| Raman spectroscopy | E¹₂g–A1g peak spacing approximately 21 cm⁻¹ for CVD MoS₂ and approximately 26 cm⁻¹ for exfoliated MoS₂; E¹₂g FWHM 2.2 cm⁻¹ for exfoliated MoS₂, 4.3 cm⁻¹ for CVT MoS₂, and 9.1 cm⁻¹ for HT MoS₂; no longitudinal-acoustic mode observed |
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| X-ray diffraction | Strong (00l) reflections for exfoliated MoS₂ before exfoliation and CVT MoS₂; broader peaks and random orientations for HT MoS₂ |
| Electron energy-loss spectroscopy, Mo edge | 2521 eV for CVT MoS₂; 2522 eV for CVD MoS₂; 2522 eV for exfoliated MoS₂; 2530 eV for HT MoS₂ |
| Electron energy-loss spectroscopy, fitted stoichiometry | MoS₂ for CVD and exfoliated MoS₂; MoS₁.₈₂O₀.₁₈ for CVT MoS₂; MoS₁.₄₅O₀.₅₅ for HT MoS₂; oxygen content below approximately 1.5 % for CVD and exfoliated MoS₂, approximately 9 % for CVT MoS₂, and approximately 27.5 % for HT MoS₂ |
| High-resolution transmission electron microscopy | (100) interplanar spacing 0.27–0.28 nm; uniform atomic arrangement, well-defined lattice fringes, and no observable defects for CVD MoS₂; uniform atomic arrangement for exfoliated MoS₂; uniform atomic arrangement with a few voids and atom dislocations for CVT MoS₂; smaller grain size with retained 2H hexagonal lattice for HT MoS₂ |
Jixi Zhang, Armin Sahinovic, Osamah Kharsah, Marika Schleberger, Rossitza Pentcheva, Rodney D. L. Smith. “A defect-defect feedback loop destabilizes MoS₂.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15007725/v1
Values presented only in spectra, diffraction patterns, microscopy images, and thermogravimetric plots were not transcribed. Simulated structures, spectra, and phase diagrams were not transcribed
| In situ variable-temperature Raman spectroscopy, standard-grade N₂ with 5 ppm O₂ | Only 2H-MoS₂ peaks at approximately 380 and 408 cm⁻¹ below 600 °C; a new peak at approximately 200 cm⁻¹ appeared near 600 °C; MoS₂ peaks disappeared above 725 °C; new peaks from approximately 126 to 740 cm⁻¹ were assigned to monoclinic P2₁/c MoO₂; the spectrum remained unchanged after cooling and after 23 days in ambient conditions |
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| Transmission electron microscopy after heat treatment and cooling | Larger sheets and smaller rounded particles; 0.35 nm lattice-fringe spacing in rounded particles, assigned to the MoO₂ (011) plane; selected-area electron diffraction indexed larger sheets to MoS₂ and rounded particles to monoclinic MoO₂ |
| Thermogravimetric analysis and variable-temperature Raman spectroscopy | Transitions at approximately 92, 262, 481, 720, and 800 °C; 0.07 % mass loss below 92 °C with increased MoS₂ Raman intensity; 0.55 % mass loss and rapid Raman-intensity decrease from 92 to 262 °C; 0.2 % mass loss and gradual Raman-intensity decrease from 262 to 481 °C; loss of MoS₂ peaks and growth of MoO₂ peaks through 720 °C; weakened MoO₂ peaks and 0.06 % mass loss through 800 °C |
| In situ variable-temperature Raman spectroscopy, 660 °C | MoS₂-, MoO₂-, and Mo₄O₁₁-predominant spectra after holding for 30 min; only MoO₃ spectra after 52 min |
| Raman spectroscopy of the heating-stage window | S₈ peaks from 100 to 350 °C; blue coating produced under N₂ yielded MoO₃ peaks after exposure to air; S₈ also appeared transiently under H₂/N₂, without a blue coating |
| In situ variable-temperature Raman spectroscopy, ultrahigh-purity N₂ | MoO₂ peaks emerged at 625 °C; MoS₂ peaks disappeared above 725 °C |
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| In situ variable-temperature Raman spectroscopy, 5 % H₂ in N₂ | MoS₂ preserved up to 800 °C; only a thermal redshift observed |
| In situ variable-temperature Raman spectroscopy, O₂ | New peaks emerged at 490 °C and MoS₂ signals disappeared at 575 °C; new peaks matched the MoO₃ standard |
| In situ variable-temperature Raman spectroscopy, N₂ to 250 °C followed by H₂/N₂ to 800 °C | Only 2H-MoS₂ peaks throughout |
| In situ variable-temperature Raman spectroscopy, N₂ to 480 °C followed by H₂/N₂ to 800 °C | MoO₂ peaks formed above 770 °C |
| Thermogravimetric analysis | Sublimation began at 725 °C; fully volatilized by 785 °C |
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| CVD MoS₂ | Stable under H₂/N₂; until 553 °C under ultrahigh-purity N₂; until 630 °C under N₂; until 393 °C under O₂ |
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| Exfoliated MoS₂ | Stable under H₂/N₂; 678 ± 14 °C under ultrahigh-purity N₂; 632 ± 7 °C under N₂; 529 °C under O₂ |
| CVT MoS₂ | Stable under H₂/N₂; 628 ± 11 °C under ultrahigh-purity N₂; 622 ± 12 °C under N₂; 495 °C under O₂ |
| HT MoS₂ | Stable under H₂/N₂; 473 ± 26 °C under ultrahigh-purity N₂; 357 ± 42 °C under N₂; 129 °C under O₂ |
| Time-resolved Raman spectroscopy under N₂ at room temperature | MoS₂ A1g intensity did not change with irradiation time up to 10 % laser intensity, 1.353 mW; increased systematically at 50 %, 6.755 mW, and above; at 100 %, 13.14 mW, peaks at 280, 816, and 991 cm⁻¹ appeared after 700 s and were assigned to MoO₃ |
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