Lakshminath Bezbaroa Central Library Digital Repository
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Recent Submissions
Synthesis and characterization of silver nanoparticles for light trapping application in thin film solar cells
(2024) Gangwar, Manvendra Singh
In the present thesis, silver nanoparticles have been synthesized by solid-state dewetting of the precursor silver films deposited at different deposition conditions (deposition time, rf power, substrate temperature) using rf sputtering technique. Surface morphology and growth dynamics of silver nanoparticles are studied using atomic force microscopy (AFM) with advanced statistical analysis. Height-height correlation function (HHCF) and power spectral density function (PSDF) are extracted from AFM data, and scaling exponents 𝛼𝑙𝑜𝑐𝑎𝑙, , 1/z and 𝛼 are determined using analysis. A direct correlation between morphology and the localized surface plasmon resonance (LSPR) properties is observed. The microstructure influence on dielectric function and plasmonic properties of silver nanoparticles (Ag NPs) is studied using spectroscopic ellipsometry (SE). Dielectric function and plasmonic properties of Ag NPs are investigated from spectroscopic ellipsometry (SE) data using a quite unique model in terms of the combination of different oscillators: Drude-Lorentz model along with two Gauss oscillators to account for intraband, interband transitions and different modes of localized surface plasmon resonance (LSPR) of Ag NPs. The influence of the substrate temperature on the growth of Ag NPs and their several properties like localized surface Plasmon resonance (LSPR), photoluminescence, and Raman spectroscopy is studied. Enhancement in PL peak intensity and Raman peak intensity is found to be in accordance with the LSPR of Ag NPs. Both simulation and experimental studies on single junction hydrogenated amorphous silicon (a-Si:H) thin film solar cells is done prior to the implementation of Ag NPs as a plasmonic back reflector in (a-Si:H) thin film solar cells. The effect of emitter layer (a-Si:H (p)) doping and absorber (a-Si:H (i)) layer thickness is studied. Further, simulation results are compared with the experimental results. A good match between simulation and experiment results is obtained. As an application part of this thesis, the role of silver nanoparticles as plasmonic back reflector for light trapping application in hydrogenated amorphous silicon (a-Si:H) thin film solar cells is explored. Excellent light trapping by plasmonic back reflector in solar cells is observed. A broadband enhancement in quantum efficiency is shown by a-Si:H thin film solar cells fabricated on the plasmonic back reflector with a gain of 47% in short circuit current density (𝐽𝑠𝑐) as compared to the flat back reflector. As a result, the improvement in the performance of the a-Si:H thin film solar with plasmonic back reflector is observed corresponding to an efficiency (η) of 8.4% against 5.6% efficiency of the a-Si:H thin-film solar cell with flat back reflector respectively.
Magnetic and Electronic Structure of few Perovskites in the form of Bulk and 2D-Superlattices
(2023) Kiran, Dokala Ravi
Complex oxide systems with the perovskite structure are becoming highly significant for modern day magneto-electronic devices because of their unique magnetic and transport properties. Mainly, perovskites with 3d-4f transition metal-rare-earth perovskites have gained widespread attention due to the strong interplay between the lattice, electron spin, orbit, and crystal structure. The present work provides a glimpse of growth of such systems using pulsed laser deposition technique and their electronic/magnetic structure in the form of 2D superlattice structures. In particular, the current work deals with the superlattices of Pr0.7Ca0.3MnO3/SrTiO3]15 and [Pr0.5Ca0.5MnO3/SrTiO3]15 on (001) oriented SrTiO3 and LaAlO3 single crystal substrates. Elastic strain induced electronic reconstructions at the interface enhanced the interlayer ferromagnetic interactions in the case of x = 0.3 superlattices on SrTiO3 exhibiting the highest HK ∼ 9 kOe and K1 ∼ 8 × 105 erg/cc. Tunable spin–flopped transition (∼ 30 kOe), significant negative exchange-bias field (HEB ∼ 2.5 kOe), huge coercive field (HC ∼ 22 kOe) and large NM (ΔM ∼ 280 emu/mole) are the unique characteristic features of the Ce incorporated YCrO3 polycrystals. The H–T phase diagram, clearly distinguishes three prominent regions below the TN (∼ 150 K), viz (i) long-range canted AFM + weak FM phase ( ), (ii) Γ24 mixed phase and (iii) robust ) AFM + FM phases. Extensive magnetization measurements reveal the existence of orbital-ordering in Pr0.45-xYbxSr0.55MnO3 accompanied by antiferromagnetic (AFM) Néel temperature, at as low as 158 K below the high- (302 K) ferromagnetic (FM) phase. Irreversible metamagnetic transitions from the AFM-FM phase occurs for a specific composition Pr40 (x = 0.05) till T ≤ 220 K. The admixture of metastable states of AFM and FM is quite robust in the investigated system whereas AFM state is mediated by Yb3+ ions, while, the FM state arising by field driven thermo-magnetic kinetics. In the Gd0.9Ce0.1CrO3, overall magnetization M(T) undergoes a second transition at the low temperatures associated with spin-flip transition triggered by the critical field, HC = 200 Oe at (10 K). The system exhibits better magneto-entropy value -ΔSM = 42 J/Kg-K which is higher than the previously reported GdCrO3 values. The reduction in the Cr-O-Cr bond angle through the substitution of Ce3+ at the Gd3+ site deduce such betterment in the magnetic entropy value. The presented works find potential utility in the fields of magnetoelectronic, thermo-magnetic sensors and spintronic device applications.
