Number Of MoS2 Layers Research Articles

The Contact Properties of Monolayer and Multilayer MoS2-Metal van der Waals Interfaces.

The contact resistance formed between MoS2 and metal electrodes plays a key role in MoS2-based electronic devices. The Schottky barrier height (SBH) is a crucial parameter for determining the contact resistance. However, the SBH is difficult to modulate because of the strong Fermi-level pinning (FLP) at MoS2-metal interfaces. Here, we investigate the FLP effect and the contact types of monolayer and multilayer MoS2-metal van der Waals (vdW) interfaces using density functional theory (DFT) calculations based on Perdew-Burke-Ernzerhof (PBE) level. It has been demonstrated that, compared with monolayer MoS2-metal close interfaces, the FLP effect can be significantly reduced in monolayer MoS2-metal vdW interfaces. Furthermore, as the layer number of MoS2 increases from 1L to 4L, the FLP effect is first weakened and then increased, which can be attributed to the charge redistribution at the MoS2-metal and MoS2-MoS2 interfaces. In addition, the p-type Schottky contact can be achieved in 1L-4L MoS2-Pt, 3L MoS2-Au, and 2L-3L MoS2-Pd vdW interfaces, which is useful for realizing complementary metal oxide semiconductor (CMOS) logic circuits. These findings indicated that the FLP and contact types can be effectively modulated at MoS2-metal vdW interfaces by selecting the layer number of MoS2.

Preparation of Few-Layered MoS2 by One-Pot Hydrothermal Method for High Supercapacitor Performance.

Molybdenum disulfide (MoS2), a typical layered material, has important applications in various fields, such as optoelectronics, catalysis, electronic devices, sensors, and supercapacitors. Extensive research has been carried out on few-layered MoS2 in the field of electrochemistry due to its large specific surface area, abundant active sites and short electron transport path. However, the preparation of few-layered MoS2 is a significant challenge. This work presents a simple one-pot hydrothermal method for synthesizing few-layered MoS2. Furthermore, it investigates the exfoliation effect of different amounts of sodium borohydride (NaBH4) as a stripping agent on the layer number of MoS2. Na+ ions, as alkali metal ions, can intercalate between layers to achieve the purpose of exfoliating MoS2. Additionally, NaBH4 exhibits reducibility, which can effectively promote the formation of the metallic phase of MoS2. Few-layered MoS2, as an electrode for supercapacitor, possesses a wide potential window of 0.9 V, and a high specific capacitance of 150 F g-1 at 1 A g-1. This work provides a facile method to prepare few-layered two-dimensional materials for high electrochemical performance.

Two-step process for the fabrication of direct FLG\\MoS2 heterostructures

MoS2 has proven its efficacy in flexible electronics, transistor devices, and various biological and chemical applications. However, it is still challenging to achieve large-area MoS2 monolayers with desired material quality and electrical properties to fulfill the requirement for practical applications. Moreover, the main strategy for the preparation of a 2D heterostructure it is based on the sequential stacking of the layered materials using wet or dry transfer methods which introduces many defects. This paper presents an economically viable and straightforward two-step methodology to obtain MoS2 thin films, encompassing magnetron sputtering deposition of Mo and subsequent annealing in a sulfur-rich environment. This approach successfully yielded MoS2 thin films on Si\\SiO2 substrates. Additionally, heterostructures consisting of few layer graphene (FLG) and MoS2 were directly obtained using the same method. The utilization of grazing incidence X-ray diffraction verified the formation of the hexagonal MoS2 phase, a finding further confirmed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) investigations revealed the successful sulfurization process, with surface-bound oxides forming only subsequent to air exposure. Comprehensive assessment involving X-ray reflectivity, atomic force microscopy and XPS collectively inferred the fabrication of thin films comprised of a small number of MoS2 layers covering the entire substrate. Electrical assessments exhibited an electrical hysteresis, demonstrating its potential for memristor applications. Overall, this study outlines a cost-effective fabrication method for producing nanoscale MoS2 thin films with excellent properties, avoiding the use of toxic gases such as H2S. These findings contribute to the potential development of cutting-edge applications.

