Browsing by Author "Archana Tiwari"

Now showing 1 - 20 of 22

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
Anharmonic phonon interactions and the Kondo effect in a FeSe/Sb2Te3/FeSe heterostructure: a proximity effect between ferromagnetic chalcogenide and di-chalcogenide
(Royal Society of Chemistry, 2022) Labanya Ghosh; Mohd Alam; Mahima Singh; Srishti Dixit; Satya Vijay Kumar; Abhineet Verma; Prashant Shahi; Yoshiya Uwatoko; Satyen Saha; Archana Tiwari; Ajay Tripathi; Sandip Chatterjee
In this report, we have introduced magnetic ordering into the nontrivial system of conventional topological insulators (TIs) by creating magnetic interfaces. In this context, antimony di-chalcogenide Sb2Te3 sandwiched between two thin layers of FeSe was prepared using the pulsed laser deposition (PLD) technique. The prepared heterostructure demonstrated good crystallinity along with homogeneous morphology displaying pyramid-shaped characteristic triangular islands. To comprehend the temperature and magnetic field modulated inter-layer properties of the prepared hetero-structure, transport, magneto-transport and magnetic properties were investigated. These properties establish the signature of the Kondo effect below 15 K, which has been attributed to the antiferromagnetic spin alignment in that temperature range. At around 150 K, longitudinal and transverse resistivity shows the metal-semiconductor transition, which was further elucidated through the anharmonic decay model in vibration phonon modes using Raman spectroscopy. Furthermore, a significant local spin evolution was explored at around 475 K by studying the magnetic properties of the system. The temperature dependency of the Raman modes confirmed the spin-phonon coupling initiated by local charge ordering at the proximity of the interface in the prepared hetero-structure. © 2022 The Royal Society of Chemistry.
Checklist of moths (Heterocera) of Tadong, Sikkim, India
(Zoo Outreach Organisation, 2021) Prayash Chettri; Yuki Matsui; Hideshi Naka; Archana Tiwari
This study attempts to create a checklist of moths recorded from two different parts of Tadong in Sikkim, located in the northeastern Himalaya of India. Out of 160 photographed specimens of moths, 133 species were identified and classified. Sixteen families of moths were recorded out of which Erebidae (30.83%) had the highest number of species followed by Geometridae (24.81%), and Crambidae (18.05%) while the other families comprised of 26.30% of the total species. © 2021. Chettri et al.
Coexistence of Kondo effect and Weak anti-localization in Topological insulator/Ferromagnetic heterostructure
(Elsevier B.V., 2024) Labanya Ghosh; Swayangsiddha Ghosh; Srishti Dixit; Mohd Alam; Neha Patel; Archana Tiwari; Prashant Shahi; Yoshiya Uwatoko; Sandip Chatterjee
The presence of a magnetic impurity in a topological insulator weakens the time-reversal symmetry by creating a limited gap at the Dirac point, and could result in the creation of new quantum states. On the other hand, causing magnetization in a topological insulator through the interlayer proximity effect to a magnetically ordered system is a better choice, as magnetic doping may have negative effects. In this report, the magnetic and magneto-transport properties of FeSe intercalated Bi2Se3 crystals and FeSe/Bi2Se3/FeSe hetero-structure have been investigated. The XPS depth profile was studied to confirm the layered structure of the hetero-structure. The weak anti-localization state in the multilayer system has been seen to coexist with the Kondo effect, which may have caused by the interfacial magnetic domains modifying the electronic characteristics at interfaces. Such magnetic spin-induced inter-layer coupling can be a pathway to room-temperature spintronic applications. © 2024
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).
