Department of Physics

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X-ray diffraction (XRD) techniques are powerful, non-destructive characterization tool with minimal sample preparation. XRD provides the first information about the materials phases, crystalline structure, average crystallite size, micro and macro strain, orientation parameter, texture coefficient, degree of crystallinity, crystal defects etc. XRD analysis provides information about the bulk, polycrystalline thin films, and multilayer structures, which is very important in various scientific and material engineering fields. This review discusses the diffraction related phenomena/principles such as powder X-ray diffraction, and thin-film/grazing incidence X-ray diffraction (GIXRD) comprehensively for thin film samples which are used frequently in various branches of science and technology. The review also covers few case studies on polycrystalline thin-film samples related to phase analysis, preferred orientation parameter (texture coefficient) analysis, stress evaluation in thin films and multilayer, multiphase content identification, bifurcation of multiphase on multilayer samples, depth profiling in thin-film/ multilayer structures, the impact of doping effect on structural properties of thin films etc., comprehensively using GIXRD/XRD. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.

World University root node

Journal of Materials Science: Materials in Electronics

Structural characterization of polycrystalline thin films by X-ray diffraction techniques

Transition metal dichalcogenides based materials exhibit promising optoelectronic properties for solar cell application. We considered the heterostructure single junction solar cell with bulk W(S/Se)2 as an absorber material and ultrathin Janus WSeTe layer as a buffer layer. The optoelectronic properties of WSeTe monolayer are calculated using density functional theory calculations. The high absorption coefficient of WS2/WSe2 makes them suitable absorber materials. The performance of layered single junction heterostructure is simulated using SCAPS-1D simulator. The device performance is evaluated to understand the effect of an absorber layer thickness, carrier concentration, defect density, work function, buffer layer carrier concentration, and interface defect density. After optimization of all the possible parameters, the maximum efficiencies noted are 18.87% and 18.1% for AZO/WSeTe/WS2 and AZO/WSeTe/WSe2 solar cells, respectively. © 2021 American Chemical Society.

Journal of Physical Chemistry C

Heterostructure AZO/WSeTe/W(S/Se)2as an Efficient Single Junction Solar Cell with Ultrathin Janus WSeTe Buffer Layer

Cs2AuBiCl6 is considered to be a potential lead-free double perovskite alternative for perovskite solar cells. Its electronic and optical properties are investigated using density functional theory. The electronic properties of Cs2AuBiCl6 material ensure a bandgap of 1.40 eV (without considering SOC) and 1.12 eV (with SOC) using mBJ exchange-correlation functional, close to the optimal bandgap for solar cell application as per the Shockley–Queisser limit. Optical properties suggest a high absorption coefficient ≈105 cm−1 with low reflectance, making it the optimal absorber material. Furthermore, the photovoltaic performance of Cs2AuBiCl6 based single-junction transparent conducting oxide (TCO)/IDL1/Cs2AuBiCl6/IDL2/Cu2O solar cell is investigated using SCAPS-1D device simulation program. The impact of electron affinity, thickness, carrier concentration, defect density, and interface defect density is examined using interface defect layer (IDL) on the photovoltaic performance. The maximum photoconversion efficiency (PCE) of ≈22.18% is noticed for optimized material's parameters. These studies on TCO/IDL1/Cs2AuBiCl6/IDL2/Cu2O solar cell will provide guidelines for designing and developing an efficient lead-free perovskite-based solar cell as an alternative to conventional halide perovskite materials based solar cell. © 2021 Wiley-VCH GmbH

Advanced Theory and Simulations

Inorganic Lead-Free Cs2AuBiCl6 Perovskite Absorber and Cu2O Hole Transport Material Based Single-Junction Solar Cells with 22.18% Power Conversion Efficiency

Write once read many times (WORM) memory devices based on the resistive switching mechanism of a sputtered amorphous BaTiO3 (am-BTO) thin film in a metal-insulator-metal structure is fabricated on a FTO coated glass substrate with a silver top contact. Fabricated devices show the switching from a low-conductance state to a high-conductance state with the formation of conductive filament(s) in the am-BTO layer. The memory characteristics are investigated as a function of thickness of am-BTO layer, which is determined by varying the deposition time. Devices with all deposited thicknesses show data retention for more than 4000 s and 300 reading cycle. Devices with 180 nm thickness show a high on-off ratio on the order of 106. The fabricated WORM devices exhibit good reading-endurance and data-retention characteristics. © 2021 Author(s).

