Faculty Publications
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Item Growth optimization and DFT investigation of doping effect on properties of VS2 monolayer crystals(Springer Science and Business Media Deutschland GmbH, 2023) Yadav, A.K.; Patel, C.; Kiran, G.; Singh, R.; Singh, A.K.; Garg, V.; Mukherjee, S.; Pandey, S.K.The vanadium disulfide (VS2) material, a prominent member of the two-dimensional materials family, has great potential to bridge the performance gap between current performance and contemporary energy storage device needs. Here, we report the optimization of the growth temperature of VS2 monolayer crystals using a chemical vapor deposition system. It is also found the crystal size increases with the increase of growth temperature up to 770 °C. Further increasing of growth temperature resulted in a reduction of crystal size. The atomic force microscopy measurement demonstrated the growth of monolayer thick VS2 crystal. Raman spectra revealed the formation of H-phase monolayer high-quality VS2 crystals. To understand the precise impact of doping on electronic properties, the substitutional doping of VS2 monolayer with chromium, molybdenum, and tungsten was also examined using density functional theory. The VS2 monolayer exhibits an indirect energy band gap that decreases after chromium doping of the VS2 lattice and vanishes after molybdenum and tungsten doping. Finally, it is found that tungsten-doped VS2 monolayer exhibits strong metallic character and other exceptional properties, making it suitable for electrodes of various energy storage devices. Graphical abstract: [Figure not available: see fulltext.]. © 2023, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.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 Fabrication of 1T VS2 Electrode-Based In-Plane Micro-Supercapacitor Using a Cost-Effective Mask-Assisted Printing Technique(John Wiley and Sons Inc, 2023) Mandal, A.; Yadav, A.K.; Pandey, S.K.; Chakrabarti, S.Vanadium disulfide (VS2) is an important member of the transition-metal dichalcogenides (TMDs) family, which offers high conductivity. In nature, it can exist in two phases, i.e., 1T and 2H. Herein, the metallic 1T VS2-based in-plane micro-supercapacitor (MSC) is fabricated by a facile-mask-assisted printing technique. Initially, the 1T VS2 nanosheets are synthesized using a simple one-pot hydrothermal route. The material characterizations have claimed the formation of a 1T phase and the density of states (DOS) reveal that the 1T phase of VS2 is metallic in nature. After experimental and theoretical investigations of synthesized nanosheets, a VS2 electrode-based in-plane MSC is fabricated using a simple mask-assisted printing technique. The fabricated device demonstrates excellent capacitance retention of 97.6% after 1000 cycles of cyclic voltammetry measurement at a 100 mV s−1 scan rate. The device also shows an excellent areal capacitance of 212.7 mF cm−2 and a high areal energy density of 10.63 μWh cm−2 at a high-power density of 4.45 mW cm−2. This low-cost and simple fabrication process can produce high-performance in-plane MSC devices. © 2023 Wiley-VCH GmbH.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 Optimization of Quantum Capacitance of Functionalized VS2 Monolayer Electrodes to Shrink Hybrid Supercapacitors for On-Chip Energy Sources(American Chemical Society, 2025) Yadav, A.K.; Thiyyakkandy, J.; Singh, R.; Das, P.P.; Ajith, K.M.; Pandey, S.K.Quantum capacitance (CQ) of the electrodes plays an important role in enhancing the performance of supercapacitors by directly affecting the overall capacitance. In this study, several approaches including doping, creating vacancy, and adsorption have been used to enhance the CQ of the vanadium disulfide (VS2) electrode using density functional theory calculation. The undoped VS2 monolayer shows a maximum CQ value of 20.19 ?F/cm2. After creating V-vacancy (Vv) in the VS2 monolayer lattice, the CQ value increased to 35.61 ?F/cm2, which is the highest among all doped and defective VS2 lattices at room temperature. When we use VS2 electrodes for supercapacitors, generally ion adsorption occurs at the electrode surface, showing the necessity to investigate the adsorption of alkali/alkaline atoms (Li, Na, K, and Mg) at the VS2 surface to know the change in different properties of the electrode. It is found that generally CQ reduces due to the adsorption of alkali/alkaline atoms at the surface, but the K-adsorption at S-vacancy (Vs) VS2 demonstrated the increment of CQ value from 21.75 to 35.32 ?F/cm2 at room temperature. Additionally, the variation of the adsorption distance of the K atom at the Vs-VS2 surface revealed an optimum distance of value 3.5 Å, indicating that the K atom (radius = 2.43 Å) stabilizes just above the VS2 surface. Moreover, augmentation in CQ was seen with a decrease in temperature and attained a value of 49.96 ?F/cm2 at 100 K. The calculated CQ and open-circuit voltage (OCV) duly confirmed that the K-adsorbed Vs-VS2 is a potential candidate for the anode of hybrid supercapacitors as it has a maximum CQ value at the positive side of the electrochemical potential and an average OCV value of +0.615 V. This study reveals that the CQ of the VS2 electrode can be increased to minimize the size of high-performance hybrid supercapacitors for its application as an on-chip energy source. © 2025 American Chemical Society.