Effect of post-exfoliation treatments on mechanically exfoliated MoS<sub>2</sub>

Budania, Prachi; Baine, Paul; Montgomery, Jenny; McNeill, David; Mitchell, S.J.N.; Modreanu, M.; Hurley, Paul K.

doi:10.1088/2053-1591/aa5d8c

Cited by 13 publications

(14 citation statements)

References 36 publications

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“…In the thermally assisted oxidation of monolayer MoS 2 crystals in air, it has been previously reported that sulfur escapes as SO 2 , , leaving oxidized Mo on the surface. − The thermal degradation of MoS 2 in UHV is likely to follow a different route from that in an O 2 -rich environment. We postulate that at 700 °C the thermal energy breaks the Mo–S covalent bonds and releases the S atoms into the vacuum.…”

Section: Discussionmentioning

confidence: 99%

“…We postulate that at 700 °C the thermal energy breaks the Mo–S covalent bonds and releases the S atoms into the vacuum. This bond-breaking process requires a higher activation temperature compared to that of the oxidation of S in an ambient environment. − Upon higher-temperature UHV annealing (> 800 °C), the SrTiO 3 substrate can supply increasing amounts of oxygen, which oxidizes the remaining Mo, converting it into MoO 2 and then into MoO 3 .…”

Section: Discussionmentioning

confidence: 99%

“…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 .…”

Section: Introductionmentioning

confidence: 99%

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Thermal Degradation of Monolayer MoS₂ on SrTiO₃ Supports

Chen

Gao

et al. 2019

J. Phys. Chem. C

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is a wide-bandgap semiconductor suitable for use in high-temperature electronics. It is therefore important to understand its thermal stability. We report the results of a study on thermal degradation of MoS 2 monolayers supported on SrTiO 3 substrates in ultrahigh vacuum (UHV). Our studies were carried out on the (111), (110), and (001) terminations of SrTiO 3 substrates, but MoS 2 was found to degrade on all of these surfaces in a similar way. By scanning tunneling microscopy, we show that MoS 2 monolayer crystals maintain their structure up to 700 °C under UHV, at which point triangular etch trenches appear along the ⟨21̅ 1̅ 0⟩ lattice directions (i.e., sulfur-terminated edge directions) of the MoS 2 crystals. The trenches are due to the preferential loss of sulfur, allowing molybdenum to be oxidized by oxygen originating from the SrTiO 3 substrate. The intensity of the A-exciton photoluminescence (PL) peak and the E 2g 1 and A 1g Raman signals reduced significantly following treatment at this temperature. The crystals continue to degrade at higher annealing temperatures in UHV until they transform into MoO x (x = 2−3) particles at 900 °C, and the optical properties characteristic of MoS 2 are lost entirely in PL and Raman spectra. The initial sulfur loss and the formation of MoO x are confirmed by X-ray photoelectron spectroscopy. The macroscopic triangular shapes of the MoS 2 crystals are retained until the residual particles evaporate at above 1000 °C. The optical properties of the 700 and 800 °C UHV-annealed samples can be partially recovered upon sulfur annealing. This work establishes a pathway of the thermal degradation of SrTiO 3 -supported monolayer MoS 2 in vacuum from smooth MoS 2 crystals to crystals with sulfur vacancies (etch trenches), followed by MoO 2 and finally MoO 3 particles. We also demonstrate how sulfur annealing can be used to heal the defects.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermal Degradation of Monolayer MoS₂ on SrTiO₃ Supports

Chen

Gao

et al. 2019

J. Phys. Chem. C

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“…However, the two techniques offer contrasting benefits and pitfalls. While, ME can ensure the premium crystal quality of the film by choosing high-grade bulk parent material, getting large area monolayer coverage is impossible in this technique [11,12]. Whereas, CVD route can synthesize continuous 1L-MoS 2 extending up to a few cm 2 area [13,14] providing the necessary platform for the fabrication of large scale integration of devices.…”

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confidence: 99%

Effect of strain and sulfur vacancies on the luminescence and valley polarization properties of CVD grown monolayer MoS$_2$ films

