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Kehao Zhang1 Donna Deng1 Shruti Subramanian1 Joshua Robinson1

1, The Pennsylvania State University, University Park, Pennsylvania, United States

Substitutional doping has been demonstrated as an efficient way to tune the electronic and optoelectronic properties of 2D materials.1,2 Beyond the singular functionalization of 2D materials, multifunctional doping of 2D materials provides opportunities to realize great potentials to 2D materials by one dopant, which can be highly compatible to advanced technologies.3 Here, we report the multifunctional doping of monolayer MoS2 for electronic and chemical sensing applications. Niobium doped MoS2 with various doping concentration (0.5 at%-57 at%) is synthesize by metal organic chemical vapor deposition on c-plane sapphire. The Fermi level is tuned from 2.0 eV above valence band maxima (VBM) to 0.3 eV below VBM (degenerate doping) as doping concentration increases. Interestingly, this Fermi level tuning exhibits a significant shift from theoretical prediction. Evident from x-ray photoelectron spectroscopy and conductive atomic force microscopy, 0.5 at% can only slightly reduce the electron concentration in monolayer MoS2. ~5 at% Nb concentration is needed to push the Fermi level to 0.2 eV above valence band maxima (p-doped) and >20 at% Nb doped MoS2 is degenerately p-doped, while <1 at% Nb for degenerate p-doping in theory. This unusual phenomenon is attributed to the strong electron doping from the sapphire substrate.4 Tunable Nb doping realizes multifunctionality of MoS2. 5 at% Nb doped MoS2 exhibits ~15x higher sensitivity (signal/noise ratio) to tetraethylammonium (TEA, a nerve agent) with <10ppb defection limit due to the enhanced conductivity and p-type conductance. Meanwhile, degenerate p-doped MoS2 provides an Ohmic contact between metals (Pt/Ir etc.) and both 2D (MoS2) and 3D (GaN) semiconductors, which may play an important role in contacting semiconductors. This work presents a promising route to cultivate the multifunctionality of doped 2D materials, enabling novel design of multifunctional electronic and sensing devices.
Reference
(1) Bhimanapati, G. R.; Lin, Z.; Meunier, V.; Jung, Y.; Cha, J. J.; Das, S.; Xiao, D.; Son, Y.; Strano, M. S.; Cooper, V. R.; et al. Recent Advances in Two-Dimensional Materials Beyond Graphene. ACS Nano 2015, 9, 11509–11539.
(2) Tedstone, A. A.; Lewis, D. J.; O’Brien, P. Synthesis, Properties, and Applications of Transition Metal-Doped Layered Transition Metal Dichalcogenides. Chem. Mater. 2016, 28, 1965–1974.
(3) Zhang, K.; Bersch, B. M.; Joshi, J.; Addou, R.; Cormier, C. R.; Zhang, C.; Xu, K.; Briggs, N. C.; Wang, K.; Subramanian, S.; et al. Tuning the Electronic and Photonic Properties of Monolayer MoS2 via In Situ Rhenium Substitutional Doping. Adv. Funct. Mater. 2018, 1706950.
(4) Zhang, K.; Borys, N. J.; Bersch, B. M.; Bhimanapati, G. R.; Xu, K.; Wang, B.; Wang, K.; Labella, M.; Williams, T. A.; Haque, M. A.; et al. Deconvoluting the Photonic and Electronic Response of 2D Materials: The Case of MoS2. Sci. Rep. 2017, 7, 16938.

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