Showing papers by "Samit K. Ray published in 2021"

Nanoceutical Fabric Prevents COVID-19 Spread through Expelled Respiratory Droplets: A Combined Computational, Spectroscopic, and Antimicrobial Study

Abstract: Centers for Disease Control and Prevention (CDC) warns the use of one-way valves or vents in face masks for potential threat of spreading COVID-19 through expelled respiratory droplets. Here, we have developed a nanoceutical cotton fabric duly sensitized with non-toxic zinc oxide nanomaterial for potential use as a membrane filter in the one-way valve for the ease of breathing without the threat of COVID-19 spreading. A detailed computational study revealed that zinc oxide nanoflowers (ZnO NFs) with almost two-dimensional petals trap SARS-CoV-2 spike proteins, responsible to attach to ACE-2 receptors in human lung epithelial cells. The study also confirmed significant denaturation of the spike proteins on the ZnO surface, revealing removal of the virus upon efficient trapping. Following the computational study, we have synthesized ZnO NF on a cotton matrix using a hydrothermal-assisted strategy. Electron-microscopic, steady-state, and picosecond-resolved spectroscopic studies confirm attachment of ZnO NF to the cotton (i.e., cellulose) matrix at the atomic level to develop the nanoceutical fabric. A detailed antimicrobial assay using Pseudomonas aeruginosa bacteria (model SARS-CoV-2 mimic) reveals excellent antimicrobial efficiency of the developed nanoceutical fabric. To our understanding, the nanoceutical fabric used in the one-way valve of a face mask would be the choice to assure breathing comfort along with source control of COVID-19 infection. The developed nanosensitized cloth can also be used as an antibacterial/anti CoV-2 washable dress material in general. ©

2D WS2 embedded PVDF nanocomposites for photosensitive piezoelectric nanogenerators with a colossal energy conversion efficiency of ∼25.6%

Abstract: Benefiting from the advantages of low cost, light weight and mechanical flexibility, piezoelectric nanogenerators have the potential for application in renewable energy harvesting from various unexplored sources. Here, we report the demonstration of the record efficiency of flexible piezoelectric nanogenerators (PENG) using composites of polyvinylidene fluoride (PVDF) and chemically exfoliated tungsten disulfide (WS2) nanosheets, which are found to be strongly photosensitive, making them attractive for self-powered optical devices. The presence of two-dimensional (2D) WS2 nanosheets in the PVDF matrix plays a dual role in enhancing the nucleation of the electroactive β-phase as well as inducing strong photosensitivity in the nanocomposite. The PVDF-WS2 composed flexible device is able to produce an enormously high output voltage of ∼116 V (for an impact of 105 kPa) and a piezoelectric energy conversion efficiency of ∼25.6%, which is the highest among the reported values for PVDF-2D material based self-poled piezoelectric nanogenerators. This self-poled piezo-phototronic device exhibits strain-dependent photocurrent at zero bias and exhibits a responsivity of 6.98 × 10−3 A W−1 at 0.75% strain under the illumination of 410 nm. The fabricated PENG is also able to harvest energy from routine human activities (finger tapping, writing on paper, mouse clicking, etc.) and movement of human body parts. These results open up a new horizon in piezo-phototronic materials through the realization of photosensitive multifunctional PENGs, which can be scaled up for fabricating compact, high performance, portable and self-powered wearable electronic devices for smart sensor applications.

Low-noise, high-detectivity, polarization-sensitive, room-temperature infrared photodetectors based on Ge quantum dot-decorated Si-on-insulator nanowire field-effect transistors.

Abstract: A CMOS-compatible infrared (IR; 1200-1700 nm) detector based on Ge quantum dots (QDs) decorated on a single Si-nanowire channel on a silicon-on-insulator (SOI) platform with a superior detectivity at room temperature is presented. The spectral response of a single nanowire device measured in a back-gated field-effect transistor geometry displays a very high value of peak detectivity ∼9.33 × 1011Jones at ∼1500 nm with a relatively low dark current (∼20 pA), which is attributed to the fully depleted Si nanowire channel on SOI substrates. The noise power spectrum of the devices exhibits a1/fγ,with the exponent,γshowing two different values of 0.9 and 1.8 owing to mobility fluctuations and generation-recombination of carriers, respectively. Ge QD-decorated nanowire devices exhibit a novel polarization anisotropy with a remarkably high photoconductive gain of ∼104. The superior performance of a Ge QDs/Si nanowire phototransistor in IR wavelengths is potentially attractive to integrate electro-optical devices into Si for on-chip optical communications.

