Department of Physics

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100 year anniversary Measurement Science and Technology logo. Purpose-led Publishing logo. A reverse electrochemical floating-layer technique of SPM tip preparation
(IOP, 2000) Gangopadhyay, Subhashis
An experimental set-up involving a combination of reverse electrochemical etching and the floating-layer technique of tip preparation is presented. In the model only dc bias is used, avoiding the shortcomings of ac bias. The collection of two tips in a single etching process and mechanical auto-breaking of the circuit are emphasized. This cost and time effective, easy in-laboratory approach yields two sharp tips without paying attention to switching off the circuit. The nature of the tip shape arising from the floating-layer technique has been explained in terms of the electrical field distribution between the electrodes. The addition of some new information together with a few established facts will enrich and enlighten the art of tip preparation.
14 Ultrathin films of nanomaterials: a lyotropic liquid crystalline system and its sensing application
(De Gruyter, 2021) Gupta, Raj Kumar; Manjuladevi, V.
The ultrathin films of nanomaterials provide remarkable features that can be potentially employed for efficient device fabrication. In this chapter, an overview of ultrathin films of nanomaterials at different interfaces, along with their sensing capabilities, is discussed. From the symmetry point of view, the ultrathin films and sensing applications of the nanoparticles with spherical geometry (eg amphiphilic gold and TiO2 nanoparticle), one-dimensional system (single-walled carbon nanotube) and two-dimensional systems (functionalized graphene) are highlighted.
3D Graphene-Based Optical Sensors
(Springer, 2023-07) Gupta, Raj Kumar; Manjuladevi, V.
3D graphene (3DG) has been utilized as a functional material for the development of gas and chemical sensors. The sensor based on optical phenomena such as surface plasmon resonance (SPR) offers label-free measurements at a very high resolution and sensitivity. It is essential for any sensor to exhibit a very high analyte adsorption capability and good perceptibility to measure changes in electrical and optical properties due to such adsorption. Although SPR is extremely sensitive, 3DG is one of the potential functional materials which can exhibit a high analyte adsorption capability. Therefore, the use of 3DG as a functional layer in SPR devices can ensure a next-generation sensor. The Kretschmann configuration in angular interrogation-based SPR sensors may offer a sensitivity of the order of 10–8 RIU. In the SPR sensor, the extent of the plasmonic field over the metallic surface is limited to a few hundred nanometres. The excellent adsorption capability of 3D graphene can be employed for bio-sensing applications. However, due to the bulk nature of 3DG, the plasmonic field during SPR-based sensing decays rapidly into the porous structure of the 3DG, and therefore, the measurement becomes unresponsive even after the efficient adsorption of the analytes. Therefore, the layer of 3D graphene can be grown over the gold surface by some bottom-up deposition mechanism with control over the thickness. The bottom-up deposition mechanism may yield monolayer, bilayer, and twisted bilayer graphene which also exhibit excellent bio-sensing merits.
The 8th workshop on high energy physics phenomenology (WHEPP-8) was held at the Indian Institute of Technology, Mumbai, India during January 5–16, 2004. One of the four working groups, group III was dedicated to QCD and heavy ion physics (HIC). The present manuscript gives a summary of the activities of group III during the workshop (see also [1] for completeness). The activities of group III were focused to understand the collective behaviours of the system formed after the collisions of two nuclei at ultra-relativistic energies from the interactions of the elementary degrees of freedom, i.e. quarks and gluons, governed by non-abelian gauge theory, i.e. QCD. This was initiated by two plenary talks on experimental overview of heavy ion collisions and lattice QCD and several working group talks and discussions.
(Springer, 2003-11) Layek, Biswanath
We show that cosmic strings moving through the plasma at the time of a first-order quark-hadron transition in the early universe generate baryon inhomogeneities, which can survive till the nucleosynthesis epoch. We find out how these inhomogeneities actually affect the calculated values of the light element abundances. Recently a wealth of observational data from various experiments have helped to reduce the uncertainties in the values of these abundances. Using these we show that it is possible to derive constraints in the presence of cosmic strings during the quark-hadron transition.
