Browsing by Author "Anup Kumar Ghosh"

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Coexistence of Kondo effect and non trivial Berry phase in Gd doped Bi2Se3: an ARPES and magneto-transport study
(Institute of Physics, 2025) Swayangsiddha Ghosh; Rahul Kunwar Singh; Srishti Dixit; Shiv Kumar; Yogendra Kumar; Kenya Shimada; Anup Kumar Ghosh; Archana Lakhani; Sandip Chatterjee
The presence of magnetic impurities in topological insulators can disrupt their time reversal symmetry and lead to the emergence of an energy gap. This study delves into the energy band structure and the Kondo effect through the introduction of Gadolinium (Gd) magnetic perturbations (at levels of x = 0.1 , 0.16 ) into a pure Bi2Se3 single crystal. In the case of the Bi1.9Gd0.1Se3 (5%) single crystal, the Kondo effect becomes observable at temperatures below 50 K. However, the unaltered parent and Bi1.84Gd0.16Se3 (8%) exhibit typical metallic behavior. The pure sample displays the highest magnetoresistance (MR) of around 225% and demonstrates quantum oscillations driven by a nontrivial berry phase. The sample doped with 5% Gd undergoes a transition from negative MR to positive MR due to a presence of mixed magnetic state resulting from the opening of a gap at the Dirac point. This gap opening is confirmed through angle-resolved photoemission spectroscopy (ARPES) measurements. The comparison of the parameters obtained from the SdH and ARPES measurements, the reduction in the k F values in the magnetotransport measurements is likely due to the band bending induced by the Schottky barrier. Thermoelectric properties are assessed across all prepared samples. The undoped sample displays the highest Seebeck coefficient and power factor values of − 398.02 μ V K − 1 and 6.83 mW mK − 2 , respectively, at room temperature. These values are notably high for thermoelectric applications at room temperature. © 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
Insight into charge conduction and relaxation in La2-xCaxFeMnO6 solid solution double perovskites
(Elsevier Ltd, 2025) Baniya R. Meena; Sandip Chatterjee; Anup Kumar Ghosh
A series of La2-xCaxFeMnO6 (where x = 0, 0.1, 0.2, 0.3, and 0.5) solid solution has been prepared by the solid-state reaction method. Single-phase disordered cubic crystal structure of crystallite size ∼ 50 nm has been confirmed by the Rietveld refinement of X-ray diffraction (XRD) data. Raman spectroscopic study shows improper ordering of MnO6 and FeO6 octahedral. The average grain size (∼ 4 µm) and elemental analysis have been estimated by SEM and EDS measurements, respectively. The electronic structure of the prepared samples has been investigated by using the X-ray photoemission spectroscopy (XPS). The value of dielectric constant has been improved from colossal (∼1826) to giant (∼15238) with low dielectric loss at room temperature due to Ca2 + doping. All samples exhibit the negative temperature coefficient of resistance (NTCR) characteristic. The electrical characteristics of both the grain and grain boundary have been investigated by the analysis of imaginary part of impedance (Z''). The non-Debye type relaxation has been explained by the non-overlapping small polaron tunnelling (NSPT) transport mechanism. I-V characteristic shows the low value of leakage current density (∼ 10−4 Amp/cm2) for all measured samples. This study may open an intriguing path for the engineering of better-performing dielectric materials for various electronic devices. © 2025
Investigations on structural and optical properties of Al-modified ZnO nanoparticles
(Springer, 2020) Shiv Kumar; Manish Kumar; Arvind Kumar; Subhash Sharma; Prashant Shahi; Sandip Chatterjee; Anup Kumar Ghosh
The current studies are concentrated on the synthesis of Al-modified ZnO nanoparticles prepared through sol–gel method for their structural and optical properties. The wurtzite structure with single phase formation for all the samples was confirmed from the Rietveld analysis on XRD data. Nano-crystalline nature (having particle size (~ 10 to 30 nm)) of all the synthesized samples have been examined by XRD and TEM data. Optical properties were carried out from UV–Vis, FTIR and Raman spectroscopy techniques. FTIR and Raman analysis also confirms the wurtzite structure and tetrahedral configuration with coordination of oxygen ions nearby the zinc ions. The UV–Vis measurement confirms that the bandgap is blue-shifted and slow red shift for lower and higher Al-concentrations in ZnO, respectively. Visible emission spectra of PL confirms the photo generated holes with deep-level emission, which is ascribed to recombination of electrons intensely spellbound in oxygen vacancies and zinc interstitials. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.