WS2 Nanosheet/Si p–n Heterojunction Diodes for UV–Visible Broadband Photodetection

Abstract: High-quality, continuous transition-metal dichalcogenide (TMD) thin films with large-area coverage are the prerequisites for practical device applications. To address the growing demand, here we re...

MoSe2–Cu2–xS/GaAs Heterostructure-Based Self-Biased Two Color-Band Photodetectors with High Detectivity

Abstract: Two-dimensional (2D) MoSe2–Cu2–xS nanocomposite-based heterojunction two color-band photodetectors on n-type GaAs have been fabricated and are reported for the first time. MoSe2–Cu2–xS nanocomposit...

Solution-Processed Black-Si/Cu2ZnSnS4 Nanocrystal Heterojunctions for Self-Powered Broadband Photodetectors and Photovoltaic Devices

Abstract: We report, for the first time, the fabrication of n-black Si (B–Si)/p-Cu2ZnSnS4 nanocrystal (CZTS NC) heterojunctions to demonstrate their photodetection and photovoltaic characteristics Inks with

MoSe2 Nanosheets with Tuneable Optical Properties for Broadband Visible Light Photodetection

Abstract: Full exploitation of two-dimensional (2D) semiconducting MoSe2, an exciting 2D transition-metal dichalcogenide, in optoelectronics is hampered because of dearth of scalable production methods. Here...

Electron-hole plasma formation dynamics observed through exciton-plasma interactions in transition metal dichalcogenides

Abstract: How do the many-particle interactions evolve in semiconductors is crucial for understanding light-matter interactions. We observe Coulomb-correlated electron-hole plasma formation via its interaction with excitons in a transition metal dichalcogenide semiconductor. We observe that under intense photoexcitation $\ensuremath{\sim}{10}^{19}$ per ${\mathrm{cm}}^{3}$, huge damping destroys the Coulomb correlation and hinders the plasma formation until a majority of the free carriers recombine and the plasma oscillation period becomes sufficiently smaller than the damping time constant. Moreover, only 1%--3% of the injected free carriers form Coulomb-correlated plasma. Our study sheds light on exciton-plasma interactions and quasistatic Coulomb screening, which play pivotal roles in device engineering.

Observation of dynamic screening in the excited exciton states in multilayered MoS 2

Abstract: Excitonic resonance and binding energies can be altered by controlling the environmental screening of the attractive Coulomb potential. Although this screening response is often assumed to be static, the time evolution of the excitonic quasiparticles manifests a frequency dependence in its Coulomb screening efficacy. In this paper, we investigate a ground (1s) and first excited exciton state (2s) in a multilayered transition metal dichalcogenide $({\mathrm{MoS}}_{2})$ upon ultrafast photoexcitation. We explore the dynamic screening effects on the latter and show its resonance frequency is the relevant frequency at which screening from the smaller-sized 1s counterparts is effective. Our finding sheds light on new avenues of external tuning on excitonic properties.

Two-dimensional ReS2: Solution to the unresolved queries on its structure and inter-layer coupling leading to potential optical applications

Abstract: Over the last few years, $\mathrm{Re}{\mathrm{S}}_{2}$ has generated a myriad of unattended queries regarding its structure, the concomitant thickness-dependent electronic properties, and its apparently contrasting experimental optical response. In this paper, with elaborate first-principles investigations, using density functional theory (DFT) and time-dependent DFT, we identify the structure of $\mathrm{Re}{\mathrm{S}}_{2}$, which is capable of reproducing and analyzing the layer-dependent optical response. The theoretical results are further validated by an in-depth structural, chemical, optical, and optoelectronic analysis of the large-area $\mathrm{Re}{\mathrm{S}}_{2}$ thin films, grown by the chemical vapor deposition (CVD) process. Micro-Raman, x-ray photoelectron spectroscopy, cross-sectional transmission electron microscopy, and energy-dispersive x-ray analysis have enabled the optimization of the uniform growth of the CVD films. The correlation between the optical and electronic properties was established by static photoluminescence and excited state transient absorption measurements. Sulfur vacancy-induced localized mid-gap states render a significantly long lifetime of the excitons in these films. The ionic gel top-gated photodetectors, fabricated from the as-prepared CVD films, exhibit a large photo-response of $\ensuremath{\sim}5$ A/W and a remarkable detectivity of $\ensuremath{\sim}{10}^{11}$ Jones. The outcome of this paper will be useful in promoting the application of vertically grown large-area films in the field of optics and opto-electronics.