A04-0580 - Na3Zr2Si2PO12-Polymer Hybrid Composites for Solid-State Supercapacitor Applications
(IMCS 2020, 2020-05) Dalvi, Anshuman
Various Na+ ions conducting composite polymer electrolytes have been developed in last three decades, but their application is limited due to poor ionic conductivity near room temperature. Recently, we have demonstrated high ionic conductivity of ∼ 10-4 Ω-1cm-1 in NASICON-polymer hybrids and found these systems useful in energy storage applications. A high ionic mobility of ~ 10-1 cm2/V-s was also reported. Present work shows a possible application of these hybrids as electrolyte/separator in all-solid-state supercapacitor. In this work, Na+ NASICON, viz. Na3Zr2Si2PO12 (NZSP) have been prepared by conventional solid state reaction route. Subsequently, their nanoparticles of size ~ 30 nm were obtained via mechanical ball milling. The nanoparticles were mixed with polymer in a ball mill until a homogeneous viscous slurry formation. Further the slurry was dried, hot pressed at ~ 80°C to obtain films of uniform thickness ~ 250µm. This way, composite films with composition (wt%) 10NaI-90(PEO1-xNZSPx), where 0 ≤ x ≤ 0.4, were obtained. Surface morphology, structural and thermal analysis were characterized using FESEM, XRD and DSC. A maximum ionic conductivity of ~ 4 x 10-5 Ω-1cm-1 at room temperature has been achieved for composite with x = 0.4. Impedance spectroscopy was used to understand mechanism of ionic transport. Further, to understand the role of ceramic fillers in enhancing the ionic conductivity, local structure of the composites was studied using x-ray absorption near edge structure spectroscopy (XANES) at Indus II Beamline 01, RRCAT, Indore. These results suggest a significant role of NASICON in providing pathways for Na+ ion transport. The ionic conductivity at room temperature for composite with x = 0.4 were further modified with EMITf and EC+PC as plasticizer. A maximum ionic conductivity of ~ 2 x 10-4 Ω-1cm-1 at room temperature has been achieved with addition of 2 wt% of EMITf in the composite. To elucidate the capacity of these electrolyte as a membrane for all solid-state ionic devices, solid state super capacitors (configuration C|CPE|C) were fabricated. These composites have been found to be competitive candidates for energy storage. A maximum specific capacitance of ~ 26 F-g-1 is obtained for composite with 2 wt% EMITf at room temperature.
Achieving high-performance parameters in NASICON-polymer composite electrolyte-based solid-state supercapacitors by interface modification
(RSC, 2025-02) Dalvi, Anshuman
The present study reveals a strategy to enhance the performance of solid-state supercapacitors based on activated carbon electrodes and a Na3Zr2Si2PO12 (NZSP) dispersed fast ionic solid polymer electrolyte membrane. The electrode–electrolyte interface is optimized using a novel ‘solvent layer’ approach to enhance supercapacitor performance. By adding a small amount of acetonitrile organic solvent (a few μL cm−2) at the electrode–electrolyte interface and utilizing high surface area (1800 m2 g−1) activated carbon, significant improvements in specific capacitance, specific energy, specific power, and cycling stability are achieved. Device performance at various operating voltages and discharge currents reveals interesting results. A specific capacitance of approximately 260 F g−1 and a high specific power of 4780 W kg−1 is achieved at 3 V/5 mA. Moreover, after 10[thin space (1/6-em)]000 galvanostatic charge–discharge cycles (1 V/1 mA), the supercapacitor exhibits ∼99% stable coulombic efficiency along with appreciably high capacitance retention (∼90%). A stack of five such cells can power an 8 V LED circuit for more than 30 minutes. Applying such a solvent layer enables effective use of the surface area of the activated carbon. Results suggest that solvent incorporation enables a local ‘gel-like’ layer formation that couples the electrode with a solid polymer electrolyte and facilitates faster charge movement across the electrode–electrolyte interface.
