Oxidative etching of S-vacancy defective MoS<sub>2</sub> monolayer upon reaction with O<sub>2</sub>

Farigliano, Lucas M.; Paredes-Olivera, Patricia A.; Patrito, E.M.

doi:10.1039/d0cp06502a

Cited by 11 publications

(12 citation statements)

References 45 publications

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“…Previous theoretical studies on oxidation of TMDs have shown that pristine mono-layers remain intact when exposed to O 2 [22,23,24], which is also in line with our experimental observations. However, O 2 molecules can readily adsorb on chalcogen vacancy defects where they can dissociate into oxygen radicals.…”

Section: Resultssupporting

confidence: 92%

“…It has been shown that such dissociation is an intermediate step for the oxidative etching of MoS 2 , which, however, is associated with relatively high energy barriers and is not feasible at room temperature [23]. In our experiments we introduce oxygen radicals directly due to the splitting of O 2 under the influence of the electron beam.…”

Section: Resultsmentioning

confidence: 99%

“…However, O 2 molecules can readily adsorb on chalcogen vacancy defects where they can dissociate into oxygen radicals. The dissociation barrier of O 2 on single vacancies of MoS 2 and MoTe 2 were predicted to be about 0.9 eV and 0.25 eV respectively [22,23,24].…”

Section: Resultsmentioning

confidence: 99%

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Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

Åhlgren¹,

Markevich²,

Sophie³

et al. 2022

Preprint

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Oxidation is the main cause of degradation of many two-dimensional materials, including transition metal dichalcogenides, under ambient conditions. Some of the materials are more affected by oxidation than others. To elucidate the oxidation-induced degradation mechanisms in transition metal dichalcogenides, the chemical effects in single layer MoS2 and MoTe2 were studied in situ in an electron microscope under controlled low-pressure oxygen environments at room temperature. MoTe2 is found to be reactive to oxygen, leading to significant degradation above a pressure of 1×10 −7 torr.Curiously, the common hydrocarbon contamination found on practically all surfaces accelerates the damage rate significantly, by up to a factor of forty. In contrast to MoTe2, MoS2 is found to be inert under oxygen environment, with all observed structural changes being caused by electron irradiation only, leading to well-defined pores with high proportion of molybdenum nanowire-terminated edges. Using density functional theory calculations, a further atomic-scale mechanism leading to the observed oxygen-related degradation in MoTe2 is proposed and the role of the carbon in the etching is explored. Together, the results provide an important insight into the oxygenrelated deterioration of two-dimensional materials under ambient conditions relevant in many fields.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

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Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

Åhlgren¹,

Markevich²,

Sophie³

et al. 2022

Preprint

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“…57 Accordingly, the transition time from the physisorbed to a nondissociated chemisorbed state at room temperature and 1 atm is ∼20 h. 57 The energy barriers required for chemisorption and their energetic states once chemisorbed are similar for V S and V 2S . 58 These predictions are consistent with our observations, which demonstrate the weak interaction of ambient air with the SV and the metastability of in-vacuum-generated SVs. However, once formed, chemisorbed O at SV is expected to be extremely stable due to a large binding energy of ∼2.4 eV 59 and high desorption energy of oxygen-bonded molecules.…”

Section: Resultsmentioning

confidence: 99%

“…However, once formed, chemisorbed O at SV is expected to be extremely stable due to a large binding energy of ∼2.4 eV 59 and high desorption energy of oxygen-bonded molecules. 58 To overcome the metastability of SVs under ambient conditions and study the impact of oxygen passivation on chemical and electronic properties of MoS 2 , we performed in situ photoemission experiments in the presence of oxygen. In doing so, we leveraged the X-ray-induced ionization of oxygen 30 to generate reactive species capable of overcoming the kinetic barrier to oxygen chemisorption.…”

Section: Resultsmentioning

confidence: 99%

Real-Time Investigation of Sulfur Vacancy Generation and Passivation in Monolayer Molybdenum Disulfide via in situ X-ray Photoelectron Spectromicroscopy

et al. 2022

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Understanding the chemical and electronic properties of point defects in two-dimensional materials, as well as their generation and passivation, is essential for the development of functional systems, spanning from next-generation optoelectronic devices to advanced catalysis. Here, we use synchrotron-based X-ray photoelectron spectroscopy (XPS) with submicron spatial resolution to create sulfur vacancies (SVs) in monolayer MoS2 and monitor their chemical and electronic properties in situ during the defect creation process. X-ray irradiation leads to the emergence of a distinct Mo 3d spectral feature associated with undercoordinated Mo atoms. Real-time analysis of the evolution of this feature, along with the decrease of S content, reveals predominant monosulfur vacancy generation at low doses and preferential disulfur vacancy generation at high doses. Formation of these defects leads to a shift of the Fermi level toward the valence band (VB) edge, introduction of electronic states within the VB, and formation of lateral pn junctions. These findings are consistent with theoretical predictions that SVs serve as deep acceptors and are not responsible for the ubiquitous n-type conductivity of MoS2. In addition, we find that these defects are metastable upon short-term exposure to ambient air. By contrast, in situ oxygen exposure during XPS measurements enables passivation of SVs, resulting in partial elimination of undercoordinated Mo sites and reduction of SV-related states near the VB edge. Correlative Raman spectroscopy and photoluminescence measurements confirm our findings of localized SV generation and passivation, thereby demonstrating the connection between chemical, structural, and optoelectronic properties of SVs in MoS2.

