Tailoring the Luminescence of Atomically Thin Semiconductors at the Sub-nanometer Scale
- PC Department Online Seminar
- Date: Apr 26, 2021
- Time: 11:00 AM (Local Time Germany)
- Speaker: Luis Parra Lopez
- Institut de Physique et de Chimie des Matériaux de Strasbourg
Moreover, due to the absence of dangling bonds in their surfaces and
their relatively easy isolation, TMDs can be stacked onto other 2D
materials . These so called Van der Waals (vdW) heterostructures
offer a new template that is appealing for opto-electronic applications.
However, the optical properties of vdW heterostructures are governed by
near field coupling mechanisms that arise at the heterointerface. These
mechanisms sensitively depend on the sub-nm distance between the layers
and therefore require a technique with sufficient resolution to
properly characterize them. Here, I will present our results aimed at
this goal. To investigate the TMDs, I used an approach that combines
photoluminescence and reflectance spectroscopies together with scanning
tunnelling microscopy (STM). To tailor the luminescence at the atomic
scale, we exploit the ultimate in-plane resolution provided by an STM
working at cryogenic temperatures and under ultra-high-vacuum
conditions. The out-of-plane control is achieved using the van-der-Waals
gap that separates the TMD from a graphene layer. I will demonstrate
that when stacked on graphene, the TMD monolayer is virtually neutral,
resulting in photoluminescence spectra composed of a single and narrow
emission line at cryogenic temperatures . In contrast to bare
monolayers that display complex excitonic manifolds with emission
spectra composed of a large number of features, arising from neutral
excitons but also charged excitonic compounds, spin-dark excitons,
localized defect-induced emission and possibly exciton-phonon replicas
[4-5]. Finally, I will demonstrate for the first time the STM induced
intrinsic luminescence of TMD-based heterostructures at low temperatures
with atomic precision, which has remained elusive ever since the
discovery of the direct bandgap transition of 1L-TMDs. Our results
support monolayer TMDs as an interesting system to investigate
light-matter interaction within an STM-junction and pave the way for
novel architectures aimed at building low dimensional devices.
 K. F. Mak, J. Shan. Nature Nanotech. 10, 216 (2016).
 Geim, A., Grigorieva, I. Nature 499, 419–425 (2013).
 Lorchat, E., López, L.E.P. et al. Nat. Nanotechnol. 15, 283–288 (2020).
 D. Vaclavkova et al. Nanotechnology 29 (2018) 325705.
 E. Courtade et al. Phys. Rev. B 96, 085302 (2017).
Meeting-ID: 938 3916 3577