Active and passive electrode matrix optimization technique to improve humidity sensing performance of MoS2-based devices: unfolding an innovative avenue
(IEEE, 2025-05) Gupta, Raj Kumar
Active electrodes” that are primarily used for the collection of carriers and “passive electrodes” that actively take part in target gas molecule dissociation (gas-induced carrier generation but not collection), owing to their catalytic nature, were judiciously coupled and optimized in a matrix for the first time with an aim to enhance humidity sensing performance of the MoS2-based devices. Intrigued by the design concept of electroencephalogram (EEG) electrode configurations, the present endeavor uniquely adapted the electrode matrix for gas-sensing scenarios. MoS2 nanoflowers were synthesized through hydrothermal deposition, while Pd electrodes, which were used both as active and passive ones, were deposited by electron beam evaporation using a suitably designed metal shadow mask. The innovation of this study lies in the strategic incorporation of catalytic Pd-based electrodes (both as active and passive), where two active electrodes ( 2×2 mm) facilitated signal transmission to the measurement unit, while multiple passive electrodes ( 0.5×0.5 mm) enabled carrier generation through catalytic dissociation of the target gas. The optimum number of passive electrodes was identified to be six offering the highest response magnitude (RM). The optimized sensor was tested across a relative humidity (RH) range of 8%–84%, demonstrating an RM of 54.4% at 84% RH. To provide deeper insight into the sensing mechanism, a theoretical model was developed to quantitatively correlate the RM with RH levels. Comparison with the existing resistive humidity sensors demonstrated the superior performance of the developed sensor, making it a strong candidate for applications in industrial humidity control, healthcare, smart IoT systems, and environmental monitoring.
Adiabatic modulation of driving protocols in periodically driven quantum systems
(ARXIV, 2024-04) Sarkar, Tapomoy Guha; Bandyopadhyay, Jayendra N.
We consider a periodically driven system where the high-frequency driving protocol consists of a sequence of potentials switched on and off at different instants within a period. We explore the possibility of introducing an adiabatic modulation of the driving protocol by considering a slow evolution of the instants when the sequence of potentials is switched on/off. We examine how this influences the long-term dynamics of periodically driven quantum systems. By assuming that the slow and fast timescales in the problem can be decoupled, we derive the stroboscopic (effective) Hamiltonian for a four-step driving sequence up to the first order in perturbation theory. We then apply this approach to a rigid rotor, where the adiabatic modulation of the driving protocol is chosen to produce an evolving emergent magnetic field that interacts with the rotor's spin. We study the emergence of diabolical points and diabolical loci in the parameter space of the effective Hamiltonian. Further, we study the topological properties of the maps of the adiabatic paths in the parameter space to the eigenspace of the effective Hamiltonian. In effect, we obtain a technique to tune the topological properties of the eigenstates by selecting various adiabatic evolution of the driving protocol characterized by different paths in the parameter space. This technique can be applied to any periodic driving protocol to achieve desirable topological effects.
Adsorbate induced self-ordering of germanium nanoislands on Si(113)
(IOP, 2007-10) Gangopadhyay, Subhashis
The impact of Ga preadsorption on the spatial correlation of nanoscale three-dimensional (3D) Ge-islands has been investigated by low-energy electron microscopy and low-energy electron diffraction. Submonolayer Ga adsorption leads to the formation of a 2D chemical nanopattern, since the Ga-terminated (2×2) domains exclusively decorate the step edges of the Si(113) substrate. Subsequent Ge growth on such a partially Ga-covered surface results in Ge 3D islands with an increased density as compared to Ge growth on clean Si(113). However, no pronounced alignment of the Ge islands is observed. Completely different results are obtained for Ga saturation coverage, which results in the formation of (112) and (115) facets regularly arranged with a periodicity of about 40 nm. Upon Ge deposition, Ge islands are formed at a high density of about 1.3×1010 cm−2. These islands are well ordered as they align at the substrate facets. Moreover, the facet array induces a reversal of the Ge islands' shape anisotropy as compared to growth on planar Si(113) substrates.
