Effects of Strategically Placed Water Droplets on Monolayer Growth of Molybdenum Disulfide

Jiang, Yan; Lin, Yuankun; Cui, Jingbiao; Philipose, Usha

doi:10.1155/2018/6192532

Cited by 3 publications

(9 citation statements)

References 29 publications

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“…The MoS 2 films were grown using CVD on 300 nm thick SiO 2 layers on Si using the same procedure we have previously reported. [22,23] The SiO 2 /Si substrate and crucibles containing S and MoO 3 were placed in a tube furnace. The tube furnace was then flushed at RT with ultrahigh purity Ar at a flow rate of 500 sccm for 10 min.…”

Section: Methodsmentioning

confidence: 99%

Structural Stability of Bilayer MoS₂ in Ambient Air

Femi-Oyetoro

Yao

Hathaway

et al. 2021

Adv Materials Inter

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contain dendritic structures with a fractal dimension consistent with a diffusionlimited aggregation process. [3,6] Although a variety of degradation prevention techniques have been reported such as encapsulation with hexagonal boron nitride [9] and polymers, [10] use of novel gate dielectrics, [11] and placement in an environment with a desiccant [3] or in a vacuum, [4] such techniques are not applicable for ambientair applications such as gas sensors. To our knowledge, the stability of bilayer (BL) and thicker-layer MoS 2 films in ambient air has not been extensively studied. It is important to understand the stability of such films for developing applications and having a better understanding of ML degradation. In this paper, we report on the structural stability of preheated and as-grown BL and thicker-layer MoS 2 films in ambient air. The films are grown using CVD on SiO 2 substrates and studied using atomic force microscopy (AFM), and Raman and PL spectroscopies.BL and thicker-layer MoS 2 and other TMD films, nanosheets, [12] and nanostructures, [13] although having indirect band gaps, have attracted considerable interest because of their useful properties. For example, BLs and thicker-layers have higher electrical conductivities than MLs due to their higher density of states and more effective screening of impurities in the substrate. [14] In addition, BL device yield is typically higher than ML device yield, due to the greater mechanical strength of BLs. [15,16] BL and thicker-layer TMD films offer layer control of properties such as spin-orbit coupling, [17] interlayer coupling, [18] and band gap. [19] Varying the twist angle between layers in BLs has been reported to result in twist-dependent valley and band alignment, [20] and Moiré pattern excitons. [21] The ambient-air degradation of CVD-grown ML MoS 2 and other ML TMD films was first reported by Gao et al. [3] They observed that ML MoS 2 and WS 2 grown on SiO 2 substrates developed extensive cracking, morphological changes, and quenching of PL after exposure to ambient air at room temperature (RT) for a period of about a year. The degradation was attributed to oxidation along grain boundaries and other defects. It was found that water vapor in the air was necessary for degradation to occur since films did not degrade in a dry box. In addition, Budania et al. [4] reported that mechanically exfoliated thin multilayer MoS 2 flakes on SiO 2 developed speckles in air at a high relative humidity (RH) of 60% over a period of about a year. Kotsakidis et al. [5] reported

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Section: Methodsmentioning

confidence: 99%

Structural Stability of Bilayer MoS₂ in Ambient Air

Femi-Oyetoro

Yao

Hathaway

et al. 2021

Adv Materials Inter

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“…The MoS 2 films were grown on 300 nm thick SiO 2 /Si substrates using sodium chloride (NaCl) as a promoter [17]. The SiO 2 substrates were prepared by dissolving 1 mg of NaCl (⩾99.5%) in 1 ml of ammonium hydroxide (28% NH 3 in H 2 O) with sonication for 10 min.…”

Section: Methodsmentioning

confidence: 99%

“…The SiO 2 substrates were prepared by dissolving 1 mg of NaCl (⩾99.5%) in 1 ml of ammonium hydroxide (28% NH 3 in H 2 O) with sonication for 10 min. The promoter was spread evenly over the substrates by spin coating at 3000 rpm for 60 s. The CVD setup and growth conditions used are the same as those previously reported [17]. Briefly, the tube furnace was cleaned by annealing at 900 °C for 2 h under air flow.…”