2D MoS2 monolayers integration with metal oxide-based artificial synapses

In this study, we report on a memristive device structure wherein monolayers of two-dimensional (2D) molybdenum disulfide (MoS2) are integrated with an ultrathin yttrium oxide (Y2O3) layer to simulate artificial synapses functionality. The proposed physical simulation methodology is implemented in COMSOL Multiphysics tool and is based on the minimization of free energy of the used materials at the applied input voltage. The simulated device exhibits a stable bipolar resistive switching and the switching voltages is significantly reduced by increasing the number of MoS2 layers, which is key to conventional low-power computing and neuromorphic applications. The device is shown to perform synaptic functionalities under various applied bias conditions. The resulting synaptic weight decreases almost linearly with the increasing number of MoS2 layers due to the increase in the device thickness. The simulation outcomes pave the way for the development of optimised metal oxide-based memristive devices through their integration with semiconducting 2D materials. Also, the 2D MoS2 integration can enable the optoelectronic operation of this memory device.

Boosting CO2 Hydrogenation to Methanol over Monolayer MoS2 Nanotubes by Creating More Strained Basal Planes.

The controlled creation, selective exposure, and activation of more basal planes while simultaneously minimizing the generation and exposure of edge sites are crucial for accelerating methanol synthesis from CO2 hydrogenation over MoS2 catalysts but remain a bottleneck. Here, we report a facile method to fabricate heteronanotube catalysts with single-layer MoS2 coaxially encapsulating the carbon nanotubes (CNTs@MoS2) through host-guest chemistry. Inheriting the long tubular structure of CNTs, the grown MoS2 nanotubes exhibit significantly more basal planes than bulk MoS2 crystals. More importantly, the tubular curvature not only promotes strain and sulfur vacancy (Sv) generation but also preferentially exposes more in-plane Sv while limiting edge Sv exposure, which is conducive to methanol synthesis. Both the strain and layer number of MoS2 can be easily and finely adjusted by altering CNT diameter and quantity of precursors. Remarkably, CNTs@MoS2 with monolayer MoS2 and maximum strain displayed methanol selectivity of 78.1% and methanol space time yield of 1.6 g gMoS2-1 h-1 at 260 °C and GHSV of 24000 mL gcat.-1 h-1, representing the best results to date among Mo-based catalysts. This study provides prospects for novel catalyst design by synthesizing coaxial tubular heterostructure to create additional catalytic sites and ultimately enhance conversion and selectivity.

First-principles study on the electronic and optical properties of pn-type SnO/MoS[formula omitted] heterojunction tuned by various intrinsic vacancy defects and layer thicknesses

The impact of various intrinsic point defects and layer thicknesses on the electronic structure and optical properties of pn-type SnO/MoS2 heterojunctions has been investigated using first-principles calculations in this study. SnO/MoS2 heterojunctions are indirect bandgap semiconductors, with a narrower bandgap compared to monolayer SnO and MoS2, which decreases with increasing thickness of SnO or MoS2 layers. Intrinsic vacancy defects with different valence states were introduced using the transfer to the real state model method, which ensures that ionized electrons or holes are placed in the real band edge states. The primary intrinsic vacancy defects in the SnO/MoS2 heterojunction are Sn vacancies, and the valence states of the defects significantly influence the defect formation energy. Under different growth conditions, the dominant defects transition between VSn2−, VSn−, VO, and VS as the Fermi level varies. The intrinsic monolayer (1/1) SnO/MoS2 heterojunction exhibits weak n-type doping characteristics, while the introduction of VSn− defects leads to a shift towards p-type doping. As the number of SnO layers increases, VSn2− and VS defects introduce defect levels of different degrees in the bandgap, acting as electron–hole recombination centers and facilitating the transition between p-type doping and metallic conductivity characteristics. Increasing the number of MoS2 layers introduces localized defect energy levels in the bandgap, leading to p-doping or n-doping characteristics. The intrinsic SnO/MoS2 heterojunction primarily absorbs in the near-ultraviolet region, while also exhibiting a certain absorption capacity in the visible and deep ultraviolet regions. The presence of Sn and S defects can enhance the response to visible light absorption.

