Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
7 results
Search Results
Item Growth of Very Large MoS2Single Crystals Using Out-Diffusion Transport and Their Use in Field Effect Transistors(Institute of Electrical and Electronics Engineers Inc., 2021) Pandey, S.K.; Izquierdo, N.; Campbell, S.Monolayer molybdenum disulfide (MoS2) is an attractive 2D material with a wide range of potential applications in the field of electronics and optoelectronics. To obtain the best performance, it is very necessary to grow large area single crystals of MoS2 (single domain) to avoid the effects of grain boundaries, but is exceptionally challenging to do this. Here, we report a novel method which we call out-diffusion vapor transport to grow large area single crystal monolayer MoS2 using an otherwise conventional chemical vapor deposition system. In this method, microchannels were created on the boat to significantly limit the region where MoOx vapor can react with S vapor to form crystals. This growth method resulted in triangular monolayer MoS2 single crystals up to ?640 ?m on a side grown on an oxidized silicon substrate, the largest crystals reported to date. Most of these crystals were multilayer at the center. This common feature has been identified in the literature as partially reduced transition metal oxide nucleates a second layer. We also achieved fully monolayer MoS2 single crystals up to ?450 ?m on a side, the largest demonstrated without the MoOx. Fabricated field effect transistors (FET) using MoS2 monolayer crystal as the active layer demonstrate a conventional n-type behavior, room-temperature mobility up to 45.5 cm2 V-1 s-1 and a maximum ON-Current (ION)/OFF-current (IOFF) ratio of 1.8 × 107. Raman and Photoluminescence results indicate that the as-grown large area monolayer crystals have high crystalline quality and uniformity with minimal defects, a finding that is consistent with the high electron mobility. This research work provides a superior technique to grow large-area high-quality single-crystal monolayer MoS2 without resorting to exotic equipment or techniques. © 2002-2012 IEEE.Item Large and Uniform Single Crystals of MoS2Monolayers for ppb-Level NO2Sensing(American Chemical Society, 2022) Patel, C.; Singh, R.; Dubey, M.; Pandey, S.K.; Upadhyay, S.N.; Kumar, V.; Sriram, S.; Than Htay, M.; Pakhira, S.; Atuchin, V.V.; Mukherjee, S.Recently, unprecedented interest has been immersed toward the synthesis of two-dimensional (2D) transition metal dichalcogenides via the chemical vapor deposition (CVD) system. Synthesis of a uniform and large-sized monolayer MoS2atomic thin film via CVD is still a major bottleneck owing to strong dependence on diverse associated growth parameters. In this work, we have proposed the most viable recipe which is suitable for controlling the nucleation density of Mo and producing a 90 μm-long MoS2monolayer crystal and (695 × 394.8) μm2large MoS2monolayered film on SiO2/Si and c-plane sapphire, respectively. Moreover, MoS2monolayer sensing performance has been thoroughly investigated for NO2exposure at room temperature with a varying response of 4-57.5 for the 100-100 ppm level. Furthermore, the MoS2monolayer sensor exhibits an ultrasensitive NO2detection with limit of detection and limit of qualification values of 1.4 and 4.6 ppb, respectively. In addition, the first-principles-based density functional theory has been employed to analyze the adsorption of NO2on the surfaces of the 2D MoS2monolayer. It is observed that the electronic band gap of the MoS2monolayer after NO2adsorption is reduced by 0.7 eV due to molecular orbital hybridization. © 2022 American Chemical Society. All rights reserved.Item Effect of Introducing Defects and Doping on Different Properties of Monolayer MoS2(John Wiley and Sons Inc, 2023) Prajakta, K.; Vinturaj, V.P.; Singh, R.; Garg, V.; Pandey, S.K.; Pandey, S.K.Herein, the comprehensive study of different properties of undoped MoS2, MoS2 lattice with sulfur (S) and, molybdenum (Mo) vacancy, and MoS2 with substitutional doping of niobium (Nb), vanadium (V), and zinc (Zn) atoms is done. The density functional theory (DFT) is used and the electronic properties like density of states, band structure, electron density, and optical properties like dielectric function, optical conductivity, and refractive index are studied. It is observed that undoped MoS2 monolayer shows direct bandgap semiconductor characteristics with a bandgap of around 1.79 eV. P-type characteristics are observed for Nb-, V-, and Zn-doped MoS2 lattices. The real part and imaginary parts of all optical parameters along x and z directions for different MoS2 supercells are found to be anisotropic in nature up to a photon energy of almost 11 eV and thereafter they show nearly isotropic nature. Finally, it is found that the obtained properties of MoS2 monolayer as per literature are suitable for next-generation MOSFET application. © 2023 Wiley-VCH GmbH.Item Theoretical investigation of electronic and optical properties of doped and defective MoSe2 monolayers(Springer, 2023) Vinturaj, V.P.; Yadav, A.K.; Jasil, T.K.; Kiran, G.; Singh, R.; Singh, A.K.; Garg, V.; Pandey, S.K.In this work, we have investigated the various electronic and optical properties of undoped molybdenum diselenide (MoSe2) monolayer, such as band structure, density of states, electron density, dielectric function, refractive index, extinction coefficient, reflectivity and energy loss function using density functional theory. Additionally, substitutional doping using niobium (Nb) and manganese (Mn) atoms and introducing defects in undoped MoSe2 lattice were