Toward Ferroelectric Control of Monolayer MoS₂

The chemical vapor deposition (CVD) of molybdenum disulfide (MoS₂) single-layer films onto periodically poled lithium niobate is possible while maintaining the substrate polarization pattern. The MoS₂ growth exhibits a preference for the ferroelectric domains polarized “up” with respect to the surface so that the MoS₂ film may be templated by the substrate ferroelectric polarization pattern without the need for further lithography. MoS₂ monolayers preserve the surface polarization of the “up” domains, while slightly quenching the surface polarization on the “down” domains as revealed by piezoresponse force microscopy. Electrical transport measurements suggest changes in the dominant carrier for CVD MoS₂ under application of an external voltage, depending on the domain orientation of the ferroelectric substrate. Such sensitivity to ferroelectric substrate polarization opens the possibility for ferroelectric nonvolatile gating of transition metal dichalcogenides in scalable devices fabricated free of exfoliation and transfer

Postgrowth Tuning of the Bandgap of Single-Layer Molybdenum Disulfide Films by Sulfur/Selenium Exchange

We demonstrate bandgap tuning of a single-layer MoS₂ film on SiO₂/Si <i>via</i> substitution of its sulfur atoms by selenium through a process of gentle sputtering, exposure to a selenium precursor, and annealing. We characterize the substitution process both for S/S and S/Se replacement. Photoluminescence and, in the latter case, X-ray photoelectron spectroscopy provide direct evidence of optical band gap shift and selenium incorporation, respectively. We discuss our experimental observations, including the limit of the achievable bandgap shift, in terms of the role of stress in the film as elucidated by computational studies, based on density functional theory. The resultant films are stable in vacuum, but deteriorate under optical excitation in air