Detection of milk adulteration using coffee ring effect and convolutional neural network
(Taylor and Francis Ltd., 2024) Tapan Parsain; Ajay Tripathi; Archana Tiwari
A low-cost and effective method is reported to identify water and synthetic milk adulteration of cow’s milk using coffee ring patterns. The cow’s milk samples were diluted with tap water (TW), distilled water (DW) and mineral water (MW) and drop cast onto glass slides to observe coffee ring patterns. The area of the ring, total particle area and average particle diameter were extracted from these patterns. For each ring, the ratio of total particle area versus total ring area was calculated. The area ratio, regardless of water adulterants, follows an exponential model with respect to average particle diameter. Unlike TW, the ratio for DW and MW adulterated milk are clustered and classified together with respect to the particle diameter. These results were independent of dilution level and are used for adulterant classification. The ring of milk adulterated using synthetic milk gave multiple concentric rings, flower-like structures, and oil globules throughout the dilution level. An Alexnet model was used to classify water and synthetic milk adulterants in authentic milk. The trained model could achieve 96.7% and 95.8% accuracy for binary and tertiary classification respectively. These results enable us to distinguish synthetic milk from pure milk and segregate DW and MW with respect to TW adulterated milk. © 2024 Taylor & Francis Group, LLC.
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
Effect of silver nanoparticles on electrical and magnetic properties of reduced graphene oxide
(Elsevier Ltd, 2022) Prajwal Chettri; Ajay Tripathi; Archana Tiwari
We report the effects of silver nanoparticles (Ag-NP) on morphological features of reduced graphene oxide (rGO) which show presence of atomic scale ripples and lattice defects. These entities present in the composite (Ag-rGO) modulates its magnetic and electrical properties. Graphene oxide (GO) and Ag-rGO are primarily paramagnetic while rGO is diamagnetic. Ag-rGO shows enhanced magnetization and hysteresis owing to the presence of defects. Magnetization is maximum in Ag-rGO synthesized using 1 mM of AgNO3. Further increase in AgNO3 concentration quenches magnetization due to excess C-O-C group present in Ag-rGO. Current-voltage (I-V) curves show transition from non-ohmic GO to ohmic rGO. In Ag-rGO, resistance decreases by at least four hundred times as compared to that of rGO and becomes n-type material. With increased Ag-NP concentration, rGO becomes susceptible to defects and loses its conductive nature. By optimizing Ag-NP concentration, both electrical and magnetic properties can be enhanced in Ag-rGO. © 2022 Elsevier Ltd
Formation of Cu-Ni enriched phases during laser processing of non-equiatomic AlSiCrMnFeNiCu high entropy alloy nanoparticles
(Elsevier Ltd, 2022) Rajesh Rawat; Bibek Kumar Singh; Archana Tiwari; N. Arun; A.P. Pathak; Yagnesh Shadangi; N.K. Mukhopadhyay; Srinivasa Rao Nelamarri; S. Venugopal Rao; A. Tripathi
Al-rich non-equiatomic high entropy alloy nanoparticles (HEA NPs) were synthesized by ablating Al40(SiCrMnFeNiCu)60 (at%) target in deionized water using nanosecond Nd:YAG pulsed laser operating at a wavelength of 1064 nm and having 8 ns pulse duration. The synthesized NPs have retained the composition and structural phases (B2 type AlFe and Cr5Si3) of the target. The colloidal solution of these NPs was further processed with a 532 nm laser. Upon laser processing, compositional and structural changes in HEA NPs are systematically investigated by using electron microscopy and spectroscopic techniques. The cyclic reheating of NPs during laser processing triggers the formation of Cu-Ni nanoprecipitate over the processed NPs. Owing to their similar ionic sizes and having FCC structural phase, Cu-Ni segregated together during the molten stage and evolve as the precipitate upon solidification. Amongst all the binary combinations of elements present in the HEA NPs, Cu-Ni phases are thermodynamically favored. Based on our experimental results, a possible growth mechanism of Cu-Ni enriched nanoprecipitate is discussed. © 2022 Elsevier B.V.
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.