Nanoceutical Fabric Prevents COVID-19 Spread through Expelled Respiratory Droplets: A Combined Computational, Spectroscopic and Anti-microbial Study

Abstract: Centers for Disease Control and Prevention (CDC) warns the use of one-way valves or vents in free masks for potential threat of spreading COVID-19 through expelled respiratory droplets. Here, we have developed a nanoceutical cotton fabric duly sensitized with non-toxic zinc oxide nanomaterial for potential use as membrane filter in the one way valve for the ease of breathing without the threat of COVID-19 spreading. A detailed computational study revealed that zinc oxide nanoflowers (ZnO NF) with almost two-dimensional petals trap SARS-CoV-2 spike proteins, responsible to attach to ACE-2 receptors in human lung epithelial cells. The study also confirm significant denaturation of the spike proteins on the ZnO surface, revealing removal of virus upon efficient trapping. Following the computational study, we have synthesized ZnO NF on cotton matrix using hydrothermal assisted strategy. Electron microscopic, steady-state and picosecond resolved spectroscopic studies confirm attachment of ZnO NF to the cotton (i.e., cellulose) matrix at atomic level to develop the nanoceutical fabric. A detailed antimicrobial assay using Pseudomonas aeruginosa bacteria (model SARS-CoV-2 mimic) reveals excellent anti-microbial efficiency of the developed nanoceutical fabric. To our understanding the novel nanoceutical fabric used in one-way valve of a face mask would be the choice to assure breathing comfort along with source control of COVID-19 infection. The developed nanosensitized cloth can also be used as antibacterial/anti CoV-2 washable dress material in general. GRAPHICAL ABSTRACT O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY A novel nanoceutical cotton fabric duly sensitized with non-toxic zinc oxide nanoflower can potentially be used as membrane filter in the one way valve of face mask to assure breathing comfort along with source control of COVID-19 infection. The nanoceutical fabric denatures the SARS-CoV-2 spike protein and makes the microorganism ineffective.

Development of Triboelectroceutical Fabrics for Potential Applications in Self-Sanitizing Personal Protective Equipment

Abstract: Attachment of microbial bodies including the corona virus on the surface of personal protective equipment (PPE) is found to be potential threat of spreading infection. Here, we report the development of a triboelectroceutical fabric (TECF) consisting of commonly available materials, namely, nylon and silicone rubber (SR), for the fabrication of protective gloves on the nitrile platform as model wearable PPE. A small triboelectric device (2 cm × 2 cm) consisting of SR and nylon on nitrile can generate more than 20 V transient or 41 μW output power, which is capable of charging a capacitor up to 65 V in only ∼50 s. The importance of the present work relies on the TECF-led antimicrobial activity through the generation of an electric current in saline water. The fabrication of TECF-based functional prototype gloves can generate hypochlorite ions through the formation of electrolyzed water upon rubbing them with saline water. Further, computational modelling has been employed to reveal the optimum structure and mechanistic pathway of antimicrobial hypochlorite generation. Detailed antimicrobial assays have been performed to establish effectiveness of such TECF-based gloves to reduce the risk from life-threatening pathogen spreading. The present work provides the rationale to consider the studied TECF, or other materials with comparable properties, as a material of choice for the development of self-sanitizing PPE in the fight against microbial infections including COVID-19. © 2021 American Chemical Society.

Substrate Dependent Synergistic Many-Body Effects in Atomically Thin Two Dimensional WS$_2$.