investigated to know the detailed effect of the same on its properties. It is found that the undoped MoSe2 monolayer demonstrates a direct energy bandgap of ~1.44 eV, which reduces after Mn, Nb doping and after introducing Mo, Se vacancy. The energy bandgap attains a very small value 0.2 eV after introducing Se vacancy defect in MoSe2 lattice. The extinction coefficient of MoSe2 monolayer demonstrates a significant increase from 1.79 to 2.66 a.u. after introducing the Mo vacancy in the undoped lattice. The variation of semiconductor to nearly semi-metallic character of MoSe2 by introducing defects makes it very suitable for the application in high-performance solar cells, photo-electrochemical cells, sensors and biosensor applications. © 2023, Indian Academy of Sciences.Item DFT Calculations for Temperature Stable Quantum Capacitance of VS2 Based Electrodes for Supercapacitors(Institute of Electrical and Electronics Engineers Inc., 2024) Yadav, A.K.; Shreevathsa, N.S.; Singh, R.; Das, P.P.; Garg, V.; Pandey, S.K.Using density functional theory calculations, we demonstrate the quantum capacitance of the VS2 electrode which can be improved by doping with non-metallic elements such as nitrogen (N), phosphorus (P), and arsenic (As) atoms. The radius, charge, and morphology of these non-metallic elements help to improve the performance of VS2 material as electrodes of supercapacitors. The As-doped VS2 monolayer demonstrated the maximum quantum capacitance of 31.2369 μF/cm2 at 300 K. At 1200 K, quantum capacitance reaches the value of 25.2149 μF/cm2, showing the inconsiderable change in value for this wide range of temperature variation. Additionally, the other important properties of undoped and doped VS2 monolayers such as density of states, energy band structure, electrical conductivity, thermal conductivity, and the Seebeck coefficient were also computed and examined in detail. The band structure of the P and As-doped VS2 monolayers showed a metallic nature, which is suitable for electrode application. In the case of As-doped VS2 material, a high figure of merit of 3.536 was observed by using DFT-D2 calculations, due to the large Seebeck coefficient and significant electrical conductivity. Our findings will be helpful in further exploring the suitability of VS2 monolayers as electrodes of supercapacitors. © 2002-2012 IEEE.Item Enhancement of Functionalized 1T-NbS2 Monolayer Properties for the Superior Anode of Na-Ion Batteries(Institute of Electrical and Electronics Engineers Inc., 2025) Jasil, T.K.; Yadav, A.K.; Maurya, G.K.; Garg, V.; Pandey, S.K.One of the most important factors influencing the performance of Na-ion batteries (NIBs) is the anode’s quality. Currently, NIB anodes have numerous disadvantages, including low capacity, rapid volume change, temperature variable conductivity and poor thermal/chemical stability. In this work, the electronic and transport properties of undoped, doped and defective 1T-NbS2 monolayers were investigated using density functional theory calculations. The maximum quantum capacitance of 1T-NbS2 with S-vacancy (VS-NbS2) changes from 20.49 to 16.92 ?F/cm2 across temperature ranges of 200 K to 1000 K, indicating its suitability as anode with temperature-stable capacity. The 1T-NbS2 monolayers exhibit high electrical conductivity with less than 6% fluctuation across a temperature range of 200 K to 1000 K, indicating thermally stable conductance. The 1T-NbS2 layered structure has substantially larger interlayer spacing of 0.615 nm than the size of Na ion (0.095 nm), as well as a relatively tiny variation (0.05 eV for VS-NbS2) in cohesive energies between sodiated and de-sodiated phases, making it a good choice for anodes. For VS-NbS2, the seebeck coefficient ranges from -5 to -40 ?V/K, which is often obtained by the most commonly used Na-metal anode, demonstrating its appropriateness as anode. According to our findings, 1T-NbS2 is a great option for thermally stable NIB electrode applications. © 2002-2012 IEEE.Item Optimization of the Properties of Functionalized BC3 Monolayer for Superior Electrode of Solid-State Sodium-Ion Batteries(John Wiley and Sons Inc, 2025) Vudumula, K.; Yadav, A.K.; Maurya, G.K.; Singh, R.; Nikhil, K.S.; Pandey, S.K.Solid-state batteries offer superior safety, high energy density, and the ability to function effectively across a wide range of temperatures. Sodium-ion (Na-ion) solid-state batteries are a promising alternative to lithium-ion batteries due to sodium's abundance and low cost. A high-quality electrode is crucial for achieving high performance in Na-ion batteries. In this study, structural stability, electronic properties, and performance of functionalized hexagonal boron carbide (BC3) are investigated for ultrathin electrodes using density functional theory (DFT). The effective adsorption of Li, Na, K, and Mg atoms at the BC3 surface is also investigated. The BC3 monolayer has a ?0.8 eV indirect bandgap, which becomes metallic after Na adsorption, making it suitable for electrode applications. Additionally, the Na-adsorbed BC3 monolayer shows the lowest adsorption energy (?1.2 eV), which is the most stable lattice structure among others. The Na-adsorbed BC3 demonstrated a theoretical capacity of 1152 mAh g?1, which is comparable with the Li-adsorbed electrode. Moreover, the Na-adsorbed BC3 electrode shows a very small variation (0.18 V) for open circuit voltage (OCV), indicating this electrode is robust in terms of voltage stability. These findings show that the functionalized BC3 ultrathin electrode is very suitable for the electrode of Na-ion solid-state batteries. © 2025 Wiley-VCH GmbH.