Mechanically milled Sn and Al–Cu–Fe quasicrystals nanocomposites: Exploring the interplay between structural evolution, magnetic softness and thermoelectric efficiency
(Elsevier Ltd, 2025) Shradha Bhatt; Pema Chida Sherpa; Yagnesh Shadangi; Radhey Shyam Tiwari; Nilay Krishna Mukhopadhyay; Ajay Tripathi; Archana Tiwari
Mechanically milled Sn and Al–Cu–Fe icosahedral quasicrystals (IQC) nanocomposites with varying Sn volume fractions (0%, 10%, 20% and 30%, designated as IQC, IQC-10Sn, IQC-20Sn and IQC-30Sn) were synthesized to investigate the influence of Sn content on their structural, magnetic, and thermoelectric properties. Structural analysis confirmed the presence of the IQC phase alongside a crystalline B2-Al (Cu,Fe) phase, with the IQC phase exhibiting high ordering as indicated by the superlattice reflection (311111). Microstructural characterization revealed large grains in pure IQC, while Sn incorporation led to the formation of smaller grains and rod-like microstructure. All samples displayed soft ferromagnetic behavior with low coercivity and remanent magnetization. The Curie temperature decreased with higher Sn concentrations, correlating with grain size reduction (from 48 nm to 12 nm) and weakened exchange interactions. The anisotropy constant, derived from the law of approach to saturation, peaked for IQC-10Sn, (9.1 × 103 erg/g at 300 K and 23.5 × 103 erg/g at 2 K) and gradually declined with increased Sn content. Thermoelectric performance was optimized in IQC-30Sn, which exhibited the lowest thermal conductivity and the highest figure of merit (5.2 × 10−3 at 300 K). Moderate Sn doping (IQC-10Sn and IQC-20Sn) enhanced magnetic properties via domain structuring and anisotropy, whereas higher doping (IQC-30Sn) improved thermoelectric efficiency by facilitating charge and phonon transport. These findings demonstrate that mechanically milled Sn and Al–Cu–Fe IQC nanocomposites can simultaneously tailor magnetic and thermoelectric performance, offering a promising pathway for developing advanced IQC-based nanocomposites for multifunctional applications. © 2025 Elsevier B.V.
Nanostructuring of AlSiCrMnFeNiCu High-Entropy Alloy via Cryomilling: Exploring Structural, Magnetic, and Thermoelectric Properties
(John Wiley and Sons Inc, 2024) Yagnesh Shadangi; Pema Chida Sherpa; Harsh Jain; S. Varalakshmi; Sandip Chatterji; Labanya Ghosh; Nilay Krishna Mukhopadhyay; Ajay Tripathi; Archana Tiwari
Efforts are made to understand the influence of milling intensity on structure, morphology, magnetic and thermoelectric properties of nonequiatomic nanostructured AlSiCrMnFeNiCu high-entropy alloy (HEA) powders prepared by cryomilling. These powders are cryomilled with different ball-to-powder ratios (BPR) and present a dual-phase structure containing a major B2-type and a minor Cr5Si3-type phase. An increase in BPR enhances the refinement of crystallite size, grain size, and particle size accompanied by a decrease in the phase fraction of the minor Cr5Si3-type phase. Magnetic measurements revealed that at room temperature, sufficient increase in BPR leads to a transition from multi-domain behavior to single-domain behavior which leads to enhancement in soft magnetic properties. Thermal measurements show the presence of different magnetic phase transitions which vary with an increase in BPR. A change of charge carrier type from p to n-type was observed as the grain size is reduced. The figure of merit decreases with the decrease in grain size from 2 × 10–5 for as-cast powders and is lowest for the smallest grain-sized sample due to a decrease in electrical conductivity. This study shows the possibility of exploring nonequiatomic low-density HEAs whose functional properties can be tailored, offering flexibility in material design for specific applications. © 2024 Wiley-VCH GmbH.
