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Shiv Nadar University

(SoNS) School of Natural Sciences

Poly-crystalline Si film is an important material for its applications in microelectronics and solar cells. In order to realize poly-crystalline Si for practical application with high performance, it needs to be fabricated at room temperature. In this paper, we present a novel technique to develop poly-crystalline Si thin films at room temperature using 500 keV Xe+ ion irradiation. Here, the Al-induced crystallization process is employed to reduce the crystallization temperature. For that, c-Al (50 nm)/a-Si (150 nm) bilayer thin films have been used for ion irradiation experiments. Structural studies show that crystallization of Si starts at a threshold fluence of 3 × 1015 ions cm-2, and crystallinity is found to increase with increasing ion fluence. The results are explained in terms of displacement spike and thermal spike due to the interaction of energetic ions with target atoms. The transport of ions in matter Monte Carlo computer simulation code has been used to estimate the number of displacements due to ion irradiation. Generation of a sufficient amount of free Si atoms at threshold fluence and diffusion of these free Si atoms along the Al grain boundary starts the nucleation process. © 2022 Author(s).

World University root node

Physics

Journal of Applied Physics

Room temperature fabrication of poly-crystalline Si thin films via Al-induced crystallization under 500 keV Xe+ion irradiation

Strain competition plays an important role in shaping the dynamics of multiple pathogen outbreaks in a population. Competition may lead to exclusion of some pathogens, while it may influence the invasion of an emerging mutant in the population. However, little emphasis has been given to understand the influence of human vaccination choice on pathogen competition or strain invasion for vaccine-preventable infectious diseases. Coupling game dynamic framework of vaccination choice and compartmental disease transmission model of two strains, we explore invasion and persistence of a mutant in the population despite having a lower reproduction rate than the resident one. We illustrate that higher perceived strain severity and lower perceived vaccine efficacy are necessary conditions for the persistence of a mutant strain. The numerical simulation also extends these invasion and persistence analyses under asymmetric cross-protective immunity of these strains. We show that the dynamics of this cross-immunity model under human vaccination choices is determined by the interplay of parameters defining the cross-immune response function, perceived risk of infection, and vaccine efficacy, and it can exhibit invasion and persistence of mutant strain, even complete exclusion of resident strain in the regime of sufficiently high perceived risk. We conclude by discussing public health implications of the results, that proper risk communication in public about the severity of the disease is an important task to reduce the chance of mutant invasion. Thus, understanding pathogen competitions under social interactions and choices may be an important component for policymakers for strategic decision-making. © 2021 Elsevier Inc.

Mathematics

Theoretical Population Biology

The effect of human vaccination behaviour on strain competition in an infectious disease: An imitation dynamic approach

The semiconductor/dielectric interface is arguably the most important region in field-effect transistors. This article investigates the performance-enhancing effects of passivation of the dielectric surface by a self-assembled layer (SAM) of silanes on organic field-effect transistors. Apart from conventional figures of merit for the devices, the energetic distribution of the density of the in-gap trap-states (trap-DOS) and the contact resistance are evaluated using numerical methods. The investigation reveals that the surface passivation of the dielectric SiO2 has a dual effect on device operation. Firstly, it establishes quantitatively that the surface passivation leads to a significant reduction in the density of both shallow and deep traps in the organic semiconductor PBTTT-C14. This effect outweighs the impact of the SAM dipoles on the device turn-on. Secondly, the contact resistance gets lowered by a factor of more than 10 due to the improved top-surface morphology of the PBTTT-C14 thin film. The lower contact resistance in devices is corroborated by lower contact potential difference between PBTTT-C14 and gold, measured using scanning kelvin probe microscopy. © 2021 IOP Publishing Ltd.

