Browsing by Author "Nimmala Arun"

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200 MeV Ag ion irradiation mediated green synthesis and self assembly of silver nanoparticles into dendrites for enhanced SERS applications
(Elsevier Ltd, 2022) Laden Sherpa; Nimmala Arun; S.V.S. Nageswara Rao; S.A. Khan; A.P. Pathak; Ajay Tripathi; Archana Tiwari
In this paper, we report green and controlled synthesis of silver nanoparticles in water with spherical, hetrogeneously shaped and extended chain like networks using pristine Bergenia ciliata root extracts and the extracts irradiated with Ag15+ swift heavy ion irradiation. The ion fluence on the thin layer of extract modifies the phytomolecules responsible for the reduction and capping of the silver ion and thus changing the morphologies and sizes of the resultant nanoparticles. In addition, the irradiation assists the nanoparticles to agglomerate via surface oxidation providing a core for the growth of dendritic assemblies. Optical, crystallographic and morphological studies reveal surface oxidation of silver nanoparticles is enhanced upon the irradiation of the phytomolecules due to which the surface chemistry of the nanoparticles changes. In addition, these silver nanoparticles and their dendritic assembly exhibit high SERS enhancement factors for methylene blue analyte. The effects of irradiation promote the dendritic assemblies, roughened surfaces over the nanoparticle clusters and hence offer higher enhancement factors as compared to those which have been synthesized using pristine plant extracts. © 2022 Elsevier Ltd
Deciphering the role of carbon quantum dots-metal nanocomposites on surface enhanced Raman scattering and photoinduced enhancement
(American Institute of Physics, 2025) Sweta Gurung; Tapan Parsain; Nimmala Arun; Anand Prakash Pathak; Ajay Tripathi; Archana Tiwari
Ag and Au nanoparticles (NP), along with carbon quantum dots (CQD), were synthesized using straightforward methods. Ag NP exhibit localized surface plasmon resonance (LSPR) at 445 nm and Au NP at 551 nm. The quantum yield of as-synthesized CQD in water has been found to be 0.46 at 350 nm excitation. Nanocomposites (Au-CQD, Ag-CQD, Ag-Au, and Ag-Au-CQD) were used as surface enhanced Raman scattering substrates for methylene blue (MB) detection. At 785 nm excitation, Ag-CQD and Ag-Au-CQD showed higher analytical enhancement factors (AEFs) of 1.1 × 10 4 and 2.5 × 10 4 , respectively, compared to Ag-Au (0.7 × 10 4 ). At 514 nm, simultaneous excitation of Ag and Au LSPR improved AEFs, especially for Ag-Au (1.7 × 10 4 ) and Ag-Au-CQD (1.8 × 10 4 ). Detection limits reached 10 − 7 M for Au-CQD and 10 − 8 M for others at 785 nm, while all composites showed a uniform detection limit of 10 − 8 M at 514 nm. AEFs were reproducible with ∼ 2%-9% relative standard deviation. Furthermore, COMSOL Multiphysics was used to analyze electric field distribution and establish a strong correlation between theoretical EFs and experimental AEFs in Ag-Au and Ag-Au-CQD nanocomposites. Additionally, photoinduced enhanced Raman scattering (PIERS) studies under 445 nm illumination revealed enhanced Raman signals via photoinduced charge transfer from CQD to metal NP. The highest enhancement was observed in Ag-Au-CQD, followed by Ag-CQD and Au-CQD, while Ag-Au without CQD showed minimal effects. Thus, the dual-wavelength approach enhances PIERS performance for sensitive MB detection. © 2025 Author(s).
