blood and releasing them in an acidic medium such as the cancerous tissues for cell apoptosis. The reported microbots can be thought of smart alternatives against the synthetic materials for targeted drug delivery applications in the pH-responsive systems. 2. Next, the feasibility of stimuli-responsive conditional movements of mushroom motor, namely a ‘logibot’ has been investigated for the construction of a host of optimized binary logic gates namely, AND, NAND, NOT, OR, NOR, and NIMPLY. The self-propelling logibot could rapidly sense the alkali-acid triggers, decide, and act on the basis of intensities of the pH triggers realized as potential outputs of the logic gates. This proved to be an eco-friendly alternative to the silicon-based computing operations for the development of intelligent pH-responsive drug delivery devices. 3. Further, an effective bacterial killing approach was explored using mushroom microbots (namely iButtonbots) that encourages the magnetic actuation to significantly improve water treatment strategies by enhance the mixing of Escherichia coli-laden water. The iButtonbots were immobilized with curcumin by electrostatic interactions, and superior bacterial killing was thus obtained using as compared to free CU due to the synergic effect. Introducing a swarm of such magnetically handled iButtonbots could be exploited for accelerated bacterial killing in contaminated areas. 4. Ultrasound-propelled ascorbic acid loaded nanomotors have been designed, namely Teabots, from Camellia sinensis that could offer efficient loading, localized transport, and release capabilities for anti-oxidative and anti-amyloidogenic responses. The motors show antioxidant properties at physiological pH range by scavenging intracellular ROS. Interestingly, the % release of ascorbic acid was significantly higher under the influence of ultrasound exposure, as compared to pH-dependent release. The motors were also efficient in the degradation of toxic amyloid fibrils preventing protein-aggregation derived diseases envisioned in treating neurodegenerative disorders. 5. We introduce a conceptual robotic platform from tea buds as a modality for magneto-robotic removal of biofilms of both Gram-positive and Gram-negative bacterial strains in a ‘Kill-n-Clean’ way. In the first platform, magnetically driven linear and spinning motions of microbots (T-Budbots) could efficiently kill and uproot the degraded biofilms, thus restoring the paths clogged by biofilm. Secondly, the microbots could ensure an efficient drug delivery system with a sustained pH dependent release of loaded drug at acidic microenvironment of biofilms resulting in bacterial killing.
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    Design and fabrication of rylene diimide based active materials, devices and applications
    (2017) Kalita, Anamika
    The thesis entitled “Design and Fabrication of Rylene Diimide Based Active Materials, Devices and Applications” deals with synthesis of various Rylene Diimide based derivatives following a simple one step condensation reaction route. The derivatives N, N'-bis(cyclohexyl)naphthalene diimide (NDI-CY2) and N, N'-bis(methylcyclohexane)naphthalene diimide (NMeCy2) were successfully employed for the OFETs application using simple, cost effective fabrication techniques and demonstrating the influence of various combinations of inorganic/polymeric dielectric layers on device performances. The conjugated perylene diimide derivative appended with histidine side group, PDI-HIS was utilized for the detection of ammonia (NH3) vapors via fabricating a simple two terminal sensor device. A new derivative of cationic naphthalene diimide, N, N′-bis(3-imidazolium-1-ylpropyl)-naphthalenediimide diiodide (NDMI) was developed for its application in detection of nitroexplosive picric acid (PA) both in aqueous and vapor phase. Furthermore, an economical and portable electronic prototype was established for visual and on-site detection of PA vapors under exceptionally realistic conditions.
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    Design and development of high performance polymer light emitting diode for solid state lighting
    (2017) Das, Dipjyoti
    The thesis entitled “Design and Development of High Performance Polymer Light Emitting Diode for Solid State Lighting” deals with fabrication of Polymer Light Emitting Diode (PLED), especially which emits white light, using different approaches such as physical doping, electroplex formation and phosphor sensitized system. The effect of processing conditions on the device performance has also been investigated. The electron transport property of polyfluorene was enhanced by incorporating strong electron acceptor moiety 1, 8-naphthalimide into polyfluorene main chain and efficient blue and white PLEDs were fabricated using this newly synthesized copolymer as emissive layer. A detailed study on the effect of electron injection barrier and the electron transport property of the widely used poly(9-vinylcarbazole) (PVK) on the device parameters such as current density, brightness and electroluminescent spectra, especially the electroplex formation of PVK based PLED is also carried out. White light was successfully obtained utilizing the concept of electroplex formation in such devices by device optimization. The effect of the device processing condition such as annealing temperature and the effect of mixed host were studied and by optimizing the annealing temperature and doping ration of the mixed host, highly efficient green PLEDs were fabricated. Furthermore, by utilizing FIrpic as the blue emitter and the bridge of energy transfer and Rubrene and DCJTB as orange/red dopant, white PLEDs utilizing the concept of phosphor sensitized system was realized.
