Emerging photoluminescence from bilayer large-area 2D MoS2 films grown by pulsed laser deposition on different substrates

Abstract

We report the growth of continuous large area bilayer films of MoS2 on different substrates by pulsed laser deposition (PLD). The growth parameters for PLD were modified in such a way that results in bilayer 2D-MoS2 films on both c-Al2O3 (0001) (sapphire) and SiO2/Si (SO) substrates. The bilayer large area crystalline nature of growth in the 2 H-phase is determined by Raman spectroscopy. Cross-sectional transmission electron microscopy confirms the distinct thinnest ordered layered structure of MoS2. Chemical analysis reveals an almost stoichiometric 2 H-phase on both the substrates. The photoluminescence intensities of both the films match very well with those of the corresponding exfoliated flakes, as well as chemical vapor deposited (CVD) films as reported in the literature. The in-situ post growth annealing with optimal film thickness acts as a solid phase epitaxy process which provides continuous crystalline layers with a smooth interface and regulates the photoluminescence properties. In contrast, the PLD grown MoS2 monolayer shows poor crystalline quality and non-uniform coverage compared to that with the exfoliated and CVD grown films.

Changes in the Photoluminescence of Monolayer and Bilayer Molybdenum Disulfide during Laser Irradiation

“…As in the 1L-MoS 2 case, we notice that the FWHMs of both A – and A° peaks decreased from 180 min when the defects began to be generated. This is contradictory to a recent report by Barvat et al, which ascribed the broadening of both PL peaks of pulsed laser-deposited MoS 2 films to a relatively higher defect concentration as compared to mechanically exfoliated MoS 2 flakes . However, our results indicate that the screening of electron–hole or electron–electron Coulomb interactions has a dominant effect on the FWHMs of both A° and A – peaks, as discussed above.…”

Thermal Degradation of Monolayer MoS2 on SrTiO3 Supports

“…Previous studies in this area were mostly carried out as part of the synthesis of MoS 2 or immediately after its growth. They were used to enhance the crystallinity, − optical properties, − , or electronic properties of the MoS 2 crystals. , A few studies also explored the thermally accelerated oxidation of MoS 2 into MoO 3 under ambient conditions, starting from 100 °C until complete transformation into MoO 3 at up to 550 °C. − In these studies, the MoS 2 samples were either monolayered (ML)/few layered (FL) (supported on SiO 2 ) or powdered. In the absence of oxygen, MoS 2 is much more stable; the atomic structure of monolayer MoS 2 crystals on Au(111) was seen to be unperturbed up to 630 °C .…”

“…Previous studies in this area were mostly carried out as part of the synthesis of MoS 2 or immediately after its growth. They were used to enhance the crystallinity, 6−10 optical properties, [6][7][8]10 or electronic properties of the MoS 2 crystals. 11,12 A few studies also explored the thermally accelerated oxidation of MoS 2 into MoO 3 under ambient conditions, starting from 100 °C until complete transformation into MoO 3 at up to 550 °C.…”

Large area few-layer TMD film growths and their applications

“…However, they observed mobilities and on/off ratios (0.124 cm 2 Vs −1 and 500, respectively) several orders of magnitude below those observed in CVD growths [51]. Barvat et al [42] observed something similar in their MoS 2 film growths, and performed further tests to conclude that sulfur deficiencies were a possible culprit. Fominski et al [52] attempted to address this stoichiometric defect by immersion of reactants in an atmosphere of low pressure sulfur vapor and hydrogen sulfide.…”

“…TMD band structures change dramatically as a function of layer number, so bilayer and trilayer films gain unique properties that can be exploited [19]. For instance, bilayer TMD films can support interlayer excitons [42]. Jeon et al [19] achieved centimeter scale selective growth of both bilayer and trilayer MoS 2 .…”