Semiconductor Science and Technology

Effect of dielectric surface passivation on organic field-effect transistors: Spectral analysis of the density of trap-states

Biopolymer-based memory devices have a multitude of potential applications in biomedical research. In this paper, we demonstrate the tunable memory behavior of the chitosan (CS) based memory devices as a function of CS thickness using the device structure of ITO/CS/Cu. Also, a clear distinction between filamentary and interfacial resistive switching was witnessed. High on/off ratios of 1870 and 1280 were observed in the filamentary resistive switching (for CS thickness of 80 nm) and interfacial resistive switching (for CS thickness of 200 nm) modes, respectively. The switching mechanism has also been analyzed using linear fit analysis and attributed to the formation and rupture of the conducting filaments, and charge accumulation at the metal/CS interface. This study opens up the possibility of developing write-once-read-many and read-and-write (RWM) random access memory devices. © 2021 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Chitosan based memory devices: Filamentary versus interfacial resistive switching

The latest fourth-generation oxazine-ring substituted thiophene-based benzoxazine monomers and polymers with variation in the degree of phenyl substitution (with and without) in the oxazine-ring were synthesized and characterized. Thiophene-based di-substituted benzoxazine undergoes ring-opening polymerization at a low temperature with a minimal mass loss during polymerization as supported by molecular geometry-guided intramolecular interactions. This class of monomers provides ample opportunities to design at the molecular level high-performance polybenzoxazines with promising smart applications. © 2022 The Royal Society of Chemistry.

Chemistry

Chemical Communications

Synthesis and thermal behaviour of thiophene-based oxazine-ring substituted benzoxazine monomers &amp; polymers

Nanoscale assembly of ultrasmall metal nanoclusters (MNCs) by means of molecular forces has proven to be a powerful strategy to engineer their molecule-like properties in multiscale dimensions. By leveraging depletion attraction as the guiding force, herein, we demonstrate the formation of kinetically trapped NCs assemblies with enhanced photoluminescence (PL) and excited state lifetimes and extend the principle to cluster impregnated cationic nanogels, nonluminescent Au(I)-thiolate complexes, and weakly luminescent CuNCs. We further demonstrate a thermal energy driven kinetic barrier breaking process to isolate these assemblies. These isolated assemblies are thermodynamically stable, built from a strong network among several discrete, ultrasmall AuNCs and exhibit several unusual properties such as high stability in various pH, strong PL, microsecond lifetimes, large Stocks shifts, and higher accumulation in the lysosome of cancer cells. We anticipate our strategy may find wider use in creating a large variety of MNC-based assemblies with many unforeseen arrangements, properties, and applications. © 2022 American Chemical Society.

Journal of Physical Chemistry Letters

Depletion Driven Assembly of Ultrasmall Metal Nanoclusters: From Kinetically Arrested Assemblies to Thermodynamically Stable, Spherical Superclusters

The importance of atomic structure to understand the superconducting β-Tungsten (W) thin films especially their critical transition temperature (Tc) and upper critical magnetic field Hc2(0) is reported. Here, Tc and Hc2(0) for a low thickness (~ 35 nm) film are found to be ~ 3.14 K and 10.72 T, whereas for a comparatively thicker (~ 60 nm) film, these are 1.38 K and 2.34 T, respectively. The β-phase is identified by grazing-incidence X-ray diffraction. The microstructure is probed by transmission electron microscopy, where high-resolution images manifest an improvement in crystallinity of the nanoscale grains in a disordered matrix with increasing film thickness. A drastic change in atomic structure corresponding to two different thicknesses is found to be associated with the change in oxygen concentration. Particularly, the existence of amorphous-W in the presence of β-W is revealed in 35 nm film, which is further supported by ab-initio calculations. Based on the atomic and microstructure, superconducting properties of the β-W films are analyzed and discussed. Graphical abstract: Correlation between the superconducting transition temperature and microstructure with varying β-tungsten film thickness [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to The Materials Research Society.