Adsorption of highly charged Gaussian polyelectrolytes onto oppositely charged surfaces
(AIP, 2016-03) Dutta, Sandipan
In many biological processes highly charged biopolymers are adsorbed onto oppositely charged surfaces of macroions and membranes. They form strongly correlated structures close to the surface which cannot be explained by the conventional Poisson-Boltzmann theory. In this work strong coupling theory is used to study the adsorption of highly charged Gaussian polyelectrolytes. Two cases of adsorptions are considered, when the Gaussian polyelectrolytes are confined (a) by one charged wall, and (b) between two charged walls. The effects of salt and the geometry of the polymers on their adsorption-depletion transitions in the strong coupling regime are discussed.
AFM studies of polycrystalline calcium sulfide thin films grown by atomic layer deposition
(Elsevier, 1999-04) Dey, Srijata
Polycrystalline CaS thin films were grown on Al2O3 films deposited on Si-wafer using the atomic layer deposition (ALD) technique. The surface structure of these films was studied by AFM and compared with respective SEM images. The polycrystalline film surfaces comprise regular shaped crystallites. First report of a possible growth mechanism is presented, on studying the variation of morphological features (i.e., roughness and size of crystallites) with thickness and growth rate.
AFM studies on Langmuir-Blodgett films of cholesterol
(Springer, 2004) Gupta, Raj Kumar
The Langmuir monolayer of cholesterol at the air-water interface exhibits a condensed phase in which the cholesterol molecules are aligned normal to the water surface. We have transferred the monolayer from water surface to different substrates by Langmuir-Blodgett (LB) technique and have studied their assembly by atomic force microscope (AFM). Our studies reveal that the aggregation of cholesterol molecules on hydrophobic surfaces leads to interesting structures. The cholesterol molecules assemble into a uniform film, elongated domains and uniformly distributed torus-shaped domains (doughnuts) for one, two and four cycles of deposition, respectively. Beyond four cycles, the molecules adsorb and desorb by an equal amount resulting in no further deposition. The formation of uniformly distributed doughnuts can be attributed to the hydrophobic interaction and reorganization of the molecules due to successive adsorption and desorption during deposition cycles. Our studies on hydrophilic surfaces show that cholesterol cannot form more than one layer of deposition.
Algebraic approach in the study of time-dependent nonlinear integrable systems: Case of the singular oscillator
(APS, 2001-03) Bandyopadhyay, Jayendra N.
The classical and the quantal problem of a particle interacting in one dimension with an external time-dependent quadratic potential and a constant inverse square potential is studied from the Lie-algebraic point of view. The integrability of this system is established by evaluating the exact invariant closely related to the Lewis and Riesenfeld invariant for the time-dependent harmonic oscillator. We study extensively the special and interesting case of a kicked-quadratic potential from which we derive a new integrable, nonlinear, area preserving, two-dimensional map that may, for instance, be used in numerical algorithms that integrate the Calogero-Sutherland-Moser Hamiltonian. The dynamics, both classical and quantal, is studied via the time-evolution operator that we evaluate using a recent method of integrating the quantum Liouville-Bloch equations [A. R. P. Rau, Phys. Rev. Lett. 81, 4785 (1990)]. The results show the exact one-to-one correspondence between the classical and the quantal dynamics. Our analysis also sheds light on the connection between properties of the su(1,1) algebra and that of simple dynamical systems.