Fulltext

Applied Physics Letters

Write-once-read-many-times resistive switching behavior of amorphous barium titanate based device with very high on-off ratio and stability

Over the past several decades, metal oxide based gas sensors are widely used for hydrogen gas sensing applications. However, their poor sensitivity and very high value of operating temperature (&gt; 300 °C) pose a severe threat over hydrogen detection due to its highly flammable nature. In recent years, a few strategies have been explored by the researchers to address these formidable challenges faced by the sensing technology. Here, we present MoS2/ZnO hybrid exhibiting higher molecular detection at low operating temperature. The ZnO film was grown using the magnetron sputtering technique, while MoS2-PVP nanocomposites (MoS2-PVP NCs) were synthesized through organic polymer assisted liquid exfoliation process. We examined the sensing performance of various MoS2/ZnO hybrids prepared by the decoration of different concentration MoS2-PVP NCs over the ZnO surface. The decoration of ZnO film through MoS2-PVP NCs increases the effective surface area and the number of active sites for the hydrogen molecules to get adsorbed, hence improved the surface reactivity to gas molecules. Interestingly, a 5 mg/mL MoS2-PVP NCs decorated ZnO sensor showed an improvement of $\sim 8$ times in sensing response as compared to the pristine ZnO based sensor upon 50 ppm hydrogen exposure. The improvement in sensing ability is primarily ascribed to electronic sensitization and spillover effects. Our results establish that the MoS2/ZnO hybrid exhibit superior hydrogen sensing behavior indicating the prominent role of MoS2-PVP NCs in hydrogen detection. © 2001-2012 IEEE.

IEEE Sensors Journal

MoS2-PVP Nanocomposites Decorated ZnO Microsheets for Efficient Hydrogen Detection

Rashba spin-orbit coupling (SOC) plays a vital role in transporting carriers under external electric field or strain in two-dimensional transition metal di-chalcogenides in the absence of inversion symmetry. Here, the effect of SOC on the electronic and thermoelectric properties of two-dimensional monolayer HfS2, HfSe2 and their Janus monolayer HfSSe has been investigated using density functional theory (DFT) and Boltzmann transport equation (BTE). A considerable enhancement in thermoelectric power factor (PF) for n-type carriers has been observed due to the SOC in all the monolayers. This enhanced power factor for n-type carriers is mainly because of increased valley degeneracy at the conduction band minima (CBM), as there is no enhancement in electron relaxation time (τ) with SOC. The lattice thermal conductivity (κph) at room temperature is very low for these monolayers compared to extensively used TMDCs such as MoS2 and WS2. This is due to the strong coupling between acoustic and optical modes, which results in low group velocity and a short lifetime of phonons in HfS2, HfSe2 and HfSSe Janus monolayers. The ultralow value of κph results a very high thermoelectric figure of merit (ZT) at room temperature for n-type carriers and which increases significantly with SOC. The highest ZT values of 0.90 (HfSe2), 0.84 (HfS2) and 0.81 (HfSSe) for n-type at 600 K has been achieved with SOC. Our theoretical investigation predicts that there is a significant effect of SOC on the thermoelectric performance of HfX2 (X = S, Se) and its Janus monolayer HfSSe and they can be a revolutionary candidate for the fabrication of a highly efficient thermoelectric power generator. © 2021 Elsevier B.V.