Role of MoS2/GNR heterostructures in the performance engineering of ultra-violet (UV) photodetector

The integration of graphene nanoribbons (GNR) with nanostructured chalcogenides like MoS2 is yielding remarkable results in the realm of opto-electronics. This collaboration enhances light-matter interactions and promotes efficient charge transfer pathways by modifying GNR's bandgap and defect levels. To exploit these advantages, we are synthesizing MoS2 and GNR heterostructures with varying ratios using a chemical route. Extensive characterizations involving XRD and SEM analysis are validating the successful creation of these heterostructures. Furthermore, we are assessing their optical properties through UV, PL, Raman, and FTIR analyses, with absorbance peaks and Raman modes being used to determine the number of MoS2 layers in each composition. Our primary focus is to develop a photodetector based on MoS2 and GNR heterostructures to enhance its performance. Fabricated through chemical process, the MoS2 and GNR heterostructures are being deposited between silver electrodes on a Si/SiO2 substrate. The resulting photodetector is expected to exhibit substantially improved photo-response and switching capabilities compared to individual nanomaterials. We anticipate that the optimized photodetection performance will feature remarkable attributes, including photo-responsivity of 18.81 mAW−1, detectivity of 46.5 × 107 jones, external quantum efficiency of 19.91, and swift response and recovery times. We expect these notable results, particularly for GNR: MoS2 ratios of 3:1 and 2:1 under 390 nm UV laser illumination, to underscore the immense practical potential of high-performance photodetectors.

Effect of Ni/Mo on the preparation of non-loaded NiMoSx catalysts and the hydrogenation performance of coal tar

Efficient and clean utilization of coal tar is one of the key technologies for efficient and clean utilization of coal. Molybdenum disulfide has been favored for its superior catalytic hydrogenation of poor-quality oil. Molybdenum disulfide catalysts doped with different contents of nickel were synthesized by a two-step method. By SEM, XRD, Raman analyses, and other analyses. non-loaded NiMoSx-0.1 catalysts with larger lateral dimensions, fewer layers, and the appearance of specific active sites at both Basal and Edge positions were synthesized when Ni/Mo = 0.1 compared to undoped molybdenum disulfide. When Ni/Mo is continuously increased, the conversion of the intermediate MoS4-xOx is severely affected, which decreases the amount of MoS2 generated and increases the number of MoS2 layers and transverse dimensions. NiMoSx-0.1 promotes the conversion of CA to CN and enhances the hydrogenation and cracking of coal tar. The total gasoline and diesel content of the hydrotreating product was increased by 13.6 % with no coke production, in addition to the viscosity, density, and average molecular mass decreasing by 90 %, 5 %, and 33 %, respectively.

The effect of binding energy on optimizing the interfacial thermal transport in metal-MoS2-dielectric nanostructures

The development of MoS2-based devices presents a significant challenge due to the poor interfacial thermal transport of metal-MoS2-dielectric structures, which results in severe thermal dissipation issues. This work aims to investigate the effects of various strategies, including modifying metal electrodes, adjusting the number of MoS2 layers, and incorporating van der Waals heterostructures, on the enhancement of interface thermal conductance (ITC) of metal-MoS2-dielectric structures. The time-domain thermoreflectance method was applied to characterize the ITC and experimental results demonstrate that the effect of regulating metal electrodes depends on the binding energy between the metal-MoS2 interfaces, which is a matter of controversy due to the large dispersion of published results. Furthermore, the increase in the number of MoS2 layers does not necessarily lead to the enhancement of the ITC of metal-MoS2-dielectric structures, as this is a comprehensive reflection of the number of layers' influence on both thermal conductance of MoS2 itself and the ITC between MoS2 and the surrounding materials. The results from the heterostructures of hBN-MoS2 and Gr-MoS2 were then systematically compared, and the results indicate the potential of Gr-MoS2 heterostructures in augmenting ITC. In addition, the nonequilibrium molecular dynamics simulation was effectively employed to gain deeper insights into the effect of binding energy on optimizing the ITC of metal-heterostructures-dielectric nanostructures. Finally, the effectiveness of these strategies in enhancing thermal properties was discussed through an analysis of interfacial binding energy. This finding provides a valuable direction for enhancing the thermal management of MoS2-based devices.

Precise Tuning of Bilayer Ultrasmall MoS2 Featuring Inhibition of Carrier Recombination and Fast Surface Chemistry for Green H2 Evolution.

