2 research outputs found
Toward Ferroelectric Control of Monolayer MoS<sub>2</sub>
The
chemical vapor deposition (CVD) of molybdenum disulfide (MoS<sub>2</sub>) single-layer films onto periodically poled lithium niobate is possible
while maintaining the substrate polarization pattern. The MoS<sub>2</sub> growth exhibits a preference for the ferroelectric domains
polarized “up” with respect to the surface so that the
MoS<sub>2</sub> film may be templated by the substrate ferroelectric
polarization pattern without the need for further lithography. MoS<sub>2</sub> 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 MoS<sub>2</sub> 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 MoS<sub>2</sub> film on SiO<sub>2</sub>/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