Investigations on structural and optical properties of ZnO and ZnO:Co nanoparticles under dense electronic excitations
(Royal Society of Chemistry, 2014) Shiv Kumar; Kandasami Asokan; Ranjan Kumar Singh; Sandip Chatterjee; Dinakar Kanjilal; Anup Kumar Ghosh
In the present study, the structural, morphological, and optical properties of Co-doped ZnO nanoparticles (NPs) prepared by a sol-gel method before and after dense electronic excitations caused by swift heavy ion irradiation have been reported. The pristine and ZnO:Co NPs were irradiated by using a 200 MeV Ag15+ ion beam at a fluence of 5 × 1012 ions per cm2. Structural characterization has been performed using X-ray diffraction (XRD) with Rietveld refinement. It shows that the samples are of single phase; grain size and tensile strain has been increased in the ion-irradiated samples. Room temperature Raman spectroscopy measurements show that microscopic structural disorders reduce the translational symmetry giving rise to local distortions in the lattice. Atomic force microscopic (AFM) studies show prominent grain boundaries and suggest that roughness of the irradiated surfaces increases strongly compared to their pristine counterparts. Optical absorption and photoluminescence (PL) studies also reflect the dopant incorporation and swift heavy ion (SHI) irradiation effect on the nanoparticles. UV-Vis absorption measurement has been utilized to estimate the optical bandgap of pristine and irradiated ZnO and Co-doped ZnO nanoparticles. Enhancement in the PL intensity has been observed in the irradiated samples with respect to their pristine counterparts which can be explained on the basis of the increase of different defect states and Zn-O bonds on the surfaces of the irradiated nanoparticles arising from surface modification. Grain boundaries have played an important role in the optical properties (absorption and PL). © The Royal Society of Chemistry 2014.
Local structure and photocatalytic properties of sol-gel derived Mn-Li co-doped ZnO diluted magnetic semiconductor nanocrystals
(Royal Society of Chemistry, 2016) Deepak Kumar Dubey; Digvijay Narayan Singh; Shiv Kumar; Chandrani Nayak; Pathik Kumbhakar; Sambhu Nath Jha; Dibyendu Bhattacharya; Anup Kumar Ghosh; Sandip Chatterjee
The structural, extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) and photocatalytic properties of sol-gel derived Zn1-y-xMnyLixO (y = 0, 0.02 and x = 0, 0.01, 0.02, 0.03, 0.04, 0.06) nanoparticles (NPs) have been investigated. A small linear increase in lattice parameters 'a' and 'c' has been observed which can be attributed to the small distortion of the Zn tetrahedron. From the Mn K-edge XANES data, it can be inferred that Mn exists as Mn2+ in the 2% Mn-doped ZnO sample. Li doping oxidizes the Mn-cations in the ZnO lattice and hence Mn exists in higher oxidation states (+2 or +3) in (Li, Mn) co-doped ZnO samples. Li doping also favors Mn metal clustering whose signature can be seen in both the Mn K-edge XANES and EXAFS spectra of the (Li, Mn) co-doped samples. UV-light driven degradation of methylene blue (MB) dye aqueous solution has also been demonstrated using pure and doped ZnO and more than 90% dye degradation has been observed within only 90 min of light irradiation. The synthesized materials with visible light emission and dye degradation activity can be used effectively in future optoelectronic devices and in water purification for cleaning of dyes. © The Royal Society of Chemistry 2016.
Physical properties of Fe-doped CdS quantum dots: single dot rectifying diode application
(Royal Society of Chemistry, 2025) Piyali Maity; Ravi Ranjan Shenthil Kumar; Shambunath Jha; Dibyendyu D. Bhattacharyya; Sandip Chatterjee; Bhola Nath Pal; Anup Kumar Ghosh
The domain of single-molecule based electronic devices has grown remarkably over the past decade by utilizing nanotechnology to improve the efficiency of device fabrication. However, most of the single-molecule devices are based on organic materials. Compared with organic molecules, quantum dots (QDs) are excellent owing to their crystalline nature, environmental stability, narrow emission band and quantum yield with tunable electronic and optoelectronic properties. Here, CdS:Fe QDs were synthesized and analyzed to assess their structural, optical, and electronic properties, and subsequently, they were implemented in fabricating single-dot rectifying diodes. EXAFS revealed the average coordination number of the doped Fe element. The ITO/TiO2/CdS:Fe quantum dot heterostructure rectifying diodes were grown by spin coating and were characterized using scanning tunneling microscopy (STM) at room temperature. STM images revealed the distribution of QDs over the substrate, and the spectra revealed the improved rectification behavior with tunneling up to ∼1000×, revealing their excellent diode functionality. Threshold voltage tuning from 1.62 eV to 0.83 eV indicated the application of these diodes for tunable electronics with low power consumption. Thus, these results indicate the promising use of CdS:Fe QDs for optimized ambient atmosphere rectifying diode applications, opening the way for innovative electronic devices with improved performance and functionality. © 2025 RSC.
