Excitonic Luminescence, X-ray Analysis and Local Band Structure of Chlorine Intercalated 2H- and 3R-MoS2 Polytypes

Abstract

Abstract-Photoluminescence and X-ray diffraction are used to investigate 2H and 3R polytypes of MoS2 layered crystals intercalated with Cl2 molecules. The spectral structure of the observed bound excitons emission is individual for each polytype, that can be used for unambiguous identification of the 2H and 3R polytypes. The DFT band structure calculations have been done for three molecular layers of 2H-MoS2 and 3R-MoS2 polytypes without and with intercalation of Cl2 molecules. The spectroscopic experimental results confirmed theoretical calculations performed for both cases and it has been demonstrated that halogen intercalation completely changes the local band structure of 2H-and 3R-MoS2 polytypes.

Edge effects in second-harmonic generation in nanoscale layers of transition-metal dichalcogenides

“…Since halogen molecule intercalation results in the formation of a bound exciton with a characteristic luminescence spectrum [5,6,10,23], mapping at the exciton line wavelength can show the distribution of The evident increase in the SH signal intensity at layer edges can be associated with the fact that the concentration of halogen molecules intercalated into the Van der Waals gap in the regions adjacent to micro crystallite boundaries is much higher than the value averaged over the microcrystallite surface. It follows from observations of the behavior of the signal inten sity of low temperature PL caused by the recombina tion of excitons bound to Cl 2 molecules (λ L1 = 1056 nm, Fig.…”

“…As shown above, halogen molecules unambig uously incorporated into the Van der Waals gap trans form a given semiconductor material from indirect to direct gap even at large crystal thicknesses, which makes it possible to explain the high SH signal inten sity observed at the 3R MoS 2 :Cl 2 microcrystallite edges. Indeed, as follows from ensity functional theory (DFT) calculations [10] of the MoS 2 :Cl 2 band struc ture, the local direct band gap is E g = 1.24 eV (G point in the Brillouin zone) in the region of intercalated halogen molecules, which provides quasi resonant conditions of SH signal generation when pumping with Ti:Al 2 O 3 laser radiation (E L = 1.55 eV).…”

“…In [10], it was shown that the presence of halogen molecules incorporated between MoS 2 layers leads not only to the formation of an energy level corresponding to this impurity, lying ~0.1 eV below the bottom of the conduction band, but also to a significant change in the band structure in the local neighborhood of the halogen molecule: the local indirect to direct gap transition occurs.…”