Abstract:Due to its unique layer-number dependent electronic band structure and strong excitonic features, atomically thin MoS is an ideal 2D system where intriguing photoexcited-carrier-induced phenomena can be detected in excitonic luminescence. We perform micro-photoluminescence (PL) measurements and observe that the PL peak redshifts nonlinearly in mono- and bi-layer MoS as the excitation power is increased. The excited carrier-induced optical bandgap shrinkage is found to be proportional to n, where n is the optic… Show more
“…Similar PL characteristics were observed in another flake on the same SiO 2 substrate, confirming that this phenomenon is reproducible (Fig. S1 ) 17 . Figure 1 ( a ) Optical microscope image of the MoS 2 flake prepared by mechanical exfoliation of MoS 2 placing on a SiO 2 substrate.…”
Photoluminescence measurements in mono- and bilayer-MoS2 on SiO2 were undertaken to determine the thermal effect of the MoS2/SiO2 interface on the optical bandgap. The energy and intensity of the photoluminescence from monolayer MoS2 were lower and weaker than those from bilayer MoS2 at low temperatures, whilst the opposite was true at high temperatures above 200 K. Density functional theory calculations suggest that the observed optical bandgap crossover is caused by a weaker substrate coupling to the bilayer than to the monolayer.
“…Similar PL characteristics were observed in another flake on the same SiO 2 substrate, confirming that this phenomenon is reproducible (Fig. S1 ) 17 . Figure 1 ( a ) Optical microscope image of the MoS 2 flake prepared by mechanical exfoliation of MoS 2 placing on a SiO 2 substrate.…”
Photoluminescence measurements in mono- and bilayer-MoS2 on SiO2 were undertaken to determine the thermal effect of the MoS2/SiO2 interface on the optical bandgap. The energy and intensity of the photoluminescence from monolayer MoS2 were lower and weaker than those from bilayer MoS2 at low temperatures, whilst the opposite was true at high temperatures above 200 K. Density functional theory calculations suggest that the observed optical bandgap crossover is caused by a weaker substrate coupling to the bilayer than to the monolayer.
“…Recent experimental and theoretical studies indicate that the dependence of exciton energies on the carrier density in TMD monolayers can result in a redshift, blueshift, or combination of both. 2,6,8,19,[22][23][24][25] In our case, the redshift of E exc in Fig. 2b reveals that the band-gap renormalization dominates the other mechanisms in WS 2 MQDs as p was increased.…”
Section: Pl Ple and Absorbance Measurementsmentioning
Due to strong Coulomb interactions, reduced screening effects, and quantum confinement, transition-metal dichalcogenide (TMD) monolayer quantum disks (MQDs) are expected to exhibit large exciton binding energy, which is beneficial for the investigation of many-body physics at room temperature. Here, we report the first observations of room-temperature many-body effects in tungsten disulfide (WS 2 ) MQDs by both optical measurements and theoretical studies. The band-gap renormalization in WS 2 MQDs was about 250 ± 15 meV as the carrier density was increased from 0.6(±0.2) × 10 12 to 8.3(±0.2) × 10 12 cm −2 . We observed a striking exciton binding energy as large as 990 ± 30 meV at the lowest carrier density, which is larger than that in WS 2 monolayers. The huge exciton binding energy in WS 2 MQDs is attributed to the extra quantum confinement in the lateral dimension. The band-gap renormalization and exciton binding energies are explained using efficient reduced screening. On the basis of the Debye screening formula, the Mott density in WS 2 MQDs was estimated to be~3.95 × 10 13 cm −2 . Understanding and manipulation of the many-body effects in two-dimensional materials may open up new possibilities for developing exciton-based optoelectronic devices.npj 2D Materials and Applications (2019) 3:46 ; https://doi.
“…This can be explained by assuming many body effects induced by an increase in the free carrier [52]. The other thing is that the (655 nm) peak due to A excitons disappeared and a new peak appeared at 680 nm.…”
The doping of element (Nb, Ta, etc.) into MoS 2 , one of the layered transition metal dichalcogenides, is a key technology for electronic devices because the lack of the p-type MoS 2 has limited the range of applications. We report that the Mo 1-x Nb x S 2 thin films were synthesized on SiO 2 /Si substrates by chemical vapor deposition (CVD). It was critical to use chloride sources (MoCl 5 and NbCl 5) for the synthesis of Mo 1-x Nb x S 2. The Nb concentration can be increased to 10% by controlling the supplied amount of Nb using a separate-flow CVD apparatus. The Raman spectra changed as the Nb concentration increased, appearing E 2 (Nb-S) vibrational mode. The photoluminescence (PL) at 655 nm, 2 attributed to emission from excitons, disappeared, when Nb was incorporated into the MoS 2. PL due to trions at 680 nm was observed for the Mo 1-x Nb x S 2 thin films.
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