Non-toxic arsenic nanoparticles for surface-enhanced Raman spectroscopy applications
(Taylor and Francis Ltd., 2024) Laden Sherpa; Chinmay C. Nayak; Arun Nimmala; Ajay Tripathi; Archana Tiwari
In this study, we present green synthesis of Arsenic nanoparticles (As NPs) using different plant extracts. The resultant As NPs exhibit diverse sizes, shapes and assembly of nanotubules. In addition, As NPs have large band gap that ranges from 3.09 to 3.88 eV. They are enriched with defect states and exhibit multiple defect related photoluminescence. Owing to the aggregation and nanotubule assembly of As NPs, they are utilized for surface-enhanced Raman spectroscopy (SERS) sensing application. Under the illumination of continuous wave 785 nm laser, these As NPs demonstrate the detection of Methylene blue dye molecules via non-plasmonic chemical enhancement of SERS signal with an enhancement factor of 10 (Formula presented.). Intriguingly, As NPs exhibit non-toxicity towards specific microbes, suggesting safety in handling during experiments and potential applications in SERS imaging and biomedicines. © 2024 Informa UK Limited, trading as Taylor & Francis Group.
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.
Phase Evolution, Stability and Magnetic Behavior of Lightweight Al–Fe Aluminide-Based Nanocomposites Processed by Mechanical Alloying, Cryomilling, and Annealing
(John Wiley and Sons Inc, 2025) Ganne Ketan Balaji; Harsh Jain; Pema Chida Sherpa; Ritik Roshan Tripathy; Yagnesh Shadangi; Vikas Shivam; Ajay Tripathi; Archana Tiwari; Nilay Krishna Mukhopadhyay
Attempts are made to synthesize Al5Fe2 aluminide-based composites by mechanical alloying (MA) and cryomilling (CM). The XRD and TEM results of the milled samples confirm the formation of a major B2-AlFe phase (0.2887 ± 0.0003 nm; cP2) along with the minor amount of Al5Fe2 phase. Nanocrystalline grains of ≈16 nm and an average particle size of 4.0 ± 0.36 μm are evident. A significant refinement in the crystallite size (≈10 nm) and average particle size (1.0 ± 0.03 μm) is achieved after 10 h CM of 60 h MAed powder. CM enhances the phase fraction of the Al5Fe2 phase. The DSC thermogram discerns three exothermic heating events due to phase transformation. These can be corroborated by the structural transformation of the B2-AlFe phase to the orthorhombic Al5Fe2 phase. The phase obtained as a result of 60 h of MA transforms to orthorhombic Al5Fe2 along with a minor amount of pre-existing B2-AlFe structure after annealing at 600 °C. It becomes more stable after annealing at 900 °C. Further, the 60 h milled sample displays soft ferromagnetic properties. The saturation magnetization decreases on CM and annealing due to phase transition from B2-AlFe to Al5Fe2 phase. Coercivity is reduced when the MA sample is annealed due to an increase in crystallite size and a reduction in lattice strain. © 2024 Wiley-VCH GmbH.
Phase Evolution, Stability and Magnetic Behavior of Lightweight Al–Fe Aluminide-Based Nanocomposites Processed by Mechanical Alloying, Cryomilling, and Annealing
(John Wiley and Sons Inc, 2024) Ganne Ketan Balaji; Harsh Jain; Pema Chida Sherpa; Ritik Roshan Tripathy; Yagnesh Shadangi; Vikas Shivam; Ajay Tripathi; Archana Tiwari; Nilay Krishna Mukhopadhyay
Attempts are made to synthesize Al5Fe2 aluminide-based composites by mechanical alloying (MA) and cryomilling (CM). The XRD and TEM results of the milled samples confirm the formation of a major B2-AlFe phase (0.2887 ± 0.0003 nm; cP2) along with the minor amount of Al5Fe2 phase. Nanocrystalline grains of ≈16 nm and an average particle size of 4.0 ± 0.36 μm are evident. A significant refinement in the crystallite size (≈10 nm) and average particle size (1.0 ± 0.03 μm) is achieved after 10 h CM of 60 h MAed powder. CM enhances the phase fraction of the Al5Fe2 phase. The DSC thermogram discerns three exothermic heating events due to phase transformation. These can be corroborated by the structural transformation of the B2-AlFe phase to the orthorhombic Al5Fe2 phase. The phase obtained as a result of 60 h of MA transforms to orthorhombic Al5Fe2 along with a minor amount of pre-existing B2-AlFe structure after annealing at 600 °C. It becomes more stable after annealing at 900 °C. Further, the 60 h milled sample displays soft ferromagnetic properties. The saturation magnetization decreases on CM and annealing due to phase transition from B2-AlFe to Al5Fe2 phase. Coercivity is reduced when the MA sample is annealed due to an increase in crystallite size and a reduction in lattice strain. © 2024 Wiley-VCH GmbH.