Center for Informatics

Journal of Materials Research

Atomic scale microstructural insights of superconducting β-tungsten thin films

Dissipative particle dynamics (DPD) simulations has been performed to study the phase transition of a mixture of cationic and anionic surfactants in an aqueous solution as a function of the total concentration in water and the relative ratio of surfactants. The impact of the relative difference between the tail lengths of the cationic and anionic surfactants on the phase diagram has been simulated by tuning the number of DPD beads in the simulation model. This research also discusses the impact of the frequently used values of the parameters associated with the harmonic bonds among the bonded DPD beads on the obtained self-Assemblies. We find remarkable differences in the resultant self-Assemblies based on different choices of harmonic bond parameters. The performed simulations show an enhanced spectrum of self-Assemblies with augmented tail lengths and disparate harmonic bond parameters. The obtained self-Assemblies are quite unique and can potentially be used in the future for various applications. We also compare the simulation results of the vesicle structures obtained by modeling the electrostatic interaction in the simulation among the charged beads by explicitly introducing charges with a long-range interaction with those obtained by tuning the implicit electrostatic interaction without the long-range interaction. The effects of the chain length of the model and the harmonic bond parameters on the internal density of DPD beads and stress profiles within the vesicles are examined closely. These results are a significant contribution to understanding the stability of the phases and tailoring of the desired vesicles. © 2022 American Chemical Society. All rights reserved.

ACS Omega

Phase Diagram Study of Catanionic Surfactants Using Dissipative Particle Dynamics

The A15 β phase of tungsten has recently attracted great interest for spintronic applications due to the finding of giant spin-Hall effect. As β phase is stabilized by oxygen, we have studied the electronic structure of O-doped β-W from first principles calculations. It is found that 20 at.% O-doping makes β phase lower in energy than α-W. These results are in good agreement with energy dispersive X-ray spectroscopy which also shows ~ 16.84 at.% O in 60 nm thick W films. The latter has predominantly β phase as confirmed by grazing incidence X-ray diffraction (XRD). The simulated XRD of bulk β having 15.79 at.% O also agrees with XRD results. Oxygen binds strongly on the surface and affects the Dirac fermion behavior in pure β-W. There is structural disorder, O-inhomogeneity, and higher density-of-states in O-doped β-W at EF compared with pure α. These results are promising to understand the properties of β-W. © 2022, The Author(s).

Fulltext

Scientific Reports

Crucial role of oxygen on the bulk and surface electronic properties of stable β phase of tungsten

Dual-room-temperature phosphorescence (DRTP) from organic molecules is of utmost importance in chemical physics. The Dexter-type triplet-to-triplet energy transfer mechanism can therefore be used to achieve DRTP at ambient conditions. Here, we report two donor–acceptor (D–A)-based guests (CQN1, CQN2) in which the donor (D) and acceptor (A) parts are held in angular orientation around the C–N single bond. Spectroscopic analysis along with computational calculations revealed that both guests are incapable of emitting either thermally activated delayed fluorescence (TADF) or RTP at ambient conditions due to large singlet–triplet gaps, which are presented to show host (benzophenone, BP)-sensitized DRTP via multiple intermolecular triplet-to-triplet energy transfer (TTET) channels that originate from the triplet state (T1BP) of BP to the triplet states (T1D, T1A) of the D and A parts (TTET-I:T1BP → T1D; TTET-II:T1BP → T1A). In addition, an intramolecular TTET channel that occurs from the T1D to T1A states of the D and A parts of CQN2 is also activated due to the low triplet (T1D)–triplet (T1A) gap at ambient conditions. The efficiency of TTET processes was found to be 100%. The phosphorescence quantum yields (ϕP) and lifetimes (τP) were shown to be 13–20% and 0.48–0.55 s, respectively. Given the high lifetime of the DRTP feature of both host–guest systems (1000:1 molar ratio), a data security application is achieved. This design principle provides the first solid proof that DRTP via radiative decay of the dark triplet states of the D and A parts of D–A-based non-TADF systems is possible, revealing a method to increase the efficiency and lifetime of DRTP. © 2022 The Authors. Published by American Chemical Society