2 research outputs found
Quantum-Confined Electronic States Arising from the MoireĢ Pattern of MoS<sub>2</sub>āWSe<sub>2</sub> Heterobilayers
A two-dimensional
(2D) heterobilayer system consisting of MoS<sub>2</sub> on WSe<sub>2</sub>, deposited on epitaxial graphene, is studied
by scanning tunneling microscopy and spectroscopy at temperatures
of 5 and 80 K. A moireĢ pattern is observed, arising from lattice
mismatch of 3.7% between the MoS<sub>2</sub> and WSe<sub>2</sub>.
Significant energy shifts are observed in tunneling spectra observed
at the maxima of the moireĢ corrugation, as compared with spectra
obtained at corrugation minima, consistent with prior work. Furthermore,
at the minima of the moireĢ corrugation, sharp peaks in the
spectra at energies near the band edges are observed for spectra acquired
at 5 K. The peaks correspond to discrete states that are confined
within the moireĢ unit cells. Conductance mapping is employed
to reveal the detailed structure of the wave functions of the states.
For measurements at 80 K, the sharp peaks in the spectra are absent,
and conductance maps of the band edges reveal little structure
Realizing Large-Scale, Electronic-Grade Two-Dimensional Semiconductors
Atomically
thin transition metal dichalcogenides (TMDs) are of
interest for next-generation electronics and optoelectronics. Here,
we demonstrate device-ready synthetic tungsten diselenide (WSe<sub>2</sub>) via metalāorganic chemical vapor deposition and provide
key insights into the phenomena that control the properties of large-area,
epitaxial TMDs. When epitaxy is achieved, the sapphire surface reconstructs,
leading to strong 2D/3D (<i>i.e.</i>, TMD/substrate) interactions
that impact carrier transport. Furthermore, we demonstrate that substrate
step edges are a major source of carrier doping and scattering. Even
with 2D/3D coupling, transistors utilizing transfer-free epitaxial
WSe<sub>2</sub>/sapphire exhibit ambipolar behavior with excellent
on/off ratios (ā¼10<sup>7</sup>), high current density (1ā10
Ī¼AĀ·Ī¼m<sup>ā1</sup>), and good field-effect
transistor mobility (ā¼30 cm<sup>2</sup>Ā·V<sup>ā1</sup>Ā·s<sup>ā1</sup>) at room temperature. This work establishes
that realization of electronic-grade epitaxial TMDs must consider
the impact of the TMD precursors, substrate, and the 2D/3D interface
as leading factors in electronic performance