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    Multimodal propulsion of synthetic microbots
    (2018) Singh, Amit Kumar
    The recent quest for miniaturization has inspired researchers to design and develop micro or nanorobots suitable for multifarious applications. The present thesis reports the fabrication of a host of micromotors composed of iron nanoparticles (FeNPs) aggregates, FeNPs coated on polymeric materials, paper, and agglomerates of pollutant carbon soot. These fabricated micromotors were employed for pH sensing, cargo transport, hydrogen generation and water detoxification applications. The Chapter 1 introduces the general introduction and basic concepts related to the self-propulsion of synthetic micro/nanoswimmers. The Chapter 2 reports a controlled migration of an iron nanoparticle (FeNP) coated polymer micromotor. The self-propulsion owing to the asymmetric catalytic decomposition of peroxide fuel was directed through a pH gradient imposed across the motor-surface, while the magnetic field induced an external control on the movement and the speed of the motor. The Chapter 3 demonstrates the design and development of a self-propelling ferrobot composed of a collection of iron nanoparticles (FeNPs). While the propulsive thrust required for the chemotactic migration of the ferrobots was generated through the ejection of hydrogen bubbles due to the reaction of aqueous formic acid (FA) with FeNP clusters on the motor surface, presence of ferromagnetic FeNPs assured “on-the-fly” remote guidance using an external magnetic field. The experiments uncovered the potential of the proposed ferrobots not only for the on-demand power supply to the portable devices but also as a single-step commercial process to produce pure hydrogen under ambient condition and devoid of greenhouse gas emission. In the Chapter 4, the self-propulsion of paper-based microjets, namely paperbots has been explored, which has multimodal chemical and magnetic controls on the motion. The Chapter 5 shows fabrication of multifunctional chemically-powered carbon soot-based microbots, namely CARBOts, by heterogeneous deposition of catalytic platinum (Pt) and magnetic nickel (Ni) nanofilms on the airborne contaminant carbon soot (CS) for environmental remediation. These magneto-catalytic CARBOts demonstrated efficient catalytic degradation of methylene blue (MB) dye in the presence of 10% (v/v) H2O2 fuel under ambient conditions. The intrinsic oleophillic nature of the CARBOts facilitated successful oil-motor interaction, which led to efficient on-the-fly capturing of oil droplets. The Chapter 6 concludes with the thesis summary and a concise discussion on the future prospects of micromotors discussed in this thesis work.
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    Surface acoustic wave devices using coupled resonance with nano- and microstructures for biosensing applications
    (2018) Trivedi, Shyam
    Surface acoustic wave (SAW) is an elastic wave that propagates on the surface of a material with its energy mainly confined to a depth of about one wavelength at the surface. Usually, SAW devices are realized on polished piezoelectric substrates with metallic interdigital transducer (IDT) made on the surface for the transduction of electrical energy to acoustic energy and vice versa. In the last few years, the demand for low cost, compact and sensitive biosensors for the detection of disease-causing pathogens has increased. SAW biosensor is an analytical device that comprises IDT on a piezoelectric substrate as transducer and a chemically functionalized active area that electivity detects a specific biological analyte. SAW biosensors are helpful because they offer real-time, label-free detection with high sensitivity and selectivity. They are a promising low-cost alternative to the conventional fluoroimmunoassay, radioimmunoassay and surface plasmon based optical biosensing techniques. Of all the SAW-based biosensing systems, Love wave (LW) devices are the most promising choice for biosensor design. Guiding layer of the LW devices keeps the energy of the wave at the surface providing high mass sensitivity and also shields the IDT from liquids. Finite element (FE) simulation of LW device considering different guiding layer materials to calculate mass sensitivity, insertion loss and the coupling coefficient of the device are presented in the thesis.