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Vortrag / Präsentation 
Klein Julian, Kuc Agnieszka, Anna Nolinder, Merbeler Fabian, Altzschner Marcus, Wierzbowski Jakob, Sigger Florian, Kreupl Franz, Wurstbauer Ursula, Holleitner Alexander, Finley Jonathan J., Kaniber Michael 
Generation of localised optically active defects in MoS2 using helium ion irradiation 
We present a systematic study of the impact of disorder on the optical properties and intervalley scattering of monolayer MoS2 [1]. Using a helium ion microscope, we locally induce defects in the 2D crystal lattice. Optical spectroscopy reveals significant shifts of both first order Raman modes E’ and A1, which are well understood in the framework of a phonon confinement model, where increasing disorder links the ion dose to the inter-defect distance. Micro-photoluminescence measurements at T=10K show how a defect-related luminescence band emerges following irradiation, red-shifted by ~180 meV with respect to the delocalised excitons. This band has an intensity which can be engineered by varying the ion dose used for exposure. We attribute the observed luminescence to originate from chemisorbed atoms/molecules at monosulphur vacancies in good agreement with density functional theory calculations. Quasi-resonant polarisation-resolved photoluminescence measurements reveal a robust degree of circular polarization ~ 85% for doses over which ion-induced luminescence is observed, in good agreement with recent theoretical results [2]. Our results demonstrate that the excellent optical properties of MoS2 are preserved for helium ion doses typically used for nano-structuring via helium ion beam lithography. Embedding monolayer MoS2 into hBN, strongly reduces the linewidth of the delocalized excitons (<5meV), approaching the homogeneous limit, whilst simultaneously increasing their optical stability [3]. In combination with helium ion irradiation, this approach enables us to controllably realise single optical active emission centres in MoS2, which show clear indications of quantum dot-like behaviour [4]. Our results demonstrate the potential of helium ion irradiation to deterministically engineer the optical properties of 2D semiconductors at the nanoscale, gain new insights into disorder and valley depolarization processes and, moreover, represent a new route to realise optically active quantum emitters in transition metal dichalcogenides in a controlled manner. [1] Klein et al. 2D Mater. 5, 011007 (2018) [2] Kaasbjerg et al. Phys. Rev. B 96, 241411(R) (2017) [3] Wierzbowski et al. Sci. Rep. 7, 12383 (2017) [4] Klein et al. in preparation (2018) 
International Union of Pure and Applied Physics (IUPAP) 
Book / Congress title:
ICPS 2018 
Date of publication:
TUM Institution:
Hybride Elektronische Systeme