Plasmonic Grating on Monolayer MoS2for Strong Photoluminescence Enhancement and Ultrasensitive Surface-Enhanced Raman Scattering (SERS) Detection
(American Chemical Society, 2025) Chetna Gautam; Sandeep Yadav; Abhay Kumar; Monalisa Pal; Anup Kumar Ghosh; Anupam Giri
Monolayer MoS2, a key 2D transition metal dichalcogenide (TMDC), offers strong potential for next-generation optoelectronic devices due to its direct bandgap and tunable optical properties. However, its ultrathin structure results in inherently weak light–matter interactions and limited photoluminescence (PL) output. Here, we demonstrate a scalable strategy for enhancing the optical response of monolayer MoS2using plasmonic nanoresonators patterned via capillary-force-assisted assembly of the thermoresponsive polymer poly(ε-caprolactone) (PCL), eliminating complex nanofabrication. Subsequent deposition of plasmonic metals (Au, Ag, Al) forms well-defined resonator arrays, enabling sequential fabrication of multiple patterns on a single layer. Optimized Au gratings (818 nm width, 2.6 nm thickness) achieved over 390-fold PL enhancement through efficient exciton–plasmon coupling. Moreover, the crossbar-type Au–Au gratings on MoS2exhibited remarkable surface-enhanced Raman scattering (SERS) sensitivity, enabling detection of rhodamine 6G down to 10–18M. This practical approach significantly amplifies light–matter interactions in 2D materials, advancing their integration into flexible photonic, sensing, and optoelectronic systems. © 2025 American Chemical Society
Structural, dielectric, and electrical transport properties of La2FeMnO6 double perovskite for multifunctional applications
(Elsevier Ltd, 2025) Baniya R. Meena; Mohd Intaf Alam; Sandip Chatterjee; Anup Kumar Ghosh
The polycrystalline La2FeMnO6 has been prepared by the solid-state reaction method. The Rietveld refinement of X-ray diffraction (XRD) data confirms a single-phase double perovskite cubic structure. The vibrational modes have been investigated by the Raman and Fourier transform infrared (FTIR) spectroscopy. The X-ray photoemission spectroscopy (XPS) measurement reveals the presence of mixed valence states of Mn and Fe cations. The dielectric, impedance, modulus, and AC conductivity measurements of La2FeMnO6 have been done over temperature range (125–300 K) and frequencies (1 kHz - 1 MHz). This material exhibits a high ε′ (∼1826) with a low dissipation factor near room temperature. The NTCR (negative temperature coefficient of resistance) characteristics of both resistivity and impedance showed the semiconducting nature of the sample. Grains and grain- boundaries play important role in the process of electrical conduction. The Cole-Cole plots follow the RC equivalent circuit and verify non-Debye-type relaxation. The value of the exponent ‘s’ suggests the non-overlapping small polaron tunneling (NSPT) process in La2FeMnO6. The NTCR characteristic of this material, with good stability factor, thermistor constant, and sensitivity factor may be useful for NTC-type thermistor. © 2024
Structural, Optical, and Electronic Properties of NixCd1–xS Quantum Dots: Implications for Photodetection Applications
(American Chemical Society, 2025) Nikita Kumari; Sandeep Dahiya; Chetna Gautam; Piyali Maity; Sandip Chatterjee; Bhola Nath Pal; Anup Kumar Ghosh
X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to study the structural and morphological characteristics of pure and Ni-doped CdS (CdS:Nix) (x = 0–6 atomic %) QDs synthesized via the hydrothermal method. Inductively coupled plasma mass spectrometry (ICP-MS) and EDS measurements have been carried out for quantifying the elemental composition. Due to Ni-doping, the short-range structural disorder causes a significant variation in the intensity of the longitudinal optical (LO) modes of Raman spectra. Optical absorption has been broadened with Ni doping, resulting in a reduction of the band gap from 2.42 eV (for CdS) to 2.36 eV (for CdS:Ni6). Photoluminescence (PL) spectra show various peaks associated with surface defects, near band emission (NBE), sulfur vacancies, photoinduced charge carrier separation, and recombination processes. To investigate the chemical states and valence band spectra of Ni-doped CdS QDs, X-ray photoemission spectroscopy (XPS) has been utilized. To realize their applicability in electronic devices, bilayer heterostructure photodetectors (PDs) have been fabricated on the glass substrate by using CdS:Nix QDs and sol–gel-derived SnO2(as a charge transport layer), viz., Glass/SnO2/CdS:Nix QD PDs. The performance of the device has been improved with a Ni-doping concentration in CdS QDs. The optimized device has been achieved with high photocurrent (28.2 mA/cm2), high figure-of-merit performance having a responsivity of 2.23 A/W, and detectivity of 2.1 × 1013Jones at a wavelength of approximately 450 nm under 5 V external bias for CdS:Ni6 QD heterostructure PD. Furthermore, this PD shows good response kinetics and are quite stable over time indicating its operational stability. © 2025 American Chemical Society
