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Realization of 2D crystalline metal nitrides via selective atomic substitution

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Science Advances  10 Jan 2020:
Vol. 6, no. 2, eaax8784
DOI: 10.1126/sciadv.aax8784
  • Fig. 1 Schematic illustration of chemical conversion from MoS2 to Mo5N6.

    (A) Structural changes from MoS2 to Mo5N6. (B) Schematics of the experimental setup for chemical conversion reactions.

  • Fig. 2 Typical optical microscope, Raman spectroscopy, and PL characterization of MoS2 and Mo5N6 flakes.

    (A) Optical images of MoS2 exfoliated on the SiO2/Si substrate. (B) Optical image of Mo5N6 converted from MoS2 in (A). (C) Comparison of Raman spectra of MoS2 and Mo5N6. Peaks labeled with “*” are from the SiO2/Si substrate. (D) Comparison of PL spectra of MoS2 and Mo5N6. (E and F) Raman intensity maps of the A1g mode of MoS2 (E) and the 215 cm−1 mode of Mo5N6 (F). Color bars show normalized Raman intensities, where “1” and “0” represent maximum and minimum intensity of Raman modes, respectively. a.u., arbitrary units.

  • Fig. 3 Crystal structure and elemental analysis of Mo5N6 samples converted from MoS2.

    (A) Low-magnification TEM image of Mo5N6. (B) SAED pattern taken by a 25 cm camera. Diffraction planes are labeled according to SAED simulation in fig. S4. Red circle corresponds to a diffraction plane blocked by TEM beam stop. (C) Filtered HAADF STEM image. Hexagonal Mo pattern is observed. Mo atoms and N atoms are labeled in blue and cyan color, respectively. (D) XPS survey spectrum of Mo5N6. (E and F) XPS spectra of Mo5N6 in Mo 3p and N 1s region (E) and Mo 3d region (F).

  • Fig. 4 Thickness characterization and analysis of samples before (MoS2) and after conversion (Mo5N6).

    (A and B) Side view of crystal structures labeled with distance between adjacent Mo layers in MoS2 and Mo5N6. (C and D) AFM images of the same flake before [MoS2 (C)] and after conversion [Mo5N6 (D)]. The white dashed lines indicate the location where we measured the thickness of the flakes. (E) AFM height profiles of the flake before [MoS2 (C)] and after conversion [Mo5N6 (D)]. (F) Correlation plot of the thickness of MoS2 and converted Mo5N6 (in black). Data points in red show the corresponding thickness ratios of Mo5N6/MoS2.

  • Fig. 5 Electrical transport measurements of Mo5N6.

    (A) Schematics of a back-gate device together with electrical connections. (B) Transfer curve of Mo5N6 transport device for both forward and reverse Vg bias with back-gate modulations. Inset: Zoomed-in image of the area indicated by the black rectangle. Negligible gate dependence of the Ids is observed in Mo5N6 transport device. (C) Output I-V curve of Mo5N6 transport device under different temperatures at zero gate voltage. Inset: Zoomed-in region of the I-V curve indicated by the red square. (D) Temperature dependence of the sheet resistance of the Mo5N6 sample.

  • Fig. 6 Conversion on WS2 and TiS2 for W5N6 and TiN.

    (A to D) Optical images of WS2 (A), W5N6 (B), TiS2 (C), and TiN (D). (E to H) Raman intensity maps of E12g mode of WS2 (E), 258 cm−1 mode of W5N6 (F), A1g mode of TiS2 (G), and 154 cm−1 mode of TiN (H). Color bars show normalized Raman intensities, where “1” and “0” represent maximum and minimum intensity of Raman modes, respectively. (I and J) Comparison of Raman spectra of WS2 and W5N6 (I) and TiS2 and TiN (J). Peak labeled with “*” is from the SiO2/Si substrate.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/2/eaax8784/DC1

    Fig. S1. Typical optical images of MoS2 and Mo5N6 flakes with different thicknesses.

    Fig. S2. Absorption spectra of MoS2 and Mo5N6 samples on quartz substrate.

    Fig. S3. AFM images of MoS2 and Mo5N6 flakes in Fig. 2.

    Fig. S4. PL intensity maps of MoS2 and Mo5N6 flake.

    Fig. S5. Structural and elemental characterizations of Mo5N6.

    Fig. S6. TEM images of Mo5N6 sample under 200-keV electron beam.

    Fig. S7. EDS spectrum of Mo5N6.

    Fig. S8. Optical, AFM, and SEM images of chemical transformation on a four-layer MoS2 flake.

    Fig. S9. Optical images of Mo5N6 flakes prepared from chemical transformations under different conditions.

    Fig. S10. Optical images and Raman spectra of a partially converted flake at 700°C.

    Fig. S11. Stability test of Mo5N6, W5N6, and TiN.

    Fig. S12. Optical and SEM images of WS2, W5N6, TiS2, and TiN flakes.

    Fig. S13. Optical and AFM images of Mo5N6 transport device.

    Fig. S14. TEM and EDS characterizations of W5N6 converted from WS2.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Typical optical images of MoS2 and Mo5N6 flakes with different thicknesses.
    • Fig. S2. Absorption spectra of MoS2 and Mo5N6 samples on quartz substrate.
    • Fig. S3. AFM images of MoS2 and Mo5N6 flakes in Fig. 2.
    • Fig. S4. PL intensity maps of MoS2 and Mo5N6 flake.
    • Fig. S5. Structural and elemental characterizations of Mo5N6.
    • Fig. S6. TEM images of Mo5N6 sample under 200-keV electron beam.
    • Fig. S7. EDS spectrum of Mo5N6.
    • Fig. S8. Optical, AFM, and SEM images of chemical transformation on a four-layer MoS2 flake.
    • Fig. S9. Optical images of Mo5N6 flakes prepared from chemical transformations under different conditions.
    • Fig. S10. Optical images and Raman spectra of a partially converted flake at 700°C.
    • Fig. S11. Stability test of Mo5N6, W5N6, and TiN.
    • Fig. S12. Optical and SEM images of WS2, W5N6, TiS2, and TiN flakes.
    • Fig. S13. Optical and AFM images of Mo5N6 transport device.
    • Fig. S14. TEM and EDS characterizations of W5N6 converted from WS2.

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