Alignment of Ge Nanoislands on Si(111) by Ga-Induced Substrate Self-Patterning
(APS, 2007-02) Gangopadhyay, Subhashis
A novel mechanism is described which enables the selective formation of three-dimensional Ge islands. Submonolayer adsorption of Ga on Si(111) at high temperature leads to a self-organized two-dimensional pattern formation by separation of the 7 7 substrate and Ga=Si 111 - 3 p 3 p R30 domains. The latter evolve at step edges and domain boundaries of the initial substrate reconstruction. Subsequent Ge deposition results in the growth of 3D islands which are aligned at the boundaries between bare and Ga-covered domains. This result is explained in terms of preferential nucleation conditions due to a modulation of the surface chemical potential.
Alignment of liquid crystals using Langmuir‒Blodgett films of unsymmetrical bent-core liquid crystals
(Taylor & Francis, 2019-02) Manjuladevi, V.; Gupta, Raj Kumar
The properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air–water interface is known to exhibit a variety of surface phases which can be transferred onto a solid substrate using the Langmuir‒Blodgett (LB) technique. Here, we have studied the LM and LB films of asymmetrically substituted bent-core LC molecules. The morphology of LB film of the molecules is found to be a controlling parameter for aligning bulk LC in the nematic phase. It was found that the LB films of the bent-core molecules possessing defects favour the planar orientation of nematic LC, whereas the LB films with fewer defects show homeotropic alignment. The defect in LB films may introduce splay or bend distortions in the nematic near the alignment layer which can govern the planar alignment of the bulk LC. The uniform layer of LB film facilitates the molecules of nematic to anchor vertically due to a strong van der Waals interaction between the aliphatic chains leading to a homeotropic alignment.
Alignment Of Liquid Crystalson Lb Films Of Stearic Acid
(CIB Tech, 2012) Gupta, Raj Kumar; Manjuladevi, V.
We formed the Langmuir monolayer of stearic acid at the air-water (A-W) interface. The Langmuir-Blodgett (LB) films were deposited on solid substrates at different surface pressures. The liquid crystal cells were prepared over such LB films. We found that these cells exhibit a tendency to align in planar orientation for the liquid crystal. We found that the liquid crystal alignment improves in cells prepared with substrates deposited at higher surface pressure like 25mN/m. We present the results on the liquid crystal alignment as a function of number of layers of LB films deposited on the substrates at various surface pressures. We propose that LB films of stearic acid can be used as an aligning agent for liquid crystals.
All-solid-state electric double layer supercapacitors using Li1.3Al0.3Ti1.7(PO4)3 reinforced solid polymer electrolyte
(Elsevier, 2022-05) Dalvi, Anshuman
In this work, we report the fabrication and characterization of all-solid-state supercapacitors based on a conductive filler dispersed solid polymer electrolyte. Fast ionic Li1.3Al0.3Ti1.7(PO4)3 (LATP) reinforced PEO-PEG-LITFSI composite solid polymer electrolyte (CSPE) membranes are prepared by milling assisted route. The electric double-layer capacitor (EDLC) cells, using a hot-roll lamination technique, are fabricated using a CSPE membrane as electrolyte and activated charcoal (surface area ∼ 817m2g−1) on graphite sheet as electrode. The EDLCs display appreciable areal capacitance of ∼ 12 Fcm−2 and ∼40 Fcm−2 at 40 °C and 80 °C, respectively at ∼0.65 mAcm2 and 2 V. These solid-state EDLCs at 40 °C exhibit stability up to ∼16,000 cycles. Further, the electrode-electrolyte (solid-solid) interface remains quite stable after the charge-discharge cycling. The electrical conductivity of the CSPE membranes correlates well with the EDLC performance. The LATP content in the CSPE membranes play important role in enhancing the capacitance. The present investigation suggests that CSPE membranes with conductivity between ∼10−4–10−5 Scm−1 are useful for low-power EDLC applications. The EDLCs cells with LATP dispersed CSPE exhibit better stability during thermal cycling between 40 °C-80 °C.