Achieving water splitting to produce green H2 , using the noble-metal-free MoS2 , has attracted huge interest from researchers. However, tuning the number of MoS2 layers precisely while obtaining small lateral sizes to surge the H2 -evolution rate is a tremendous challenge. Here, a bottom-up strategy is designed for the in situ growth of ultrasmall lateral-sized MoS2 with tunable layers on CdS nanorods (CN) by controlling the decomposition temperature and concentration of substrate seed (NH4 )2 MoS4 . Here, the bilayer MoS2 and CN coupling (2L-MoS2 /CN) exhibits the optimum photocatalytic activity. Compared to thicker MoS2 , the 2L-MoS2 has sufficient reduction capacity to drive photocatalytic H2 evolution and the ultrasmall lateral size provides more active sites. Meanwhile, the indirect bandgap, in contrast to the direct bandgap of the monolayer MoS2 , suppresses the carrier recombination transferred to 2L-MoS2 . Under the synergistic effect of both, 2L-MoS2 /CN has fast surface chemical reactions, resulting in the photocatalytic H2 -evolution rate of up to 41.86mmol g-1 h-1 . A novel strategy is provided here for tuning the MoS2 layers to achieve efficient H2 evolution.

Solvent effects on the drop cast films of few layers of MoS2 primed by facile exfoliation to realize optical and structural properties

MoS2, a two-dimensional (2D) layered material with variable bandgap and high stability, can be employed in optical and electronic applications due to its outstanding structural, electrical, and optical properties. The fabrication of MoS2 devices in a facile way is highly inevitable to minimize the time consumption and the cost due to its far-reaching and ceaseless applications. On behalf of their various applications, we have employed sonication-assisted liquid phase exfoliation of MoS2 followed by drop casting the sample in a glass plate for further characterization. MoS2 nanosheets were fabricated by exfoliating bulk MoS2 powder in different solvents with varying surface tension such as Ethanol, Ethylene Glycol (EG), Polyvinyl Pyrrolidone (PVP), Dimethylformamide (DMF), and Dimethyl Sulfoxide (DMSO). The structural and optical properties of the sample were analyzed using XRD, AFM, UV spectroscopy, photoluminescence (Pl) and Raman spectroscopy. The formation of 2D MoS2 film with (0 0 2) planes were identified and the thickness of the exfoliated nanosheets was confirmed to be in the nano regime. The optical properties of MoS2 revealed the existence of the spin–orbit coupling and the exciton-plasmon (plexitonic) coupling induced Rabi splitting in the Pl spectra, which increased with a reduction in layer number, and a negative correlation between Pl intensity and Rabi splitting is established. The variation in layer number of MoS2 on different solvents has been studied using the difference in Raman shift between E12g and A1g modes.

The Effect of Sonication Parameters on the Thickness of the Produced MoS2 Nano-Flakes

Liquid Phase Exfoliation (LPE) is a common route to produce two-dimensional MoS2 nanosheets. In this research, MoS2 powder is exfoliated by an ultrasonic probe (sonicator) in a water-ethanol solution. It is reported that MoS2 as a prototype 2D Transition Metal Dichalcogenide, has a band gap that increases with a decreasing number of layers. There are some factors that affect the average band gap energy value and the thickness of the exfoliated flakes. We varied different parameters of the ultrasonic probe like power, pulse percentage and time duration of sonication to investigate the effects on the number of MoS2 layers. Our findings from the UV-Visible spectra, SEM, FESEM and TEM images indicate that the minimum thickness for these samples was acquired at 50% of the input power of the sonicator we used (65 W) and the optimum pulse percentage is 50%. The current study also found that the average amount of band gap increased with an increase in sonication time, and then remained unchanged after 60 minutes.

Large area MoS2 thin film growth by direct sulfurization

In this study, we present the growth of monolayer MoS2 (molybdenum disulfide) film. Mo (molybdenum) film was formed on a sapphire substrate through e-beam evaporation, and triangular MoS2 film was grown by direct sulfurization. First, the growth of MoS2 was observed under an optical microscope. The number of MoS2 layers was analyzed by Raman spectrum, atomic force microscope (AFM), and photoluminescence spectroscopy (PL) measurement. Different sapphire substrate regions have different growth conditions of MoS2. The growth of MoS2 is optimized by controlling the amount and location of precursors, adjusting the appropriate growing temperature and time, and establishing proper ventilation. Experimental results show the successful growth of a large-area single-layer MoS2 on a sapphire substrate through direct sulfurization under a suitable environment. The thickness of the MoS2 film determined by AFM measurement is about 0.73 nm. The peak difference between the Raman measurement shift of 386 and 405 cm−1 is 19.1 cm−1, and the peak of PL measurement is about 677 nm, which is converted into energy of 1.83 eV, which is the size of the direct energy gap of the MoS2 thin film. The results verify the distribution of the number of grown layers. Based on the observation of the optical microscope (OM) images, MoS2 continuously grows from a single layer of discretely distributed triangular single-crystal grains into a single-layer large-area MoS2 film. This work provides a reference for growing MoS2 in a large area. We expect to apply this structure to various heterojunctions, sensors, solar cells, and thin-film transistors.

