Panoply of Ni-Doping-Induced Reconstructions, Electronic Phases, and Ferroelectricity in 1T-MoS${}_2$

Abstract

The distorted phases of monolayer 1T-MoS${}_2$ have distinct electronic properties, with potential applications in optoelectronics, catalysis, and batteries. We theoretically investigate the use of Ni-doping to generate distorted 1T phases, and find not only the ones usually reported but also two further phases ($3\times 3$ and $4\times 4$), depending on the concentration and the substitutional or adatom doping site. Corresponding pristine phases are stable after dopant removal, which might offer a potential route to experimental synthesis. We find large ferroelectric polarizations, most notably in $3\times 3$ which -- compared to the recently measured 1T${}^{\prime \prime }$ -- has 100 times greater ferroelectric polarization, a lower energy, and a larger bandgap. Doped phases include exotic multiferroic semimetals, ferromagnetic polar metals, and improper ferroelectrics with only in-plane polarization switchable. The pristine phases have unusual multiple gaps in the conduction bands, with possible applications for intermediate band solar cells, transparent conductors, and nonlinear optics.

30 pages, 4 figures, 3 tables

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