Abstract: Mott transition has been realized in atomically thin monolayer (ML) of two dimensional semiconductors (WS$_2$) via optically excited carriers above a critical carrier density through many body interactions. The above nonlinear optical transition occurs when excited electron hole pairs in ML WS2 continuum heavily interact with each other followed by transformation into a collective electron hole plasma phase (EHP), by losing their identity as individual quasiparticles. This is manifested by the alluring red-shift-blue-shift crossover (RBC) phenomena of the excitonic peaks in the emission spectra, resulting from the synergistic attraction-repulsion processes at the Mott-transition point. A systematic investigation of many-body effects is reported on ML WS$_2$, while considering the modulated dielectric screening of three different substrates, viz., silicon dioxide, sapphire, and gold. Substrate doping effects on ML WS$_2$ are discussed using the Raman fingerprints and PL spectral weight, which are further corroborated using theoretical DFT calculations. Further the substrate dependent excitonic Bohr radius of ML WS$_2$ is extracted via modelling the emission energy shift with Lennard-Jones potential. The variation of Mott point as well as excitonic Bohr radius is explained via substrate induced dielectric screening effect for both the dielectric substrates, which is however absent in ML WS$_2$ on Au. Our study therefore reveals diverse many-body ramifications in 2D semiconductors and offers decisive outlooks on selecting the impeccable substrate materials for innovative device engineering.

Two-Dimensional Material-Based Quantum Dots for Wavelength-Selective, Tunable, and Broadband Photodetector Devices

Abstract: The rise of atomically thin two-dimensional (2D) materials brings a revolution in material science and engineering, and encouraged worldwide scientists to integrate desired 2D materials into electrical circuitry by non-covalent interactions. Regardless of some unique properties including super-flexibility, broadband absorption and high carrier mobility, the weak optical absorption due to the thinness of 2D layers restricts their commercial use for photodetection. On contrary, quantum dot (QD) of 2D materials can overcome the weak absorption problem due to the strong quantum confinement, high absorption coefficient combined with the superlative features and properties of 2D layers. Therefore, 2D QDs have become a powerful contender for next-generation photodetection technology. Moreover, bandgap engineering by controlling the QD size due to strong quantum confinement and further integration with other materials are the most adaptable strategy to design high-performance, wavelength-tunable multicolour photodetector devices. It should be noted that the optical sensing for the infrared spectral region is of paramount importance in recent years, for many applications, especially environmental monitoring, security camera, military application, etc., but such applications in 2D-based QDs are limited. Alternatively, QD-based photodetector fabrication strategies such as epitaxial growth, heterostructure integration, functionalization and colloidal synthesis became mature from a material science perspective to achieve a broad spectral tunability. This chapter provides a comprehensive summary over the latest scientific and technological progress of QD-based photodetectors fabricated for the ultraviolet to infrared regime using van der Waals (vdW) materials, focusing mainly on carbon-based QDs, transition metal dichalcogenides (TMDCs) and black phosphorus (BP) QDs. We first start with the structural and optical properties of various 2D QDs. Secondly, the several strategies to synthesize 2D QDs and the different state-of-the-art device fabrication technology to improve the device performance have been described by addressing the inherent critical challenges. Thereafter, a brief but essential survey of emerging 2D QDs and their on-chip integration with other semiconductors in heterostructure form for photodetection application have been discussed. Finally, the chapter summarizes the comparison of performance of several 2D QD-based photodetectors highlighting the underlying challenges and opportunities for the future development of vdW QD-based research to realize their industrial scale-up.

Room Temperature Detection of Formaldehyde with Economical and Ecofriendly Graphene Quantum Dot Ink Treated Paper-Based Sensor

Abstract: Renewed interest for volatile organic compound (VOC) sensors using nanomaterials are increasing due to several limitations of existing commercially available sensors for healthcare, food quality, and environmental applications. A disposable, flexible, and room temperature, paper-based formaldehyde sensor has been developed using graphene quantum dot ink as the sensing material. The PEDOT:PSS conductive ink acts as an electrode on the porous paper substrate with graphene quantum dot ink as sensing material making the device novel, low cost, and potential candidate for large area roll to roll solution process-able formaldehyde sensors fabrication. The sensitivity is measured for a concentration varying from 7 to 20 ppm exposure of formaldehyde at ambient temperature at dry air condition. The sensor device shows a sensitivity of 0.26% at 15 ppm HCHO. The p-type GQDs reveal a resistance increment of the sensing film in presence of reducing gas HCHO, which is explained using charge transfer dynamics between sensing film and HCHO molecules. The finding may lead to new opportunities in flexible formaldehyde sensors operating at room temperature for healthcare applications.