Hexagonal Carbon Nanoplates Decorated with Layer-Engineered MoS2: High-Performance Cathode Materials for Zinc-Ion Batteries.

Hexagonal carbon nanoplates bearing MoS2 (HCN@MoS2) were synthesized using two-dimensional (2D) microporous organic polymers as templating materials. The layer number of MoS2 in HCN@MoS2 and the 2D morphology of composites were critical factors to achieve high-performance cathode materials for aqueous zinc-ion batteries. The best cathode performance was obtained with HCN@MoS2 bearing 2-3 layered MoS2 (HCN@MoS2-2), showing excellent discharge capacities of 602 mAh/g (@50 mA/g), 498 mAh/g (@0.1 A/g), and 328 mAh/g (@1 A/g). The promising electrochemical performance of HCN@MoS2-2 is attributable to the facilitated insertion of zinc ions into 2-3 layered MoS2 due to the reduced lattice energy and the efficient electrochemical utilization of composite materials.

2H-MoS 2 Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

2H-MoS ₂ Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

Enhancement and sensing applications of ultra-narrow band circular dichroism of the chiral nanopore films based on Bragg reflector.

Narrow-band circular dichroism (CD) has attracted considerable attention in the high-sensitivity detection of chiral molecules and chiral catalysis. However, achieving dynamic adjustment of narrow-band CD signals is challenging. In this study, we introduce a disruption layer (DL) and molybdenum disulfide (MoS2) into an L-shaped chiral nanohole array based on a distributed Bragg reflector (DBR), forming L-shaped chiral nanoholes (LCNAs/DL-DBR/MoS2), and investigate the mechanism of CD signal generation. Simulation results show that LCNAs/DL-DBR/MoS2 generate three narrow-band CD signals in the visible region. Analysis of the near-field electric field maps reveals that the three CD peaks of LCNAs/DL-DBR/MoS2 are caused by three Tamm resonances in the DBR layer. The producing and adjusting mechanisms of the CD signals are achieved by changing the structural parameters and the number of MoS2 layers. Dynamic adjustment of the CD signals of LCNAs/DL-DBR/MoS2 can be achieved by changing the environmental temperature. Furthermore, by altering the refractive index of the environment and the DBR layer, it is demonstrated that LCNAs/DL-DBR/MoS2 has a high-quality factor. Our theoretical simulations aid in the design of UNB chiral devices, opening up new avenues for environmental monitoring and the detection of chiral molecules with exceptional sensitivity.

Enhancement and Sensing Application of Ultra-Narrowband Circular Dichroism in the Chiral Nanostructures Based on Monolayer MoS2 and a Distributed Bragg Reflector.

Narrowband circular dichroism (CD) has aroused wide concerns in high-sensitivity detections of chiral molecular and chiral catalysis. Nevertheless, the dynamical adjustment of ultra-narrowband (UNB) CD signals is hard to achieve. In this work, single-layer molybdenum disulfide (MoS2), vanadium dioxide (VO2), and a distributed Bragg reflector (DBR) are introduced into X-shaped chiral nanostructures (XCNs) for overcoming the above challenge. The simulation results show that XCNs can generate four strong UNB CD signals in the near-infrared band, and XCNs/MoS2 can further enhance the UNB CD signals. The full width at half-minimum of UNB CD signals can reach 0.14 nm. The electric field distributions of XCNs/MoS2 show that the four CD signals originate from the coupling between the guided mode resonances along the x and y axes in the VO2 layer and the Tamm plasmon polaritons along the x and y axes in the DBR layer. Four UNB CD peaks can be actively tuned by varying the structural parameters, the number of MoS2 layers, and the environmental temperature. The FOM of XCNs/MoS2 can reach 1487 by changing the refractive index of the DRB layers. These findings contribute to the design of UNB chiral devices and provide new possibilities for environmental monitoring and ultrasensitive detection of chiral molecules.