All-solid-state Na+ ion supercapacitors using Na3Zr2Si2PO12-polymer hybrid films as electrolyte
(Elsevier, 2021-09) Dalvi, Anshuman
We report all-solid-state Na+ ion electrical double layer capacitors (EDLCs) for the first time in this study. These are fabricated using a novel Na+ ion solid polymer electrolyte (SPE) and high surface area (877 m2-g−1) activated carbon electrodes. Using salt (NaI), polyethylene oxide (PEO) and nano particles of Na3Zr2Si2PO12 (NZSP), hybrid electrolyte films with compositions 10NaI-90[PEO1-xNZSPx], where 0 ≤ x ≤ 0.7 are synthesized by a novel milling assisted route. The freestanding flexible film for x = 0.7 exhibits a maximum ionic conductivity of ~ 10−4 Ω−1 cm−1 at room temperature. The 2032 type EDLC with graphite current collector and polymer electrolyte film of composition x = 0.4 exhibits notably high value of specific capacitance (~ 104 F-g−1), and specific energy (~ 44 Wh-Kg−1) with a voltage stability window of ~ 2 volts. The NZSP content in the electrolyte influence the EDLC performance. The EDLCs with graphite sheet as current collector offer superior performance as compared to copper. Galvanostatic charge-discharge studies suggest stability of these supercapacitors at least upto ~ 400 cycles.
All-Solid-State Supercapacitors Based on Na+ Ion Composite Solid Polymer Electrolyte: Tailoring the Interface by Solvent Layer Approach
(SSRN, 2023-12) Dalvi, Anshuman
The present investigation proposes a novel approach to improve the performance of all solid-state supercapacitors (ASSCs). These ASSCs having a composite solid polymer electrolyte membrane (CSPE) and high surface area activated carbon (~ 1800 m2/g) electrodes exhibit improved performance when a novel strategy of ‘solvent layer approach’ at the electrode-electrolyte interface is used. Applying a nominal amount of acetonitrile (~3-5μl/cm2) at the interface leads to higher values of specific capacitance (~260F-g-1 at 2V, 1 mA), coulombic efficiency ~ 99 % and stability at least up to ~ 10000 cycles. It is demonstrated that a stack of five such cells can power an 8V LED circuit for more than 30 minutes. Results suggest that these supercapacitors are predominantly electric-double layer type in nature.
The American Astronomical Society logo. The Institute of Physics logo. An X-Ray and Near-Infrared Study of Young Stars in the Carina Nebula
(IOP, 2007) Vaidya, Kaushar
We present a multiwavelength study of the central region of the Carina Nebula, including Trumpler 16 and part of Trumpler 14. Our analysis of the Chandra X-Ray Observatory archival data led to the identification of 454 X-ray sources. These sources were then cross-identified with optical photometric and spectroscopic information available from the literature and with newly obtained near-infrared (JHKs) imaging observations. A total of 38 known OB stars are found to be X-ray emitters. All the O stars and early-B stars follow the nominal relation between the X-ray and bolometric luminosities, LX ~ 10-7Lbol. A few mid- to late-B stars are found to be associated with X-ray emission, likely attributable to T Tauri companions. We discovered 16 OB star candidates that suffer a large extinction in the optical wave bands. Some 300 sources have the X-ray and infrared characteristics of late-type pre-main-sequence stars. Our sample represents the most comprehensive census of the young stellar population in the Carina Nebula so far and should be useful for the study of the star formation history of this massive starburst region. We also report the finding of a compact (2' × 4') group of 10 relatively bright X-ray sources, all of which are detected in the near-infrared wavelengths and are highly reddened. The group is spatially coincident with the dark V-shaped dust lane bisecting the Carina Nebula and may be part of an embedded association. The distribution of the young stellar groups surrounding the H II region associated with Trumpler 16 is consistent with the collect-and-collapse scenario of triggered star formation.