Dual metal ion (Fe3+ and As3+) sensing and cell bioimaging using fluorescent carbon quantum dots synthesised from Cynodon dactylon
(Elsevier Ltd, 2023) Sweta Gurung; Neha; Nimmala Arun; Mayank Joshi; Tanya Jaiswal; Anand P. Pathak; Parimal Das; Amaresh Kumar Singh; Ajay Tripathi; Archana Tiwari
In this study, water dispersible fluorescent carbon quantum dot (CQD) has been synthesised, having an average size of 8.6 ± 0.4 nm using Cynodon dactylon (CD) following microwave assisted green synthetic one-step method. As-prepared CQD fluoresces strongly at 444 nm having a quantum yield of 1% in water when excited at 350 nm. This fluorescence of CQD is sensitive toward As3+ and Fe3+ metal ions. These CQD are utilized for dual metal ion fluorescence sensing; turn-on fluorescence sensing for As3+ and turn-off fluorescence sensing for Fe3+ ions. Limit of detection for As3+ and Fe3+ ions has been found to be 19 nM and 0.10 μM respectively, which is the lowest value reported for As3+ without any functionalization. The adsorption kinetics of As3+ and Fe3+ ions on CQD have been examined using pseudo-first-order-kinetic model revealing that physical adsorption is dominant over chemical processes in this work. For 0.41 g/L and 1.90 g/L dose of CQD, the equilibrium adsorption capacity was found to be 1.57 × 10−6 mg/g, 2.91 × 10−7 mg/g, and 1.01 × 10−5 mg/g, 1.69 × 10−6 mg/g respectively for As3+ and Fe3+ ions. Despite having low quantum yield in water, as-prepared CQD showed low cytotoxicity and good tolerance against photodegradation of biological cells at concentrations lower than 62.5 μg/mL and when the cells are illuminated up to 12 h. Owing to this, the synthesised CQD have been utilized as fluorescent probes for in itro cell imaging. © 2023 Elsevier Ltd
Effects of ion irradiation induced phase transformations and oxygen vacancies on the leakage current characteristics of HfO2 thin films deposited on GaAs
(Institute of Physics, 2025) K. Vinod Anil Kumar; Nimmala Arun; Akkanaboina Mangababu; Ambuj Mishra; Sunil C. Ojha; Anand Prakash Pathak; S. V.S. Nageswara Rao
We report on ion-induced phase transformations, defect dynamics related to oxygen vacancies and the resulting leakage current characteristics of RF sputtered HfO2 thin films grown on GaAs. A systematic growth of HfO2 grains and ion prompted phase transformations of HfO2 to crystalline phases such as monoclinic and tetragonal/orthorhombic (mixed phase) in otherwise amorphous HfO2 thin films have been observed after irradiation. At lower fluences, ion induced enhancement in the dielectric properties of HfO2 thin films resulted in a reduction in the leakage current, whereas ion prompted defect formation at higher fluences caused a systematic increase in the leakage current density. Further, the effects of Poole-Frenkel tunneling and Fowler-Nordheim tunneling on the leakage current have also been investigated. These mechanisms showed the existence of impurities in the as-grown films. Photoluminescence study suggests that the variation in the defect configuration related to O-vacancies and the slight shift in the peak positions due to swift heavy ion irradiation are responsible for the observed changes in electrical characteristics. This study offers worthwhile information for considering the effects of electronic excitation prompted defect annealing and defect creation on the performance of HfO2/GaAs based photonic and optoelectronic devices, particularly, when such devices are operated in a radiation harsh environment. © 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
Green synthesis of strongly luminescent Si/SiO2 nanoparticles using Actinidia deliciosa
(Bellwether Publishing, Ltd., 2021) Sweta Gurung; Nimmala Arun; Ajay Tripathi; Anand P. Pathak; Archana Tiwari
Here we present green synthesis of highly luminescent Si/SiO (Formula presented.) nanoparticles having an average size of (Formula presented.) by one step reduction of 3-aminopropyltriethoxysilane using Actinidia deliciosa as a green reducing agent in water. These water dispersible nanoparticles present an absorption edge at 3.34 eV. An uneven surface oxidation of these nanoparticles appears due to which variable defect sites and their corresponding energy levels are involved in the emission processes. This is why, an excitation dependent emission in these nanoparticles is observed where by decreasing the excitation energy, the emission peak redshifts. The maximum emission quantum yield in these nanoparticles is found to be 27% at 350 nm when the reaction mixture was kept for 5 days. The emission energy and the intensity are found to be dependent on the reaction time due to which their quantum efficiencies also vary. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
Thermal and light-induced electrical properties in nanocomposites of reduced graphene oxide and silver nanoparticles
(Springer, 2023) Sweta Gurung; Nimmala Arun; Anand P. Pathak; Srinivasa Rao Nelamarri; Ajay Tripathi; Archana Tiwari
We present synthesis of nanocomposites of silver nanoparticles with reduced graphene oxide (Ag–rGO) using one-step, one-pot method where polyvinylpyrrolidone and ethylene glycol are, respectively, utilized as capping and reducing agents. The average particle size of Ag NP reduces by 16-folds when the composite is formed with rGO. We have examined the anharmonicity, thermal expansion, and thermal conductivities in rGO and Ag–rGO, while evaluating their crystallite sizes and defect densities using temperature-dependent Raman spectroscopy. The thermal conductivity of rGO and Ag–rGO at ∼ 300 K have been found to be 2.86 ± 0.09 Wm - 1 K - 1 and 1.69 ± 0.06 Wm - 1 K - 1 , respectively. Owing to increase in defects in Ag–rGO, their thermal conductivity has been found to be smaller than that of rGO. In addition, I–V hysteresis loops are obtained for rGO and Ag–rGO and are used to explain variation in space charges and electrical resistances in the presence and absence of plasmonic excitation. In rGO, the electrical resistance remains nearly constant irrespective of the illumination, whereas in Ag–rGO a significant drop in the resistance upon illumination at 532 nm is observed. The increase in current is ascribed to plasmon-mediated charge transfer from nanoparticles to rGO surface. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.