Performance Enhancement of SPR Biosensor Using Graphene-MoS2 Hybrid Structure.

We investigate a high-sensitivity surface plasmon resonance (SPR) biosensor consisting of a Au layer, four-layer MoS2, and monolayer graphene. The numerical simulations, by the transfer matrix method (TMM), demonstrate the sensor has a maximum sensitivity of 282°/RIU, which is approximately 2 times greater than the conventional Au-based SPR sensor. The finite difference time domain (FDTD) indicates that the presence of MoS2 film generates a strong surface electric field and enhances the sensitivity of the proposed SPR sensor. In addition, the influence of the number of MoS2 layers on the sensitivity of the proposed sensor is investigated by simulations and experiments. In the experiment, MoS2 and graphene films are transferred on the Au-based substrate by the PMMA-based wet transfer method, and the fabricated samples are characterized by Raman spectroscopy. Furthermore, the fabricated sensors with the Kretschmann configuration are used to detect okadaic acid (OA). The okadaic acid–bovine serum albumin bioconjugate (OA-BSA) is immobilized on the graphene layer of the sensors to develop a competitive inhibition immunoassay. The results show that the sensor has a very low limit of detection (LOD) of 1.18 ng/mL for OA, which is about 22.6 times lower than that of a conventional Au biosensor. We believe that such a high-sensitivity SPR biosensor has potential applications for clinical diagnosis and immunoassays.

The same band alignment of two hybrid 2D/3D vertical heterojunctions formed by combining monolayer MoS2 with semi-polar (11–22) GaN and c-plane (0001) GaN

Traditional c-plane (0001) GaN based devices are subject to a strong polarization field at the hetero-interfaces which handicaps the performance of photoelectric devices. However, the semi-polar (11–22) GaN has great potential for reducing the polarization effects compared with c-plane (0001) GaN. Here, we have fabricated MoS2/(11–22) GaN heterojunction and determined the band alignment by X-ray photoelectron spectroscopy (XPS). For comparison, the band alignment of MoS2/(0001) GaN heterojunction has also been measured to explore the influence of GaN with different crystal orientations on the energy band of MoS2/GaN heterojunction. Surprisingly, the band alignments of the two MoS2/GaN heterojunctions are the same, which could be caused by the unsaturated and omnidirectional properties of van der Waals forces at the interface of MoS2 and GaN. The measurement result of the valence band offsets (VBOs) of the two MoS2/GaN heterojunctions is 1.54 ± 0.15 eV. And the conduction band offsets (CBOs) are determined to be 0.29 ± 0.15 eV, revealing type-II band alignments of the two heterojunctions. We have also confirmed the number of MoS2 layers on the MoS2/GaN heterojunctions by Raman spectroscopy and the orientations of the GaN substrates by X-ray diffraction. The determination of band alignments between two-dimensional (2D) MoS2 and three-dimensional (3D) semi-polar (11–22) GaN opens up a way for modeling and designing high performance photoelectric devices based on hybrid MoS2/semi-polar GaN heterojunctions.

The impact of strain on growth mode in chemical vapor deposited mono- and few-layer MoS2

-The development of high-quality chemical vapor-deposited mono- and few-layer MoS2 is of high relevance for future applications in functional devices. Consequently, a detailed understanding of the growth mode and the parameters affecting it is important. Here, we show for the case of mono- and few-layer MoS2 grown on Muscovite mica, how strain and temperature impact the growth mode. We show how misleading the determination of the number of MoS2 layers is, solely based on Raman spectroscopy due to the occurrence of strain and changes in the growth mode. A combination of atomic force microscopy, Raman spectroscopy, and ab initio calculations reveal that that the growth at 500 °C synthesis temperature exhibits a strained layer-by-layer growth of up to three mono-layers, whereas at 700 °C, a strain release occurs and layer-by-layer growth is confined to the first mono-layer only. We relate the occurrence of strain to the formation of gas bubbles below the MoS2 film, escaping the mica sheets during high temperature synthesis. Our analysis shows that mica substrates can be used to study strain in 2D materials without the need to apply external stress and that a detailed knowledge of the MoS2 morphology is necessary to correctly interpret the Raman results.