Physics

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The present study discusses the synthesis of yttrium and tin-doped barium titanate using sol–gel synthesis route, and explores their structural, morphological, and ferroelectric properties. Yttrium nitrate and stannic chloride were used to dope barium titanate synthesized using barium acetate and titanium butoxide. The phase of the sol–gel prepared samples with composition Ba1-1.5xYxTi1-zSnzO3; x = 0.0, 0.005, 0.01 for each z = 0.0, and 0.05 was investigated using X-ray diffraction (XRD). The Raman spectra were obtained to investigate their lattice vibrations. The doping-induced variation in the morphology and grain size of these samples was studied using SEM micrographs, which revealed an increase in grain size with tin-doping and grain growth inhibition caused by yttrium incorporation. The DC conductivity of these samples was measured from RT to 350 °C. The samples were also inspected for their ferroelectric properties. The maximum dielectric constant of 9586 (1 kHz) at its Curie temperature and 5611 at 40 °C was observed for 0.5 mol% yttrium and 5 mol% tin co-doped sample which also displayed the highest density. The P-E hysteresis behavior and piezoelectric coefficient (d33) were also studied. [Figure not available: see fulltext.]. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

World University root node

(SoNS) School of Natural Sciences

Journal of Sol-Gel Science and Technology

Cumulative effect of yttrium and tin co-doping on the structural and ferroelectric properties of sol–gel derived barium titanate

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).

Journal of Applied Physics

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

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 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

We present photoabsorption (PA) response and resistive switching (RS) behavior of ZnO thin films that were ion implanted, at many fluences, with 50 keV Ti ions. Photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), UV–Visible spectroscopy and conductive- Atomic Force Microscopy (c-AFM) have been utilized to study the role of oxygen vacancies (OV ) in the evolution of the PA and RS properties. Grazing incidence X-ray diffraction (GIXRD) and Raman Scattering results suggest an improvement in the crystallinity of the films with ion fluence. Enhancement in oxygen vacancy, with fluence, appears to be responsible for higher photo response in the UV–Vis range. Additionally, engineering of bandgap, exhibiting systematic reduction in bandgap- energy with fluence, introduces enhanced absorption in visible regime. For the films implanted at the highest fluence, an asymmetric RS behavior is observed. A Switching behavior, from a high resistance state to a low resistance state, is demonstrated under positive bias conditions. However, for negative bias conditions a rectifying nature is seen. Oxygen vacancies play a crucial role in the modulation of PA response as well as in RS mechanism. Migration of these oxygen vacancies contribute to the formation of conducting filament which may be crucial for the observation of RS phenomenon at the highest fluence. © 2021 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Resistive switching properties and photoabsorption behavior of Ti ion implanted ZnO thin films

Memristors are one of the fastest developing electronic devices in the field of data storage and brain inspired neural computing. As a two terminal device, memristors are numerously utilized as resistive random access memories (RRAM) and energy efficient artificial synapses. Herein, the fabrication of perovskite-type rubidium lead chloride quantum dots (RPCQDs) is reported as a functional layer in a memristive system. The device, Al/RPCQDs/indium doped tin oxide (ITO), exhibits a cycling-induced decrease in SET voltage, where Al and ITO work as a top and bottom electrode respectively. However, time dependent self-recovery to the pristine state is observed in the Al/RPCQDs/ITO device. In contrast, the self-rejuvenation is suppressed when a buffer capped conducting polymer (BCCP) is incorporated on the ITO layer to make a Al/RPCQDs/BCCP/ITO structure. This customized device structure successfully retains the reproducible bipolar switching behavior without severe deviation in operating voltages, which helps in studying reliable memristive properties. In addition, the Al/RPCQDs/BCCP/ITO memristive device also demonstrates some essential synaptic functions such as pair-pulse facilitation, long-term potentiation, and long-term depression. © 2022 Wiley-VCH GmbH.

Advanced Electronic Materials

Influence of Nanoscale Charge Trapping Layer on the Memory and Synaptic Characteristics of a Novel Rubidium Lead Chloride Quantum Dot Based Memristor

Nanostructures of layered 2D materials have been proven one of the significant recent trends for visible-light-driven photocatalysis because of their unique morphology, effective optical adsorption, and rich active sites. Herein, we synthesized ultrathin-layered MoS2 nanoflowers and nanosheets with rich active sites by using a facile hydrothermal technique. The photocatalytic performance of the as-synthesized MoS2 nanoflowers (NF) and nanosheets (NS) were investigated for the photodegradation of MB (methylene blue), MG (malachite Green), and RhB (rhodamine B) dye under visible light irradiations. Ultrathin-layered nanoflowers showed faster degradation (96% in 150 min) in RhB under visible light irradiation, probably due to a large number of active sites and high available surface area. The kinetic study demonstrated that the first-order kinetic model best explained the process of photodegradation. The MoS2 nanoflowers catalysts has similar catalytic performance after four consecutive cyclic performances, demonstrating their good stability. The results showed that the MoS2 nanoflowers have outstanding visible-light-driven photocatalytic activity and could be an effective catalyst for industrial wastewater treatment. © 2022 American Chemical Society. All rights reserved.