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|
Identifier |
000438128 |
Title |
Pulsed laser induced doping of two-dimensional crystals |
Alternative Title |
Εμπλουτισμός διδιάστατων κρυστάλλων με χρήση παλμικού λέιζερ |
Author
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Δεμερίδου, Ιωάννα Ε
|
Thesis advisor
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Κομίνης, Ιωάννης
Στρατάκης, Εμμανουήλ
|
Reviewer
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Κιοσέογλου, Γεώργιος
Γεωργακίλας, Αλέξανδρος
Ρακιτζής, Πέτρος
Πελεκάνος, Νικόλαος
Κυμάκης, Ε.
|
Abstract |
Two-dimensional transition metal dichalcogenides (2D-TMDs) attract worldwide interest in the
last few decades since the successful isolation and characterization of graphene. TMDs are
semiconductors and provide unique optoelectronic properties attributed to their ultrathin nature. As
their numbers of layers decreases, turned from an indirect to direct bandgap semiconductor with
possible applications in visible range optoelectronic devices. Here, we investigate the optical
properties of monolayer WS2, a member of the TMD family, and the effects of the UV pulsed laserinduced doping.
We proposed a novel doping method that modulates the electron density in a 1L-WS2. Chlorinedoped tungsten disulfide monolayer (1L-WS2) with tunable charge carrier concentration has been
realized by pulsed laser irradiation of the atomically thin lattice in a chlorine environment. A
systematic shift of the neutral exciton peak, in the photoluminescence spectra, towards lower
energies indicates the reduction of the crystal’s electron density. The capability to progressively
tune the carrier density upon variation of the exposure time is demonstrated. The Fermi level shift
is correlated to the respective electron density modulation due to the chlorine species. At the same
time, is found that the effect can be reversed upon continuous-wave laser scanning of the monolayer
in the air. Such bidirectional control of the Fermi level, coupled with the capability offered by
lasers to process at pre-selected locations, can be advantageously used for spatially resolved doping
modulation in 1L-WS2 with micrometric resolution.
This process has boosted interests in controlling valley polarized light emission of doped
monolayer WS2. TMDs have interesting spin/valley properties due to the large spin-orbit coupling
and the non-equivalent valleys in their band structure. We demonstrate spin-valley polarization
tunability by more than 40% in 1L-WS2 via photochlorination. The reduction of circular
polarization, after the photochlorination treatment, was attributed to the reduction of defect sites in
the crystal lattice and consequently to the increase of the non-radiative exciton lifetime. Theoretical
simulations and ultrafast time-resolved transient absorption measurements support our findings.
Furthermore, we show that the degree of valley polarization strongly depends on the relationship
between the doping and the supporting layer of TMDs. These results shed light on the significant
role of the substrate on valley polarization in monolayer TMDs. These findings make TMDs
promising materials for future applications and computing architectures.
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Language |
English |
Subject |
2D-materials |
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Chlorine |
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Monolayer WS2 |
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Photoluminescence |
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Ptotochemical doping |
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Διδιάστατοι κρύσταλλοι |
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Μονοστρωματικός κρύσταλλος WS2 |
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Φωτοφωταύγεια |
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Φωτοχημικός εμπλουτισμός |
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Χλώριο |
Issue date |
2021-03-10 |
Collection
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School/Department--School of Sciences and Engineering--Department of Physics--Doctoral theses
|
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Type of Work--Doctoral theses
|
Permanent Link |
https://elocus.lib.uoc.gr//dlib/e/3/5/metadata-dlib-1615201326-643965-2735.tkl
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Views |
752 |