40 research outputs found
We’ve Come a Long Way Maybe: Reflections of Women in The Academy
This essay provides narratives of five women in academy – specifically within the communication studies professoriate. They share experiences of equity (or lack thereof), motherhood, identity management, work-life balance, youthfulness, and illness. Overall, the stories presented seek to problematize ongoing difficulties for women in the academy with the hopes of sparking discussion and ongoing debate
Spectrally narrow exciton luminescence from monolayer MoS2 exfoliated onto epitaxially grown hexagonal BN
The strong light-matter interaction in transition Metal dichalcogenides
(TMDs) monolayers (MLs) is governed by robust excitons. Important progress has
been made to control the dielectric environment surrounding the MLs, especially
through hexagonal boron nitride (hBN) encapsulation, which drastically reduces
the inhomogeneous contribution to the exciton linewidth. Most studies use
exfoliated hBN from high quality flakes grown under high pressure. In this
work, we show that hBN grown by molecular beam epitaxy (MBE) over a large
surface area substrate has a similarly positive impact on the optical emission
from TMD MLs. We deposit MoS and MoSe MLs on ultrathin hBN films (few
MLs thick) grown on Ni/MgO(111) by MBE. Then we cover them with exfoliated hBN
to finally obtain an encapsulated sample : exfoliated hBN/TMD ML/MBE hBN. We
observe an improved optical quality of our samples compared to TMD MLs
exfoliated directly on SiO substrates. Our results suggest that hBN grown
by MBE could be used as a flat and charge free substrate for fabricating
TMD-based heterostructures on a larger scale.Comment: 5 pages, 3 figure
Revealing exciton masses and dielectric properties of monolayer semiconductors with high magnetic fields
In semiconductor physics, many essential optoelectronic material parameters
can be experimentally revealed via optical spectroscopy in sufficiently large
magnetic fields. For monolayer transition-metal dichalcogenide semiconductors,
this field scale is substantial --tens of teslas or more-- due to heavy carrier
masses and huge exciton binding energies. Here we report absorption
spectroscopy of monolayer MoS, MoSe, MoTe, and WS in very high
magnetic fields to 91~T. We follow the diamagnetic shifts and valley Zeeman
splittings of not only the exciton's ground state but also its excited
, , ..., Rydberg states. This provides a direct experimental
measure of the effective (reduced) exciton masses and dielectric properties.
Exciton binding energies, exciton radii, and free-particle bandgaps are also
determined. The measured exciton masses are heavier than theoretically
predicted, especially for Mo-based monolayers. These results provide essential
and quantitative parameters for the rational design of opto-electronic van der
Waals heterostructures incorporating 2D semiconductors.Comment: updated; now also including data on MoTe2. Accepted & in press,
Nature Commu
Exciton states in monolayer MoSe2 and MoTe2 probed by upconversion spectroscopy
Transitions metal dichalcogenides (TMDs) are direct semiconductors in the
atomic monolayer (ML) limit with fascinating optical and spin-valley
properties. The strong optical absorption of up to 20 % for a single ML is
governed by excitons, electron-hole pairs bound by Coulomb attraction. Excited
exciton states in MoSe and MoTe monolayers have so far been elusive due
to their low oscillator strength and strong inhomogeneous broadening. Here we
show that encapsulation in hexagonal boron nitride results in emission line
width of the A:1 exciton below 1.5 meV and 3 meV in our MoSe and
MoTe monolayer samples, respectively. This allows us to investigate the
excited exciton states by photoluminescence upconversion spectroscopy for both
monolayer materials. The excitation laser is tuned into resonance with the
A:1 transition and we observe emission of excited exciton states up to 200
meV above the laser energy. We demonstrate bias control of the efficiency of
this non-linear optical process. At the origin of upconversion our model
calculations suggest an exciton-exciton (Auger) scattering mechanism specific
to TMD MLs involving an excited conduction band thus generating high energy
excitons with small wave-vectors. The optical transitions are further
investigated by white light reflectivity, photoluminescence excitation and
resonant Raman scattering confirming their origin as excited excitonic states
in monolayer thin semiconductors.Comment: 14 pages, 7 figures, main text and appendi
Le syndrome d'insuffisance limbique cornéen lié au syndrome Kid [keratitis, ichtyosis, deafness]
POITIERS-BU MĂ©decine pharmacie (861942103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF