Faculty Publications

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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.
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.
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.

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