Chakrabarti¹,

Mujeeb²,

Dhar³

2022

Preprint

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Using temperature dependent photoluminescence (PL), polarization resolved PL and Raman spectroscopy, we investigate the effect of in situ vacuum annealing as well as the relaxation of strain on the luminescence and the valley polarization properties of large area strictly monolayer (1L)-MoS 2 , grown on sapphire and SiO 2 /Si substrates by a microcavity based chemical vapor deposition (CVD) technique. The study shows that the strain as well as the physisorption of air molecules at the sulfur vacancy (V S ) sites play key roles in governing the optical quality of CVD grown 1L-MoS 2 . Removal of air molecules from the V S sites enhances the relative strength of the A-exciton/trion transition as compared to the broad luminescence (BL) band arising from those defects at low temperatures. It has also been found that such removal helps in improving the valley polarization property of the film. Relaxation of biaxial tensile strain, which has been achieved by post growth transferring of 1L-MoS 2 film from the sapphire to a SiO 2 /Si substrate by a polystyrene assisted transfer process, is also found to be helpful to get back the high polarization character (∼80%) of the valleys. The study further shows that the transfer process not only facilitates the removal of physisorbed air molecules from the V S sites but also puts in place a long lasting capping layer on MoS 2 that shields the film from reacting with air and hence enhances the relative yield of A-exciton/trion transition by suppressing the BL transition. The study thus creates an opportunity to use CVD grown large area 1L-MoS 2 for the development of optoelectronic as well as valleytronic devices for practical applications for the future.

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“…For example, exfoliated samples are superior in quality but they fail in terms of scalability. Typical size of monolayer regions in these flakes is not more than a few tens of micrometer [8,9]. Therefore, fabrication of large scale integrated circuits is not possible on such layers.…”

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confidence: 99%

Tunability of electrical and thermoelectrical properties of monolayer MoS$_2$ through oxygen passivation

Deb,

Bhattacharyya,

Chakrabarti

et al. 2020

Preprint

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Electric and thermoelectric properties of strictly monolayer MoS2 films, which are grown using a novel micro-cavity based CVD growth technique, have been studied under diverse environmental and annealing conditions. Resistance of a thermoelectric device that is fabricated on a continuous monolayer MoS2 layer using photolithography technique has been found to reduce by about six orders of magnitudes upon annealing in vacuum at 525 K. Seebeck coefficient of the layer also reduces by almost an order of magnitude upon annealing. When the sample is exposed to oxygen atmosphere, these parameters return to their previous values. In fact, it has been found that the electron concentration, mobility as well as the thermoelectric power of the material can be tuned by controlling the temperature of annealing and oxygen exposure. Once established, these values are maintained as long as the layer is not exposed to oxygen environment. This can offer a unique way to control doping in the material provided an effective encapsulation method is devised. Such control is an important step forward for device application. The effect has been attributed to the passivation of di-sulfur vacancy donors present in the MoS2 film by physisorbed oxygen molecules. Band structural calculations using density functional theory have been carried out, results of which indeed validate this picture.

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Effect of post-exfoliation treatments on mechanically exfoliated MoS₂

Cited by 13 publications

References 36 publications

Thermal Degradation of Monolayer MoS₂ on SrTiO₃ Supports

Thermal Degradation of Monolayer MoS₂ on SrTiO₃ Supports

Effect of strain and sulfur vacancies on the luminescence and valley polarization properties of CVD grown monolayer MoS$_2$ films

Tunability of electrical and thermoelectrical properties of monolayer MoS$_2$ through oxygen passivation

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Effect of post-exfoliation treatments on mechanically exfoliated MoS2

Cited by 13 publications

References 36 publications

Thermal Degradation of Monolayer MoS2 on SrTiO3 Supports

Thermal Degradation of Monolayer MoS2 on SrTiO3 Supports

Effect of strain and sulfur vacancies on the luminescence and valley polarization properties of CVD grown monolayer MoS$_2$ films

Tunability of electrical and thermoelectrical properties of monolayer MoS$_2$ through oxygen passivation

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Effect of post-exfoliation treatments on mechanically exfoliated MoS₂

Thermal Degradation of Monolayer MoS₂ on SrTiO₃ Supports

Thermal Degradation of Monolayer MoS₂ on SrTiO₃ Supports