Two-dimensional ReS2: Solution to the Unresolved Queries on Its Structure and Inter-layer Coupling Leading to Potential Optical Applications

Abstract: Over the last few years, ReS2 has generated a myriad of unattended queries regarding its structure, the concomitant thickness dependent electronic properties and apparently contrasting experimental optical response. In this work, with elaborate first-principles investigations, using density functional theory (DFT) and time-dependent DFT (TDDFT), we identify the structure of ReS2, which is capable of reproducing and analyzing the layer-dependent optical response. The theoretical results are further validated by an in-depth structural, chemical, optical and optoelectronic analysis of the large-area ReS2 thin films, grown by chemical vapor deposition (CVD) process. Micro-Raman (MR), X-ray photoelectron spectroscopy (XPS), cross-sectional transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDAX) have enabled the optimization of the uniform growth of the CVD films. The correlation between the layer-dependent optical and electronic properties of the excited states was established by static photoluminescence (PL) and transient absorption (TA) measurements. Sulfur vacancy-induced localized mid-gap states render a significantly long life-time of the excitons in these films. The ionic gel top-gated photo-detectors, fabricated from the as-prepared CVD films, exhibit a large photo-response of ~ 5 A/W and a remarkable detectivity of ~ 1011 Jones. The outcome of the present work will be useful to promote the application of vertically grown large-area films in the field of optics and opto-electronics.

High Responsivity Gate Tunable UV-Visible Broadband Phototransistor Based on Graphene-WS2 Mixed Dimensional (2D-0D) Heterostructure

Abstract: Recent progress in the synthesis of highly stable, eco-friendly, cost-effective transition metal-dichalcogenides (TMDC) quantum dots (QDs) with their broadband absorption spectrum and wavelength selectivity features have led to their increasing use in broadband photodetectors. With the solution based processing, we demonstrate a super large (~ 0.75 mm^2), UV-Vis broadband (365-633 nm), phototransistor made of WS_2 QDs decorated CVD graphene as active channel with extraordinary stability and durability in ambient condition (without any degradation of photocurrent till 4 months after fabrication). Here, colloidal 0D WS_2-QDs are used as the photo absorbing material and graphene acts as the conducting channel. A high photoresponsivity (3.1 x 10^2 A/W), higher detectivity (2.2 x 10^12 Jones) and low noise equivalent power (4 x 10^{-14} W/Hz^0.5) are obtained at a low bias voltage (V_{ds} = 1V) at an illumination of 365 nm with an optical power as low as 0.8 \mu W/cm^2, which can further be tuned by modulating the gate bias. While comparing the photocurrent between two different morphologies of WS_2 (QDs and 2D nanosheets), a significant enhancement of photocurrent is observed in case of QDs based device. Ab initio density functional theory based calculations further support our observation, revealing the role of quantum confinement for the enhanced photo response. Our work reveals a strategy towards making a scalable, cost-effective, highly performing hybrid two-dimensional (2D/0D) photo detector with graphene-WS_2 QDs, paving the way towards the next generation optoelectronic applications.

Development of Tribo-Electroceutical Fabrics for Potential Application in Self-sanitizing Personal Protective Equipment (PPE)

Abstract: Attachment of microbial bodies including coronavirus on the surface of personal protective equipment (PPE) is found to be potential threat of spreading infection. Here, we report the development of a novel tribo-electroceutical fabric (TECF) consisting of commonly available materials namely Nylon, and Silicone Rubber (SR) for the fabrication of protective gloves on Nitrile platform, as a model wearable PPE. A small triboelectric device (2 cm x 2 cm) consisting of SR and Nylon on Nitrile can generate more than 20 volt transient or 41 {micro}W output power, which is capable of charging a capacitor up to 65 V in only [~]50 sec. The novelty of the present work relies on the TECF led anti-microbial activity through the generation of an electric current in saline water. The fabrication of TECF based functional prototype gloves can generate hypochlorite ions through the formation of electrolysed water upon rubbing them with saline water. Further a computational modelling has been employed to reveal the optimum structure and mechanistic pathway of anti-microbial hypochlorite generation. Detailed anti-microbial assays have been performed to establish effectiveness of such TECF based gloves to reduce the risk from life threatening pathogen spreading. The present work provides the rationale to consider the studied TECF, or other material with comparable properties, as material of choice for the development of self-sanitizing PPE in the fight against microbial infections including COVID-19.