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Atomic‐Scale Oxygen‐Mediated Etching of 2D MoS₂ and MoTe₂

Åhlgren

Markevich

Sophie

et al. 2022

Adv Materials Inter

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In contrast, MoTe 2 has been reported to be one of the most reactive TMDs. [9] However, not much is known about the atomic-level processes leading to the drastically different behavior of these materials.Aberration corrected (scanning) transmission electron microscopy (STEM) provides access to the exact atomic structure of materials with a sub-second time resolution. However, high energy electrons used for imaging can also cause structural changes, as has been already demonstrated for both MoS 2 and MoTe 2 . In MoS 2 , continuous electron exposure leads quickly to the formation of sulfur vacancies [10] through a combined effect of electronic excitations and knock-on damage, [11] which first agglomerate into vacancy lines before pores with molybdenum-rich edges appear. [12] In contrast, presumably due to suppressed knock-on damage resulting from the larger mass of Te compared to S, vacancy formation in MoTe 2 is considerably slower allowing dynamic phase transitions to take place without removal of atoms. [13] Nevertheless, structural changes are inevitable during prolonged imaging of both materials. Therefore, in order to study oxidation-related structural changes, they must be separated from pure electronirradiation-induced effects. This requires an instrument with ultra high vacuum and means to introduce a controlled low-pressure atmosphere around the sample during imaging. [14] Such experiments have already revealed that chemical etching in graphene takes place at a partial oxygen pressures of >3 × 10 −8 torr, [15] well below typical pressures of TEM instruments with side entry holders, leading to pore growth that starts at defective sites. [16] Pristine graphene areas remain unaffected. However, similar studies remain lacking for all other 2D materials.Here, we use the same strategy to compare the behavior of suspended 2D MoS 2 and MoTe 2 mono-layers under low-pressure (9 × 10 −10 − 4 × 10 −7 torr) oxygen atmospheres in situ while being imaged at atomic resolution via STEM. Under electron irradiation, O 2 molecules can split into atomic oxygen, accelerating the chemical effects up to an experimentally accessible time scale. In our experiments, structural damage in MoS 2 shows no dependency on the oxygen partial pressure, displaying the well-known [10,12,17] electron-beam-related creation of vacancies and later pores with molybdenum-rich edge structures. In contrast, in MoTe 2 there is a marked difference in structural changes at different oxygen pressures. Specifically, in ultra high vacuum, damage in MoTe 2 is similar to that in MoS 2 apart from Oxidation is the main cause of degradation of many 2D materials, including transition metal dichalcogenides (TMDs), under ambient conditions. Some of the materials are more affected by oxidation than others. To elucidate the oxidationinduced degradation mechanisms in TMDs, the chemical effects in single layer MoS 2 and MoTe 2 are studied in situ in an electron microscope under controlled low-pressure oxygen environments at room temperature. MoTe 2 is found to be reac...

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Oxidative etching of S-vacancy defective MoS₂ monolayer upon reaction with O₂

Abstract: The reactions of O2 with S vacancy sites within a MoS2 monolayer were investigated using Density Functional Theory calculations. We considered the following defects: single S vacancy, double S vacancy,...

Cited by 11 publications

References 45 publications

Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

Real-Time Investigation of Sulfur Vacancy Generation and Passivation in Monolayer Molybdenum Disulfide via in situ X-ray Photoelectron Spectromicroscopy

Atomic‐Scale Oxygen‐Mediated Etching of 2D MoS₂ and MoTe₂

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Oxidative etching of S-vacancy defective MoS2 monolayer upon reaction with O2

Abstract: The reactions of O2 with S vacancy sites within a MoS2 monolayer were investigated using Density Functional Theory calculations. We considered the following defects: single S vacancy, double S vacancy,...

Cited by 11 publications

References 45 publications

Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

Real-Time Investigation of Sulfur Vacancy Generation and Passivation in Monolayer Molybdenum Disulfide via in situ X-ray Photoelectron Spectromicroscopy

Atomic‐Scale Oxygen‐Mediated Etching of 2D MoS2 and MoTe2

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Oxidative etching of S-vacancy defective MoS₂ monolayer upon reaction with O₂

Atomic‐Scale Oxygen‐Mediated Etching of 2D MoS₂ and MoTe₂