Unraveling the physical properties of Mn-doped CdS diluted magnetic semiconductor quantum dots for potential application in quantum spintronics
(Springer, 2022) Piyali Maity; Ravi Kumar; S.N. Jha; D. Bhattacharyya; Ranjan Kumar Singh; Sandip Chatterjee; Anup Kumar Ghosh
The tunability of structural, optical, electronic, and magnetic properties in semiconductor quantum dots (QDs) makes them promising materials for multiple spintronic and optoelectronic applications. However, controlling the size of QDs to tune these properties is challenging due to their quantum size and high sensitivity to the ambient atmosphere. Here, we demonstrate successfully synthesized tunable Mn-doped cadmium sulfide (0% ≤ Mn ≤ 6%) diluted magnetic semiconductor QDs by hot injection chemical route. XRD and TEM studies confirmed that undoped and Mn-doped CdS QDs are polycrystalline in cubic phase without having any dopant-related signature. The XPS study shows the spin–orbit split due to Mn-doping and the atomic percentage of each element present in the prepared sample has been calculated from XPS data. XANES (X-ray Absorption Near Edge Structure) study shows that the Cd has the same oxidation state (+2) in the undoped and Mn-doped CdS QDs and also Mn has +2 oxidation state in Mn-doped CdS QDs. Extended X-ray Absorption Fine Structure (EXAFS) measurements show local structural disorder in higher doping concentration of Mn. It also shows that due to Mn doping, the coordination number of S in all the Mn-doped samples have the S vacancy compared to undoped CdS. No significant change has been observed in FTIR spectra after Mn doping. Raman spectra exhibits two longitudinal optical (LO) modes at 299 cm−1 and 598 cm−1. The intensity of the first LO peak decreases rapidly and linearly due to local structural and short-range disorder induced with increasing Mn concentration in CdS. UV–Vis spectroscopy reveals non-linear variation of bandgap energy showing the downwards bowing with increasing Mn-doping concentration. PL and TRPL indicate appearance of surface defect states with Mn-doping. TRPL spectra show decrease in decay time due to Mn‐doping. Room temperature ferromagnetism of Mn-doped CdS QDs confirms the diluted magnetic semiconductor behavior, which would play key role in quantum spintronics. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Wafer scale growth of single crystal two-dimensional van der Waals materials
(Royal Society of Chemistry, 2024) Chetna Gautam; Baishali Thakurta; Monalisa Pal; Anup Kumar Ghosh; Anupam Giri
Two-dimensional (2D) van der Waals (vdW) materials, including graphene, hexagonal boron nitride (hBN), and metal dichalcogenides (MCs), form the basis of modern electronics and optoelectronics due to their unique electronic structure, chemical activity, and mechanical strength. Despite many proof-of-concept demonstrations so far, to fully realize their large-scale practical applications, especially in devices, wafer-scale single crystal atomically thin highly uniform films are indispensable. In this minireview, we present an overview on the strategies and highlight recent significant advances toward the synthesis of wafer-scale single crystal graphene, hBN, and MC 2D thin films. Currently, there are five distinct routes to synthesize wafer-scale single crystal 2D vdW thin films: (i) nucleation-controlled growth by suppressing the nucleation density, (ii) unidirectional alignment of multiple epitaxial nuclei and their seamless coalescence, (iii) self-collimation of randomly oriented grains on a molten metal, (iv) surface diffusion and epitaxial self-planarization and (v) seed-mediated 2D vertical epitaxy. Finally, the challenges that need to be addressed in future studies have also been described. © 2024 The Royal Society of Chemistry.