Optical Spectroscopy of Lithium Doped Monolayer MoS2
ABSTRACT
We describe our results on the Raman and circular polarization resolved photoluminescence (PL) spectroscopy of Lithium (Li) doped monolayer MoS2 under ultra-high vacuum conditions. Through detailed analysis of the Raman and PL spectra, we show the evolution of structural disorder in the MoS2 lattice with Li doping. We further discuss the changes in the optical spectra in terms of disorder-activated intervalley scattering in the electronic structure of MoS2.
PRESENTER
Nihit Saigal
Indian Institute of Science
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This interesting experimental report on Li doping of monolayer MoS_2 reminds me of my transport experiments on Li doping of monolayer graphene, which were reported on these two journal papers:
“Alkali doping of graphene: The crucial role of high-temperature annealing”, Phys. Rev. B 94, 201405(R) (2016) and
“Weak localization measurements of electronic scattering rates in Li-doped epitaxial graphene”, Phys. Rev. B 100, 161405(R) (2019).
The second paper is more related to these observations. We observed enhancement of intervalley scattering in graphene by Li doping and we partially explained it by extra carriers in the graphene interacting with residual disorder. While Li adtom deposition is not adding to defects in graphene, intervalley scattering rate for a given density of short-range scatterers would generically be proportional to the graphene density of states. Thus, an increase in intervalley scattering rate is expected purely due to the doping effect from Li, enhancing the scattering rate from preexisting short-range defects in graphene. I am just curious if a similar scenario can partially explain the enhancement of intervalley scattering in your Li doped monolayer MoS_2 system? It is also important to know what was the density of Li adatoms that was deposited on MoS_2? For example, does 150 sec Li deposition time mean close to a monolayer of Li on MoS_2?
Thank you for the comment, Ali. I have also received your email. I will soon reply to your comment.
Dear Ali,
Thank you for your comment.
While it might be possible to explain the enhancement of intervalley scattering due to the interaction of additional carriers with the residual disorder in your case, I would like to point you to the supplementary information of our paper (App. Phys. Lett. 112, 121902 (2018)) where we show the effect of potassium doping on monolayer MoS2. In the case of K doping, we observe the changes in the Raman spectrum which indicate that there is n-type doping of MoS2 but no new Raman modes appear. Correspondingly, we do not see any significant change in the valley polarization of K doped MoS2 in our PL spectra. Thus, we concluded that in the absence of additional disorder due to structural defects, the intervalley scattering processes are not dominant in our case.
As an answer to your second question, in our case 100s of Lithium deposition corresponded to 0.13 monolayer of Li on MoS2. Please see our paper for more details.
Thank you again,
Nihit