82 research outputs found
Trion confinement in monolayer MoSe2 by carbon nanotube local gating
We have successfully confined trions into a one-dimensional restricted space
of a MoSe2 device with CNT gate electrodes. The dry transfer process, including
deterministic dry transfer of aligned CNTs, has led to an hBN-encapsulated
MoSe2 device with CNT back gate electrodes. In contrast to a location without
CNT gate electrodes, applying voltage via CNT gate electrodes significantly
alters PL spectra at a location with CNT gate electrodes. PL imaging has
revealed that image contrast from trions is linear along the CNT electrode
underneath, consistent with 1D confinement of trions in response to the CNT
local gating. The confinement width obtained from the PL image is 5.5 x 10^2
nm, consistent with nanoscale 1D confined trions with the diffraction limit
broadening. This work has demonstrated electrical control of excitonic states
at the nanoscale, leading to novel optoelectronic properties and exciton
devices in the future
The Atomic and Electronic structure of 0{\deg} and 60{\deg} grain boundaries in MoS2
We have investigated atomic and electronic structure of grain boundaries in
monolayer MoS2, where relative angles between two different grains are 0 and 60
degree. The grain boundaries with specific relative angle have been formed with
chemical vapor deposition growth on graphite and hexagonal boron nitride
flakes; van der Waals interlayer interaction between MoS2 and the flakes
restricts the relative angle. Through scanning tunneling microscopy and
spectroscopy measurements, we have found that the perfectly stitched structure
between two different grains of MoS2 was realized in the case of the 0 degree
grain boundary. We also found that even with the perfectly stitched structure,
valence band maximum and conduction band minimum shows significant blue shift,
which probably arise from lattice strain at the boundary
Two-dimensional atomic-scale ultrathin lateral heterostructures
Ultrathin lateral heterostructures of monolayer MoS2 and WS2 have
successfully been realized with the metal-organic chemical vapor deposition
method. Atomic-resolution HAADF-STEM observations have revealed that the
junction widths of lateral heterostructures range from several nanometers to
single-atom thickness, the thinnest heterojunction in theory. The interfaces
are atomically flat with minimal mixing between MoS2 and WS2, originating from
rapid and abrupt switching of the source supply. Due to one-dimensional
interfaces and broken rotational symmetry, the resulting ultrathin lateral
heterostructures, 1~2 mixed-dimensional structures, can show emergent
optical/electronic properties. The MOCVD growth developed in this work allows
us to access various ultrathin lateral heterostructures, leading to future
exploration of their emergent properties absent in each component alone
Observation of biexcitonic emission at extremely low power density in tungsten disulfide atomic layers grown on hexagonal boron nitride
Monolayer transition metal dichalcogenides (TMDCs) including WS2, MoS2, WSe2 and WS2, are two-dimensional semiconductors with direct bandgap, providing an excellent field for exploration of many-body effects in 2-dimensions (2D) through optical measurements. To fully explore the physics of TMDCs, the prerequisite is preparation of high-quality samples to observe their intrinsic properties. For this purpose, we have focused on high-quality samples, WS2 grown by chemical vapor deposition method with hexagonal boron nitride as substrates. We observed sharp exciton emissions, whose linewidth is typically 22~23 meV, in photoluminescence spectra at room temperature, which result clearly demonstrates the high-quality of the current samples. We found that biexcitons formed with extremely low-excitation power (240 W/cm^2) at 80 K, and this should originate from the minimal amount of localization centers in the present high-quality samples. The results clearly demonstrate that the present samples can provide an excellent field, where one can observe various excitonic states, offering possibility of exploring optical physics in 2D and finding new condensates
Motion of methanol adsorbed in porous coordination polymer with paramagnetic metal ions
Molecular motions of methanol adsorbed in 1D nano-channels of pillared-layer coordination polymer with paramagnetic metal ions have been studied by 2H NMR together with X-ray crystallography
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