The
emergence of two-dimensional (2D) materials launched a fascinating
frontier of flatland electronics. Most crystalline atomic layer materials
are based on layered van der Waals materials with weak interlayer
bonding, which naturally leads to thermodynamically stable monolayers.
We report the synthesis of a 2D insulator composed of a single atomic
sheet of honeycomb structure BeO (h-BeO), although its bulk counterpart
has a wurtzite structure. The h-BeO is grown by molecular beam epitaxy
(MBE) on Ag(111) thin films that are also epitaxially grown on Si(111)
wafers. Using scanning tunneling microscopy and spectroscopy (STM/S),
the honeycomb BeO lattice constant is determined to be 2.65 Å
with an insulating band gap of 6 eV. Our low-energy electron diffraction
measurements indicate that the h-BeO forms a continuous layer with
good crystallinity at the millimeter scale. Moiré pattern analysis
shows the BeO honeycomb structure maintains long-range phase coherence
in atomic registry even across Ag steps. We find that the interaction
between the h-BeO layer and the Ag(111) substrate is weak by using
STS and complementary density functional theory calculations. We not
only demonstrate the feasibility of growing h-BeO monolayers by MBE,
but also illustrate that the large-scale growth, weak substrate interactions,
and long-range crystallinity make h-BeO an attractive candidate for
future technological applications. More significantly, the ability
to create a stable single-crystalline atomic sheet without a bulk
layered counterpart is an intriguing approach to tailoring 2D electronic
materials.
acarbonyls. While transferance of /mc.co to the M-CO linkages in M(CO)s(CS) is certainly reasonable, this may be a poor approximation for the M-CS linkages. Consequently the/cs and /mcs values contain some uncertainty which cannot be removed given the present frequency data; 13C substitution at the thiocarbonyl carbons is necessary to refine all the force constants in the M-CS linkages.
The
ability to engineer atomically thin nanoscale lateral junctions
is critical to lay the foundation for future two-dimensional (2D)
device technology. However, the traditional approach to creating a
heterojunction by direct growth of a heterostructure of two different
materials constrains the available band offsets, and it is still unclear
if large built-in potentials are attainable for 2D materials. The
electronic properties of atomically thin semiconducting transition
metal dichalcogenides (TMDs) are not static, and their exciton binding
energy and quasiparticle band gap depend strongly on the proximal
environment. Recent studies have shown that this effect can be harnessed
to engineer the lateral band profile of a monolayer TMD to create
a lateral electronic junction. Here we demonstrate the synthesis of
a nanoscale lateral junction in monolayer MoSe2 by intercalating
Se at the interface of an hBN/Ru(0001) substrate. The Se intercalation
creates a spatially abrupt modulation of the local hBN/Ru work function,
which is imprinted directly onto an overlying MoSe2 monolayer
to create a lateral junction with a large built-in potential of 0.83
± 0.06 eV. We spatially resolve the MoSe2 band profile
and work function using scanning tunneling spectroscopy to map out
the nanoscale depletion region. The Se intercalation also modifies
the dielectric environment, influencing the local band gap renormalization
and increasing the MoSe2 band gap by ∼0.26 ±
0.1 eV. This work illustrates that environmental proximity engineering
provides a robust method to indirectly manipulate the band profile
of 2D materials outside the limits of their intrinsic properties.
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