Synthesis, Photo-Physical Properties and Applications of Novel Metal Nanoclusters
(2024) Sarkar, Priyanka
The contents embodied in this thesis is divided into seven chapters. Chapter 1 is an introductory chapter which gives a concise and lucid introduction to the field and reports the major scientific contributions relevant to metal Nanoclusters. The introductory chapter represents an overview of the synthesis procedures, photo-physical properties, factors affecting its photo-physical properties and applications of these metal nanoclusters to diverse fields. Chapter 2 provides a detailed description of the material and methods used throughout the thesis. Chapter 3 describes synthesis of a biocompatible DTT (Dithiothreitol)-reduced LYS(Lysozyme) capped silver nanoclusters(AgNCs) and its application for selective and sensitive detection of Cu2+ and VB12. Detailed detection mechanism was studied. These AgNCs were also able to detect Cu2+ and VB12 inside live cells as well. Chapter 4 describes synthesis of a DTT reduced BSA(Bovine Serum Albumin) capped dual-emissive AgNCs and its application for selective and sensitive ratiometric detection of Cu2+ and IO4-. Detailed detection mechanism was studied. Chapter 5 describes a top-down synthetic approach to synthesize time-controlled two differently emissive copper nanoclusters (green and blue CuNCs) from a non-luminescent copper nanoparticles(CuNPs). Later, blue emissive CuNCs were utilized for detection of Fe3+ and GSH(Glutathione) via fluorescence turn-off-on mechanism. Detailed detection mechanism was studied. Chapter 6 reports two different strategies to produce AIDF (Aggregation induced delayed fluorescence)-based luminescent materials at room temperature from GSH-capped CuNCs by (1) simply modifying the solvent environment and (2) introducing of gadolinium (Gd3+) ions. Detailed analysis were investigated to reveal the generation mechanism of these AIDF properties. Further, Gd3+ induced AIDF of GSH-CuNCs were utilized to selectively detect Cr+6 ions. Chapter 7 provides a concise summary with future prospects.
Crystalline Molecular and Nanoparticle Assemblies with Optoelectronic Application Potential
(2024) Bhakat, Arin
The current thesis describes the production and prospective use of molecular crystals and crystallization-induced nanomaterial assembly. The current thesis reveals that the surface of molecular crystals can serve as an appropriate SERS platform. The surface functionality of molecular crystals can participate in non-covalent interactions with the deposited analyte molecules, allowing for efficient photoinduced charge transfer. The current thesis also shows that inorganic molecular crystals can exhibit metallic characteristics and cause surface plasmon. These molecular crystals may be exploited as a possible SERS substrate due to their excellent spectrum stability, simplicity of synthesis, outstanding environmental stability, biocompatibility, target molecule selectivity, and molecular cooperativity. The thesis also depicts the tuning of NC characteristics as a dopant inside molecular crystals, which sheds light on the methods for inducing tuneable phosphorescence features on simple metal NCs via ordered packing structures inside molecular crystals by altering the surrounding environment and electronic confinements. Furthermore, we used the intermolecular interaction-based surface complexation approach that causes molecular crystal formation to self-assemble nanomaterials into the crystalline superstructure.
Design of Cryptographic Primitives for Wireless Communication and Blockchain Mining
(2024) Goswami, Sushree Sila P
The rising reliance on the internet across various sectors has heightened the importance of security measures, given the potential threat posed by cyber attackers who could corrupt or misuse data. This thesis explores the implementation of diverse cryptographic algorithms—DES, RSA, AES, ECC, and ECCDH—on FPGA (Field Programmable Gate Array). In secure wireless
communications, stream ciphers are preferred for their hardware implementation simplicity. The design of stream ciphers generally involves using a pseudorandom number generator to produce a keystream, which masks the plaintext through a XOR operation, resulting in cipher text. This research presents the realization of these designs using Verilog Hardware Description Language and their implementation on FPGA. Experimental results indicate that a modified SNOW 2.0 architecture is 13% more resource-efficient and 19% more efficient overall compared to the traditional SNOW 2.0, and 104% more efficient than existing architectures. Security is paramount in electronic communication, particularly in wireless networks like LTE, where cryptographic algorithms are vital for protecting sensitive data. While software implementations are straightforward, they often lack the speed required for real-time communication devices, necessitating hardware implementations of cryptographic processors. This thesis introduces a novel SNOW3G crypto processor for 4G LTE security, optimized for area, power, and efficiency. Implemented on the Zynq ZC702 FPGA, this design uses only 0.31% of available area and achieves significant efficiency and low power consumption, making it suitable for mobile devices.