Journal of Alloys and Compounds

Spin orbit coupling induced enhancement of thermoelectric performance of HfX2 (X = S, Se) and its Janus monolayer

Advancing from eight imaginary worlds of octonion algebra, for the first time we introduce dodecanion algebra, a mathematical universe made of twelve imaginary worlds one inside another. The difference between eight and twelve imaginary worlds is that the Fano plane that sets the products of imaginary vectors is replaced by a triplet of manifolds that could coexist in three forms. In the proposed algebra product tensors-like quaternion, octonion, dodecanion, and icosanion are deconstructed as a composition of prime dimensional tensors. We propose a generic conformal cylinder of imaginary worlds, similar to modulo or clock arithmetic, using that one could build the group multiplication tables of multinions, which would enable developing the associated algebra. Space-time (st) metric is known, we added two concepts, 15 geometric shapes as topology (T) and 15 primes as symmetry (S) to build a new metric, space-time-topology-prime(stTS) for a self-operating mathematical universe with n nested imaginary worlds. The stTS metric delivers a decision as shape-changing geometry with time, following fractal information theory (FIT) proposed earlier for hypercomputing in the brain. FIT includes two key aspects, the geometric musical language (GML) and the phase prime metric (PPM) that operates using clock architectures spread over 12 dimensions. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Lecture Notes in Networks and Systems

A Space-Time-Topology-Prime, stTS Metric for a Self-operating Mathematical Universe Uses Dodecanion Geometric Algebra of 2-20 D Complex Vectors

We report an analytical model to investigate an atom-cavity interaction phenomenon with the consideration of a two-level atom and a quantized mode of the cavity field in the form of harmonic oscillation. Accordingly, we consider the matrix form of a special type of two-level Hamiltonian consisting of three units, explaining a two-level atom, a quantum harmonic oscillator to be equivalent to a quantized cavity-mode field, and an interaction matrix between them, which are connected by some iteration parameters. The iteration parameters of the proposed Hamiltonian have judiciously been modulated to encounter an exceptional point (EP). A specific closed parameter space encircling the embedded EP has been considered to study the dynamics of the coupled states in the context of a flip-of-state phenomenon. We also incorporate a deliberate phase difference between the two unperturbed levels associated with the atomic system and study the phase induced interaction between them in the context of state-flipping around the identified EP. The proposed analytical model indeed opens up a fertile platform to explore a range of interesting applications associated with the atom-cavity interaction. © 2021 IOP Publishing Ltd.

Physica Scripta

Hosting of exceptional points in an atom-field interaction Hamiltonian and manipulation of light states

We investigate the dynamics of quantum correlation (QC) under the effects of reservoir memory, as a resource for quantum information and computation tasks. Quantum correlations of two-qubit systems are used for implementing quantum teleportation successfully, and for investigating how teleportation fidelity, violation of Bell-CHSH inequality, quantum steering and entanglement are connected with each other under the influence of noisy environments. Both Markovian and non-Markovian channels are considered, and it is shown that the decay and revival of correlations follow the hierarchy of quantum correlations in the state space. Noise tolerance of quantum correlations is checked for different types of unital and non-unital quantum channels, with and without memory. The quantum speed limit time (τQSL) is investigated from the perspective of memory of quantum noise, and the corresponding dynamics is used to analyze the evolution of quantum correlations. We establish the connection between information backflow, quantum speed limit time and dynamics of quantum correlations for non-Markovian quantum channels. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

Quantum Information Processing

Hierarchy of quantum correlations under non-Markovian dynamics

This work demonstrates a facile way to fabricate ultrastretchable thermo- and mechanochromic fiber with healable metallic conductivity. Thermochromic hollow elastic fiber is prepared by using silicone composite with thermochromic pigment. Once the fiber forms, gallium-based liquid metal is injected into the fiber. The composite fiber with liquid metal core shows uniform color change along the fiber by applying Joule heating through the liquid metal wire. The fiber with multiple thermochromic pigment locally distributed along the fiber shows serial color change by increased current. The healable conductivity of the metal core is demonstrated by restoring electrical conductivity near room temperature. When it is in a solid state, the wire can fracture during deformation, thus the wire loses conductivity. However, upon body heating, the wire can rewire, because of the low melting point of the metal (gallium, 29.8 °C). This healing ability of the metal core can allow the fiber to have healable thermochromic behavior. Stretching a liquid metal wire can change the geometry of the wires, resulting in a color change because of increased resistance while Joule heating is applied. This thermo- and mechanochromic fiber with liquid metal core would find use in wearable and conformal electronics, electronic textiles, and soft robotics. © 2021 Wiley-VCH GmbH