Browsing by Author "Suyash Rai"

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2D materials for flexible electronics
(Elsevier, 2022) Suyash Rai; Himanshu Mishra; Vijay K Singh; Tejendra K Gupta; Anchal Srivastava
Since the breakthrough of graphene, two-dimensional (2D) materials have attracted immense research interest due to their unique electronic, optical, and mechanical properties, holding great potential for harnessing their applications in next-generation electronics, optoelectronics, and biomedical fields. The most striking feature of 2D materials is their atomic thickness, which makes them feasible to adhere to any kind of surface without losing much of their inherent properties. With this advantage, 2D materials can be integrated into various flexible and stretchable electronic devices in a conventional and scalable fashion. Here in this chapter the synthesis of 2D materials using different top-down and bottom-up methods followed by various efficient transfer methods has been discussed thoroughly. After that, state-of-the-art flexible device applications of 2D materials in electronics, sensors, and energy storage devices, along with their future possibilities, are discussed. © 2023 Elsevier Ltd. All rights reserved.
2D SnS2 Nanostructure-Derived Photocatalytic Degradation of Organic Pollutants Under Visible Light
(Frontiers Media S.A., 2021) Rohit Ranjan Srivastava; Pramod Kumar Vishwakarma; Umakant Yadav; Suyash Rai; Sima Umrao; Rajiv Giri; Preeti Suman Saxena; Anchal Srivastava
Wastewater produced by the textile industry contains various dyes and organic compounds that directly or indirectly affect surface water or groundwater pollution. Visible-light-driven semiconductor photocatalysis is the leading pathway for the degradation of environmental pollutants. Herein we report the bottom-up hydrothermal growth of 2D tin disulfide nanostructures (SnS2 NSs) for the efficient photodegradation of organic pollutants such as Rhodamine B (Rh.B) and Methyl Violet (M.V) in an aqueous medium under visible light (λ > 400 nm) irradiation. The as-synthesized SnS2 NSs were characterized by various structural, morphological, and optical techniques such as XRD, RAMAN, TEM, UV–Vis, Brunauer–Emmett–Teller, etc. Furthermore, the low bandgap (∼1.6 eV), the high surface area (56 m2/g), and the anionic nature of SnS2 NSs attribute to it as an efficient photocatalyst for photocatalytic applications. The photocatalytic properties of SnS2 NSs showed good degradation efficiency of 94 and 99.6% for Rh. B and M.V, respectively, in 25 min. The kinetic rate constant of these dyes was estimated by using the Langmuir–Hinshelwood model. Here we also performed the recyclability test of the photocatalyst and discussed the plausible mechanism for the photocatalytic degradation of organic pollutants. The XPS spectra of SnS2 NSs were studied before and after the photodegradation of Rh.B and M.V, indicating the high stability of the photocatalyst. Moreover, in vitro cytotoxicity was also evaluated against human cervical cancer cell lines (HeLa cells) with different concentrations (0–1,000 μg/ml) of as-synthesized SnS2 NSs. This intended work provides a possible treatment for the degradation of organic pollutants under visible light to balance the aquatic ecosystems. Copyright © 2021 Srivastava, Kumar Vishwakarma, Yadav, Rai, Umrao, Giri, Saxena and Srivastava.
A comprehensive review on graphene-based materials as biosensors for cancer detection
(Oxford University Press, 2023) Rim M. Alsharabi; Suyash Rai; Hamed Y. Mohammed; Maamon A. Farea; Sesha Srinivasan; Preeti S. Saxena; Anchal Srivastava
Nowadays, cancer is increasingly becoming one of the foremost threats to human being life worldwide, and diagnosing this deadly disease is one of the major priorities of researchers. Described as a monolayer-thin-sheet of hexagonally patterned carbon atoms, ‘graphene’ is considered an innovative evergreen carbon material ideal for a wide array of sensing applications and nanotechnologies. Graphene-based materials (GBMs) have acquired a huge share of interest in the scope of biosensor fabrication for early and accurate cancer diagnosis. Herein, we have insights reviewed the various routes and technologies for synthesized graphene, and GBMs including 3D graphene (i.e. hydrogels, foams, sponges and porous) and 0D graphene (i.e. quantum dots). Moreover, we have introduced the different types of graphene/GBMs biosensors (i.e. electrochemical biosensors, optical biosensors, field-effect transistors biosensors, electrochemiluminescence biosensors and microfluidics biosensors) and their merits and applications for cancer prestage detection. © The Author(s) 2022. Published by Oxford University Press.
