3 research outputs found
Gap States at Low-Angle Grain Boundaries in Monolayer Tungsten Diselenide
Two-dimensional
(2D) transition metal dichalcogenides (TMDs) have
revealed many novel properties of interest to future device applications.
In particular, the presence of grain boundaries (GBs) can significantly
influence the material properties of 2D TMDs. However, direct characterization
of the electronic properties of the GB defects at the atomic scale
remains extremely challenging. In this study, we employ scanning tunneling
microscopy and spectroscopy to investigate the atomic and electronic
structure of low-angle GBs of monolayer tungsten diselenide (WSe<sub>2</sub>) with misorientation angles of 3–6°. Butterfly
features are observed along the GBs, with the periodicity depending
on the misorientation angle. Density functional theory calculations
show that these butterfly features correspond to gap states that arise
in tetragonal dislocation cores and extend to distorted six-membered
rings around the dislocation core. Understanding the nature of GB
defects and their influence on transport and other device properties
highlights the importance of defect engineering in future 2D device
fabrication
Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides
The
nature and extent of electronic screening at heterointerfaces
and their consequences on energy level alignment are of profound importance
in numerous applications, such as solar cells, electronics <i>etc.</i> The increasing availability of two-dimensional (2D)
transition metal dichalcogenides (TMDs) brings additional opportunities
for them to be used as interlayers in “van der Waals (vdW)
heterostructures” and organic/inorganic flexible devices. These
innovations raise the question of the extent to which the 2D TMDs
participate actively in dielectric screening at the interface. Here
we study perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) monolayers
adsorbed on single-layer tungsten diselenide (WSe<sub>2</sub>), bare
graphite, and Au(111) surfaces, revealing a strong dependence of the
PTCDA HOMO–LUMO gap on the electronic screening effects from
the substrate. The monolayer WSe<sub>2</sub> interlayer provides substantial,
but not complete, screening at the organic/inorganic interface. Our
results lay a foundation for the exploitation of the complex interfacial
properties of hybrid systems based on TMD materials
Electronic Properties of a 1D Intrinsic/p-Doped Heterojunction in a 2D Transition Metal Dichalcogenide Semiconductor
Two-dimensional
(2D) semiconductors offer a convenient platform
to study 2D physics, for example, to understand doping in an atomically
thin semiconductor. Here, we demonstrate the fabrication and unravel
the electronic properties of a lateral doped/intrinsic heterojunction
in a single-layer (SL) tungsten diselenide (WSe<sub>2</sub>), a prototype
semiconducting transition metal dichalcogenide (TMD), partially covered
with a molecular acceptor layer, on a graphite substrate. With combined
experiments and theoretical modeling, we reveal the fundamental acceptor-induced
p-doping mechanism for SL-WSe<sub>2</sub>. At the 1D border between
the doped and undoped SL-WSe<sub>2</sub> regions, we observe band
bending and explain it by Thomas–Fermi screening. Using atomically
resolved scanning tunneling microscopy and spectroscopy, the screening
length is determined to be in the few nanometer range, and we assess
the carrier density of intrinsic SL-WSe<sub>2</sub>. These findings
are of fundamental and technological importance for understanding
and employing surface doping, for example, in designing lateral organic
TMD heterostructures for future devices