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The influence of Mg doping on the nucleation of self-induced GaN nanowires
GaN nanowires were grown without any catalyst by plasma-assisted molecular beam
epitaxy. Under supply of Mg, nanowire nucleation is faster, the areal density of
wires increases to a higher value, and nanowire coalescence is more pronounced
than without Mg. During nanowire nucleation the Ga desorption was monitored insitu
by line-of-sight quadrupolemass spectrometry for various substrate temperatures.
Nucleation energies of 4.0±0.3 eV and 3.2±0.3 eV without and with Mg supply were
deduced, respectively. This effect has to be taken into account for the fabrication of
nanowire devices and could be employed to tune the NW areal density
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
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