A Lithography-Free Fabrication of Low-Operating Voltage-Driven, Very Large Channel Length Graphene Field-Effect Transistor with NH3Sensing Application
(Institute of Electrical and Electronics Engineers Inc., 2020) Nitesh K. Chourasia; Abhishek Kumar Singh; Suyash Rai; Anand Sharma; P. Chakrabarti; Anchal Srivastava; Bhola N. Pal
Large-area-based field-effect transistor (FET) gas sensor has the potential to provide a larger sensing area for a chemical analyte. So far, graphene FETs (GFETs) are mostly fabricated by expensive lithographic techniques with a minimum channel length. We have demonstrated a simple way to fabricate a very large channel length of 0.45 mm GFET using ion-conducting dielectric with thermally evaporate source/drain electrodes and has been demonstrated for an application of ambient atmosphere ammonia gas sensing. Ion-conducting Li5AlO4 gate dielectric has reduced operating voltage up to 2.0 V with good current saturation. The chemical vapor deposition (CVD) grown uniform monolayer of graphene has been used as an active channel layer of FET. The fabricated device has been tested for different concentrations of ammonia in ambient environment conditions at 25 °C temperature, which indicates that the Dirac point voltage of the device varies up to 0.8 V when the concentration of ammonia has been changed from 0 to 3 ppm. Moreover, this study also reveals that this GFET is capable of detecting ammonia up to the concentration level of 0.1 ppm. © 1963-2012 IEEE.
A novel approach for rapid and sensitive detection of Zika virus utilizing silver nanoislands as SERS platform
(Elsevier B.V., 2023) Manish Nath Tripathi; Poonam Jangir; Aakriti; Suyash Rai; Mayank Gangwar; Gopal Nath; Preeti S. Saxena; Anchal Srivastava
To control the spread of the disease, the Zika virus (ZIKV), a flavivirus infection spread by mosquitoes and common in across the world, needs to be accurately and promptly diagnosed. This endeavour gets challenging when early-stage illnesses have low viral loads. As a result, we have created a biosensor based on surface-enhanced Raman scattering (SERS) for the quick, accurate, and timely diagnosis of the Zika virus. In this study, a glass coverslip was coated with silver nanoislands, which were then utilized as the surface for creating the sensing platform. Silver nanoislands exhibit strong plasmonic activity and good conductive characteristics. It enhances the Raman signals as a result and gives the SERS platform an appropriate surface. The created platform has been applied to Zika virus detection. With a limit of detection (LOD) of 0.11 ng/mL, the constructed sensor exhibits a linear range from 5 ng/mL to 1000 ng/mL. Hence, even at the nanogram scale, this technique may be a major improvement over clinical diagnosis approaches for making proper, precise, and accurate Zika virus detection. © 2023 Elsevier B.V.
Characterizations of nanoscale two-dimensional materials and heterostructures
(Elsevier, 2020) Anchal Srivastava; Chandra Shekhar Pati Tripathi; Vijay Kumar Singh; Rohit Ranjan Srivastava; Sumit Kumar Pandey; Suyash Rai; Ravi Dutt; Amit Kumar Patel
In recent years, two-dimensional (2D) atomically thin crystals ranging from insulator to superconductor such as graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDs), etc. have attracted extensive attention due to their exceptional properties and many potential applications in various areas. In this chapter we focus on the experimental characterization of 2D materials and their heterostructures andcover brief introduction and detailed structural, optical, and chemical characterizations of some important 2D materials. © 2020 Elsevier Inc.
Functionalized WS2 Quantum Dots as Fluorescent Nanoprobes for In Vivo Bioimaging
(American Chemical Society, 2023) Suyash Rai; Vijay K. Singh; Brijesh Singh Chauhan; S. Srikrishna; Preeti S. Saxena; Anchal Srivastava
The strong fluorescence and high photostability of inorganic quantum dots (QDs) have envisaged them as superior fluorescent probes for biomedical imaging applications compared to organic dyes that are highly prone to photobleaching. However, earlier reports suggest that the potential use of inorganic QDs can be ensured only if they remain fluorescent and stably dispersed in water and other biological fluids under a wide pH range. In the present work, we address in detail the influence of pH (range 1.0-13.0) on the photophysical properties of functionalized tungsten disulfide QDs (f-WS2-QDs) synthesized using a facile, eco-friendly, and single-step hydrothermal approach. Experimental findings suggest that the fluorescence nature of as-produced f-WS2-QDs remains highly stable in harsh acidic to basic media. The PL stability and dispersion of f-WS2-QDs in aqueous media are explained in terms of various functional groups present over the QDs’ surface, which causes surface passivation of the QDs during hydrothermal growth leading to the high solubility and stable fluorescence of QDs in aqueous media. Furthermore, as a proof of concept, we have also demonstrated that the f-WS2-QDs could be potentially used as a fluorescent probe for high-contrast in vivo imaging of Drosophila third instar larvae. Thus, we anticipate that the present investigation may provide insight into the scientific community for the development of pH-universal inorganic QDs for biological applications. © 2023 American Chemical Society.
Low-temperature photoluminescence and Raman study of monolayer WSe2 for photocarrier dynamics and thermal conductivity
(American Institute of Physics, 2024) Suyash Rai; Anchal Srivastava
Low-temperature PL analysis reveals an intriguing temperature-dependent emission pattern in WSe2: excitonic dominance above the 150 K Debye temperature, a balance between excitonic and trionic emissions at 150 K, and trionic dominance below this threshold. At lower temperatures, both excitons and trions display linearly polarized emissions, with polarization increasing from 0% at 300 K to 23% (excitons) and 7% (trions) at 150 K, and 12% for trions at 90 K. Moreover, the synthesized monolayer of WSe2 exhibits high thermal conductivity (246 W m−1 K−1 for A 1 g and 185 W m−1 K−1 for E 2 g 1 modes). This property is attributed to Se vacancies and defects at triangle edges, which redirect phonons, reducing scattering and enabling efficient heat transport along boundaries. The unveiling of these novel insights within the synthesized 2D WSe2 material holds significant promise for its potential applications in nano-optoelectronics. Its demonstrated efficiency in dissipating heat, coupled with improved thermal stability, suggests the possibility of employing it in future devices. This could facilitate compact designs and the miniaturization of advanced technological tools, showcasing the material's potential for practical implementation. © 2024 Author(s).
