Browsing by Author "Anand Prakash Pathak"

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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).
Effects of heavy ion irradiation on the electrical properties of HfTiOx-based MOS devices
(Taylor and Francis Ltd., 2025) R. Sai Prasad Goud; Sravani Machiboyina; G. Prashanth; Akkanaboina Mangababu; Kanaka Ravi Kumar; Bharatha Aparna; Banothu Saidulu; Saif Ahmad khan; S. V.S. Nageswara Rao; Anand Prakash Pathak
This manuscript presents our recent investigations on the effects of swift heavy ion irradiation on the electrical properties of Hafnium Titanium Oxide (HfTiOx)-based Metal Oxide Semiconductor (MOS) devices. Al/HfTiOx/Si MOS devices were irradiated with 120 MeV Ag9+ ions over a range of fluences (1 E 11–1 E 13 ions/cm2). A systematic study on defects generated by heavy ion irradiation on MOS devices has been analysed thoroughly by using current–voltage (I-V) and capacitance–voltage (C-V) measurements. The radiation damage on these devices is explained by examining the role of various conduction mechanisms observed in leakage currents before and after irradiation. Hence, this work will provide valuable insights regarding radiation damage in HfTiOx-based MOS devices in space and medical applications. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
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.
Phase evolution and morphological transformation of high-entropy alloy FeMnNiAlSiC nanoparticles via sequential picosecond laser ablation and nanosecond laser annealing
(Royal Society of Chemistry, 2025) Bibek Kumar Singh; Yagnesh Shadangi; Harsh Jain; R. Sai Prasad Goud; Nilay Krishna Mukhopadhyay; Anand Prakash Pathak; Venugopal Rao Soma; Archana Tiwari; Ajay Tripathi
This study investigates the morphological evolution and enhanced crystallinity of FeMnNiAlSiC high-entropy alloy (HEA) nanoparticles (NPs) synthesized using a picosecond laser operating in burst mode and subsequently processed with a nanosecond laser in deionized water (DW). The initial synthesis via pulsed laser ablation in liquid (PLAL) revealed distinct phases, like B2, γ-brass, Fe5Si3, and body-centered cubic (BCC), as confirmed by high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) data. Elemental mapping indicated enrichment of B2-type phases (Al-Fe and Al-Ni) in the larger NPs, while smaller NPs exhibited γ-brass and Fe5Si3-type phases. Following nanosecond laser processing, the NPs displayed significant morphological transformations, including the emergence of hollow structures, as well as enhanced crystallinity. Post-processing analysis demonstrated the evolution of B2 and Fe5Si3-type phases, driven by a laser-induced annealing effect, which resembles the traditional furnace annealing. This dual-stage laser approach effectively combines the rapid synthesis of NPs with structural refinement, offering a versatile pathway for tailoring material properties. These findings underscore the potential of laser-based techniques in the controlled synthesis and structural modulation of HEA NPs, paving the way for applications in catalysis, energy conversion, and advanced functional materials. © 2025 The Royal Society of Chemistry.
Structural characterization of AlCuFe icosahedral quasicrystal nanoparticles synthesized using femtosecond laser ablation
(Springer, 2025) Bibek Kumar Singh; Dipanjan Banerjee; Akkanaboina Mangababu; Yagnesh Shadangi; Nilay Krishna Mukhopadhyay; Rajesh Rawat; Anand Prakash Pathak; Venugopal Rao Soma; Archana Tiwari; Ajay Tripathi
The AlCuFe icosahedral quasicrystal (IQC) targets prepared using two different methods- (1) vacuum induction melting followed by annealing, and (2) spray forming, have been subjected to femtosecond laser ablation in deionized water (DI water) for 54 min. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) pattern analysis of the synthesized nanoparticles (NPs) revealed the presence of IQC phases. NPs obtained from the induction-melted IQC target contained Al13Fe4 and β-Al(Fe,Cu) phases along with the IQC phase, reflecting the phase composition of the bulk target. In contrast, NPs from the spray-formed target exhibited only the IQC phase. Both samples also showed the presence of CuO and amorphous Al2O3. The ablated region of the target surface showed the formation of grooves and bumps. In addition, the formation of liquid vortices during the ablation process was ascertained by the presence of macropores in the ablated region of the target’s surface. I-V plots obtained from the ablated region and the non-ablated region of the target’s surface revealed an increase in the resistance post-ablation. This increase is attributed to the presence of defects and surface oxidation that incurred during the laser irradiation. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.