Speaker
Description
Transition metal dichalcogenides (TMDs) are perhaps the most promising substitute for graphene for building the next generation of low-dimensional functional materials. In addition to the versatile chemical composition and stoichiometry, dimensionality plays a key role in determining the characteristics of TMDs. Nanodevices in static or dynamic conditions experience nanotribological effects leading to major challenges in their design, control and reliability [1]. Notably, previous studies of (bulk) thin-film MoS$_2$ have reported on its so-called superlubric properties in Ultra High/High Vacuum conditions, with friction coefficients ranging between 0.001-0.005 [2]. However, pure MoS$_2$ deposited by sputtering is limited by the fact it very easily oxidises into Molybdenum Trioxide (MoO$_3$) in humid air. Investigations in recent years have thus focused on the doping of TMDs with particular metals and non-metals which provide the desirable properties which can rectify this issue [3]. What is interesting, then, is to explore among existing dopants the underlying properties or mechanisms which govern the formation of stable phases in these structures.
To that end, we have performed a computational investigation to study the doping of monolayer and bilayer MoS$_2$ from first principles using the Alloy Theory Automated Toolkit (ATAT) [4] together with the Vienna Ab initio Simulation Package (VASP) [5, 6]. We constructed the temperature/composition phase diagrams for a selected group of dopants, in order to provide guidelines for their experimental synthesis. We also seek to propose a mechanism leading to the formation of the doped compounds in terms of the atomic types forming the structure and the electronic environment in which they are embedded. The study will be extended to multilayer systems and then submitted to an impactful scientific journal. Since searching for the stabilisation energies of new dopants has no intrinsic ties to tribology, these new structures may prove to be useful in fields beyond tribology such as opto-electronics, photovoltaic devices, lithium ion batteries, hydrogen evolution catalysis, desulfurization of fossil fuels, transistors, photodetectors, DNA detection, nanoelectromechanical systems, and memory devices [7, 8, 9, 10].
Note: This work is supported by the project "Novel nanostructures for engineering applications" No. CZ.02.1.01/0.0/0.0/16_026/0008396.
References
[1] Gnecco, E. & Meyer, E. Fundamentals of Friction and Wear on the Nanoscale, Springer (2007)
[2] J. M. Martin et al, Phys. Rev. B 48, 10583 (1993)
[3] A. K. Singh et al, iScience 24, 103532 (2021)
[4] A. van de Walle et al, Calphad 26, 539 (2002)
[5] G. Kresse et al, Comp. Mater. Sci. 6, 15 (1996)
[6] G. Kresse et al, Phys. Rev. B 59, 1758 (1999)
[7] H. Tian et al, Nano Today 11(6), 763 (2016)
[8] A. B. Kaul, J. Mater. Res. 29(3), 348 (2014)
[9] M. Chhowalla et al, Nat. Chem. 5(4), 263 (2013)
[10] A. K. Geim et al. Nature 499(7459), 419 (2013)