Magnetic response of monolayer H-phase VS2 nanosheets at room temperature: Implications for spintronics device
(Taiwan Institute of Chemical Engineers, 2025) Amit Kumar Patel; Suyash Rai; Sajal Rai
Background: Transition metal dichalcogenides (TMDs), explicitly monolayer vanadium disulfide (VS2) in its H-phase, have gained remarkable attention due to their semiconducting nature, intrinsic magnetic properties at room temperature (RT), and potential use in future spintronic devices. Method: In this study, we report an optimized, simple, and scalable synthesis of monolayer H-phase VS2 crystal using an atmospheric pressure chemical vapor deposition (APCVD) technique. Significant findings: The Raman spectra and High-resolution transmission electron microscopy (HRTEM) image of the as-synthesized VS2 crystal reveal that the as-synthesized sample has an H-phase, and atomic force microscopy (AFM) confirms the presence of a monolayer with a step height of ∼ 0.7 nm. Further, the room temperature magnetic force microscopy (MFM) study gives a phase shift of 0.68° to 0.06° for the sample-tip variation from 20 nm to 140 nm in steps of 20 nm, suggesting an intrinsic long-range magnetic ordering in the as-synthesized VS2 crystal. The decrease in the MFM phase shift exhibits exponential dependence on the sample to AFM tip distance. Finally, our MFM phase shift measurement findings suggest a RT magnetic response in monolayer H-phase VS2 crystal. These results are much higher than the other previously reported MFM responses of metallic T-phase VS2, indicating robust experimental evidence for the magnetic behavior of monolayer H-phase VS2. Our study introduces a pathway to explore the opportunity for highly efficient future spintronic devices using 2D magnetic materials at RT. © 2025 Taiwan Institute of Chemical Engineers
Optimizing Large-Area Growth of MoS2Using Advanced Precursor Engineering: A Pathway to Scalable and High-Quality Synthesis
(American Chemical Society, 2025) Sajal Rai; Suyash Rai; Amit Kumar Patel; Anchal Srivastava
The chemical vapor deposition (CVD) for the growth of transition-metal dichalcogenides (TMDs) remains a significant focus of research due to the critical need for producing high-quality films on a large scale for various applications. The selection of starting materials for Mo and S sources plays a critical role in determining the layers and morphologies of MoS2 films. Different sources influence these aspects differently. Traditionally, most studies have relied on commercially available MoO3 powder and elemental sulfur, which often require high reaction temperatures and yield low efficiencies. In this research, MoS2 was synthesized using the CVD method, and its structural properties were analyzed by varying the growth temperature and precursors. Notably, synthesized h-MoO3 outperformed its commercial counterpart. Additionally, a novel precursor, Na2MoO4, was designed and used as a Mo source for the growth of MoS2. The findings revealed the successful synthesis of both monolayer triangular crystals and continuous 2D MoS2 films. The triangular 2D crystals, synthesized using h-MoO3, had an average size of 30–50 μm and a monolayer thickness of approximately 0.9 nm. When α-Na2MoO4 was employed as the Mo precursor, a continuous 2D film with a lateral size extending to the centimeter scale was achieved. Additionally, a model explaining the growth mechanism capable of producing TMD monolayers was proposed. © 2025 American Chemical Society
Unveiling the electrical and photo-physical properties of intrinsic n-type 2D WSe2for high performance field-effect transistors
(American Institute of Physics Inc., 2022) Suyash Rai; Vijay K. Singh; Rahul Pendurthi; Joseph R. Nasr; Saptarshi Das; Anchal Srivastava
Atomically thin semiconducting 2D transition metal dichalcogenides have garnered remarkable attention from the scientific community due to their prodigious contributions in the field of next-generation electronic and optoelectronic devices. In this continuation, we report a facile synthesis protocol of monolayer WSe2 films via the atmospheric-pressure chemical vapor deposition (APCVD) technique using hydrothermally synthesized hexagonal-phase tungsten oxide (h-WO3) nanorods. The as synthesized WSe2 crystal is a monolayer of ∼0.9 nm thickness as confirmed by atomic force microscopy. The confocal Raman and photoluminescence (PL) mapping suggests that the grown monolayer WSe2 triangles have lattice defects at edge sites, with a slight red-shift of ∼2 nm in PL, a blue-shift of ∼2 cm-1 in Raman peak and reduction in both the intensities. Confocal time-resolved PL mapping at edges reveals a fast-decay component of ∼582 ps and a slow-decay component of ∼2.18 ns that also signifies the presence of lattice defects, which serves as localized-states for photon-generated charge excitons. Furthermore, we have also investigated its electrical property by devising field-effect transistors (FETs). The fabricated WSe2 based FET shows intrinsic n-type behavior. WSe2 FET offers an electron mobility (μ) of ∼13.2 cm2 V-1 s-1, current ON/OFF ratio of ∼107 with a subthreshold slope (SS) of ∼397 mV/decade, which is relatable to the other reported works on WSe2 based FETs. In addition, the device exhibits very high on-current of order of ∼150 μA/μm. These results indicate that h-WO3 nanorod assisted APCVD synthesized WSe2 has prospective of being a competitor for next-generation optoelectronic, and valley-tronic devices. © 2022 Author(s).