Refining shape and size of silver nanoparticles using ion irradiation for enhanced and homogeneous SERS activity
(Springer, 2024) Laden Sherpa; Arun Nimmala; S. V. S. Nageswara Rao; S.A. Khan; Anand P. Pathak; Ajay Tripathi; Archana Tiwari
We present green synthesis of silver nanoparticles in water using unirradiated and Ag15+ ion irradiated phytoextracts of Bergenia Ciliata leaf, Eupatorium adenophorum leaf, Rhododendron arboreum leaf and flower. The use of different plant extracts and their subsequent ion irradiation allow for successful refinement of nanoparticle size and morphology. Due to changes in reducing and capping agents the nanoparticle surface functionalization also varies which not only controls the morphology but also allows for surface oxidation and aggregation processes. In this work, we have synthesized silver nanoparticles which exhibit sizes in the range from 13 to 24 nm and having shapes like spherical, quasispherical, trigonal, hexagonal, cylindrical, dendritic assemblies, and porous nanoparticles. Owing to changes in the size and shape of the nanoparticles, their direct bandgap (2.05 eV - 2.48 eV) and local surface plasmon resonance (420 nm - 490 nm) could also be tuned. These nanoparticles are examined as SERS substrates, where their enhancement factors, limit of detection for methylene blue, and SERS substrate homogeneity have been tested. It has been observed the nanoparticles synthesized using unirradiated plant extracts present an enhancement factor of 106 with a limit of detection 10-8 M. Whereas nanoparticles with refined morphology and shapes upon irradiation present high enhancement factors of >107 and detection limit down to 10-9 M. In addition, uniformity in Raman spectra over the SERS substrates has been obtained for selected Ag NPs substrates synthesized using irradiated extracts with minimum relative standard deviation in enhancement factor < 12%. © The Author(s) 2024.
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.
Structure, electrical and thermal transport properties of Sn reinforcedAl-Cu-Fe quasicrystalline matrix composite prepared by mechanical milling and subsequent annealing
(Elsevier Ltd, 2023) Yagnesh Shadangi; Shradha Bhatt; Priyatosh Pradhan; Archana Tiwari; Ajay Tripathi; Kausik Chattopadhyay; Nilay Krishna Mukhopadhyay
The present work deals with the structure, electrical and thermal transport properties of Al-Cu-Fe quasicrystal (IQC) reinforced with soft Sn phase (10–30 vol%) processed by mechanical milling and subsequent annealing. The 40 h milled powder of IQC-Sn nanocomposite contains IQC phase along with other crystalline phases i.e. B2-Al(Cu, Fe) (a = 0.29 nm; cP2) and monoclinic Al13Fe4 (a = 1.549 nm, b = 0.808 nm, c = 1.248 nm; α = γ = 90°, β = 107.72°; mC102). The IQC phase was also found to be ordered from the existence (311111) superlattice reflection of IQC. The phase fraction of IQC phase increased (in comparison with the crystalline phases) on annealing of IQC-Sn powder milled powder at 800 °C. The nano quasi-crystalline and nano-crystalline nature of these IQC and crystalline phases in milled and annealed powders were observed through transmission electron microscopy. The nano-beam diffraction (NBD) of the annealed samples confirmed the presence of nearer to 5-fold symmetry corresponding to the IQC phase. The electrical and thermal transport properties of milled and annealed samples were studied. The electrical and thermal transport properties of annealed sample was higher than that of the milled IQC-Sn nanocomposite powders. The ratio of electrical and thermal conductivity for IQC-20Sn annealed sample was found to be the highest (σ/ κ ∼4704 SK/W). These findings suggest the possibility of using IQC-Sn annealed nanocomposites for potential application as thermoelectric materials. © 2023 Elsevier B.V.
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.