Section: Methodsmentioning

confidence: 99%

Rapid ambient degradation of monolayer MoS₂ after heating in air

et al. 2019

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We report that heating chemical vapor deposition grown monolayer MoS2 in air at temperatures as low as 285 °C for 2 h results in rapid degradation of the monolayer within 2.5 weeks of ambient air exposure after heating. We find that the rapid degradation proceeds via the growth of dendrites on the basal plane that have a fractal dimension close to that of diffusion-limited aggregation. We also observe dendrites in unheated samples that have been in ambient air for a year. We explain the rapid degradation after heating to an increase in MoO3. We propose that the mechanism for dendrite growth involves the diffusion of H2O to oxide sites. This results in the liquefication of the oxides. The liquefied oxides do not protect the surface from further oxidation. Putting heated samples in a dry box for 2 weeks immediately after heating prevents the rapid degradation from occurring.

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“…The optical contrast between monolayers, bi-layer, and tri-layers as well as the bare substrate is obvious and has been reported before. 18 The physical characteristics of the MoS2 films on the same substrate were further examined using AFM. The AFM images (Figure 4) depicts a height profile around a single isolated triangular domain and around a star-like flake.…”

Section: Resultsmentioning

confidence: 99%

“…After 10 min, the furnace was gradually cooled to room temperature. 18 Characterization Details. An Olympus microscope with a maximum magnification of 1000 × was used to capture images of the MoS2 films.…”

Section: Methodsmentioning

confidence: 99%

Analyzing growth kinematics and fractal dimensions of molybdenum disulfide films

et al. 2021

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Though the positive role of alkali halides in realizing large area growth of transition metal dichalcogenide layers has been validated, the film-growth kinematics has not yet been fully established. This work presents a systematic analysis of the MoS2 morphology for films grown under various pre-treatment conditions of the substrate with sodium chloride (NaCl). At an optimum NaCl concentration, the domain size of the monolayer increased by almost two orders of magnitude compared to alkali-free growth of MoS2. The results show an inverse relationship between fractal dimension and areal coverage of the substrate with monolayers and multi-layers, respectively. Using the Fact-Sage software, the role of NaCl in determining the partial pressures of Mo- and S-based compounds in gaseous phase at the growth temperature is elucidated. The presence of alkali salts is shown to affect the domain size and film morphology by affecting the Mo and S partial pressures. Compared to alkali-free synthesis under the same growth conditions, MoS2 film growth assisted by NaCl results in ≈81% of the substrate covered by monolayers. Under ideal growth conditions, at an optimum NaCl concentration, nucleation was suppressed, and domains enlarged, resulting in large area growth of MoS2 monolayers. No evidence of alkali or halogen atoms were found in the composition analysis of the films. On the basis of Raman spectroscopy and photoluminescence measurements, the MoS2 films were found to be of good crystalline quality.

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Effects of Strategically Placed Water Droplets on Monolayer Growth of Molybdenum Disulfide

Cited by 3 publications

References 29 publications

Structural Stability of Bilayer MoS₂ in Ambient Air

Structural Stability of Bilayer MoS₂ in Ambient Air

Rapid ambient degradation of monolayer MoS₂ after heating in air

Analyzing growth kinematics and fractal dimensions of molybdenum disulfide films

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Effects of Strategically Placed Water Droplets on Monolayer Growth of Molybdenum Disulfide

Cited by 3 publications

References 29 publications

Structural Stability of Bilayer MoS2 in Ambient Air

Structural Stability of Bilayer MoS2 in Ambient Air

Rapid ambient degradation of monolayer MoS2 after heating in air

Analyzing growth kinematics and fractal dimensions of molybdenum disulfide films

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Product

Resources

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Structural Stability of Bilayer MoS₂ in Ambient Air

Structural Stability of Bilayer MoS₂ in Ambient Air

Rapid ambient degradation of monolayer MoS₂ after heating in air